JP4883702B2 - Dot measuring method and apparatus, program, and image forming apparatus - Google Patents

Description

  The present invention relates to a dot measurement method and apparatus, a program, and an image forming apparatus, and in particular, a technique for measuring a landing position and a dot diameter of a dot ejected by a liquid ejection head typified by an inkjet head or a volume of an ejection droplet. About.

  Patent Document 1 proposes a technique for detecting a landing position deviation of dots ejected by a liquid ejection head. According to the document 1, dots that are independent from each nozzle of the head are ejected, the result of the droplet ejection is imaged, and a straight line (trajectory) drawn by the dots is calculated and compared with a reference straight line. , Measuring the position of isolated dots.

Patent Document 2 calculates a density (integrated density) of a certain area (area) by forming a line pattern with ink in order to obtain the ejection amount from the nozzle, and reading the entire line pattern with an image sensor. Based on this density, the ejection amount of the ink used for the line pattern is obtained.
JP 2006-284406 A JP-A-10-230593

  However, since the technique described in Patent Document 1 measures the dot position of an isolated dot in which a dot ejected from each nozzle is not connected to another dot, an image pickup apparatus (image reading apparatus) that reads each isolated dot ) Requires an extremely high resolution corresponding to the dot diameter. Specifically, a resolution comparable to the measurement accuracy of isolated dots (for example, an accuracy of the order of 1 μm or less) is required, or it is necessary to perform imaging at a high resolution that can clearly capture the edge of one dot. . The technique described in Patent Document 1 mainly calculates a dot landing position (dot position) and cannot simultaneously calculate the dot diameter.

  On the other hand, in the technique described in Patent Document 2, the measurement target is the ink discharge amount, and it is not possible to simultaneously measure the landing positions of the dots ejected by each nozzle.

  The present invention has been made in view of such circumstances, and uses an imaging device having a resolution (for example, about 5 μm / pixel) lower than a high resolution (for example, 1 μm / pixel) required for resolution of isolated dots. However, it is possible to provide a dot measurement method and apparatus capable of simultaneously measuring a dot position and a dot diameter with the same degree of accuracy as an isolated dot measurement (for example, an accuracy of the order of 1 μm), and a computer program and an image forming apparatus used therefor. With the goal.

  In order to achieve the above object, the dot measurement method according to the present invention is configured to discharge liquid droplets from each nozzle of a liquid discharge head in which a plurality of nozzles are arranged onto a discharge target medium, and A line pattern forming step of forming a line pattern by dot rows corresponding to each nozzle by moving the ejection medium relative to each other and causing the liquid droplets ejected from each nozzle to land on the medium to be ejected And an image pickup apparatus having a light receiving element array that intersects the line direction of the line pattern at a predetermined angle while conveying the ejection target medium on which the line pattern is formed in the first direction. Pattern reading for acquiring electronic image data representing the captured image by capturing the line pattern with the imaging device while moving in a second direction different from FIG. A profile graph acquisition step for acquiring a plurality of profile bluffs for one line pattern representing a fluctuation of an image signal value in a one-dimensional pixel row that obliquely crosses the line pattern from the electronic image data, and one line An extreme value position corresponding to the density center of the line pattern and a first edge position and a second edge position corresponding to the left and right edges of the line pattern are calculated from each of the plurality of profile graphs acquired for the pattern. A feature position calculation step and a plurality of extreme value positions, first edge positions, and second edge position data calculated for the same line pattern by the feature position calculation step, respectively, using the least square method, the line pattern The line center approximate line corresponding to the extreme value position indicating the density center of the An approximate straight line calculating step for calculating a first edge approximate straight line corresponding to the first edge position of the pattern and a second edge approximate straight line corresponding to the second edge position of the line pattern, and the approximate straight line calculating step. A step of calculating the vertical distance between the line center approximate lines corresponding to the adjacent line patterns from the line center approximate line for each line pattern obtained, and calculating the dot landing position from the calculated distance; and the above approximate line calculation A line width calculating step of calculating a vertical distance between straight lines of the first edge approximate straight line and the second edge approximate straight line with respect to the same line pattern obtained in the step and obtaining the value as a line width of the line pattern; The relationship between the dot diameter and the line width formed on the target medium, and the relationship between the volume of the ejected liquid droplet and the line width Based on the correlation information acquisition step of acquiring at least one of the relationship, the line width value obtained in the line width calculation step and the relationship known in the correlation information acquisition step, And a measurement value calculation step of obtaining at least one value of the dot width and the volume of the ejected droplet from the line width value.

  In addition, the dot measuring device according to the present invention is configured to cause the liquid ejection head and the ejection target medium to be relative to each other while ejecting liquid droplets from the nozzles of the liquid ejection head in which a plurality of nozzles are arranged onto the ejection target medium. The object to be measured is formed by forming a line pattern with dot rows corresponding to each nozzle in the first direction by causing the liquid droplets ejected from each nozzle to land on the medium to be ejected. An image pickup apparatus having a conveying unit that conveys the light receiving element array intersecting at a predetermined angle with respect to a line direction of the line pattern on the object to be measured conveyed by the conveying unit. While the object to be measured is transported in the direction of, the line pattern on the object to be measured is imaged by the imaging device while moving in a second direction different from the first direction. A plurality of pattern reading means for obtaining electronic image data representing an image, and profile bluffs representing fluctuations in image signal values in a one-dimensional pixel array that obliquely crosses the line pattern from the electronic image data. An extreme value position corresponding to the density center of the line pattern and first and second edges corresponding to the left and right edges of the line pattern, respectively, from the profile graph acquisition means to be acquired and a plurality of profile graphs acquired for one line pattern. Feature position calculation means for calculating one edge position and second edge position, and data on extreme value positions, first edge positions and second edge positions calculated for the same line pattern by the feature position calculation means, Extreme value indicating the center of density of the line pattern using the least square method An approximate straight line for calculating a line center approximate straight line corresponding to the position, a first edge approximate straight line corresponding to the first edge position of the line pattern, and a second edge approximate straight line corresponding to the second edge position of the line pattern The vertical distance between the line center approximate lines corresponding to the adjacent line patterns is calculated from the calculation means and the line center approximate line for each line pattern obtained by the approximate line calculation means, and the dot landing position is calculated from the calculated value. Calculates the vertical distance between the first edge approximate straight line and the second edge approximate straight line with respect to the same line pattern obtained by the calculated landing position calculating means and the approximate straight line calculating means, and the value is used as the line width of the line pattern. The required line width calculation means and the combination of a predetermined liquid and the medium to be ejected in advance, the dot diameter and the label formed on the medium to be ejected. Correlation information storage means for storing correlation information that has known at least one of the relationship between the in width and the relationship between the volume of the ejected droplet and the line width, and the line width calculation means. Based on the line width value and the correlation information stored in the correlation information storage means, the measured value for obtaining at least one value of the corresponding dot diameter and ejected droplet volume from the line width value And a calculating means.

  Furthermore, the program according to the present invention includes the profile graph acquisition unit, the feature position calculation unit, the approximate straight line calculation unit, the landing position calculation unit, the line width calculation unit, and the correlation in the dot measurement device according to the present invention described above. It is a program for causing a computer to function as information storage means and the measurement value calculation means.

  An image forming apparatus according to the present invention includes the above-described dot measuring device according to the present invention and the liquid ejection head.

  According to the present invention, the dot landing position and the dot diameter can be determined simultaneously (from the same captured image). Thereby, the formation of the line pattern (sample chart) for measurement and the number of times of imaging can be reduced to one (minimum). Compared with the conventional method, high-precision measurement can be performed with a low-resolution imaging apparatus, and the data size of the captured image can be reduced, the processing time can be increased, and the reading time can be reduced.

  Furthermore, according to the present invention, since the line pattern is read while conveying the recording medium, there is no need to stop the conveyance for measurement, and the image reading apparatus is installed on the conveyance path in the image forming apparatus. Is possible.

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

  Here, an application example of the ink dot landing position and dot diameter measurement by the ink jet recording apparatus will be described. First, the overall configuration of the ink jet recording apparatus will be described.

(First embodiment)
[Description of Inkjet Recording Device]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus. As shown in the figure, the ink jet recording apparatus 10 includes a plurality of ink jet recording heads ("" provided corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. Corresponding to “liquid discharge head”, hereinafter referred to as “head”.) Ink storage / stores the printing unit 12 having 12K, 12C, 12M, and 12Y and the ink supplied to each of the heads 12K, 12C, 12M, and 12Y. A loading unit 14, a paper feeding unit 18 that supplies recording paper 16 as a recording medium, a decurling unit 20 that removes curling of the recording paper 16, and a nozzle surface (ink ejection surface) of the printing unit 12. A belt conveyance unit 22 that is arranged and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, an image reading device 24 that reads a printing result by the printing unit 12, and a recorded recording paper ( And a discharge unit 26 for discharging the lint product) to the outside.

  The ink storage / loading unit 14 has an ink tank that stores ink of a color corresponding to each of the heads 12K, 12C, 12M, and 12Y, and each tank has a head 12K, 12C, 12M, and 12Y through a required pipe line. Communicated with. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When a plurality of types of recording media (media) can be used, an information recording body such as a barcode or a wireless tag that records media type information is attached to a magazine, and information on the information recording body is read by a predetermined reader. It is preferable to automatically determine the type of recording medium to be used (media type) and to perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28.

  After the decurling process, the cut recording paper 16 is sent to the belt conveyance unit 22. The belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 forms a horizontal plane (flat surface). ing.

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the printing unit 12 and the sensor surface of the image reading device 24 inside the belt 33 spanned between the rollers 31 and 32. The recording paper 16 is sucked and held on the belt 33 by sucking the suction chamber 34 with a fan 35 to a negative pressure. In place of the suction adsorption method, an electrostatic adsorption method may be adopted.

  The power of the motor (reference numeral 88 in FIG. 6) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The held recording paper 16 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorption roll, etc., an air blow method of blowing clean air, or a combination thereof.

  Although a roller / nip conveyance mechanism may be used instead of the belt conveyance unit 22, if the roller / nip conveyance is performed in the printing area, the roller is brought into contact with the printing surface of the sheet immediately after printing, so that the image is likely to bleed. Since there is a problem, it is preferable to carry the suction belt so that the image surface is not brought into contact with the print area as in this example.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 12K, 12C, 12M, and 12Y of the printing unit 12 has a length corresponding to the maximum paper width of the recording paper 16 targeted by the inkjet recording apparatus 10, and the nozzle surface has a recording medium of the maximum size. This is a full-line type head in which a plurality of nozzles for ink discharge are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 2).

  The heads 12K, 12C, 12M, and 12Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side in the recording paper 16 feed direction. 12K, 12C, 12M, and 12Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 16.

  A color image can be formed on the recording paper 16 by discharging different colors of ink from the heads 12K, 12C, 12M, and 12Y while the recording paper 16 is being transported by the belt transporting section 22.

  As described above, according to the configuration in which the full-line heads 12K, 12C, 12M, and 12Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 16 and the printing unit in the paper feeding direction (sub-scanning direction) The image can be recorded on the entire surface of the recording paper 16 by performing the operation of moving the 12 relatively once (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited.

  The image reading device 24 arranged at the rear stage of the printing unit 12 includes an image sensor for imaging the droplet ejection results by the heads 12K, 12C, 12M, and 12Y. From the droplet ejection image read by the image sensor, the nozzle eyes It functions as a means for checking for clogging, landing position deviation, droplet volume variation, and other ejection defects.

  The image reading device 24 includes, for example, a CCD line sensor having a light receiving element (photoelectric conversion element) row wider than a droplet discharge width (image recording width in the main scanning direction) by the heads 12K, 12C, 12M, and 12Y. And a moving mechanism for moving (scanning) this. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used. Further, the method of the image sensor is not limited to the CCD, and other image sensors such as CMOS can be used.

  A test pattern (sample chart) printed by the ink heads 12K, 12C, 12M, and 12Y of each color is read by the image reading device 24, and ejection detection of each head is performed. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like. Details will be described later.

  A post-drying unit 42 is provided downstream of the image reading device 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the head will be described. Since the structures of the respective heads 12K, 12C, 12M, and 12Y for each color are common, the heads are represented by the reference numeral 50 in the following.

  FIG. 2 (a) is a plan perspective view showing an example of the structure of the head 50, and FIG. 2 (b) is an enlarged view of a part thereof. FIG. 3 is a plan perspective view showing another example of the structure of the head 50, and FIG. 4 is a three-dimensional configuration of one-channel droplet discharge elements (ink chamber units corresponding to one nozzle 51) serving as a recording element unit. FIG. 4 is a cross-sectional view (a cross-sectional view taken along line 4-4 in FIG. 2A).

  In order to increase the dot pitch printed on the recording paper 16, it is necessary to increase the nozzle pitch in the head 50. As shown in FIGS. 2A and 2B, the head 50 of this example includes a plurality of ink chamber units (liquid chambers) including nozzles 51 serving as ink discharge ports, pressure chambers 52 corresponding to the nozzles 51, and the like. It has a structure in which the droplet ejection elements 53 are arranged in a staggered matrix (two-dimensionally), thereby projecting so as to be aligned along the head longitudinal direction (direction perpendicular to the paper feed direction) (orthographic projection) ) To achieve a high density of substantial nozzle interval (projection nozzle pitch).

  A configuration in which the nozzle row having a length corresponding to the full width Wm of the recording paper 16 is configured in a direction (arrow M direction; main scanning direction) substantially orthogonal to the feeding direction (arrow S direction; sub-scanning direction) of the recording paper 16 is as follows. It is not limited to this example. For example, instead of the configuration of FIG. 2 (a), as shown in FIG. 3, recording paper is formed by connecting short head modules 50 'in which a plurality of nozzles 51 are two-dimensionally arranged in a staggered manner. You may comprise the line head which has a nozzle row of the length corresponding to the full width of 16.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape (see FIGS. 2 (a) and 2 (b)), and the nozzle 51 is located at one of the diagonal corners. An outlet for supplying ink (supply port) 54 is provided on the other side. The shape of the pressure chamber 52 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon and other polygons, a circle, and an ellipse.

  As shown in FIG. 4, each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54. The common channel 55 communicates with an ink tank (not shown) as an ink supply source, and the ink supplied from the ink tank is distributed and supplied to each pressure chamber 52 via the common channel 55.

  An actuator 58 having an individual electrode 57 is joined to a pressure plate (vibrating plate that also serves as a common electrode) 56 constituting a part of the pressure chamber 52 (the top surface in FIG. 4). By applying a drive voltage between the individual electrode 57 and the common electrode, the actuator 58 is deformed and the volume of the pressure chamber 52 is changed, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. The actuator 58 is preferably a piezoelectric element using a piezoelectric material such as lead zirconate titanate or barium titanate. After the ink is ejected, when the displacement of the actuator 58 returns to its original state, new ink is refilled into the pressure chamber 52 from the common channel 55 through the supply port 54.

  By controlling the driving of the actuator 58 corresponding to each nozzle 51 according to the dot arrangement data generated from the input image, ink droplets can be ejected from the nozzle 51. A desired image can be recorded on the recording paper 16 by controlling the ink ejection timing of each nozzle 51 in accordance with the transport speed while transporting the recording paper 16 in the sub-scanning direction at a constant speed.

  As shown in FIG. 5, the ink chamber units 53 having the above-described structure are arranged in a constant arrangement pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle ψ that is not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in an oblique lattice shape.

That is, by adopting a structure in which a plurality of ink chamber units 53 are arranged in the direction of the angle ψ at a uniform pitch d in the main scanning direction, the pitch P _N of the nozzles projected so as to align in the main scanning direction is d × cosψ next, the main scanning direction, substantially hence the nozzles 51 can be handled as the equivalent arranged linearly at a fixed pitch P _N. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  When driving a nozzle with a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and the nozzles are sequentially driven from one side to the other for each block, etc., and one line (1 in the width direction of the paper (direction perpendicular to the paper conveyance direction)) Driving a nozzle that prints a line of dots in a row or a line consisting of dots in a plurality of rows is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scanning as described in (3) above is preferable. That is, nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, Nozzles 51-31,..., 51-36 as one block,...), And the nozzles 51-11, 51-12,. One line is printed in 16 width directions.

  On the other hand, by relatively moving the above-mentioned full line head and the paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. Defined as sub-scan.

  The direction indicated by one line (or the longitudinal direction of the belt-like region) recorded by the main scanning is referred to as the main scanning direction, and the direction in which the sub scanning is performed is referred to as the sub scanning direction. In other words, in the present embodiment, the conveyance direction of the recording paper 16 is the sub-scanning direction, and the direction orthogonal to it is the main scanning direction.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In the present embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is adopted. However, in the practice of the present invention, the method of ejecting ink is not particularly limited. Instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

[Explanation of control system]
FIG. 6 is a block diagram showing a system configuration of the inkjet recording apparatus 10. As shown in the figure, the inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a ROM 75, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like. It has.

  The communication interface 70 is an interface unit (image input unit) that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 72 controls the communication interface 70, the image memory 74, the motor driver 76, the heater driver 78, and the like, and performs communication control with the host computer 86, read / write control of the image memory 74 and the ROM 75, and the like. At the same time, a control signal for controlling the motor 88 and the heater 89 of the transport system is generated.

  The ROM 75 stores programs executed by the CPU of the system controller 72 and various data necessary for control. The ROM 75 may be a non-rewritable storage means, or may be a rewritable storage means such as an EEPROM. The image memory 74 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 76 is a driver (driving circuit) that drives the conveyance motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processes and corrections for generating a print control signal from image data (original image data) in the image memory 74 in accordance with the control of the system controller 72. And a controller that supplies the generated print data (dot data) to the head driver 84.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 6, the image buffer memory 82 is shown in a form associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 70 and stored in the image memory 74. At this stage, for example, RGB image data is stored in the image memory 74.

  In the ink jet recording apparatus 10, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory 74 is sent to the print control unit 80 via the system controller 72, and digital halftoning using a threshold matrix, error diffusion, or the like in the print control unit 80. It is converted into dot data for each ink color by processing.

  That is, the print control unit 80 performs processing for converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 80 is stored in the image buffer memory 82.

  The head driver 84 generates a drive signal for driving the actuator 58 corresponding to each nozzle 51 of the head 50 based on print data (that is, dot data stored in the image buffer memory 182) given from the print control unit 80. Output. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  When a drive signal output from the head driver 84 is applied to the head 50, ink is ejected from the corresponding nozzle 51. An image is formed on the recording paper 16 by controlling the ink ejection from the head 50 in synchronization with the conveyance speed of the recording paper 16.

  As described above, the ejection amount and ejection timing of ink droplets from each nozzle are controlled via the head driver 84 based on the dot data generated through the required signal processing in the print controller 80. Thereby, a desired dot size and dot arrangement are realized.

  The image reading device 24 includes a line sensor 241 (for example, a CCD image sensor or a CMOS image sensor) and a movement drive mechanism 242 that moves the line sensor 241. Although a specific form of the movement drive mechanism 242 is not shown, the movement drive mechanism 242 includes a mechanism unit that movably supports the line sensor 241, an electric drive motor, a power transmission mechanism thereof, and the like. The image reading device 24 reads the printed image (line pattern of the sample chart) by the line sensor 241, and provides information of the read image (electronic image data obtained by imaging) to the system controller 72.

  The system controller 72 and the print control unit 80 function as arithmetic processing means for processing image data obtained from the image reading device 24, and information on dot landing positions and dot diameters (ink volumes) acquired by a dot measurement method described later. In addition, various corrections are made to the head 50 based on satellite, dust / dust detection information, and the like, and control is performed to perform cleaning operations (nozzle recovery operations) such as preliminary ejection, suction, and wiping as necessary.

[Outline of dot measurement method]
In order to understand the dot measurement technique according to the embodiment of the present invention as a whole, an outline is first described. The dot measurement method according to the present embodiment is generally performed by the following procedure (steps 1 to 8).

  (Step 1): The ink to be measured is ejected from each nozzle of the inkjet head onto the recording paper, the head and the recording paper are relatively moved, and the ink ejected from each nozzle corresponds to each nozzle. A line pattern based on dot rows is formed on the recording paper. That is, a sample chart (measurement chart) in which a line pattern is formed using the ink to be measured is formed.

  The timing for forming this measurement chart is not particularly limited, such as when the head is attached, when there is a change that makes it impossible to recover the droplet ejection position due to maintenance, when a predetermined period has elapsed, at the start of work inspection, etc. It depends on the combination of head and maintenance unit.

  (Step 2): The recording paper is used with respect to the line direction of the line pattern formed in Step 1 (corresponding to the sub-scanning direction when a page-wide full-line head is used, which is referred to as “S direction”). While conveying, image the line pattern while scanning the image sensor on the conveyance path in a predetermined direction (in a plane parallel to the recording paper and perpendicular to the conveyance path direction) obliquely across the line pattern, Electronic image data of a captured image (an image obtained by reading a line pattern) is acquired.

  (Step 3): Profile graph representing fluctuations in the image signal value of the one-dimensional pixel array crossing the line pattern for the pixel position (X, Y) of the captured image (electronic image data) obtained by reading the line pattern in Step 2 Are obtained for one line pattern.

  (Step 4): For a plurality of profile graphs for one line pattern obtained in Step 3, each profile graph corresponds to the peak position corresponding to the density center of the line pattern (corresponding to “extreme position”, but white is the maximum) When corresponding to a value, it corresponds to “valley position”, but for convenience of explanation, both may be collectively referred to as “peak position”), and left and right edge positions (“first edge” of the line pattern) Position ”and“ second edge position ”). Note that there are two left and right edges in the width direction of the line pattern, and the position where the signal value becomes a predetermined gradation value corresponding to the edge in the profile graph is determined as the edge position.

  In calculating the edge position and the peak position, a known interpolation calculation is used based on the one-dimensional pixel grid position and the signal value (gradation value) of the profile graph, and the one-dimensional pixel grid position interval (pixels) in the profile graph is used. It is preferable to calculate the position with higher accuracy than (pitch). In this way, the peak position and the two edge positions are calculated from each profile graph for one line pattern.

  (Step 5): Data of peak positions and edge positions respectively obtained from a plurality of profile graphs for the same line pattern in Step 4 are aggregated, and approximation corresponding to the peak position of one line pattern is performed using the least square method. Approximate straight lines corresponding to straight lines and edge positions (two on the left and right) are calculated.

  (Step 6): For one line pattern, using two approximate lines corresponding to the two left and right edge positions, the vertical distance between the two lines is calculated, and the vertical distance is calculated as the line width of the line pattern. To do. Also, by using the approximate line corresponding to the peak position of each line pattern, the line pattern interval (distance between adjacent line patterns) is calculated from the vertical distance between the approximate lines corresponding to the peak positions of adjacent line patterns. calculate.

  (Step 7): On the other hand, by knowing the relationship (correlation) between the dot diameter and the line width with a predetermined combination of ink and recording paper, and also knowing the relationship between the volume of the ejected droplet and the dot diameter. The correlation data (corresponding table or the like) is stored in a storage means such as a memory.

  (Step 8): Based on the known relationship between the line width and the dot diameter (ink volume), the corresponding dot diameter (ink volume) is calculated from the line width of the line pattern calculated in step 6. Further, the relative droplet ejection position of each nozzle is calculated from the line pattern interval calculated in step 6.

  As described above, according to the present embodiment, the dot diameter (ink volume) and the dot landing position can be calculated simultaneously based on one imaging of the sample chart including the line pattern. . Further, since the dot diameter is calculated based on the line pattern, it is not necessary to calculate the area by clearly imaging the isolated dots as in the conventional case, and it is possible to use an imaging device having a relatively low resolution.

  Hereinafter, the dot measurement method according to the present embodiment will be described in more detail.

[1. (Description of line pattern in sample chart)
FIG. 7 is a schematic diagram illustrating an example of a line pattern formed on a recording sheet by an inkjet head. In FIG. 7, the vertical direction indicated by the arrow S represents the conveyance direction (sub-scanning direction) of the recording paper, and the horizontal direction indicated by the arrow M orthogonal thereto represents the longitudinal direction (main scanning direction) of the head 50. In the figure, for the sake of simplification, a head in which a plurality of nozzles are arranged in a row is illustrated. However, as described in FIG. 2, a matrix head in which a plurality of nozzles are two-dimensionally arranged is naturally used. Applicable. That is, the two-dimensional array of nozzle groups can be handled as being substantially equivalent to a single nozzle array by considering a substantial nozzle array that is orthogonally projected onto a straight line along the main scanning direction.

  By transporting the recording paper 16 while ejecting liquid droplets from the nozzles 51 of the head 50 toward the recording paper 16, ink droplets land on the recording paper 16, and as shown in FIG. A dot row (line pattern 92) in which dots 90 of the landing ink are arranged in a line is formed.

  FIG. 7 shows an example of a line pattern formed on the recording paper 16 when the landing position of the actually ejected ink and the ink volume fluctuate with respect to the regular nozzle arrangement in the head 50. ing.

  Each line pattern 92 is formed by droplet ejection from one nozzle. In the case of a line head having a high recording density, if droplets are simultaneously ejected from all nozzles, dots from adjacent nozzles partially overlap each other, so that a line of one dot row is not obtained. In order to prevent the line patterns 92 from overlapping each other, it is desirable that at least one nozzle, preferably three nozzles or more, be provided between the nozzles that are simultaneously ejected.

  FIG. 7 shows an example in which three nozzles are spaced apart. Each line pattern reflects the characteristics of the corresponding nozzle, and the landing positions (dot positions) and the dot diameters vary due to the characteristics of the individual nozzles, resulting in irregularities in the line pattern.

  In order to obtain a line pattern for all the nozzles 51 in the head 50, for example, a sample chart as shown in FIG. 8 is formed. In other words, in order to avoid the overlap of the line patterns, if an interval of 3 nozzles is provided, the nozzle number i (i = 1, 2, 3,...) Is attached from the end of the nozzle row in the head 50. A block in which a plurality of line patterns are formed in a direction perpendicular to the conveyance direction by nozzles having nozzle numbers corresponding to multiples, and a line pattern in the direction perpendicular to the conveyance direction by nozzles having nozzle numbers corresponding to multiples of 4 plus 1. Block formed with a plurality of nozzles having a nozzle number corresponding to a multiple of 4 plus 2 Nozzle with a nozzle number corresponding to a block formed with a plurality of line patterns in a direction perpendicular to the transport direction and a nozzle number corresponding to a multiple of 4 plus 3 A block consisting of four blocks such as a block in which a plurality of line patterns are formed in a direction perpendicular to the transport direction. To create a sample chart of forming a down pattern. Thereby, the line pattern about all the nozzles can be obtained.

  That is, in the line head, nozzle numbers constituting nozzle rows (substantially nozzle rows obtained by orthographic projection) arranged in a line substantially along the main scanning direction are sequentially arranged from the end in the main scanning direction. When n is given, n is an integer greater than or equal to 0, and for example, the droplet ejection timing is changed for each group (block) of nozzle numbers 4n, 4n + 1, 4n + 2, 4n + 3, and line patterns are formed respectively.

  As a result, as shown in FIG. 8, the line patterns of each block do not overlap each other, and the lines do not overlap each other in the block, so that independent lines (not overlapping other lines) are formed for all nozzles. it can. Note that other sample chart examples devised to increase the position detection accuracy between different blocks more than the position accuracy of the image reading apparatus will be described later (FIGS. 24 to 26).

[2. (Reading sample chart)
FIG. 9 shows an image reading apparatus that scans a line pattern 92 formed on the recording paper 16 and a line sensor 100 (corresponding to reference numeral 241 in FIG. 6) for reading the line pattern 92 in the horizontal direction (X direction). It is a figure which shows relative positional relationship.

  In FIG. 9, for convenience of explanation, the line sensor 100 in which the light receiving elements (photoelectric conversion elements) 101 are arranged in a line is shown. However, in actuality, R (red), G (green), and B (blue). A three-line sensor (so-called RGB line sensor) having a light-receiving element array for each RGB including color filters for each color is used. The light receiving surface of the line sensor 100 is disposed in parallel with the reading surface of the object to be imaged (the recording paper surface on which the line pattern 92 is recorded), and the light receiving element array is orthogonal to the recording paper conveyance direction (that is, (Parallel to the main scanning direction).

  Each line pattern 92 formed on the recording paper 16 by the line head is formed by droplet ejection from one nozzle. The recording paper 16 on which the line pattern 92 is formed is transported downward (y direction) in FIG. 9, and the line sensor 100 is in the lateral direction of FIG. 9 (perpendicular to the transport direction of the recording paper 16). Moved.

  That is, by capturing the image while moving the recording paper 16 relatively in the transport direction (y direction) and also moving the line sensor 100 in the light receiving element arrangement direction (x direction in FIG. 9), the entire surface of the sample chart ( All line patterns) are captured as electronic image data.

  Assuming that the conveyance speed of the recording paper 16 in the conveyance direction is Vy (mm / sec) and the movement speed of the line sensor is Vx (mm / sec), each light receiving element 101 on the line sensor 100 is moved by the two-axis simultaneous movement. As shown in the drawing, the image of the line pattern 92 is captured while passing obliquely on the recording paper 16 at an angle θ determined by the ratio of Vx and Vy. In FIG. 9, a cell 102 indicates the scanning position of the light receiving element 101 that passes (relatively moves) on the recording paper 16 in time series. When attention is paid to the locus of a certain light receiving element (for example, reference numeral 101j), it moves along the line of the filled cell (pixel) indicated by reference numeral 103 in FIG. The scanning is performed on a straight line having an angle θ that obliquely crosses the pattern 92. The same applies to each light receiving element of the line sensor 100, and the line sensor 100 as a whole is read through a parallelogram area as shown in FIG.

  FIG. 10 shows image data read by the image reading apparatus. Reference numeral 104 in FIG. 10 indicates a pixel of the image data, and each pixel 104 has a signal value (tone value) reflecting the optical density of the subject (here, the density of the line pattern). The horizontal direction in FIG. 10 is the X axis, and the vertical direction perpendicular thereto is the Y axis, and the pixel grid position on the image data is expressed as coordinates (X, Y). In FIG. 10, the ratio of the pixel (cell) and dot size of the image data does not necessarily reflect the actual ratio, and for the sake of convenience of description, the pixel unit is drawn larger than the actual (others). The same applies to the drawings).

  As described with reference to FIG. 9, the correspondence between each imaging position of each light receiving element 101 of the line sensor 100 and the actual position on the recording paper 16 is the relative movement between the recording paper 16 and the line sensor 100 (Vy and Vx). When the image data acquired by the method described in FIG. 9 is returned to the cross coordinate system, a line is formed on the electronic image data having a two-dimensional pixel lattice as shown in FIG. The pattern 92 is recorded as an oblique line that obliquely crosses the pixel grid.

Assuming that the arrangement pitch (pixel pitch) of the light receiving elements 101 in the line sensor 100 is sp (mm / pixel) (see FIG. 9), the pixel size XPixel_size in the X direction on the image data shown in FIG.
XPixel_size = sp (mm / pixel)
It is represented by For the pixel size YPixel_size in the Y direction, the reading cycle of the line sensor 100 is T (sec / pixel),
SXPixel_size = Vx (mm / sec) x T (sec / pixel)
SYPixel_size = Vy (mm / sec) x T (sec / pixel)
As
YPixel_size = {(SXPixel_size) ² + (SYPixel_size) ² } ^1/2
It becomes.

  The imaged line pattern is imaged on the image data in a state inclined at an angle θ determined by the ratio of Vx (mm / sec) and Vy (mm / sec).

  As described above, the sample chart of the line pattern formed on the recording paper 16 is read by the imaging device of the image reading device and converted into electronic image data. The reading resolution at this time is preferably 1200 DPI (Dots Per Inch) or more.

[3. Analysis of captured image data)
Next, processing contents of electronic image data acquired by imaging will be described.

  Image analysis is performed on the read image data with a color corresponding to the type of ink. Regarding the relationship between the ink color and the processing channel (color, RGB), the color (processing channel) having the maximum contrast among the RGB is selected for each ink. That is, it is desirable to perform analysis using a signal R for cyan ink, G for magenta ink, B for yellow ink, and G for black ink. For the other special colors, a color having the maximum contrast may be selected from among RGB. On the contrary, it is preferable to use a color (channel) signal that has the minimum contrast for the ink to be measured when determining dust / dust as will be described later. If the contrast is the same for multiple channels, select a color with less noise.

  Specific contents of the captured image data analysis are as follows. First, based on the electronic image data obtained by imaging, a profile graph representing the fluctuation of the image signal value of the one-dimensional pixel column along the lattice direction (here, the Y direction) crossing each line pattern is obtained.

  FIG. 11 schematically shows the relationship between a one-dimensional pixel column for obtaining a profile graph and a line pattern on a sample chart. In the figure, the range of the pixel column filled with halftone dots indicates the portion of the jth one-dimensional pixel column that crosses the line pattern where the image signal value is increased by the ink dot of the line pattern.

  As shown in FIG. 11, there are a plurality of one-dimensional pixel rows (pixel rows arranged in the reading scanning direction (Y direction)) crossing one line pattern, and a profile graph is obtained from each pixel row. A plurality of profile graphs are obtained for the line pattern.

  FIG. 12 shows an example of a profile graph. The horizontal axis in FIG. 12 represents the pixel position in the Y direction, and the vertical axis represents the image signal value (that is, a value reflecting the density). The plurality of curves (graphs) in FIG. 12 have different pixel positions in the X direction. As shown in the drawing, a plurality of profile graphs are obtained corresponding to pixel positions in the X direction. The profile graph shows fluctuations in brightness. Here, the higher the dot density by ink, the larger the image signal value, and the portion where no dot exists (the portion of the recording paper, that is, white) is the image. The signal value is low.

  The peak position of the profile graph substantially corresponds to the center of the line width of the line pattern, and the pixel position where the image signal value becomes a predetermined value (for example, the gradation value indicated by density “70” in FIG. 12) is the line pattern. Edge position (boundary position in the width direction).

  Specifically, the gradation value corresponding to the edge position from each profile graph, and the pixel position (both left and right) that becomes a gradation value by interpolation calculation from this gradation value or a position that changes across this gradation value are displayed. calculate. Also, the peak position corresponding to the position having the highest optical density of the line pattern (in the case of the density signal, luminance signal, and brightness signal, the valley position having the smallest signal value) is calculated. When calculating the peak position, the extreme value position of the change in the signal value is calculated from the preceding and following signal values by interpolation calculation.

  For each line pattern read from the sample chart, the edge position (left and right) and peak position are calculated from the corresponding profile graphs, and these information are collected to convert the position information into a physical distance on the recording paper. To do.

  For example, when the edge position of the profile graph is detected as a position (x, y) on the image, the position (x, y) is converted to a position on the recording paper.

  The relationship between the position Ps (x, y) on the image shown in FIG. 10 and the corresponding position on the actual recording paper is as follows.

The position in the X direction on the recording paper is XPixel_size × x + YPixel_size × y × cos (θ)
The Y-direction position on the recording paper is YPixel_size × y × sin (θ)
That is, the position Ps (x, y) on the image is the position on the recording paper (XPixel_size × x + YPixel_size × y × cos (θ), YPixel_size × y × sin (θ))
(Unit: [mm]).

  However, for θ, tan (θ) = − Vy / Vx.

When Vx is zero, θ is π / 2, and the position on the recording paper is
(XPixel_size × x, | Vy × T | × y)
It becomes.

  The position (x, y) detected in the profile graph on the image data is converted to the position (X, Y) on the recording paper by the above conversion, and the line pattern of the line pattern is calculated by the least square calculation of the edge position and the least square calculation of the peak position. An edge position straight line and a peak position straight line are obtained. In calculating the approximate line based on the least square method for each of the left and right edge positions and the peak positions corresponding to each line pattern, these three approximate lines may be obtained independently, so that the slopes of the lines match. An approximate straight line may be obtained with a restriction on.

  Based on the approximate straight line obtained as described above, the vertical distance between the approximate straight line corresponding to the left edge of each line pattern and the approximate straight line corresponding to the right edge is calculated to obtain the line width.

  In addition, when obtaining an approximate line, if the calculation is performed with restrictions so that the slopes of the straight lines match, there is no problem with the above method. However, if three approximate lines are obtained independently, the corresponding line pattern Obtain the center position of the edge position (for example, simply specify the average position of the edge position coordinates as the center position), and apply the X coordinate of the center position of the left edge position to the approximate straight line of the left edge to obtain the Y coordinate Then, the distance between the X coordinate, the Y coordinate, and the approximate straight line of the right edge is obtained. Next, the X coordinate of the center coordinate of the right edge position is applied to the approximate straight line of the right edge to obtain the Y coordinate. And the distance between the Y coordinate and the approximate straight line of the left edge. The average value of these two distances is taken as the line width.

  Regarding the peak position, the distance between the line patterns can be obtained using the same method as described above. That is, when the approximate straight lines corresponding to the peak positions corresponding to the respective line patterns are calculated so that the slopes are matched so as to be parallel between the respective line patterns, the distance between the approximate straight lines corresponding to the adjacent peak positions is This corresponds to the interval between the dot landing positions formed from the nozzles.

  On the other hand, when the approximate straight line is obtained so as not to be parallel in each line pattern, the center position of the peak position corresponding to each line pattern is obtained. For example, the average value of the X coordinate at the peak position corresponding to each line pattern is obtained, and the average value of the X coordinate is applied to the approximate straight line to obtain the Y coordinate. The distance between the X and Y coordinates and the approximate straight line corresponding to the peak position of the adjacent line pattern is obtained. Next, the center position of the peak position of the adjacent line pattern is obtained, and the distance from the approximate curve corresponding to the other line pattern is obtained. The average value of these two distances is taken as the interval between the dot landing positions formed from the nozzles.

[4. Method for obtaining the dot diameter (ink volume) based on the line width of the line pattern]
After the line width of the line pattern is specified by the image analysis described above, the dot diameter (ink volume) is calculated by the following method based on the line width information.

  That is, according to a combination of a predetermined recording paper type and ink, an isolated dot (preferably a plurality) is formed on the recording paper with ink ejected from one nozzle, and then a line pattern is formed. By imaging using the attached high-resolution camera, the dot diameter of the isolated dot and the line width of the line pattern are measured from the obtained image data. In this way, the sample chart B in which the isolated dots and the line pattern are paired is measured, and a conversion function indicating the relationship between the isolated dot diameter and the line width of the line pattern (“dot diameter−line width indicating the correlation between the dot diameter and the line width”). Correlation function ") is obtained in advance. The dot diameters of the isolated dots and the line widths of the dot rows that are ejected in a line form have different spread rates and are not the same value.

  The sample chart B is the same (same type) recording paper and ink combination (recording conditions) as the above-described measurement sample chart A.

  Further, the line pattern portion of the sample chart B has already been described [2. Sample chart reading], [3. The line width is calculated by a technique (hereinafter referred to as “method of the present embodiment”) by “captured image data analysis”. Then, a conversion function representing the relationship between the line width measured by the microscope camera and the line width of the line pattern measured by the method according to this embodiment (correlation between the measurement result by the microscope camera and the measurement result by the method of this embodiment). “Measurement result correlation function”) to be expressed is obtained in advance.

  By combining the above two conversion functions (“dot diameter-line width correlation function”, “measurement result correlation function”), the line width information of the line pattern measured by the method of this embodiment is converted into the dot diameter information. Can be converted to Note that the relationship between the isolated dot diameter and the line width obtained by the method of this embodiment may be obtained as a direct conversion function.

  Furthermore, the ink volume flying from the nozzle is measured by a known method, the dot diameter formed by the dots of the ink volume is measured with a microscope camera, and the relationship between the ink volume and the dot diameter is converted into a conversion function (ink volume and dot ("Volume-dot diameter correlation function" indicating the correlation between diameters) and the conversion function ("volume-dot diameter correlation function") and the above-mentioned two conversion functions ("dot diameter-line width correlation function", "measurement") In combination with the result correlation function "), the ink volume can be obtained from the line width information.

  When measuring isolated dots and determining the dot diameter, it is desirable to measure a plurality of isolated dots and use the average value.

  The “measurement result correlation function”, “volume-dot diameter correlation function”, and “dot diameter-line width correlation function” are obtained by calculating the relationship between two variables representing the measurement results as a polynomial function by curve fitting using a polynomial. The conversion function may be used as a polynomial. Alternatively, the relationship between the two variables representing the measurement result is obtained by performing a known noise shaving process or smoothing process to obtain the two variables after processing as a table format, and when using the function, a known spline function, The conversion function may be used by linear interpolation.

  An example of a method for obtaining the “volume-dot diameter correlation function” will be described. The volume of ink flying from a specific nozzle is obtained a plurality of times by a known method, the average value is calculated, and the ink flying from the specific nozzle is dot-dotted. Suitable for printing on the same (same type) recording paper as the sample chart A for measurement, measure multiple dot diameters with a microscope camera, calculate the average value, and convert the relationship between ink volume and dot diameter to a conversion function (ink "Volume-dot diameter correlation function") indicating the correlation between volume and dot diameter.

  As a method for measuring the volume of ink flying from the known nozzle, a method of imaging a flying object with a high-speed camera, or receiving a plurality of droplets in a container, the weight of the container before droplet ejection and A method can be used in which the weight of one droplet is obtained from the difference in the weights of the containers and the number of droplet ejections, and the ink volume is obtained from the ink density.

[Specific examples of image analysis processing contents]
This will be described in more detail below.

  (Procedure 1) For each line pattern block of the captured image data obtained by reading the measurement sample chart A described in FIG. 8, as shown in FIG. 13, a quadrilateral that crosses each line pattern block (dotted line in the figure) A profile showing the fluctuation of the signal value in the scanning direction by scanning the image in the direction of the arrow at a rough interval (for example, near the center and both ends as shown by the arrow in the figure) along the rectangle shown in FIG. Get the graph.

  An example is shown in FIGS. 14 and 15, the horizontal axis represents the pixel position, and the vertical axis represents the signal value of the image. However, in FIGS. 14 and 15, here, the higher the dot density by ink, the smaller the signal value, and the portion where the dot does not exist (the portion of the recording paper, that is, white) has a large signal value. It has become. In this respect, the significance of the signal value is different from the graph described with reference to FIG. 12 (the magnitude relationship between the density and the signal value is opposite).

  (Procedure 2) Next, the profile graph obtained in Procedure 1 is cut horizontally by a predetermined signal value to obtain intersecting coordinates.

  Then, the signals are classified in the order in which the signals change (white to black, or black to white), and are counted for each coordinate corresponding to the same order and the same signal changing direction. In this way, the left edge and the right edge corresponding to the same line pattern can be classified across image scans.

  (Procedure 3) Based on the obtained coordinate group of the right edge for each line pattern, a straight line forming the edge is obtained by using a least square method or the like. Similarly, a straight line forming the left edge is obtained.

  (Procedure 4) A straight line corresponding to the left and right edges obtained for each line pattern, and a quadrilateral including each line pattern (see FIG. 16), and a line by the upper and lower sides of the first quadrangle (see FIG. 13), a line A quadrilateral that is between patterns and does not include a line pattern is determined (see FIG. 17).

  At this time, the line pattern cannot be completely included depending on the predetermined signal value defining the edge, but the quadrilateral including the line pattern is expanded in parallel to the straight line corresponding to the left edge (the same applies to the right). A quadrilateral that completely contains the line pattern can be determined.

[Shading correction]
The image reading apparatus has non-uniformity of a read signal called shading. As shown in FIGS. 14 and 15, in the profile graph, the level of white and black varies between graphs corresponding to each line pattern. appear. Such fluctuations in the monochrome level adversely affect the calculation accuracy (position accuracy) of the edge position based on the signal value (tone value). Therefore, the following shading correction is performed from the viewpoint of improving the position accuracy.

  Assuming that the X direction is the horizontal (horizontal) direction and the light receiving elements of the line sensor are arranged, the Y direction is the vertical (vertical) direction, and the sub-scanning direction of the line sensor, each of the four sides including the line pattern is used as the shading correction. With respect to the shape (refer to each quadrilateral shown by a thick line in FIG. 16), shading correction in the X direction and shading correction in the Y direction are performed as follows.

[Shading correction method in X direction]
(1) First, a signal value corresponding to black is determined in the quadrilateral including the line pattern described in FIG. In the determination method, a signal corresponding to black is obtained as a minimum value or maximum value (in the X direction in the quadrilateral), and averaged in the Y direction to determine a signal value corresponding to black. This signal value is assumed to be “BKi”.

  (2) On the other hand, in the quadrilateral that does not include the line pattern described with reference to FIG. 17, the signal corresponding to white is the minimum value in the X direction for an image obtained by low-pass processing the image in the X direction within the quadrilateral. Alternatively, the maximum value is obtained and determined as a table associated with the Y coordinate for each Y direction. This table is set as “WH_TBLi (Y)”, and a signal value “WHi” averaged in the Y direction is obtained.

  In this way, the above values (BKi, WHi) are obtained for all quadrilaterals (a quadrilateral including a line pattern and a quadrilateral not including a line pattern).

  (3) Next, an average value BKave of quadrilateral BKi including each line pattern and an average value WHave of quadrilateral WHi not including each line pattern are obtained.

  (4) In a quadrilateral including each line pattern, a correction value for correcting shading in the X direction is determined as follows.

(5) BKi of the quadrangle including the line pattern of interest, X1i as the center coordinate in the X direction, WHi corresponding to white on the left side of the quadrangle not including the line pattern adjacent to the quadrilateral as WH0i, and the X direction If the center coordinates are X0i, the right side WHi is WH2i, and the center coordinates in the X direction are X2i,
When the X coordinate is X0i,
Output signal = gain0 x input signal + offset0
gain0 = (WHave -BKave) / (WH0i -BKi), offset0 = -gain0 × BKi + BKave
That is, a linear transformation is defined such that when the input value is BKi, the output value is BKave, and when the input value is WH0i, the output value is WHave.

(6) Similarly, when the X coordinate is X1i, when the input value is BKi, the output value is BKave, and when the input value is (WH0i + WH2i) / 2, the linear conversion is such that the output value becomes WHave ( (Formula)
Output signal = gain1 x input signal + offset1
Define

(7) Similarly, when the X coordinate is X2i, the input value is BKi, the output value is BKave, and when the input value is WH2i, the linear transformation is such that the output value is WHave (the following equation)
Output signal = gain2 x input signal + offset2
Define

(8) Using the formula defined above, when the X coordinate is between X0i and X1i (X0i <x <X1i),
gain (x) = s × gain0 + t × gain1,
offset (x) = s × offset0 + t × offset1
However, s = (X1i-x) / (X1i-X0i), t = (x-X0i) / (X1i-X0i)
Apply
When the X coordinate is between X1i and X2i (X1i <x <X2i),
gain (x) = s × gain1 + t × gain2
offset (x) = s × offset1 + t × offset2
However, s = (X2i-x) / (X2i-X1i), t = (x-X1i) / (X2i-X1i)
The following formula is applied: Output value = gain (x) x Input value + offset (x)
To correct in the X direction.

[Shading correction method in Y direction]
Next, shading correction in the Y direction will be described. In the quadrilateral including the line pattern described with reference to FIG. 16, a correction value for correcting shading in the Y direction is determined as follows.

(1) WH_TBLi (Y) corresponding to the white on the left side of the quadrilateral that does not include the line pattern and is adjacent to the target quadrilateral (including the line pattern) is set as WH_TBL0i (Y), and WH_TBLi (Y) corresponding to the right side ) Is WH_TBL1i (Y),
Determine the whitest data WhPeak0 in WH_TBL0i (Y) and
Scale0 (Y) = WhPeak0 / WH_TBL0i (Y)
Determine.

(2) Similarly, the whitest data WhPeak1 in WH_TBL1i (Y) is determined and
Scale1 (Y) = WhPeak1 / WH_TBL1i (Y)
Determine.

  (3) Then, Scalek (Y) for correcting the signal value corresponding to white so as to be constant in the Y direction is obtained.

Scalek (Y) = {Scale0 (Y) + Scale1 (Y)} / 2
(4) Correction is performed as follows. The signal S (X, Y) of the coordinates (X, Y) is
S ′ (X, Y) = gain (X) × S (X, Y) + Offset (X)
S ″ (X, Y) = Scalek (Y) × S ′ (X, Y)
However, Scalek (Y) differs depending on the quadrangle (k) including the corresponding line pattern.

[Get profile graph corresponding to line pattern]
(Procedure 5) For the quadrilateral that completely includes the line pattern described in Procedure 4, the image is scanned in the X direction or the Y direction as indicated by the thick arrow in FIG. Get a profile graph showing the variation. The profile graph performs the above-described shading correction according to the coordinates (X, Y) to be scanned.

  The profile graph is preferably subjected to low-pass filter processing in order to reduce noise.

  In FIG. 16, a profile graph obtained from a quadrilateral including the k-th line pattern is expressed as follows.

ProfGraphYkx (Y): Scan in the Y direction (x: X coordinate in the quadrilateral)
ProfGraphXky (X): Scan in X direction (Y: Y coordinate in quadrilateral)
[Process to identify peak position]
(Procedure 6) In the profile graph obtained in the above procedure 5, when the magnitude relation of the signal values is white> black, the position of the valley of the profile graph is shown. When the magnitude relation is white <black, the profile A peak position (corresponding to the nozzle ejection position) is determined as the peak position of the graph.

The peak position when the valley position is the peak position is determined as follows. That is, in the case of a profile graph obtained by scanning three points satisfying [Si-1 ≧ Si and Si <Si + 1], or [Si-1> Si and Si ≦ Si + 1], in the X direction, (X, S) = {(xi-1, Si-1), (xi, Si), (xi + 1, Si + 1)} is obtained as a quadratic function (ax ² + bx + c) The X coordinate -b / (2a) taken is taken as the peak position coordinate. The Y coordinate is the Y coordinate that is the base point of the scan. S is a signal value on the profile graph after the correction process, and the subscript indicates that scanning is performed in one pixel unit in a predetermined direction (X direction or Y direction) (continuous subscripts are in a predetermined direction). Indicates that they are adjacent.)

In the case of a profile graph obtained by scanning in the Y direction, instead of the above three points (x, S), [Si-1 ≧ Si and Si <Si + 1] or [Si-1> Si and Three points (Y, S) = {(yi-1, Si-1), (yi, Si), (yi + 1, Si + 1)} satisfying Si≤Si + 1] are used. A quadratic function (ay ² + by + c) is obtained and the Y coordinate −b / (2a) taking the extreme value is used as the peak position coordinate. At this time, the X coordinate used as the base point of the scanning is used as the X coordinate.

On the other hand, the peak position when the peak position is the peak position is three points satisfying [Si-1 ≦ Si and Si> Si + 1] or [Si-1 <Si and Si ≧ Si + 1]. , The profile graph obtained by scanning in the X direction passes through (x, S) = {(xi-1, Si-1), (xi, Si), (xi + 1, Si + 1)}. A quadratic function (ax ² + bx + c) is obtained, the X coordinate −b / (2a) taking the extreme value is used as the coordinate of the peak position, and the Y coordinate used as the base point of the scanning is used as the Y coordinate.

In the case of a profile graph obtained by scanning in the Y direction, three points satisfying [Si-1 ≦ Si and Si> Si + 1] or [Si-1 <Si and Si ≧ Si + 1] ( Y, S) = {(yi -1, Si-1), (yi, Si), (yi + 1, Si + 1)} seeking quadratic function through ^{(ay 2 + by + c)} , an extreme value The Y coordinate -b / (2a) is the coordinate of the peak position, and the X coordinate that is the base point of the scan is used as the X coordinate.

  Thus, the peak position can be specified with high accuracy by obtaining the extreme value (peak position) by quadratic function approximation.

[Process to identify edge position]
(Procedure 7) Next, the process of specifying the edge position from the profile graph obtained in the procedure 5 will be described. The edge position is determined as follows when one of the left and right edges (here, “edge L” on the left side) is determined, where T is a predetermined gradation value serving as a reference for determining the edge of the line width. To do.

(A) When the valley position is the peak position When the valley position is the peak position, the following three conditions are satisfied: Si-1> Si and Si> Si + 1, and Si ≧ T and T ≧ Si + 1. In the case of a profile graph obtained by scanning the dots in the X direction, (x, S) = {(xi-1, Si-1), (xi, Si), (xi + 1, Si + 1)} Among them, the X coordinate of the intersection of the straight line passing through the two points (xi, Si) and (xi + 1, Si + 1) corresponding to Si and Si + 1 and the straight line of the gradation value T is defined as the edge position (edge L ). The Y coordinate at this time is the Y coordinate that is the base point of the scanning.

  In the case of a profile graph obtained by scanning in the Y direction, three points (y, S) = {that satisfy Si-1> Si and Si> Si + 1, and Si ≧ T and T ≧ Si + 1. Of (yi-1, Si-1), (yi, Si), (yi + 1, Si + 1)}, two points (yi, Si), (yi + 1, The coordinates of the intersection of the straight line passing through (Si + 1) and the straight line of the gradation value T are used as the coordinates of the edge position (edge L). The X coordinate at this time is the X coordinate that is the base point of the scan.

(B) When the peak position is the peak position When the peak position is the peak position, three conditions satisfying Si-1 <Si and Si <Si + 1, and Si≤T and T≤Si + 1 are satisfied. Of the points, two points corresponding to Si and Si + 1 ((xi, Si), (xi + 1, Si + 1) when scanned in the X direction, (yi, Si) when scanned in the Y direction. , (Yi + 1, Si + 1)) and the coordinates of the intersection of the line of gradation value T are the coordinates of the edge position (edge L).

  Similarly, with respect to the other edge (here, “edge R” on the right side), when the valley position is the peak position, Si−1 <Si and Si <Si + 1, and Si ≦ T and T ≦ Si In the case of a profile graph obtained by scanning three points satisfying +1 in the X direction, (x, S) = {(xi-1, Si-1), (xi, Si), (xi + 1, X + 1 of the intersection of the straight line passing through the two points (xi, Si) and (xi + 1, Si + 1) corresponding to Si and Si + 1 and the straight line of the gradation value T Is the coordinates of the edge position (edge L). The Y coordinate at this time is the Y coordinate that is the base point of the scanning.

  In the case of a profile graph obtained by scanning in the Y direction, three points (y, S) = {satisfying Si-1 <Si and Si <Si + 1, and Si≤T and T≤Si + 1. Of (yi-1, Si-1), (yi, Si), (yi + 1, Si + 1)}, two points (yi, Si), (yi + 1, The coordinates of the intersection between the straight line passing through (Si + 1) and the straight line of the gradation value T are taken as the coordinates of the edge position (edge R). The X coordinate at this time is the X coordinate that is the base point of the scan.

  In the case where the peak position is the peak position, Si-1> Si and Si> Si + 1, and Si ≧ Si + 1 among the three points satisfying Si ≧ T and T ≧ Si + 1. Two corresponding points ((xi, Si), (xi + 1, Si + 1 when scanned in the X direction), (yi, Si), (yi + 1, Si + 1) when scanned in the Y direction The coordinate of the intersection of the straight line passing through and the straight line of the gradation value T is defined as the coordinate of the edge position (edge R).

  As described above, since the coordinates of the edge position are calculated from the intersection of the straight line passing through the two points sandwiching the predetermined gradation value T serving as a reference value for determination and the straight line of T, the accuracy of the captured image is more accurate than the resolution of the captured image. The edge position can be specified.

[Additional processing to further improve measurement accuracy]
[Satellite measures]
In some cases, a sub-droplet (so-called satellite droplet) separated from the main droplet may be generated for a specific nozzle for some reason such as nozzle failure. Satellite dots may be formed when the satellite droplets adhere to positions different from the main droplets on the recording paper. In this case, as shown in FIG. 18, in the line pattern of the sample chart, the dot row 116 of the satellite dots 114 due to the landing of the sub-droplet is added to the dot row 112 due to the landing of the sub-droplet to the dot row 112 due to the landing of the main droplet. become.

  As shown in FIG. 19A, the profile graph crossing a normal line pattern without satellites has symmetry about the peak position (the horizontal axis is the pixel position in the Y direction). On the other hand, the profile graph that crosses the line pattern including the satellite dots 114 has an asymmetric shape because it includes satellite signal components as shown in FIG. 19B, for example. Therefore, the presence or absence of satellite dots is determined from the asymmetry of the profile graph corresponding to the line pattern and the presence of sub-peaks (due to satellites), and recalculation is performed by determining the amount of deviation from the edge estimation position.

  The following method can be used as a specific processing example for determining the presence or absence of satellite dots.

  That is, the profile graph of a line pattern including satellites is as shown in FIG. When the interval between the left edge position and the peak position in the profile graph is t0 and the interval between the peak position and the right edge position is t1, R = t0 / (t0 + t1) is about 0.5 when the profile graph is symmetrical. Become. On the other hand, since the symmetry is lost when satellites are included, the value of R deviates from 0.5 and takes a value close to 0 or 1.

  Therefore, if the absolute value D = ABS (R−0.5), which is the difference between the R value and “0.5”, is larger than the predetermined value, it is determined that there is a satellite. Although it is desirable to determine the optimum value experimentally and determine the optimum value, it can be approximately 0.07 or more.

  If satellites are detected, the information is saved and used for control such as head maintenance (cleaning operation to restore nozzle ejection performance, such as nozzle suction, preliminary ejection, and nozzle surface wiping). It is also possible to do.

[Countermeasures against dust and dust when scanning]
In addition, dust or dust may adhere to the sample chart for some reason, and it is assumed that dust or dust (hereinafter referred to as “dust”) adversely affects line pattern reading and image analysis. . Reference numeral 120 in FIG. 18 shows a state in which dust adhering to the sample chart is imaged. The following measures will be taken as countermeasures against such dust and dust.

  In general, dust does not have an absorption peak, so the RGB signal shows similar fluctuations with respect to dust. Therefore, the presence / absence of dust is determined from the read wavelength data deviated from the absorption wavelength of the ink to be measured, and the profile data including the influence of dust is excluded from the calculation.

  For example, when calculating a dot position and a dot diameter by reading a line pattern formed with cyan ink, dust and cyan ink (indicating the largest fluctuation in the R signal) are used for the G signal (or B signal). It can be calculated that the influence of the dust is reduced by determining that the position where the signal fluctuation is large is affected by the dust and excluding it from the profile graph used for calculating the peak position / edge position.

[Trash / dust countermeasure processing example]
Specifically, the following processing is performed. For the dust / dust detection channel that is different from the color channel used for the processing after calculating the edge position and peak position, the statistical value for each signal value at the calculated position (each of the left and right edge positions and peak position), specifically, Calculate the mean and standard deviation σ (sigma).

  When the signal value of the dust / dust detection channel is more than ± 3σ (sigma) from the average value (average value + 3σ or more, or average value −3σ or less), the signal value is considered to be affected by dust, Delete (exclude) position data. At this time, when the coordinates are real numbers, rounded integer positions are used.

  If the contrast of different dust / dust detection channels is high, such as black ink, the statistical value (average value) of the vertical distance between the straight line calculated by the least-squares method described later and the coordinate position used for the least-squares And the standard deviation σ), and if the distance is more than ± 3σ, the position data is deleted and a straight line by the least square method is calculated again.

  Similarly to satellite detection, if dust or dust is detected, the information is saved and head maintenance (cleaning operation to restore nozzle ejection performance, such as nozzle suction, preliminary ejection, and nozzle surface wiping) It can also be used for control such as implementing

[Calculation of straight line by least square method]
(Procedure 8) As described in Procedures 6 and 7, for the quadrangle k including the line pattern, the peak position and the edge L obtained as described above from a plurality of profile graphs crossing the line pattern existing in the quadrilateral. Based on the data of the coordinates (X, Y) of the edge R, straight lines AX + BY + C = 0 corresponding to the peak position, the edge L, and the edge R are obtained using the least square method. A straight line corresponding to the peak position is Pk, a straight line corresponding to the edge L is Lk, and a straight line corresponding to the edge R is Rk.

[Measurement of dot landing position (effective nozzle position) and line width]
(Procedure 9) From the straight line Pk, the straight line Lk, and the straight line Rk obtained by multiplying the minimum with respect to the quadrangle k including the line pattern by the procedure 8, the nozzle position (dot landing position) and the line width are set as follows. So ask.

(a) Line width calculation method The line width D is calculated as an average value of D0 and D1 obtained as follows. That is, an intersection C0 between the straight line RVk and the straight line Lk that passes through the center coordinates of the quadrangle k including the line pattern is obtained, and a vertical distance D0 between the intersection C0 and the straight line Rk is obtained (see FIG. 21). It should be noted that a physical distance corresponding to one pixel can be converted into a physical distance by multiplying XY by a physical distance corresponding to one pixel at the stage of the X coordinate and Y coordinate before calculating the distance.

  Similarly, an intersection C1 between the straight line LVk and the straight line Rk passing through the center coordinates of the quadrangle k including the line pattern is obtained, and a vertical distance D1 between the intersection C1 and the straight line Rk is obtained.

Then, from the obtained vertical distances D0 and D1, the following expression D = (D0 + D1) / 2
To obtain the line width D.

(B) Method for calculating nozzle position For the dot landing position (that is, effective nozzle position), the average value θ of the inclination of the straight line Pk is calculated for each quadrangle k, and the inclination θV perpendicular to this inclination is obtained. Then, a straight line BaseLine having the inclination θV passing through the center position of the entire line pattern block (which may be the average value of the center positions of the respective quadrilaterals k) is obtained, and the intersection point CPk between the straight line BaseLine and each straight line Pk is determined.

  A distance between points CPk arranged in a straight line on the straight BaseLine represents an effective nozzle interval. Further, the position of the point CPk corresponds to an effective nozzle position (dot landing position by droplet ejection of each nozzle).

  When there are a plurality of such line pattern blocks (for example, when the sample chart described in FIG. 8 is used), the average value of the slopes of the straight line Pk in all the blocks is calculated, and the slope θV perpendicular to this slope is calculated. In each block, a straight line BaseLine passing through the center position BCk in each block is obtained (see FIG. 22), and an intersection CPk between the straight line BaseLine corresponding to this block and each straight line Pk determined by the line pattern included in the block. (See FIG. 23).

  Next, a common reference line CommonBaseLine (inclination θV) passing through the center position AC of all the blocks is obtained, and as shown in FIG. 23, the intersection BCCk with the perpendicular line dropped from the center position BCk on each straight line BaseLine to the common reference line CommonBaseLine. The parameters (Move_Xk, Move_Yk) for translation from BCk to BCCk are calculated, and the CPk is translated using the parameters (Move_Xk, Move_Yk). This is equivalent to mapping a BaseLine to a common reference line CommonBaseLine. Note that Move_Xk represents the amount of translation in the X-axis direction, and Move_Yk represents the amount of translation in the Y-axis direction.

  In this way, since all the blocks can be mapped onto the common reference line CommonBaseLine, the dot formation position (nozzle position) divided into each block is obtained as a common one-dimensional coordinate.

  However, nozzle positions belonging to different blocks mapped on the common reference line CommonBaseLine may have an error due to the influence of the conveyance accuracy of the image reading apparatus and the sensor pitch. Even though the nozzle positions are adjacent to each other, they are separated from each other as a block of line patterns on the sample chart, and therefore it is assumed that the measurement result is strongly influenced by the above fluctuation.

[Process to correct position error between line pattern blocks]
As an example of means for solving such a problem, in order to increase the position detection accuracy between different blocks more than the position accuracy of the reading apparatus, a sample chart having a configuration illustrated in FIGS. 24 to 26 is employed. Is preferred.

  In FIG. 24, a line based on a reference nozzle (nozzle number 0 in FIG. 24) is formed in all line pattern blocks. That is, the sample shown in FIG. 24 includes a line pattern (denoted by reference numeral 130) formed by a common nozzle serving as a reference for all line pattern blocks in the chart.

  It is possible to reduce errors by uniformly translating the nozzle positions belonging to each block on the common reference line CommonBaseLine so that the position (peak position) of the reference line pattern matches in each block.

  FIG. 25 is an example of another measurement pattern in consideration of correction of a position error between blocks. In FIG. 25, a line pattern block including nozzles having a nozzle number of 5 m (where m is an integer equal to or greater than 0) is formed in the subsequent stage (lower stage) of the block of line patterns using 4n + 3 nozzles. The nozzles included in 5m include nozzles of 4n, 4n + 1, 4n + 2, and 4n + 3 evenly. That is, in a block of line patterns with 5 m nozzles, the lines at m = 0, 1, 2, 3 are 4n (n = 0), 4n + 1 (n = 1), 4n + 2 (n = 2), 4n + 3 ( Recording is performed by the same nozzle as the nozzle of n = 3) (hereinafter the same).

  For this reason, alignment between coordinates determined in each block can be performed based on each line position of the 5 m block. In addition, although the example which added the line pattern by the nozzle of 5 m was shown here, the same thing is possible if it is not a multiple of 5, but is an integer which is not a multiple of 4. The same applies to nozzles having a certain common multiple.

  In FIG. 25, assuming that the nozzle position belonging to the block corresponding to the nozzle number of 5 m (m = 0, 1, 2, 3...) Is correct, the nozzles of other blocks are aligned so that the nozzle positions belonging to the 5 m block are aligned. Used when correcting the position.

  The position correction method will be described with a specific example.

  The 5 m line pattern block shown at the bottom of FIG. 25 includes nozzles with nozzle numbers 0, 5, 10, 15, and 20. For example, paying attention to the 21st nozzle position, since “21” belongs to the block (4n + 1), the nozzle numbers 5 and 25 belong to the same 5m and (4n + 1) blocks and sandwich “21”. For 5th and 25th positions on 5m, the translation parameter is determined so that 5th on 4n + 1 and 5th on 4n + 1 coincide with each other. A parameter for extending the distance between No. 5 and No. 25 is determined so as to match. Nozzle No. 21 corrects the position using the parallel movement and expansion parameters.

That is, the position by the 5th nozzle belonging to the 5m block is expressed as “P5 @ 5m”, the 25th position belonging to the 5m block is “P25 @ 5m”, and the position by the 5th nozzle belonging to the (4n + 1) block is “P5 @ ( 4n + 1) ", when the position by the 25th nozzle belonging to the (4n + 1) block is expressed as" P25 @ (4n + 1) "
(Output) = COEFA x {(Input value)-P5 @ (4n + 1)} + COEFB
However, COEFA = (P25 @ 5n −P5 @ 5n) / (P25 @ (4n + 1) −P5 @ (4n + 1)), COEFB = P5 @ 5n
It is corrected.

  In addition, when it cannot pinch | interpose in the nozzle position which belongs commonly as mentioned above, it correct | amends with the same correction parameter as the nearest position which belongs commonly. For example, nozzle number 1 (belonging to the 4n + 1 block) performs the same correction as when sandwiched between the closest common nozzle numbers 5 and 25.

  FIG. 26 shows another example of the measurement pattern in consideration of correction of the position error between blocks.

  FIG. 26 shows an example in which the nozzle positions belonging to the blocks sandwiched between the reference blocks (4n blocks in the figure) are corrected based on the fluctuation of the reference blocks.

  In FIG. 26, the same block as the block (4n) at one end is formed at the other end (the lowermost stage in FIG. 26). With such a configuration, it is possible to identify the variation in the positional relationship of the same nozzle between the same two upper and lower (4n) blocks, and the variation in the identified positional relationship is sandwiched between both blocks. It can be reflected in the block (4n + 1, 4n + 2, 4n + 3).

  In FIG. 26, regarding the position Ui of the upper 4n block and the position Li of the lower 4n block, the distance in the Y direction between the upper and lower blocks is 4B, and the distance in the Y direction between the blocks is B. Here, taking nozzle number 1 as an example, as shown in FIG. 27, for 4n nozzles 0 and 4 sandwiching nozzle number 1, positions PU0 and PU1 in the upper block, and positions PL0 and PL1 in the lower stage The conversion from the upper stage 4n to the lower stage 4n with respect to the block 4n + 1 to which the nozzle number 1 belongs is as follows.

(Output value) = COEFS x {(Input value)-PU0} + COEFT
However, COEFS = (PL1-PL0) / (PU1-PU0)
COEFT = PL0
As is clear from FIG. 27, the 4n + 1 block is 3B away from the Y-direction distance 4B from the upper stage 4n to the lower stage 4n.
(Output value) = COEFS x {(Input value)-PU0)} + COEFT
However, COEFS = (PS1-PS0) / (PU1-PU0)
COEFT = PL0
PS0 = PL0 + (PU0−PL0) × 3/4
PS1 = PL1 + (PU1-PL1) × 3/4
The position of nozzle number 1 is corrected using the following correction formula.

  When there is no sandwiching position, the nearest 4n nozzle number is used, and a correction formula between these two is applied.

  Next, the flow of dot measurement processing according to the present embodiment will be described with reference to a flowchart.

[Flowchart Example 1]
FIG. 28 is a flowchart illustrating a first example. As illustrated, first, a sample chart is read at a predetermined oblique angle to obtain electronic image data of a captured image (step S110).

  As described with reference to FIGS. 13, 16, and 17, the white area and the line area are specified from the captured image, and the white level and the black level in each area are determined (step S112 in FIG. 28).

  Then, a shading correction table corresponding to each line area is created from the obtained white level and black level information (step S114). The method for performing shading correction in the X direction and the Y direction is as described above.

  Subsequently, in each line region, an edge position (left and right) and a peak position (which may be a valley position, and so on) are specified from the profile graph (step S116).

  Next, a dust / dust detection subroutine (described in FIG. 29) is executed (step S120).

  FIG. 29 shows a flowchart of dust / dust detection processing. When the dust / dust detection subroutine shown in the figure starts, it is first determined whether a dust / dust detection channel has been set (step S210). If YES, the process proceeds to step S212. In step S212, an average value and a standard deviation of gradation values corresponding to edge positions obtained from the profile graph of the dust / dust detection channel are calculated, and the obtained average value ± (standard deviation × 3) is set as an upper limit and a lower limit. Set to exclude edge positions (obtained from the measurement channel) corresponding to gradation values outside the upper limit to lower limit (for dust / dust detection channels).

  Subsequently, in step S214, the average value and standard deviation of the gradation values corresponding to the peak position obtained from the profile graph of the dust / dust detection channel are calculated, and the obtained average value ± (standard deviation × 3) is the upper limit. The lower limit is set to exclude the peak position (obtained from the measurement channel) corresponding to the gradation value (of the dust / dust detection channel) outside the upper limit to the lower limit.

  On the other hand, if the dust / dust detection channel is not set in step S210, the determination in step S210 is NO, and the process proceeds to step S222.

  In step S222, a least square line is calculated from each edge position calculated from a plurality of profile graphs in the same line region, a vertical distance between the obtained straight line and each edge position is calculated, and an average value of these vertical distances is calculated. And obtain the standard deviation. The obtained average value ± (standard deviation × 3) is set as the upper limit and the lower limit, and the edge position (obtained from the measurement channel) corresponding to the vertical distance outside the range between the upper limit and the lower limit is excluded.

  Subsequently, in step S224, a least square line is calculated from each peak position calculated from a plurality of profile graphs in the same line region, a vertical distance between the obtained straight line and each peak position is calculated, and these vertical distances are calculated. Find the mean and standard deviation of. The obtained average value ± (standard deviation × 3) is set as the upper limit and the lower limit, and the peak position (obtained from the measurement channel) corresponding to the vertical distance outside the range between the upper limit and the lower limit is excluded.

  After the processing of step S214 or S224, the process exits the subroutine of FIG. 29 and returns to the flow of FIG. 28 (step S119).

  In step S119 in FIG. 28, a process of converting the pixel coordinate system on the image data to the coordinate system on the recording paper is performed. The conversion method is as already described with reference to FIG.

  Thereafter, in step S120 of FIG. 28, least square lines are calculated from the edge positions and peak positions that are not excluded in the dust / dust detection process (step S118) (step S120).

  An average value of the slopes of the least square lines is obtained, and a straight line BaseLine (denoted as “straight line BL”) perpendicular to the slope average value and passing through the center coordinates of the line turn block is obtained (step S122).

  Next, in step S124, the distance between the two edge approximate straight lines belonging to one line pattern and the straight line BL is calculated, and the obtained distance is set as the “line width”. Further, the distance between each intersection of the line pattern peak approximation straight line and the straight line BL is calculated, and the obtained distance is defined as a “line interval”. The “line interval” obtained in this way indicates the dot landing position by each nozzle.

  Then, based on the relationship between the line width and the dot diameter (or ink volume), which is known in advance, the process of converting the line width information into the dot diameter and / or ink volume information ( Step S126).

  Information on the dot landing position (line interval) and dot diameter (ink volume) obtained by the above process is input to the ink jet recording apparatus and used for droplet ejection correction and head maintenance control.

[Flowchart example 2]
FIG. 30 is a flowchart illustrating a second example. As shown in the figure, first, a sample chart is read at a predetermined oblique angle to obtain electronic image data (step S310).

  Next, the process proceeds to step S312, and it is determined whether or not block processing 1 (subroutine processing described with reference to FIG. 31) has been completed for all line pattern blocks in the sample chart. If NO is determined in step S312, the process proceeds to step S314, and block processing 1 is performed on an unprocessed block.

  FIG. 31 is a flowchart showing the subroutine contents of the block process 1. When the block processing 1 subroutine shown in the figure is started, first, a white area and a line area are specified for the target line turn block, and a white level and a black level of each area are determined (step S410). . Then, a shading correction table corresponding to each line area is created (step S414).

  In each line region, an edge position (left and right) and a peak position (which may be a valley position, and so on) are specified from the profile graph (step S416).

Next, a dust / dust detection subroutine (described in FIG. 29) is executed (step S).
418). Thereafter, conversion processing from the image coordinates to the coordinate system on the recording paper is performed (step S419), and a least square line is calculated from the determined edge position and peak position (step S422).

  Further, the center coordinate Pi of the block is determined, and the average value Θi of the slopes of the least square lines of the block is obtained (step S424).

  In step S426, the nozzle number corresponding to the block is associated with each straight line. Then, an undischarge nozzle determination process (described in the flow of FIG. 32) described later is performed, and an undischarge nozzle is specified (step S426 in FIG. 31). After the process of step S426, the process exits the subroutine of FIG. 31 and returns to the flow of FIG. 30 (step S312).

  FIG. 32 is a flowchart showing a subroutine of undischarge nozzle determination processing. As shown in the drawing, in the undischarge nozzle determination process, first, q is obtained by dividing the line pattern interval adjacent to each other in the block by the expected value of the adjacent lie pattern interval in the block (step S440). If the integer value Q obtained by rounding off the obtained q is 1 or more, Q-1 is set as the number of undischargeable nozzles, and the nozzle number is advanced by the number of undischargeable nozzles (step S442). In this way, the process for specifying the undischarge nozzle is ended, and the process returns to step S312 in FIG.

  When the block process 1 is completed for all the blocks on the sample chart, a YES determination is made in step S312 of FIG. 30, and the process proceeds to step S316. In step S316, an average value Θave between the blocks of the average value Θi of the least squares of each block is obtained, and similarly, an interblock average value Pave of the center coordinates Pi of each block is obtained (step S316).

  Next, in each block, a straight line BLi serving as a reference for each block is obtained as a straight line that is perpendicular to the slope average value Θave and passes through the center coordinates Pi of each line pattern block, and a common reference line CommonBaseLine (“ Is expressed as a straight line that is perpendicular to the slope average value Θave and passes through the center coordinates Pave of all line pattern blocks (step S318).

  In the reference straight line BLi of each block and the common reference straight line CBL of all the blocks, the parameter MOVEi for translating the point on BLi to the point on CBL so that the perpendicular line dropped from the point on BLi to CBL corresponds to each BLi (Step S320).

  Next, the process proceeds to step S322, and it is determined whether or not block processing 2 (subroutine processing described with reference to FIG. 33) has been completed for all line pattern blocks in the sample chart. If NO is determined in step S322, the process proceeds to step S324, and the block process 2 is performed on the unprocessed block.

  FIG. 33 is a flowchart showing the subroutine contents of the block process 2. When the processing of the figure starts, first, the coordinates of the intersection of two edge approximate lines belonging to one line pattern and the reference line BLi of the block are calculated, and the peak approximate line of the line pattern and the reference line of the block are calculated. The coordinates of each intersection with BLi are calculated (step S450). Then, the intersection obtained by the calculation is converted into coordinates on the CBL using the parallel movement parameter MOVEi to the reference straight line CBL of all blocks (step S452). After the process of step S452, the process exits the subroutine of FIG. 33 and returns to the flow of FIG. 30 (step S322).

  When the block process 2 is completed for all blocks on the sample chart, a YES determination is made in step S322 in FIG. 30, and the process proceeds to step S326. In step S326, the calculated coordinates on the reference straight line CBL of all the blocks of each nozzle are rearranged in nozzle order. Then, for each rearranged nozzle, the distance between the coordinates on the two edge approximate straight lines and the straight line CBL is calculated, and the distance obtained by this calculation is set as the line width (step S326).

  Then, based on the relationship between the line width and the dot diameter (or ink volume) that is known in advance, a process for converting the line width information into the dot diameter and / or ink volume information is performed ( Step S328).

[Example 3 of a flowchart]
FIG. 34 is a flowchart showing a third example. As shown in the figure, first, a sample chart is read at a predetermined oblique angle to obtain electronic image data (step S510).

  Next, the process proceeds to step S512, and it is determined whether or not the block process 1 (subroutine process described with reference to FIG. 31) has been completed for all the line pattern blocks in the sample chart. If NO is determined in step S512, the process proceeds to step S514, and the block process 1 is performed on the unprocessed block.

  When the block processing is completed for all blocks on the sample chart, a YES determination is made in step S512, and the process proceeds to step S516. In step S516, the straight line CBL serving as a reference for all the blocks is obtained as a straight line that is perpendicular to the average inclination Θ0 of the least square lines of the reference block (5 m nozzle) and passes through the center coordinate Po of the reference block (5 m nozzle). .

  Next, proceeding to step S518, the coordinates of the intersection point between the two edge approximate straight lines belonging to the line pattern belonging to the reference block (5 m nozzle) and the reference straight line CBL of the block are calculated. Also, the coordinates of each intersection point between the peak approximate straight line of the line pattern belonging to the reference block (5 m nozzle) and the reference straight line CBL of the block are calculated (step S518).

  Then, the coordinates of the intersection obtained by the calculation in step S518 are converted into one-dimensional coordinates on the reference straight line CBL (step S520).

  Next, the process proceeds to step S522, and it is determined whether or not the block process 3 (subroutine process described with reference to FIG. 35) has been completed for all the line pattern blocks in the sample chart. If NO is determined in step S522, the process proceeds to step S524, and the block process 3 is performed on the unprocessed block.

  FIG. 35 is a flowchart showing the subroutine contents of the block process 3. When the process of FIG. 6 starts, first, a straight line BLi serving as a reference for each block is obtained as a straight line that is perpendicular to the inclination average value Θi and passes through the center coordinates Pi of each line pattern block (step S610).

  Next, proceeding to step S612, the coordinates of the intersection of the two edge approximate lines belonging to one line pattern and the reference line BLi of the block are calculated. Also, the coordinates of each intersection between the peak approximate straight line of the line pattern and the reference straight line BLi of the block are calculated (step S612).

  Then, the calculated intersection point is converted into one-dimensional coordinates on the reference straight line BLi (step S614).

  Next, a nozzle number common to the nozzle number belonging to the block and the reference block (5 m nozzle) is extracted, and for the common nozzle number, the one-dimensional coordinate sequence Xij on the reference straight line BLi of the block and the reference block ( A conversion function Fi that satisfies the input data string Xij and the output data string Yi is obtained for the one-dimensional coordinate Yj on the reference straight line CBL (5 m nozzle) (step S616).

  Using this conversion function Fi, the one-dimensional coordinates on the reference straight line BLi obtained before the line pattern belonging to the block are converted into one-dimensional coordinates on the reference straight line CBL of the reference block (5 m nozzle) (step S618). ).

  FIG. 36 is a diagram for explaining the conversion function Fi for the block i. The nozzles 5, 25, and 45 belonging to the block (4N + 1 nozzle) are common to the reference block (5m nozzle).

  The conversion function Fi has a conversion characteristic in which one-dimensional coordinates on the reference line BLi of these common nozzles are input and one-dimensional coordinates Yj on the reference line CBL of all blocks are output.

  Such characteristics may be used as linear interpolation, or may be used as Lagrange interpolation or spline interpolation.

  It is possible to use an interpolation function that has characteristics that always convert from Xij to Yj and that maps other points smoothly.

  Using such a conversion function Fi and interpolation processing, the coordinates on the straight line BLi (the coordinates of the nozzles 5, 9, 13,...) Are converted into coordinates on the reference straight line CBL common to all blocks. .

  When the interpolation process is linear interpolation, the extrapolation process converts all the coordinates on the reference line BLi of the nozzle 1 to the coordinates on the reference line CBL common to the lock as the interpolation characteristic similar to the nearest interpolation process.

  Thus, after the process of step S618 in FIG. 35 is completed, the process exits the subroutine in FIG. 35 and returns to the flow in FIG. 34 (step S522).

  When the block process 3 is completed for all the blocks on the sample chart, a YES determination is made in step S522 in FIG. 34, and the process proceeds to step S526. In step S526, the calculated coordinates on the reference line CBL of the reference block of each nozzle are rearranged in nozzle order.

  For each rearranged nozzle, the distance between the coordinates on the two edge approximate straight lines and the straight line CBL is calculated and set as the line width. For each of the rearranged nozzles, the distance between the coordinates on the peak approximate straight line of the line pattern and the straight line CBL is calculated as the line interval.

  Then, based on the relationship between the line width and the dot diameter (and / or ink volume) that is known in advance, a process for converting the line width information into information on the dot diameter and / or ink volume is performed. (Step S528).

  As described above, according to the dot measurement method according to the present embodiment, the following effects can be obtained.

  (1) A dot landing position and a dot diameter (and / or ink volume) can be measured simultaneously and with high accuracy from electronic image data obtained by imaging (reading) a single sample chart. For this reason, the formation of the sample chart and the number of imaging can be minimized.

  (2) Compared with a conventional reading method in which an oblique angle is not given at the time of image reading, reading can be performed at a lower resolution, and measurement can be performed with higher accuracy than the resolution. For this reason, it is possible to reduce the image size, increase the processing time, and shorten the reading time.

  (3) Since dust / dust is determined based on a color channel image different from the absorption peak of the ink to be measured and the peak position and edge position corresponding to the dust / dust position are excluded from the calculation target, -The influence of dust can be reduced.

  (4) To reduce the influence of the characteristic difference (aperture, gradation characteristics, element spacing error) of each light receiving element of the line sensor by using a line sensor to image at an oblique angle with respect to the line pattern. Can do.

  In other words, when there is a characteristic difference (aperture size, gradation characteristics, error in light receiving element spacing, etc.) between the light receiving elements of the imaging device (line sensor), the angle is not given (the light receiving element rows are line pattern lines). When the scanning is performed along the line direction, the peak position and the edge position of a specific line pattern are imaged with only one light receiving element, and the dot position and dot diameter calculated as a result are It is strongly influenced by the characteristic difference of the light receiving element.

  On the other hand, as described with reference to FIG. 9, since the plurality of light receiving elements cross the line pattern by reading at an oblique angle, the peak position and the edge position of the line pattern are imaged by the plurality of light receiving elements. become. As a result, the characteristic differences of the light receiving elements are averaged, and the dot positions and dot diameters calculated as a result are reduced by the influence of the characteristic differences of the light receiving elements.

  (5) Since the image is read at an oblique angle with respect to the transport direction while transporting the measurement sample (sample chart), it is not necessary to stop the transport for measurement. For this reason, an image reading device can be installed on the conveyance path in the printer (image forming device), and a series of steps from sample chart formation (line pattern printing) to reading and measurement by subsequent image analysis are possible. The operation can be continuously performed by a printer control program (on-line measurement is possible). It is also possible to perform measurement without cutting the roll paper in advance.

[Study on tilt angle, resolution and measurement accuracy during image reading]
FIG. 37 shows the result of measuring the line pattern by changing the resolution (4800 DPI, 2400 DPI, 1200 DPI) and the reading angle level. Here, the “reading angle” corresponds to an angle formed by the line pattern 92 in FIG. 10 and the one-dimensional pixel array arranged in the Y direction across the line pattern 92, and is an angle represented by (90 ° −θ) in FIG. 10. It is.

  The Y axis in FIG. 37 is a value obtained by averaging the absolute values of the difference between the reference measurement value and the line pitch measurement value under each condition. It can be seen that the measurement accuracy is the best around a reading angle of around 8 degrees.

  As can be seen from the fact that the measurement result with a resolution of 2400 DPI and a reading angle of around 8 degrees is better than the measurement result with a resolution of 4800 DPI and a reading angle of 0 degrees, the measurement accuracy is improved by the reading angle.

  According to FIG. 37, since the particularly preferable reading angle range is 4 to 8 degrees, the value of tan (90−θ) in FIGS. 9 to 10 is 0.069927 to 0.140541. Temporarily, when the printing speed of A4 size (210 × 297 mm) paper is 100 ppm ([page par minute]), the paper transport speed Vy is 500 [mm / sec]. Therefore, the preferable moving speed Vx of the line sensor is 34.96 [ mm / sec) to 70.27 [mm / sec].

  When the line sensor resolution is 2400 DPI, the pixel pitch is sp = 0.010583 [mm / pixel], that is, 10.583 [μm / pixel].

  When the Y-direction pixel size YPixel_size on the image data is equal to the pixel pitch sp = 0.010583 [mm / pixel], the reading cycle T is 2.09607E-05 to 2.11151E-05 [sec / pixel], that is, 20.9607. 21. 1151 [μsec / pixel]. When this is converted into a frequency, 47.35945975 to 47.70838925 [kHz] are obtained. Needless to say, if the printing speed is decreased, Vx also decreases at the same ratio, and the reading cycle T becomes longer at an inverse ratio.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  FIG. 38 is a schematic diagram illustrating another configuration example of the image reading apparatus. In the form shown in the figure, the recording paper 16 is moved in the Y direction at the conveyance speed V1, and the line sensor 300 (reference numeral in FIG. 6) has an inclination of an angle γ (an angle not orthogonal to the conveyance direction) with respect to the conveyance direction. 241) is moved (scanned) at a speed V2 as shown in FIG. 38 (in a direction perpendicular to the column direction of the light receiving elements 301 in the line sensor 300).

  The velocity V2 at this time can be divided into a component of V2 × sin (γ) of the Y direction component and a component of V2 × cos (γ) of the X direction component. That is, the relative velocity in the Y direction is V1 + V2 × sin (γ), and the relative velocity in the X direction is V2 × cos (γ).

  Alternatively, the form shown in FIG. 39 is also possible. That is, in the form shown in FIG. 39, the recording paper 16 is moved in the Y direction at the conveyance speed V1, and the line sensor 300 having an inclination γ with respect to the conveyance direction is moved in the X direction as shown in the speed V3. A configuration for moving in the direction orthogonal to the transport direction is provided.

  FIG. 40 shows the recording paper when reading is performed while moving the line sensor 300 arranged at an angle γ with respect to the conveyance path direction while conveying the recording paper 16 as shown in FIG. 38 or FIG. 16 shows the pixel positions on 16 in time series.

  In the case of the form of FIG. 38, since the relative movement is obtained by combining the conveyance speed V1 in the Y direction and the movement speed V2 of the line sensor 300, the Y direction speed Vy = V1 + V2 × sin (γ), the X direction in FIG. Vx = V2 × cos (γ). The illustrated angle α is tan (α) = − Vy / Vx, and angle β = angle γ.

  In the case of the form of FIG. 39, when applied to FIG. 40, the Y-direction speed Vy = V1, the X-direction speed Vx = V3, tan (α) = − Vy / Vx, and angle β = angle γ.

  FIG. 41 shows image data read by the image reading apparatus exemplified in FIGS.

  When the image data acquired by the method described in FIG. 40 is returned to the orthogonal coordinate system, the line pattern is recorded as an oblique line on the image data as shown in FIG.

  The arrangement pitch (pixel pitch) of the light receiving elements 301 in the line sensor 300 is set to sp (mm / pixel) (see FIG. 40), the sensor moving speed in the X direction is Vx (mm / sec), and the recording paper conveyance speed in the Y direction is set. Assuming Vy (mm / sec), the pixel size YPixel_size in the Y direction on the image data shown in FIG. 41 is expressed by YPixel_size = sp (mm / pixel).

For the pixel size XPixel_size in the Y direction on the image data, the reading cycle of the line sensor 302 is T (sec / pixel),
SXPixel_size = Vx (mm / sec) x T (sec / pixel),
SYPixel_size = Vy (mm / sec) x T (sec / pixel)
As
XPixel_size = {(SXPixel_size) ² + (SYPixel_size) ² } ^1/2
It becomes.

  The line pattern 92 is imaged in an inclined state at an angle determined by the ratio of Vx (mm / sec) and Vy (mm / sec) on the image data.

  As described in the first embodiment, a profile graph that crosses the line pattern in the X direction on the image data is set for the image captured in this way, and the edge position of the profile graph is set as the image. Detect as upper position (x, y). This position (x, y) is converted to a position on the recording paper.

  Considering the relationship between the position Ps (x, y) on the image data and the corresponding position on the recording paper, the Y-direction distance on the image (that is, the length of YPixel_size × y) with the predetermined position on the recording paper as the origin ) Can be decomposed into two components according to the angle β. That is, it can be decomposed into the following components.

X direction on recording paper: −YPixel_size × y × sin (β)
Y direction on recording paper: YPixel_size x y x cos (β)
Similarly, the X-direction distance (that is, the length of XPixel_size × x) on the image can be decomposed into the following two components by the angle α.

X direction on recording paper: XPixel_size × x × cos (α)
Y direction on recording paper: XPixel_size × x × sin (α)
Accordingly, the correspondence between the position (x, y) on the image and the position on the recording paper is as follows.

The X position on the recording paper is
X = −YPixel_size × y × sin (β) + XPixel_size × x × cos (α)
The position in the Y direction on the recording paper is
Y = YPixel_size × y × cos (β) + XPixel_size × x × sin (α)
That is, the position (x, y) detected in the profile graph on the image data is converted into the position (X, Y) on the recording paper by the above conversion, and the line is obtained by the least square calculation of the edge position and the least square calculation of the peak position. A pattern edge position straight line and a peak position straight line are obtained. The subsequent processing is the same as the example described in the first embodiment.

(Modification 1)
In the embodiment shown in FIG. 1, the image reading device 24 is provided in the inkjet recording device 10, and the recording paper 16 is conveyed by the common belt conveyance unit 22, while the line sensor (reference numeral 241 in FIG. 6) of the image reading device 24. 9, the configuration in which the line pattern is read by moving the reference numeral 100 in FIG. 9 and the reference numeral 300 in FIGS. 38 to 40 has been described. However, the conveying unit in the printing unit and the conveying unit in the reading unit by the image reading device 24 are separately provided. A configuration configured as follows is also possible.

  Further, in the above-described embodiment, an arithmetic processing function for dot measurement is incorporated in the system controller (reference numeral 72 in FIG. 6) and / or the printer control unit (reference numeral 80) in the inkjet recording apparatus 10 and obtained from the image reading apparatus. In the above example, the image data is processed by the system controller (or a combination of this and the printer control unit) in the ink jet recording apparatus. However, the processing function of the image data obtained from the image reading apparatus is controlled by the external device of the printer. It is also possible to do this.

(Modification 2)
[Configuration example of dot measurement device]
Next, a configuration example of another dot measurement device using the above-described dot measurement method will be described. A program (dot measurement processing program) for causing a computer to execute the image analysis processing algorithm used for dot measurement of this example is created, and the computer is operated by this program, thereby causing the computer to function as an arithmetic unit of the dot measurement device be able to.

  FIG. 42 is a block diagram illustrating a configuration example of a dot measurement device. The dot measuring device 200 shown in the figure includes an image reading device 24 and a computer 210 that performs image analysis calculations and the like.

  As described in the first and second embodiments, the image reading device 24 includes an RGB line sensor that reads a line pattern on a sample chart, and moves and moves the line sensor in the scanning direction. A sensor driving circuit, a signal processing circuit for A / D converting a sensor output signal (imaging signal) and converting the digital signal data into a predetermined format are provided.

  The computer 210 includes a main body 212, a display (display unit) 214, and an input device (input unit for inputting various instructions) 216 such as a keyboard and a mouse. In the main body 212, a central processing unit (CPU) 220, a RAM 222, a ROM 224, an input control unit 226 that controls signal input from the input device 216, a display control unit 228 that outputs a display signal to the display 214, A hard disk device 230, a communication interface 232, a media interface 234, and the like are included, and these circuits are connected to each other via a bus 236.

  The CPU 220 functions as an overall control device and arithmetic device (arithmetic means). The RAM 222 is used as a temporary storage area for data and a work area when the CPU 220 executes a program. The ROM 224 is a rewritable nonvolatile storage unit that stores a boot program for operating the CPU 220, various setting values, network connection information, and the like. The hard disk device 230 stores an operating system (OS), various application software (programs), data, and the like.

  The communication interface 232 is means for connecting to an external device or a communication network according to a predetermined communication method such as USB (Universal Serial Bus), LAN, Bluetooth (registered trademark). The media interface 234 is means for performing read / write control of an external storage device 238 typified by a memory card, magnetic disk, magneto-optical disk, or optical disk.

  In this example, the image reading device 24 and the computer 210 are connected via the communication interface 232, and captured image data read by the image reading device 24 is taken into the computer 210. In addition, a configuration in which the captured image data acquired by the image reading device 24 is temporarily stored in the external storage device 238 and the captured image data is taken into the computer 210 through the external storage device 238 is also possible.

  The image analysis processing program in the dot measurement method according to the embodiment of the present invention is stored in the hard disk device 230 or the external storage device 238, and the program is read out as needed and expanded in the RAM 222 and executed. Is done. Alternatively, an aspect in which the program is provided by a server installed on a network (not shown) connected via the communication interface 232 is possible, and an aspect in which an arithmetic processing service by the program is provided by a server on the Internet. Is also possible.

  The operator can input various initial value settings by operating the input device 216 while viewing an application window (not shown) displayed on the display 214, and can check the calculation result on the display 214. it can.

  The calculation result data (measurement result) can be stored in the external storage device 238 or output to the outside via the communication interface 232. Information on the measurement result is input to the ink jet recording apparatus via the communication interface 232 or the external storage device 238.

(Modification 3)
In the above embodiment, an inkjet recording apparatus using a page-wide full-line head having a nozzle row having a length corresponding to the entire width of the recording medium has been described. However, the scope of application of the present invention is not limited to this, and serial The present invention can also be applied to an ink jet recording apparatus that performs image recording by a plurality of head scans while moving a short recording head, such as a type (shuttle scan type) head.

  In the above description, an ink jet recording apparatus is illustrated as an example of an image forming apparatus. However, the scope of application of the present invention is not limited to this, and a functional liquid or other various liquids can be used as an ejection medium using a liquid ejection head. The present invention can be applied to various types of devices (coating devices, coating devices, wiring drawing devices, fine structure forming devices, and the like) that spray toward the surface. That is, the present invention relates to dot landing positions in various liquid ejection devices that eject (spray) liquid, such as industrial precision coating devices, resist printing devices, wiring drawing devices for electronic circuit boards, dyeing devices, and coating devices. It can be widely applied as a technique for measuring the dot diameter (droplet volume).

[Appendix]
As will be understood from the description of the embodiments of the invention described in detail above, the present specification includes disclosure of various technical ideas including the invention described below.

  (Invention 1): While ejecting liquid droplets from the nozzles of the liquid ejection head in which a plurality of nozzles are arranged onto the ejection target medium, the liquid ejection head and the ejection target medium are relatively moved, and each nozzle is moved. A line pattern forming step of forming a line pattern by dot rows corresponding to each nozzle by causing the liquid droplets discharged from the liquid droplets to land on the medium to be discharged, and a medium to be discharged on which the line pattern is formed While moving the imaging device having a light receiving element array intersecting the line direction of the line pattern at a predetermined angle in a second direction different from the first direction, A pattern reading step of acquiring electronic image data representing the captured image by capturing a line pattern with the imaging device, and the line pattern from the electronic image data. A profile graph acquisition step for acquiring a plurality of profile bluffs for one line pattern, and a plurality of profiles acquired for one line pattern. A feature position calculating step for calculating an extreme value position corresponding to the density center of the line pattern, a first edge position and a second edge position corresponding to both left and right edges of the line pattern, and the feature position calculation from the graph, respectively. Using the least square method for each of the extreme position data, the first edge position, and the second edge position data that are calculated for the same line pattern by the process, it corresponds to the extreme value position that indicates the density center of the line pattern. The line center approximate straight line to be performed and the vicinity of the first edge corresponding to the first edge position of the line pattern An approximate straight line calculating step for calculating a straight line and a second edge approximate straight line corresponding to the second edge position of the line pattern, and a line center approximate straight line for each line pattern obtained in the approximate straight line calculating step are adjacent to each other. The vertical position between the line center approximate lines corresponding to the line pattern is calculated, and the landing position calculation step for obtaining the dot landing position from the calculated value, and the first edge approximate line for the same line pattern obtained in the approximate line calculation step And the second edge approximate straight line, the vertical distance between the straight lines is calculated, and the value is obtained as the line width of the line pattern, and is previously formed on the target medium by a combination of a predetermined liquid and target medium. Correlation information to know at least one of the relationship between the dot diameter and the line width and the relationship between the volume of the ejected droplet and the line width Based on the line width value obtained in the notification obtaining step, the line width value obtained in the line width calculating step, and the relationship known in the correlation information obtaining step, the dot diameter and the discharge corresponding to the line width value are obtained. There is provided a dot measurement method comprising a measurement value calculation step for obtaining at least one value of a volume of a droplet.

  The image signal value of the captured image differs in the form of the profile graph depending on what the vertical axis is. When the optical density of the line pattern is plotted on the vertical axis, the signal value of the line pattern portion is large and the signal value of the non-line pattern portion is small. Therefore, the “extreme position corresponding to the density center of the line pattern” is It becomes the position of local maximum. On the other hand, if the luminance signal or brightness signal of the image data is plotted on the vertical axis, the signal value of the line pattern portion is small and the signal value of the non-line pattern portion is large. “Position” is the position of the minimum value of the profile graph.

  For the calculation of the extreme value position, it is desirable to use an interpolation method using a quadratic function or the like. In calculating the first edge position and the second edge position, it is desirable to use linear interpolation to specify the position with higher accuracy than the reading resolution.

  The correspondence between the pixel position information in the electronic image data and the actual physical distance on the medium to be ejected is defined by the reading resolution, the conveyance speed in the first direction, and the movement speed in the second direction. Therefore, it can be converted by mathematical processing. A correspondence relationship (conversion function) between the two coordinate systems is obtained in advance, and coordinate conversion processing is performed. The conversion from the pixel coordinate system on the image data to the actual coordinate system on the target medium is defined by a conversion formula, so in which coordinate system the calculation proceeds, and at which calculation stage the coordinate conversion is performed Or, there is arbitraryness. In the examples described in the first and second embodiments, from the viewpoint of ease of calculation processing, calculation error, etc., coordinate conversion is performed after detection of the edge position and peak position, and an approximate straight line is obtained in the physical space on the recording paper. However, in principle, for linear conversion, it is also possible to perform coordinate conversion after obtaining an approximate straight line in a coordinate system on image data.

  As a configuration example of the liquid discharge head in the present invention, a full-line head in which a plurality of nozzles are arranged over a length corresponding to the entire width of the discharge target medium can be used. In this case, a plurality of relatively short recording head modules having nozzle rows that are less than the length corresponding to the full width of the medium to be ejected are combined, and the nozzles having a length corresponding to the full width of the medium as a whole are connected. There is an aspect that constitutes a column.

  A full-line type head is usually arranged along a direction orthogonal to the feeding direction (conveying direction) of the medium to be ejected, but is oblique with a predetermined angle with respect to the direction orthogonal to the conveying direction. There may be a mode in which the head is arranged along the direction.

  The “ejection medium” is a medium that receives adhesion of droplets ejected from the nozzles (ejection ports) of the liquid ejection head, and is a printing medium, an image forming medium, a recording medium, an image receiving medium, and an ejection medium in an inkjet printer. Media, intermediate transfer members and the like are included. The form and material of the medium are not particularly limited, and are continuous paper, cut paper, sealing paper, resin sheets such as OHP sheets, films, cloths, printed circuit boards on which wiring patterns are formed, rubber sheets, metal sheets, etc. Regardless of material and shape, various media are included.

  A transport unit that moves the ejected medium and the liquid ejecting head relative to each other is configured to convey the ejected medium with respect to the stopped (fixed) head, to move the head with respect to the stopped ejected medium, Alternatively, any of the modes in which both the head and the medium to be ejected are moved is included. When forming a color image using an inkjet head, a recording head may be arranged for each color of a plurality of colors (recording liquids), and a configuration capable of ejecting a plurality of colors from one printing head. It is good.

  As the imaging device used in the present invention, a line sensor (linear image sensor) can be used, and an area sensor can also be used. Although the reading resolution depends on the size of the dot to be measured, for example, it is preferably 12000 DPI or more for dot measurement in an inkjet printer that realizes photographic image recording.

  (Invention 2): A dot measurement method according to Invention 1, wherein a color image sensor is used as the imaging device and electronic image data of a color image representing the captured image is acquired.

  When measuring multiple types of liquids having different absorption characteristics, such as when measuring dots with a plurality of colors of ink, it is preferable to use a color image sensor capable of color separation as the imaging device. For example, an imaging device having an RGB primary color filter or an imaging device having a CMY complementary color filter is used.

  When a color image sensor is used, a profile graph is obtained using a signal of a color channel that maximizes contrast in consideration of the absorption spectrum of the liquid to be measured.

  (Invention 3): Among the read image data for each wavelength range acquired according to the spectral sensitivity characteristic of the color image sensor, the wavelength having the highest sensitivity with respect to the absorption peak wavelength of the liquid ejected from the liquid ejection head A dust determination processing step for determining the presence or absence of the influence of dust in the captured image based on a profile graph obtained from read image data in a wavelength range other than the range, and the dust determination processing step has an influence of dust And a dust influence data exclusion process step of performing a process of excluding data having the influence of the dust from the calculation target in at least one of the feature position calculation step and the approximate straight line calculation step when determined. The dot measuring method according to invention 2 is provided.

  According to this aspect, it is possible to perform computation with reduced influence of dust.

  (Invention 4): The profile graph includes a symmetry determination processing step for determining the symmetry of the graph centered on the extreme value position, and when the symmetry determination processing step determines that the symmetry is low, An invention comprising an asymmetric data exclusion process step for performing a process of excluding data corresponding to the profile graph with low symmetry from a calculation target in at least one of the feature position calculation step and the approximate line calculation step The dot measurement method according to any one of 1 to 3 is provided.

  According to this aspect, it is possible to determine the presence / absence of a satellite from the symmetry of the profile graph, and it is possible to perform an operation with reduced influence of the satellite.

  (Invention 5): The line pattern forming step forms a plurality of line pattern blocks by changing the position in the line direction of the line pattern on a single target medium, and each line pattern block is common. A dot measurement method according to any one of inventions 1 to 4, further comprising a reference line pattern formed by droplet ejection from a nozzle.

  According to this aspect, it is possible to perform alignment between each line pattern block using a reference line pattern formed by droplet ejection from the same nozzle.

  (Invention 6): In the line pattern forming step, a plurality of line pattern blocks are formed at different positions in the line direction of the line pattern on a single target medium, and at least of the plurality of line pattern blocks. One line pattern block includes a line pattern formed by droplet ejection from a nozzle in common with a line pattern belonging to another line pattern block at a different position. The described dot measurement method is provided.

  According to this aspect, it is possible to perform alignment between each line pattern block using a line pattern line formed by droplet ejection from the same nozzle.

  (Invention 7): Inter-block alignment that performs alignment processing between different line pattern blocks based on the positional relationship of line patterns that are formed by droplet ejection from the common nozzle and belong to different line pattern blocks A dot measurement method according to invention 5 or 6, characterized by comprising a processing step.

  (Invention 8): In the pattern reading step, a line sensor is used as the imaging device, and the imaging is performed by relatively moving the discharge medium on which the line pattern is formed and the line sensor. A dot measurement method according to any one of inventions 1 to 7, wherein the dot measurement method is provided.

  (Invention 9): While ejecting liquid droplets from the respective nozzles of the liquid ejection head in which a plurality of nozzles are arranged onto the ejection target medium, the liquid ejection head and the ejection target medium are relatively moved, and the respective nozzles are moved. Conveying means for conveying in a first direction an object to be measured formed by forming a line pattern with dot rows corresponding to each nozzle by causing the liquid droplets discharged from the liquid to land on the medium to be discharged; An imaging device having a light receiving element array that intersects at a predetermined angle with respect to a line direction of the line pattern on the object to be measured conveyed by the conveying means, in the first direction by the conveying means. Electronic image data representing the captured image is obtained by capturing the line pattern on the object to be measured with the imaging device while moving the object in a second direction different from the first direction. A pattern reading unit for acquiring a plurality of profile bluffs representing fluctuations in image signal values in a one-dimensional pixel array that obliquely crosses the line pattern from the electronic image data for one line pattern And an extreme value position corresponding to the density center of the line pattern, a first edge position corresponding to both right and left edges of the line pattern, and a second edge, respectively, from each of the plurality of profile graphs acquired for one line pattern. A least square method is used for feature position calculation means for calculating edge positions, and for extreme value positions, first edge positions, and second edge position data calculated for the same line pattern by the feature position calculation means. Line center corresponding to the extreme value position indicating the density center of the line pattern An approximate line calculating means for calculating a straight line, a first edge approximate line corresponding to the first edge position of the line pattern, and a second edge approximate line corresponding to the second edge position of the line pattern; A landing position calculating means for calculating a vertical distance between line center approximate lines corresponding to adjacent line patterns from a line center approximate line for each line pattern obtained by the straight line calculating means, and calculating a dot landing position from the calculated distance; Calculating a vertical distance between straight lines of the first edge approximate line and the second edge approximate line with respect to the same line pattern obtained by the approximate line calculation means, and obtaining the value as the line width of the line pattern; The relationship between the dot diameter and the line width formed on the medium to be ejected by a combination of a predetermined liquid and the medium to be ejected in advance, and the ejection liquid Correlation information storage means for storing correlation information in which at least one of the relations between the volume of the droplet and the line width is known, the value of the line width obtained by the line width calculation means, and the correlation Based on the correlation information stored in the information storage means, a measurement value calculation means for obtaining at least one value of the corresponding dot diameter and discharge droplet volume from the line width value was provided. A dot measuring device characterized by the above is provided.

  The dot measuring device according to the present invention may be separated from a droplet discharge device (such as an ink jet recording device or a wiring drawing device) that discharges a droplet, or may be incorporated in the droplet discharge device.

  (Invention 10): The profile graph acquisition means, the characteristic position calculation means, the approximate straight line calculation means, the landing position calculation means, the line width calculation means, the correlation information storage means, A program for causing a computer to function as measurement value calculation means is provided.

  The dot measuring device according to the ninth aspect can be realized by combining the image reading device having the imaging device specified by the ninth aspect and the computer incorporating the program according to the tenth aspect.

  (Invention 11): An image forming apparatus including the dot measuring device according to Invention 9 and the liquid discharge head is provided.

Overall configuration diagram of inkjet recording apparatus Plane perspective view showing structural example of head Plane perspective view showing another configuration example of a full-line head Sectional drawing which follows the 4-4 line in FIG. Enlarged view showing the nozzle arrangement of the head Block diagram showing system configuration of inkjet recording apparatus Schematic diagram illustrating irregularities in line pattern due to nozzle characteristics The figure which shows the 1st example of the sample chart for a measurement The figure which shows the relative relationship between the line pattern formed on the recording paper, and the imaging position by the scanning of the line sensor for reading this The figure which shows the example of the image data acquired by the reading method of FIG. Illustration of the relationship between a one-dimensional pixel array that crosses a line pattern and a profile graph Figure showing an example of a profile graph Explanatory diagram of image analysis processing The figure which shows the example of the profile graph which scans an image in the arrow direction of FIG. 13, and shows the fluctuation | variation of the signal value of the scanning direction The figure which shows the example of the profile graph which scans an image in the arrow direction of FIG. 13, and shows the fluctuation | variation of the signal value of the scanning direction Explanatory diagram of image analysis processing Explanatory diagram of image analysis processing Explanatory diagram including the influence of satellite and dust Illustration of profile graph shape Illustration of profile graph shape due to satellite dot effect Illustration of the line width calculation method Illustration of nozzle position calculation method Illustration of nozzle position calculation method The figure which shows the 2nd example of the sample chart for a measurement The figure which shows the 3rd example of the sample chart for a measurement The figure which shows the 4th example of the sample chart for a measurement Illustration of alignment processing between blocks Flow chart illustrating the flow of dot measurement processing (first example) Flow chart showing contents of dust / dust detection processing Flow chart illustrating the flow of dot measurement processing (second example) The flowchart which shows the content of the block process 1 in FIG. Flowchart showing contents of undischarge nozzle determination processing The flowchart which shows the content of the block process 2 in FIG. Flow chart illustrating the flow of dot measurement processing (third example) The flowchart which shows the content of the block process 3 in FIG. Explanatory diagram of conversion function Fi Graph showing the relationship between reading angle and measurement accuracy by resolution Main part explanatory drawing of 2nd Embodiment The figure which shows the modification of the form of FIG. The figure which shows the relative relationship of the imaging position by the scanning (the scanning example shown in FIG. 38 or FIG. 39) of the line pattern formed on the recording paper, and the line sensor for reading this The figure which shows the example of the image data acquired by the reading method of FIG. Block diagram showing another configuration example of the dot measuring device

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 12K, 12C, 12M, 12Y ... Head, 16 ... Recording paper, 24 ... Image reading device, 50 ... Head, 51 ... Nozzle, 52 ... Pressure chamber, 58 ... Actuator, 72 DESCRIPTION OF SYMBOLS ... System controller, 80 ... Print control part, 90 ... Dot, 92 ... Line pattern, 241 ... Line sensor, 242 ... Movement drive mechanism, 100, 300 ... Line sensor, 101, 301 ... Light receiving element, 200 ... Dot measuring device, 210: Computer

Claims (11)

Liquid ejected from each nozzle by relatively moving the liquid ejection head and the ejection medium while ejecting droplets onto the ejection medium from each nozzle of the liquid ejection head in which a plurality of nozzles are arranged A line pattern forming step of forming a line pattern by a dot row corresponding to each nozzle by landing the droplet on the ejection target medium;
An imaging apparatus having a light receiving element array that intersects the line direction of the line pattern at a predetermined angle while transporting the ejection target medium on which the line pattern is formed in a first direction is different from the first direction. A pattern reading step of acquiring electronic image data representing the captured image by capturing the line pattern with the imaging device while moving in a second direction;
A profile graph acquisition step for acquiring a plurality of profile bluffs for one line pattern representing fluctuations in image signal values in a one-dimensional pixel row that obliquely crosses the line pattern from the electronic image data;
An extreme value position corresponding to the density center of the line pattern and a first edge position and a second edge position corresponding to the left and right edges of the line pattern, respectively, from each of the plurality of profile graphs acquired for one line pattern. A feature position calculating step for calculating
For the extreme value position, first edge position, and second edge position data calculated for the same line pattern by the feature position calculation step, the least square method is used to indicate the density center of the line pattern. Approximation for calculating a line center approximate line corresponding to the value position, a first edge approximate line corresponding to the first edge position of the line pattern, and a second edge approximate line corresponding to the second edge position of the line pattern. Straight line calculation process;
Calculate the vertical distance between the line center approximate lines corresponding to adjacent line patterns from the line center approximate line for each line pattern obtained in the approximate line calculation step, and calculate the landing position from which the dot landing position is obtained Process,
A line width calculating step of calculating a vertical distance between straight lines of the first edge approximate line and the second edge approximate line with respect to the same line pattern obtained in the approximate line calculation step, and obtaining the value as a line width of the line pattern;
Know in advance at least one of the relationship between the dot diameter and the line width formed on the medium to be ejected and the relationship between the volume of the ejected droplet and the line width by combining a predetermined liquid and the medium to be ejected. Correlation information acquisition process,
Based on the line width value obtained in the line width calculation step and the relationship known in the correlation information obtaining step, the line width value is used to calculate the corresponding dot diameter and ejection droplet volume. A measurement value calculation step for obtaining at least one of the values;
A dot measurement method characterized by comprising:   The dot measurement method according to claim 1, wherein a color image sensor is used as the imaging device, and electronic image data of a color image representing the captured image is acquired. Among read image data for each wavelength range acquired according to the spectral sensitivity characteristics of the color image sensor, a wavelength range other than the wavelength range having the highest sensitivity with respect to the wavelength of the absorption peak of the liquid discharged from the liquid discharge head Based on the profile graph obtained from the read image data of, having a dust determination processing step of determining the presence or absence of the influence of dust in the captured image,
When it is determined in the dust determination processing step that there is an influence of dust, in at least one of the characteristic position calculation step and the approximate straight line calculation step, a process of excluding data having the influence of the dust from the calculation target The dot measurement method according to claim 2, further comprising a dust influence data exclusion processing step to be performed. A symmetry determination process for determining the symmetry of the graph centered on the extreme value position for the profile graph;
When it is determined that the symmetry is low in the symmetry determination processing step, in at least one of the feature position calculation step and the approximate line calculation step, data corresponding to the profile graph with low symmetry is calculated from the calculation target. The dot measurement method according to any one of claims 1 to 3, further comprising an asymmetric data exclusion process step of performing an exclusion process.   In the line pattern forming step, a plurality of line pattern blocks are formed on a single ejection medium by changing the position in the line direction of the line pattern, and each line pattern block is ejected from a common nozzle. The dot measurement method according to claim 1, wherein the dot measurement method includes a reference line pattern formed by: The line pattern forming step forms a plurality of line pattern blocks at different positions with respect to the line direction of the line pattern on a single target medium,
The at least one line pattern block among the plurality of line pattern blocks includes a line pattern formed by droplet ejection from a nozzle common to line patterns belonging to line pattern blocks at different positions. Item 5. The dot measurement method according to any one of Items 1 to 4.   An inter-block alignment processing step for performing alignment processing between different line pattern blocks based on the positional relationship of line patterns formed by droplet ejection from the common nozzle and belonging to different line pattern blocks. The dot measuring method according to claim 5 or 6.   In the pattern reading step, a line sensor is used as the imaging device, and the imaging is performed by relatively moving the ejection medium on which the line pattern is formed and the line sensor. Item 8. The dot measurement method according to any one of Items 1 to 7. Liquid ejected from each nozzle by relatively moving the liquid ejection head and the ejection medium while ejecting droplets onto the ejection medium from each nozzle of the liquid ejection head in which a plurality of nozzles are arranged Conveying means for conveying in a first direction an object to be measured formed by forming a line pattern with a dot row corresponding to each nozzle by causing the droplet to land on the ejection medium;
An imaging apparatus having a light receiving element array that intersects at a predetermined angle with respect to a line direction of the line pattern on the object to be measured conveyed by the conveying means in the first direction by the conveying means. Electronic image data representing the captured image is acquired by capturing the line pattern on the object to be measured by the imaging device while moving the object in a second direction different from the first direction during transportation of the object. Pattern reading means;
Profile graph acquisition means for acquiring a plurality of profile bluffs for one line pattern representing fluctuations in image signal values in a one-dimensional pixel row that obliquely crosses the line pattern from the electronic image data;
An extreme value position corresponding to the density center of the line pattern and a first edge position and a second edge position corresponding to the left and right edges of the line pattern, respectively, from each of the plurality of profile graphs acquired for one line pattern. Characteristic position calculating means for calculating
For the extreme value position, the first edge position, and the second edge position data calculated for the same line pattern by the feature position calculation means, the least square method is used to indicate the density center of the line pattern. Approximation for calculating a line center approximate line corresponding to the value position, a first edge approximate line corresponding to the first edge position of the line pattern, and a second edge approximate line corresponding to the second edge position of the line pattern. Straight line calculation means;
Calculate the vertical distance between the line center approximate lines corresponding to adjacent line patterns from the line center approximate line for each line pattern obtained by the approximate line calculation means, and calculate the landing position from which the dot landing position is obtained Means,
A line width calculating means for calculating a vertical distance between straight lines of the first edge approximate straight line and the second edge approximate straight line with respect to the same line pattern obtained by the approximate straight line calculating means, and obtaining the value as a line width of the line pattern;
Know in advance at least one of the relationship between the dot diameter and the line width formed on the medium to be ejected and the relationship between the volume of the ejected droplet and the line width by combining a predetermined liquid and the medium to be ejected. Correlation information storage means for storing the correlation information;
Based on the line width value obtained by the line width calculation means and the correlation information stored in the correlation information storage means, from the line width value, out of the corresponding dot diameter and ejection droplet volume A measurement value calculating means for obtaining at least one value;
A dot measuring apparatus comprising:   10. The profile graph acquisition means, the characteristic position calculation means, the approximate straight line calculation means, the landing position calculation means, the line width calculation means, the correlation information storage means, and the measurement value calculation means in the dot measurement device according to claim 9. As a program to make the computer function as.   An image forming apparatus comprising the dot measurement device according to claim 9 and the liquid ejection head.

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