Printing method and printing system

Abstract

The invention provides a printing method and a printing system capable of efficiently performing high-quality printing. A printing method uses a robot arm provided with a print head having a plurality of nozzles for discharging ink, the printing method relatively moves an object and the print head along a print path using the robot arm, and discharges the ink from each of the nozzles at a predetermined timing. In a printing method in which a plurality of nozzles are arranged to print a print pattern on an object by applying an ink jet voltage to the print head to eject the ink from the nozzles, the ink jet voltage is varied in accordance with an inclination of a nozzle surface with respect to a horizontal plane, the nozzle surface having the plurality of nozzles arranged therein.

Description

Technical Field

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

[0002] The robot for painting a vehicle body described in Patent Document 1 includes a robotic arm, a moving device that reciprocates the robotic arm in one direction along the floor surface of a painting booth, and a painting head mounted at the end of the robotic arm. Further, the robotic arm has a first rotating arm on the base end side and a second rotating arm on the end side. And, in the robot for painting a vehicle body, in order to stabilize the supply of ink to the painting head, while keeping the second rotating arm horizontal, ink is ejected from the painting head, thereby performing painting on the vehicle body.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2023-145056

[0004] However, when the painting head is inclined with respect to the horizontal, a height difference is generated between the multiple nozzles formed in the painting head, and the ink ejection speed of the nozzle located more on the upper side in the vertical direction is more likely to decrease. When the ink ejection speed decreases, the ink reaches the terminal velocity before landing on the vehicle body, and the landing position on the vehicle body deviates greatly from the ideal landing position, or it becomes difficult to land on the vehicle body due to atomization during flight. As a result, the printing quality deteriorates. Summary of the Invention

[0005] The printing method of the present invention uses a robotic arm equipped with a printing head, wherein the printing head has multiple nozzles for ejecting ink, and the printing method uses the robotic arm to relatively move an object and the printing head along a printing track, and ejects the ink from each of the nozzles at a predetermined timing, thereby printing a printed pattern on the object.

[0006] The printing head is configured to eject the ink from the nozzle by being applied with an inkjet voltage.

[0007] In the printing method, the inkjet voltage is changed according to the inclination of the nozzle surface on which multiple nozzles are arranged with respect to the horizontal plane.

[0008] The printing system of the present invention includes: a robotic arm equipped with a printing head, the printing head having multiple nozzles for ejecting ink; and

[0009] a control device that controls the driving of the robotic arm.

[0010] The printing system relatively moves an object and the printing head along a printing track, and ejects the ink from each of the nozzles at a predetermined timing, thereby printing a printed pattern on the object.

[0011] The print head is configured to eject the ink from the nozzles by applying an inkjet voltage.

[0012] The control device varies the inkjet voltage according to the inclination of the nozzle surface on which a plurality of the nozzles are arranged with respect to the horizontal plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is an overall view of the printing system according to the first embodiment.

[0014] Figure 2 is a view showing Figure 1 a top view of the moving table and the print head included in the shown robot.

[0015] Figure 3 is an exploded perspective view showing the print head.

[0016] Figure 4 is a perspective sectional view showing the print head.

[0017] Figure 5 is a view showing the circuit structure of the print head.

[0018] Figure 6 is a view showing the print head in a horizontal state.

[0019] Figure 7 is a view showing the print head in an inclined state.

[0020] Figure 8 is a flowchart showing the printing method.

[0021] Figure 9 is a view showing an example of the printing track.

[0022] Figure 10 is a view showing a table for determining the relationship between the inclination of the print head and the inkjet voltage.

[0023] Figure 11 is a view showing the circuit structure of the print head included in the printing system according to the second embodiment.

[0024] Figure 12 is a view showing the structure of the distal end portion of the robot included in the printing system according to the third embodiment.

[0025] Figure 13 is a view for explaining a method of detecting the ejection speed of ink I.

[0026] Figure 14 is a view showing the print head of the printing system according to the fourth embodiment.

[0027] Figure 15It is a diagram showing a table for determining the relationship between the inclination of the print head and the inkjet voltage.

[0028] Explanation of Reference Numerals

[0029] 1: Printing system; 2: Robot; 3: Robot main body; 31: Base; 32: Robot arm; 321: Arm; 322: Arm; 323: Arm; 324: Arm; 325: Arm; 326: Arm; 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: Print head; 5B: Print head; 5C: Print head; 5M: Print head; 5Y: Print head; 51: Nozzle plate; 52: Pressure chamber forming substrate; 53: Vibration plate; 54: Sealing part; 561: Reservoir; 562: Ink chamber; 563: Nozzle; 564: Piezoelectric vibration element; 565: Switch element; 566: Power supply circuit; 6: Inertial sensor; 7: Inkjet speed detection unit; 71: Camera; 72: Image processing unit; 8: Control device; A: First direction; B: Second direction; D: Separation distance; Fn: Nozzle surface; I: Ink; J1: Joint; J2: Joint; J3: Joint; J4: Joint; J5: Joint; J6: Joint; Q: Printing track; Q1: Printing track; Q2: Printing track; S1: Drive condition determination step; S2: Printing step; T: Table; Vi: Inkjet voltage; W: Object; θ: Inclination. Detailed Description of the Invention

[0030] Hereinafter, the printing method and printing system of the present invention will be described in detail based on the embodiments shown in the drawings.

[0031] First Embodiment

[0032] Figure 1 It is an overall view of the printing system according to the first embodiment. Figure 2 It shows Figure 1 A top view of the moving stage and the print head provided in the shown robot. Figure 3 It is an exploded perspective view showing the print head. Figure 4 It is a three-dimensional cross-sectional view showing the print head. Figure 5 It is a diagram showing the circuit structure of the print head. Figure 6 It is a diagram showing the print head in a horizontal state. Figure 7 It is a diagram showing the print head in an inclined state. Figure 8 It is a flowchart showing the printing method. Figure 9 It is a diagram showing an example of the printing track. Figure 10 It is a diagram showing a table for determining the relationship between the inclination of the print head and the inkjet voltage.

[0033] Figure 1The printing system 1 shown has a robot 2 that prints on an object W and a control device 8 that controls the driving of the robot 2. In addition, the robot 2 has: a robot body 3 having a robotic arm 32, a moving worktable 4 disposed at the end of the robotic arm 32, a printing head 5 disposed on the moving worktable 4, and an inertial sensor 6 disposed on the printing head 5 and serving as a vibration meter. In such a printing system 1, the robotic arm 32 is used to move the printing head 5 along a printing track Q, and ink I is ejected from the printing head 5 at a predetermined timing, thereby performing a printing operation on the object W.

[0034] It should be noted that in the printing system 1 of the present embodiment, the object W is fixed, and the object W and the printing head 5 are relatively moved by only moving the printing head 5. However, this is not limited thereto, and the object W and the printing head 5 may also be relatively moved by moving the printing head 5 and the object W together.

[0035] Robot body 3

[0036] As Figure 1 shown, the robot body 3 is a six-axis vertical articulated robot having six drive axes, and has: a base 31 fixed to a mounting table, a floor, etc.; and a robotic arm 32 rotatably connected to the base 31. In addition, the robotic arm 32 is structured such that six arms 321, 322, 323, 324, 325, 326 are sequentially rotatably connected from the base 31 side, and includes six joints J1, J2, J3, J4, J5, J6. Specifically, the arm 321 is rotatably connected to the base 31 via the joint J1. The arm 322 is rotatably connected to the arm 321 via the joint J2. The arm 323 is rotatably connected to the arm 322 via the joint J3. The arm 324 is rotatably connected to the arm 323 via the joint J4. The arm 325 is rotatably connected to the arm 324 via the joint J5. The arm 326 is rotatably connected to the arm 325 via the joint J6.

[0037] In addition, among the joints J1 to J6, the joints J2, J3, J5 are respectively bending joints, and the joints J1, J4, J6 are respectively twisting joints. Although not shown, drive mechanisms are provided at the respective joints J1, J2, J3, J4, J5, J6. The drive mechanism includes a motor, a speed reducer that decelerates the rotation of the motor to increase torque and output it, and an encoder that detects the rotation amount of the joint. And by independently moving the respective joints J1, J2, J3, J4, J5, J6, the printing head 5 disposed at the end of the robotic arm 32 can be moved in a desired direction at a desired attitude and speed.

[0038] However, the structure of the robot main body 3 is not particularly limited. For example, the number of arms provided by the robotic arm 32 is not limited to six. In addition, the robot main body 3 can also be a dual-arm robot, a horizontal multi-joint robot (SCARA robot), etc. In addition, the robot main body 3 may not be fixed to a mounting table, the floor, etc., and can be an object that can move by itself.

[0039] Moving worktable 4

[0040] As Figure 1 shown, the moving worktable 4 is arranged at the end of the robotic arm 32, that is, the arm 326. The moving worktable 4 is used for the position correction of the print head 5. As Figure 2 shown, the moving worktable 4 has: a base 40, which is supported by the arm 326; a first worktable 41, which linearly moves relative to the base 40 in a first direction A; and a second worktable 42, which linearly moves relative to the first worktable 41 in a second direction B orthogonal to the first direction A. And the print head 5 is arranged on the second worktable 42.

[0041] In addition, the moving worktable 4 has: a first worktable drive unit 45, which moves the first worktable 41 relative to the base 40 along the first direction A; and a second worktable drive unit 46, which moves the second worktable 42 relative to the first worktable 41 along the second direction B. The first worktable drive unit 45 and the second worktable drive unit 46 respectively include piezoelectric actuators 400 that are driven by the expansion and contraction of piezoelectric vibration elements caused by energization. By transmitting the vibration of the piezoelectric actuator 400 to the first worktable 41 and the second worktable 42, they are moved. In this way, by using the piezoelectric actuator 400, the movement amount and movement speed of the first worktable 41 and the second worktable 42 can be finely and accurately controlled, and the switching of the movement direction also becomes sensitive. In addition, miniaturization and weight reduction of the moving worktable 4 can also be achieved. Therefore, the position correction of the print head 5 can be performed with higher precision.

[0042] Among them, the structure of the moving worktable 4 is not particularly limited. For example, the first worktable drive unit 45 and the second worktable drive unit 46 can also be structures that use drive sources other than the piezoelectric actuator 400, such as motors that rotate by energization. In addition, the moving worktable 4 can also have a third worktable that linearly moves in a direction orthogonal to the first direction A and the second direction B, and a fourth worktable that rotates and moves around an axis orthogonal to the first direction A and the second direction B. In addition, the moving worktable 4 can also be omitted. In this case, the print head 5 is installed on the arm 326, and the position correction of the print head 5 can be performed by the robotic arm 32.

[0043] Print head 5

[0044] As Figure 2As shown, the print head 5 is disposed on the second worktable 42. The print head 5 is not particularly limited. In the present embodiment, it is an inkjet head of a piezoelectric drive type. As Figure 3 and Figure 4 shown, such a print head 5 has a structure in which a nozzle plate 51, a pressure chamber forming substrate 52, a vibration plate 53, and a sealing portion 54 are laminated, and has a reservoir 561 as a common ink chamber, a plurality of ink chambers 562 branched from the reservoir 561, and a plurality of nozzles 563 formed in each ink chamber 562. The plurality of ink chambers 562 are arranged in a line in a direction orthogonal to the printing track Q. In addition, piezoelectric vibration elements 564 are respectively disposed on the vibration plate 53 forming the top of each ink chamber 562. It should be noted that, as Figure 5 shown, hereinafter, for the sake of convenience of explanation, the surface on which a plurality of nozzles 563 are arranged is also referred to as the "nozzle surface Fn".

[0045] In the print head 5 having such a structure, ink I is supplied from the reservoir 561 to each ink chamber 562. And, an inkjet voltage Vi is applied to the piezoelectric vibration element 564 at a predetermined timing for each ink chamber 562, and by vibrating the piezoelectric vibration element 564, the ink I is ejected from the nozzle 563. Therefore, while moving the print head 5 along the printing track Q, the ink I is ejected from each nozzle 563 at a predetermined timing and made to land on the object W, thereby printing a predetermined printed image (a printing pattern described later) on the object W.

[0046] It should be noted that, as Figure 5 shown, each piezoelectric vibration element 564 is connected to a common power supply circuit 566 via a switching element 565 such as a thin film transistor (TFT). And, the power supply circuit 566 applies the inkjet voltage Vi to the piezoelectric vibration element 564 to which the switching element 565 has become on. Therefore, by switching the on / off of each switching element 565, the ink I can be ejected from a predetermined nozzle 563 at a predetermined timing.

[0047] Among them, the structure of the print head 5 is not particularly limited. For example, as in the fourth embodiment described later, it may also be a structure capable of performing multicolor printing by arranging and disposing a plurality of print heads 5 along the printing track Q. Specifically, for example, it may also be possible to perform full-color printing by arranging a print head 5 that ejects black ink I, a print head 5 that ejects cyan ink I, a print head 5 that ejects magenta ink I, and a print head 5 that ejects yellow ink I along the printing track Q. In addition, the print head 5 is not limited to the above-mentioned inkjet head of the piezoelectric drive type. For example, it may also be an inkjet head such as a thermal type using the film boiling phenomenon of the ink I, a bubble jet type that generates bubbles in the ink I by applying heat and ejects the ink I, and an electrostatic actuator type that ejects the ink I by displacing and vibrating the vibration plate by electrostatic force.

[0048] Inertial Sensor 6

[0049] like Figure 1 as well as Figure 2 As shown, the inertial sensor 6 is disposed on the printing head 5 to detect the vibration of the printing head 5. It should be noted that the "vibration" refers to unnecessary displacement of the printing head 5 other than the displacement along the printing track Q. The inertial sensor 6 is not particularly limited as long as it can detect vibration, and for example, a three-axis acceleration sensor that detects acceleration in three mutually orthogonal axial directions can be used.

[0050] Control device 8

[0051] like Figure 1 As shown, the control device 8 is electrically connected to the robot 2 to control the driving of the robot 2. Specifically, the control device 8 controls the driving of the robot body 3, the movable table 4, the printing head 5, and the inertial sensor 6 independently or in conjunction with each other. Such a control device 8 is composed of, for example, a computer, and has a processor (CPU) for processing information, a memory connected to the processor in a communicable manner, 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.

[0052] The configuration of the printing system 1 has been described above. Next, a method of printing on an object W using the printing system 1 will be described. Prior to this, problems of the conventional printing method will be described.

[0053] As described above, the print head 5 is a structure in which a plurality of ink chambers 562 are connected to a liquid reservoir 561. In such a structure, Figure 6 As shown in FIG. 1 , when the nozzle surface Fn is along a horizontal plane (hereinafter also referred to as a “horizontal state”), there is no height difference between the plurality of ink chambers 562, and the pressure (water pressure) of the ink I in each ink chamber 562 is equal to each other. Therefore, when the ink ejection voltage Vi is equal, the ejection speed of the ink I from each nozzle 563 is equal to each other. In addition, in this case, the pressure of the ink I in each ink chamber 562 is sufficiently high, and the ejection speed of the ink I from each nozzle 563 is also sufficiently high. Therefore, the ink I ejected from each nozzle 563 appropriately lands on the object W without reaching the terminal speed in the middle of the flight.

[0054] On the other hand, Figure 7As shown, when the nozzle surface Fn is inclined with respect to the horizontal plane (hereinafter also referred to as the "inclined state"), a height difference is generated among the plurality of ink chambers 562. Therefore, the higher the ink chamber 562 is located in the vertical direction, the higher the pressure (water pressure) of the ink I, and the lower the ink chamber 562 is located in the vertical direction, the lower the pressure (water pressure) of the ink I. Therefore, for example, when an inkjet voltage Vi of the same magnitude as in the horizontal state is applied to each piezoelectric vibration element 564, the ejection speed of the ink I ejected from the nozzle 563 of the ink chamber 562 located in the upper side in the vertical direction decreases. Consequently, the ink I reaches the terminal velocity before landing on the object W, the landing position of the object W deviates significantly from the ideal landing position, or the diameter of the dot formed by landing becomes larger, or atomization occurs during flight, making it difficult for the ink I to land on the object W itself. As a result, the printing quality deteriorates. The greater the inclination angle θ of the nozzle surface Fn with respect to the horizontal plane, that is, in other words, the greater the height difference among the plurality of ink chambers 562 (the difference between the uppermost ink chamber 562 and the lowermost ink chamber 562), the more significant this tendency becomes, and it is most significant when the inclination angle θ = 90°.

[0055] Therefore, in the printing system 1, in order to ensure that the ink I ejected from each nozzle 563, particularly the nozzle 563 located in the upper side in the vertical direction, lands on the object W with sufficient speed even in the inclined state without reaching the terminal velocity during flight, the ink ejection voltage Vi is changed according to the inclination angle θ of the nozzle surface Fn. Specifically, as the inclination angle θ of the nozzle surface Fn increases, the inkjet voltage Vi is increased. As the inkjet voltage Vi is increased, the piezoelectric vibration element 564 vibrates significantly, and the ejection speed of the ink I ejected from the nozzle 563 becomes faster. Therefore, it is possible to compensate for the decrease in the ejection speed caused by the decrease in the pressure of the ink I in the ink chamber 562 by increasing the ejection speed based on the increase in the inkjet voltage Vi. Therefore, it is possible to ensure that the ink I ejected from each nozzle 563, particularly the nozzle 563 located in the upper side in the vertical direction, lands on the object W without reaching the terminal velocity during flight. Therefore, the deviation of the landing position of the ink I, the enlargement of the dot diameter, and the non-landing are suppressed, and high printing quality can be achieved.

[0056] Next, the printing method based on the printing system 1 will be described in detail. As Figure 8 shown, the printing method based on the printing system 1 includes: a driving condition determination step S1 of determining driving conditions such as the printing track Q; and a printing step S2 of performing printing on the object W based on the driving conditions determined in the driving condition determination step S1.

[0057] Driving condition determination step S1

[0058] In the driving condition determination step S1, first, the control device 8 acquires the shape data of the object W. The shape data of the object W is acquired using the CAD (computer-aided design) data of the object W. Thereby, high-precision shape data can be acquired. Note that the method for acquiring the shape data of the object W is not limited thereto. For example, it may also be acquired from measurement data obtained by measuring the object W using a measuring device such as a 3D scanner.

[0059] Next, the control device 8 determines the printing track Q based on the acquired shape of the object W, the structure of the print head 5, and the printing pattern printed on the object W. For example, as Figure 9 shown, the printing track Q is determined. That is, in the printing step S2, in order to print the printing pattern on the object W, it is determined how to move the print head 5 relative to the object W. It should be noted that Figure 9 an example of the shown printing track Q includes: a printing track Q1 in which the inclination θ of the nozzle surface Fn is 90° and which is inclined with respect to the vertical direction; and a printing track Q2 in which the inclination θ of the nozzle surface Fn is 45° and which is inclined with respect to the vertical direction. In particular, the printing tracks Q1 and Q2 are horizontal respectively. Thereby, as described above, a pressure difference is generated in the plurality of ink chambers 562 in the print head 5, and it is easy to generate deviations in the landing positions of the ink I ejected from the nozzles 563 located on the upper side in the vertical direction, dot diameter expansion, non-landing, etc. Therefore, the advantages of the printing method of the present embodiment can be enjoyed more significantly.

[0060] Here, the printing pattern printed on the object W is not particularly limited, and a pattern is preferably used. The pattern includes, for example, in addition to patterns, pictures, photos, characters, marks, etc., and refers to patterns other than patterns that are completely filled. In this way, by printing a pattern as the printing pattern, the reduction in printing quality due to deviations in the landing positions of the ink I, dot diameter expansion, non-landing, etc. is significantly shown. Therefore, the effects of the printing method of the present embodiment can be enjoyed more significantly.

[0061] Next, the control device 8 determines the moving speed of the print head 5 along the printing track Q. The control device 8 also determines the timing of ejecting the ink I from each nozzle 563 based on the determined printing track Q and the printing pattern printed on the object W. In other words, for each nozzle 563, the control device 8 determines the ejection / non-ejection of the ink I for each ink jet control cycle. Through the above, the printing track Q and the driving conditions of the print head 5 are determined, and the driving condition determination step S1 is ended.

[0062] Printing step S2

[0063] In the printing step S2, first, the control device 8 positions the print head 5 at the starting point of the printing track Q1 based on the driving conditions determined in the driving condition determination step S1. Next, in a state where the print head 5 is located at the starting point of the printing track Q1, the control device 8 detects the inclination θ of the nozzle surface Fn based on the posture of the robotic arm 32 calculated from the outputs of the encoders provided in the respective joints J1, J2, J3, J4, J5, and J6. In this way, based on the posture of the robotic arm 32, the inclination θ can be easily and highly accurately detected. Next, the control device 8 determines the inkjet voltage Vi applied to each piezoelectric vibration element 564 during the printing operation along the printing track Q1 based on the detected inclination θ. Specifically, as the inclination θ of the nozzle surface Fn increases, the control device 8 increases the inkjet voltage Vi to increase the ejection speed of each ink I so that regardless of the inclination θ, the ink I ejected from all the nozzles 563 lands on the object W without reaching the terminal velocity during flight. Thereby, it is possible to effectively suppress the deviation of the landing position, the diameter expansion of the dots, and the non-landing of the ink I ejected from the nozzles 563 located on the upper side in the vertical direction, particularly during the printing operation along the printing track Q1.

[0064] In the present embodiment, a table T showing the relationship between the inclination θ and the inkjet voltage Vi as shown in Figure 10 is pre-stored in the control device 8, and the control device 8 determines the inkjet voltage Vi in four levels based on the table T. According to such a method, the inkjet voltage Vi can be easily determined. It should be noted that the table T can be generated, for example, through prior experiments, simulations, etc. Among them, as a method for determining the inkjet voltage Vi, there is no particular limitation. For example, the inkjet voltage Vi can be adjusted in three levels, or can be adjusted in multiple levels of five levels or more. In addition, a function showing the relationship between the inclination θ and the inkjet voltage Vi can be pre-generated, and by substituting the inclination θ into this function, the inkjet voltage Vi can be substantially determined without levels. According to the table T, during the printing operation along the printing track Q1, the inclination θ = 90°, so the inkjet voltage Vi = 36V. Here, in the print head 5 of the present embodiment, as shown in Figure 5 it is configured to apply the inkjet voltage Vi from a common power supply circuit 566 to each piezoelectric vibration element 564. Therefore, it is impossible to change the inkjet voltage Vi for each piezoelectric vibration element 564 at the same time, and the inkjet voltage Vi of 36V is applied to all the piezoelectric vibration elements 564.

[0065] Next, the control device 8 moves the print head 5 along the print track Q1 at a predetermined speed, applies the previously determined inkjet voltage Vi to a predetermined piezoelectric vibration element 564 at a predetermined timing, and ejects the ink I from the corresponding nozzle 563. Thus, the printing operation along the print track Q1 ends. Here, as in the present embodiment, it is preferable that the inclination θ is constant during the printing operation along the print track Q1 as one scan. Thus, if the inkjet voltage Vi is determined at the start of the printing operation along the print track Q1, the inkjet voltage Vi can be made constant during the printing operation along the print track Q1. Therefore, the control of the print head 5 becomes simple.

[0066] After the printing along the print track Q1 ends, the control device 8 positions the print head 5 at the start point of the print track Q2. Next, in a state where the print head 5 is located at the start point of the print track Q2, the control device 8 detects the inclination θ of the nozzle surface Fn based on the posture of the robotic arm 32 calculated from the outputs of the encoders provided in the respective joints J1, J2, J3, J4, J5, J6. Next, the control device 8 determines the inkjet voltage Vi applied to each piezoelectric vibration element 564 during the printing operation along the print track Q2 based on the detected inclination θ. The determination method is the same as when printing along the print track Q1.

[0067] Next, the control device 8 moves the print head 5 along the print track Q2 at a predetermined speed, applies the previously determined inkjet voltage Vi to a predetermined piezoelectric vibration element 564 at a predetermined timing, and ejects the ink I from the corresponding nozzle 563. Through the above, the printing of the printed pattern on the object W ends. In this way, by changing the inkjet voltage Vi according to the inclination θ of the nozzle surface Fn, it is possible to effectively suppress deviations in the landing position of the ink I ejected from the nozzle 563 located on the upper side in the vertical direction, dot diameter expansion, non-landing, etc. during the printing operation along the print track Q. Therefore, high printing quality can be achieved. In particular, in the present embodiment, the inclination θ is different when printing along the print track Q1 and when printing along the print track Q2, and accordingly, the inkjet voltage Vi is also different. In this way, by adopting a structure that can change the inkjet voltage Vi during the printing operation, the degree of freedom of the printing operation increases.

[0068] It should be noted that during the printing operations along the print tracks Q1 and Q2, the control device 8 also detects the vibration of the print head 5 based on the output of the inertial sensor 6 and controls the drive of the moving worktable 4 to eliminate the detected vibration. Specifically, the drive of the moving worktable 4 is controlled to apply a vibration to the print head 5 that is in a phase opposite to the detected vibration. Thus, the vibration of the print head 5 in the printing step S2 is suppressed, and higher-quality printing can be performed.

[0069] As described above, the printing method using the printing system 1 has been explained, but the printing method is not particularly limited. For example, the inkjet voltage Vi may also be determined in the driving condition determination step S1. In this case, the control device 8 may determine the inkjet voltage Vi based on the inclination θ of the print head 5 included in the print tracks Q1 and Q2, where the print tracks Q1 and Q2 are determined in the driving condition determination step S1. That is, in the present embodiment, the measured value of the inclination θ is used to determine the inkjet voltage Vi, but the set value of the inclination θ may also be used to determine the inkjet voltage Vi.

[0070] As described above, the printing system 1 of the present embodiment has been explained. The printing method using such a printing system 1 is as described above: using a robotic arm 32 equipped with a print head 5, where the print head 5 has a plurality of nozzles 563 for ejecting ink I. This printing method uses the robotic arm 32 to relatively move the object W and the print head 5 along the print track Q, and ejects ink I from each nozzle 563 at a predetermined timing, thereby printing a printed pattern on the object W. The print head 5 is configured to eject ink I from the nozzle 563 by being applied with an inkjet voltage Vi. In the said printing method, the inkjet voltage Vi is changed according to the inclination θ of the nozzle surface Fn on which a plurality of nozzles 563 are arranged with respect to the horizontal plane. According to such a method, it is possible to effectively suppress the deviation of the landing position of the ink I ejected from the nozzle 563 located on the upper side in the vertical direction, the diameter expansion of the dots, non-landing, etc. during the printing operation along the print track Q. Therefore, high printing quality can be achieved.

[0071] In addition, as described above, in the printing method using the printing system 1, as the inclination θ becomes larger, the inkjet voltage Vi is increased. According to such a method, it is possible to more reliably and effectively suppress the deviation of the landing position of the ink I ejected from the nozzle 563 located on the upper side in the vertical direction, the diameter expansion of the dots, non-landing, etc. during the printing operation along the print track Q.

[0072] In addition, as described above, in the printing method using the printing system 1, the printed pattern is a pattern. In this way, by printing a pattern as the printed pattern, the reduction in printing quality due to the deviation of the landing position of the ink I, the diameter expansion of the dots, non-landing, etc. is significantly shown, so that the effect based on the printing method can be more significantly enjoyed.

[0073] In addition, as described above, in the printing method using the printing system 1, the inkjet voltage Vi is determined based on the table T for determining the relationship between the inkjet voltage Vi and the inclination θ. According to such a method, the inkjet voltage Vi can be easily determined.

[0074] In addition, as described above, in the printing method using the printing system 1, the inclination θ is detected based on the attitude of the robotic arm 32. According to such a method, the inclination θ can be easily detected.

[0075] In addition, as described above, in the printing method using the printing system 1, the printing track Q is inclined with respect to the vertical direction. Therefore, a pressure difference of the ink I is generated between the plurality of ink chambers 562 in the print head 5, resulting in a reduction in printing quality due to deviations in the landing position, dot diameter expansion, non-landing, etc. Therefore, by inclining the printing track Q with respect to the vertical direction, the effects based on the printing method can be more significantly enjoyed.

[0076] In addition, as described above, in the printing method using the printing system 1, the inkjet voltage Vi is changed during the printing operation. According to such a method, the degree of freedom of the printing operation is increased.

[0077] In addition, as described above, in the printing method using the printing system 1, the print head 5 includes: a plurality of ink chambers 562 in which respective nozzles 563 are formed; a reservoir 561 connected to each of the ink chambers 562; and a plurality of piezoelectric vibration elements 564 that vibrate the wall surfaces of the respective ink chambers 562, and by applying the inkjet voltage Vi to each of the piezoelectric vibration elements 564, the ink I is ejected from each of the nozzles 563. By using the print head 5 having such a structure, problems such as deviations in the landing position of the ink I, dot diameter expansion, non-landing, etc. are likely to occur. Therefore, the effects based on the printing method can be more significantly enjoyed.

[0078] In addition, as described above, the printing system 1 includes: a robotic arm 32 having a print head 5 with a plurality of nozzles 563 for ejecting the ink I; and a control device 8 that controls the drive of the robotic arm 32. The printing system relatively moves the object W and the print head 5 along the printing track Q, and ejects the ink I from each of the nozzles 563 at a predetermined timing, thereby printing a printing pattern on the object W. The print head 5 is configured to eject the ink I from the nozzles 563 by being applied with the inkjet voltage Vi, and the control device 8 changes the inkjet voltage Vi according to the inclination θ of the nozzle surface Fn on which the plurality of nozzles 563 are arranged with respect to the horizontal plane. According to such a structure, it is possible to effectively suppress deviations in the landing position of the ink I ejected from the nozzles 563 located particularly on the upper side in the vertical direction, dot diameter expansion, non-landing, etc. during the printing operation along the printing track Q. Therefore, high printing quality can be achieved.

[0079] Second Embodiment

[0080] Figure 11 It is a diagram showing the circuit structure of the print head included in the printing system according to the second embodiment.

[0081] Except that the structure of the print head 5 and the method of changing the inkjet voltage Vi are different, this embodiment is the same as the foregoing first embodiment. It should be noted that in the following description, regarding this embodiment, the differences from the foregoing first embodiment will be mainly described, and the same matters will be omitted. In addition, in the drawings of this embodiment, the same reference numerals are assigned to the same structures as those in the foregoing embodiment.

[0082] As Figure 5 shown, in the foregoing first embodiment, the inkjet voltage Vi is applied to each piezoelectric vibration element 564 from a common power supply circuit 566. Therefore, in terms of its structure, it is impossible to change the inkjet voltage Vi for each piezoelectric vibration element 564, but the inkjet voltage Vi for all the piezoelectric vibration elements 564 is changed together. In such a structure, regarding the nozzle 563 located on the upper side in the vertical direction, although the ejection speed of the ink I can be increased to suppress the deviation of the landing position, non-landing, etc., regarding the nozzle 563 located on the lower side in the vertical direction, there is a concern that the ejection speed of the ink I is too high.

[0083] In contrast, in the print head 5 of this embodiment, a dedicated power supply circuit 566 is connected to each piezoelectric vibration element 564, and the inkjet voltage Vi can be independently changed for each piezoelectric vibration element 564. Therefore, the ejection speed of the ink I from each nozzle 563 can be independently changed. According to such a structure, for example, for the nozzle 563 located on the upper side in the vertical direction, the ejection speed of the ink I is increased by increasing the inkjet voltage Vi to suppress the deviation of the landing position, the diameter expansion of the dots, non-landing, etc., and for the nozzle 563 located on the lower side in the vertical direction, the ejection speed of the ink I can be prevented from rising excessively by reducing the inkjet voltage Vi. That is, by reducing the difference in the ejection speed of the ink I from each nozzle 563, preferably by making it equal, the ejection speed of the ink I from each nozzle 563 can be easily made to fall within the allowable speed range. Therefore, higher-quality printing can be performed.

[0084] As described above, in the printing method of this embodiment, the inkjet voltage Vi is changed for each piezoelectric vibration element 564. According to such a method, the difference in the ejection speed of the ink I from each nozzle 563 can be reduced, preferably made equal, and the ejection speed of the ink I from each nozzle 563 can be easily made to fall within the allowable speed range. Therefore, higher-quality printing can be performed.

[0085] According to such a second embodiment, the same effects as those of the foregoing first embodiment can also be achieved.

[0086] Third Embodiment

[0087] Figure 12This is a diagram showing the structure of the end part of the robot included in the printing system according to the third embodiment. Figure 13 This is a diagram for explaining a method of detecting the ejection speed of Ink I.

[0088] The printing system of the present embodiment is the same as the printing system of the first embodiment described above, except that it includes an inkjet speed detection unit 7 for detecting the ejection speed of Ink I. It should be noted that in the following description, regarding the present embodiment, the description will focus on the differences from the above-described embodiment, and the description of the same matters will be omitted. In addition, in the diagrams of the present embodiment, the same reference numerals are assigned to the same structures as those in the above-described embodiment.

[0089] As Figure 12 shown, the printing system 1 of the present embodiment includes an inkjet speed detection unit 7 for detecting the ejection speed of Ink I from each nozzle 563. In addition, the inkjet speed detection unit 7 includes: a camera 71 fixed to the moving worktable 4 together with the print head 5; and an image processing unit 72 for processing the image captured by the camera 71. When the print head 5 is moved along the printing track Q, the camera 71 is located immediately behind the print head 5 and captures Ink I landing on the object W. The image processing unit 72 detects the ejection speed of Ink I ejected from the print head 5 based on the image captured by the camera 71. Specifically, as Figure 13 shown, the image processing unit 72 detects the separation distance D between a pair of adjacent Inks I(n) and I(n + 1) along the printing track Q from the image obtained by the camera 71, and based on the detected separation distance D, the moving speed of the print head 5, the ejection timing of Inks I(n) and I(n + 1), that is, the ejection time difference, and the distance between the nozzle 563 and the object W, detects the ejection speed of Ink I from each nozzle 563. It should be noted that in the driving condition determination step S1, parameters other than the separation distance D are determined as the driving conditions. According to such a method, the inkjet speed can be simply detected.

[0090] Among them, as the structure of the inkjet speed detection unit 7, it is sufficient to be able to detect the ejection speed of at least one Ink I from the nozzle 563, and there is no particular limitation.

[0091] Further, the control device 8 changes the inkjet voltage Vi based on the ejection speed of the ink I detected by the image processing unit 72. That is, the inkjet voltage Vi determined based on the table T is corrected. Specifically, when the ejection speed of the ink I from at least one of the nozzles 563 exceeds the allowable speed, the inkjet voltage Vi is reduced by a predetermined value so that the ejection speed of all the ink I from the nozzles 563 falls within the allowable speed. On the contrary, when the ejection speed of the ink I from at least one of the nozzles 563 is less than the allowable speed, the inkjet voltage Vi is increased by a predetermined value so that the ejection speed of all the ink I from the nozzles 563 falls within the allowable speed. With such a configuration, the inkjet voltage Vi can be appropriately changed in combination with the actual ejection state of the ink I, and thus higher-quality printing can be performed.

[0092] As described above, in the printing method of the present embodiment, the inkjet voltage Vi is changed based on the ejection speed of the ink I from the nozzle 563. With such a method, the inkjet voltage Vi can be appropriately changed in combination with the actual ejection state of the ink I, and thus higher-quality printing can be performed.

[0093] According to such a third embodiment, the same effects as those of the foregoing first embodiment can also be achieved.

[0094] Fourth Embodiment

[0095] Figure 14 FIG. is a diagram showing a print head of a printing system according to the fourth embodiment. Figure 15 FIG. is a diagram showing a table for determining the relationship between the inclination of the print head and the inkjet voltage.

[0096] Except for the different structure of the print head 5, the printing system of the present embodiment is the same as the printing system of the foregoing first embodiment. It should be noted that in the following description, regarding the present embodiment, the description will focus on the differences from the foregoing embodiments, and the description of the same matters will be omitted. In addition, in the drawings of the present embodiment, the same reference numerals are assigned to the same structures as those in the foregoing embodiments.

[0097] As Figure 14 shown, the print head 5 of the present embodiment has a print head 5B for ejecting black ink I, a print head 5C for ejecting cyan ink I, a print head 5M for ejecting magenta ink I, and a print head 5Y for ejecting yellow ink I, which are arranged along the printing track Q. It should be noted that the structures of the respective print heads 5B, 5C, 5M, and 5Y are the same as those of the print head 5 in the foregoing first embodiment.

[0098] In addition, as Figure 14As shown, during the printing operation, the printing track Q is in the vertical direction. In this case, in each of the print heads 5B, 5C, 5M, and 5Y, since the multiple ink chambers 562 are arranged in the horizontal direction, there is no difference in the ejection speed of the ink I from each nozzle 563. However, since the atmospheric pressure of the print head located on the lower side in the vertical direction is higher, the deviation of the landing position is likely to become larger. That is, if the inkjet voltage Vi is set to the same value among the print heads 5B, 5C, 5M, and 5Y, when the ink I ejected from the print head 5 located on the lower side in the vertical direction lands on the object W, there is a concern that a deviation in the landing position, an enlargement of the dot, or non-landing may occur. Therefore, in the present embodiment, as shown in the table T of Figure 15 shown, for each inclination angle θ, the inkjet voltage Vi of each print head 5B, 5C, 5M, and 5Y is determined such that the inkjet voltage Vi of the print head 5 located on the lower side in the vertical direction is larger. Thereby, high printing quality can be achieved.

[0099] As described above, in the printing method of the present embodiment, the printing track Q is in the vertical direction. Therefore, a difference occurs in the ejection speed of the ink I among the multiple print heads arranged along the printing track Q, and a decrease in printing quality due to a deviation in the landing position, an enlargement of the dot, non-landing, etc. of the ink I ejected from the print head located on the lower side in the vertical direction is exhibited. Therefore, by the printing track Q being in the vertical direction, the effects based on the printing method can be more significantly enjoyed.

[0100] According to such a fourth embodiment, the same effects as those of the foregoing first embodiment can also be achieved.

[0101] As described above, the printing method and printing system of the present invention have been described based on the illustrated embodiments, but the present invention is not limited thereto, and the structures and processes of each part can be replaced with any structures and processes having the same functions. In addition, any other structures 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, the printing method uses a robotic arm equipped with a print head, wherein the print head has a plurality of nozzles for ejecting ink, the printing method uses the robotic arm to relatively move an object and the print head along a printing track, and ejects the ink from each of the nozzles at a predetermined timing, thereby printing a printed pattern on the object, the print head is configured to eject the ink from the nozzle by applying an inkjet voltage, in the printing method, the inkjet voltage is varied according to the inclination of a nozzle surface on which a plurality of the nozzles are arranged with respect to the horizontal plane.

2. The printing method according to claim 1, characterized in that, as the inclination becomes larger, the inkjet voltage is increased.

3. The printing method according to claim 1, characterized in that, the printed pattern is a pattern.

4. The printing method according to claim 1, characterized in that, the inkjet voltage is determined based on a table for determining the relationship between the inkjet voltage and the inclination.

5. The printing method according to claim 1, characterized in that, the inclination is detected based on the posture of the robotic arm.

6. The printing method according to claim 1, characterized in that, the inkjet voltage is changed based on the ejection speed of the ink from the nozzle.

7. The printing method according to claim 1, characterized in that, the printing track is inclined with respect to the vertical direction.

8. The printing method according to claim 1, characterized in that, the printing track is along the vertical direction.

9. The printing method according to claim 1, characterized in that, the inkjet voltage is changed during the printing operation.

10. The printing method according to claim 1, characterized in that, the print head has: a plurality of ink chambers in which each of the nozzles is formed; a reservoir connected to each of the ink chambers; and a plurality of piezoelectric vibration elements for vibrating the wall surface of each of the ink chambers, in the printing method, the ink is ejected from each of the nozzles by applying the inkjet voltage to each of the piezoelectric vibration elements.

11. The printing method according to claim 10, characterized in that, the inkjet voltage is changed for each of the piezoelectric vibration elements.

12. A printing system, characterized in that, Comprising: a robotic arm equipped with a print head having a plurality of nozzles for ejecting ink; and a control device for controlling the drive of the robotic arm, the printing system relatively moves an object and the print head along a printing track, and ejects the ink from each of the nozzles at a predetermined timing, thereby printing a printed pattern on the object, the print head is configured to eject the ink from the nozzle by applying an inkjet voltage, the control device changes the inkjet voltage according to the inclination of a nozzle surface on which a plurality of the nozzles are arranged with respect to the horizontal plane.

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