Printing method and printing system

Abstract

To provide a printing method and a printing system that can efficiently perform high-quality printing.SOLUTION: A printing method uses a robot arm comprising a print head having a plurality of nozzles for discharging an ink, and prints a printing pattern on an object by discharging the ink from each nozzle at prescribed timing while moving the object and the print head relatively along a printing trajectory. The print head is so configured as to discharge the ink in such a manner that an ink discharge voltage is applied thereto, and changes the ink discharge voltage according to inclination of nozzle surfaces of the plurality of arranged nozzles with respect to a horizontal plane.SELECTED DRAWING: Figure 10

Description

Technical Field

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

Background Art

[0002] The robot for vehicle body painting described in Patent Document 1 includes a robot arm, a moving device that reciprocates the robot arm in one direction along the floor surface of the painting chamber, and a painting head attached to the tip of the robot arm. The robot arm has a first rotating arm on the base end side and a second rotating arm on the tip end side. In the robot for vehicle body painting, in order to stabilize the supply of ink to the painting head, while keeping the second rotating arm horizontal, ink is discharged from the painting head to paint the vehicle body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the painting head is inclined with respect to the horizontal, a height difference occurs between a plurality of nozzles formed in the painting head, and the ink discharge speed is more likely to decrease for the nozzles located on the upper side in the vertical direction. When the ink discharge speed decreases, the ink reaches the terminal speed before landing on the vehicle body, and the landing position on the vehicle body deviates greatly from the ideal landing position, or the ink becomes mist during flight, making it difficult to land on the vehicle body itself. As a result, the printing quality deteriorates.

Means for Solving the Problems

[0005] The printing method of the present invention uses a robotic arm equipped with a print head having a plurality of nozzles for ejecting ink, and while relatively moving an object and the print head along a printing trajectory, ejects the ink from each of the nozzles at a predetermined timing to print a printing pattern on the object. The print head is configured to eject the ink from the nozzles when an ink ejection voltage is applied. The ink ejection voltage is changed according to the inclination of the nozzle surface on which the plurality of nozzles are arranged with respect to the horizontal plane.

[0006] The printing system of the present invention includes a robotic arm equipped with a print head having a plurality of nozzles for ejecting ink, and a control device for controlling the driving of the robotic arm. It is a printing system that prints a printing pattern on an object by relatively moving the object and the print head along a printing trajectory and ejecting the ink from each of the nozzles at a predetermined timing. The print head is configured to eject the ink from the nozzles when an ink ejection voltage is applied. The control device changes the ink ejection voltage according to the inclination of the nozzle surface on which the plurality of nozzles are arranged with respect to the horizontal plane.

Brief Description of the Drawings

[0007]

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Embodiments for Carrying Out the Invention

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

[0009] <First Embodiment> FIG. 1 is an overall view of a printing system according to the first embodiment. FIG. 2 is a plan view showing a moving stage and a printing head provided in the robot shown in FIG. 1. FIG. 3 is an exploded perspective view showing the printing head. FIG. 4 is a perspective sectional view showing the printing head. FIG. 5 is a diagram showing the circuit configuration of the printing head. FIG. 6 is a diagram showing the printing head in a horizontal state. FIG. 7 is a diagram showing the printing head in an inclined state. FIG. 8 is a flowchart showing a printing method. FIG. 9 is a diagram showing an example of a printing track. FIG. 10 is a diagram showing a table for determining the relationship between the inclination of the printing head and the ink ejection voltage.

[0010] The printing system 1 shown in Fig. 1 includes a robot 2 that performs printing on an object W, and a control device 8 that controls the driving of the robot 2. The robot 2 includes a robot body 3 having a robot arm 32, a moving stage 4 disposed at the tip of the robot arm 32, a printing head 5 disposed on the moving stage 4, and an inertial sensor 6 serving as a vibration meter disposed on the printing head 5. In such a printing system 1, the printing operation on the object W is performed by moving the printing head 5 along the printing track Q using the robot arm 32 and discharging ink I from the printing head 5 at a predetermined timing.

[0011] Note that in the printing system 1 of the present embodiment, the object W is fixed, and only the printing head 5 is moved to relatively move the object W and the printing head 5. However, the present invention is not limited to this, and the object W and the printing head 5 may be relatively moved by moving both the printing head 5 and the object W.

[0012] ≪Robot Body 3≫ As shown in Fig. 1, the robot body 3 is a six-axis vertical articulated robot having six drive axes, and includes a base 31 fixed to a mounting table, a floor, etc., and a robot arm 32 rotatably connected to the base 31. The robot arm 32 has a configuration in which six arms 321, 322, 323, 324, 325, and 326 are rotatably connected in this order from the base 31 side, and includes six joints J1, J2, J3, J4, J5, and 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.

[0013] Among the joints J1 to J6, joints J2, J3, and J5 are bending joints, respectively, and joints J1, J4, and J6 are torsion joints, respectively. Although not shown, each of the joints J1, J2, J3, J4, J5, and J6 is provided with a drive mechanism including a motor, a speed reducer that reduces the rotation of the motor to increase torque and outputs it, and an encoder that detects the amount of rotation of the joint. By moving each of the joints J1, J2, J3, J4, J5, and J6 independently, the print head 5 disposed at the tip of the robot arm 32 can be moved in a desired direction at a desired posture and speed.

[0014] However, the configuration of the robot body 3 is not particularly limited. For example, the number of arms provided in the robot arm 32 is not limited to six. Further, the robot body 3 may be a dual-arm robot, a horizontal multi-joint robot (scalar robot), or the like. Further, the robot body 3 may not be fixed to a mounting table, the floor, or the like, and may be capable of self-propelling.

[0015] ≪Moving stage 4≫ As shown in FIG. 1, the moving stage 4 is disposed at the tip of the robot arm 32, that is, on the arm 326. The moving stage 4 is used for position correction of the print head 5. As shown in FIG. 2, the moving stage 4 includes a base 40 supported by the arm 326, 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 print head 5 is disposed on the second stage 42.

[0016] 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 vibration element due to energization, and by transmitting the vibration of the piezoelectric actuator 400 to the first and second stages 41 and 42, these stages are moved. 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 also becomes sensitive. Also, miniaturization and weight reduction of the moving stage 4 can be achieved. Therefore, the position correction of the print head 5 can be performed more accurately.

[0017] 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 when energized. 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 print head 5 may be attached to the arm 326, and the position correction of the print head 5 may be performed by the robot arm 32.

[0018] ≪Print Head 5≫ As shown in FIG. 2, the print head 5 is disposed on the second stage 42. Although not particularly limited as the print head 5, in the present embodiment, it is an inkjet head of a piezo drive system. Such a print head 5 has a structure in which a nozzle plate 51, a pressure chamber forming substrate 52, a diaphragm 53, and a sealing portion 54 are laminated, and includes a reservoir 561 which is 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. Further, piezoelectric vibration elements 564 are respectively disposed on the diaphragm 53 forming the ceiling portion of each ink chamber 562. As shown in FIG. 5, hereinafter, for convenience of explanation, the surface on which the plurality of nozzles 563 are arranged is also referred to as a "nozzle surface Fn".

[0019] In the print head 5 having such a configuration, ink I is supplied from the reservoir 561 to each ink chamber 562. Then, an ink ejection voltage Vi is applied to the piezoelectric vibration element 564 at a predetermined timing for each ink chamber 562, and the piezoelectric vibration element 564 is vibrated to eject the ink I from the nozzle 563. Therefore, by moving the print head 5 along the printing track Q and ejecting the ink I from each nozzle 563 at a predetermined timing and landing it on the object W, a predetermined printed image (print pattern described later) is printed on the object W.

[0020] As shown in FIG. 5, each piezoelectric vibration element 564 is connected to a common power supply circuit 566 via a switch element 565 such as a thin film transistor (TFT). Then, the power supply circuit 566 applies an ink ejection voltage Vi to the piezoelectric vibration element 564 for which the switch element 565 is ON. Therefore, by switching the ON / OFF of each switch element 565, the ink I can be ejected from a predetermined nozzle 563 at a predetermined timing.

[0021] However, the configuration of the print head 5 is not particularly limited. For example, as in the fourth embodiment described later, a configuration in which multiple print heads 5 are arranged along the print track Q to enable multi-color printing may be used. Specifically, for example, 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 may be arranged along the print track Q to enable full-color printing. In addition, the print head 5 is not limited to the above-mentioned inkjet head of the piezo drive type. For example, the print head 5 may be an inkjet head of a thermal type that utilizes the film boiling phenomenon of the ink I, a bubble ejection type that generates bubbles in the ink I by applying heat to eject the ink I, an electrostatic actuator type that displaces and vibrates a vibration plate by electrostatic force to eject the ink I, or the like.

[0022] <Inertial Sensor 6> 1 and 2, the inertial sensor 6 is disposed on the print head 5 and detects vibrations of the print head 5. Note that the "vibration" refers to unnecessary displacements other than the displacement of the print head 5 along the print trajectory Q. There are no particular limitations on the inertial sensor 6 as long as it can detect vibrations, and for example, a three-axis acceleration sensor that detects accelerations in three mutually perpendicular axial directions can be used.

[0023] <Control device 8> As shown in FIG. 1, the control device 8 is electrically connected to the robot 2 and controls the driving of the robot 2. Specifically, the control device 8 controls the driving of the robot body 3, the moving stage 4, the print head 5, and the inertial sensor 6, either independently or in conjunction with each other. Such a control device 8 is, for example, composed of a computer, and has a processor (CPU) for processing information, a memory communicatively connected to the processor, and an external interface for connecting 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.

[0024] The configuration of the printing system 1 has been described above. Next, a printing method for the object W using the printing system 1 will be described. Before that, however, the problems of the conventional printing method will be described.

[0025] As described above, the print head 5 has a configuration in which a plurality of ink chambers 562 are connected to the reservoir 561. In such a configuration, as shown in FIG. 6, when the nozzle surface Fn is along the horizontal plane (hereinafter also referred to as the "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 becomes 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. Also, 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 during flight.

[0026] On the other hand, as shown in FIG. 7, when the nozzle surface Fn is inclined with respect to the horizontal plane (hereinafter also referred to as the "inclined state"), a height difference occurs between the plurality of ink chambers 562. Therefore, the pressure (water pressure) of the ink I becomes higher in the ink chamber 562 located on the lower side in the vertical direction, and the pressure (water pressure) of the ink I becomes lower in the ink chamber 562 located on the upper side in the vertical direction. Therefore, for example, when an ink ejection 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 on the upper side in the vertical direction decreases. Along with this, the ink I reaches the terminal speed before landing on the object W, the landing position on the object W is greatly deviated from the ideal landing position, the diameter of the dot formed by the landing becomes large, or it becomes difficult to land on the object W due to atomization during flight. As a result, the print quality deteriorates. This tendency becomes more prominent as the inclination θ of the nozzle surface Fn with respect to the horizontal plane increases, that is, in other words, as the height difference between the plurality of ink chambers 562 (the difference between the ink chamber 562 located at the uppermost end and the ink chamber 562 located at the lowermost end) increases, and is most prominent at an inclination θ = 90°.

[0027] Therefore, in the printing system 1, even in the inclined state, the ink I ejected from each nozzle 563, particularly the nozzle 563 located on the upper side in the vertical direction, lands on the object W while maintaining a sufficient speed without reaching the terminal speed during flight. The ink ejection voltage Vi is changed according to the inclination θ of the nozzle surface Fn. Specifically, as the inclination θ of the nozzle surface Fn increases, the ink ejection voltage Vi increases. As the ink ejection voltage Vi increases, the piezoelectric vibration element 564 vibrates more strongly, and the ejection speed of the ink I ejected from the nozzle 563 increases. Therefore, the decrease in the ejection speed due to the decrease in the pressure of the ink I in the ink chamber 562 can be compensated by the increase in the ejection speed due to the increase in the ink ejection voltage Vi. Therefore, the ink I ejected from each nozzle 563, particularly the nozzle 563 located on the upper side in the vertical direction, can land on the object W without reaching the terminal speed during flight. Therefore, the deviation of the landing position of the ink I, the dot diameter expansion, and the non-landing are suppressed, and high printing quality can be exhibited.

[0028] Next, the printing method by the printing system 1 will be described in detail. As shown in FIG. 8, the printing method by the printing system 1 includes a driving condition determination step S1 for determining driving conditions such as a printing track Q, and a printing step S2 for performing printing on the object W based on the driving conditions determined in the driving condition determination step S1.

[0029] ≪Driving Condition Determination Step S1≫ 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, highly accurate shape data can be acquired. However, the method for acquiring the shape data of the object W is not limited to this, and for example, it may be acquired from measurement data obtained by measuring the object W using a measuring instrument such as a 3D scanner.

[0030] Next, the control device 8 determines the print trajectory Q, for example, as shown in FIG. 9, based on the acquired shape of the object W, the configuration of the print head 5, and the print pattern to be printed on the object W. That is, in the printing step S2, it determines how to move the print head 5 relative to the object W in order to print the print pattern on the object W. Note that an example of the print trajectory Q shown in FIG. 5 includes a print trajectory Q1 inclined with respect to the vertical direction with a nozzle surface Fn having an inclination θ of 90°, and a print trajectory Q2 inclined with respect to the vertical direction with a nozzle surface Fn having an inclination θ of 45°. In particular, the print trajectories Q1 and Q2 are horizontal. As a result, as described above, a pressure difference occurs in the multiple ink chambers 562 in the print head 5, which makes it easier for the ink I ejected from the nozzle 563 located on the upper side in the vertical direction to shift in the landing position, the dots to expand, and the ink I to not land, so that the advantages of the printing method of this embodiment can be more prominently enjoyed.

[0031] Here, the printing pattern printed on the object W is not particularly limited, but is preferably a pattern. The pattern includes, for example, pictures, photographs, characters, symbols, etc., other than solid patterns. In this way, by printing a pattern as the printing pattern, the deterioration of print quality due to the deviation of the landing position of the ink I, the enlargement of the dot diameter, non-landing, etc. becomes more noticeable, so that the effect of the printing method of this embodiment can be more significantly enjoyed.

[0032] Next, the control device 8 determines the movement speed of the print head 5 along the print trajectory Q. The control device 8 further determines the timing of ejecting ink I from each nozzle 563 based on the determined print trajectory Q and the print pattern to be printed on the target W. In other words, the control device 8 determines whether or not to eject ink I for each nozzle 563 for each ink ejection control cycle. In this way, the print trajectory Q and the drive conditions of the print head 5 are determined, and the drive condition determination step S1 is completed.

[0033] <Printing step S2> In the printing step S2, first, the control device 8 positions the print head 5 at the starting point of the print track Q1 based on the driving conditions determined in the driving condition determination step S1. Next, with the print head 5 positioned at the starting point of the print 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 for each of the joints J1, J2, J3, J4, J5, and J6. In this way, by relying on the posture of the robotic arm 32, the inclination θ can be detected easily and accurately. Next, the control device 8 determines the ink ejection voltage Vi to be applied to each piezoelectric vibration element 564 during the printing operation along the print track Q1 based on the detected inclination θ. Specifically, the control device 8 increases the ink ejection voltage Vi as the inclination θ of the nozzle surface Fn increases, and increases the ejection speed of each ink I so that all the ink I ejected from all the nozzles 563 lands on the object W without reaching the terminal speed during flight regardless of the inclination θ. Thereby, during the printing operation along the print track Q1, it is possible to effectively suppress the deviation of the landing position, the dot diameter expansion, non-landing, etc. of the ink I ejected from the nozzles 563 located particularly on the upper side in the vertical direction.

[0034] In this embodiment, a table T showing the relationship between the inclination θ and the ink ejection voltage Vi as shown in FIG. 10 is stored in advance in the control device 8, and the control device 8 determines the ink ejection voltage Vi in four steps based on the table T. According to such a method, the ink ejection voltage Vi can be easily determined. Note that the table T can be generated, for example, by prior tests, simulations, etc. However, the method for determining the ink ejection voltage Vi is not particularly limited. For example, the ink ejection voltage Vi may be adjusted in three steps, or may be adjusted in multiple steps of five or more steps. Further, a function showing the relationship between the inclination θ and the ink ejection voltage Vi may be generated, and the ink ejection voltage Vi may be determined substantially continuously by substituting the inclination θ into the function. Based on the table T, since the inclination θ = 90° during the printing operation along the printing track Q1, the ink ejection voltage Vi = 36V. Here, in the print head 5 of this embodiment, as shown in FIG. 5, since the ink ejection voltage Vi is applied from the common power supply circuit 566 to each piezoelectric vibration element 564, the ink ejection voltage Vi cannot be changed for each piezoelectric vibration element 564 at the same time, and the ink ejection voltage Vi of 36V is applied to all the piezoelectric vibration elements 564.

[0035] Next, while moving the control device 8 along the printing track Q1 at a predetermined speed, the control device 8 applies the ink ejection voltage Vi determined earlier to a predetermined piezoelectric vibration element 564 at a predetermined timing to eject the ink I from the corresponding nozzle 563. Thereby, the printing operation along the printing track Q1 is completed. Here, as in this embodiment, it is preferable that the inclination θ is constant during the printing operation along the printing track Q1 for one scan. Thereby, if the ink ejection voltage Vi is determined when starting the printing operation along the printing track Q1, the ink ejection voltage Vi can be made constant during the printing operation along the printing track Q1. Therefore, the control of the print head 5 becomes simple.

[0036] After the printing along the printing track Q1 is completed, the control device 8 positions the printing head 5 at the starting point of the printing track Q2. Next, with the printing head 5 positioned at the starting point of the printing 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 each of the joints J1, J2, J3, J4, J5, and J6. Next, the control device 8 determines the ink ejection voltage Vi to be applied to each piezoelectric vibration element 564 during the printing operation along the printing track Q2 based on the detected inclination θ. The determination method is the same as when along the printing track Q1.

[0037] Next, the control device 8 moves along the printing track Q2 at a predetermined speed and applies the ink ejection voltage Vi determined earlier to a predetermined piezoelectric vibration element 564 at a predetermined timing to eject the ink I from the corresponding nozzle 563. Thus, the printing of the print pattern on the object W is completed. In this way, by changing the ink ejection voltage Vi according to the inclination θ of the nozzle surface Fn, during the printing operation along the printing track Q, particularly 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 dot diameter expansion, non-landing, etc. can be effectively suppressed. Therefore, high printing quality can be achieved. In particular, in this embodiment, the inclination θ is different when printing along the printing track Q1 and when printing along the printing track Q2, and the ink ejection voltage Vi also differs accordingly. In this way, by adopting a configuration that allows the ink ejection voltage Vi to be changed during the printing operation, the degree of freedom of the printing operation is increased.

[0038] In addition, the control device 8 further detects the vibration of the printing head 5 based on the output of the inertial sensor 6 during the printing operations along the printing tracks Q1 and Q2, 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 with an opposite phase to the detected vibration is applied to the printing head 5. Thereby, the vibration of the printing head 5 during the printing step S2 is suppressed, and higher-quality printing becomes possible.

[0039] The printing method using the printing system 1 has been described above, but the printing method is not particularly limited. For example, the ink ejection voltage Vi may be determined in the driving condition determination step S1. In this case, the control device 8 may determine the ink ejection voltage Vi based on the inclination θ of the print head 5 included in the print tracks Q1 and Q2 determined in the driving condition determination step S1. That is, in the present embodiment, the ink ejection voltage Vi is determined using the measured value of the inclination θ, but the ink ejection voltage Vi may also be determined using the set value of the inclination θ.

[0040] The printing system 1 of the present embodiment has been described above. As described above, the printing method using such a printing system 1 uses a robot arm 32 including a print head 5 having a plurality of nozzles 563 for ejecting ink I, and moves the object W and the print head 5 relative to each other along the print track Q while ejecting the ink I from each nozzle 563 at a predetermined timing to print a print pattern on the object W. The print head 5 is configured to eject the ink I from the nozzle 563 when the ink ejection voltage Vi is applied, and changes the ink ejection 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 method, during the printing operation along the print track Q, it is possible to effectively suppress the deviation of the landing position of the ink I ejected from the nozzles 563 located particularly on the upper side in the vertical direction, the dot diameter expansion, non-landing, etc. Therefore, high printing quality can be exhibited.

[0041] Also, as described above, in the printing method using the printing system 1, the larger the inclination θ, the larger the ink ejection voltage Vi. According to such a method, it is possible to more reliably suppress the deviation of the landing position of the ink I ejected from the nozzles 563 located particularly on the upper side in the vertical direction, the dot diameter expansion, non-landing, etc. during the printing operation along the print track Q.

[0042] Also, as described above, in the printing method using the printing system 1, the printing pattern is a pattern. By printing a pattern as the printing pattern in this way, the deterioration of print quality due to the deviation of the landing position of the ink I, the diameter expansion of the dots, non-landing, etc. becomes prominent, so the effect of the printing method can be more prominently enjoyed.

[0043] Also, as described above, in the printing method using the printing system 1, the ink ejection voltage Vi is determined based on the table T that defines the relationship between the ink ejection voltage Vi and the inclination θ. According to such a method, the ink ejection voltage Vi can be easily determined.

[0044] Also, as described above, in the printing method using the printing system 1, the inclination θ is detected based on the posture of the robot arm 32. According to such a method, the inclination θ can be easily detected.

[0045] Also, 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 occurs between the plurality of ink chambers 562 in the print head 5, and the deterioration of print quality due to the deviation of the landing position, the diameter expansion of the dots, non-landing, etc. appears. Therefore, since the printing track Q is inclined with respect to the vertical direction, the effect of the printing method can be more prominently enjoyed.

[0046] Also, as described above, in the printing method using the printing system 1, the ink ejection voltage Vi is changed during the printing operation. According to such a method, the degree of freedom of the printing operation increases.

[0047] Also, as described above, in the printing method using the printing system 1, the print head 5 has a plurality of ink chambers 562 in which each nozzle 563 is formed, a reservoir 561 connected to each ink chamber 562, and a plurality of piezoelectric vibration elements 564 that vibrate the wall surfaces of the respective ink chambers 562. By applying an ink ejection voltage Vi to each piezoelectric vibration element 564, ink I is ejected from each nozzle 563. By using a print head 5 having such a configuration, problems such as displacement of the landing position of the ink I, dot diameter expansion, and non-landing are likely to occur. Therefore, the effects of the printing method can be enjoyed more significantly.

[0048] Also, as described above, the printing system 1 includes a robot arm 32 having a print head 5 with a plurality of nozzles 563 for ejecting ink I, and a control device 8 for controlling the drive of the robot arm 32. The printing system prints a print pattern on the object W by relatively moving the object W and the print head 5 along the print track Q and ejecting the ink I from each nozzle 563 at a predetermined timing. The print head 5 is configured to eject the ink I from the nozzle 563 when the ink ejection voltage Vi is applied, and the control device 8 changes the ink ejection 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 configuration, during the printing operation along the print track Q, it is possible to effectively suppress displacement of 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. Therefore, high print quality can be exhibited.

[0049] <Second Embodiment> FIG. 11 is a diagram showing the circuit configuration of a print head included in the printing system according to the second embodiment.

[0050] This embodiment is the same as the first embodiment described above, except that the configuration of the print head 5 and the method of changing the ink ejection voltage Vi are different. In the following description, regarding this embodiment, the differences from the first embodiment described above will be mainly explained, and the description of the same matters will be omitted. Also, in the drawings of this embodiment, the same reference numerals are given to the same configurations as those in the above-described embodiments.

[0051] In the first embodiment described above, as shown in FIG. 5, the ink ejection voltage Vi is applied from the common power supply circuit 566 to each piezoelectric vibration element 564. Therefore, due to its configuration, the ink ejection voltage Vi cannot be changed for each piezoelectric vibration element 564, and the ink ejection voltage Vi for all the piezoelectric vibration elements 564 is changed collectively. In such a configuration, for the nozzles 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., for the nozzles 563 located on the lower side in the vertical direction, there is a possibility that the ejection speed of the ink I may increase too much.

[0052] On the other hand, in the print head 5 of this embodiment, a dedicated power supply circuit 566 is connected to each piezoelectric vibration element 564, and the ink ejection 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 configuration, for example, for the nozzles 563 located on the upper side in the vertical direction, by increasing the ink ejection voltage Vi, the ejection speed of the ink I is increased, and while suppressing the deviation of the landing position, the diameter expansion of the dots, non-landing, etc., for the nozzles 563 located on the lower side in the vertical direction, by lowering the ink ejection voltage Vi, it is possible to prevent the ejection speed of the ink I from increasing excessively. That is, by reducing the difference in the ejection speed of the ink I from each nozzle 563, preferably, by making them equal, the ejection speed of the ink I from each nozzle 563 can be easily kept within the allowable speed. Therefore, higher-quality printing can be performed.

[0053] As described above, in the printing method according to the present embodiment, the ink ejection 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 kept within the allowable speed. Therefore, higher-quality printing can be performed.

[0054] Also, according to such a second embodiment, the same effects as those of the first embodiment described above can be exhibited.

[0055] <Third Embodiment> FIG. 12 is a diagram showing the configuration of the tip of the robot included in the printing system according to the third embodiment. FIG. 13 is a diagram for explaining a method of detecting the ejection speed of the ink I.

[0056] 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 ink ejection speed detection unit 7 that detects the ejection speed of the ink I. In the following description, regarding the present embodiment, the differences from the above-described embodiments will be mainly described, and the description of the same matters will be omitted. Also, in each figure of the present embodiment, the same components as those of the above-described embodiments are denoted by the same reference numerals.

[0057] As shown in FIG. 12, the printing system 1 of the present embodiment includes an ink ejection speed detection unit 7 that detects the ejection speed of the ink I from each nozzle 563. The ink ejection speed detection unit 7 includes a camera 71 fixed to the moving stage 4 together with the print head 5, and an image processing unit 72 that processes the image captured by the camera 71. When the print head 5 is moved along the print track Q, the camera 71 is positioned immediately behind the print head 5 and captures the ink I that has landed on the object W. The image processing unit 72 detects the ejection speed of the ink I ejected from the print head 5 based on the image captured by the camera 71. Specifically, as shown in FIG. 13, the image processing unit 72 detects the separation distance D between a pair of adjacent inks I(n) and I(n + 1) along the print track Q from the image acquired by the camera 71, and based on the detected separation distance D, the moving speed of the print head 5, the ejection timing of the inks I(n) and I(n + 1), that is, the ejection time difference, and the distance between the nozzle 563 and the object W, it detects the ejection speed of the ink I from each nozzle 563. Note that the parameters other than the separation distance D are determined as driving conditions in the driving condition determination step S1. According to such a method, the ink ejection speed can be easily detected.

[0058] However, the configuration of the ink ejection speed detection unit 7 is not particularly limited as long as it can detect the ejection speed of the ink I from at least one nozzle 563.

[0059] Then, the control device 8 changes the ink ejection voltage Vi based on the ejection speed of the ink I detected by the image processing unit 72. That is, it corrects the ink ejection voltage Vi determined based on the table T. Specifically, when the ejection speed of the ink I from at least one nozzle 563 exceeds the allowable speed, the ink ejection voltage Vi is decreased by a predetermined value to keep the ejection speed of the ink I from all the nozzles 563 within the allowable speed. Conversely, when the ejection speed of the ink I from at least one nozzle 563 is less than the allowable speed, the ink ejection voltage Vi is increased by a predetermined value to keep the ejection speed of the ink I from all the nozzles 563 within the allowable speed. According to such a configuration, the ink ejection voltage Vi can be appropriately changed according to the actual ejection situation of the ink I, so that higher-quality printing can be performed.

[0060] As described above, in the printing method of the present embodiment, the ink ejection voltage Vi is changed based on the ejection speed of the ink I from the nozzle 563. According to such a method, the ink ejection voltage Vi can be appropriately changed according to the actual ejection situation of the ink I, so that higher-quality printing can be performed.

[0061] Also, according to such a third embodiment, the same effects as those of the first embodiment described above can be achieved.

[0062] <Fourth Embodiment> FIG. 14 is a diagram showing a print head of a printing system according to the fourth embodiment. FIG. 15 is a diagram showing a table for determining the relationship between the inclination of the print head and the ink ejection voltage.

[0063] The printing system of the present embodiment is the same as the printing system of the first embodiment described above, except that the configuration of the print head 5 is different. In the following description, regarding the present embodiment, the differences from the above-described embodiments will be mainly described, and the description of the same matters will be omitted. Also, in the drawings of the present embodiment, the same reference numerals are given to the same configurations as those of the above-described embodiments.

[0064] As shown in FIG. 14, the print head 5 of the present embodiment includes a print head 5B that discharges black ink I, a print head 5C that discharges cyan ink I, a print head 5M that discharges magenta ink I, and a print head 5Y that discharges yellow ink I. These are arranged side by side along the print track Q. Note that the configurations of the respective print heads 5B, 5C, 5M, and 5Y are the same as those of the print head 5 in the first embodiment described above.

[0065] Also, in the printing operation, as shown in FIG. 14, the print track Q extends along the vertical direction. In this case, in each of the print heads 5B, 5C, 5M, and 5Y, since the plurality of ink chambers 562 are arranged side by side in the horizontal direction, there is no difference in the discharge speed of the ink I from each nozzle 563. However, since the atmospheric pressure is higher for the print head located on the lower side in the vertical direction, the deviation of the landing position tends to be larger. That is, if the ink discharge voltage Vi is set to the same value among the print heads 5B, 5C, 5M, and 5Y, when the ink I discharged from the print head 5 located on the lower side in the vertical direction lands on the object W, there is a possibility that the deviation of the landing position, the diameter expansion of the dots, or non-landing may occur. Therefore, in the present embodiment, as in the table T shown in FIG. 15, for each inclination θ, the ink discharge voltage Vi of each print head 5B, 5C, 5M, and 5Y is determined such that the ink discharge voltage Vi becomes larger for the print head 5 located on the lower side in the vertical direction. Thereby, high printing quality can be exhibited.

[0066] As described above, in the printing method according to the present embodiment, the print track Q extends along the vertical direction. Therefore, there is a difference in the discharge speed of the ink I among the plurality of print heads arranged along the print track Q, and a decrease in printing quality due to the deviation of the landing position of the ink I discharged from the print head located on the lower side in the vertical direction, the diameter expansion of the dots, non-landing, etc. appears. Therefore, due to the print track Q extending along the vertical direction, the effects of the printing method can be enjoyed more significantly.

[0067] Also, according to such a fourth embodiment, the same effects as those of the first embodiment described above can be exhibited.

[0068] The printing method and printing system of the present invention have been described with reference 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. In addition, any other arbitrary configuration and process may be added to the present invention. Further, the embodiments may be combined as appropriate.

Description of Reference Numerals

[0069] 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... Printing head, 5B... Printing head, 5C... Printing head, 5M... Printing head, 5Y... Printing head, 51... Nozzle plate, 52... Pressure chamber forming substrate, 53... Diaphragm, 54... Sealing portion, 561... Reservoir, 562... Ink chamber, 563... Nozzle, 564... Piezoelectric vibration element, 565... Switch element, 566... Power supply circuit, 6... Inertial sensor, 7... Ink ejection 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... Driving condition determination step, S2... Printing step, T... Table, Vi... Ink ejection voltage, W... Object, θ... Tilt

Claims

1. A printing method for printing a printing pattern on an object by using a robot arm including a print head having a plurality of nozzles for discharging ink, and relatively moving the object and the print head along a printing track while discharging the ink from each of the nozzles at a predetermined timing, wherein the print head is configured to discharge the ink from the nozzles when an ink discharge voltage is applied, and the ink discharge voltage is changed according to an inclination of a nozzle surface on which the plurality of nozzles are arranged with respect to a horizontal plane.

2. The printing method according to claim 1, wherein the ink discharge voltage is increased as the inclination increases.

3. The printing method according to claim 1, wherein the printing pattern is a pattern.

4. The printing method according to claim 1, wherein the ink discharge voltage is determined based on a table defining a relationship between the ink discharge voltage and the inclination.

5. The printing method according to claim 1, wherein the inclination is detected based on an attitude of the robot arm.

6. The printing method according to claim 1, wherein the ink discharge voltage is changed based on a discharge speed of the ink from the nozzles.

7. The printing method according to claim 1, wherein the printing track is inclined with respect to a vertical direction.

8. The printing method according to claim 1, wherein the printing track is along a vertical direction.

9. The printing method according to claim 1, wherein the ink discharge voltage is changed during the printing operation.

10. The print head includes a plurality of ink chambers in which the nozzles are formed, a reservoir connected to each of the ink chambers, and a plurality of piezoelectric vibration elements that vibrate wall surfaces of the ink chambers. The printing method according to claim 1, wherein the ink is discharged from each of the nozzles by applying the ink discharge voltage to each of the piezoelectric vibration elements.

11. The printing method according to claim 10, wherein the ink discharge voltage is changed for each of the piezoelectric vibration elements.

12. A printing system including a robot arm including a print head having a plurality of nozzles for discharging ink, and a control device configured to control driving of the robot arm, the printing system printing a printing pattern on an object by relatively moving the object and the print head along a printing track while discharging the ink from each of the nozzles at a predetermined timing. The printing head is configured to eject the ink from the nozzles when an ink ejection voltage is applied. The control device changes the ink ejection voltage according to the inclination of the nozzle surface on which the plurality of nozzles are arranged with respect to the horizontal plane. A printing system characterized by this.

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