Three-dimensional object printing device and printing method

Abstract

To more appropriately perform printing on a workpiece regardless of the shape or the like of a workpiece.SOLUTION: A three-dimensional object printing device includes: a liquid discharge head that discharges liquid; and a movement mechanism that holds the liquid discharge head and moves the liquid discharge head relative to a three-dimensional workpiece. The first discharge number being the number of times of discharge per unit area of the liquid in a first size toward a first area of the workpiece from the liquid discharge head when a first gradation value is input is greater than the second discharge number being the number of times of discharge per unit area of the liquid in the first size toward a second area of the workpiece from the liquid discharge head when the first gradation value is input.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, there is known a three-dimensional object printing device that uses a robot to perform inkjet printing on the surface of a three-dimensional workpiece. For example, an inkjet printer described in Patent Document 1 includes an inkjet head and a robot arm that supports the inkjet head. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-175358 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, there was a risk that printing could not be performed properly when printing on a three-dimensional workpiece having concave or convex parts. [Means for solving the problem]

[0005] In order to solve the above problems, one aspect of a three-dimensional object printing device disclosed herein includes a liquid ejection head that ejects liquid, and a moving mechanism that holds the liquid ejection head and moves the liquid ejection head relative to a three-dimensional workpiece, wherein a first number of shots, which is the number of times a first size of liquid is ejected per unit area from the liquid ejection head toward a first region of the workpiece when a first gradation value is input, is greater than a second number of shots, which is the number of times the first size of liquid is ejected per unit area from the liquid ejection head toward a second region of the workpiece when the first gradation value is input.

[0006] One aspect of the printing method disclosed herein is a printing method in a three-dimensional printing device including a liquid ejection head that ejects liquid and a moving mechanism that holds the liquid ejection head and moves the liquid ejection head relative to a three-dimensional workpiece, the method including the steps of ejecting liquid of a first size from the liquid ejection head toward a first region of the workpiece, with a first ratio being the proportion of liquid of the first size contained per unit area, and ejecting liquid of the first size from the liquid ejection head toward a second region of the workpiece, with a second ratio being the proportion of liquid of the first size contained per unit area. [Brief description 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. [Diagram 2] FIG. 2 is a block diagram showing the electrical configuration of the three-dimensional object printing device according to the first embodiment. [Diagram 3] FIG. 4 is a diagram showing a flow of a printing method according to the first embodiment. [Figure 4] 5A to 5C are diagrams for explaining the operation of the robot during a printing operation in the first embodiment. [Diagram 5] FIG. 4 is a diagram illustrating an example of a print area. [Figure 6] FIG. 2 is a diagram showing an example of a first region, a second region, and a third region. [Figure 7] FIG. 13 is a diagram showing the relationship between the gradation value and the number of droplets of each size in a second region. [Figure 8] FIG. 13 is a diagram showing the relationship between the gradation value and the number of droplets of each size in a first region. [Figure 9] FIG. 13 is a diagram showing the relationship between the position in the third region and the number of liquid droplets of each size. [Figure 10] FIG. 13 is a diagram showing an example of the ratio of liquid particles of each size contained per unit area in a second region. [Figure 11] FIG. 13 is a diagram showing an example of the ratio of liquid particles of each size contained per unit area in a first region. [Figure 12]13A to 13C are diagrams illustrating the operation of a robot during a printing operation in a second embodiment. [Figure 13] 11A to 11C are diagrams illustrating other example shapes of the workpiece. [Figure 14] 11A to 11C are diagrams illustrating other example shapes of the workpiece. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, preferred embodiments of the present disclosure will be described 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 some parts are shown diagrammatically to facilitate understanding. In addition, the scope of the present disclosure is not limited to these forms unless otherwise specified in the following description to the effect that the present disclosure is limited.

[0009] For convenience of explanation, the following description will use the mutually intersecting X-axis, Y-axis, and Z-axis as appropriate. In addition, in the following description, one direction along the X-axis is the X1 direction, and the direction opposite to the X1 direction is the X2 direction. Similarly, the opposite directions along the Y-axis are the Y1 direction and the Y2 direction. In addition, 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 a robot 2 (described later) is installed. Typically, the Z-axis is a vertical axis, and the Z2 direction corresponds to the downward direction in the 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. The X axis, the Y axis, and the Z axis are typically mutually orthogonal, but are not limited thereto, and may not be orthogonal. For example, the X axis, the Y axis, and the Z axis may intersect each other at an angle within a range of 80° to 100°.

[0012] 1-1. Overview of the three-dimensional printing device 1 is a perspective view showing an outline of a three-dimensional object printing apparatus 1 according to a 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 includes a surface WF1 and a surface WF2. The surface WF1 is a flat surface that is inclined with respect to the horizontal plane. The surface WF2 is a flat surface that is parallel to the horizontal plane. The surface to be printed may be a surface other than the surface WF among the multiple surfaces of the workpiece W. Furthermore, the size, shape, or installation posture of the workpiece W or the surface WF is not limited to the example shown in FIG. 1 and is arbitrary.

[0014] As shown in Fig. 1, the three-dimensional object printing apparatus 1 has a robot 2 which is an example of a "moving mechanism", a head unit 3 including a liquid ejection head 3a, a controller 5, and a measurement unit 9. Below, these will first be briefly described in order based on Fig. 1.

[0015] The robot 2 is a robot that changes the position and orientation of the head unit 3 in the world coordinate system. Here, the robot 2 holds the liquid ejection head 3a and moves the liquid ejection head 3a relative to a three-dimensional workpiece W. In the example shown in Fig. 1, the robot 2 is a so-called six-axis vertical articulated robot.

[0016] As shown in FIG. 1, the robot 2 has a base 210 and an arm 220 .

[0017] The base 210 is a platform that supports the arm 220. In the example shown in Fig. 1, the base 210 is fixed to an installation surface such as a floor surface or a base facing the Z1 direction by screwing or the like. The installation surface to which the 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 dolly, or the like.

[0018] The arm 220 is connected to the base 210 and changes the position and orientation of the liquid ejection head 3a relative to the workpiece W. More specifically, the arm 220 is a six-axis robot arm that three-dimensionally changes the position and orientation of the head unit 3 relative to the base 210. Specifically, the arm 220 has arms 221, 222, 223, 224, 225, and 226, which are connected in this order.

[0019] The arm 221 is connected to the base 210 via a joint J1 so as to be rotatable around a rotation axis O1. The arm 222 is connected to the arm 221 via a joint J2 so as to be rotatable around a rotation axis O2. The arm 223 is connected to the arm 222 via a joint J3 so as to be rotatable around a rotation axis O3. The arm 224 is connected to the arm 223 via a joint J4 so as to be rotatable around a rotation axis O4. The arm 225 is connected to the arm 224 via a joint J5 so as to be rotatable around a rotation axis O5. The arm 226 is connected to the arm 225 via a joint J6 so as to be rotatable around a 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 for rotating one of the two corresponding adjacent members relative to the other. The assembly of the drive mechanisms of the joints J1 to J6 corresponds to an arm drive mechanism 2a shown in Fig. 2, which will be described later.

[0022] The rotation axis O1 is an axis perpendicular to an installation surface (not shown) to which the base 210 is fixed. The rotation axis O2 is an axis perpendicular to the rotation axis O1. The rotation axis O3 is an axis parallel to the rotation axis O2. The rotation axis O4 is an axis perpendicular to the rotation axis O3. The rotation axis O5 is an axis perpendicular to the rotation axis O4. The rotation axis O6 is an axis perpendicular to the rotation axis O5.

[0023] With regard to these rotation axes, "perpendicular" refers not only to the case where the angle between the two rotation axes is exactly 90°, but also to the case where the angle between the two rotation axes is offset within a range of about ±5° from 90°. Similarly, "parallel" refers not only to the case where the two rotation axes are exactly parallel, but also to the case where one of the two rotation axes is inclined relative to the other axis within a range of about ±5°. Furthermore, the orientation of these rotation axes is not limited to the example shown in FIG. 1.

[0024] A head unit 3 is attached as an end effector to an arm 226 which is the tip of the arm 220 of the robot 2. In the example shown in Fig. 1, the head unit 3 is fixed to the arm 226 by screws or the like.

[0025] 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. The liquid ejection head 3a has a plurality of nozzles n, and although not shown, the liquid ejection head 3a is provided with a piezoelectric element, which is a driving element, and a cavity that contains ink for each nozzle n. Here, the piezoelectric element ejects ink from the nozzle corresponding to the cavity by changing the pressure of the cavity corresponding to the piezoelectric element. Such a liquid ejection head 3a is obtained, for example, by bonding a plurality of substrates, such as silicon substrates, which have been appropriately processed by etching or the like, with an adhesive or the like. Note that, instead of the piezoelectric element, a heater that heats the ink in the cavity may be used as a driving element for ejecting ink from the nozzle.

[0026] The ink is not particularly limited, and examples thereof include water-based ink in which a coloring material such as a dye or pigment is dissolved in a water-based solvent, curable ink using a curable resin such as an ultraviolet curable type, and solvent-based ink in which a coloring material such as a dye or pigment is dissolved in an organic solvent. Among them, curable ink is preferably used. The curable ink is not particularly limited, and may be, for example, any of a heat curable type, a photocurable type, a radiation curable type, and an electron beam curable type, but a photocurable type such as an ultraviolet curable type is preferable. The ink is not limited to a solution, and may be an ink in which a coloring material or the like is dispersed as a dispersoid in a dispersion medium. In addition, the ink is not limited to an ink containing a coloring material, and may be, for example, an ink containing conductive particles such as metal particles for forming wiring or the like as a dispersoid, a clear ink, or a treatment liquid for surface treatment of the workpiece W.

[0027] In addition to the liquid ejection head 3a, the head unit 3 may have, for example, a valve mechanism that opens and closes depending on the pressure of the ink in the liquid ejection head 3a, and may have a light source that emits energy such as light, heat, electron beams, or radiation to harden or solidify the ink on the workpiece W.

[0028] The measurement unit 9 is a device that measures the shape of the workpiece W, and includes an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary MOS) image sensor that images the workpiece W. The measurement unit 9 is not particularly limited as long as it is capable of acquiring three-dimensional shape data of the target three-dimensional object, and may be any of various sensors also called three-dimensional sensors or vision sensors.

[0029] Here, the measuring unit 9 may be a sensor such as a passive sensor or an active sensor based on the principle of triangulation, or may be a sensor such as a focus-based or time-of-flight (TOF) sensor based on the principle of coaxial surveying. Examples of passive sensor methods based on the principle of triangulation include binocular vision, trinocular vision, and multi-baseline stereo methods. Examples of active sensor methods based on the principle of triangulation include active stereo methods such as spot light projection, slit projection, spatial coding, random dot stereo, and phase shift, as well as moire and photometric stereo. Examples of focus-based sensor methods based on the principle of coaxial surveying include Depth from Focus and Depth from Defocus. Examples of time-of-flight sensor methods based on the principle of coaxial surveying include time difference measurement and phase difference measurement.

[0030] A three-axis image capture coordinate system is set in the measurement unit 9. The image capture coordinate system may be associated with the above-mentioned robot coordinate system by calibration. Then, the measurement unit 9 generates shape data indicating the three-dimensional shape of the target object in the image capture coordinate system.

[0031] 1, the positional relationship between the measuring unit 9 and the workpiece W is fixed. The installation mode of the measuring unit 9 is not limited to a mode in which the positional relationship with respect to the workpiece W is fixed, and for example, the measuring unit 9 may be supported by the robot 2. Furthermore, imaging by the measuring unit 9 may be performed manually.

[0032] 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.

[0033] 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 device 1 according to the first embodiment. FIG. 2 shows electrical components among the components of the three-dimensional object printing device 1. As shown in FIG. 2, the three-dimensional object printing device 1 has, in addition to the components shown in FIG. 1 described above, a control module 6 communicatively connected to the controller 5, and a computer 7 communicatively connected to the controller 5, the control module 6, and the measurement unit 9. Here, the controller 5, the control module 6, and the computer 7 constitute a control unit 8. The control unit 8 controls the operations of the robot 2 and the head unit 3. Each part of the control unit 8 will be described below in order based on FIG. 2.

[0034] 2 may be appropriately divided, some of the components may be included in other components, or the components may be integrated with other components. For example, some or all of the functions of the controller 5 or the control module 6 may be implemented by a computer 7, or may be implemented by another external device such as a personal computer (PC) connected to the controller 5 via a network such as a local area network (LAN) or the Internet.

[0035] 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.

[0036] The controller 5 includes a memory circuit 5a and a processing circuit 5b.

[0037] The storage circuit 5a stores various programs executed by the processing circuit 5b and various data processed by the processing circuit 5b. The storage circuit 5a includes one or both of semiconductor memories, for example, a volatile memory such as a random access memory (RAM) and a non-volatile memory such as a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM) or a programmable ROM (PROM). Note that a part or the whole of the storage circuit 5a may be included in the processing circuit 5b.

[0038] The storage circuit 5a stores route information Da.

[0039] The path information Da is used to control the operation of the robot 2, and is information indicating the position and posture of the liquid ejection head 3a on the path along which the liquid ejection head 3a should move when performing a printing operation. The position and posture of the liquid ejection head 3a are defined based on the tool center point of the robot 2. The tool center point may be located, for example, at the center of the nozzle surface, which is the tip surface of the liquid ejection head 3a, or may be a position spaced apart from the liquid ejection head 3a in the ink ejection direction. The path information Da is expressed, for example, by coordinate values ​​in a coordinate system such as a work coordinate system, a base coordinate system, or a world coordinate system. The path information Da is generated by the processing circuit 7b, and input from the processing circuit 7b to the storage circuit 5a. When the path information Da is expressed using coordinate values ​​in the work coordinate system, it is used to control the operation of the robot 2 after being converted from the coordinate values ​​in the work coordinate system to the coordinate values ​​in the base coordinate system or the world coordinate system.

[0040] 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. The processing circuit 5b includes, for example, a processor such as one or more CPUs (Central Processing Units). Note that the processing circuit 5b may include a programmable logic device such as an FPGA (field-programmable gate array) instead of or in addition to a CPU.

[0041] Here, the arm driving mechanism 2a is an assembly of driving mechanisms for the above-mentioned 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.

[0042] The processing circuit 5b performs inverse kinematic calculation, which is a calculation for converting the path information Da into movement amounts such as the rotation angle and rotation speed of each joint J of the robot 2. Then, the processing circuit 5b outputs a control signal Sk1 based on the output D1 from each encoder of the arm driving mechanism 2a so that the movement amounts such as the actual rotation angle and rotation speed of each joint J become the above-mentioned 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 driving mechanism 2a. Here, the control signal Sk1 is corrected by the processing circuit 5b based on the output from a distance sensor (not shown) as necessary.

[0043] 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 arm driving mechanism 2a. For example, the processing circuit 5b generates, as the signal D3, a trigger signal including a pulse at a timing when the output D1 from one of the multiple encoders becomes a predetermined value.

[0044] The control module 6 is a circuit that controls the ink ejection operation of the head unit 3 based on a signal D3 output from the controller 5 and print data Img 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.

[0045] The timing signal generating circuit 6a generates a timing signal PTS based on the signal D3. The timing signal generating circuit 6a is formed of, for example, a timer that starts generating the timing signal PTS in response to detection of the signal D3.

[0046] The power supply circuit 6b receives power from a commercial power supply (not shown) and generates various predetermined potentials. The generated potentials are appropriately supplied to the control module 6 and each part 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.

[0047] 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 3b of the head unit 3.

[0048] The control signal SI is a digital signal for specifying the operating state of the drive element of the liquid ejection head 3a of the head unit 3. Specifically, the control signal SI is a signal for specifying whether or not to supply a drive signal Com, which will be described later, 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 for defining the waveform of the drive signal Com. The latch signal LAT and the change signal CNG are signals used in conjunction with the control signal SI to specify the drive timing of the drive element, thereby specifying the ejection timing of ink from the nozzle. The clock signal CLK is a reference clock signal synchronized with the timing signal PTS.

[0049] The control circuit 6c described above includes, for example, one or more processors such as a CPU, etc. Note that the control circuit 6c may include a programmable logic device such as an FPGA instead of or in addition to a CPU.

[0050] The drive signal generating 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 generating circuit 6d has, for example, a DA conversion circuit and an amplifier circuit. In the drive signal generating 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, among the waveforms included in the drive signal Com, a signal having a waveform that is actually supplied to the drive element is a drive pulse PD. The drive pulse PD is supplied from the drive signal generating circuit 6d to the drive element via the switch circuit 3b of the head unit 3.

[0051] Here, the switch circuit 3b 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 supplied as the drive pulse PD based on a control signal SI.

[0052] The computer 7 has a function of controlling the operation of the measurement unit 9, a function of generating path information Da, a function of supplying information such as the path information Da to the controller 5, and a function of supplying information such as print data Img to the control module 6.

[0053] The computer 7 includes a storage circuit 7a and a processing circuit 7b. The computer 7 may also include an input device such as a keyboard or a mouse for receiving operations from a user, and may also include a display device such as a liquid crystal panel for displaying information required for generating the path information Da.

[0054] The storage circuit 7a stores various programs executed by the processing circuit 7b and various data processed by the processing circuit 7b. The storage circuit 7a includes, for example, one or both of semiconductor memories, a volatile memory such as a RAM, and a non-volatile memory such as a ROM, an EEPROM, or a PROM. Note that a part or the whole of the storage circuit 7a may be included in the processing circuit 7b.

[0055] The memory circuit 7a stores path information Da, work information Dc, print data Img, a program PR, and firing number tables TB1 and TB2.

[0056] The work information Dc is data representing at least a part of the shape of the work W. Specifically, the work information Dc is, for example, three-dimensional data in a format such as STL (Standard Triangulated Language) that represents the shape of the work W by a plurality of 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 indicating the front and back of the polygon surface. The work information Dc is generated by imaging the work W by the measurement unit 9. The work information Dc may be obtained by converting CAD (computer-aided design) data indicating the three-dimensional shape of the work W as necessary. The work information Dc may be represented by using coordinate values ​​of a work coordinate system, or may be represented by point cloud data using coordinate values ​​of a base coordinate system or a world coordinate system. The work information Dc may be represented by a formula or the like, and the format of the work information Dc may be appropriately converted as necessary.

[0057] The print data Img is information that indicates an image to be printed on the workpiece W for each path (pass) of the print path indicated by the path information Da.

[0058] The program PR is a program for generating path information Da and for printing based on the path information Da.

[0059] Each of the ejection number tables TB1 and TB2 is information indicating the correspondence between the gradation value of the image and the number of times liquid of each size is ejected per unit area, and is selectively used in the rasterization process described below when generating the print data Img.

[0060] The processing circuit 7b realizes each of the above-mentioned functions by executing a program such as the program PR. The processing circuit 7b includes, for example, one or more processors such as a CPU. Note that the processing circuit 7b may include a programmable logic device such as an FPGA instead of or in addition to a CPU.

[0061] The processing circuit 7b executes the program PR to realize various functions for a printing method described below, including obtaining path information Da and generating print data Img. In particular, the processing circuit 7b has a function of determining the size of ink ejected from the liquid ejection head 3a based on the measurement results of the measurement unit 9. The details of the printing method will be described later with reference to Figures 3 to 11.

[0062] As 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 and the signal D3, thereby performing a printing operation. In the printing operation, the robot 2 changes the position and posture of the liquid ejection head 3a based on the path information Da, while the liquid ejection head 3a ejects ink from the liquid ejection head 3a toward the workpiece W at appropriate timing based on the print data Img and the signal D3. As a result, an image based on the print data Img is formed on the workpiece W.

[0063] 1-3.Printing method Fig. 3 is a diagram showing the flow of the printing method according to the first embodiment. The printing method is executed using the above-mentioned three-dimensional object printing device 1, and as shown in Fig. 3, includes, in this order, a step S10 of acquiring path information Da, a step S20 of performing image processing for generating print data Img, and a step S30 of performing a printing operation.

[0064] In step S10, a plurality of teaching points that define the relative positions of the workpiece W and the liquid ejection head 3a in a virtual space are set, and path information Da relating to a set of the plurality of teaching points is acquired. This acquisition is executed by the processing circuit 7B, for example, by online teaching or offline teaching.

[0065] In step S20, print data Img is generated by image processing image information (not shown). This generation is performed by the processing circuit 7b. In this embodiment, step S20 includes step S21, which performs color conversion processing, step S22, which performs binarization processing, and step S23, which performs rasterization processing, in this order.

[0066] In step S21, image information (not shown) is subjected to a color conversion process to generate ink color data represented by density values ​​for each ink color. This color conversion process converts the color values ​​represented by the image information for each pixel from the coordinate values ​​of a color space such as the RGB color space in the image information to the coordinate values ​​of a color space such as the CMY color space for the liquid ejection head 3a. A color conversion table (not shown) is used for this color conversion process. This color conversion table indicates the correspondence between the luminance values ​​represented by the coordinate values ​​of a color space such as the RGB color space used to express the colors represented by the image information, and the density values ​​represented by the coordinate values ​​of a color space such as the CMY color space used to express the colors represented by the print data Img. Therefore, in this color conversion table, the image information is converted into ink color data represented by density values ​​for each ink color by using the luminance values ​​as input values ​​and the density values ​​as output values. In step S21, before the color conversion process, a process of converting the resolution of the image information into the resolution of the print data Img is performed as necessary.

[0067] Step S22 generates quantization data by quantizing the ink color data obtained in step S21. This quantization process uses the above-mentioned tone number tables TB1 and TB2 to convert the tone value of each pixel group composed of a plurality of pixels indicated by the ink color data into the tone value of each of the plurality of pixels based on the path information Da. More specifically, this quantization process divides the area to be printed on the workpiece W into a first area RP1, a second area RP2, and a third area RP3 (to be described later) based on the path information Da, and then performs quantization of the first area RP1 using the tone number table TB1, quantization of the second area RP2 using the tone number table TB2, and quantization of the third area RP3 using the tone number tables TB1 and TB2. A dither pattern (not shown) is used in this quantization process. This dither pattern defines a threshold value for converting the tone value of a pixel group composed of a plurality of pixels into the tone value of each of the plurality of pixels for each of the plurality of pixels. Here, the ink color data is N (N is a natural number) - valued data indicating the tone value of a pixel group composed of the plurality of pixels. The quantization data is M (M is a natural number satisfying 2 ≤ M < N) - valued data indicating the tone value of each of the plurality of pixels. Details of step S22 will be described later with reference to FIGS. 7 to 11.

[0068] Step S23 generates print data Img by rasterizing the quantization data. This rasterization process generates print data Img by distributing the quantization data to a plurality of scans when recording an image by distributing it to a plurality of scans on the area to be printed on the workpiece W. Although not shown, a mask pattern is used in this rasterization process. This mask pattern defines whether to distribute the quantization data to each of the plurality of scans.

[0069] In step S30, printing is performed on the workpiece W using the path information Da from step S10 and the print data Img from step S20. Step S30 includes a first printing step S31, a second printing step S32, and a third printing step S33. The order of execution of the first printing step S31, the second printing step S32, and the third printing step S33 is not particularly limited, but in the embodiment exemplified below, the order is the second printing step S32, the third printing step S33, and the first printing step S31.

[0070] The first printing process S31 is a process for printing a first region RP1 (described later) of the workpiece W. The second printing process S32 is a process for printing a second region RP2 (described later) of the workpiece W. The third printing process S33 is a process for printing a third region RP3 (described later) of the workpiece W.

[0071] As described above, the printing method in the three-dimensional object printing apparatus 1 includes a first printing step S31 and a second printing step S32. The first printing step S31 is a step of ejecting ink of the first size L from the liquid ejection head 3a toward a first region RP1 of the work W, with the ratio of the ink of the first size L contained per unit area being a first ratio. The second printing step S32 is a step of ejecting ink of the first size L from the liquid ejection head 3a toward a second region RP2 of the work W, with the ratio of the ink of the first size L contained per unit area being a second ratio. The first ratio corresponds to the "first number of shots" described later. The second ratio corresponds to the "second number of shots" described later.

[0072] In this way, by making the ratio of ink of the first size L to the first region RP1 and the second region RP2 different from each other, the size of the ink ejected is changed depending on the printing location on the workpiece W. This allows more appropriate printing on the workpiece W even if the distance between the liquid ejection head 3a and the workpiece W, etc. changes.

[0073] 4 is a diagram for explaining the operation of the robot 2 during a printing operation in the first embodiment. In FIG. 4, a case where printing is performed on a surface WF of a workpiece W placed at a position further in the X2 direction than the robot 2 is illustrated.

[0074] In the printing operation of step S30 shown in Fig. 3 described above, ink is appropriately ejected from nozzles n based on print data Img and applied to the workpiece W, thereby printing with ink on the workpiece W. At this time, the robot 2 changes the position and attitude of the liquid ejection head 3a based on the path information Da. Through this printing operation, the liquid ejection head 3a moves in the main scanning direction DS along a movement path RU based on the position information of the path information Da, while maintaining a predetermined attitude with respect to the surface WF based on the attitude information of the path information Da. The movement path RU is the path from position PS to position PE.

[0075] 4, the movement path RU extends along the X-axis when viewed in the Z2 direction. During printing operation, the robot 2 mainly operates three joints J, namely, joint J2, joint J3, and joint J5, among the six joints J. In this embodiment, the main scanning direction DS is the X1 direction when viewed in the direction along the Z-axis.

[0076] 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 work W are not limited to the example shown in FIG. 4 and are arbitrary. The movement path RU is determined according to the shape, printing range, installation position and installation posture of the work W, and is not limited to the example shown in FIG. 4 and is arbitrary. The position and number of the joints J to be operated in the printing operation are determined according to the movement path RU and the posture of the head unit 3 with respect to the work W during the printing operation. The main scanning direction DS may be the X1 direction when viewed in the direction along the Z axis, or may be a direction inclined or perpendicular to the X axis.

[0077] Fig. 5 is a diagram showing an example of a printing area RP. Fig. 5 shows the workpiece W and the robot 2 as viewed in the Z2 direction. Note that, for ease of viewing, Fig. 5 shows only the base 210 of the components of the robot 2, and omits the arm 220 and head unit 3.

[0078] In the printing operation of step S30 shown in Figure 3 described above, the robot 2 changes the relative position of the liquid ejection head 3a with respect to the workpiece W, while the liquid ejection head 3a ejects ink, thereby printing in the printing area RP on the workpiece W.

[0079] 5, the surface WF1 is located between the surface WF2 and the base 210. Here, the printing area RP is an area spanning the surfaces WF1 and WF2.

[0080] Fig. 6 is a diagram showing an example of the first region RP1, the second region RP2, and the third region RP3. Fig. 6 shows the workpiece W and the liquid ejection head 3a as viewed in the direction along the Y axis. Note that in Fig. 6, the liquid ejection head 3a at any timing during the execution of the printing operation is appropriately shown by a two-dot chain line.

[0081] As shown in FIG. 6, the print area RP is divided into a first area RP1, a second area RP2, and a third area RP3.

[0082] The first region RP1 is a region provided on the surface WF1. The second region RP2 is a region provided on the surface WF2. The third region RP3 is a region including the boundary between the surface WF1 and the surface WF2, and is located between the first region RP1 and the second region RP2. Therefore, when viewed in the direction along the Z axis, these regions are arranged in the order of the second region RP2, the third region RP3, and the first region RP1 toward the X1 direction. The width of the third region RP3 is not particularly limited, but is preferably as small as possible. The third region RP3 may be provided as necessary, or may be omitted.

[0083] As described above, the surface WF2 is a flat surface parallel to the horizontal plane, whereas the surface WF1 is a flat surface inclined relative to the horizontal plane. Therefore, when a virtual plane is set along the installation surface BN of the workpiece W, the angle θ1 between the first region RP1 and the virtual plane is larger than the angle θ2 between the second region RP2 and the virtual plane. In the example shown in FIG. 6, the angle θ2 is 0°. Note that the angles θ1 and θ2 are not limited to the example shown in FIG. 6, and are arbitrary. For example, the angle θ2 does not have to be 0° as long as it is smaller than the angle θ1.

[0084] Here, the distance PG1 in the ink ejection direction between the liquid ejection head 3a and the first region RP1 when ejecting ink from the liquid ejection head 3a toward the first region RP1 is greater than the distance PG2 in the ink ejection direction between the liquid ejection head 3a and the second region RP2 when ejecting ink from the liquid ejection head 3a toward the second region RP2. This makes it possible to prevent contact between the workpiece W and the liquid ejection head 3a during printing on the first region RP1. In addition, by reducing the distance PG2, the print quality on the second region RP2 can be improved. Note that, hereinafter, the distances PG1 and PG2 may be referred to as the distance PG without distinction.

[0085] However, when the distance PG1 is increased, the ink ejected from the liquid ejection head 3a becomes more susceptible to the effects of air currents and the like before landing on the first region RP1. For this reason, when the size of the ink ejected from the liquid ejection head 3a toward the first region RP1 and the size of the ink ejected toward the second region RP2 are equal to each other, the ink landing deviation is more likely to occur in printing on the first region RP1 than in printing on the second region RP2. Therefore, the print quality of the first region RP1 is lower than that of the second region RP2, and as a result, there is a risk that the workpiece W cannot be printed appropriately.

[0086] 6, the attitude of the liquid ejection head 3a is constant. Therefore, due to the difference between the angles θ1 and θ2, the ink landing angle for the second region RP2 is close to 90°, whereas the ink landing angle for the first region RP1 is far from 90°. As a result, in this respect as well, the ink landing deviation is more likely to occur in printing on the first region RP1 than in printing on the second region RP2, and there is a risk that printing on the workpiece W cannot be performed appropriately.

[0087] Therefore, in the three-dimensional object printing device 1, the usage ratio of the sizes of ink ejected is changed depending on the printing location of the workpiece W. In this embodiment, it is possible to selectively eject three different sizes of ink from the liquid ejection head 3a, and the number of shots, which is the number of times that ink of each size is ejected per unit area toward the first region RP1, the second region RP2, and the third region RP3, differs from each other.

[0088] As described above, the three-dimensional object printing apparatus 1 includes the measurement unit 9 and the control unit 8. The measurement unit 9 measures the shape of the workpiece W. The control unit 8 determines the size of the ink to be ejected from the liquid ejection head 3a based on the measurement results of the measurement unit 9. This allows the ink size to be changed according to the measurement results of the measurement unit 9, making it possible to print more appropriately according to the shape of the workpiece W.

[0089] More specifically, the greater the distance PG between the liquid ejection head 3a and the workpiece W, the higher the proportion of ink of the first size L contained in the area. In this way, the size of the ink is changed according to the distance PG between the liquid ejection head 3a and the workpiece W, so that printing on the workpiece W can be performed more appropriately. The greater the distance PG, the more likely it is that the ink will land misaligned on the workpiece W, but by increasing the proportion of ink of the first size L, it is possible to suppress the overall misalignment of recording dots due to the landing misalignment. As a result, image degradation such as white streaks and color misalignment can be suppressed.

[0090] Furthermore, the greater the inclination angle of the surface to be printed in, the higher the proportion of ink of the first size L that is included. In this way, the size of the ink changes according to the inclination angle, allowing for more appropriate printing on the workpiece W. The greater the inclination angle, the more likely it is that the ink will land misaligned on the workpiece W, but by increasing the proportion of ink of the first size L, it is possible to reduce overall misalignment of recording dots due to landing misalignment. As a result, image degradation such as white streaks and color misalignment can be reduced.

[0091] Fig. 7 is a diagram showing the relationship between the gradation values ​​in the second region RP2 and the number of droplets of each size. This relationship is an example of the correspondence relationship shown in the droplet number table TB2. Fig. 7 shows the relationship between the gradation values ​​corresponding to the second region RP2 among the gradation values ​​shown by the ink color data described above and the number of droplets of each size of ink, the first size L, the second size M, and the third size S. The order of the ink sizes from largest to smallest is first size L, followed by second size M, and third size S.

[0092] When printing in the second region RP2, it is preferable to use ink of the second size M and the third size S as much as possible, as this makes it possible to reduce the distance PG2 as mentioned above and also from the standpoint of improving print quality, as these inks are less likely to produce a grainy appearance in the printed image.

[0093] In the example shown in FIG. 7, the gradation value indicated by the ink color data can take a value from 0 to 255.

[0094] Here, when the gradation value is within the range of 0 or more and less than k1a, as the gradation value increases, the number of shots of the third size S changes from 0 to c1a. Meanwhile, in this case, the number of shots of the first size L and the second size M is 0. k1a is an integer greater than 0 and less than 255. c1a is an integer greater than 1.

[0095] Also, when the gradation value is within the range of k1a or more and less than k1b, the number of shots of the third size S is constant at c1a. On the other hand, in this case, as the gradation value increases, the number of shots of the second size M changes from 0 to c1b, but the number of shots of the first size L is 0. k1b is an integer greater than k1a0 and less than 255. c1b is an integer greater than c1a.

[0096] Furthermore, when the gradation value is within the range of k1b to 255, the number of shots of the second size M is constant at c1b, and the number of shots of the third size S is constant at c1a. In this case, however, as the gradation value increases, the number of shots of the first size L changes from 0 to c1c, where c1c is an integer greater than c1b.

[0097] In the above-described number of ink shots table TB2, for example, when the gradation value K shown in FIG. 7 is input, the number of ink shots of the first size L is 0, the number of ink shots of the second size M is a value between c1a and c1c, and the number of ink shots of the third size S is c1a.

[0098] Here, the gradation value K is an example of a "first gradation value." The amount of ink ejected per unit area from the liquid ejection head 3a toward the first region RP1 when the gradation value K is input is equal to the amount of ink ejected per unit area from the liquid ejection head 3a toward the second region RP2 when the gradation value K is input. Therefore, an amount of ink according to the input gradation value K is ejected toward each of the first region RP1 and the second region RP2.

[0099] In this way, the number of times ink of the first size L is ejected per unit area from the liquid ejection head 3a toward the second region RP2 of the workpiece W when the gradation value K is input is an example of the "second shot count." When the gradation value K is input, the second shot count is 0, so that the graininess of the printed image in the second region RP2 can be suppressed.

[0100] Furthermore, the number of times that ink of the second size M is ejected per unit area from the liquid ejection head 3a toward the second region RP2 when the gradation value K is input is an example of the "fourth number of shots."

[0101] Fig. 8 is a diagram showing the relationship between the gradation values ​​in the first region RP1 and the number of droplets of each size. This relationship is an example of the correspondence relationship shown in the droplet number table TB1. Fig. 8 shows the relationship between the gradation values ​​corresponding to the first region RP1 among the gradation values ​​shown by the ink color data described above and the number of droplets of each size of ink, first size L, second size M, and third size S. The size relationship of these ink sizes is the same as in Fig. 7 described above, from largest to smallest, with first size L, second size M, and third size S.

[0102] When printing on the first region RP1, since the distance PG1 is greater than the distance PG1 as described above, in order to improve print quality, it is preferable to use ink of the first size L, which is less likely to cause landing deviation, as much as possible.

[0103] In the example shown in FIG. 8, the gradation values ​​indicated by the ink color data can take values ​​from 0 to 255, similar to the above-mentioned FIG.

[0104] Here, when the gradation value is within the range of 0 or more and less than k2a, the number of shots of the third size S changes from 0 to c2a as the gradation value increases. Meanwhile, in this case, the number of shots of the first size L and the second size M is 0. k2a is an integer greater than 0 and smaller than k1a in FIG. 7 described above. c2a is an integer greater than 1 and smaller than c1a in FIG. 7 described above.

[0105] Also, when the gradation value is within the range of k2a or more and less than k2b, the number of shots of the third size S is constant at c2a. Meanwhile, in this case, as the gradation value increases, the number of shots of the second size M changes from 0 to c2b, but the number of shots of the first size L is 0. k2b is an integer greater than k2a and smaller than k1b in FIG. 7. c2b is an integer greater than c2a and smaller than c1b in FIG. 7.

[0106] Furthermore, when the gradation value is within the range of k2b to 255, the number of shots of the second size M is constant at c2b, and the number of shots of the third size S is constant at c2a. In this case, however, as the gradation value increases, the number of shots of the first size L changes from 0 to c2c, where c2c is an integer greater than c2b.

[0107] In the above-described ejection number table TB1, for example, when the gradation value K shown in FIG. 8 is input, the number of ink ejections of the first size L is greater than c2b, the number of ink ejections of the second size M is c2b, and the number of ink ejections of the third size S is c2a.

[0108] In this way, when a gradation value K is input, the number of times ink of the first size L is ejected per unit area from the liquid ejection head 3a toward the first region RP1 of the workpiece W is an example of the "first number of shots," and is greater than the aforementioned "second number of shots."

[0109] The size of the ink ejected is changed depending on the printing location on the workpiece W. This allows more appropriate printing on the workpiece W even if the distance between the liquid ejection head 3a and the workpiece W, etc. changes. In contrast, in an embodiment in which the first and second numbers of shots are equal to each other, the size of the ink ejected is constant, so if the distance between the liquid ejection head 3a and the workpiece W, etc. changes depending on the shape of the workpiece W, the print quality may not be stable.

[0110] Furthermore, the number of times ink of the second size M, which is smaller than the first size L, is ejected per unit area from the liquid ejection head 3a toward the first region RP1 when the gradation value K is input is an example of the "third number of shots," and is less than the above-mentioned "fourth number of shots." This makes it possible to suppress the graininess of the printed image in the second region RP2. In contrast, in a mode in which ink of the second size M is not used, if the amount of ink of the first size L is large, there is a risk that graininess will occur in the printed image.

[0111] Specifically, if the distance PG is large, there is a risk that small droplets of liquid may land misaligned or turn into mist due to disturbances. Therefore, the three-dimensional object printing device 1 can suppress image degradation by changing the size of the droplets ejected according to the distance PG.

[0112] Also, in the first region RP1, which is an inclined surface, printing using smaller sized liquid is avoided. In other words, in the second region RP2, which is a flat surface, printing is done using as small sized liquid as possible. If printing is done only with the first size L ink, the printed image will have a grainy feel, but by printing using smaller sized liquid in the second region RP2, which is a flat surface, it is possible to reduce the graininess of the image after printing in the second region RP2, which is a flat surface.

[0113] As described above, in the three-dimensional object printing device 1, an image is formed on the workpiece W using ink of a first size L, ink of a second size M, and ink of a third size S smaller than the second size M. This makes it possible to efficiently widen the range of gradation values.

[0114] Fig. 9 is a diagram showing the relationship between the position in the third region RP3 and the number of droplets of each size of liquid. Fig. 9 shows the relationship between the position in the third region RP3 and the number of droplets of each size of ink, first size L, second size M, and third size S, when the gradation value indicated by the ink color data described above is K. The order of the ink sizes from largest to smallest is first size L, second size M, and third size S, just like in Figs. 7 and 8 described above.

[0115] When printing in the third region RP3, the number of ink droplets of the first size L, the second size M and the third size S is varied depending on the position of the third region RP3 in order to make less noticeable the difference between the print image of the first region RP1 and the print image quality of the second region RP2 due to the difference in the number of ink droplets of the first size L, the second size M and the third size S for the first region RP1 and the second region RP2 described above.

[0116] 9, the number of ink droplets of the first size L decreases continuously from the first region RP1 to the second region RP2. Meanwhile, the number of ink droplets of the second size M and the third size S increases continuously from the first region RP1 to the second region RP2. Each of these droplet numbers may change stepwise or nonlinearly from the first region RP1 to the second region RP2.

[0117] In this way, the number of times that ink of the first size L is ejected per unit area from the liquid ejection head 3a toward the third region RP3, which is an area located between the first region RP1 and the second region RP2 of the workpiece W, decreases from the first region RP1 toward the second region RP2. As a result, the number of ejections of ink of the first size L decreases from the first region RP1 toward the second region RP2. Therefore, it is possible to suppress a sudden change in the graininess of the print image quality from the first region RP1 toward the second region RP2.

[0118] Fig. 10 is a diagram showing an example of the ratio of liquid of each size contained per unit area PX in the second region RP2. Fig. 11 is a diagram showing an example of the ratio of liquid of each size contained per unit area PX in the first region RP1. Figs. 10 and 11 show the arrangement of ink arranged in a unit area PX when the gradation value indicated by the ink color data described above is K. The unit area PX corresponds to a pixel group made up of a plurality of images indicated by the ink color data described above. In the example shown in Figs. 10 and 11, the number of pixels making up the pixel group is 16.

[0119] As shown in FIG. 10, in the unit area PX of the second region RP2, the number of ink droplets of the first size L is 0, the number of ink droplets of the second size M is 6, and the number of ink droplets of the third size S is 8.

[0120] In contrast, as shown in Fig. 11, in the unit area PX of the first region RP1, the number of ink droplets of the first size L is three, the number of ink droplets of the second size M is two, and the number of ink droplets of the third size S is four. Here, since the gradation value of the unit area PX shown in Fig. 11 is equal to the gradation value of the unit area PX shown in Fig. 10, the total amount of ink on the unit area PX shown in Fig. 10 and the total amount of ink on the unit area PX shown in Fig. 11 are equal to each other.

[0121] In the above-described first embodiment, printing can be performed appropriately regardless of the shape of the three-dimensional workpiece W.

[0122] 2. Second embodiment A second embodiment of the present disclosure will be described below. In the following example, 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 will be omitted as appropriate.

[0123] 12 is a diagram for explaining the operation of the robot 2 during a printing operation in the second embodiment. This embodiment is similar to the first embodiment described above, except that the shape of the workpiece W is different and the direction of movement of the liquid ejection head 3a during printing is different.

[0124] In the example shown in Fig. 12, the entire surface WF of the workpiece is a plane parallel to a horizontal plane. Here, the entire area of ​​the surface WF in the direction along the X-axis is the printing area RP. In this embodiment, the main scanning direction DS is the X2 direction when viewed in the direction along the Z-axis. The main scanning direction DS may also be the X1 direction.

[0125] Here, the printing area RP is divided into a first area RP1, a second area RP2, and a third area RP3. However, when viewed in the direction along the Z axis, these areas are arranged in the order of the second area RP2, the third area RP3, and the first area RP1 in the X2 direction. The widths of the first area RP1, the second area RP2, and the third area RP3 are not particularly limited, but are determined, for example, based on the distance from the base 210. For example, the area of ​​the printing area RP where the distance is greater than or equal to a predetermined distance is the first area RP1, and after providing the third area RP3 of an appropriate width, the remaining area is the second area RP2.

[0126] Here, the distance d1 between the first region RP1 and the base 210 when ink is ejected from the liquid ejection head 3a toward the first region RP1 is longer than the distance d2 between the second region RP2 and the base 210 when ink is ejected from the liquid ejection head 3a toward the second region RP2. As a result, the greater the extension amount of the arm 220, the higher the proportion of ink of the first size L that is contained in the region. In this way, the size of the ink is changed according to the extension amount of the arm 220, so that it is possible to print on the workpiece W more appropriately.

[0127] The greater the extension amount of the arm 220, the less stable the arm 220 becomes, which makes it easier for misalignment of the ink droplets to occur on the workpiece W, but by increasing the proportion of ink of the first size L, it is possible to suppress the overall misalignment of the recording dots due to the misalignment of the droplets. As a result, it is possible to suppress image degradation such as white streaks and color misalignment.

[0128] According to the second embodiment described above, printing can be performed appropriately regardless of the three-dimensional shape of the workpiece W. Note that the same effect as in this embodiment can be obtained even when printing is performed in a posture in which the workpiece W in the first embodiment is rotated 180° around the Z axis.

[0129] 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 illustrated below. Note that two or more embodiments selected from the following exemplary embodiments can be appropriately combined as long as they are not contradictory to each other.

[0130] 3-1. Variation 1 The shape of the workpiece W is not limited to the above-mentioned form.

[0131] 13 and 14 are diagrams showing other examples of the shape of the workpiece W. The workpiece W shown in FIG. 13 has a pair of flat surfaces WFa, a concave curved surface WFb, and a convex curved surface WFc. When printing on such a workpiece W, printing is performed using the firing number table TB2 with the flat surfaces WFa as the second region, while printing is performed using the firing number table TB1 with the curved surfaces WFb and WFc as the first region. This allows printing to be performed appropriately, similar to the first embodiment described above.

[0132] The workpiece W shown in Fig. 14 has a pair of flat surfaces WFa, a bottom surface WFd of a recess, and a side surface WFe of the recess. When printing on such a workpiece W, printing is performed using the firing number table TB2 with the flat surface WFa as the second region, while printing is performed using the firing number table TB1 with the bottom surface WFd and the side surface WFe as the first region. This allows printing to be performed appropriately, similar to the first embodiment described above.

[0133] 3-2. Variation 2 In the above embodiment, a mode in which borderless printing is performed is exemplified, but the present invention is not limited to this mode, and the printing start position and printing end position may be positions away from the corners of the workpiece W.

[0134] 3-3. Variation 3 Not only can the ratio of each size of liquid used be different between the first region RP1 and the second region RP2, but the waveform of the drive signal Com used for printing on the first region RP1 or the movement speed of the liquid ejection head 3a can be made different from that used for printing on the second region RP2 in order to reduce misalignment of the ink landing in the first region RP1.

[0135] 3-4. Variation 4 In the above-mentioned embodiment, a configuration in which a six-axis vertical multi-axis robot is used as the moving mechanism is exemplified, but is not limited to this configuration. The moving mechanism may be, for example, a vertical multi-axis robot other than six axes, or a horizontal multi-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 the balance between the print quality in the printing operation and the degree of freedom of the robot's operation in the non-printing operation, it is preferable that the robot is a multi-axis robot with six or more axes.

[0136] 3-5. Variation 5 In the above embodiment, the head may be fixed to the robot by gripping the head with a gripping mechanism such as a hand attached as an end effector of the robot, but the present invention is not limited to this configuration.

[0137] 3-6. Variation 6 In the above-mentioned embodiment, the robot is exemplified as a robot that moves the head, but the present invention is not limited to this configuration, and may be configured such that, for example, the position of the liquid ejection head is fixed, and the robot moves the workpiece, thereby changing the position and posture of the workpiece three-dimensionally relative to the head. In this case, for example, the workpiece is gripped by a gripping mechanism such as a hand attached to the tip of the robot arm.

[0138] 3-7. Variation 7 In the above embodiment, a configuration in which printing is performed using one type of ink is exemplified, but the present disclosure is not limited to this configuration and can also be applied to a configuration in which printing is performed using two or more types of ink. When two or more types of ink are used, a shot number table for the first region and a shot number table for the second region are prepared for each type of ink.

[0139] 3-8. Variation 8 In the above embodiment, two types of tables are used, a shot number table TB1 for the first region and a shot number table TB2 for the second region, but three or more different tables may be used for each region to be printed. Also, the shot number table TB2 shown in Fig. 7 and the shot number table TB1 shown in Fig. 8 are each merely examples, and are not intended to be limiting. For example, the number of ink shots for each of the second size M and the third size S may be gradually reduced after exceeding a predetermined gradation value.

[0140] 3-9. Variation 9 The use of the three-dimensional printing device of the present disclosure is not limited to printing images. For example, a three-dimensional printing device that ejects a solution of a color material is used as a manufacturing device that forms a color filter for a liquid crystal display device. Also, a three-dimensional printing device that ejects a solution of a conductive material is used as a manufacturing device that forms wiring and electrodes for a wiring board. Also, a three-dimensional printing device can be used as a jet dispenser that applies a liquid such as an adhesive to a medium.

[0141] 4. Notes The following is a summary of this disclosure.

[0142] (Additional Note 1) A three-dimensional object printing device of a first aspect, which is a preferred example of the present disclosure, comprises a liquid ejection head that ejects liquid, and a moving mechanism that holds the liquid ejection head and moves the liquid ejection head relative to a three-dimensional workpiece, wherein a first number of shots, which is the number of times a first size of liquid is ejected per unit area from the liquid ejection head toward a first region of the workpiece when a first gradation value is input, is greater than a second number of shots, which is the number of times the first size of liquid is ejected per unit area from the liquid ejection head toward a second region of the workpiece when the first gradation value is input.

[0143] In the above embodiment, the first number of shots is greater than the second number of shots, so that the size of the ejected liquid is changed depending on the printing location on the workpiece. This allows the workpiece to be printed more appropriately even if the distance between the liquid ejection head and the workpiece changes. In contrast, in an embodiment in which the first number of shots and the second number of shots are equal, the size of the ejected liquid is constant, so if the distance between the liquid ejection head and the workpiece changes depending on the shape of the workpiece, the print quality may not be stable.

[0144] (Note 2) In the second aspect, which is a preferred example of the first aspect, a third number of shots, which is the number of times that a second size of liquid smaller than the first size is ejected from the liquid ejection head toward the first region per unit area when the first gradation value is input, is smaller than a fourth number of shots, which is the number of times that the second size of liquid is ejected from the liquid ejection head toward the second region per unit area when the first gradation value is input. In the above aspect, it is possible to suppress graininess of the printed image in the second region. In contrast, in an aspect in which the second size of liquid is not used, if the amount of the first size of liquid increases, there is a risk of graininess being generated in the printed image.

[0145] (Note 3) In the third aspect, which is a preferred example of the second aspect, an image is formed on the workpiece by the first size liquid, the second size liquid, and a third size liquid smaller than the second size. In the above aspect, the range of gradation values ​​can be efficiently expanded.

[0146] (Note 4) In a fourth aspect, which is a preferred example of any of the first to third aspects, the amount of liquid ejected per unit area from the liquid ejection head toward the first region when the first gradation value is input is equal to the amount of liquid ejected per unit area from the liquid ejection head toward the second region when the first gradation value is input. In the above aspects, an amount of liquid according to the input gradation value is ejected toward each of the first and second regions.

[0147] (Additional Note 5) In a fifth aspect, which is a preferred example of any of the first to fourth aspects, the second number of shots is 0. In the above aspect, graininess of the printed image in the second region can be suppressed.

[0148] (Note 6) In the sixth aspect, which is a preferred example of any of the first to fifth aspects, the number of times the first size liquid is ejected per unit area from the liquid ejection head toward a third area, which is an area located between the first and second areas of the workpiece, decreases from the first area toward the second area. In the above aspects, the number of ejections of the first size liquid decreases from the first area toward the second area. Therefore, it is possible to suppress a sudden change in the graininess of the print image quality from the first area toward the second area.

[0149] (Note 7) In the seventh aspect, which is a preferred example of any one of the first to sixth aspects, a measuring unit that measures the shape of the workpiece and a control unit that determines the size of the liquid to be ejected from the liquid ejection head based on the measurement result of the measuring unit are provided. In the above aspects, the size of the liquid is changed according to the measurement result of the measuring unit, so that printing can be more appropriately performed according to the shape of the workpiece.

[0150] (Note 8) In the eighth aspect, which is a preferred example of any of the first to seventh aspects, the distance between the liquid ejection head and the first region when liquid is ejected from the liquid ejection head toward the first region is greater than the distance between the liquid ejection head and the second region when liquid is ejected from the liquid ejection head toward the second region. In the above aspects, the greater the distance between the liquid ejection head and the workpiece, the higher the proportion of liquid of the first size contained in the region. In this way, the size of the liquid is changed according to the distance between the liquid ejection head and the workpiece, so that the workpiece can be printed more appropriately.

[0151] (Note 9) In the ninth aspect, which is a preferred example of any one of the first to eighth aspects, when a virtual plane is set along the installation surface of the workpiece, the angle between the first region and the virtual plane is larger than the angle between the second region and the virtual plane. In the above aspects, the larger the inclination angle of the region, the higher the proportion of the first size liquid contained. In this way, the size of the liquid is changed according to the inclination angle, so that the workpiece can be printed more appropriately.

[0152] (Appendix 10) In the tenth aspect, which is a preferred example of any one of the first to ninth aspects, the movement mechanism includes a base and an arm connected to the base for changing the position and attitude of the liquid ejection head relative to the workpiece, and the distance between the first region and the base when liquid is ejected from the liquid ejection head toward the first region is longer than the distance between the second region and the base when liquid is ejected from the liquid ejection head toward the second region. In the above aspect, the greater the extension amount of the arm, the higher the proportion of liquid of the first size contained in the region. In this way, the size of the liquid is changed according to the extension amount of the arm, so that printing can be performed more appropriately on the workpiece.

[0153] (Appendix 11) A printing method of an eleventh aspect, which is a preferred example of the present disclosure, is a printing method in a three-dimensional printing device including a liquid ejection head that ejects liquid, and a moving mechanism that holds the liquid ejection head and moves the liquid ejection head relative to a three-dimensional workpiece, the method including the steps of ejecting liquid of a first size from the liquid ejection head toward a first region of the workpiece, with the proportion of liquid of the first size contained per unit area being a first ratio, and ejecting liquid of the first size from the liquid ejection head toward a second region of the workpiece, with the proportion of liquid of the first size contained per unit area being a second ratio.

[0154] In the above embodiment, the ratio of the first size liquid to the first region and the second region is different from each other, so that the size of the liquid to be discharged is changed depending on the printing location on the workpiece. This allows more appropriate printing on the workpiece even if the distance between the liquid discharge head and the workpiece changes. [Explanation of symbols]

[0155] 1...3D object printing device, 2...robot (movement mechanism), 2a...arm drive mechanism, 3...head unit, 3a...liquid ejection head, 3b...switch circuit, 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, 7B...processing circuit, 7a...memory circuit, 7b...processing circuit, 8...control unit, 9...measurement unit, 210...base, 220...a arm, 221...arm, 222...arm, 223...arm, 224...arm, 225...arm, 226...arm, BN...mounting surface, CLK...clock signal, CNG...change signal, Com...drive signal, D1...output, D3...signal, DS...main scanning direction, Da...path information, Dc...work information, Img...print data, J...joint, J1...joint, J2...joint, J3...joint, J4...joint, J5...joint, J6...joint, K...tone value, L...first size, LAT...latch signal, M ...second size, n...nozzle, O1...rotation axis, O2...rotation axis, O3...rotation axis, O4...rotation axis, O5...rotation axis, O6...rotation axis, PD...driving pulse, PE...position, PG...distance, PG1...distance, PG2...distance, PR...program, PS...position, PTS...timing signal, PX...unit area, RP...printing area, RP1...first area, RP2...second area, RP3...third area, RU...movement path, S...third size, S10...process, S20...process, S21...process, S22...process , S23...process, S30...process, S31...first printing process, S32...second printing process, S33...third printing process, SI...control signal, Sk1...control signal, TB1...number of shots table, TB2...number of shots table, VBS...offset potential, VHV...power supply potential, W...work, WF...surface, WF1...surface, WF2...surface, WFa...flat surface, WFb...curved surface, WFc...curved surface, WFd...bottom surface, WFe...side surface, d1...distance, d2...distance, dCom...waveform designation signal, θ1...angle, θ2...angle.

Claims

1. A liquid ejection head that ejects liquid; a moving mechanism that holds the liquid ejection head and moves the liquid ejection head relative to a three-dimensional workpiece, a first number of shots, which is the number of times that liquid of a first size is ejected per unit area from the liquid ejection head toward the first region of the work when a first gradation value is input, is greater than a second number of shots, which is the number of times that liquid of the first size is ejected per unit area from the liquid ejection head toward the second region of the work when the first gradation value is input; A three-dimensional object printing device.

2. a third number of shots, which is the number of times that liquid of a second size smaller than the first size is ejected per unit area from the liquid ejection head toward the first region when the first gradation value is input, is smaller than a fourth number of shots, which is the number of times that liquid of the second size is ejected per unit area from the liquid ejection head toward the second region when the first gradation value is input.

2. The three-dimensional object printing apparatus according to claim 1 .

3. an image is formed on the workpiece by the liquid of the first size, the liquid of the second size, and the liquid of a third size smaller than the second size; 3. The three-dimensional object printing device according to claim 2 .

4. a discharge amount per unit area of ​​liquid discharged from the liquid discharge head toward the first region when the first gradation value is input is equal to a discharge amount per unit area of ​​liquid discharged from the liquid discharge head toward the second region when the first gradation value is input; The three-dimensional object printing device according to any one of claims 1 to 3.

5. The second number of shots is 0. The three-dimensional object printing device according to any one of claims 1 to 3.

6. the number of times the liquid of the first size is ejected per unit area from the liquid ejection head toward a third region, which is a region located between the first region and the second region of the workpiece, decreases from the first region toward the second region; The three-dimensional object printing device according to any one of claims 1 to 3.

7. A measuring unit for measuring a shape of the workpiece; a control unit that determines a size of the liquid to be ejected from the liquid ejection head based on a measurement result of the measurement unit. The three-dimensional object printing device according to any one of claims 1 to 3.

8. a distance between the liquid ejection head and the first region when liquid is ejected from the liquid ejection head toward the first region is greater than a distance between the liquid ejection head and the second region when liquid is ejected from the liquid ejection head toward the second region; The three-dimensional object printing device according to any one of claims 1 to 3.

9. When a virtual plane is set along the installation surface of the workpiece, an angle between the first region and the virtual plane is larger than an angle between the second region and the virtual plane; The three-dimensional object printing device according to any one of claims 1 to 3.

10. The moving mechanism includes: A base and an arm connected to the base and configured to change a position and a posture of the liquid ejection head relative to the workpiece; a distance between the first region and the base when liquid is ejected from the liquid ejection head toward the first region is longer than a distance between the second region and the base when liquid is ejected from the liquid ejection head toward the second region; The three-dimensional object printing device according to any one of claims 1 to 3.

11. A liquid ejection head that ejects liquid; a moving mechanism that holds the liquid ejection head and moves the liquid ejection head relative to a three-dimensional workpiece, a step of discharging liquid of a first size from the liquid discharge head toward a first region of the workpiece, the ratio of the liquid of the first size contained per unit area being a first ratio; and ejecting the liquid of the first size from the liquid ejection head toward a second region of the workpiece, with a ratio of the liquid of the first size contained per unit area being a second ratio. A printing method comprising:

Images