Printing method and robot system

Abstract

The invention provides a printing method and a robot system capable of performing high-quality printing. The printing method includes: a trial printing step of performing trial printing on an object for trial printing by discharging ink from a nozzle while moving the object for trial printing having the same shape as the object and a print head relative to each other along a print track; a measurement step in which the color of a test print image formed by the test print is measured by the spectroscopic camera; a control determination step for determining the control of the nozzle on the basis of the result of the measurement step; and a main printing step of performing printing on the object by discharging the ink from the nozzle on the basis of the control determined in the control determination step while moving the object and the print head relative to each other along the print path.

Description

Technical Field

[0001] The present invention relates to a printing method and a robot system. Background Art

[0002] The painting robot described in Patent Document 1 includes a robot main body having an arm and a nozzle head unit attached to the front end of the arm. Further, while moving the nozzle head unit relative to an object using the robot main body, ink is ejected from the nozzle head unit toward the object, thereby performing printing on the object. In addition, a plurality of nozzles arranged in a prescribed direction are provided in the nozzle head unit. Here, if the separation distance between the nozzle and the object is large, there is a possibility that the printed image may shift, warp, deform, etc., resulting in a reduction in printing quality. Therefore, in Patent Document 1, for nozzles with a separation distance from the object equal to or greater than a prescribed value, the printing width for each scan is controlled by not ejecting ink, in an attempt to suppress a reduction in printing quality.

[0003] Patent Document 1: International Publication No. 2021 / 255896

[0004] However, in the painting robot of Patent Document 1, even if the separation distance between the nozzle and the object is small, the printing quality is reduced due to the shape and gradient of the object. Summary of the Invention

[0005] The printing method of the present invention uses a robot equipped with a print head having a nozzle for ejecting ink, and performs a printing operation on the object by ejecting the ink from the nozzle while relatively moving the object and the print head along a printing track. The printing method includes:

[0006] A trial printing step of performing trial printing on a trial printing object having the same shape as the object by ejecting the ink from the nozzle while relatively moving the trial printing object having the same shape as the object and the print head along the printing track;

[0007] A measurement step of measuring a trial printing image formed by the trial printing with a spectroscopic camera;

[0008] A control determination step of determining the control of the nozzle based on the result of the measurement step; and

[0009] An official printing step of performing printing on the object by ejecting the ink from the nozzle based on the control determined in the control determination step while relatively moving the object and the print head along the printing track.

[0010] The robot system of the present invention has:

[0011] A robot equipped with a print head having a nozzle for ejecting ink;

[0012] A control device that controls the driving of the robot; and

[0013] A spectroscopic camera

[0014] While relatively moving an object and the print head along a printing track, the ink is ejected from the nozzle to perform a printing operation on the object.

[0015] While relatively moving a trial-printing object having the same shape as the object and the print head along the printing track, the ink is ejected from the nozzle to perform a trial print on the trial-printing object.

[0016] The spectroscopic camera measures a trial-print image formed by the trial print.

[0017] Based on the result of the measurement, the control of the nozzle is determined.

[0018] While relatively moving the object and the print head along the printing track, the ink is ejected from the nozzle based on the determined control to perform printing on the object. Description of the Drawings

[0019] Figure 1 is an overall view of a robot system according to a preferred embodiment.

[0020] Figure 2 is a top view showing Figure 1 a moving stage and a print head included in the robot shown.

[0021] Figure 3 is a diagram for explaining problems that occur when printing an object having a shape with a gradient.

[0022] Figure 4 is a diagram for explaining problems that occur when printing an object having a shape with a gradient.

[0023] Figure 5 is a flowchart showing a printing process.

[0024] Figure 6 is a schematic diagram showing a case where Lab values are calculated for each pixel of a spectroscopic camera.

[0025] Figure 7 is a diagram showing a state where a spectroscopic camera is covered with a light-shielding member.

[0026] Explanation of Reference Numerals

[0027] 1: Robot system; 10: Robot; 2: Robot main body; 21: Base; 22: Robot arm; 221: Arm; 222: Arm; 223: Arm; 224: Arm; 225: Arm; 226: Arm; 3: Printing head; 31: Nozzle; 310: Nozzle row; 310a: Nozzle row; 310b: Nozzle row; 310c: Nozzle row; 310d: Nozzle row; 4: Moving stage; 40: Base; 400: Piezoelectric actuator; 41: First stage; 42: Second stage; 45: First stage drive unit; 46: Second stage drive unit; 5: Spectral camera; 6: Inertial sensor; 9: Control device; A: First direction; B: Second direction; Fw: Printed surface; Fw0: Printed surface; Fw1: Upper surface; Fw2: Side surface; Fw3: Circular surface; I: Ink; J1: Joint; J2: Joint; J3: Joint; J4: Joint; J5: Joint; J6: Joint; L: Lighting; P0: Test print image; Px: Pixel; Q: Printing track; S1: Test printing step; S2: Measurement step; S3: Control determination step; S4: Official printing step; Sh: Light-shielding member; W: Object; W0: Object for test printing. Detailed implementation mode

[0028] Hereinafter, the printing method and the robot system of the present invention will be described in detail based on the embodiments shown in the drawings.

[0029] Figure 1 It is an overall view of the robot system according to a preferred embodiment. Figure 2 It shows Figure 1 A top view of the moving stage and the printing head provided in the robot shown. Figure 3 And Figure 4 They are respectively diagrams for explaining the problems that occur when printing an object having a gradient shape. Figure 5 It is a flowchart showing the printing process. Figure 6 It is a schematic diagram showing the case of calculating the Lab value for each pixel of the spectral camera. Figure 7 It is a diagram showing the state where the spectral camera is covered by the light-shielding member.

[0030] Figure 1 The robot system 1 shown is applied to a printing system for performing a printing operation on an object W. The robot system 1 includes a robot 10 for printing on the object W, a control device 9 for controlling the drive of the robot 10, and a spectral camera 5 for measuring the object W. In addition, the robot 10 includes a robot main body 2 having a robot arm 22, a moving stage 4 disposed at the front end of the robot arm 22, a printing head 3 disposed on the moving stage 4, and an inertial sensor 6 disposed on the printing head 3.

[0031] In such a robot system 1, while moving the print head 3 relative to the object W using the robotic arm 22, ink I is ejected from the print head 3 at a prescribed timing, thereby performing a printing operation on the object W.

[0032] In addition, in the robot system 1 of the present embodiment, the object W is fixed and only the print head 3 is moved to relatively move the object W and the print head 3. However, it is not limited thereto, and the object W and the print head 3 may be relatively moved by moving the print head 3 and the object W together.

[0033] Robot main body 2

[0034] As Figure 1 shown, the robot main body 2 is a six-axis vertical articulated robot having six drive axes, and includes a base 21 fixed to a mounting table, the ground, etc. and a robotic arm 22 rotatably connected to the base 21.

[0035] The robotic arm 22 has a structure in which six arms 221, 222, 223, 224, 225, and 226 are rotatably connected in this order from the base 21 side, and includes six joints J1, J2, J3, J4, J5, and J6. Specifically, the arm 221 is rotatably connected to the base 21 via the joint J1, the arm 222 is rotatably connected to the arm 221 via the joint J2, the arm 223 is rotatably connected to the arm 222 via the joint J3, the arm 224 is rotatably connected to the arm 223 via the joint J4, the arm 225 is rotatably connected to the arm 224 via the joint J5, and the arm 226 is rotatably connected to the arm 225 via the joint J6.

[0036] In addition, among the joints J1 to J6, the joints J2, J3, and J5 are respectively bending joints, and the joints J1, J4, and J6 are respectively twisting joints. In addition, although not shown, drive mechanisms are provided at the respective joints J1, J2, J3, J4, J5, and J6. The drive mechanism includes a motor, a speed reducer that decelerates the rotation of the motor to increase the torque and outputs it, and an encoder that detects the rotation amount of the joint. Moreover, by independently moving the respective joints J1, J2, J3, J4, J5, and J6, the robotic arm 22 can be moved in a desired direction at a desired posture and speed.

[0037] However, the structure of the robot main body 2 is not particularly limited. For example, the number of arms included in the robotic arm 22 is not limited to six. In addition, the robot main body 2 may also be a dual-arm robot, a horizontal articulated robot (SCARA robot), etc. In addition, the robot main body 2 may not be fixed to a mounting table, the ground, etc. and may be able to travel by itself.

[0038] Moving stage 4

[0039] As Figure 1As shown, the moving stage 4 is arranged at the front end of the robotic arm 22, i.e., the arm 226. The moving stage 4 is used for the position calibration of the print head 3. As Figure 2 shown, the moving stage 4 has: a base 40 supported by the arm 226; a first stage 41 that linearly moves relative to the base 40 in a first direction A; and a second stage 42 that linearly moves relative to the first stage 41 in a second direction B orthogonal to the first direction A. Moreover, the print head 3 is arranged on the second stage 42.

[0040] In addition, the moving stage 4 has: a first stage driving unit 45 that moves the first stage 41 relative to the base 40 along the first direction A; and a second stage driving unit 46 that moves the second stage 42 relative to the first stage 41 along the second direction B. The first and second stage driving units 45 and 46 each include a piezoelectric actuator 400 that drives by using the expansion and contraction of a piezoelectric element generated by energization. By transmitting the vibration of the piezoelectric actuator 400 to the first and second stages 41 and 42, they are moved. Thus, by using the piezoelectric actuator 400, the movement amount and movement speed of the first and second stages 41 and 42 can be finely and highly accurately controlled, and the switching of the movement direction is also agile. In addition, miniaturization and weight reduction of the moving stage 4 can also be achieved. Therefore, the position calibration of the print head 3 can be performed with higher accuracy.

[0041] However, the structure of the moving stage 4 is not particularly limited. For example, the first and second stage driving units 45 and 46 may also be structures that use a driving source other than the piezoelectric actuator 400, such as a motor that rotates by energization. In addition, the moving stage 4 may further have a third stage that linearly moves in a direction orthogonal to the first direction A and the second direction B, and a fourth stage that rotates around an axis orthogonal to the first direction A and the second direction B. In addition, the moving stage 4 may be omitted. In this case, as long as the position calibration of the print head 3 is performed by using the robotic arm 22.

[0042] Print head 3

[0043] As Figure 2 shown, the print head 3 is arranged on the second stage 42. The print head 3 is not particularly limited. In the present embodiment, an inkjet head using a piezoelectric driving method is used. Although the inkjet head using the piezoelectric driving method is not shown, it has an ink chamber, a vibration plate that is a part of the wall surface constituting the ink chamber, a piezoelectric element that vibrates the vibration plate, and a nozzle 31 connected to the ink chamber. In such a structure, if a voltage is applied to the piezoelectric element to vibrate the piezoelectric element, the vibration plate vibrates, and the ink I in the ink chamber is ejected from the nozzle 31.

[0044] In addition, as Figure 2As shown in the figure, four nozzle rows 310 are formed along the printing track Q on the front end face of the print head 3. The nozzle rows 310 include a plurality of nozzles 31 arranged at equal intervals in a direction orthogonal to the printing track Q. Moreover, black ink I is ejected from each nozzle 31 of the nozzle row 310a, cyan ink I is ejected from each nozzle 31 of the nozzle row 310b, magenta ink I is ejected from each nozzle 31 of the nozzle row 310c, and yellow ink I is ejected from each nozzle 31 of the nozzle row 310d. With such a print head 3, full-color printing can be performed.

[0045] Moreover, while moving the print head 3 along the printing track Q and ejecting ink I from each nozzle 31 at a prescribed timing so that it lands on the object W, a prescribed printed image is printed on the object W. Thus, by having a plurality of nozzles 31 arranged in a direction orthogonal to the printing track Q, the printing range per scan of the print head 3 is expanded, and printing operations can be effectively performed.

[0046] However, the structure of the print head 3 is not particularly limited. For example, the number and arrangement of the nozzles 31, the color of the ink I ejected from the nozzles 31, etc. are not particularly limited. For example, one, two, or three of the four nozzle rows 310 may be omitted to form a structure capable of performing monochromatic printing. In addition, the structure of the print head 3 is not limited to the above-described piezoelectric drive type inkjet head. For example, it may be a thermal type utilizing the film boiling phenomenon of the ink I, a bubble ejection type that ejects the ink I by generating bubbles by applying heat, an electrostatic actuator type that displaces and vibrates a diaphragm by electrostatic force to eject the ink I, or the like inkjet head.

[0047] Inertial sensor 6

[0048] As Figure 1 and Figure 2 shown in the figure, the inertial sensor 6 is disposed on the print head 3 to detect the vibration of the print head 3. In addition, the "vibration" refers to an unnecessary displacement other than the displacement of the print head 3 along the printing track Q. As the inertial sensor 6, as long as it can detect vibration, it is not particularly limited. For example, a three-axis acceleration sensor that detects acceleration in three mutually orthogonal axial directions can be used.

[0049] Control device 9

[0050] As Figure 1As shown, the control device 9 is electrically connected to the robot 10 to control the driving of the robot 10. Specifically, the control device 9 controls the driving of the robot body 2, the printing head 3, the moving stage 4, and the inertial sensor 6 independently or in conjunction with each other. Such a control device 9 is composed of, for example, a computer, and has a processor (CPU) for processing information, a memory connected to the processor so as to be communicable, and an external interface for connecting to an external device. Various programs that can be executed by the processor are stored in the memory, and the processor can read and execute the programs stored in the memory.

[0051] The configuration of the robot system 1 has been described above. Next, a printing method on an object W using the robot system 1 will be described. Figure 3 as well as Figure 4 , explain the existing problems. Figure 3 In the example shown, the printed surface Fw of the object W is a non-planar shape, that is, a gradient shape, and is composed of an upper surface Fw1 along the horizontal direction, a side surface Fw2 along the vertical direction, and a circular surface Fw3 located between them and curved into an arc shape. In addition, in the example shown in the figure, the printing track Q is set to be a straight line toward the back side of the paper. Moreover, while the printing head 3 is moved along the printing track Q using the robot 10, the ink I is ejected from each nozzle 31 at a specified timing and landed on a specified portion of the printed surface Fw, thereby printing a specified printing image on the printed surface Fw.

[0052] Here, since the printed surface Fw is not a plane, the distances from the plurality of nozzles 31 to the printed surface Fw are different. In the example shown in the figure, the distances from the nozzles 31 located in the center of the print head 3 to the printed surface Fw are the shortest, and as they shift toward both sides, the distances from the nozzles 31 to the printed surface Fw gradually increase. Figure 4 As shown, the greater the distance between the nozzle 31 and the printed surface Fw, that is, the greater the flight distance of the ink I, the greater the diffusion of the ink I during flight and the larger the landing area. In addition, since the ink I is ejected while the print head 3 is moved, the greater the flight distance of the ink I, the more the landing position of the ink I is offset toward the front side of the printing track Q. In addition, unlike the distance, due to the inclination of the landing part, the ink I sags and expands due to its own weight after landing, and as a result, the landing area becomes larger. In particular, in the example shown in the figure, the ink I that lands on the side Fw2 along the vertical direction is prone to sag and expand due to its own weight. In this way, if the landing area of ​​the ink I becomes larger due to the distance between the nozzle 31 and the printed surface Fw or the inclination of the printed surface Fw, the amount of ink I per unit area decreases, and the brightness of the part becomes higher. In addition, due to the offset of the landing position of the ink I, the color tone changes. Therefore, the color reproducibility relative to the sample image (the image to be printed) is poor, resulting in a decrease in printing quality.

[0053] In order to suppress such a reduction in printing quality, in the robot system 1, before printing the sample image on the object W (hereinafter, also referred to as "official printing"), a test print of the sample image is performed on the test printing object W0 having the same shape as the object W, the color reproducibility of the printed image with respect to the sample image is confirmed, and the result is fed back to the control of the nozzle 31 in the official printing.

[0054] That is, in the robot system 1, first, the test printing object W0 is prepared, and a test print of the sample image is performed on the test printing object W0. Next, the color of the printed image printed by the test print is measured by the spectroscopic camera 5. Next, based on the measurement result of the spectroscopic camera 5, the color difference ΔE between the sample image and the printed image (hereinafter, also referred to as "actual printed image") actually printed on the test printing object W0 is detected. Next, the control of each nozzle 31 including the ejection timing of the ink I, the ejection speed of the ink I, the ejection amount of the ink I, etc. is determined so as to reduce the detected color difference ΔE, preferably to make the color difference ΔE zero. Then, the ink I is ejected from each nozzle 31 based on the determined control, and the official printing on the object W is performed. According to such a method, excellent color reproducibility can be exhibited, the actual printed image can be made close to the sample image, and preferably made to coincide. Therefore, high printing quality can be exhibited. Hereinafter, the printing method based on the robot system 1 will be described in detail.

[0055] As Figure 5 shown, the printing method based on the robot system 1 includes: a test printing step S1 for performing a test print; a measurement step S2 for measuring the test print image P0 printed by the test printing step S1 by the spectroscopic camera 5; a control determination step S3 for determining the control of the print head 3 based on the result of the measurement step S2; and an official printing step S4 for performing printing based on the control determined by the control determination step S3. Hereinafter, each of the steps S1 to S4 will be described in sequence.

[0056] Test printing step S1

[0057] In the test printing step S1, first, the printing track Q is determined based on the shape of the printed surface Fw of the object W and the sample image printed on the printed surface Fw of the object W in the official printing step S4. That is, in order to print the sample image on the printed surface Fw, it is determined how to move the print head 3 relative to the object W is better. Regarding the shape of the printed surface Fw, for example, it is preferable to use the 3D CAD (computer-aided design) data of the object W. Thereby, the shape of the printed surface Fw can be obtained with high precision, and the printing track Q can be further optimized.

[0058] Next, based on the printing track Q and the sample image, the control of each nozzle 31 is determined. Specifically, mainly the timing of ejecting the ink I from each nozzle 31, the ejection speed of the ink I, and the ejection amount of the ink I are determined. At this time, for the nozzles 31 whose distance from the printing surface Fw exceeds a specified value, it is also possible to set them not to eject the ink I. Thereby, it is possible to effectively suppress the reduction in printing quality caused by the deviation, warping, deformation, etc. of the printed image due to excessive deviation of the landing position. In addition, when determining the control of each nozzle 31, in addition to the printing track Q and the sample image, for example, the background color of the printing surface Fw can also be considered.

[0059] Next, an object W0 for test printing is prepared. The object W0 for test printing has a printing surface Fw0 having at least the same shape as the printing surface Fw of the object W. In addition, the "same shape" means that in addition to the case where the shapes are exactly the same, it also includes the case where there is an error of a degree that can be regarded as the same shape from common technical knowledge. Furthermore, elements affecting the printing quality such as the constituent material of the printing surface Fw0 of the object W0 for test printing and the texture of the surface are the same as those of the object W. Thereby, it is possible to perform test printing under conditions closer to actual printing, and it is possible to accurately measure the color reproducibility of the actual printed image in the subsequent measurement step S2. In particular, in the present embodiment, the remaining part of the object W is used as the object W0 for test printing. Thereby, if individual differences are not considered, the object W and the object W0 for test printing are exactly the same, and it is possible to perform test printing under the same conditions as actual printing.

[0060] Next, while moving the print head 3 relative to the object W0 for test printing along the printing track Q, the control device 9 ejects the ink I from each nozzle 31 based on the control determined as described above. Thereby, a test print image P0 as an actual printed image is printed on the printing surface Fw0. In addition, during this printing operation, the control device 9 detects the vibration of the print head 3 based on the output of the inertial sensor 6, and controls the drive of the moving stage 4 to eliminate the detected vibration. Specifically, the drive of the moving stage 4 is controlled to apply a vibration to the print head 3 having a phase opposite to the detected vibration. Thereby, it is possible to suppress the vibration of the print head 3 during the printing operation and perform higher-quality printing.

[0061] Measurement step S2

[0062] In the measurement step S2, after the test print image P0 is sufficiently dried, the color of the test print image P0 is measured by the spectroscopic camera 5. Specifically, while irradiating the illumination light onto the test print object W0, the test print image P0 is photographed by the spectroscopic camera 5. According to the spectroscopic camera 5, the spectroscopic spectrum can be obtained for each pixel of the spectroscopic camera 5. Therefore, in each part of the test print image P0, the color difference ΔE from the sample image can be detected. In particular, the spectroscopic camera 5 of the present embodiment can obtain spectroscopic data of 16 wavelengths in the visible light region (400 nm to 700 nm). Therefore, the color gamut that the spectroscopic camera 5 can represent and the number of colors that can be represented are more than those of an RGB camera, and subtle color differences that are difficult to detect in an RGB camera can be detected. Therefore, the color difference ΔE between the test print image P0 and the sample image can be detected with higher accuracy.

[0063] Next, the image obtained by the spectroscopic camera 5 is analyzed to extract the test print image P0. Next, the color of the test print image P0 is measured for each pixel of the spectroscopic camera 5. Then, as Figure 6 shown, the Lab value of the color, that is, the coordinates in the Lab color space, is obtained for each pixel. In addition, in the Lab color space, L represents luminance (brightness), and a and b represent hue. In this way, by obtaining the Lab value of the color, the color of each pixel can be quantitatively obtained.

[0064] In addition, in the present embodiment, before obtaining the Lab value, the white balance (color temperature) of the test print image P0 is adjusted. Thereby, the Lab value of the color of each pixel can be obtained with high accuracy without being affected by the imaging environment. The method for adjusting the white balance is not particularly limited. For example, before the spectroscopic camera 5 photographs the test print image P0, the spectroscopic camera 5 can also photograph a black-and-white adjustment plate that serves as a reference for white balance, and adjust the white balance based on the result. In addition, the adjustment plate and the test print image P0 can be arranged in parallel, and the spectroscopic camera 5 can photograph the adjustment plate and the test print image P0 simultaneously, and adjust the white balance of the test print image P0 that appears in the same image based on the color of the adjustment plate that appears in the photographed image.

[0065] In addition, for example, as Figure 7 shown, the test print object W0 can also be covered with a light-shielding member Sh during photographing to block external light, and then the test print object W0 is irradiated with the illumination L disposed inside the light-shielding member Sh. As the above structure, the imaging environment is maintained constant, and thereby the environment after white balance adjustment is adjusted.

[0066] In addition, for example, when an ultraviolet curable ink is used as Ink I, when the trial print image P0 is captured by the spectral camera 5, illumination light containing ultraviolet rays may be irradiated onto the trial print image P0. Thereby, it is possible to dry the trial print image P0 while performing the measurement based on the spectral camera 5. Therefore, the measurement step S2 can be started earlier, and the cycle time of the printing operation can be shortened.

[0067] Control determination step S3

[0068] The control determination step S3 determines the control of the print head 3 based on the result of the measurement step S2. Specifically, first, the color difference ΔE between the trial print image P0 and the sample image is detected for each pixel of the spectral camera 5. Then, based on the detected color difference ΔE, the control of each nozzle 31 determined in the trial printing step S1 is corrected so that the color difference ΔE becomes smaller, preferably the color difference ΔE becomes zero, and the control of each nozzle 31 for the next full-scale printing step S4 is determined. In addition, in the present embodiment, as the control of each nozzle 31, at least one of the ejection amount of Ink I ejected from the nozzle 31, the ejection speed of Ink I ejected from the nozzle 31, and the timing of ejecting Ink I from the nozzle 31 is corrected. Since these items are all items that are easy to correct, the color difference ΔE can be reduced simply accordingly.

[0069] In addition, the method of correcting the driving conditions of the print head 3 is the same for each pixel. Therefore, for the sake of convenience of explanation, the following description will be given taking one pixel Px as a representative, and the description of other pixels will be omitted. For example, when the Lab values (L, a, b) of the trial print image P0 in the pixel Px are (L0, a0, b0), and the Lab values (L, a, b) of the same part of the sample image are (Lr, ar, br), first, their color difference ΔE is calculated. In addition, in the calculation of the color difference ΔE, the following formula (1) can be used.

[0070]

[0071] Next, it is determined whether the calculated color difference ΔE is within the correctable range. That is, it is determined whether the color difference ΔE can be reduced to a preset allowable range by correcting the control of each nozzle 31. Then, based on the determination result, it is determined whether to eject Ink I to this part or not. Specifically, when it is determined that the color difference ΔE can be reduced to the allowable range, Ink I is ejected to this part. On the contrary, when it is determined that the color difference ΔE cannot be reduced to the allowable range, Ink I is not ejected to this part. That is, this part is printed as blank in the full-scale printing step S4. Thereby, unreasonable color correction is not performed on the part corresponding to the pixel Px, and instead, a decrease in printing quality such as an increase in the color difference ΔE can be suppressed.

[0072] When it is determined that the color difference ΔE can be reduced to the allowable range, next, the cause of the color difference ΔE is determined. That is, it is determined whether the cause of the color difference ΔE is caused by the distance between the nozzle 31 and the printing surface Fw0 (the flight distance of the ink I), or by the gradient (inclination) of the printing surface Fw0, or by both. Then, based on the determination result, the control of each nozzle 31 set in the trial printing step S1 is corrected.

[0073] Specifically, when it is determined that the cause of the color difference ΔE is caused by the distance between the nozzle 31 and the printing surface Fw0, for example, the ejection amount of the ink I used for printing the portion corresponding to the pixel Px is increased to reduce the brightness and reduce the deviation of the brightness. Further, the ejection speed of the ink I is increased to reduce the deviation of the landing position and reduce the deviation of the hue. Alternatively, the ejection timing of the ink I can be advanced to reduce the deviation of the landing position and reduce the deviation of the hue, or the ejection speed of the ink I can be increased and the ejection timing of the ink I can be advanced to reduce the deviation of the landing position and reduce the deviation of the hue.

[0074] In addition, the same applies when it is determined that the cause of the color difference ΔE is caused by both the distance between the nozzle 31 and the printing surface Fw0 and the shape of the printing surface Fw0. That is, the ejection amount of the ink I used for printing the portion corresponding to the pixel Px is increased to reduce the brightness and reduce the deviation of the brightness. Further, the ejection speed of the ink I is increased to reduce the deviation of the landing position and reduce the deviation of the hue. Alternatively, the ejection timing of the ink I can be advanced to reduce the deviation of the landing position and reduce the deviation of the hue, or the ejection speed of the ink I can be increased and the ejection timing of the ink I can be advanced to reduce the deviation of the landing position and reduce the deviation of the hue.

[0075] On the other hand, when it is determined that the cause of the color difference ΔE is caused by the gradient of the printing surface Fw0, for example, the ejection amount of the ink I used for printing the portion corresponding to the pixel Px is increased to reduce the brightness and reduce the deviation of the brightness.

[0076] By performing such correction on all the pixels located on the trial printing image P0, the correction of the control of each nozzle 31 is completed, and the control of each nozzle 31 in the formal printing step S4 is determined.

[0077] In addition, the method for correcting the driving conditions of the print head 3 is not particularly limited. For example, it is also possible to determine the control of each nozzle 31 in the official printing step S4 without determining the cause of the color difference ΔE. In addition, when the shape of the surface Fw to be printed is constant along the printing track Q and the relative positional relationship between each nozzle 31 and the surface Fw to be printed remains constant during printing, it is also possible to arbitrarily extract one pixel for each scan line, and based on the color difference ΔE in this pixel, correct all the pixels included in the same scan line together. Specifically, in the present embodiment, each nozzle column 310 includes seven nozzles 31 arranged orthogonally to the printing track Q, so seven scan lines are formed on the surface Fw to be printed. Therefore, for each scan line, at least one pixel is arbitrarily extracted from the multiple pixels arranged on the scan line and the color difference ΔE is calculated, and based on the calculated color difference ΔE, all the pixels arranged on the same scan line are corrected together. This is because it can be presumed that the color difference ΔE is generated for the same reason in all the pixels located on the same scan line. According to such a method, the number of pixels for calculating the color difference ΔE can be significantly reduced, and accordingly, the time taken for the control determination step S3 can be shortened.

[0078] In addition, in the present embodiment, as the proof printing image P0, a sample image printed in the official printing is used, but the proof printing image P0 may not be a sample image. For example, as the proof printing image P0, an image for proof printing set in advance may also be printed, and based on the result, the color difference ΔE generated in the sample image printed by the official printing is estimated, and the control of each nozzle 31 in the official printing step S4 is determined.

[0079] Official printing step S4

[0080] In the official printing step S4, based on the driving conditions of the print head 3 determined in the control determination step S3, official printing on the object W is performed. That is, while the control device 9 moves the print head 3 relative to the object W along the printing track Q, ink I is ejected from each nozzle 31 based on the control of each nozzle 31 determined in the control determination step S3. Thereby, the printed image is printed on the surface Fw to be printed. In addition, during this printing operation, the control device 9 detects the vibration of the print head 3 based on the output of the inertial sensor 6, and controls the drive of the moving stage 4 to eliminate the detected vibration. Specifically, the drive of the moving stage 4 is controlled to apply a vibration to the print head 3 with a phase opposite to the detected vibration. Thereby, the vibration of the print head 3 during the printing operation can be suppressed, and higher-quality printing can be performed.

[0081] According to the above printing method, since the color difference ΔE between the actual printed image printed on the object W and the sample image is sufficiently suppressed, high printing quality can be achieved.

[0082] The above describes the robot system 1. As described above, the printing method performed by such a robot system 1 uses a robot 10 having a print head 3 with a nozzle 31 that ejects ink I. By relatively moving the object W and the print head 3 along a print track Q while ejecting ink I from the nozzle 31, a printing operation on the object W is performed. The printing method includes: a trial printing step S1, in which trial printing on a trial printing object W0 having the same shape as the object W is performed by relatively moving the trial printing object W0 and the print head 3 along the print track Q while ejecting ink I from the nozzle 31; a measurement step S2, in which a trial printing image P0 formed by the trial printing is measured by a spectroscopic camera 5; a control determination step S3, in which the control of the nozzle 31 is determined based on the result of the measurement step S2; and an official printing step S4, in which printing on the object W is performed by relatively moving the object W and the print head 3 along the print track Q while ejecting ink I from the nozzle 31 based on the control determined in the control determination step S3. According to such a printing method, a printed image with a color difference ΔE from the sample image sufficiently suppressed is obtained. Therefore, high printing quality can be achieved.

[0083] In addition, as described above, in the measurement step S2, the color of the trial printing image P0 is measured for each pixel of the spectroscopic camera 5. Thus, in the control determination step S3, the control of the nozzle 31 can be determined with higher accuracy.

[0084] In addition, as described above, in the control determination step S3, as the control of the nozzle 31, the ejection amount of the ink I ejected from the nozzle 31 is determined. Thus, the control of the nozzle 31 can be simply determined.

[0085] In addition, as described above, in the control determination step S3, the ejection amount of the ink I ejected from the nozzle 31 is determined for each pixel of the spectroscopic camera 5. Thus, high printing quality can be achieved.

[0086] In addition, as described above, in the control determination step S3, as the control of the nozzle 31, it is determined whether to eject or not eject the ink I from the nozzle 31. Thus, unreasonable color correction is not performed, and a decrease in printing quality can be suppressed.

[0087] In addition, as described above, in the control determination step S3, as the control of the nozzle 31, the ejection speed of the ink I is determined. Thus, the control of the nozzle 31 can be simply determined.

[0088] In addition, as described above, in the control determination step S3, as the control of the nozzle 31, the ejection timing of the ink I is determined. Thus, the control of the nozzle 31 can be simply determined.

[0089] In addition, as described above, in the measurement step S2, the white balance of the trial print image P0 is adjusted. Thereby, the color difference ΔE can be calculated with high precision without being affected by the imaging environment.

[0090] In addition, as described above, the ink I has ultraviolet curability. In the measurement step S2, light containing ultraviolet rays is used as illumination light, and the measurement using the spectroscopic camera 5 is performed. Thereby, the ink I can be cured while the spectroscopic camera 5 is measuring. Therefore, it is not necessary to dry the ink I before measuring with the spectroscopic camera 5, and the cycle time of the printing operation can be shortened.

[0091] In addition, as described above, the robot system 1 includes: a robot 10 having a print head 3 with a nozzle 31 for ejecting the ink I; a control device 9 for controlling the driving of the robot 10; and a spectroscopic camera 5. By relatively moving the object W and the print head 3 along the print track Q while ejecting the ink I from the nozzle 31, printing on the object W is performed. By relatively moving the trial-print object W0 having the same shape as the object W and the print head 3 along the print track Q while ejecting the ink I from the nozzle 31, trial printing on the trial-print object W0 is performed. The spectroscopic camera 5 measures the trial print image P0 formed by the trial printing, determines the control of the nozzle 31 based on the measurement result, and performs printing on the object W by ejecting the ink I from the nozzle 31 based on the determined control while relatively moving the object W and the print head 3 along the print track Q. According to such a printing method, a printed image with the color difference ΔE from the sample image sufficiently suppressed is obtained. Therefore, high printing quality can be achieved.

[0092] As described above, the printing method and the robot system of the present invention have been described with respect to the illustrated embodiments, but the present invention is not limited thereto. The structures and processes of each part can be replaced with any structures and processes having the same functions. In addition, any other constituent elements and processes can be added to the present invention. In addition, the embodiments can be appropriately combined.

Claims

1. A printing method, characterized in that: A robot having a print head having a nozzle for ejecting ink is used, and a printing operation is performed on the object by ejecting ink from the nozzle while the object and the print head are relatively moved along a printing track, The printing method comprises: a trial printing step of performing trial printing on the trial printing object by ejecting the ink from the nozzle while relatively moving the trial printing object having the same shape as the object and the print head along the printing track; a measuring step of measuring a test printing image formed by the test printing by a spectroscopic camera; a control determination step of determining control of the nozzle based on a result of the measuring step; and The main printing step performs printing on the object by ejecting the ink from the nozzle based on the control determined in the control determination step while relatively moving the object and the print head along the print track.

2. The printing method according to claim 1, wherein: In the measuring step, the color of the trial print image is measured for each pixel of the spectroscopic camera.

3. The printing method according to claim 1, wherein: In the control determination step, as control of the nozzle, an ejection amount of the ink ejected from the nozzle is determined.

4. The printing method according to claim 3, wherein: In the control determination step, the ejection amount is determined for each pixel of the spectroscopic camera.

5. The printing method according to claim 1, wherein: In the control determination step, as control of the nozzle, it is determined whether the ink is ejected or not ejected from the nozzle.

6. The printing method according to claim 1, wherein: In the control determination step, as control of the nozzle, an ejection speed of the ink is determined.

7. The printing method according to claim 1, wherein: In the control determination step, as control of the nozzle, the ejection timing of the ink is determined.

8. The printing method according to claim 1, wherein: In the measuring step, the white balance of the trial print image is adjusted.

9. The printing method according to claim 1, wherein: The ink is UV curable. In the measuring step, the measurement is performed by the spectroscopic camera using light containing ultraviolet rays as illumination light.

10. A robot system, characterized in that: have: A robot having a printing head having a nozzle for ejecting ink; A control device for controlling the driving of the robot; and Spectroscopic camera, The printing operation on the object is performed by ejecting the ink from the nozzle while the object and the print head are relatively moved along a printing track, wherein: The test printing is performed on the test printing object by ejecting the ink from the nozzle while the test printing object having the same shape as the object and the print head are relatively moved along the printing track, measuring a test printing image formed by the test printing by the spectroscopic camera, determining control of the nozzle based on the result of the determination, Printing on the object is performed by ejecting the ink from the nozzle based on the determined control while the object and the print head are relatively moved along the printing track.

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