Printing method and robot system

Abstract

To provide a printing method and a robot system that can perform printing with high quality.SOLUTION: The printing method includes: a trial printing step of performing trial printing on a trial-printing target by discharging ink from a nozzle while moving the trial-printing target and a printing head relatively to each other, the trial-printing target shape having a shape same as that of a target; ; a measuring step of measuring, by using a spectroscopic camera, a color of a trial-printed image formed by the trial-printing; a control determining step of determining control of the nozzle on the basis of a measured result in the measuring step; and a final-printing step of performing printing on the target by discharging the ink from the nozzle on the basis of a control determined in the control determining step, while moving the target and the printing head relatively to each other along a printing track.SELECTED DRAWING: Figure 5

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 body having an arm, and a nozzle head unit attached to the tip of the arm. Then, while moving the nozzle head unit relative to an object using the robot body, ink is ejected from the nozzle head unit toward the object to perform printing on the object. Further, the nozzle head unit is provided with a plurality of nozzles arranged in a predetermined direction. Here, if the separation distance between the nozzle and the object is large, there is a risk that the printed image may be displaced, distorted, or warped, resulting in a decrease in print quality. Therefore, in Patent Document 1, for nozzles with a separation distance from the object of a predetermined value or more, ink is not ejected to control the printing width per scan, and an attempt is made to suppress a decrease in print quality.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the painting robot of Patent Document 1, even if the separation distance between the nozzle and the object is small, the print quality may deteriorate depending on the shape and gradient of the object.

Means for Solving the Problems

[0005] The printing method of the present invention uses a robot equipped with a print head having nozzles for discharging ink, and performs a printing operation on the object by discharging the ink from the nozzles while relatively moving the object and the print head along a printing track. A trial printing step of performing a trial printing on the trial printing object having the same shape as the object by discharging the ink from the nozzles while relatively moving the trial printing object having the same shape as the object and the print head along the printing track. A measurement step of measuring the trial printing image formed by the trial printing with a spectroscopic camera. A control determination step of determining the control of the nozzles based on the result of the measurement step. A main printing step of performing printing on the object by discharging the ink from the nozzles based on the control determined in the control determination step while relatively moving the object and the print head along the printing track.

[0006] The robot system of the present invention includes a robot equipped with a print head having nozzles for discharging ink, A control device for controlling the driving of the robot, And a spectroscopic camera. A robot system that performs a printing operation on an object by discharging the ink from the nozzles while relatively moving the object and the print head along a printing track. Performs a trial printing on the trial printing object having the same shape as the object by discharging the ink from the nozzles while relatively moving the trial printing object having the same shape as the object and the print head along the printing track. Measures the trial printing image formed by the trial printing with the spectroscopic camera. Determines the control of the nozzles based on the result of the measurement. Performs printing on the object by discharging the ink from the nozzles based on the determined control while relatively moving the object and the print head along the printing track.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the printing method and robot system of the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

[0009] FIG. 1 is an overall view of a robot system according to a preferred embodiment. FIG. 2 is a plan view showing a moving stage and a print head provided in the robot shown in FIG. 1. FIGS. 3 and 4 are diagrams for explaining problems that occur when printing on an object having a sloped shape, respectively. FIG. 5 is a flowchart showing a printing process. FIG. 6 is a schematic diagram showing a state in which Lab values are calculated for each pixel of a spectroscopic camera. FIG. 7 is a diagram showing a state in which the spectroscopic camera is covered with a shade.

[0010] The robot system 1 shown in Fig. 1 is applied to a printing system that performs a printing operation on an object W. The robot system 1 includes a robot 10 that performs printing on the object W, a control device 9 that controls the driving of the robot 10, and a spectroscopic camera 5 that measures the object W. Further, the robot 10 includes a robot body 2 having a robot arm 22, a moving stage 4 disposed at the tip 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.

[0011] In such a robot system 1, while moving the printing head 3 relative to the object W using the robot arm 22, the printing operation on the object W is performed by discharging ink I from the printing head 3 at a predetermined timing.

[0012] Note that in the robot system 1 of the present embodiment, the object W is fixed and only the printing head 3 is moved to relatively move the object W and the printing head 3. However, the present invention is not limited to this, and the object W and the printing head 3 may be relatively moved by moving both the printing head 3 and the object W.

[0013] ≪Robot Body 2≫ As shown in Fig. 1, the robot body 2 is a six-axis vertical articulated robot having six drive axes, and includes a base 21 fixed to a mounting table, a floor, etc., and a robot arm 22 rotatably connected to the base 21.

[0014] The robot arm 22 is configured such that six arms 221, 222, 223, 224, 225, and 226 are rotatably connected in this order from the base 21 side, and is provided with 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.

[0015] Among the joints J1 to J6, the joints J2, J3, and J5 are bending joints, respectively, and the joints J1, J4, and J6 are torsion joints, respectively. Although not shown, a drive mechanism including a motor, a speed reducer that decelerates the rotation of the motor to increase torque and outputs it, and an encoder that detects the amount of rotation of the joint is installed at each of the joints J1, J2, J3, J4, J5, and J6. By moving each of the joints J1, J2, J3, J4, J5, and J6 independently, the robot arm 22 can be moved in a desired direction at a desired posture and speed.

[0016] However, the configuration of the robot body 2 is not particularly limited. For example, the number of arms provided in the robot arm 22 is not limited to six. Also, the robot body 2 may be a dual-arm robot, a horizontal multi-joint robot (scalar robot), or the like. Further, the robot body 2 may not be fixed to a mounting table, the floor, etc., and may be capable of self-propelling.

[0017] ≪Moving stage 4≫ As shown in FIG. 1, the moving stage 4 is disposed at the tip of the robot arm 22, that is, on the arm 226. The moving stage 4 is used for position correction of the printing head 3. As shown in FIG. 2, the moving stage 4 includes a base 40 supported by the arm 226, a first stage 41 that linearly moves in a first direction A with respect to the base 40, and a second stage 42 that linearly moves in a second direction B orthogonal to the first direction A with respect to the first stage 41. The printing head 3 is disposed on the second stage 42.

[0018] Further, the moving stage 4 includes a first stage driving unit 45 that moves the first stage 41 along the first direction A with respect to the base 40, and a second stage driving unit 46 that moves the second stage 42 along the second direction B with respect to the first stage 41. The first and second stage driving units 45 and 46 each include a piezoelectric actuator 400 that is driven by utilizing the expansion and contraction of a piezoelectric element by energization, and the vibration of the piezoelectric actuator 400 is transmitted to the first and second stages 41 and 42 to move them. In this way, by using the piezoelectric actuator 400, the moving amounts and moving speeds of the first and second stages 41 and 42 can be controlled finely and with high precision, and the switching of the moving direction can also be made sensitive. In addition, the size and weight of the moving stage 4 can be reduced. Therefore, the position correction of the printing head 3 can be performed more accurately.

[0019] However, the configuration of the moving stage 4 is not particularly limited. For example, the first and second stage driving units 45 and 46 may have a configuration using a driving source other than the piezoelectric actuator 400, such as a motor that rotates by energization. Further, the moving stage 4 may further include a third stage that linearly moves in a direction orthogonal to the first direction A and the second direction B, or a fourth stage that rotates around an axis orthogonal to the first direction A and the second direction B. Also, the moving stage 4 may be omitted. In this case, the position correction of the printing head 3 may be performed by the robot arm 22.

[0020] ≪Printing Head 3≫ As shown in FIG. 2, the print head 3 is disposed on the second stage 42. Although not particularly limited, in this embodiment, an inkjet head using a piezo drive method is used as the print head 3. The piezo drive type inkjet, although not shown, has an ink chamber, a diaphragm constituting a part of the wall surface of the ink chamber, a piezo element for vibrating the diaphragm, and a nozzle 31 connected to the ink chamber. In such a configuration, when a voltage is applied to the piezo element to vibrate the piezo element, the diaphragm vibrates and the ink I in the ink chamber is ejected from the nozzle 31.

[0021] Also, as shown in FIG. 2, on the front end surface of the print head 3, four nozzle rows 310 are formed along the print track Q, each having a plurality of nozzles 31 arranged at equal intervals along a direction orthogonal to the print track Q. From each nozzle 31 of the nozzle row 310a, black ink I is ejected, from each nozzle 31 of the nozzle row 310b, cyan ink I is ejected, from each nozzle 31 of the nozzle row 310c, magenta ink I is ejected, and from each nozzle 31 of the nozzle row 310d, yellow ink I is ejected. According to such a print head 3, full-color printing becomes possible.

[0022] Then, while moving the print head 3 along the print track Q, ink I is ejected from each nozzle 31 at a predetermined timing and landed on the object W, whereby a predetermined printed image is printed on the object W. Thus, by having a plurality of nozzles 31 arranged in a direction orthogonal to the print track Q, the printing range per scan of the print head 3 is widened, and the printing operation can be performed efficiently.

[0023] However, the configuration 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 configuration capable of single-color printing. Further, the configuration of the print head 3 is not limited to the above-described piezo-driven inkjet head. For example, it may be an inkjet head such as a thermal method using the film boiling phenomenon of the ink I, a bubble ejection method that generates bubbles in the ink I by applying heat to eject the ink I, or an electrostatic actuator method that displaces and vibrates a diaphragm by electrostatic force to eject the ink I.

[0024] ≪Inertial sensor 6≫ As shown in FIGS. 1 and 2, the inertial sensor 6 is disposed on the print head 3 and detects the vibration of the print head 3. Note that the “vibration” means unnecessary displacement other than the displacement along the print track Q of the print head 3. The inertial sensor 6 is not particularly limited as long as it can detect vibration. For example, a three-axis acceleration sensor that detects accelerations in three mutually orthogonal directions can be used.

[0025] ≪Control device 9≫ As shown in FIG. 1, the control device 9 is electrically connected to the robot 10 and controls the drive of the robot 10. Specifically, the control device 9 controls the drives of the robot body 2, the print 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 includes a processor (CPU) that processes information, a memory communicably connected to the processor, and an external interface that connects to an external device. Various programs executable by the processor are stored in the memory, and the processor can read and execute the programs stored in the memory.

[0026] The configuration of the robot system 1 has been described above. Next, a method of printing on the object W using the robot system 1 will be described. Before that, based on FIGS. 3 and 4, the conventional problems will be described. In the example shown in FIG. 3, the printed surface Fw of the object W has a non-planar shape, that is, a shape with a gradient, and includes a top surface Fw1 along the horizontal direction, a side surface Fw2 along the vertical direction, and a round surface Fw3 located between them and curved in an arc shape. Also, in the illustrated example, the printing track Q is set linearly toward the back side of the paper surface. Then, while moving the print head 3 along the printing track Q using the robot 10, the ink I is ejected from each nozzle 31 at a predetermined timing and landed on a predetermined location on the printed surface Fw, so that a predetermined printed image is printed on the printed surface Fw.

[0027] Here, since the printed surface Fw is non-planar, the distances from the plurality of nozzles 31 to the printed surface Fw are different. In the illustrated example, the distance between the nozzle 31 located at the center of the print head 3 and the printed surface Fw is the shortest, and the distance between the nozzle 31 and the printed surface Fw gradually increases as it deviates from the center to both sides. Then, as shown in FIG. 4, as the distance between the nozzle 31 and the printed surface Fw, that is, the flight distance of the ink I increases, the ink I spreads during flight and the landing area becomes larger. Also, since the ink I is ejected while moving the print head 3, as the flight distance of the ink I increases, the landing position of the ink I shifts to the front side of the printing track Q. Also, apart from the distance, depending on the inclination of the landing location, after landing, the ink I spreads due to its own weight, resulting in an increase in the landing area. In particular, in the illustrated example, the ink I landed on the side surface Fw2 along the vertical direction easily spreads due to its own weight. Thus, when the landing area of the ink I increases 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 corresponding part increases. Also, the hue changes due to the shift of the landing position of the ink I. Therefore, the color reproducibility with respect to the sample image (the image to be printed) is poor, leading to a deterioration in print quality.

[0028] In order to suppress such a deterioration in print quality, in the robot system 1, before printing a sample image on the object W (hereinafter also referred to as "this printing"), a trial printing of the sample image is performed on a trial 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 nozzles 31 in this printing.

[0029] That is, in the robot system 1, first, a trial printing object W0 is prepared, and a trial printing of the sample image is performed on the trial printing object W0. Next, the color of the printed image printed by the trial printing is measured by the spectral camera 5. Next, based on the measurement result by the spectral camera 5, a color difference ΔE between the sample image and the printed image (hereinafter also referred to as "actual printed image") actually printed on the trial printing object W0 is detected. Next, the control of each nozzle 31 including the discharge timing of the ink I, the discharge speed of the ink I, the discharge amount of the ink I, etc. is determined so that the detected color difference ΔE becomes small, preferably so that the color difference ΔE becomes zero. Then, by discharging the ink I from each nozzle 31 based on the determined control, this printing on the object W is performed. According to such a method, excellent color reproducibility can be exhibited, and the actual printed image can be made close to, preferably identical to, the sample image. Therefore, high print quality can be exhibited. Hereinafter, the printing method by the robot system 1 will be described in detail.

[0030] As shown in FIG. 5, the printing method by the robot system 1 includes a trial printing step S1 of performing trial printing, a measurement step S2 of measuring the trial printed image P0 printed by the trial printing step S1 with the spectral camera 5, a control determination step S3 of determining the control of the print head 3 based on the result of the measurement step S2, and a main printing step S4 of performing printing based on the control determined in the control determination step S3. Hereinafter, each step S1 to S4 will be described in order.

[0031] ≪Trial Printing Step S1≫ In the trial printing step S1, first, a printing trajectory Q is determined based on the shape of the printing surface Fw of the object W and the sample image to be printed on the printing surface Fw of the object W in this printing step S4. That is, in order to print the sample image on the printing surface Fw, it is determined how to move the print head 3 relative to the object W. Regarding the shape of the printing 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 printing surface Fw can be acquired with high accuracy, and the printing trajectory Q can be further optimized.

[0032] Next, based on the printing trajectory Q and the sample image, the control of each nozzle 31 is determined. Specifically, mainly, the timing of discharging the ink I from each nozzle 31, the discharge speed of the ink I, and the discharge amount of the ink I are determined. At this time, for the nozzles 31 whose distance from the printing surface Fw exceeds a predetermined value, the setting may be such that the ink I is not discharged. Thereby, it is possible to effectively suppress a decrease in print quality due to displacement, warping, distortion, etc. of the printed image caused by excessive displacement of the landing position. When determining the control of each nozzle 31, in addition to the printing trajectory Q and the sample image, for example, the background color of the printing surface Fw may be considered.

[0033] Next, a trial printing object W0 for trial printing is prepared. The trial printing object W0 has at least a printing surface Fw0 having the same shape as the printing surface Fw of the object W. Note that the “same shape” includes not only the case where the shapes completely match, but also the case where there is an error to such an extent that they can be regarded as the same shape from a common technical sense. Furthermore, for the trial printing object W0, elements that affect the print quality, such as the constituent material of the printing surface Fw0 and the texture of the surface, are the same as those of the object W. Thereby, the trial printing can be performed under conditions closer to the actual printing, and the color reproducibility of the actual printed image can be accurately measured in the next measurement step S2. In particular, in this embodiment, the surplus object W is used as the trial printing object W0. Thereby, if individual differences are not considered, the object W and the trial printing object W0 completely match, and the trial printing can be performed under the same conditions as the actual printing.

[0034] Next, while moving the print head 3 along the print track Q with respect to the object W0 for trial printing, the control device 9 discharges the ink I from each nozzle 31 based on the control determined as described above. As a result, a trial print image P0 as an actual printed image is printed on the print surface Fw0. Further, during the 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 driving of the moving stage 4 so that the detected vibration is canceled. Specifically, the driving of the moving stage 4 is controlled so that a vibration having a reverse phase with respect to the detected vibration is applied to the print head 3. Thereby, the vibration of the print head 3 during the printing operation is suppressed, and higher-quality printing becomes possible.

[0035] ≪Measurement step S2≫ In the measurement step S2, after the trial print image P0 is sufficiently dried, the color of the trial print image P0 is measured with the spectral camera 5. Specifically, while irradiating the object W0 for trial printing with illumination light, the trial print image P0 is imaged with the spectral camera 5. According to the spectral camera 5, since a spectral spectrum can be acquired for each pixel of the spectral camera 5, the color difference ΔE from the sample image can be detected for each part of the trial print image P0. In particular, the spectral camera 5 of the present embodiment can acquire spectral data for 16 wavelengths in the visible light region (400 nm to 700 nm). Therefore, the color gamut that the spectral camera 5 can represent and the number of colors that can be represented are larger than those of an RGB camera, and subtle color differences that are difficult to detect with an RGB camera can be detected. Therefore, the color difference ΔE between the trial print image P0 and the sample image can be detected with higher accuracy.

[0036] Next, the image acquired by the spectral camera 5 is analyzed to extract the trial print image P0. Next, the color of the trial print image P0 is measured for each pixel of the spectral camera 5. Then, as shown in FIG. 6, the Lab value of the color, that is, the coordinates in the Lab color space, is acquired for each pixel. In the Lab color space, L represents lightness (brightness), and a and b represent hue. In this way, by acquiring the Lab value of the color, the color of each pixel can be quantitatively acquired.

[0037] In this embodiment, before acquiring the Lab values, the white balance (color temperature) of the test print image P0 is adjusted. As a result, the Lab values of the colors of each pixel can be accurately acquired without being affected by the imaging environment. The method for adjusting the white balance is not particularly limited. For example, before imaging the test print image P0 with the spectral camera 5, the spectral camera 5 may image a black-and-white adjustment board that serves as a white balance reference, and adjust the white balance based on the result. Alternatively, the adjustment board and the test print image P0 may be arranged side by side, and the spectral camera 5 may image the adjustment board and the test print image P0 simultaneously, and the white balance of the test print image P0 shown in the imaged image may be adjusted based on the color of the adjustment board shown in the imaged image.

[0038] Also, for example, as shown in FIG. 7, when imaging, the test print object W0 is covered with a shade Sh to block external light, and further, the test print object W0 is illuminated with the illumination L arranged inside the shade Sh, and the imaging environment is kept constant, thereby preparing an environment in which the white balance is adjusted.

[0039] Also, for example, when using an ultraviolet curable ink as the ink I, when imaging the test print image P0 with the spectral camera 5, the test print image P0 may be irradiated with illumination light including ultraviolet rays. As a result, the measurement by the spectral camera 5 can be performed while drying the test print image P0. Therefore, the measurement step S2 can be started earlier, and the cycle time of the printing operation can be shortened.

[0040] ≪Control determination step S3≫ The control determination step S3 determines the control of the print head 3 based on the result of the measurement step S2. Specifically, first, for each pixel of the spectroscopic camera 5, the color difference ΔE between the test print image P0 and the sample image is detected. Then, based on the detected color difference ΔE, the control of each nozzle 31 determined in the test print step S1 is corrected so that the color difference ΔE becomes smaller, preferably, so that the color difference ΔE becomes zero, and the control of each nozzle 31 for the next main print step S4 is determined. In the present embodiment, as the control of each nozzle 31, at least one of the discharge amount of the ink I discharged from the nozzle 31, the discharge speed of the ink I discharged from the nozzle 31, and the timing of discharging the 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 easily reduced accordingly.

[0041] Note that since the method of correcting the driving conditions of the print head 3 is the same for each pixel, hereinafter, for the sake of convenience of explanation, one pixel Px will be representatively described, and the description of other pixels will be omitted. For example, when the Lab value (L, a, b) of the test print image P0 in the pixel Px is (L0, a0, b0) and the Lab value (L, a, b) at the same location in the sample image is (Lr, ar, br), first, these color differences ΔE are calculated. Note that the following formula (1) can be used to calculate the color difference ΔE.

[0042]

Equation

[0043] 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 within a preset allowable range by correcting the control of each nozzle 31. Then, based on the determination result, it is decided whether to eject the ink I to that location or not. Specifically, if it is determined that the color difference ΔE can be reduced to within the allowable range, the ink I is ejected to that location. Conversely, if it is determined that the color difference ΔE cannot be reduced to within the allowable range, the ink I is not ejected to that location. That is, this part is printed as a blank in this printing step S4. Thereby, unreasonable color correction to the location corresponding to the pixel Px is not performed, and instead, a decrease in print quality such as an increase in the color difference ΔE can be suppressed.

[0044] If it is determined that the color difference ΔE can be reduced to within the allowable range, next, the cause of the color difference ΔE is identified. That is, it is determined whether the cause of the color difference ΔE is due to the distance between the nozzle 31 and the printing surface Fw0 (the flying distance of the ink I), due to the gradient (slope) of the printing surface Fw0, or both. Then, based on the determination result, the control of each nozzle 31 set in the test printing step S1 is corrected.

[0045] Specifically, if it is determined that the cause of the color difference ΔE is due to the distance between the nozzle 31 and the printing surface Fw0, for example, the ejection amount of the ink I for printing the location corresponding to the pixel Px is increased to lower the lightness and reduce the lightness deviation. 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 may 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 may be increased and the ejection timing of the ink I may be advanced to reduce the deviation of the landing position and reduce the deviation of the hue.

[0046] Similarly, the same applies when it is determined that the cause of the color difference ΔE is due to both the distance between the nozzle 31 and the surface to be printed Fw0 and the shape of the surface to be printed Fw0. That is, the ejection amount of the ink I for printing the portion corresponding to the pixel Px is increased to lower 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 may 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 may be increased and the ejection timing of the ink I may be advanced to reduce the deviation of the landing position and reduce the deviation of the hue.

[0047] On the other hand, when it is determined that the cause of the color difference ΔE is due to the gradient of the surface to be printed Fw0, for example, the ejection amount of the ink I for printing the portion corresponding to the pixel Px is increased to lower the brightness and reduce the deviation of the brightness.

[0048] By performing such correction for all the pixels on the test print image P0, the correction of the control of each nozzle 31 is completed, and the control of each nozzle 31 in the main printing step S4 is determined.

[0049] Note that the method for correcting the driving conditions of the print head 3 is not particularly limited. For example, without specifying the cause of the color difference ΔE, the control of each nozzle 31 in this printing step S4 may be determined. Further, 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 is kept constant during printing, at least one pixel may be arbitrarily extracted for each scanning line, and all the pixels included in the same scanning line may be corrected collectively based on the color difference ΔE at the said pixel. Specifically, in the present embodiment, since each nozzle row 310 includes seven nozzles 31 arranged orthogonally to the printing track Q, seven scanning lines are formed on the surface Fw to be printed. Therefore, for each scanning line, at least one pixel is arbitrarily extracted from a plurality of pixels arranged on the scanning line to calculate the color difference ΔE, and all the pixels arranged on the same scanning line are corrected collectively based on the calculated color difference ΔE. This is because it can be estimated that the color difference ΔE is caused by the same reason for all the pixels located on the same scanning line. According to such a method, the number of pixels for calculating the color difference ΔE is significantly reduced, and accordingly, the time required for the control determination step S3 can be shortened.

[0050] Also, in the present embodiment, the sample image printed in this printing is used as the trial print image P0, but the trial print image P0 may not be a sample image. For example, as the trial print image P0, a preset image for trial printing may be printed, and based on the result, the color difference ΔE generated in the sample image printed by this printing may be estimated, and the control of each nozzle 31 in this printing step S4 may be determined.

[0051] ≪This printing step S4≫ In this printing step S4, printing on the object W is performed based on the driving conditions of the print head 3 determined in the control determination step S3. That is, the control device 9 moves the print head 3 along the printing track Q with respect to the object W, and discharges the ink I from each nozzle 31 based on the control of each nozzle 31 determined in the control determination step S3. Thereby, a printed image is printed on the printing surface Fw. Further, during the 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 driving of the moving stage 4 so that the detected vibration is canceled. Specifically, the driving of the moving stage 4 is controlled so that vibration of the opposite phase to the detected vibration is applied to the print head 3. Thereby, the vibration of the print head 3 during the printing operation is suppressed, and higher-quality printing becomes possible.

[0052] According to the printing method as described above, 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 exhibited.

[0053] The above describes the robot system 1. As described above, the printing method performed by such a robot system 1 uses a robot 10 equipped with a printing head 3 having nozzles 31 for discharging ink I, and discharges ink I from the nozzles 31 while relatively moving the object W and the printing head 3 along the printing track Q to perform a printing operation on the object W. Along the printing track Q, a trial printing step S1 of performing a trial printing on the trial printing object W0 having the same shape as the object W by discharging ink I from the nozzles 31 while relatively moving the trial printing object W0 and the printing head 3, a measurement step S2 of measuring the trial printing image P0 formed by the trial printing with the spectroscopic camera 5, a control determination step S3 of determining the control of the nozzles 31 based on the result of the measurement step S2, and a main printing step S4 of performing printing on the object W by discharging ink I from the nozzles 31 based on the control determined in the control determination step S3 while relatively moving the object W and the printing head 3 along the printing track Q. According to such a printing method, a printing image with a sufficiently suppressed color difference ΔE from the sample image can be obtained. Therefore, high printing quality can be exhibited.

[0054] Also, 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. Thereby, in the control determination step S3, the control of the nozzles 31 can be determined more accurately.

[0055] Also, as described above, in the control determination step S3, as the control of the nozzles 31, the discharge amount of the ink I discharged from the nozzles 31 is determined. Thereby, the control of the nozzles 31 can be easily determined.

[0056] Also, as described above, in the control determination step S3, the discharge amount of the ink I discharged from the nozzles 31 is determined for each pixel of the spectroscopic camera 5. Thereby, high printing quality can be exhibited.

[0057] Also, as described above, in the control determination step S3, as control of the nozzle 31, it is determined whether to eject the ink I from the nozzle 31 or not. Thereby, forced color correction is not performed, and a decrease in print quality can be suppressed.

[0058] Also, as described above, in the control determination step S3, as control of the nozzle 31, the ejection speed of the ink I is determined. Thereby, the control of the nozzle 31 can be easily determined.

[0059] Also, as described above, in the control determination step S3, as control of the nozzle 31, the ejection timing of the ink I is determined. Thereby, the control of the nozzle 31 can be easily determined.

[0060] Also, as described above, in the measurement step S2, the white balance of the test print image P0 is adjusted. Thereby, the color difference ΔE can be accurately calculated without being affected by the imaging environment.

[0061] Also, as described above, the ink I has ultraviolet curability, and in the measurement step S2, measurement by the spectroscopic camera 5 is performed using light including ultraviolet light as illumination light. Thereby, since the ink I can be cured simultaneously with the measurement by the spectroscopic camera 5, it is not necessary to dry the ink I before measurement by the spectroscopic camera 5, and the cycle time of the printing operation can be shortened.

[0062] Also, as described above, the robot system 1 includes a robot 10 having a print head 3 with a nozzle 31 for discharging ink I, a control device 9 for controlling the drive of the robot 10, and a spectroscopic camera 5. The robot system 1 performs a printing operation on the object W by discharging the ink I from the nozzle 31 while relatively moving the object W and the print head 3 along the print track Q. Along the print track Q, a trial print is performed on the trial print object W0 having the same shape as the object W by discharging the ink I from the nozzle 31 while relatively moving the trial print object W0 and the print head 3. The trial print image P0 formed by the trial print is measured by the spectroscopic camera 5, the control of the nozzle 31 is determined based on the measurement result, and the ink I is discharged 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 to perform printing on the object W. According to such a printing method, a printed image with a sufficiently suppressed color difference ΔE from the sample image can be obtained. Therefore, high printing quality can be exhibited.

[0063] As described above, the printing method and the robot system of the present invention have been described with respect to the illustrated embodiments. However, the present invention is not limited thereto, and the configuration and process of each part can be replaced with any configuration and process having the same function. Further, any other arbitrary components and processes may be added to the present invention. Also, the embodiments may be appropriately combined.

Description of Reference Numerals

[0064] 1…Robot system, 10…Robot, 2…Robot 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…Spectroscopic camera, 6…Inertial sensor, 9…Control device, A…First direction, B…Second direction, Fw…Printing surface, Fw0…Printing surface, Fw1…Upper surface, Fw2…Side surface, Fw3…Round surface, I…Ink, J1…Joint, J2…Joint, J3…Joint, J4…Joint, J5…Joint, J6…Joint, L…Illumination, P0…Test print image, Px…Pixel, Q…Printing track, S1…Test print step, S2…Measurement step, S3…Control decision step, S4…Main printing step, Sh…Shade, W…Object, W0…Object for test printing

Claims

1. A printing method for performing a printing operation on an object by discharging ink from a nozzle while relatively moving the object and the printing head along a printing track using a robot equipped with a printing head having a nozzle for discharging ink, a trial printing step of performing a trial printing on a trial printing object having the same shape as the object by discharging the ink from the nozzle while relatively moving the trial printing object and the printing head along the printing track, a measurement step of measuring a trial printing image formed by the trial printing with a spectroscopic camera, a control determination step of determining control of the nozzle based on the result of the measurement step, and a main printing step of performing printing on the object by discharging the ink from the nozzle based on the control determined in the control determination step while relatively moving the object and the printing head along the printing track. The printing method is characterized by including these steps.

2. The printing method according to claim 1, wherein in the measurement step, the color of the trial printing 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, the discharge amount of the ink discharged from the nozzle is determined.

4. The printing method according to claim 3, wherein in the control determination step, the discharge 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 to discharge the ink from the nozzle or not.

6. The printing method according to claim 1, wherein in the control determination step, as control of the nozzle, the discharge 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 discharge timing of the ink is determined.

8. The printing method according to claim 1, wherein in the measurement step, the white balance of the trial printing image is adjusted.

9. The ink has ultraviolet curability, and the printing method according to claim 1, wherein in the measurement step, measurement by the spectroscopic camera is performed using light including ultraviolet light as illumination light.

10. a robot equipped with a printing head having a nozzle for discharging ink, a control device for controlling the driving of the robot, and a spectroscopic camera. A robot system that performs a printing operation on an object by discharging the ink from the nozzles while relatively moving the object and the printing head along a printing track. A trial printing is performed on the trial printing object having the same shape as the object by discharging the ink from the nozzles while relatively moving the trial printing object having the same shape as the object and the printing head along the printing track. The trial printing image formed by the trial printing is measured by the spectroscopic camera. Based on the result of the measurement, the control of the nozzles is determined. A robot system characterized in that printing on the object is performed by discharging the ink from the nozzles based on the determined control while relatively moving the object and the printing head along the printing track.

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