Three-dimensional object printer and printing method

Abstract

To improve printing quality.SOLUTION: A three-dimensional printer includes: a liquid discharge head that discharges liquid toward a workpiece; a multi-joint robot that has a distal end portion supporting the liquid discharge head and changes a relative position of the liquid discharge head with respect to the workpiece; a detection part that detects operation of the liquid discharge head in a scanning direction; and a control part that controls operation of the liquid discharge head and the multi-joint robot. The control part acquires speed information related to speed of the liquid discharge head on the basis of a detection result of the detection part, and controls a discharge timing of the liquid discharge head on the basis of the speed information.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a three-dimensional object printing device and a printing method. [Background technology]

[0002] There are known three-dimensional printing devices that use an inkjet printing method to print on the surface of a three-dimensional workpiece. For example, the device described in Patent Document 1 has a robot arm and a print head fixed to the tip of the robot arm, and prints an image on the target object using ink from the print head. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-050832 Summary of the Invention [Problem to be solved by the invention]

[0004] In the device described in Patent Document 1, there is a risk that the landing position of ink ejected from the print head will shift due to operational errors of the robot arm, resulting in a deterioration in print quality. [Means for solving the problem]

[0005] One aspect of the three-dimensional object printing device disclosed herein comprises a liquid ejection head that ejects liquid toward a workpiece, a multi-joint robot having a tip that supports the liquid ejection head and changes the relative position of the liquid ejection head with respect to the workpiece, a detection unit that detects the movement of the liquid ejection head in the scanning direction, and a control unit that controls the operation of the liquid ejection head and the multi-joint robot, wherein the control unit obtains speed information regarding the speed of the liquid ejection head based on the detection result of the detection unit, and controls the ejection timing of the liquid ejection head based on the speed information.

[0006] One aspect of the printing method disclosed herein is a printing method using a three-dimensional printing device that includes a liquid ejection head that ejects liquid toward a workpiece, a multi-joint robot that has a tip that supports the liquid ejection head and changes the relative position of the liquid ejection head with respect to the workpiece, and a detection unit that detects movement of the liquid ejection head in the scanning direction, and includes a step of acquiring speed information regarding the speed of the liquid ejection head based on the detection result of the detection unit, and a step of controlling the ejection timing of the liquid ejection head based on the speed information. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view showing an outline of a three-dimensional object printing device according to a first embodiment. FIG. [Figure 2] FIG. 1 is a block diagram showing the electrical configuration of a three-dimensional object printing device according to a first embodiment. [Figure 3] FIG. 2 is a perspective view showing a schematic configuration of a head unit according to the first embodiment. [Figure 4] FIG. 10 illustrates an example of a printing operation. [Figure 5] 4 is a flowchart showing a printing method according to the first embodiment. [Figure 6] 5 is a flowchart showing the flow of correction processing in the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of acceleration information during execution of a preparatory movement. [Figure 8] 8 is a diagram showing values ​​obtained by simply integrating the acceleration indicated by the acceleration information shown in FIG. 7. FIG. [Figure 9] FIG. 8 is a diagram illustrating low-frequency components of the acceleration information shown in FIG. [Figure 10] FIG. 8 is a diagram illustrating high-frequency components of the acceleration information shown in FIG. [Figure 11] FIG. 11 is a diagram showing an example of speed information based on high-frequency components shown in FIG. [Figure 12] 12 is a diagram showing an example of ejection timing based on the velocity information shown in FIG. 11. FIG. [Figure 13]FIG. 10 is a block diagram showing the electrical configuration of a three-dimensional object printing device according to a second embodiment. [Figure 14] 10 is a flowchart showing the flow of correction processing in the second embodiment. [Figure 15] FIG. 10 is a diagram illustrating an example of acceleration information during execution of a preparatory movement. [Figure 16] FIG. 10 is a diagram illustrating an example of angular velocity information during execution of a preparatory movement. [Figure 17] FIG. 10 is a diagram illustrating an example of acceleration information from which a gravitational acceleration component has been subtracted. [Figure 18] FIG. 18 is a diagram illustrating low-frequency components of the acceleration information shown in FIG. [Figure 19] FIG. 18 is a diagram illustrating high-frequency components of the acceleration information shown in FIG. [Figure 20] FIG. 20 is a diagram showing an example of speed information based on high-frequency components shown in FIG. 19. [Figure 21] 21 is a diagram showing an example of ejection timing based on the velocity information shown in FIG. 20. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the present disclosure will be described below with reference to the accompanying drawings. Note that the dimensions and scale of each part in the drawings may differ from the actual dimensions and are shown schematically to facilitate understanding. Furthermore, the scope of the present disclosure is not limited to these embodiments unless otherwise specified in the following description to the effect that the present disclosure is limited.

[0009] For ease of explanation, the following description will use the mutually intersecting X-axis, Y-axis, and Z-axis as appropriate. Also, hereinafter, one direction along the X-axis is the X1 direction, and the direction opposite the X1 direction is the X2 direction. Similarly, the opposite directions along the Y-axis are the Y1 direction and the Y2 direction. Also, the opposite directions along the Z-axis are the Z1 direction and the Z2 direction.

[0010] Here, the X-axis, Y-axis, and Z-axis correspond to the coordinate axes of a world coordinate system set in a space in which the robot 2 (described later) is installed. Typically, the Z-axis is a vertical axis, and the Z2 direction corresponds to the downward vertical direction. A base coordinate system based on the position of a base 210 (described later) of the robot 2 is associated with the world coordinate system by calibration. For convenience, the following describes an example in which the operation of the robot 2 is controlled using the world coordinate system as the robot coordinate system.

[0011] The Z axis does not have to be a vertical axis. Furthermore, the X axis, Y axis, and Z axis are typically perpendicular to one another, but this is not a limitation and they may not be perpendicular. For example, the X axis, Y axis, and Z axis may intersect each other at an angle between 80° and 100°.

[0012] 1-1. Overview of the 3D printing device 1 is a perspective view showing an outline of a three-dimensional object printing apparatus 1 according to the first embodiment. The three-dimensional object printing apparatus 1 is an apparatus that performs printing on the surface of a three-dimensional workpiece W by an inkjet method.

[0013] The workpiece W has a surface WF to be printed. In the example shown in FIG. 1, the surface WF is a convex curved surface that protrudes in the Z1 direction so as to be parallel to the Y axis. The curvature of the surface WF may vary depending on the position along the X axis, or may be constant over the entire area along the X axis. The printing target may be a surface other than the surface WF among the multiple surfaces of the workpiece W. Furthermore, the size, shape, or installation orientation of the workpiece W is not limited to the example shown in FIG. 1 and may be arbitrary. For example, the surface WF may have a shape that follows a spherical surface.

[0014] As shown in Fig. 1, the three-dimensional object printing device 1 has a robot 2, which is an example of an "articulated robot," a head unit 3, and a controller 5. These will be briefly described below in order, first with reference to Fig. 1.

[0015] The robot 2 is an articulated robot that moves the workpiece W relative to the head unit 3. In the example shown in Fig. 1, the robot 2 is a so-called six-axis vertical articulated robot.

[0016] The robot 2 has a tip E that supports a liquid ejection head 3a (described later) and changes the position of the liquid ejection head 3a relative to the workpiece W. More specifically, as shown in FIG.

[0017] Base 210 is a platform that supports arm 220. In the example shown in Fig. 1, base 210 is fixed by screws or the like to an installation surface such as a floor surface or a base facing in the Z1 direction. The installation surface to which base 210 is fixed may be a surface facing any direction and is not limited to the example shown in Fig. 1, and may be, for example, a wall, a ceiling, a surface of a movable cart, or the like.

[0018] Arm 220 is a six-axis robot arm having a base end attached to base 210 and a tip E that changes its position and posture three-dimensionally relative to the base end. Specifically, arm 220 has arms 221, 222, 223, 224, 225, and 226, which are also called links, and these are connected in this order.

[0019] Arm 221 is connected to base 210 via joint J1 so as to be rotatable around rotation axis O1. Arm 222 is connected to arm 221 via joint J2 so as to be rotatable around rotation axis O2. Arm 223 is connected to arm 222 via joint J3 so as to be rotatable around rotation axis O3. Arm 224 is connected to arm 223 via joint J4 so as to be rotatable around rotation axis O4. Arm 225 is connected to arm 224 via joint J5 so as to be rotatable around rotation axis O5. Arm 226 is connected to arm 225 via joint J6 so as to be rotatable around rotation axis O6.

[0020] Each of the joints J1 to J6 is a mechanism that rotatably connects one of two adjacent members among the base 210 and the arms 221 to 226 to the other. Note that, hereinafter, each of the joints J1 to J6 may be referred to as a "joint J."

[0021] Although not shown in FIG. 1, each of the joints J1 to J6 is provided with a drive mechanism that rotates one of the two corresponding adjacent members relative to the other. The drive mechanism includes, for example, a motor that generates a drive force for the rotation, a reducer that reduces and outputs the drive force, and an encoder such as a rotary encoder that detects the amount of movement, such as the angle of the rotation. The assembly of the drive mechanisms for the joints J1 to J6 corresponds to an arm drive mechanism 2a shown in FIG. 2, which will be described later. The assembly of the encoders for the joints J1 to J6 corresponds to a motion detection unit 2a1 shown in FIG. 2, which will be described later.

[0022] A head unit 3 is attached as an end effector to the arm 226, which is the tip E of the robot 2. Here, the head unit 3 is fixed to the arm 226 by screws or the like.

[0023] The head unit 3 is an assembly having a liquid ejection head 3a that ejects ink, which is an example of a "liquid," toward the workpiece W and a detection unit 3c, and has a first nozzle row NL1 and a second nozzle row NL2.

[0024] The detection unit 3c is a sensor that detects the movement of the liquid ejection head 3a in the scanning direction, and is, for example, an inertial sensor that detects one or both of the acceleration and angular velocity applied to the liquid ejection head 3a. In this embodiment, the detection unit 3c has an acceleration sensor and detects the acceleration applied to the liquid ejection head 3a. The detection unit 3c is not limited to detecting acceleration as long as it can detect a physical quantity corresponding to the speed of the liquid ejection head 3a in the scanning direction. For example, the detection unit 3c may be a sensor such as a tracking sensor that detects the speed or position of the liquid ejection head 3a in the scanning direction. Furthermore, the detection unit 3c may be configured to detect two or more physical quantities corresponding to the speed of the liquid ejection head 3a in the scanning direction, as in the second embodiment described below.

[0025] The ink is not particularly limited, but may be, for example, an ultraviolet curable ink. Note that the ink is not limited to ink containing a coloring material, and may be, for example, ink containing conductive particles such as metal particles as dispersoids for forming wiring, or may be clear ink, or may be a treatment liquid for surface treatment of the workpiece W.

[0026] The controller 5 is a robot controller that controls the driving of the robot 2. Below, the electrical configuration of the three-dimensional object printing apparatus 1 will be described with reference to FIG. 2, including a detailed description of the controller 5.

[0027] 1-2. Electrical configuration of the 3D printing device FIG. 2 is a block diagram showing the electrical configuration of the three-dimensional object printing apparatus 1 according to the first embodiment. FIG. 2 shows the electrical components of the three-dimensional object printing apparatus 1. As shown in FIG. 2, the three-dimensional object printing apparatus 1 has a control unit 8 in addition to the components shown in FIG. 1 described above. The control unit 8 has the function of controlling the operation of the liquid ejection head 3a and the robot 2. In the example shown in FIG. 2, the control unit 8 has a controller 5, a control module 6 communicatively connected to the controller 5, and a computer 7 communicatively connected to the controller 5 and the control module 6. Each part of the control unit 8 will be described below in order with reference to FIG. 2.

[0028] 2 may be divided appropriately, some may be included in other components, or may be integrated with other components. For example, some or all of the functions of the controller 5 or control module 6 may be implemented by a computer 7, or may be implemented by another external device such as a PC (personal computer) connected to the controller 5 via a network such as a LAN (Local Area Network) or the Internet.

[0029] The controller 5 has a function of controlling the driving of the robot 2 and a function of generating a signal D3 for synchronizing the ink ejection operation of the head unit 3 with the operation of the robot 2.

[0030] The controller 5 includes a memory circuit 5a and a processing circuit 5b.

[0031] The storage circuitry 5a stores various programs executed by the processing circuitry 5b and various data processed by the processing circuitry 5b. Note that part or all of the storage circuitry 5a may be included in the processing circuitry 5b.

[0032] The storage circuit 5a stores route information Da.

[0033] The path information Da is used to control the operation of the robot 2 and indicates the target position and target orientation of the liquid ejection head 3a or the head unit 3 along the path along which the liquid ejection head 3a or the head unit 3 should move during printing. Here, the position and orientation of the liquid ejection head 3a are defined by the position and orientation of the tool center point TCP (described later) of the robot 2. Therefore, the path information Da includes position information indicating the target position of the tool center point TCP and orientation information indicating the target orientation of the tool center point TCP. For example, the position information is expressed by multiple coordinate values ​​indicating the target position in the robot coordinate system, and the orientation information is expressed by multiple vectors indicating the target orientation corresponding to the target position. The tool center point TCP is a virtual point whose positional relationship with the liquid ejection head 3a is fixed, and may be located at a distance from the liquid ejection head 3a. The path information Da may also be expressed using a work coordinate system. In this case, the path information Da is used to control the operation of the robot 2 after converting the coordinate values ​​of the work coordinate system into coordinate values ​​of the base coordinate system or the world coordinate system.

[0034] The processing circuit 5b controls the operation of the arm driving mechanism 2a of the robot 2 based on the path information Da, and generates a signal D3.

[0035] Here, the arm drive mechanism 2a is an assembly of drive mechanisms for the aforementioned joints J1 to J6, and for each joint J, it has a motor for driving the joint of the robot 2 and an encoder for detecting the rotation angle of the joint of the robot 2. The assembly of the encoders for the joints J1 to J6 constitutes the motion detection unit 2a1. The motion detection unit 2a1 is provided on the robot 2 and detects the motion of the robot 2. In this way, the three-dimensional object printing device 1 is equipped with the motion detection unit 2a1.

[0036] The processing circuit 5b performs inverse kinematics calculations, which are calculations that convert the path information Da into movement quantities such as the rotation angle and rotation speed of each joint J of the robot 2. The processing circuit 5b then outputs a control signal Sk1 based on the output D1 from each encoder of the movement detection unit 2a1 so that the movement quantities such as the actual rotation angle and rotation speed of each joint J match the aforementioned calculation results based on the path information Da. The control signal Sk1 is a signal for controlling the driving of the motor of the arm drive mechanism 2a. Here, the control signal Sk1 may be corrected by the processing circuit 5b, as necessary, based on the output from a distance sensor (not shown).

[0037] Furthermore, the processing circuit 5b generates a signal D3 based on an output D1 from at least one of the multiple encoders included in the motion detection unit 2a1. For example, the processing circuit 5b generates, as the signal D3, a trigger signal including a pulse at the timing when the output D1 from one of the multiple encoders reaches a predetermined value.

[0038] The control module 6 is a circuit that controls the ink ejection operation of the head unit 3 based on the signal D3 output from the controller 5, and the print data Img and timing information Dt from the computer 7. The control module 6 has a timing signal generation circuit 6a, a power supply circuit 6b, a control circuit 6c, and a drive signal generation circuit 6d.

[0039] The timing signal generating circuit 6a generates a timing signal PTS based on the signal D3 and the timing information Dt. The timing signal generating circuit 6a is a circuit that generates the timing signal PTS at the timing indicated by the timing information Dt, and starts generating the timing signal PTS when the signal D3 is detected.

[0040] By generating such timing signal PTS, the control unit 8 determines the start timing for discharging liquid from the liquid discharge head 3a based on the detection result of the operation detection unit 2a1. This makes it possible to simply synchronize the operation of the robot 2 and the operation of the liquid discharge head 3a. It also makes it possible to improve the accuracy of both the discharge timing of the liquid discharge head 3a and the acquisition timing of the speed information D2b.

[0041] Although not shown, the timing signal generation circuit 6a includes, for example, a clock source, a pre-timing signal generation circuit, and a delay circuit. The clock source is an oscillator such as a crystal oscillator that outputs a clock signal at a constant frequency. The pre-timing signal generation circuit is a timer that generates a pulse every predetermined number of clock cycles of the clock signal from the clock source. The timer starts operating upon detection of signal D3, thereby generating a pre-timing signal synchronized with signal D3. The delay circuit is a timer that generates a pulse every predetermined number of clock cycles of the clock signal from the clock source, based on each pulse of the pre-timing signal from the pre-timing signal generation circuit, and generates a timing signal PTS that is delayed relative to the pre-timing signal from the pre-timing signal generation circuit.

[0042] The power supply circuit 6b receives power from a commercial power supply (not shown) and generates various predetermined potentials. The generated potentials are supplied appropriately to the control module 6 and each component of the head unit 3. For example, the power supply circuit 6b generates a power supply potential VHV and an offset potential VBS. The offset potential VBS is supplied to the head unit 3. The power supply potential VHV is also supplied to the drive signal generation circuit 6d.

[0043] The control circuit 6c generates a control signal SI, a waveform designation signal dCom, a latch signal LAT, a clock signal CLK, and a change signal CNG based on the timing signal PTS. These signals are synchronized with the timing signal PTS. Of these signals, the waveform designation signal dCom is input to the drive signal generation circuit 6d, and the other signals are input to the switch circuit 3e of the head unit 3.

[0044] The control signal SI is a digital signal that specifies the operating state of the drive elements of the liquid ejection head 3a of the head unit 3. Specifically, the control signal SI is a signal that specifies whether or not to supply a drive signal Com (described below) to the drive element based on the print data Img. This specification, for example, specifies whether or not to eject ink from the nozzle corresponding to the drive element, or specifies the amount of ink ejected from the nozzle. The waveform specification signal dCom is a digital signal that defines the waveform of the drive signal Com. The latch signal LAT and change signal CNG are used in conjunction with the control signal SI to specify the drive timing of the drive element, thereby specifying the timing of ink ejection from the nozzle. The clock signal CLK is a reference clock signal synchronized with the timing signal PTS.

[0045] The drive signal generation circuit 6d is a circuit that generates a drive signal Com for driving each drive element of the liquid ejection head 3a of the head unit 3. Specifically, the drive signal generation circuit 6d includes, for example, a DA conversion circuit and an amplifier circuit. In the drive signal generation circuit 6d, the DA conversion circuit converts the waveform designation signal dCom from the control circuit 6c from a digital signal to an analog signal, and the amplifier circuit amplifies the analog signal using the power supply potential VHV from the power supply circuit 6b to generate the drive signal Com. Here, of the waveforms included in the drive signal Com, the signal with the waveform actually supplied to the drive element is the drive pulse PD. The drive pulse PD is supplied from the drive signal generation circuit 6d to the drive element via the switch circuit 3e of the head unit 3.

[0046] Here, the switch circuit 3e is a circuit including a switching element that switches whether or not at least a part of the waveform included in the drive signal Com is to be supplied as the drive pulse PD based on the control signal SI.

[0047] The computer 7 has a function to generate path information Da and timing information Dt, a function to supply information such as the path information Da to the controller 5, and a function to supply information such as print data Img and timing information Dt to the control module 6.

[0048] The computer 7 includes a memory circuit 7a and a processing circuit 7b. In addition, although not shown, the computer 7 includes an input device such as a keyboard or a mouse for accepting operations from a user. The computer 7 may also include a display device such as a liquid crystal panel for displaying information necessary for generating the path information Da and the timing information Dt.

[0049] The storage circuitry 7a stores various programs executed by the processing circuitry 7b and various data processed by the processing circuitry 7b. The storage circuitry 7a includes, for example, one or both of semiconductor memories, such as a volatile memory such as RAM and a nonvolatile memory such as a ROM, EEPROM, or PROM. Note that part or all of the storage circuitry 7a may be included in the processing circuitry 7b.

[0050] The memory circuit 7a stores path information Da, work information Dc, print data Img, acceleration information D2a, speed information D2b, timing information Dt, and a program PR1.

[0051] The work information Dc is data that represents the shape of at least a portion of the workpiece W. Specifically, the work information Dc is, for example, three-dimensional data in STL (Standard Triangulated Language) format or the like that represents the shape of the workpiece W using multiple polygons. The work information Dc includes coordinate information, which is information about the coordinates of each vertex of the polygon, and vector information, which is information about normal vectors that indicate the front and back of the polygon faces. The work information Dc is obtained by converting CAD (computer-aided design) data that represents the three-dimensional shape of the workpiece W as needed. The work information Dc may be expressed using coordinate values ​​in a work coordinate system, or may be expressed as point cloud data using coordinate values ​​in a base coordinate system or a world coordinate system. The work information Dc may also be expressed using mathematical formulas, etc., and the format of the work information Dc may be appropriately converted as needed.

[0052] The print data Img is information indicating an image to be printed on the workpiece W for each path (pass) of the printing path indicated by the path information Da. Here, the image to be ultimately printed on the workpiece W is represented by a collection of dots, which are tiny points, and printing is performed by applying ink droplets corresponding to the dots onto the workpiece W. The image to be printed is composed of an image formed by ink droplets ejected from a first nozzle row NL1 (described below) and an image formed by ink droplets ejected from a second nozzle row NL2 (described below) superimposed on each other. In this embodiment, the print data Img includes first print data for the first nozzle row NL1 (described below) and second print data for the second nozzle row NL2 (described below). The first print data is information indicating an image formed by ink droplets ejected from the first nozzle row NL1 (described below) of the image to be ultimately printed on the workpiece W. On the other hand, the second print data is information indicating an image formed by ink droplets ejected from the second nozzle row NL2 (described below) of the image to be ultimately printed on the workpiece W.

[0053] The acceleration information D2a is information indicating the acceleration of the liquid ejection head 3a in the scanning direction, and is acquired based on the movement information D2. The movement information D2 is information indicating the detection result of the detection unit 3c, and indicates the movement of the liquid ejection head 3a in the scanning direction. The movement information D2 in this embodiment includes the acceleration information D2a. Therefore, the acceleration information D2a in this embodiment is acquired by acquiring the movement information D2.

[0054] The velocity information D2b is information relating to the velocity of the liquid ejection head 3a, and is acquired based on the movement information D2. In this embodiment, the velocity information D2b is generated by performing processing such as integration processing, which will be described later, on the acceleration information D2a.

[0055] The timing information Dt is information indicating the ejection timing of the liquid ejection head 3a, and is generated based on the speed information D2b.

[0056] The program PR1 is a program for executing various processes for generating the timing information Dt.

[0057] The processing circuit 7b realizes the above-mentioned functions by executing programs such as the program PR1, etc. The processing circuit 7b includes, for example, one or more processors such as CPUs.

[0058] The processing circuit 7b executes the program PR1 to perform various processes for generating the timing information Dt. As a result, the processing circuit 7b generates the timing information Dt based on the movement information D2 indicating the detection result of the detection unit 3c. In this embodiment, the processing circuit 7b acquires acceleration information D2a based on the movement information D2 during the execution of a preparatory movement (described below), acquires speed information D2b based on the acceleration information D2a, and generates the timing information Dt based on the speed information D2b.

[0059] In this way, the control unit 8 is capable of performing the preparatory operation and printing operation described below, and acquires speed information D2b regarding the speed of the liquid ejection head 3a based on the detection results of the detection unit 3c, and controls the ejection timing of the liquid ejection head 3a based on the speed information D2b.

[0060] In the three-dimensional object printing device 1 described above, the driving of the robot 2 is controlled based on the path information Da, and the driving of the liquid ejection head 3a is controlled based on the print data Img, timing information Dt, and signal D3, thereby performing a printing operation. During the printing operation, the robot 2 changes the position and posture of the liquid ejection head 3a based on the path information Da, causing the liquid ejection head 3a to eject ink as ink droplets from the liquid ejection head 3a toward the workpiece W at appropriate timing based on the print data Img and signal D3. The ejected ink droplets fly through space and then adhere to the workpiece W. Note that this adhesion of the ink droplets is sometimes referred to as the impact of ink droplets. In this manner, an image based on the print data Img is formed on the workpiece W.

[0061] Furthermore, in the three-dimensional object printing apparatus 1, a preparatory operation and a correction process are executed prior to the printing operation, as described below. The preparatory operation is similar to the printing operation except that temporary timing information Dt is used. However, during the preparatory operation, ink droplets do not need to be ejected from the liquid ejection head 3a. The ejection timing indicated by the temporary timing information Dt is, for example, a fixed time interval. During the correction process, the temporary timing information Dt is corrected based on the movement information D2 during the execution of the preparatory operation, thereby generating timing information Dt to be used in the printing operation. This results in timing information Dt that reduces deviations in the landing positions of ink droplets due to operational errors of the robot 2, etc.

[0062] In this way, in the three-dimensional object printing device 1, the ejection timing of the liquid ejection head 3a is controlled based on the speed information D2b related to the speed of the liquid ejection head 3a, so degradation of print quality can be reduced even if speed variations occur in the scanning direction of the liquid ejection head 3a due to operational errors of the robot 2, etc. This makes it possible to improve print quality compared to conventional methods.

[0063] In contrast, in a configuration in which the ejection timing of the liquid ejection head 3a is at fixed time intervals, if variations in the speed of the liquid ejection head 3a in the scanning direction occur due to operational errors of the robot 2, the intervals at which the ink ejected as droplets from the liquid ejection head 3a hits the workpiece W will vary, or the ink ejected as droplets from the liquid ejection head 3a will merge, resulting in a decrease in print quality.

[0064] 1-3.Head unit configuration FIG. 3 is a perspective view showing a schematic configuration of the head unit 3 of the first embodiment. For convenience, the following description will be made using the mutually intersecting a-axis, b-axis, and c-axis as appropriate. In the following description, one direction along the a-axis is the a1 direction, and the direction opposite the a1 direction is the a2 direction. Similarly, the opposite directions along the b-axis are the b1 direction and the b2 direction. Furthermore, the opposite directions along the c-axis are the c1 direction and the c2 direction.

[0065] Here, the a-axis, b-axis, and c-axis correspond to the coordinate axes of the tool coordinate system set in the head unit 3, and the relative position and orientation relationship with the world coordinate system or the robot coordinate system changes depending on the operation of the robot 2. In the example shown in FIG. 3, the c-axis is an axis parallel to the rotation axis O6. The a-axis, b-axis, and c-axis are typically perpendicular to each other, but are not limited to this. For example, they may intersect at an angle between 80° and 100°. The tool coordinate system and the base coordinate system or the robot coordinate system are associated with each other by calibration.

[0066] The tool coordinate system is set with the tool center point TCP as its reference. Therefore, the position and orientation of the liquid ejection head 3a are determined with the tool center point TCP as its reference. In the example shown in FIG. 3, the tool center point TCP is located at the center of the nozzle surface FN. Note that the position of the tool center point TCP is not limited to the example shown in FIG. 3, and may be, for example, a position spaced apart from the liquid ejection head 3a in the ink ejection direction DE. In this case, a printing path RU, which will be described later, is set on the surface of the workpiece W.

[0067] As described above, the head unit 3 has a liquid ejection head 3a and a detection unit 3c. These are supported by a support 3f indicated by a two-dot chain line in FIG. 3. In the example shown in FIG. 3, the head unit 3 has one liquid ejection head 3a, but the number is not limited to that shown in FIG. 3 and may be two or more. The head unit 3 may also have elements other than the liquid ejection head 3a and the detection unit 3c, such as a pressure adjustment valve that adjusts the pressure of the ink in the liquid ejection head 3a, and a light source that emits energy such as light, heat, an electron beam, or radiation to harden or solidify the ink on the workpiece W.

[0068] The support 3f is attached to the arm 226 described above. Therefore, the liquid ejection head 3a and the detection unit 3c are collectively supported on the arm 226 by the support 3f. Therefore, the relative positions of the liquid ejection head 3a and the detection unit 3c with respect to the arm 226 are fixed. In the example shown in FIG. 3, the detection unit 3c is disposed in the b2 direction with respect to the liquid ejection head 3a. Note that the position of the detection unit 3c is not limited to the example shown in FIG. 3 and can be arbitrarily positioned.

[0069] The liquid ejection head 3a has a nozzle surface FN and a plurality of nozzles N opening in the nozzle surface FN. The nozzle surface FN is the nozzle surface on which the nozzles N open, and is made of, for example, a material such as silicon (Si) or metal. Alternatively, if another member is arranged as a component of the head unit 3 on a plane extending from the nozzle surface, the nozzle surface FN is a surface formed by the plate surface of the nozzle plate and the surface of the other member. The plurality of nozzles N are divided into a first nozzle row NL1 and a second nozzle row NL2, which are arranged at intervals along the a-axis. Each of the first nozzle row NL1 and the second nozzle row NL2 is a collection of a plurality of nozzles N linearly arranged in the nozzle row direction DN, which is the direction along the b-axis. Here, elements associated with each nozzle N of the first nozzle row NL1 and elements associated with each nozzle N of the second nozzle row NL2 in the liquid ejection head 3a are configured to be approximately symmetrical to each other in the direction along the a-axis.

[0070] The direction in which the first nozzle row NL1 and the second nozzle row NL2 are aligned is along the a-axis and is parallel to the main scanning direction DS, which is the direction in which the liquid ejection head 3a moves during the preliminary operation and the printing operation. The first nozzle row NL1 and the second nozzle row NL2 constitute the nozzle row NL.

[0071] Although not shown, the liquid ejection head 3a has a piezoelectric element, which is a drive element, and a cavity that contains ink for each nozzle N. Here, the piezoelectric element changes the pressure in the cavity corresponding to the piezoelectric element, thereby ejecting ink from the nozzle corresponding to the cavity in the ejection direction DE, which is the direction c2. Such a liquid ejection head 3a can be obtained, for example, by bonding together, with an adhesive, multiple substrates, such as silicon substrates, that have been appropriately processed by etching or the like. Note that instead of the piezoelectric element, a heater that heats the ink in the cavity may be used as the drive element for ejecting ink from the nozzle.

[0072] The detector 3c detects the acceleration of the liquid ejection head 3a in the scanning direction. The detector 3c has, for example, a three-axis acceleration sensor corresponding to the a-axis, b-axis, and c-axis. The detector 3c may also include a sensor other than an acceleration sensor, such as an angular velocity sensor.

[0073] 1-4.Printing method 4 is a diagram showing an example of a printing operation, in which printing is performed on the surface WF of the workpiece W placed at a position further away from the robot 2 in the X2 direction.

[0074] During the printing operation, ink is appropriately ejected from the nozzles N based on the print data Img and timing information Dt and applied to the workpiece W, thereby printing with ink on the workpiece W. At this time, the robot 2 changes the position and posture of the liquid ejection head 3a based on the path information Da. Thus, the printing operation is the operation of the three-dimensional object printing device 1 in which the robot 2 moves the workpiece W and the head unit 3 relative to each other in the main scanning direction DS, while the head unit 3 ejects ink droplets at multiple different times. Through this printing operation, the liquid ejection head 3a moves along a printing path RU based on the position information in the path information Da, while maintaining a predetermined posture with respect to the surface WF based on the posture information in the path information Da. The printing path RU is the path from position PS to position PE.

[0075] Here, the control unit 8 can print the image represented by the print data Img over multiple passes as needed. In this case, the image represented by the print data Img is formed by a collection of multiple images corresponding to the multiple passes. The multiple images are aligned in the sub-scanning direction that intersects with the main scanning direction DC, and have an overlapping area where two adjacent images from the multiple images partially overlap each other. In the overlapping area, the ejection operation from nozzle N is controlled so that the recording ratio by nozzle N is shared between one pass and the other pass.

[0076] 4, the printing path RU extends along the X-axis when viewed in the Z2 direction. That is, the main scanning direction DS is parallel to the X-axis when viewed in the direction along the Z-axis. During the printing operation, the robot 2 mainly operates three of the joints J: joint J2, joint J3, and joint J5. By aligning the rotation axes of the three joints J parallel to the Y-axis and operating only these three joints J, the liquid ejection head 3a can be moved in the main scanning direction DS while reducing meandering in directions intersecting the main scanning direction DS compared to an embodiment in which four or more joints J are operated.

[0077] The robot 2 may perform a printing operation by operating four or more of the six joints J. In this case, the installation position and installation posture of the workpiece W are not limited to the example shown in FIG. 4 and are arbitrary. The printing path RU is determined according to the shape, printing range, installation position, installation posture, etc. of the workpiece W, and is not limited to the example shown in FIG. 4 and is arbitrary. The positions and number of joints J to be operated in a printing operation are determined according to the printing path RU and the posture of the head unit 3 relative to the workpiece W during the printing operation.

[0078] In the above printing operation, the operation of the robot 2 is controlled so that the head unit 3 moves at a constant speed along the printing path RU. However, even if the head unit 3 is moved at such a constant speed, errors in the movement speed actually occur. For this reason, if the ejection timing of the liquid ejection head 3a is at regular time intervals, such speed errors can degrade the quality of the printed image. Furthermore, when printing an image represented by the print data Img in multiple passes, there are problems such as noticeable differences in shading between overlapping areas of the image corresponding to each pass and non-overlapping areas, and print quality degrades due to differences in ejection timing between images corresponding to two adjacent passes caused by such errors.

[0079] Therefore, in order to prevent such a decrease in image quality, the timing information Dt is corrected in the three-dimensional object printing apparatus 1. This point will be described in detail below.

[0080] 5 is a flowchart showing the printing method according to the first embodiment. The printing method includes steps S10, S20, and S30 in this order.

[0081] In step S10, the control unit 8 executes a preparatory operation of scanning the liquid ejection head 3a along the printing path RU, and acquires acceleration information D2a.

[0082] At this time, the control unit 8 determines the timing to acquire the speed information D2b based on the detection result of the motion detection unit 2a1. This improves the accuracy of the timing to acquire the speed information D2b. That is, it is possible to acquire the speed information D2b synchronized with the motion of the robot 2 with high accuracy.

[0083] In step S20, the control unit 8 generates timing information Dt based on the acceleration information D2a during the execution of the preparatory movement in step S10.

[0084] In step S30, the control unit 8 executes a printing operation in which the liquid ejection head 3a is scanned along the printing path RU and ejects liquid from the liquid ejection head 3a toward the workpiece W. At this time, the control unit 8 corrects the ejection timing of the liquid ejection head 3a using timing information Dt based on the acceleration information D2a during the preparatory operation of step S10. Therefore, the control unit 8 controls the ejection timing of the liquid ejection head 3a during the printing operation of step S30 based on the acceleration information D2a during the preparatory operation of step S10. As a result, the ejection timing during the printing operation of step S30 is corrected based on the acceleration information D2a when the liquid ejection head 3a is actually scanned along the printing path RU, thereby making it possible to suitably improve print quality.

[0085] In step S30, the control unit 8 determines, based on the detection result of the operation detection unit 2a1, the timing to start the printing operation in which liquid is ejected from the liquid ejection head 3a toward the workpiece W. This makes it possible to synchronize the operation of the robot 2 with the start timing of the printing operation, thereby reducing discrepancies in the printing position and the start timing of the printing operation.

[0086] 6 is a flowchart showing the flow of the correction process in step S20 in the first embodiment. Step S20 includes step S21 and step S22, in this order. As a result, the printing method using the three-dimensional object printing apparatus 1 includes step S21 and step S22.

[0087] Step S21 is a process of acquiring speed information D2b relating to the speed of the liquid ejection head 3a based on the detection result of the detection unit 3c. In this embodiment, step S21 includes step S21a, step S21b, and step S21c, in this order.

[0088] In step S21a, the control unit 8 acquires acceleration information D2a relating to the acceleration of the liquid ejection head 3a based on the detection result of the detection unit 3c. The detection result of the detection unit 3c is acquired as movement information D2.

[0089] In step S21b, the control unit 8 calculates the scanning speed by performing arithmetic processing on the acceleration information D2a using a high-pass filter. As a result, even if the acceleration information D2a contains information regarding errors, such as changes in the direction of gravitational acceleration relative to the liquid ejection head 3a due to changes in the attitude of the liquid ejection head 3a, the errors can be easily removed and a highly accurate scanning speed can be calculated. By executing step S21b in this manner, the control unit 8 generates speed information D2b.

[0090] In step S21c, the control unit 8 calculates the scanning speed, which is the speed in the scanning direction of the liquid ejection head 3a moved along the printing path RU, based on the acceleration information D2a. As a result, in step S21c, the control unit 8 obtains speed information D2b based on the acceleration information D2a.

[0091] Step S22 is a process of controlling the ejection timing of the liquid ejection head 3a based on the speed information D2b. In this embodiment, in step S22, the ejection timing of the liquid ejection head 3a is controlled based on the speed information D2b that is based on the acceleration information D2a. By executing step S22 in this manner, the control unit 8 generates timing information Dt. This allows for rapid and highly accurate acceleration information D2a to be obtained.

[0092] Thus, in step S22, the control unit 8 controls the ejection timing of the liquid ejection head 3a during the printing operation in step S30 based on the scanning speed, which is the speed in the scanning direction of the liquid ejection head 3a moved along the printing path RU. This allows the ejection timing of the liquid ejection head 3a to be suitably controlled in accordance with the shape of the printing path RU or the workpiece W. When printing on a workpiece W having a non-planar surface as the printing target, the position and orientation of the liquid ejection head 3a must be changed in accordance with the shape of the printing surface. In this case, the component of the gravitational acceleration acting on the liquid ejection head 3a in the scanning direction changes. Therefore, even if the acceleration detected by the acceleration sensor serving as the detection unit 3c is converted directly into a speed, an error will occur between the acceleration and the actual speed of the liquid ejection head 3a in the scanning direction.

[0093] FIG. 7 is a diagram showing an example of acceleration information D2a during the preparatory operation of step S20. In FIG. 7, the vertical axis represents acceleration in the scanning direction indicated by the acceleration information D2a during the preparatory operation of step S20, and the horizontal axis represents time. Here, the acceleration in the scanning direction indicated by the acceleration information D2a is a detection value of the detection unit 3c along the detection axis along the scanning direction. This detection axis is, for example, acceleration in the direction along the a-axis shown in FIG. 3 described above. Note that FIG. 7 shows acceleration information D2a when the liquid ejection head 3a is moved along a printing path RU along a convexly curved printing surface as shown in FIG. 3 described above. This acceleration information D2a is acquired in step S21a described above.

[0094] Fig. 8 is a diagram showing values ​​obtained by simply integrating the acceleration indicated by the acceleration information D2a shown in Fig. 7. In Fig. 8, the vertical axis represents values ​​obtained by simply integrating the acceleration indicated by the acceleration information D2a shown in Fig. 7, and the horizontal axis represents time.

[0095] For example, when the liquid ejection head 3a is moved along the printing path RU as shown in FIG. 4, not only the position of the liquid ejection head 3a but also the attitude of the liquid ejection head 3a changes. Therefore, the detection value of the detection axis along the scanning direction of the detector 3c includes error components such as acceleration due to movement of the liquid ejection head 3a in the scanning direction, as well as acceleration due to changes in the attitude of the liquid ejection head 3a. The error components include the scanning direction component of gravitational acceleration that changes due to changes in the attitude of the liquid ejection head 3a. Hereinafter, this error component will also be referred to as a noise component.

[0096] Therefore, even if the liquid ejection head 3a moves at an approximately constant speed along the printing path RU, if the acceleration indicated by the acceleration information D2a shown in Figure 7 is simply integrated, the value obtained by the integration process will be significantly affected by the error component, as shown in Figure 8.

[0097] In this embodiment, the error due to the gravitational acceleration acting on the liquid ejection head 3a is larger than the other error components. Therefore, as shown in FIG. 7, at the print start position on the print path RU, the scanning direction component of the gravitational acceleration acting on the liquid ejection head 3a is negative, resulting in a negative acceleration in the scanning direction. On the other hand, at the print end position on the print path RU, the scanning direction component of the gravitational acceleration is positive, resulting in a positive acceleration in the scanning direction. Thus, in this embodiment, fluctuations in the scanning direction component of the gravitational acceleration acting on the liquid ejection head 3a due to changes in the orientation of the liquid ejection head 3a significantly affect the acceleration. Therefore, simply integrating the acceleration indicated by the acceleration information D2a does not yield the correct speed in the scanning direction.

[0098] Fig. 9 is a diagram showing the low-frequency components of acceleration information D2a shown in Fig. 7. Fig. 10 is a diagram showing the high-frequency components of acceleration information D2a shown in Fig. 7. In Fig. 9, the vertical axis represents the low-frequency components of acceleration information D2a shown in Fig. 7, and the horizontal axis represents time. In Fig. 10, the vertical axis represents the high-frequency components of acceleration information D2a shown in Fig. 7, and the horizontal axis represents time.

[0099] The graphs in FIGS. 9 and 10 are part of the acceleration information D2a shown in FIG. 7, and show the acceleration during the period from when the liquid ejection head 3a starts to move along the printing path RU until it stops.

[0100] The fluctuations in gravitational acceleration due to the error components described above occur gradually because they are caused by changes in the posture of the liquid ejection head 3a, which moves at a nearly constant speed along the printing path RU. Therefore, the fluctuations in gravitational acceleration appear in a relatively low frequency range. As shown in Figure 9, the fluctuations in gravitational acceleration appear in the low frequency components of acceleration in the scanning direction.

[0101] In contrast, fluctuations in acceleration due to movement of the liquid ejection head 3a in the scanning direction occur in shorter cycles than fluctuations in gravitational acceleration because they are based on factors such as operational errors in the joints J of the robot 2. Therefore, fluctuations in acceleration due to movement of the liquid ejection head 3a in the scanning direction appear in a relatively high frequency range. As shown in Figure 10, the fluctuations in acceleration due to movement of the liquid ejection head 3a in the scanning direction appear in the high frequency components of the acceleration in the scanning direction.

[0102] Therefore, in the aforementioned step S21b, a calculation process using a high-pass filter is performed on the acceleration information D2a. As a result, the aforementioned error components, which are low-frequency components, are removed as noise components, and high-frequency components are extracted from the acceleration indicated by the acceleration information D2a, as shown in FIG. 10. The cutoff frequency of the high-pass filter is determined depending on the movement speed of the robot 2, and is not particularly limited, but is, for example, approximately 30 Hz to 100 Hz. The calculation process may be analog or digital.

[0103] Here, the fluctuations in gravitational acceleration caused by changes in the attitude of the liquid ejection head 3a, which are the larger of the error components, appear in a relatively low frequency range, so this error component can be removed by performing calculation processing using this high-pass filter.

[0104] Fig. 11 is a diagram showing an example of speed information D2b based on the high frequency components shown in Fig. 10. In Fig. 11, the vertical axis represents a value obtained by integrating the high frequency components shown in Fig. 10, and the horizontal axis represents time.

[0105] In step S21c, an integration process is performed on the high-frequency components extracted in step S21b, thereby calculating the scanning speed, which is the speed in the scanning direction of the liquid ejection head 3a moved along the printing path RU, as shown in Fig. 11. In this way, in step S21c, the scanning speed is calculated based on the acceleration information D2a. As a result, speed information D2b indicating the scanning speed is obtained.

[0106] Fig. 12 is a diagram showing an example of the ejection timing based on Fig. 11. In Fig. 12, the vertical axis shows a correction value for correcting the ejection interval, with the ejection interval at which ink droplets are ejected from the liquid ejection head 3a in the virtual timing information Dt set to 0. The positive side of the vertical axis shows a correction value that widens the ejection interval, and the negative side of the vertical axis shows a correction value that narrows the ejection interval. The horizontal axis shows the number of times ink is ejected from the liquid ejection head 3a during a printing operation.

[0107] In step S22, the ejection timing of the liquid ejection head 3a is calculated based on the speed information D2b so as to cancel out the fluctuation in the scanning speed indicated by the speed information D2b.

[0108] Specifically, when the speed at which the liquid ejection head 3a moves is high, the intervals at which ink droplets land are increased. Therefore, when the speed at which the liquid ejection head 3a moves is higher than a predetermined threshold, the ejection timing is corrected to narrow the ejection intervals. On the other hand, when the speed at which the liquid ejection head 3a moves is low, the intervals at which ink droplets land are reduced. Therefore, when the speed at which the liquid ejection head 3a moves is lower than a predetermined threshold, the ejection timing is corrected to widen the ejection intervals.

[0109] By correcting the intervals in the provisional timing information Dt in this way, the ejection timing of the liquid ejection head 3a during the execution of the printing operation in step S30 is calculated.

[0110] As described above, in the three-dimensional object printing device 1, the ejection timing of the liquid ejection head 3a is controlled based on the speed information D2b related to the speed of the liquid ejection head 3a. Therefore, even if variations in the speed of the liquid ejection head 3a in the scanning direction occur due to operational errors of the robot 2 or the like, degradation of print quality can be reduced. This improves print quality compared to conventional methods. Furthermore, even when printing an image represented by the print data Img in multiple passes, degradation of print quality due to noticeable differences in shading between overlapping areas and non-overlapping areas of the images corresponding to each pass or differences in scanning speed between images corresponding to two adjacent passes can be reduced.

[0111] 2. Second embodiment A second embodiment of the present disclosure will be described below. In the following exemplary embodiment, for elements whose actions and functions are similar to those of the first embodiment, the reference numerals used in the description of the first embodiment will be used, and detailed descriptions of each element will be omitted as appropriate.

[0112] 13 is a block diagram showing the electrical configuration of a three-dimensional object printing device 1A according to the second embodiment. The three-dimensional object printing device 1A is configured similarly to the three-dimensional object printing device 1 of the first embodiment, except that it uses program PR2 instead of program PR1 of the first embodiment and that the detection unit 3c is capable of detecting acceleration and angular velocity.

[0113] The detection unit 3c of this embodiment includes an angular velocity sensor and is capable of detecting the angular velocity applied to the liquid ejection head 3a. The angular velocity sensor is, for example, a three-axis angular velocity sensor. Angular velocity information D2c is stored in the memory circuit 7a of this embodiment. The angular velocity information D2c is information indicating the angular velocity applied to the liquid ejection head 3a and is acquired based on the movement information D2. The movement information D2 of this embodiment includes angular velocity information D2c in addition to acceleration information D2a. Therefore, the acceleration information D2a and angular velocity information D2c of this embodiment are acquired by acquiring the movement information D2.

[0114] The processing circuitry 7b of this embodiment executes the program PR2 to perform various processes for generating timing information Dt. As a result, the processing circuitry 7b generates the timing information Dt based on movement information D2 indicating the detection result of the detection unit 3c. In this embodiment, the processing circuitry 7b acquires acceleration information D2a and angular velocity information D2c based on the movement information D2 during the execution of a preparatory movement (described below), acquires velocity information D2b based on the movement information D2 and the angular velocity information D2c, and generates the timing information Dt based on the velocity information D2b.

[0115] 14 is a flowchart showing the flow of correction processing in Embodiment 2. Step S20 of the three-dimensional object printing apparatus 1A includes steps S21A and S22.

[0116] Step S21A is the same as step S21 in the first embodiment, except for the addition of steps S21d and S21e. However, step S21a in this embodiment acquires angular velocity information D2c in addition to acceleration information D2a based on movement information D2. Thus, in step S21a, control unit 8 acquires angular velocity information D2c related to the angular velocity of liquid ejection head 3a based on the detection result of detection unit 3c.

[0117] After step S21a, in step S21d, the control unit 8 calculates the gravitational acceleration acting on the liquid ejection head 3a based on the angular velocity information D2c. As a result, even if the acceleration information D2a contains information relating to an error such as a change in the direction of the gravitational acceleration relative to the liquid ejection head 3a due to a change in the attitude of the liquid ejection head 3a, the error can be easily removed, and a highly accurate scanning speed can be calculated.

[0118] After step S21d, in step S21e, control unit 8 subtracts the gravitational acceleration calculated in step S21d from the acceleration indicated by acceleration information D2a, thereby removing the gravitational acceleration component included in the acceleration indicated by acceleration information D2a.

[0119] After step S21e, steps S21b and S21c are executed in this order, similar to the first embodiment.

[0120] Fig. 15 is a diagram showing an example of acceleration information D2a during execution of the preparatory movement. In Fig. 15, the vertical axis represents acceleration in the scanning direction indicated by acceleration information D2a during execution of the preparatory movement in step S20, and the horizontal axis represents time. In step S21a of this embodiment, acceleration information D2a as shown in Fig. 15 is obtained, as in the first embodiment.

[0121] The acceleration in the scanning direction shown in FIG. 15 includes not only the acceleration of the liquid ejection head 3a when it is scanned, but also a component of the gravitational acceleration acting on the liquid ejection head 3a along the scanning direction.

[0122] 16 is a diagram showing an example of angular velocity information D2c during the execution of the preparatory movement. In FIG. 16, the vertical axis represents the angular velocity indicated by the angular velocity information D2c during the execution of the preparatory movement of step S20, and the horizontal axis represents time. The angular velocity is the angular velocity around the b-axis, which is the pitching axis of the liquid ejection head 3a.

[0123] The angular velocity shown in FIG. 16 is generated in step S21d based on movement information D2 indicating the detection result of the detector 3c.

[0124] 17 is a diagram showing an example of acceleration information D2a obtained by subtracting the gravitational acceleration component from angular velocity information D2c, where the vertical axis represents the acceleration indicated by acceleration information D2a corrected by subtracting the gravitational acceleration component from angular velocity information D2c, and the horizontal axis represents time.

[0125] In step S21d, the gravitational acceleration component in the scanning direction acting on the liquid ejection head 3a is calculated based on the angular velocity information D2c.

[0126] In step S21e, the acceleration information D2a is corrected by subtracting the gravitational acceleration calculated in step S21d from the acceleration in the scanning direction indicated by the acceleration information D2a, as shown in Fig. 17. That is, in step S21e, the acceleration of the liquid ejection head 3a in the scanning direction is calculated with the gravitational acceleration component removed.

[0127] Fig. 18 is a diagram showing low-frequency components of acceleration information D2a shown in Fig. 17. Fig. 19 is a diagram showing high-frequency components of acceleration information D2a shown in Fig. 17. Fig. 20 is a diagram showing an example of speed information D2b based on the high-frequency components shown in Fig. 19. Fig. 21 is a diagram showing an example of ejection timing based on speed information D2b shown in Fig. 20.

[0128] The acceleration information D2a after step S21e may also contain low-frequency components as shown in Fig. 18 and high-frequency components as shown in Fig. 19. Therefore, in this embodiment, in step S21b, a calculation process using a high-pass filter is performed on the acceleration information D2a after step S21e. As a result, the above-mentioned error components, which are low-frequency components, are removed as noise components.

[0129] Thereafter, as in the first embodiment, steps S21c and S22 are executed in this order to calculate the scanning speed, which is the speed in the scanning direction of the liquid ejection head 3a moved along the printing path RU, as shown in FIG. 20, and then, based on the speed information D2b, the ejection timing of the liquid ejection head 3a is corrected so as to cancel out fluctuations in the scanning speed indicated by the speed information D2b.

[0130] As described above, in step S21A, the control unit 8 calculates the speed of the liquid ejection head 3a in the scanning direction based on the acceleration information D2a and the gravitational acceleration. As a result, the ejection timing during the printing operation in step S30 is corrected based on the acceleration information D2a obtained when the liquid ejection head 3a is actually scanned along the printing path RU, thereby making it possible to suitably improve print quality.

[0131] Furthermore, in steps S21A and S22, the control unit 8 controls the ejection timing of the liquid ejection head 3a based on the angular velocity information D2c and the velocity information D2b. This allows the scanning speed to be calculated with high precision based on the acceleration information D2a. As a result, the ejection timing of the liquid ejection head 3a can be more appropriately controlled.

[0132] 3. Variations Each of the above-mentioned exemplary embodiments can be modified in various ways. Specific modified embodiments that can be applied to each of the above-mentioned embodiments are exemplified below. Two or more embodiments arbitrarily selected from the following examples can be appropriately combined within the scope of not contradicting each other.

[0133] 3-1. Variation 1 In the above-described embodiment, the movement direction of the liquid ejection head 3a when performing a printing operation is the X1 direction when viewed along the Z axis, but this is not limiting. For example, when viewed along the Z axis, the movement direction of the liquid ejection head 3a when performing a printing operation may be the X2 direction, when viewed along the Z axis, the movement direction of the liquid ejection head 3a when performing a printing operation may be a direction perpendicular to the X axis when viewed along the Z axis, or when viewed along the Z axis, the movement direction of the liquid ejection head 3a when performing a printing operation may be a direction inclined to both the X axis and the Y axis when viewed along the Z axis.

[0134] 3-2. Variation 2 In the above-described embodiment, a configuration using a six-axis vertical multi-axis robot is exemplified as the robot, but the configuration is not limited to this. The robot may be, for example, a multi-joint robot other than a six-axis robot. Furthermore, the arm of the robot may have an extension mechanism or a linear motion mechanism in addition to a joint formed by a rotation mechanism. However, from the viewpoint of balancing the print quality during printing operations and the degree of freedom of the robot's operation during non-printing operations, it is preferable that the robot be a multi-axis robot with six or more axes.

[0135] 3-3. Variation 3 In the above-described embodiment, the head is fixed to the robot using screws or the like, but is not limited to this. For example, the head may be fixed to the robot by gripping it with a gripping mechanism such as a hand attached as an end effector of the robot.

[0136] 3-4. Variation 4 In the above-described embodiment, a configuration in which printing is performed using one type of ink is exemplified, but this is not limited to this configuration, and the present disclosure can also be applied to a configuration in which printing is performed using two or more types of ink. Furthermore, the number of nozzle rows is not limited to two, and may be three or more.

[0137] 3-5. Variation 5 In the above embodiment, the acceleration information is obtained based on the movement information obtained by the preparatory operation, but the preparatory operation may be omitted and the acceleration information may be obtained based on the movement information during the printing operation. In this case, the ejection timing of the liquid ejection head 3a is corrected in real time using timing information based on the acceleration information obtained during the printing operation.

[0138] 4. Notes A summary of this disclosure is provided below.

[0139] (Appendix 1) A first aspect, which is a preferred example of a three-dimensional object printing device of the present disclosure, comprises a liquid ejection head that ejects liquid toward a workpiece, a multi-joint robot that has a tip that supports the liquid ejection head and changes the position of the liquid ejection head relative to the workpiece, a detection unit that detects the movement of the liquid ejection head in the scanning direction, and a control unit that controls the operation of the liquid ejection head and the multi-joint robot, wherein the control unit obtains speed information regarding the speed of the liquid ejection head based on the detection result of the detection unit, and controls the ejection timing of the liquid ejection head based on the speed information.

[0140] In the above-described aspect, the ejection timing of the liquid ejection head is controlled based on speed information relating to the speed of the liquid ejection head, so that even if speed variations occur in the scanning direction of the liquid ejection head due to operational errors of the articulated robot, degradation of print quality can be reduced, resulting in improved print quality compared to conventional methods.

[0141] In contrast, in a configuration in which the ejection timing of the liquid ejection head is at fixed time intervals, if variations in the speed of the liquid ejection head in the scanning direction occur due to operational errors of the articulated robot, the intervals at which the liquid ejected as droplets from the liquid ejection head hits the workpiece will vary, or the liquid ejected as droplets from the liquid ejection head will combine, resulting in a decrease in print quality.

[0142] (Note 2) In a second aspect, which is a preferred example of the first aspect, the detection unit detects the acceleration of the liquid ejection head in the scanning direction, and the control unit obtains acceleration information related to the acceleration of the liquid ejection head based on the detection result of the detection unit, obtains the velocity information based on the acceleration information, and controls the ejection timing of the liquid ejection head based on the velocity information. In the above aspect, acceleration information can be obtained quickly and with high accuracy.

[0143] (Supplementary Note 3) In a third aspect, which is a preferred example of the second aspect, the control unit is capable of executing a preparatory operation of scanning the liquid ejection head along a printing path, and a printing operation of scanning the liquid ejection head along the printing path and ejecting liquid from the liquid ejection head toward the workpiece, and controls the ejection timing of the liquid ejection head during the printing operation based on the acceleration information during the execution of the preparatory operation. In the above aspect, the ejection timing during the printing operation is corrected based on the acceleration information when the liquid ejection head is actually scanned along the printing path, thereby making it possible to suitably improve print quality.

[0144] (Supplementary Note 4) In a fourth aspect, which is a preferred example of the third aspect, the control unit calculates a scanning speed, which is the speed in the scanning direction of the liquid ejection head moved along the printing path, based on the acceleration information, and controls the ejection timing of the liquid ejection head during the printing operation based on the scanning speed. In the above aspect, the ejection timing of the liquid ejection head can be suitably controlled according to the shape of the printing path or the workpiece. Here, when printing on a workpiece having a non-planar surface as the printing target, the position and orientation of the liquid ejection head must be changed according to the shape of the printing surface. In this case, because the direction of gravitational acceleration relative to the liquid ejection head changes, even if the acceleration detected by the acceleration sensor serving as the detection unit is directly converted to a speed, an error will occur between the acceleration and the speed of the liquid ejection head in the scanning direction.

[0145] (Supplementary Note 5) In a fifth aspect, which is a preferred example of the fourth aspect, the control unit calculates the scanning speed by performing arithmetic processing on the acceleration information using a high-pass filter. In this aspect, even if the acceleration information contains information regarding errors such as changes in the direction of gravitational acceleration relative to the liquid ejection head due to changes in the attitude of the liquid ejection head, the errors can be easily removed, and a highly accurate scanning speed can be calculated.

[0146] (Supplementary Note 6) In the sixth aspect, which is a preferred example of any of the second to fifth aspects, the detection unit can detect an angular velocity acting on the liquid ejection head, and the control unit acquires angular velocity information relating to the angular velocity of the liquid ejection head based on the detection result of the detection unit, and controls the ejection timing of the liquid ejection head based on the angular velocity information and the velocity information. In this aspect, the scanning speed can be calculated with high precision based on acceleration information. As a result, the ejection timing of the liquid ejection head can be more suitably controlled.

[0147] (Supplementary Note 7) In a seventh aspect, which is a preferred example of the sixth aspect, the control unit calculates the gravitational acceleration acting on the liquid ejection head based on the angular velocity information, and calculates the velocity of the liquid ejection head in the scanning direction based on the acceleration information and the gravitational acceleration. In the above aspect, the ejection timing during execution of a printing operation is corrected based on acceleration information obtained when the liquid ejection head is actually scanned along a printing path, thereby making it possible to suitably improve print quality.

[0148] (Supplementary Note 8) In an eighth aspect, which is a preferred example of any of the first to seventh aspects, the articulated robot further includes a motion detection unit that is provided in the articulated robot and detects the motion of the articulated robot, and the control unit determines the start timing of liquid ejection from the liquid ejection head based on the detection result of the motion detection unit. In this aspect, the motion of the robot and the motion of the liquid ejection head can be easily synchronized. Furthermore, the accuracy of both the ejection timing of the liquid ejection head and the timing of acquiring speed information can be improved.

[0149] (Supplementary Note 9) In a ninth aspect which is a preferred example of the eighth aspect, the control unit determines the timing to acquire the speed information based on the detection result of the motion detection unit. In the above aspect, the accuracy of the timing to acquire the speed information can be improved.

[0150] (Appendix 10) A tenth aspect, which is a preferred example of the printing method of the present disclosure, is a printing method using a three-dimensional printing device that includes a liquid ejection head that ejects liquid toward a workpiece, an articulated robot that has a tip that supports the liquid ejection head and changes the position of the liquid ejection head relative to the workpiece, and a detection unit that detects movement of the liquid ejection head in the scanning direction, and includes the steps of: acquiring speed information regarding the speed of the liquid ejection head based on the detection result of the detection unit; and controlling the ejection timing of the liquid ejection head based on the speed information.

[0151] In the above-described aspect, the ejection timing of the liquid ejection head is controlled based on speed information relating to the speed of the liquid ejection head, so that even if speed variations occur in the scanning direction of the liquid ejection head due to operational errors of the articulated robot, degradation of print quality can be reduced, resulting in improved print quality compared to conventional methods. [Explanation of symbols]

[0152] 1...three-dimensional object printing device, 1A...three-dimensional object printing device, 2...robot (articulated robot), 2a...arm drive mechanism, 2a1...motion detection unit, 3...head unit, 3a...liquid ejection head, 3c...detection unit, 3e...switch circuit, 3f...support, 5...controller, 5a...memory circuit, 5b...processing circuit, 6...control module, 6a...timing signal generation circuit, 6b...power supply circuit, 6c...control circuit, 6d...drive signal generation circuit, 7...computer, 7a...memory circuit, 7 b...processing circuit, 8...control unit, 210...base, 220...arm, 221...arm, 222...arm, 223...arm, 224...arm, 225...arm, 226...arm, CLK...clock signal, CNG...change signal, Com...drive signal, D1...output, D2...movement information, D2a...acceleration information, D2b...velocity information, D2c...angular velocity information, D3...signal, DE...ejection direction, DN...nozzle array direction, DS...main scanning direction, Da...path information, Dc...workpiece information, Dt... Timing information, E...tip, FN...nozzle surface, Img...print data, J...joint, J1...joint, J2...joint, J3...joint, J4...joint, J5...joint, J6...joint, LAT...latch signal, N...nozzle, NL...nozzle row, NL1...first nozzle row, NL2...second nozzle row, O1...rotating axis, O2...rotating axis, O3...rotating axis, O4...rotating axis, O5...rotating axis, O6...rotating axis, PD...drive pulse, PE...position, PR1...program, PR2...program, PS...position, PTS...timing signal, RU...printing path, S10...step, S20...step, S21...step, S21A...step, S21a...step, S21b...step, S21c...step, S21d...step, S21e...step, S22...step, S30...step, SI...control signal, Sk1...control signal, TCP...tool center point, VBS...offset potential, VHV...power supply potential, W...work, WF...surface, dCom...waveform designation signal.

Claims

1. a liquid ejection head that ejects liquid toward the workpiece; an articulated robot having a tip portion that supports the liquid ejection head and that changes the position of the liquid ejection head relative to the workpiece; a detection unit that detects the movement of the liquid ejection head in a scanning direction; a control unit that controls the operation of the liquid ejection head and the articulated robot, The control unit acquiring speed information relating to the speed of the liquid ejection head based on the detection result of the detection unit; controlling the ejection timing of the liquid ejection head based on the speed information; A three-dimensional object printing device characterized by the above.

2. the detection unit detects acceleration of the liquid ejection head in a scanning direction, The control unit acquiring acceleration information relating to the acceleration of the liquid ejection head based on the detection result of the detection unit; acquiring the velocity information based on the acceleration information; controlling the ejection timing of the liquid ejection head based on the speed information; The three-dimensional object printing device according to claim 1 .

3. The control unit a preliminary operation of scanning the liquid ejection head along a printing path, and a printing operation of scanning the liquid ejection head along the printing path and ejecting liquid from the liquid ejection head toward the workpiece, controlling the ejection timing of the liquid ejection head during the execution of the printing operation based on the acceleration information during the execution of the preliminary operation; The three-dimensional object printing device according to claim 2 .

4. The control unit calculating a scanning speed, which is a speed in a scanning direction of the liquid ejection head moved along the printing path, based on the acceleration information; controlling the ejection timing of the liquid ejection head during the execution of the printing operation based on the scanning speed; The three-dimensional object printing device according to claim 3 .

5. The control unit calculating the scanning velocity by performing arithmetic processing on the acceleration information using a high-pass filter; The three-dimensional object printing device according to claim 4 .

6. the detection unit is capable of detecting an angular velocity applied to the liquid ejection head, The control unit acquiring angular velocity information relating to the angular velocity of the liquid ejection head based on the detection result of the detection unit; controlling the ejection timing of the liquid ejection head based on the angular velocity information and the velocity information; The three-dimensional object printing device according to any one of claims 2 to 5.

7. The control unit calculating gravitational acceleration acting on the liquid ejection head based on the angular velocity information; calculating a velocity of the liquid ejection head in a scanning direction based on the acceleration information and the gravitational acceleration; The three-dimensional object printing device according to claim 6.

8. a motion detection unit provided in the articulated robot for detecting a motion of the articulated robot; The control unit determining a start timing for ejecting liquid from the liquid ejection head based on a detection result of the operation detection unit; The three-dimensional object printing device according to claim 1 .

9. The control unit determining a timing to acquire the speed information based on a detection result of the motion detection unit; The three-dimensional object printing device according to claim 8.

10. a liquid ejection head that ejects liquid toward the workpiece; an articulated robot having a tip portion that supports the liquid ejection head and that changes the position of the liquid ejection head relative to the workpiece; a detection unit that detects movement of the liquid ejection head in a scanning direction, acquiring speed information relating to the speed of the liquid ejection head based on the detection result of the detection unit; and controlling the ejection timing of the liquid ejection head based on the speed information. A printing method characterized by:

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