Printing method and robot system

Abstract

To provide a printing method and a robot system that can efficiently perform printing with high quality.SOLUTION: The printing method performs printing on a target by discharging ink from a nozzle while moving the target and a printing head relatively to each other along a printing track, using a robot provided with the printing head having the nozzle for discharging the ink. The printing method controls speed at which the nozzle discharges the ink, in accordance with a separation distance between the nozzle and the target, where the control of the discharging speed is performed in accordance with magnitude of voltages for discharging which are applied to the printing head.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

[0002] The painting robot described in Patent Document 1 has a robot body equipped with an arm and a nozzle head unit attached to the tip of the arm. Then, while moving the nozzle head unit relative to the object using the robot body, ink is ejected from the nozzle head unit toward the object to perform printing on the object. Further, the nozzle head unit is provided with a plurality of nozzles arranged in a predetermined direction. Here, if the separation distance between the nozzle and the object is large, there is a risk that the printed image may shift, warp, distort, etc., resulting in a decrease in print quality. Therefore, in Patent Document 1, for nozzles with a separation distance from the object of a predetermined value or more, ink is not ejected to control the printing width per scan, and an attempt is made to suppress a decrease in print quality.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the painting robot of Patent Document 1, since the printing width per scan decreases by not ejecting ink from nozzles with a separation distance from the object of a predetermined value or more, accordingly, the number of scans of the nozzle head unit increases, and the time required for printing becomes longer.

Means for Solving the Problems

[0005] The printing method of the present invention uses a robot equipped with a print head having nozzles for discharging ink, and performs a printing operation on the object by discharging the ink from the nozzles while relatively moving the object and the print head along a printing track. The discharge speed of the ink from the nozzles is controlled according to the separation distance between the nozzles and the object.

[0006] The robot system of the present invention includes a robot equipped with a print head having nozzles for discharging ink, and a control device that controls the driving of the robot. It is a robot system that performs a printing operation on an object by discharging the ink from the nozzles while relatively moving the object and the print head. The control device controls the discharge speed of the ink from the nozzles according to the separation distance between the nozzles and the object.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the printing method and the robot 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 robot 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 a schematic diagram showing a deviation of the landing position. FIG. 4 is a flowchart showing a printing process. FIG. 5 is a perspective view showing an example of a printing track. FIG. 6 is a diagram showing the relationship between the separation distance and the discharge voltage.

[0010] The robot system 1 shown in FIG. 1 is applied to a printing system that performs a printing operation on an object W. The robot system 1 includes a robot 10 that performs printing on the object W, and a control device 9 that controls the driving of the robot 10. Further, the robot 10 includes a robot body 2 having a robot arm 22, a moving stage 4 disposed at the tip of the robot arm 22, a printing head 3 disposed on the moving stage 4, and an inertial sensor 6 as a vibration meter disposed on the printing head 3.

[0011] In such a robot system 1, while moving the printing head 3 along a predetermined printing track Q with respect to the object W using the robot arm 22, the ink I is discharged from the printing head 3 at a predetermined timing and discharge speed to perform a printing operation on the object W.

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

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

[0014] The robot arm 22 is configured such that six arms 221, 222, 223, 224, 225, and 226 are rotatably connected in this order from the base 21 side, and includes six joints J1, J2, J3, J4, J5, and J6. Specifically, the arm 221 is rotatably connected to the base 21 via the joint J1, the arm 222 is rotatably connected to the arm 221 via the joint J2, the arm 223 is rotatably connected to the arm 222 via the joint J3, the arm 224 is rotatably connected to the arm 223 via the joint J4, the arm 225 is rotatably connected to the arm 224 via the joint J5, and the arm 226 is rotatably connected to the arm 225 via the joint J6.

[0015] Among the joints J1 to J6, the joints J2, J3, and J5 are bending joints, respectively, and the joints J1, J4, and J6 are torsion joints, respectively. In addition, a drive mechanism including a motor, a speed reducer that decelerates the rotation of the motor to increase the torque and outputs it, and an encoder that detects the amount of rotation of the joint is installed at each of the joints J1, J2, J3, J4, J5, and J6. By moving each of the joints J1, J2, J3, J4, J5, and J6 independently, the print head 3 disposed at the tip of the robot arm 22 can be moved in a desired direction at a desired posture and speed.

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

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

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

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

[0020] <<Printing Head 3>> As shown in FIG. 2, the print head 3 is disposed on the second stage 42. The print head 3 is not particularly limited, but in this embodiment, an inkjet head of a piezo drive system is used. The inkjet of the piezo drive system has an ink chamber, a diaphragm constituting a part of the wall surface of the ink chamber, a piezo element (piezoelectric element) for vibrating the diaphragm, and a nozzle 31 connected to the ink chamber. In such a piezo drive type inkjet head, when a voltage (hereinafter also referred to as "discharge voltage") is applied to the piezo element to vibrate the piezo element, the diaphragm vibrates and the ink I in the ink chamber is discharged from the nozzle 31. Here, the larger the discharge voltage, the larger the amplitude of the diaphragm, and thus the faster the discharge speed of the ink I from the nozzle 31. Conversely, the smaller the discharge voltage, the smaller the amplitude of the diaphragm, and thus the slower the discharge speed of the ink I from the nozzle 31. In the robot system 1, the discharge speed of the ink I is controlled by changing the discharge voltage applied to the piezo element.

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

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

[0023] However, the configuration of the print head 3 is not particularly limited. For example, the number and arrangement of the nozzles 31, the color of the ink I ejected from each nozzle 31, etc. are not particularly limited. For example, the number of nozzles 31 included in each nozzle row 310 may be six or less, or may be eight or more. Also, for example, one, two, or three of the four nozzle rows 310 may be omitted.

[0024] Further, the configuration of the print head 3 is not limited to the above-described piezo-driven inkjet head. For example, it may be a thermal method using the film boiling phenomenon of the ink I, a bubble ejection method in which bubbles are generated in the ink I by applying heat to eject the ink I, an electrostatic actuator method in which a diaphragm is displaced and vibrated by an electrostatic force to eject the ink I, or other inkjet heads.

[0025] ≪Inertial sensor 6≫ As shown in FIGS. 1 and 2, the inertial sensor 6 is disposed on the print head 3 and detects the vibration of the print head 3. Note that the "vibration" means unnecessary displacement other than the displacement along the print track Q of the print head 3. The inertial sensor 6 is not particularly limited as long as it can detect vibration. For example, a three-axis acceleration sensor that detects accelerations in three mutually orthogonal directions can be used.

[0026] ≪Control device 9≫ As shown in FIG. 1, the control device 9 is electrically connected to the robot 10 and controls the drive of the robot 10. Specifically, the control device 9 controls the drives of the robot body 2, the print head 3, the moving stage 4, and the inertial sensor 6 independently or in conjunction with each other. Such a control device 9 is composed of, for example, a computer and includes a processor (CPU) that processes information, a memory communicably connected to the processor, and an external interface that connects to an external device. Various programs executable by the processor are stored in the memory, and the processor can read and execute the programs stored in the memory.

[0027] The configuration of the robot system 1 has been described above. Next, a printing method for the object W using the robot system 1 will be described. Before that, based on FIG. 3, the conventional problems will be described.

[0028] The larger the separation distance D between the nozzle 31 and the object W, the longer the time (hereinafter also referred to as "flight time") from when the ink I is ejected until it lands on the object W. Also, as shown in FIG. 3, the ink I flies while having a velocity component in the moving direction of the print head 3. Therefore, the longer the flight time, the more the actual landing position T of the ink I deviates to the front side of the print track Q with respect to the target landing position Tr. And this deviation of the landing position causes misregistration, blurring, distortion, etc. in printing, and as a result, the print quality deteriorates.

[0029] Therefore, in the above-mentioned Patent Document 1, when the separation distance D exceeds the allowable value, the ink I is not ejected from the nozzle 31, thereby suppressing the deterioration of the print quality. However, with such a control method, the print area per one scan of the print head 3 becomes narrow, and accordingly, the number of scans of the print head 3 increases, and the time required for printing becomes long. Therefore, the cycle time of the printing operation becomes long, and efficient printing cannot be performed.

[0030] Therefore, in the robot system 1, as the separation distance D increases, the ejection speed of the ink I is increased to shorten the flight time and suppress the deviation of the landing position T with respect to the target landing position Tr. According to such a method, it is possible to suppress the deterioration of the print quality caused by the deviation of the landing position without narrowing the print area per one scan of the print head 3. Therefore, high-quality printing can be performed in a shorter time. Hereinafter, the printing method by the robot system 1 will be described in detail.

[0031] As shown in FIG. 4, the printing method by the robot system 1 includes a drive condition determination step S1 for determining the drive conditions of the print track Q and the print head 3, and a printing step S2 for performing printing on the object W based on the conditions determined in the drive condition determination step S1.

[0032] <<Drive condition determination step S1>> In the drive condition determination step S1, first, the control device 9 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. As a result, since highly accurate shape data can be acquired, the drive conditions of the printing track Q and the print head 3 can be accurately determined. 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.

[0033] Next, the control device 9 determines the printing track Q based on the acquired shape of the object W and the configuration of the print head 3 stored in advance, for example, as shown in FIG. 5. That is, in the printing step S2, it is determined how to move the print head 3 with respect to the object W. In the example shown in FIG. 5, the printed surface of the object W is a semi-circular curved surface, but the shape of the printed surface is not particularly limited, and for example, it may be a flat surface, a curved surface, or a wavy surface.

[0034] Next, the control device 9 determines the moving speed of the print head 3. The control device 9 further determines the timing of discharging the ink I from each nozzle 31 based on the sample image data to be printed on the object W. In other words, the control device 9 determines the discharge / non-discharge of the ink I for each nozzle 31 for each ink discharge control cycle.

[0035] Next, the control device 9 acquires the separation distance D between each nozzle 31 and the object W for each ink ejection control cycle based on the shape data of the object W and the printing trajectory Q. Then, the control device 9 determines the ejection speed of the ink I for each nozzle 31 for each ink ejection control cycle based on the acquired separation distance D. Here, as described above, the ejection speed of the ink I is controlled by the ejection voltage applied to the piezoelectric element. Therefore, the control device 9 determines the ejection voltage applied to the piezoelectric element so that the ejection speed of the ink I becomes a predetermined speed for each nozzle 31 based on the separation distance D.

[0036] Specifically, the greater the ejection voltage, the higher the ink ejection speed. Therefore, the control device 9 increases the ejection voltage applied to the piezoelectric element corresponding to the nozzle 31 as the separation distance D increases to increase the ejection speed of the ink I, and adjusts it so that the deviation of the landing position T from the target landing position Tr is within a predetermined value regardless of the separation distance D. That is, the ejection voltage is adjusted so that the flight time of the ink I is substantially constant regardless of the separation distance D. Thereby, it is possible to suppress a decrease in print quality due to deviation of the landing position. As described above, by controlling the ejection speed of the ink I by the ejection voltage, the ejection speed of the ink I can be easily and accurately controlled. However, the method of controlling the ejection speed of the ink I is not particularly limited.

[0037] In this embodiment, the control device 9 stores in advance data Da indicating the relationship between the separation distance D and the ejection voltage as shown in FIG. 6, and the control device 9 adjusts the ejection voltage in three steps based on the data Da. According to such a method, the ejection voltage can be easily determined. Note that the data Da can be generated, for example, by prior tests, simulations, etc. However, the method of determining the ejection voltage is not particularly limited, and for example, the ejection voltage may be adjusted in two steps, or may be adjusted in multiple steps of four or more steps. Further, a function indicating the relationship between the separation distance D and the ejection voltage may be generated, and the ejection voltage may be determined substantially steplessly by substituting the separation distance D into the function.

[0038] As described above, the driving conditions of the printing track Q and the print head 3 are determined, and the driving condition determination step S1 ends. In this way, by measuring the separation distance D before the printing operation, the driving conditions of the print head 3 can be determined before printing, so that the printing operation can be easily performed.

[0039] ≪Printing Step S2≫ In the printing step S2, the control device 9 drives the robot arm 22 to move the print head 3 along the printing track Q at a predetermined moving speed, and controls the driving of the print head 3 based on the driving conditions (ejection timing and ejection speed) of the print head 3 determined in the driving condition determination step S1 to perform the printing operation. As a result, the deviation of the landing position T from the target landing position Tr is suppressed, so that a high-quality image with less deviation, blurring, distortion, etc. is printed on the object W.

[0040] Also, in the printing step S2, during the printing operation, the vibration of the print head 3 is detected based on the output of the inertial sensor 6, and the driving of the moving stage 4 is controlled so that the detected vibration is canceled. Specifically, the driving of the moving stage 4 is controlled so that a vibration with a reverse phase is applied to the print head 3 with respect to the detected vibration. As a result, the vibration of the print head 3 during the printing step S2 is suppressed, and higher-quality printing becomes possible.

[0041] The above describes the robot system 1. As described above, the printing method using such a robot system 1 uses a robot 10 provided with a print head 3 having nozzles 31 for discharging ink I, and discharges ink I from the nozzles 31 while relatively moving the object W and the print head 3 along the print track Q to perform a printing operation on the object W. The discharge speed of the ink I from the nozzles 31 is controlled according to the separation distance D between the nozzles 31 and the object W. According to such a method, regardless of the separation distance D, the deviation of the landing position T from the target landing position Tr can be effectively suppressed. Therefore, ink I can be discharged from the nozzles 31 with a large separation distance D, and the decrease in print quality due to the deviation of the landing position can be suppressed without narrowing the print area per scan of the print head 3. As a result, high-quality printing can be performed in a shorter time.

[0042] Also, as described above, the control of the discharge speed is performed by the magnitude of the discharge voltage applied to the print head 3. According to such a method, the discharge speed can be controlled simply and accurately.

[0043] Also, as described above, the control device 9 increases the discharge voltage and the discharge speed as the separation distance D increases. Thereby, the deviation of the landing position can be effectively suppressed.

[0044] Also, as described above, the discharge voltage is determined based on the data Da indicating the relationship between the predetermined separation distance D and the discharge voltage. Thereby, the discharge voltage can be easily determined.

[0045] Also, as described above, the separation distance D is measured before the printing operation. Thereby, since the driving conditions of the print head 3 can be determined before printing, the printing operation can be easily performed.

[0046] Also, as described above, the separation distance D is obtained based on the CAD data of the object W and the print track Q. Thereby, the separation distance D can be accurately obtained.

[0047] Also, as described above, the robot system 1 includes a robot 10 having a print head 3 with a nozzle 31 for discharging ink I, and a control device 9 for controlling the drive of the robot 10. The robot system 1 performs a printing operation on the object W by discharging the ink I from the nozzle 31 while relatively moving the object W and the print head 3. The control device 9 controls the discharge speed of the ink I from the nozzle 31 according to the separation distance D between the nozzle 31 and the object W. According to such a robot system 1, regardless of the separation distance D, the deviation of the landing position T from the target landing position Tr can be effectively suppressed. Therefore, the ink I can be discharged from the nozzle 31 with a large separation distance D, and the decrease in print quality due to the deviation of the landing position can be suppressed without narrowing the print area per scan of the print head 3. As a result, high-quality printing can be performed in a shorter time.

[0048] <Second Embodiment> FIG. 7 is a diagram showing the configuration of the tip of the robot included in the robot system according to the second embodiment.

[0049] This embodiment is the same as the first embodiment described above except that the printing method is different. In the following description, regarding this embodiment, the differences from the first embodiment described above will be mainly described, and the description of the same matters will be omitted. Also, in the drawings of this embodiment, the same components as those in the above-described embodiment are denoted by the same reference numerals.

[0050] In the first embodiment described above, the discharge speed of the ink I was determined in the drive condition determination step S1. However, in this embodiment, the discharge speed of the ink I is determined during the printing step S2. That is, in the drive condition determination step S1, conditions other than the discharge voltage are determined, and in the printing step S2, the printing operation is performed while determining the discharge voltage. According to such a method, the time required for the drive condition determination step S1 can be shortened, and the efficiency of the printing operation can be improved.

[0051] As shown in FIG. 7, the robot 10 of the present embodiment has a distance sensor 8 that is disposed on the print head 3 and measures the separation distance D' from the object W. The distance sensor 8 is located on the front side of the print track Q with respect to the print head 3 during the printing step S2. The control device 9 measures, using the distance sensor 8, the separation distance D' from a location in front of the print head 3 at a location along the print track Q during the movement of the print head 3 in the printing step S2.

[0052] Furthermore, the control device 9 calculates the separation distance D when each nozzle 31 faces the location based on the separation distance D'. Then, the control device 9 determines the ejection speed of the ink I to be landed on the location, that is, the ejection voltage applied to the piezo element, based on the calculated separation distance D, and controls the driving of the print head 3 with the determined ejection voltage. Such an operation is repeatedly performed at a predetermined cycle during the movement of the print head 3.

[0053] According to such a printing method, high-quality printing with less deviation, blur, distortion, etc. can be performed on the object W without previously determining the ejection voltage applied to each piezo element of the print head 3.

[0054] As described above, in the printing method of the present embodiment, the separation distance D is measured during the printing operation. Thereby, the time required for the drive condition determination step S1 can be shortened, and the efficiency of the printing operation can be improved.

[0055] Also, such a second embodiment can exhibit the same effects as those of the first embodiment described above.

[0056] As described above, the printing method and the robot system of the present invention have been explained with reference to the illustrated embodiments. However, the present invention is not limited thereto, and the configurations and steps of each part can be replaced with any configurations and steps having the same functions. Further, any other arbitrary components and steps may be added to the present invention. Also, the embodiments may be combined as appropriate. Further, the control device 9 for controlling the discharge speed of the ink I may be a control device that is not connected to the robot 10 and is electrically connected to the print head 3.

Explanation of Reference Numerals

[0057] 1…Robot system, 10…Robot, 2…Robot body, 21…Base, 22…Robot arm, 221…Arm, 222…Arm, 223…Arm, 224…Arm, 225…Arm, 226…Arm, 3…Print head, 31…Nozzle, 310…Nozzle row, 310a…Nozzle row, 310b…Nozzle row, 310c…Nozzle row, 310d…Nozzle row, 4…Moving stage, 40…Base, 400…Piezoelectric actuator, 41…First stage, 42…Second stage, 45…First stage drive unit, 46…Second stage drive unit, 6…Inertial sensor, 8…Distance sensor, 9…Control device, A…First direction, B…Second direction, D…Separation distance, D’…Separation distance, Da…Data, I…Ink, J1…Joint, J2…Joint, J3…Joint, J4…Joint, J5…Joint, J6…Joint, Q…Printing track, S1…Drive condition determination step, S2…Printing step, T…Landing position, Tr…Target landing position, W…Object

Claims

1. A printing method that uses a robot equipped with a print head having nozzles for ejecting ink, and performs a printing operation on an object by ejecting the ink from the nozzles while relatively moving the object and the print head along a printing track, characterized in that the ejection speed of the ink from the nozzles is controlled according to the separation distance between the nozzles and the object.

2. The printing method according to claim 1, wherein the control of the ejection speed is performed by the magnitude of the ejection voltage applied to the print head.

3. The printing method according to claim 2, wherein the greater the separation distance, the greater the ejection voltage is increased to increase the ejection speed.

4. The printing method according to claim 3, wherein the ejection voltage is determined based on data indicating the relationship between the separation distance and the ejection voltage determined in advance.

5. The printing method according to claim 4, wherein the separation distance is measured before the printing operation.

6. The printing method according to claim 5, wherein the separation distance is obtained based on the CAD data of the object and the printing track.

7. The printing method according to claim 4, wherein the separation distance is measured during the printing operation.

8. A robot system having a robot equipped with a print head having nozzles for ejecting ink, and a control device for controlling the drive of the robot, and performs a printing operation on an object by ejecting the ink from the nozzles while relatively moving the object and the print head, characterized in that the control device controls the ejection speed of the ink from the nozzles according to the separation distance between the nozzles and the object. ​

Images