Image processing device, image processing method and program, image forming device, and method for manufacturing printed matter

Abstract

To provide an image processing device, an image processing method and a program which enable impact position deviation with respect to a curved printing surface to be corrected in a short time and at low cost, without performing mechanical and electrical ejection timing control, an image forming device and a printed matter manufacturing method.SOLUTION: An image processing device obtains first pixel data having pixel rows respectively allocated to a plurality of nozzles arranged on a planar nozzle surface of an inkjet head; calculates first deviations of an ink impact position from an impact target position for each nozzle, using geometric models representing the inkjet head and a print target having a curved printing surface; and generates second pixel data having the pixel rows of the first pixel data deviated, in accordance with the calculated first deviation for each nozzle.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an image processing apparatus, an image processing method and program, an image forming apparatus, and a method for producing printed matter, and more particularly to a technique for forming an image on a curved printing surface. [Background technology]

[0002] Inkjet printers that use a single-pass method and an inkjet head with ink-ejecting nozzles arranged in a two-dimensional matrix are known. When printing on a flat surface with such a printer, the timing of ejection from each nozzle is adjusted according to the speed of the printing surface, the nozzle's position in the transport direction, the ink flight distance between the nozzle and the printing surface, and the ink ejection speed, to prevent variations in the ink landing position.

[0003] On the other hand, when printing on a curved surface with such a printer, what differs from when printing on a flat surface is that the ink flight distance varies depending on the nozzle position. Patent Document 1 discloses a technology that calculates the amount of landing error from the relationship between the nozzle position of the inkjet head and the landing position, and adjusts the landing error for each nozzle position by changing the ejection timing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-228243 Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology described in Patent Document 1, the amount (time) of shift in ejection timing is on the order of microseconds, and the CPU (Central Processing Unit) cannot keep up with the processing. Therefore, electrical adjustment is required on the hardware side. However, adjusting the ejection timing by hardware for thousands to tens of thousands of nozzles requires large circuit scale, which is problematic in that it requires more labor and costs than software.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide an image processing device, an image processing method and program, an image forming device, and a method for manufacturing printed matter that corrects the deviation of the landing position on a curved printing surface in a short time and at low cost without mechanical or electrical ejection timing control. [Means for solving the problem]

[0007] One aspect of an image processing device for achieving the above object is an image processing device that processes first pixel data for forming an image in an image forming device, and includes at least one processor and at least one memory that stores instructions to be executed by the at least one processor. The image forming device includes an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface, a movement mechanism that moves the inkjet head and a printing object having a curved printing surface relatively to each other, the movement mechanism performing the relative movement while maintaining constant the flight distance, which is the distance between each of the plurality of nozzles and the printing surface, and a control device that controls the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement. The at least one processor acquires first pixel data having pixel rows assigned to each nozzle, in which the pixels are arranged in ejection order, calculates a first deviation amount of the ink landing position from the target landing position for each nozzle using a geometric model representing the inkjet head and the printing object, and generates second pixel data by shifting the pixel row of the first pixel data in the direction of the pixel ejection order according to the calculated first deviation amount for each nozzle. According to this aspect, it is possible to correct the deviation of the landing position on the curved printing surface in a short time and at low cost without performing mechanical or electrical ejection timing control.

[0008] The control device preferably ejects ink from the multiple nozzles at a first ejection timing among multiple ejection timings corresponding to the multiple ejection period signals, where the ink ejected from the nozzle with a first flight distance lands at a target landing position on the printing object to which the ink moves relatively. This makes it possible to calculate the first deviation amount using the nozzle with the first flight distance as a reference.

[0009] The geometric model preferably includes the shape of the object to be printed and the coordinates of the position of each nozzle, and the at least one processor calculates the flying distance for each nozzle.

[0010] It is preferable that the geometric model includes the ink ejection speed, and that at least one processor calculates the flight time, which is the time from when ink is ejected from each nozzle to when it lands on the printing surface, based on the flight distance and ink ejection speed for each nozzle, and calculates a first deviation amount for each nozzle based on the flight time for each nozzle.

[0011] It is preferable that the geometric model includes a speed of relative movement, and that at least one processor calculates a relative movement speed of the landing position based on the speed of relative movement, calculates a relative movement distance of the landing position for each nozzle based on the flight time for each nozzle and the relative movement speed of the landing position, and calculates a first deviation amount for each nozzle based on the relative movement distance of the landing position for each nozzle.

[0012] Preferably, the at least one processor calculates, as the first deviation amount for each nozzle, a difference in the relative movement distance of the landing position for each nozzle, using the relative movement distance of the landing position of the nozzle with the smallest relative movement distance as a reference.

[0013] It is preferable to measure a second amount of deviation of the ink landing position from the target landing position for each nozzle from the result of forming an image on the printing surface of a target using the second pixel data in an image forming apparatus, and to generate third pixel data by shifting the pixel row of the second pixel data in the arrangement direction according to the measured second amount of deviation for each nozzle. The third pixel data allows for more accurate correction of the landing position deviation.

[0014] It is preferable that the printing object has a cylindrical surface at a constant distance from the central axis, and that the movement mechanism rotates the printing object around the central axis.

[0015] One aspect of an image forming apparatus for achieving the above object is an image forming apparatus comprising: the above image processing device; an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing object having a curved printing surface, wherein the movement mechanism performs relative movement while maintaining constant the flight distance, which is the distance between each of the plurality of nozzles and the printing surface; and a control device that controls the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement.

[0016] One aspect of an image processing method for achieving the above-mentioned object is an image processing method for processing first pixel data for forming an image in an image forming apparatus, the image forming apparatus comprising: an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing object having a curved printing surface, the movement mechanism performing the relative movement while maintaining constant the flight distance, which is the distance between each of the plurality of nozzles and the printing surface; and a control device for controlling the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement. The image processing method comprises the steps of: acquiring first pixel data having pixel rows assigned to each nozzle, the pixel rows being arranged in order of ejection; calculating a first amount of deviation of the ink landing position from the target landing position for each nozzle using a geometric model representing the inkjet head and the printing object; and generating second pixel data by shifting the pixel rows of the first pixel data in the direction of the pixel ejection order according to the calculated first amount of deviation for each nozzle.

[0017] One aspect of a method for manufacturing a printed matter in an image forming apparatus for achieving the above object is a method for manufacturing a printed matter in an image forming apparatus, the image forming apparatus comprising: an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing object having a curved printing surface, the movement mechanism performing the relative movement while maintaining constant a flight distance, which is the distance between each of the plurality of nozzles and the printing surface; and a control device for controlling the ejection timing of the plurality of nozzles using an ejection period signal according to the relative movement, wherein pixel rows assigned to each nozzle are a step of calculating a first deviation amount of the ink landing position from the target landing position for each nozzle using a geometric model representing the inkjet head and the object to be printed; a step of generating second pixel data by shifting the pixel row of the first pixel data in the direction of the pixel ejection order according to the calculated first deviation amount for each nozzle; and a step of moving the inkjet head and the object to be printed, which has a curved printing surface, relatively to each other, and ejecting ink from multiple nozzles based on the generated second pixel data to form an image on the printing surface of the object to be printed.

[0018] Another aspect of a method for manufacturing a printed matter in an image forming apparatus for achieving the above object is a method for manufacturing a printed matter in an image forming apparatus, the image forming apparatus comprising: an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing object having a curved printing surface, the movement mechanism performing the relative movement while maintaining constant a flight distance, which is the distance between each of the plurality of nozzles and the printing surface; and a control device for controlling the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement, the method comprising: a step of calculating a first deviation amount of an ink landing position from a target landing position for each nozzle using a geometric model representing the inkjet head and the printing object, the step of calculating the first deviation amount for each shape of the printing object; a step of acquiring first pixel data having a pixel row assigned to a plurality of nozzles, the pixel row being arranged in order of ejection; a step of generating second pixel data by shifting the pixel row of the first pixel data in the direction of arrangement of the pixel ejection order according to the calculated first shift amount for each nozzle, the second pixel data being generated for each shape of the print object; a step of linking and storing the shape of the print object and the generated second pixel data; a step of acquiring the first shape of a first print object for forming an image on the printing surface; a step of acquiring the second pixel data linked to the acquired first shape; and a step of moving the inkjet head and the first print object relatively, and ejecting ink from the plurality of nozzles based on the acquired second pixel data to form an image on the printing surface of the first print object.

[0019] One aspect of a program for achieving the above object is a program for causing a computer to execute the image processing method described above. This aspect may also include a computer-readable non-transitory storage medium on which this program is recorded. [Effects of the Invention]

[0020] According to the present invention, it is possible to correct deviations in landing positions on a curved printing surface in a short time and at low cost without mechanical or electrical ejection timing control. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a plan view of the nozzle surface of an inkjet head. [Figure 2] FIG. 2 is a top view showing how an inkjet head is used to print on a print target transported in the Y direction. [Figure 3] FIG. 3 is a side view of the inkjet head and the printing target. [Figure 4] FIG. 4 is a top view of the printing surface of the printing object printed under the conditions of FIG. [Figure 5] FIG. 5 is a side view of the inkjet head and the printing target. [Figure 6] FIG. 6 is a top view of the printing surface of the printing object printed under the conditions of FIG. [Figure 7] FIG. 7 is a side view of the inkjet head and the printing target. [Figure 8] FIG. 8 is a top view of the printing surface of the printing object printed under the conditions of FIG. [Figure 9] FIG. 9 is a side view of the inkjet head and the printing target. [Figure 10] FIG. 10 is a top view of the printing surface of the printing object printed under the conditions of FIG. [Figure 11] FIG. 11 is a diagram for explaining a geometric model representing an inkjet head and a printing target. [Figure 12] FIG. 12 is an explanatory diagram of each parameter of the geometric model. [Figure 13] FIG. 13 is an explanatory diagram of each parameter of the geometric model. [Figure 14] FIG. 14 is an explanatory diagram of each parameter of the geometric model. [Figure 15] FIG. 15 is a flowchart showing the image processing method according to the first embodiment. [Figure 16] FIG. 16 is a diagram showing the result of printing input image data on a flat surface. [Figure 17] FIG. 17 shows the results of printing on a curved surface under the conditions of FIG. [Figure 18] FIG. 18 is a diagram for explaining a method for generating image data. [Figure 19] FIG. 19 is a diagram showing the image data after correction. [Figure 20] FIG. 20 is a side view of the inkjet head and the printing target. [Figure 21] FIG. 21 is a top view of the printing surface of the printing object printed under the conditions of FIG. [Figure 22] FIG. 22 is a flowchart showing an image processing method according to the second embodiment. [Figure 23] FIG. 23 is an example of image data to be printed in step S11. [Figure 24] FIG. 24 is a diagram showing the result of printing on a curved surface in step S11 laid out on a flat surface. [Figure 25] FIG. 25 is a flowchart showing a method for producing a printed matter according to the third embodiment. [Figure 26] FIG. 26 is a process diagram for explaining each step of the method for producing a printed matter according to the third embodiment. [Figure 27] FIG. 27 is a schematic diagram showing an image forming apparatus according to the fourth embodiment. [Figure 28] FIG. 28 is a perspective view of the ink-jet head. [Figure 29] FIG. 29 is an enlarged view of a portion of the nozzle surface. [Figure 30] FIG. 30 is a plan view of the nozzle arrangement section. [Figure 31] FIG. 31 is a vertical cross-sectional view showing the three-dimensional structure of the ejector. [Figure 32] FIG. 32 is a functional block diagram of a control system of the image forming apparatus. [Figure 33] FIG. 33 is a block diagram showing the configuration of the image processing unit. [Figure 34] FIG. 34 is a diagram for explaining a change in the ejection timing of a certain nozzle. DETAILED DESCRIPTION OF THE INVENTION

[0022] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] <Conventional image forming apparatus> [Inkjet head] 1 is a plan view of the nozzle surface 12 of the inkjet head 10. The nozzle surface 12 has a parallelogram shape in plan view, with a long-side end face along the X direction, which is the width direction of the object to be printed, and a short-side end face along the U direction, which is at a certain angle with respect to the Y direction, which is the direction of relative movement of the object to be printed (e.g., the transport direction).

[0024] A plurality of nozzles 14 are arranged in a two-dimensional matrix in the X and U directions on the nozzle surface 12. In the example shown in Fig. 1, five nozzle rows are arranged along the U direction, with four nozzles 14 arranged along the X direction. The projected nozzle row obtained by projecting each nozzle 14 along the X direction can be considered equivalent to a single nozzle row in which the nozzles 14 are arranged at equal intervals at a nozzle density that achieves the maximum printing resolution in the X direction.

[0025] [Issues when printing on a flat surface] FIG. 2 is a top view showing how an inkjet head 10 is used to print on a print target 1 being transported in the Y direction. The print surface 1A of the print target 1 is flat, and the nozzle surface 12 and print surface 1A face each other in parallel. The inkjet head 10 has four nozzles 14 arranged along positions L1, L2, L3, L4, and L5 in the X direction. Note that the nozzles 14 are shown in a see-through manner in FIG. 2. Also, in FIG. 2, the target landing position P along the X direction on the print surface 1A of the print target is shown. A This shows:

[0026] 3 is a side view of the inkjet head 10 and the printing target 1, showing the case where ink droplets are ejected simultaneously from all of the nozzles 14. In Fig. 3, ink droplet D1 is an ink droplet ejected from the nozzle 14 at position L1, ink droplet D2 is an ink droplet ejected from the nozzle 14 at position L2, ink droplet D3 is an ink droplet ejected from the nozzle 14 at position L3, ink droplet D4 is an ink droplet ejected from the nozzle 14 at position L4, and ink droplet D5 is an ink droplet ejected from the nozzle 14 at position L5.

[0027] Here, the ink droplet D3 ejected from the nozzle 14 at the position L3 is dropped at the target landing position P A The ink droplets D1, D2, D3, D4, and D5 are ejected at the same ejection speed at the timing when they land on the printing surface 1A of the printing object 1. Therefore, the ink droplets D1, D2, D3, D4, and D5 are ejected simultaneously and land on the printing surface 1A of the printing object 1 at the same time.

[0028] 4 is a top view of the printing surface 1A of the printing object 1 printed under the conditions of FIG. 3. As shown in FIG. 4, the ink droplet D3 ejected from the nozzle 14 at the position L3 is dropped onto the target landing position P A It has landed on.

[0029] In contrast, ink droplets D1 and D2 ejected from the nozzles 14 at positions L1 and L2, which are located upstream in the transport direction from the nozzle 14 at position L3, land at the target position P A In addition, ink droplets D4 and D5 ejected from nozzles 14 at positions L4 and L5 located downstream in the transport direction from nozzle 14 at position L3 land at target landing position P on print surface 1A. A The droplets land upstream in the transport direction.

[0030] Thus, when performing single-pass printing on a flat surface using a two-dimensional matrix inkjet head, the ink landing position will vary unless the ejection timing of each nozzle is adjusted according to (1) the movement speed of the printing surface to be printed, (2) the nozzle's position in the transport direction, (3) the ink throw distance (hereinafter referred to as "throw distance") between the nozzle and the printing surface, and (4) the ink ejection speed.

[0031] In the example of Figure 3, the target impact position P A In order to land ink droplets at the positions L1 and L2, the ejection timing of the nozzles 14 at positions L1 and L2 must be earlier than the ejection timing of the nozzle 14 at position L3, and the ejection timing of the nozzles 14 at positions L4 and L5 must be later than the ejection timing of the nozzle 14 at position L3.

[0032] The inkjet head 10 can select, as the ejection timing for each nozzle, one of a plurality of ejection cycle signals output in accordance with the transport position of the print target 1. Therefore, for the nozzles 14 at positions L1 and L2, the inkjet head 10 can make the ejection timing earlier than the ejection cycle signal selected as the ejection timing for the nozzle 14 at position L3. Also, for the nozzles 14 at positions L4 and L5, the inkjet head 10 can make the ejection timing later than the ejection cycle signal selected as the ejection timing for the nozzle 14 at position L3.

[0033] 5 is a side view of the inkjet head 10 and the printing target 1, showing a case where ink droplets are ejected at different ejection timings from each nozzle 14. In the example shown in FIG. A The ink droplets are ejected in the order D1, D2, D3, D4, and D5 so that they land on the printing surface 1A of the printing object 1 in the order D1, D2, D3, D4, and D5.

[0034] 6 is a top view of the printing surface 1A of the printing target 1 printed under the conditions of FIG. 5. As shown in FIG. 5, all of the ink droplets D1, D2, D3, D4, and D5 land at the target landing position P A In this way, by adjusting the ejection timing of each nozzle 14, it is possible to make ink droplets ejected from all nozzles 14 land at their respective target landing positions.

[0035] The ejection timing can be controlled based on information on (1) the moving speed of the printing surface, (2) the nozzle position in the transport direction, (3) the throw distance, and (4) the ink ejection speed.

[0036] Here, "(1) the moving speed of the printing surface" can be detected by a transport synchronization signal obtained from a transport device (not shown). "(2) the nozzle transport direction position" can be obtained from nozzle mapping information of the nozzle surface 12 of the inkjet head 10. "(3) the throw distance" can be adjusted by adjusting the position of the inkjet head 10 so that it falls within the specification range. "(4) the ink ejection speed" can be obtained from the drive waveform of the nozzle 14.

[0037] When printing on a flat printing surface, as long as the device configuration is constant, "(2) Nozzle transport direction position," "(3) Throw distance," and "(4) Ink ejection speed" do not change once they are determined. Therefore, it is important to consider "(1) Print surface movement speed."

[0038] [Challenges when printing on curved surfaces] When printing using a two-dimensional matrix inkjet head, there are many cases where the printing surface is curved. For example, there is a known case where printing is done on paper that is adsorbed and transported to an impression drum. In recent years, with the trend toward label-free printing, there has also been an increase in printing directly on the sides of PET bottles and other containers. However, because two-dimensional matrix inkjet heads have multiple nozzles arranged on the same plane, if the printing surface is curved, "(3) throw distance" will vary depending on the nozzle position.

[0039] FIG. 7 is a side view of the inkjet head 10 and the printing target 2. The printing target 2 is cylindrical and has a printing surface 2A with a constant radius of curvature. The printing target 2 rotates around the central axis of the cylinder while maintaining the throw distance of each nozzle 14 constant. As shown in FIG. 7, the throw distance of the nozzle 14 at position L3 is the shortest, TD3, and the throw distance of the nozzle 14 at position L5 is the longest, TD5.

[0040] 7 shows a case where ink droplets D1, D2, D3, D4, and D5 are simultaneously ejected from nozzles 14 at positions L1, L2, L3, L4, and L5 in the X direction onto a printing object 2 rotating counterclockwise. In this case, the ink droplet D3 ejected from the nozzle 14 at position L3 lands at the target landing position P A Ink droplets D1, D2, D3, D4, and D5 are ejected at the timing when they land on the nozzle surface.

[0041] 8 is a top view of the printing surface 2A of the printing object 2 printed under the conditions of FIG. 7. As shown in FIG. 8, the ink droplet D3 ejected from the nozzle 14 at the position L3 is dropped to the target landing position P A It has landed on.

[0042] In contrast, ink droplets D1 and D2 ejected from the nozzles 14 at positions L1 and L2 located upstream in the rotation direction from the nozzle 14 at position L3, and ink droplets D4 and D5 ejected from the nozzles 14 at positions L4 and L5 located downstream in the rotation direction from the nozzle 14 at position L3, land at the target position P AThe bullets land downstream in the direction of rotation.

[0043] 9 is a side view of the inkjet head 10 and the printing object 2. In FIG. 9, when ink is ejected from all nozzles 14 under the conditions of FIG. 5 onto the printing object 2 rotating counterclockwise, that is, when the printing surface is flat, ink droplets ejected from all nozzles 14 land at the target position P A 9, ink droplets are ejected in the order D1, D2, D3, D4, and D5.

[0044] 10 is a top view of the printing surface 2A of the printing target 2 printed under the conditions of FIG. 9. As shown in FIG. 10, the ink droplet D3 ejected from the nozzle 14 at the position L3 lands at the target position P A On the other hand, ink droplets D1, D2, D4, and D5 land at the target landing position P A The landing positions of ink droplets D1, D2, D4, and D5 are determined by the rotation speed of the printing target 2, the ejection speed, the radius of curvature of the printing target 2, and the nozzle positions.

[0045] As such, when the printing surface is curved, the desired print results cannot be achieved by printing in the same way as when the printing surface is flat. Therefore, when printing on a curved surface using a two-dimensional matrix inkjet head, it is necessary to control the ejection timing of each nozzle by taking into account the "(3) throw distance" between each nozzle and the landing position. Furthermore, when printing on a cylindrical target that has irregularities along its length, even more complex control of the ejection timing is required.

[0046] The above problem can be solved by using an inkjet head with a uniform throw distance for each nozzle, where the nozzles are positioned on a curved surface with a negative curvature radius (a curved surface with a curvature direction opposite to that of the target surface) with the same absolute value. However, developing and manufacturing inkjet heads tailored to the target surface's curvature radius requires significant costs. Furthermore, printing on targets with different curvature radii using the same printing device can result in ink droplet placement errors and poor image quality. Therefore, when printing on targets with varying diameters, such as cans and bottles, printing assuming a single curvature radius can result in inconsistent print quality.

[0047] The above problem can also be solved by changing the ink ejection speed by changing the ejection waveform for each nozzle according to the throw distance. However, this method requires sending a large amount of waveform data to the head, and cannot be applied to heads that drive all nozzles with a single drive waveform.

[0048] First Embodiment The image processing method according to the first embodiment calculates the amount of deviation of the landing position of ink droplets ejected from each nozzle from the target landing position using a geometric model in a system in which the throw distance of each nozzle is constant during printing, and by shifting the image data before printing in advance according to the amount of deviation, the deviation of the ink landing position in the relative movement direction caused by the shape of the printing surface is improved, thereby improving the ink landing accuracy. Hereinafter, the deviation of the landing position of ink droplets from the target landing position refers to the amount of deviation in the relative movement direction between the inkjet head and the printing object.

[0049] [Calculation of impact position deviation using a geometric model] In the first embodiment, first, (1) the ink flight time from when ink is ejected from each nozzle of the inkjet head until it lands, and (2) the movement speed of the landing position are calculated taking into account at least one of the following parameters:

[0050] Inkjet head nozzle arrangement (nozzle mapping information) - Rotation speed of the printing object (surface speed of the printing surface) Ink ejection speed - Radius of curvature of the printing surface X, Y, Z, and θ relative to the rotation axis of the printing object XYZ Deviation (Positional deviation between the origin of the reference rotation axis and the origin of the rotation axis of the printing target) θ relative to the rotation axis of the printing object XYZ The discrepancy (The tilt of the rotation axis of the printing target in the X, Y, and Z directions relative to the tilt of the reference rotation axis) - Landing position during printing In the case of an inkjet head capable of ejecting ink droplets of a plurality of sizes, the "ink ejection speed" may be prepared for each ink droplet size, or may be a constant value regardless of the ink droplet size.

[0051] These parameters may be design values ​​or may be calculated from design data such as 2D (2-Dimensions) or 3D (3-Dimensions) CAD (computer aided design) drawings.

[0052] Next, the delay time for each nozzle is calculated from the calculated "(1) ink flight time" and "(2) landing position movement speed."

[0053] These processes are performed using a geometric model. FIG. 11 is a diagram for explaining the geometric model according to this embodiment. Also, FIGS. 12, 13, and 14 are explanatory diagrams of the parameters of the geometric model. Here, the inkjet head 200 and the printing target 210 are shown as the geometric model of the inkjet head 10 and the printing target 2. In this embodiment, for simplicity, a two-dimensional geometric model is used, and the amount of deviation is calculated on the YZ plane. Note that a three-dimensional geometric model may also be used. As shown in FIGS. 11 to 14, the conditions of the geometric model are as follows: (1) The printing object 210 is a cylinder (cylinder) with a radius R [mm], and the printing surface 212 (an example of a "printing surface") is the side surface of the cylinder. (2) The center of the bottom surface of the cylinder of the printing target 210 is the origin position, and the cylinder rotates from the Z axis to the Y axis direction around the X axis. (3) A total of N nozzles 204 are arranged on the flat nozzle surface 202 of the inkjet head 200, with n nozzles per row. (4) The nozzle surface 202 of the inkjet head 200 is perpendicular to the Z axis. (5) The position of the nozzle surface 202 of the inkjet head 200 in the Z direction is z0. (6) The nozzle number i of each nozzle 204 arranged on the nozzle surface 202 is assigned from 1 to n along the Y axis. (7) The coordinates of each nozzle 204 are (y(i), z0), and the throw distance of nozzle number i is TD(i) [mm].

[0054] As shown in FIGS. 13 and 14, the operating conditions of the geometric model are as follows: (1) The cylinder of the printing target 210 rotates at a constant rotational speed ω [rad / s] (an example of the "speed of relative movement"). (2) The ink is ejected parallel to the Z axis and travels in a straight line at a constant speed v [mm / s].

[0055] 15 is a flowchart showing the image processing method according to the first embodiment. The image processing method can be realized using computer hardware and software (not shown).

[0056] In step S1, the computer calculates the throw distance TD(i) of each nozzle 204 with nozzle number i.

[0057] If the coordinates on the side surface of the cylinder where an ink droplet ejected from the nozzle 204 with nozzle number i lands are (y(i), z(i)), TD(i) of the nozzle 204 with nozzle number i is expressed by the following equation 1.

[0058] TD(i)={(y(i)-y(i)) 2 +(z0-z(i)) 2} 1 / 2=z0-z(i) ... (Equation 1) Here, z(i) is expressed by the following equation 2.

[0059] z(i)=(R 2 -y(i) 2 ) 1 / 2 …(Formula 2) In step S2, the computer calculates the flight time t(i) of the ink ejected from nozzle number i from the throw distance TD(i) calculated in step S1 and the ink ejection speed. If the ink ejection speed is v, the flight time t(i) is expressed by the following equation 3.

[0060] t(i)=TD(i) / v …(Equation 3) In step S3, the computer calculates the moving speed Vs of the impact position (an example of the "relative moving speed of the impact position"). The printing surface 212 is the side surface of a uniform cylinder with a radius R [mm], and the moving speed Vs of the impact position is the same regardless of the position on the side surface. The moving speed Vs of the impact position is expressed by the following equation 4.

[0061] Vs=R×ω…(Formula 4) In step S4, the computer calculates, from the flight time t(i) calculated in step S2 and the movement speed Vs calculated in step S3, the movement distance L(i) (an example of a "relative movement distance") of the printing position of nozzle 204 from the time when the nozzle 204 with nozzle number i ejects an ink droplet until the ink droplet lands on the printing surface 212. The movement distance L(i) of the printing position is expressed by the following equation 5.

[0062] L(i)=Vs×t(i) In step S5, the computer calculates the deviation amount ΔL(i) of the landing position, which is the difference between the movement distance L(i) of the printing position of each nozzle 204 and the nozzle with the shortest movement distance L(i) of the printing position (an example of a "difference in relative movement distance"), based on the movement distance L(i) of the printing position of each nozzle 204 calculated in step S4. If the nozzle number of the nozzle with the shortest movement distance L(i) of the printing position is p, the deviation amount ΔL(i) of the landing position of the nozzle 204 with nozzle number i is expressed by the following equation 6.

[0063] ΔL(i)=L(i)-L(p) ...(Equation 6) In step S6, the computer corrects the image data based on the amount of deviation in landing position for each nozzle 204 calculated in step S5.

[0064] [Image data correction based on calculated deviation amount] This section explains how to correct image data based on the amount of deviation in the landing position. To simplify the explanation, we will assume that the size of the input image data is 3 pixels in the X direction by 20 pixels in the Y direction, and that a line three pixels wide is printed by printing three pixels each using 20 nozzles 204, numbered 1 to 20.

[0065] This input image data is an example of "first pixel data." Pixel data is, for example, data in which pixels are arranged two-dimensionally, such as dot data after halftone processing. The pixel data only needs to have pixels arranged in at least the X direction. The columns of the input image data along the Y direction are an example of "pixel columns" assigned to each nozzle 204, and in each pixel column, the pixels are arranged in ejection order. The Y direction in which the pixels of a pixel column are arranged in ejection order is an example of the "direction in which the pixels are arranged in the ejection order."

[0066] Here, the input image data is dot data in which each pixel indicates the presence or absence of an ink droplet to be ejected. Each pixel may also indicate the size of an ink droplet. Furthermore, the input image data may be data that is the same as the printing resolution, and each pixel may also be data that indicates density.

[0067] Figure 16 shows the result of printing input image data on a flat surface. Figure 16 also shows the nozzle number of the nozzle that ejected each ink droplet. As shown in Figure 16, the print result shows that each column of ink droplets ejected from each nozzle is aligned in the row direction (X direction), forming a straight line three pixels wide, which matches the input image data.

[0068] Fig. 17 shows the results of printing on a curved surface under the conditions of Fig. 16, i.e., when each nozzle is ejected at a timing that results in a straight line on a flat surface similar to the input image data. As shown in Fig. 17, the printed result does not match the input image data, as each column of ink droplets ejected from each nozzle does not form a straight line in the row direction.

[0069] Fig. 18 is a diagram for explaining a method for generating image data. In Fig. 18, pixels of the input image data are shifted by the amount of displacement of the impact position calculated using a geometric model, and the impact timing is earlier the further up in the X direction, and later the further down in the X direction.

[0070] To print on a curved surface in accordance with the input image data, first calculate the number of pixels (= integer) to be corrected for each nozzle from the deviation (see Equation 6) of the impact position for the nozzle with the smallest throw distance (shortest movement distance of the print position). Then, based on the calculated deviation for each nozzle, shift the image data so that the ejection timing is changed by the deviation amount. For example, if there is a deviation of one pixel downstream in the relative movement direction, shift one column of image data corresponding to the nozzle position one pixel upstream so that ejection occurs one pixel earlier. For columns with small deviation amounts, blank spaces are inserted upstream to create data from which no ink is ejected.

[0071] In the example shown in FIG. 18, the nozzle with the smallest throw distance is nozzle number 3. The impact position of nozzle number 1 is shifted by 50 μm relative to the nozzle with the smallest throw distance (nozzle number 3). If the print resolution is 1200 dpi (dots per inch), the distance between dots is approximately 21.17 μm, so the impact position shift of 50 μm is equivalent to 2 pixels, since 50 / 21.17 ≒ 2.36. Therefore, the shift amount of the data corresponding to nozzle number 1 is 2 pixels.

[0072] Additionally, the impact position of nozzle number 2 is shifted by 20 μm relative to the nozzle with the smallest throw distance. Since 20 / 21.17 ≒ 0.94, this impact position shift of 20 μm corresponds to one pixel. Therefore, the data corresponding to nozzle number 2 is shifted by 1 pixel.

[0073] Similarly, the offset amounts of the landing positions of nozzle numbers 3, 4, 5, . . . , 19, and 20 are 0, 18, 40, . . . , 22, and 45 μm, respectively, and the offset amounts of the corresponding data are 0, 1, 2, .

[0074] Next, output image data is created taking the calculated amount of shift into consideration. Figure 19 shows the output image data after correction. Note that blank areas in Figure 19 represent data that does not eject ink. As shown in Figure 19, the data corresponding to the nozzle with nozzle number 1 is shifted upward in the Y direction (equivalent to the upstream side) by 1 pixel. This indicates that the ejection timing is advanced by the amount of upward shift. Similarly, the data corresponding to the nozzles with nozzle numbers 2, 3, 4, 5, ..., 19, and 20 are shifted upward in the Y direction by 1, 0, 1, 2, ..., 1, and 2 pixels, respectively. Note that a shift amount of 0 pixel means that the data is not shifted.

[0075] By correcting the image in this way, the image size (pixel row) of the output image data becomes larger in the transport direction compared to the input image data according to the maximum deviation amount. For example, if the image length of the input image data in the relative movement direction is 3 pixels and the maximum deviation amount is 2 pixels, the image length of the corrected output image data will be 5 pixels. This output image data is an example of "second pixel data."

[0076] By using this output image data to print at the same timing as when printing on a flat printing surface in an image forming device (not shown), i.e., at the printing timing in a system where the throw distance of each nozzle is the same, an image can be formed in which the landing position in the relative movement direction is corrected.

[0077] 20 is a side view of the inkjet head 10 and the printing object 2. In FIG. 20, image data corrected based on the calculated deviation amount is used to calculate the landing position P of ink droplets ejected from all nozzles 14 under the conditions of FIG. 9, i.e., when the printing surface is flat. A 10 shows the case where ink is ejected at the timing when it lands on the ink droplet.

[0078] Fig. 21 is a top view of the printing surface 2A of the printing target 2 printed under the conditions of Fig. 20. As shown in Fig. 21, all of the ink droplets D1, D2, D3, D4, and D5 land at the target landing position P A In this way, it is possible to make the ink droplets land on the target positions on the curved surface with the same ejection timing as when printing on a flat printing surface. In other words, it is possible to print on a curved printing surface in the same way as on a flat printing surface.

[0079] As described above, according to the first embodiment, it is possible to reduce the adjustment time (downtime) in the actual device. Furthermore, according to the first embodiment, since mechanical and electrical ejection timing control is not required, it can be implemented in a short time and at low cost.

[0080] <Second embodiment> The image processing method according to the second embodiment performs printing using the image data corrected in the first embodiment, measures the amount of deviation from the print result, and reflects this in the amount of deviation, thereby allowing the droplets to land at the target positions with even greater accuracy.

[0081] FIG. 22 is a flowchart showing an image processing method according to the second embodiment.

[0082] In step S11, the image forming apparatus (not shown) prints image data onto the curved surface, taking into account the amount of deviation in landing positions calculated using the geometric model. That is, the image data, created in the first embodiment, in which pixel data has been shifted in advance to account for the amount of deviation in landing positions, is used for printing at the same throw distance and transport speed as the geometric model. The throw distance is adjusted so that the nozzles and landing positions are closest to each other.

[0083] 23 shows an example of input image data printed in step S11. This input image data is data for printing a straight line extending in the X direction by ejecting one ink droplet from each nozzle number. A computer (not shown) generates output image data from this input image data based on the amount of landing position deviation calculated using a geometric model, and the image forming device prints the generated output image data.

[0084] In step S12, the user lays out the print result printed on the curved surface on a flat surface and measures the amount of deviation in the landing position of the ink ejected from each nozzle in the transport direction (an example of the "second deviation amount"), using the location where the ink lands earliest on the upstream side in the transport direction as a reference.

[0085] Figure 24 is a diagram showing the results of printing on a curved surface in step S11 laid out on a flat surface. Figure 24 also shows the amount of deviation in landing positions measured in step S12. Here, the amounts of deviation in landing positions for nozzle numbers 1, 2, 3, 4, 5, ... are 50, 20, 0, 18, 40, ... [μm], respectively.

[0086] In step S13, the amount of deviation in the landing position of each nozzle is measured, and the measured value is used as the deviation amount for each nozzle and reflected in the deviation amount. The processes of steps S11 and S12 may be repeated to measure the amount of deviation in the landing position of each nozzle multiple times, and the average value of the multiple measurements may be used as the deviation amount for each nozzle.

[0087] In the example shown in FIG. 24, the shift amounts for nozzle numbers 1, 2, 3, 4, 5, . . . are 2, 1, 0, 1, 2, .

[0088] This offset amount is reflected in the output image data to generate measured and corrected image data. This measured and corrected image data is an example of "third pixel data." Using the measured and corrected image data makes it possible to land droplets at the target positions with even greater accuracy.

[0089] <Third embodiment> In the third embodiment, image data for each shape of the printing object is stored in advance, the shape of the printing object is measured before printing, and image data for printing is selected from the stored image data based on the measurement results, so that printing is performed at a timing that matches the curvature of the printing surface.

[0090] Fig. 25 is a flowchart showing a method for producing a printed matter according to the third embodiment, and Fig. 26 is a process diagram for explaining each step of the method for producing a printed matter according to the third embodiment.

[0091] In step S21 (process P1), the user samples multiple print objects and measures their diameters (an example of the "shape of the print object"). In the example shown in Figure 26, the diameters DM1, DM2, and DM3 of three print objects 3-1, 3-2, and 3-3 are shown, respectively.

[0092] In step S22 (process P2), a computer (not shown) calculates the amount of deviation from the target landing position for each nozzle for each printing target based on the diameter and geometric model acquired in step S21. The example shown in Fig. 26 shows deviation amounts A1, A2, and A3 for each nozzle for three printing targets 3-1, 3-2, and 3-3, respectively.

[0093] In step S23 (process P3), the computer creates output image data by shifting the input image data according to the amount of misalignment for each nozzle calculated in step S23. The example shown in Fig. 26 shows output image data I1, I2, and I3 corresponding to the amounts of misalignment A1, A2, and A3 for each nozzle. The output image data I1, I2, and I3 are associated with the respective diameters measured in step S21 and stored in a database (not shown).

[0094] In step S24 (process P4), the image forming apparatus (not shown) measures the diameter (an example of the "first shape") of the conveyed print target (an example of the "first print target") before printing. In the example shown in FIG. 26, the measured diameter DX of print target 3-X is shown.

[0095] In step S25 (process P5), the image forming apparatus obtains output image data associated with the diameter measured in step S24 from the database. For example, if the diameter DX=DM1, output image data I1 is obtained. If the diameter DX=DM2, output image data I2 is obtained. The image forming apparatus controls the inkjet head 10 based on the obtained output image data to form an image on the printing target 3-X, as shown in FIG. 26.

[0096] In this way, according to the image processing method of the third embodiment, even if there is variation in the curvature of the printing surface of the printing target, it is possible to make the ink droplets land at the target landing positions with high precision.

[0097] <Fourth embodiment> 27 is a schematic diagram showing an image forming apparatus 20 according to a fourth embodiment. The image forming apparatus 20 prints an image (an example of image formation) on a printing object 4 having a printing surface 4A with a certain radius of curvature. The printing object 4 is, for example, a can, a glass bottle, a plastic bottle, or a cylindrical cardboard box.

[0098] 27, the image forming apparatus 20 includes inkjet heads 22C, 22M, 22Y, and 22K. The inkjet head 22C ejects cyan ink droplets, the inkjet head 22M ejects magenta ink droplets, the inkjet head 22Y ejects yellow ink droplets, and the inkjet head 22K ejects black ink droplets.

[0099] The image forming apparatus 20 includes a transport mechanism 86 (see FIG. 32). The print target 4 is transported by the transport mechanism 86 to positions facing the nozzle surfaces 24 (see FIG. 28) of the inkjet heads 22C, 22M, 22Y, and 22K in order.

[0100] The image forming apparatus 20 includes a rotation mechanism 88 (see FIG. 32, an example of a "relative movement mechanism") that rotates the printing target 4 around the central axis of the printing target 4 at positions facing the inkjet heads 22C, 22M, 22Y, and 22K, respectively.

[0101] The image forming apparatus 20 configured as above first transports the printing object 4 to a position facing the nozzle surface 24 of the inkjet head 22C using the transport mechanism 86. At the position facing the nozzle surface 24 of the inkjet head 22C, the image forming apparatus 20 rotates the printing object 4 around its central axis using the rotation mechanism 88. The image forming apparatus 20 ejects cyan ink from the multiple nozzles 26 (see FIG. 30 ) of the inkjet head 22C to form an image on the printing surface 4A of the printing object 4.

[0102] Next, the image forming device 20 uses the transport mechanism 86 to transport the printing object 4 to a position facing the nozzle surface 24 of the inkjet head 22M. At the position facing the nozzle surface 24 of the inkjet head 22M, the image forming device 20 uses the rotation mechanism 88 to rotate the printing object 4 around the central axis as the rotation axis. The image forming device 20 ejects magenta ink from the multiple nozzles 26 of the inkjet head 22M to form an image on the printing surface 4A of the printing object 4.

[0103] Similarly, the image forming device 20 uses the inkjet head 22Y and the inkjet head 22K to form an image on the printing surface 4A of the printing object 4. As a result, a color image is formed on the printing surface 4A of the printing object 4.

[0104] [Inkjet head] The same configuration can be applied to the inkjet heads 22C, 22M, 22Y, and 22K. In the following explanation, the configuration of the inkjet head 22C will be explained as a representative.

[0105] Figure 28 is a perspective view of inkjet head 22C. Inkjet head 22C is a line-type liquid ejection head with a nozzle row that can print the entire printing area in the length direction of the cylinder of printing object 4 (the length direction from bottom surface to bottom surface) at a specified resolution with a single relative movement. This type of liquid ejection head is also called a full-line liquid ejection head. The length direction of the cylinder of printing object 4 is perpendicular to the transport direction and rotation direction of printing object 4.

[0106] The inkjet head 22C has a nozzle surface 24. On the nozzle surface 24, nozzles 26 (see FIG. 30) that eject ink are arranged two-dimensionally.

[0107] The inkjet head 22C has a structure in which a plurality of head modules 28-i are connected in a row along the longitudinal direction, where i is an integer from 1 to n. The head modules 28-i are attached to and integrated with a support frame 30. Each head module 28-i is provided with a cable 32 for electrical connection.

[0108] [Nozzle arrangement] Figure 29 is an enlarged view of a portion of the nozzle surface. The nozzle surface 24-i of the head module 28-i is a parallelogram. Dummy plates 34 are attached to both ends of the support frame 30. The nozzle surface 24 of the inkjet head 22C, together with the surface 34A of the dummy plate 34, has an overall rectangular shape.

[0109] A strip-shaped nozzle arrangement section 36-i is provided in the center of the nozzle surface 24-i of the head module 28-i. The nozzle arrangement section 36-i essentially functions as the nozzle surface 24-i. The nozzles 26 are provided in the nozzle arrangement section 36-i. Figure 29 shows a nozzle row 38 made up of a plurality of nozzles 26.

[0110] 30 is a plan view of the nozzle arrangement section 36-i. The X direction is the central axis direction of the printing object 4, and the Y direction is the transport direction of the printing object 4. A plurality of nozzles 26 are arranged two-dimensionally on the nozzle surface 24-i of the head module 28-i.

[0111] The head module 28-i has a planar shape of a parallelogram having a long side end face along the V direction inclined at an angle β with respect to the central axis direction of the printing object 4, and a short side end face along the W direction inclined at an angle α with respect to the transport direction of the printing object 4.

[0112] In the head module 28-i, a plurality of nozzles 26 are arranged in a matrix in the row direction along the V direction and the column direction along the W direction. In the case of a liquid ejection head in which a plurality of nozzles 26 are arranged in a matrix, a projected nozzle array obtained by projecting each nozzle 26 in the matrix array along the nozzle array direction can be considered equivalent to a single nozzle array in which the nozzles 26 are arranged at approximately equal intervals at a nozzle density that achieves the maximum recording resolution in the nozzle array direction. The projected nozzle array is a nozzle array obtained by orthogonally projecting each nozzle 26 in a two-dimensional nozzle array along the nozzle array direction.

[0113] "Approximately equal intervals" means that the droplet ejection points are substantially equal intervals as printable droplets in the image forming apparatus 20. For example, the concept of equal intervals also includes cases where the intervals are slightly different to account for manufacturing errors and / or droplet movement on the medium due to impact interference. The projected nozzle array essentially corresponds to the nozzle array. When the projected nozzle array is taken into consideration, a nozzle number indicating the nozzle position can be assigned to each nozzle in the order in which the projected nozzles are lined up along the nozzle array direction.

[0114] The arrangement of the nozzles 26 of the inkjet head 22C is not limited, and various nozzle arrangements can be adopted. For example, instead of a two-dimensional matrix arrangement, a linear nozzle arrangement, a V-shaped nozzle arrangement, or a polygonal nozzle arrangement such as a W-shape in which V-shaped arrangements are repeated may be adopted.

[0115] [Ejector configuration] 31 is a longitudinal cross-sectional view showing the three-dimensional structure of an ejector. The ejector 40 includes a nozzle 26, a pressure chamber 44 communicating with the nozzle 26, and a piezoelectric element 52. The nozzle 26 communicates with the pressure chamber 44 via a nozzle flow path 42. The pressure chamber 44 communicates with a supply-side common branch flow path 48 via an individual supply path 46.

[0116] The diaphragm 50 that forms the top surface of the pressure chamber 44 has a conductive layer that functions as a common electrode corresponding to the lower electrode of the piezoelectric element 52. The conductive layer is not shown. The pressure chamber 44, the walls of the other flow path portions, and the diaphragm 50 can be made of silicon. The material of the diaphragm 50 is not limited to silicon, and it can also be made of a non-conductive material such as resin. The diaphragm 50 itself may be made of a metal material such as stainless steel, and the diaphragm 50 may also function as a common electrode.

[0117] A piezoelectric unimorph actuator is formed by stacking piezoelectric elements 52 on a vibration plate 50. A drive voltage is applied to the individual electrodes 54, which are the upper electrodes of the piezoelectric elements 52, to deform the piezoelectric bodies 56, which in turn deflect the vibration plate 50 and change the volume of the pressure chambers 44. The pressure change that accompanies the change in volume of the pressure chambers 44 acts on the ink, causing it to be ejected from the nozzles 26.

[0118] When the piezoelectric element 52 returns to its original state after ink is ejected, new ink is filled into the pressure chamber 44 from the supply-side common branch channel 48 through the individual supply channel 46. The operation of filling the pressure chamber 44 with ink is called refilling.

[0119] The shape of the pressure chamber 44 in a plan view is not particularly limited, and various shapes are possible, such as a rectangle or other polygon, a circle, or an ellipse. A cover plate 58 is provided above the individual electrode 54. The cover plate 58 is a member that maintains a movable space 60 for the piezoelectric element 52 and seals the periphery of the piezoelectric element 52.

[0120] A supply-side ink chamber and a recovery-side ink chamber (not shown) are formed above the cover plate 58. The supply-side ink chamber is connected to a supply-side common main flow channel (not shown) via a communication passage (not shown). The recovery-side ink chamber is connected to a recovery-side common main flow channel (not shown) via a communication passage (not shown).

[0121] [Control system configuration example] 32 is a functional block diagram of a control system of the image forming apparatus 20. As shown in Fig. 32, the image forming apparatus 20 includes a system controller 70, a communication unit 72, an operation unit 76, a display unit 78, a program storage unit 80, an image memory 82, a conveyance control unit 84, and a print control unit 92.

[0122] The system controller 70 is an overall control unit that comprehensively controls each unit of the image forming apparatus 20. The system controller 70 is an arithmetic unit that performs various arithmetic processing. The system controller 70 is a memory controller that controls reading and writing of data in memory.

[0123] The communication unit 72 includes a communication interface (not shown) and transmits and receives data to and from a host computer 74 connected to the communication interface.

[0124] The operation unit 76 includes operation members such as operation buttons, a keyboard, and a touch panel. The operation unit 76 may include a plurality of types of operation members. Information input using the operation unit 76 is transmitted to the system controller 70. The system controller 70 generates command signals for executing various processes in accordance with the information transmitted from the operation unit 76. The system controller 70 transmits the command signals to processing units that perform various processes.

[0125] The display unit 78 includes a display device (not shown) such as a liquid crystal panel, and a display driver (not shown). The display unit 78 displays various information such as various setting information and abnormality information of the device on the display device in response to commands from the system controller 70. The display unit 78 may be a touch panel type display device and may also function as the operation unit 76.

[0126] The program storage unit 80 stores programs used by each unit of the image forming apparatus 20. The various programs stored in the program storage unit 80 are read out via the system controller 70 and executed by each unit of the apparatus.

[0127] The image memory 82 functions as a temporary storage unit for various data including image data. Data is read from and written to the image memory 82 via the system controller 70. Image data received from the host computer 74 via the communication unit 72 is stored in the image memory 82.

[0128] The transport control unit 84 controls the operation of the transport mechanism 86 and the rotation mechanism 88. The rotation mechanism 88 is equipped with an encoder 90 that outputs a pulse signal corresponding to the rotation of the printing target (an example of an "ejection period signal corresponding to relative movement").

[0129] The print control unit 92 controls the ejection of ink from the inkjet heads 22C, 22M, 22Y, and 22K in response to commands from the system controller 70.

[0130] The print control unit 92 includes a waveform generation unit 94 , a waveform storage unit 96 , a drive circuit 98 , and an image processing unit 100 .

[0131] 33 is a block diagram showing the configuration of the image processing unit 100. As shown in FIG. 33, the image processing unit 100 (an example of an “image processing device”) includes a processor 102 and a memory 104.

[0132] Processor 102 executes instructions stored in memory 104. The hardware structure of processor 102 is various processors as shown below. The various processors include a CPU (Central Processing Unit), which is a general-purpose processor that executes software (programs) and functions as various functional units, a GPU (Graphics Processing Unit), which is a processor specialized for image processing, a PLD (Programmable Logic Device), which is a processor whose circuit configuration can be changed after manufacture such as an FPGA (Field Programmable Gate Array), and a dedicated electrical circuit, such as an ASIC (Application Specific Integrated Circuit), which is a processor having a circuit configuration designed specifically for executing specific processing.

[0133] A single processing unit may be configured with one of these various processors, or may be configured with two or more processors of the same or different types (e.g., multiple FPGAs, a combination of a CPU and an FPGA, or a combination of a CPU and a GPU). Also, multiple functional units may be configured with a single processor. Examples of multiple functional units configured with a single processor include, first, a configuration in which a single processor is configured with a combination of one or more CPUs and software, as typified by a client or server computer, and this processor operates as multiple functional units. Second, a configuration in which a processor is used to realize the functions of an entire system including multiple functional units on a single IC (Integrated Circuit) chip, as typified by an SoC (System On Chip). In this way, the various functional units are configured with one or more of the above-mentioned various processors as a hardware structure.

[0134] Furthermore, the hardware structure of these various processors is, more specifically, an electric circuit made up of a combination of circuit elements such as semiconductor elements.

[0135] The memory 104 stores instructions to be executed by the processor 102. The memory 104 includes a RAM (Random Access Memory) and a ROM (Read Only Memory), not shown. The processor 102 uses the RAM as a working area, executes software using image processing programs and parameters stored in the ROM, and also executes various processes of the image processing unit 100 by using parameters stored in the ROM, etc.

[0136] The memory 104 also stores a geometric model representing the inkjet head 200 and the object 210 to be printed.

[0137] The processor 102 generates dot data from input image data and includes a color separation processing unit 106, a color conversion processing unit 108, a correction processing unit 110, a halftone processing unit 112, a shift amount calculation unit 114, and a pixel shifting unit 116.

[0138] The color separation processing unit 106 performs color separation processing on the input image data. For example, if the input image data is expressed in RGB, the input image data is separated into data for each color of R (red), G (green), and B (blue).

[0139] The color conversion processing unit 108 converts the image data for each color separated into R, G, and B into C, M, Y, and K corresponding to the ink colors.

[0140] The correction processing unit 110 performs correction processing on the image data for each color converted into C, M, Y, and K. Examples of correction processing include gamma correction processing, density unevenness correction processing, and abnormal recording element correction processing.

[0141] The halftone processing unit 112 converts the color-separated image data for each color, which is expressed in multiple gradations, such as 0 to 255, into dot data expressed in two values, "eject" and "not eject," or in three or more values, such as "eject large droplets," "eject small droplets," and "not eject." The halftone processing unit 112 applies predetermined halftone processing rules. Examples of halftone processing rules include dithering and error diffusion.

[0142] The deviation amount calculation unit 114 calculates the deviation amount (an example of a "first deviation amount") of the ink landing position from the target landing position for each nozzle 26 using a geometric model representing the inkjet heads 22C, 22M, 22Y, and 22K and the printing object 4.

[0143] The pixel shifting unit 116 generates output image data (second pixel data) by shifting the pixel rows of the input image data (first pixel data) in the direction of the pixel ejection order, according to the amount of shift for each nozzle 26 calculated by the shift amount calculation unit 114.

[0144] The image processing unit 100 can execute the image processing methods according to the first and second embodiments.

[0145] 32, the waveform generating section 94 generates the waveform of the driving voltage. The waveform storing section 96 stores the waveform of the driving voltage.

[0146] The print control unit 92 (an example of a "control device") determines the ejection timing and ink ejection amount for each pixel position based on the dot data generated by the image processing unit 100, and generates a control signal that determines the ejection timing for each pixel position and the drive voltage and ejection timing according to the ink ejection amount.

[0147] The ejection timing for each pixel is selected from among multiple ejection timings synchronized with the pulse signal output from the encoder 90, and a first ejection timing is selected at which the ink ejected from the nozzle 26 lands at the target landing position on the printing object when the flight distance is a first distance.

[0148] The drive circuit 98 generates a drive voltage having a drive waveform corresponding to the dot data. The drive circuit 98 supplies the drive voltage to the inkjet heads 22C, 22M, 22Y, and 22K. When the drive voltage and control signals are supplied to the inkjet heads 22C, 22M, 22Y, and 22K, ink is ejected from each nozzle 26 of the inkjet heads 22C, 22M, 22Y, and 22K, and the ejected ink forms dots on the printing surface of the printing target.

[0149] Figure 34 is a diagram for explaining changes in the ejection timing of a certain nozzle 26. The upper part of Figure 34 shows a pulse signal output from the encoder 90, which corresponds to an ejection period signal. The horizontal axis represents time, and the vertical axis represents voltage. In the example shown in Figure 34, pulse signals are output at times T1, T2, T3, and T4.

[0150] The middle part of Fig. 34 shows the ejection timing when input image data is printed as is. In the example shown in Fig. 34, ink is ejected onto the first pixel at timing T3, and onto the second pixel at timing T4.

[0151] The lower part of Figure 34 shows the ejection timing when output image data is printed. This output image data is obtained by shifting the pixel row corresponding to a nozzle 26 in the input image data by one pixel upstream in the relative movement. As shown in Figure 34, when printing this output image data, ink is ejected for the first pixel at timing T2, and ink for the second pixel at timing T3. In other words, ink for each pixel is ejected at a timing that is one ejection cycle earlier than when printing input image data. This allows each pixel to land one pixel upstream in the relative movement of the printing surface 4A of the printing target 4 compared to when the input image data is printed.

[0152] Similarly, if the pixel row corresponding to a nozzle 26 in the input image data is shifted two pixels upstream in the relative movement, ink is ejected for the first pixel at timing T1, and ink for the second pixel at timing T2. This allows each pixel to land two pixels upstream in the relative movement of the printing surface 4A of the printing target 4 compared to when the input image data is printed.

[0153] In this way, the image forming apparatus 20 can shift the ejection timing in pixel units by shifting the pixels of the image data using the ejection period signal as is, without mechanical or electrical ejection timing control, thereby enabling the droplets to land at the target landing positions with high precision.

[0154] In the image forming device 20 configured in this manner, inkjet heads 22C, 22M, 22Y, and 22K are moved relative to the printing object 4, and ink is ejected from multiple nozzles 26 based on output image data generated by the image processing method of the first embodiment, thereby forming an image on the printing surface 4A of the printing object 4, thereby producing a printed matter.

[0155] <Other> Here, an example has been described in which a cylindrical (cylinder-shaped) printing target is printed on by an inkjet head while the target is rotated around the central axis of the cylinder as the axis of rotation, but the cylindrical (cylinder-shaped) printing target may also be printed on by an inkjet head while moving along its central axis. Furthermore, the shape of the printing surface of the printing target is not limited to a cylindrical surface, but may also be a spherical surface, a wavy surface, a sloped surface, or the like. Furthermore, the printing target is not limited to a moving object, as long as the inkjet head and the printing target move relative to each other.

[0156] That is, each embodiment is applicable to an apparatus that performs printing by relatively moving a plurality of nozzles while maintaining constant the flight distance, which is the distance between each nozzle and the printing surface.

[0157] Furthermore, each embodiment is not limited to single-pass printing, in which printing is performed by a single relative movement between the inkjet head and the printing object, but can also be applied to multi-pass printing, in which an image is completed by multiple relative movements, as long as the flight distances of the multiple nozzles are kept constant during one relative movement.

[0158] The technical scope of the present invention is not limited to the scope described in the above embodiments. The configurations and the like in each embodiment can be appropriately combined with each other within the scope that does not deviate from the spirit of the present invention. [Explanation of symbols]

[0159] 1, 2, 3-1, 3-2, 3-3, 3-X, 4... Printing target 1A, 2A, 4A…Printed surface 10...Inkjet head 12...Nozzle surface 14...Nozzle 20...Image forming device 22C, 22K, 22M, 22Y... Inkjet heads 24, 24-i...Nozzle surface 26...Nozzle 28-i...Head module 30...Support frame 32…Cable 34...Dummy plate 34A…Surface 36-i...Nozzle arrangement section 38...Nozzle row 40...Ejector 42...Nozzle flow path 44...Pressure chamber 46…Individual supply route 48…Supply side common tributary flow path 50...Diaphragm 52...Piezoelectric element 54…Individual electrode 56...Piezoelectric material 58...Cover plate 60…Movable space 70...System controller 72…Communications Department 74...Host computer 76...Operation unit 78...Display section 80...Program storage section 82...Image memory 84...Transport control unit 86...Transport mechanism 88...Rotation mechanism 90...Encoder 92...Print control unit 94...Waveform generation section 96...Waveform storage section 98...Drive circuit 100...Image processing unit 102...Processor 104...Memory 106...Color separation processing unit 108...Color conversion processing unit 110...Correction processing unit 112...Halftone processing unit 114...Quantity calculation section 116...Pixel shift section 200...Inkjet head 202...Nozzle surface 204...Nozzle 210...Printing target 212...Printed surface A1, A2, A3...Misalignment amount D1, D2, D3, D4, D5... ink droplets DM1, DM2, DM3…Diameter I1, I2, and I3...output image data L1, L2, L3, L4, L5…Position P A … Target impact position P1 to P5: Image formation process S1 to S5, S11 to S13... Image processing steps S21 to S25: Steps in the manufacturing process for printed materials

Claims

1. An image processing device that processes first pixel data for forming an image in an image forming device, at least one processor; at least one memory storing instructions for execution by said at least one processor; Equipped with the image forming apparatus, an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing target having a curved printing surface, the movement mechanism maintaining constant a flight distance, which is a distance between each of the plurality of nozzles and the printing surface; a control device that controls the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement; Equipped with The printing target has a cylindrical surface with a constant distance from a central axis, the moving mechanism rotates the printing object around the central axis, The at least one processor acquiring first pixel data having pixel rows allocated to the respective nozzles, the pixel rows being arranged in order of ejection; calculating a first deviation amount of an ink landing position from a target landing position for each nozzle using a geometric model representing the inkjet head and the printing object; generating second pixel data by shifting the pixel row of the first pixel data in the arrangement direction of the ejection order of the pixels in accordance with the calculated first shift amount for each nozzle; Image processing device.

2. the control device ejects ink from the plurality of nozzles at a first ejection timing among a plurality of ejection timings corresponding to the plurality of ejection period signals, the first ejection timing being such that ink ejected from a nozzle having a first flight distance lands at a target landing position on the printing object that moves relatively; The image processing device according to claim 1 .

3. the geometric model includes a shape of the printing object and coordinates of the positions of the respective nozzles; the at least one processor calculates a flight distance for each nozzle.

3. The image processing device according to claim 1 or 2.

4. the geometric model includes an ejection velocity of the ink; the at least one processor calculates a flight time, which is a time from when ink is ejected from the nozzle to when ink lands on the printing surface, for each nozzle based on the flight distance for each nozzle and the ink ejection speed; calculating the first deviation amount for each nozzle based on the flight time for each nozzle; The image processing device according to claim 3 .

5. the geometric model includes a velocity of the relative movement; The at least one processor calculating a relative movement speed of the impact position based on the speed of the relative movement; calculating a relative movement distance of the landing position for each nozzle based on the flight time for each nozzle and the relative movement speed of the landing position; calculating the first deviation amount for each nozzle based on the relative movement distance of the landing position for each nozzle; The image processing device according to claim 4 .

6. The at least one processor calculating a difference in the relative movement distance of the landing position for each nozzle as the first deviation amount for each nozzle, using the relative movement distance of the landing position of the nozzle whose relative movement distance is the smallest as a reference; The image processing device according to claim 5 .

7. measuring a second deviation amount of an ink landing position from a target landing position for each nozzle from a result of forming an image on the printing surface of the printing target in the image forming device using the second pixel data; generating third pixel data by shifting the pixel row of the second pixel data in the arrangement direction in accordance with the second shift amount measured for each nozzle; The image processing device according to claim 1 .

8. An image processing device according to any one of claims 1 to 7; an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing target having a curved printing surface, the movement mechanism maintaining constant a flight distance, which is a distance between each of the plurality of nozzles and the printing surface; a control device that controls the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement; An image forming apparatus comprising:

9. An image processing method for processing first pixel data for forming an image in an image forming device, comprising: the image forming apparatus, an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing target having a curved printing surface, the movement mechanism maintaining constant a flight distance, which is a distance between each of the plurality of nozzles and the printing surface; a control device that controls the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement; Equipped with The printing target has a cylindrical surface with a constant distance from a central axis, the moving mechanism rotates the printing object around the central axis, acquiring first pixel data having pixel rows assigned to the respective nozzles, the pixel rows being arranged in ejection order; calculating a first deviation amount of an ink landing position from a target landing position for each nozzle using a geometric model representing the inkjet head and the printing target; generating second pixel data by shifting the pixel row of the first pixel data in the arrangement direction of the ejection order of the pixels according to the calculated first shift amount for each nozzle; An image processing method comprising:

10. A method for producing a printed matter in an image forming apparatus, the image forming apparatus, an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing target having a curved printing surface, the movement mechanism maintaining constant a flight distance, which is a distance between each of the plurality of nozzles and the printing surface; a control device that controls the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement; Equipped with The printing target has a cylindrical surface with a constant distance from a central axis, the moving mechanism rotates the printing object around the central axis, acquiring first pixel data having pixel rows assigned to the respective nozzles, the pixel rows being arranged in ejection order; calculating a first deviation amount of an ink landing position from a target landing position for each nozzle using a geometric model representing the inkjet head and the printing target; generating second pixel data by shifting the pixel row of the first pixel data in the arrangement direction of the ejection order of the pixels according to the calculated first shift amount for each nozzle; a step of moving the inkjet head and a printing object having a curved printing surface relative to each other, and ejecting ink from the plurality of nozzles based on the generated second pixel data to form an image on the printing surface of the printing object; A method for manufacturing a printed matter comprising the steps of:

11. A method for producing a printed matter in an image forming apparatus, the image forming apparatus, an inkjet head having a plurality of nozzles arranged two-dimensionally on a flat nozzle surface; a movement mechanism for relatively moving the inkjet head and a printing target having a curved printing surface, the movement mechanism maintaining constant a flight distance, which is a distance between each of the plurality of nozzles and the printing surface; a control device that controls the ejection timing of the plurality of nozzles using an ejection period signal corresponding to the relative movement; Equipped with The printing target has a cylindrical surface with a constant distance from a central axis, the moving mechanism rotates the printing object around the central axis, a step of calculating a first deviation amount of an ink landing position from a target landing position for each nozzle using a geometric model representing the inkjet head and the printing object, the first deviation amount being calculated for each shape of the printing object; acquiring first pixel data having pixel rows assigned to the respective nozzles, the pixel rows being arranged in ejection order; generating second pixel data by shifting the pixel row of the first pixel data in the arrangement direction of the ejection order of the pixels in accordance with the calculated first shift amount for each nozzle, wherein the second pixel data is generated for each shape of the printing target; a step of storing the shape of the printing object and the generated second pixel data in association with each other; acquiring a first shape of a first printing object on which an image is to be formed; acquiring the second pixel data associated with the acquired first shape; a step of moving the inkjet head and the first printing object relative to each other and ejecting ink from the plurality of nozzles based on the acquired second pixel data to form an image on a printing surface of the first printing object; A method for manufacturing a printed matter comprising the steps of:

12. A program for causing a computer to execute the image processing method according to claim 9.

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