Printing device

Abstract

To improve printing quality in a printing device using a robot.SOLUTION: A printing device has a head, and a robot changing a position and a posture of the head to a workpiece. The head includes a first nozzle array on which a plurality of nozzles discharging a first ink are aligned, and a second nozzle array on which a plurality of nozzles discharging a second ink are aligned. The robot has an arm portion that has a tip end, a base end, and a plurality of joints, and a base portion connected to the base end. At the tip end, the head is supported. The brightness of the second ink is lower than the brightness of the first ink. The plurality of joints have a first joint that is the closest joint to the tip end among the plurality of joints. The first joint is a rotary mechanism around a first rotation shaft, and when viewed in a direction along the first rotation shaft, a distance between the second nozzle array and the first rotation shaft is smaller than a distance between the first nozzle array and the first rotation shaft.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a printing apparatus.

Background Art

[0002] An inkjet printing apparatus using a robot such as an articulated robot is known. For example, the apparatus described in Patent Document 1 includes a head that is an inkjet head and a robot that holds the head.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When printing using a plurality of colors of ink, generally, a plurality of nozzle arrays for each color of ink are provided in the head. Patent Document 1 does not describe anything about the arrangement of a plurality of nozzle arrays when discharging a plurality of colors of ink. In a printing apparatus that moves the head using a robot, when printing using a plurality of colors of ink, it is desired to realize an appropriate arrangement of a plurality of nozzle arrays so as to obtain good printing quality.

Means for Solving the Problems

[0005] In order to solve the above problems, one aspect of the printing apparatus according to the present disclosure includes a first nozzle row in which a plurality of nozzles for discharging a first ink are arranged, and a second nozzle row in which a plurality of nozzles for discharging a second ink are arranged. A head including: an arm having a tip, a base end, and a plurality of joints; and a base portion connected to the base end, wherein the head is supported at the tip, and a robot for changing the position and orientation of the head with respect to a workpiece. The lightness of the second ink is lower than the lightness of the first ink. The plurality of joints include a first joint that is the joint closest to the tip among the plurality of joints. The first joint is a rotation mechanism around a first rotation axis, and when viewed in the direction along the first rotation axis, the distance between the second nozzle row and the first rotation axis is smaller than the distance between the first nozzle row and the first rotation axis.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

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Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0007] Hereinafter, preferred embodiments according to the present disclosure will be described with reference to the accompanying drawings. Note that the dimensions and scales of each part in the drawings are appropriately different from the actual ones, and there are also parts schematically shown for easy understanding. Further, the scope of the present disclosure is not limited to these embodiments unless otherwise specified in the following description.

[0008] In the following description, for convenience, the X-axis, Y-axis, and Z-axis that intersect each other are appropriately used. 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 directions opposite to each other along the Y-axis are the Y1 direction and the Y2 direction. Also, the directions opposite to each other along the Z-axis are the Z1 direction and the Z2 direction.

[0009] Here, the X-axis, Y-axis, and Z-axis correspond to the coordinate axes of the world coordinate system set in the space where the 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 the base 210 of the robot 2 described later is associated with the world coordinate system by calibration. In the following, for convenience, a case where the world coordinate system is used as the robot coordinate system to control the operation of the robot 2 is exemplified.

[0010] Note that the Z-axis does not have to be a vertical axis. Also, the X-axis, Y-axis, and Z-axis are typically perpendicular to each other, but are not limited thereto and may not be perpendicular. For example, the X-axis, Y-axis, and Z-axis may intersect each other at an angle within the range of 80° or more and 100° or less.

[0011] 1. First Embodiment 1-1. Outline of the Printing Device FIG. 1 is a perspective view showing an outline of a printing apparatus 1 according to the first embodiment. The printing apparatus 1 is an apparatus that performs printing on the surface of a workpiece W by an inkjet method.

[0012] The workpiece W has a surface WF to be printed. In the example shown in FIG. 1, the workpiece W is a rectangular parallelepiped and the surface WF is a plane. During printing, the workpiece W is supported by a structure such as a predetermined installation table, a robot hand, or a conveyor as necessary. Note that the mode such as the shape or size of the workpiece W or the surface WF is not limited to the example shown in FIG. 1 and is arbitrary. For example, the surface WF may have a curved or bent portion, or the workpiece W may be a sheet material such as paper or cloth. Also, the position or posture of the workpiece W or the surface WF during printing may be arbitrary as long as printing is possible and is not limited to the example shown in FIG. 1.

[0013] As shown in FIG. 1, the printing apparatus 1 includes a robot 2, a head unit 3, a controller 5, a piping unit 10, and a wiring unit 11. Hereinafter, these will be briefly described in order.

[0014] The robot 2 is a robot that changes the position and posture of the head unit 3 in the world coordinate system. In the example shown in FIG. 1, the robot 2 is a so-called six-axis vertical articulated robot.

[0015] As shown in FIG. 1, the robot 2 includes a base 210 and an arm 220.

[0016] The base 210 is a table 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 in the Z1 direction by screwing or the like. Note that 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. For example, it may be a surface of a wall, a ceiling, a movable cart, or the like.

[0017] The wrist 220 is a six-axis robotic arm having a proximal end EB attached to the base 210 and a distal end ET that changes its position and orientation three-dimensionally with respect to the proximal end EB. Specifically, the wrist 220 has arms 221, 222, 223, 224, 225, and 226, also referred to as links. These are connected in the order of arms 221, 222, 223, 224, 225, and 226.

[0018] The arm 221 is connected to the base 210 via a joint 230_1 so as to be rotatable about a rotation axis O1. The arm 222 is connected to the arm 221 via a joint 230_2 so as to be rotatable about a rotation axis O2. The arm 223 is connected to the arm 222 via a joint 230_3 so as to be rotatable about a rotation axis O3. The arm 224 is connected to the arm 223 via a joint 230_4 so as to be rotatable about a rotation axis O4. The arm 225 is connected to the arm 224 via a joint 230_5 so as to be rotatable about a rotation axis O5. The arm 226 is connected to the arm 225 via a joint 230_6 so as to be rotatable about a rotation axis O6. Note that the joint 230_6 is an example of the "first joint", and the rotation axis O6 is an example of the "first rotation axis". The joint 230_5 is an example of the "second joint", and the rotation axis O5 is an example of the "second rotation axis".

[0019] Each of the joints 230_1 to 230_6 is a mechanism that rotatably connects one of two adjacent members among the base 210 and the arms 221 to 226 to the other. Hereinafter, each of the joints 230_1 to 230_6 may be referred to as "joint 230". Here, the proximal end EB is one end of the wrist 220 whose position in the base coordinate system does not change even when the joint 230 rotates, and the distal end ET is the other end of the wrist 220 whose position in the base coordinate system changes due to the rotation of the joint 230_6. The proximal end EB can be defined, for example, as the intersection of the boundary between the base 210 and the arm 221 and the rotation axis O1. Also, the distal end ET can be defined, for example, as the intersection of the end face of the arm 226 that is farthest from the arm 225 or the plane extending the end face and the rotation axis O6.

[0020] Although not shown in FIG. 1, each of the joints 230_1 to 230_6 is provided with a drive mechanism for rotating one of the corresponding two members with respect to the other. The drive mechanism includes, for example, a motor that generates a driving force for the rotation, a speed reducer that decelerates and outputs the driving force, and an encoder such as a rotary encoder that detects an operation amount such as the angle of the rotation. The assembly of the drive mechanisms of the joints 230_1 to 230_6 corresponds to the arm drive mechanism 2a shown in FIG. 2 described later. Further, the motor corresponds to the motors 2a1 to 2a6 shown in FIG. 2.

[0021] 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.

[0022] Regarding these rotation axes, the term "perpendicular" includes not only the case where the angle formed by two rotation axes is exactly 90°, but also the case where the angle formed by two rotation axes deviates within a range of about ±5° from 90°. Similarly, the term "parallel" includes not only the case where two rotation axes are exactly parallel, but also the case where one of the two rotation axes is inclined within a range of about ±5° with respect to the other.

[0023] At the tip ET of the arm portion 220 of the robot 2 described above, as an end effector, the head unit 3 is mounted in a state of being fixed by screwing or the like.

[0024] The head unit 3 is an assembly having a head 3a that discharges a plurality of types of inks having different lightnesses toward the work W. In the present embodiment, the head unit 3 has, in addition to the head 3a, a pressure regulating valve 3b and an energy emitting portion 3c. The details of the head unit 3 will be described based on FIG. 3 described later.

[0025] In this embodiment, a case where four types of inks, i.e., a first ink, a second ink, a third ink, and a fourth ink having different lightness levels from each other, are used is exemplified. The lightness levels of these inks are, in descending order, the first ink, the third ink, the fourth ink, and the second ink. When performing full-color printing, typically, these four types of inks are a yellow ink, a magenta ink, a cyan ink, and a black ink. In this case, the first ink is a yellow ink, the second ink is a black ink, and among the third ink and the fourth ink, one is a magenta ink and the other is a cyan ink. Here, the lightness can be defined, for example, as the lightness in the CIE L*a*b* color space defined by the International Commission on Illumination (CIE). In this embodiment, the lightness in the CIE L*a*b* color space is 83 for the yellow ink, 54 for the magenta ink, 56 for the cyan ink, and 11 for the black ink. Note that the value of the lightness of the ink is obtained, for example, by creating a predetermined color patch by applying the ink on a medium such as printing paper and then measuring the color of the color patch with a colorimeter. Here, the comparison of the lightness levels of multiple types of inks is performed by creating color patches using the same amount of ink for each of the multiple types of inks on the same medium and comparing the measured values of the color patches of the multiple types of inks.

[0026] Each such ink is, for example, a liquid medium in which a coloring material such as a dye or a pigment is dissolved or dispersed in a solvent. Note that each ink may be an aqueous ink in which a coloring material such as a dye or a pigment is dissolved in an aqueous solvent, a curable ink using a curable resin such as an ultraviolet curable type, or a solvent-based ink in which a coloring material such as a dye or a pigment is dissolved in an organic solvent, etc., but a curable ink is preferably used. The curable ink is not particularly limited and may be, for example, any of a thermosetting type, a photocuring type, a radiation curing type, and an electron beam curing type, etc., but a photocuring type such as an ultraviolet curable type is preferable. Further, the ink containing the coloring material is not limited to a yellow ink, a magenta ink, a cyan ink, and a black ink, and may be, for example, a white ink, a gray ink, a light cyan ink, a light magenta ink, etc.

[0027] The piping section 10 and the wiring section 11 are each connected to the head unit 3. The piping section 10 is a group of pipes that supply ink from an ink tank (not shown) to the head unit 3. The wiring section 11 is a wiring or a group of wirings that supply an electric signal for driving the head 3a.

[0028] The controller 5 is a robot controller that controls the driving of the robot 2. Hereinafter, based on FIG. 2, the electrical configuration of the printing apparatus 1 will be described including a detailed description of the controller 5.

[0029] 1-2. Electrical Configuration of the Printing Apparatus FIG. 2 is a block diagram showing the electrical configuration of the printing apparatus 1 according to the first embodiment. In FIG. 2, among the components of the printing apparatus 1, the electrical components are shown. As shown in FIG. 2, in addition to the components shown in FIG. 1 described above, the printing apparatus 1 includes a control module 6 communicably connected to the controller 5, and a computer 7 communicably connected to the controller 5 and the control module 6.

[0030] Note that each of the electrical components shown in FIG. 2 may be appropriately divided, a part thereof may be included in other components, or it may be integrally configured with other components. For example, part or all of the functions of the controller 5 or the control module 6 may be realized by the computer 7, or may be realized 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.

[0031] 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 in the head unit 3 with the operation of the robot 2.

[0032] The controller 5 includes a storage circuit 5a and a processing circuit 5b.

[0033] The memory circuit 5a stores various programs executed by the processing circuit 5b and various data processed by the processing circuit 5b. The memory circuit 5a includes, for example, one or both semiconductor memories of a volatile memory such as a RAM (Random Access Memory) and a non-volatile memory such as a ROM (Read Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a PROM (Programmable ROM). Note that part or all of the memory circuit 5a may be included in the processing circuit 5b.

[0034] Path information Da is stored in the memory circuit 5a. The path information Da is information indicating the path along which the head unit 3 should move and the posture of the head unit 3 in the path. The path information Da is generated using, for example, information obtained by direct teaching or offline teaching, and information such as CAD (computer-aided design) data indicating the shape of the workpiece W. The path information Da is represented using, for example, coordinate values in a base coordinate system or a world coordinate system. The above path information Da is input from the computer 7 to the memory circuit 5a.

[0035] The processing circuit 5b controls the operation of the arm drive mechanism 2a of the robot 2 based on the path information Da and generates a signal D3. The processing circuit 5b includes, for example, one or more processors such as a CPU (Central Processing Unit). 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 the CPU.

[0036] Here, the arm drive mechanism 2a is an assembly of the drive mechanisms of the aforementioned joints 230_1 to 230_6. For each joint 230, it has motors 2a1 to 2a6 for driving the joint 230 and an encoder (not shown) for detecting the rotation angle of the joint 230. Note that motor 2a1 is the motor for driving joint 230_1. Motor 2a2 is the motor for driving joint 230_2. Motor 2a3 is the motor for driving joint 230_3. Motor 2a4 is the motor for driving joint 230_4. Motor 2a5 is the motor for driving joint 230_5. Motor 2a6 is the motor for driving joint 230_6.

[0037] The processing circuit 5b performs inverse kinematics calculation, which is an operation to convert the path information Da into operation amounts such as the rotation angle and rotation speed of each joint 230 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 drive mechanism 2a so that the operation amounts such as the actual rotation angle and rotation speed of each joint 230 become the aforementioned calculation results based on the path information Da. The control signal Sk1 is a signal for controlling the drive of the motors of the arm drive mechanism 2a. Here, the control signal Sk1 is corrected by the processing circuit 5b based on the output from a distance meter (not shown) as necessary. The distance meter is installed in the head unit 3, for example, and outputs a signal according to the distance to the workpiece W.

[0038] Also, the processing circuit 5b generates a signal D3 based on the output D1 from at least one of the plurality of encoders of the arm drive mechanism 2a. For example, the processing circuit 5b generates a trigger signal including a pulse at the timing when the output D1 from one of the plurality of encoders becomes a predetermined value as the signal D3.

[0039] The control module 6 is a circuit that controls the ink ejection operation in the head unit 3 based on the signal D3 output from the controller 5 and the print data Img from the computer 7. The control module 6 includes a timing signal generation circuit 6a, a power supply circuit 6b, a control circuit 6c, and a drive signal generation circuit 6d.

[0040] The timing signal generation circuit 6a generates a timing signal PTS based on the signal D3. The timing signal generation circuit 6a is composed of, for example, a timer that starts generating the timing signal PTS upon detection of the signal D3. The timing signal PTS includes, for example, pulses defined based on the output D1.

[0041] The power supply circuit 6b receives power supply from a commercial power supply (not shown) and generates various predetermined potentials. The generated various potentials are appropriately supplied to each part of the control module 6 and 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. Also, the power supply potential VHV is supplied to the drive signal generation circuit 6d.

[0042] The control circuit 6c generates a print data 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. Among 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.

[0043] The print data signal SI is a digital signal for specifying the operating state of the drive elements of the head 3a of the head unit 3. Specifically, the print data signal SI specifies whether to supply the drive signal Com, which will be described later, to the drive element based on the print data. By this specification, for example, it is specified whether to eject ink from the nozzle corresponding to the drive element, or 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 used in combination with the print data signal SI, and define the ejection timing of the ink from the nozzle by defining the drive timing of the drive element. The clock signal CLK is a reference clock signal synchronized with the timing signal PTS.

[0044] The above control circuit 6c includes, for example, a processor such as one or more CPUs. Note that the control circuit 6c may include a programmable logic device such as an FPGA instead of or in addition to the CPU.

[0045] The drive signal generation circuit 6d is a circuit that generates a drive signal Com for driving each drive element of the head 3a of the head unit 3. Specifically, the drive signal generation circuit 6d has, for example, a DA conversion circuit and an amplification circuit. In the drive signal generation circuit 6d, the DA conversion circuit converts the waveform specification signal dCom from the control circuit 6c from a digital signal to an analog signal, and the amplification 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, the signal of 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 to supply at least a part of the waveforms included in the drive signal Com as the drive pulse PD based on the print data signal SI.

[0047] The computer 7 has a function of supplying information such as the path information Da to the controller 5 and a function of supplying information such as the print data Img to the control module 6. In addition to these functions, the computer 7 of the present embodiment has a function of controlling the drive of the energy emitting unit 3c. The computer 7 is, for example, a desktop or notebook computer installed with a program for realizing these functions.

[0048] 1-3. Configuration of the head unit FIG. 3 is a perspective view showing a schematic configuration of the head unit 3 used in the first embodiment. In the following description, for convenience, the a-axis, b-axis, and c-axis that intersect each other are appropriately used. Also, in the following description, one direction along the a-axis is the a1 direction, and the direction opposite to the a1 direction is the a2 direction. Similarly, the directions opposite to each other along the b-axis are the b1 direction and the b2 direction. Also, the directions opposite to each other along the c-axis are the c1 direction and the c2 direction.

[0049] 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 attitude relationship with the world coordinate system or the robot coordinate system described above change due to the operation of the robot 2 described above. In the example shown in FIG. 3, the c-axis is an axis parallel to the rotation axis O6 described above. Note that the a-axis, b-axis, and c-axis are typically orthogonal to each other, but are not limited thereto, and may intersect at an angle within a range of 80° or more and 100° or less, for example. Note that the tool coordinate system and the base coordinate system or the robot coordinate system are associated with each other by calibration. Also, the tool coordinate system is set such that, for example, the center of the ejection surface FN described below becomes the reference (TCP: tool center point).

[0050] As described above, the head unit 3 includes a head 3a, a pressure regulating valve 3b, and an energy emitting unit 3c. These are supported by a support 3f shown by a two-dot chain line in FIG. 3. In the example shown in FIG. 3, the number of each of the head 3a and the pressure regulating valve 3b included in the head unit 3 is one, but the number is not limited to the example shown in FIG. 3 and may be two or more. Further, the installation position of the pressure regulating valve 3b is not limited to the head unit 3, and may be, for example, an arm 226 or the like, or a position fixed to the base 210.

[0051] The support 3f is made of, for example, a metal material or the like and is a substantially rigid body. In the example shown in FIG. 3, the support 3f has a flat plate shape extending in a direction orthogonal to the a-axis. In the present embodiment, the head 3a is attached to the surface of the support 3f facing the a1 direction. On the other hand, the energy emitting unit 3c is attached to the surface of the support 3f facing the a2 direction. Note that the shape of the support 3f is not limited to the example shown in FIG. 3 and is arbitrary, and may be, for example, a box shape or the like.

[0052] The above support 3f is attached to the aforementioned arm 226. Therefore, the head 3a, the pressure regulating valve 3b, and the energy emitting unit 3c are collectively supported by the arm 226 by the support 3f. For this reason, the relative positions of the head 3a, the pressure regulating valve 3b, and the energy emitting unit 3c with respect to the arm 226 are fixed. In the example shown in FIG. 3, the pressure regulating valve 3b is disposed at a position in the c1 direction with respect to the head 3a. The energy emitting unit 3c is disposed at a position in the a2 direction with respect to the head 3a.

[0053] The head 3a has a discharge surface FN and a plurality of nozzles N that open to the discharge surface FN. The discharge surface FN is a nozzle surface where the nozzles N open, and is constituted by, for example, the surface of a nozzle plate in which the nozzles N are provided as through holes in a plate-like member made of a material such as silicon (Si) or metal.

[0054] In the example shown in FIG. 3, the normal direction of the ejection surface FN is the c2 direction. Here, the rotation axis O6 intersects the ejection surface FN. In the illustration, when viewed in the direction along the rotation axis O6, the center PC of the ejection surface FN coincides with the rotation axis O6. Note that when viewed in the direction along the rotation axis O6, the center PC of the ejection surface FN and the rotation axis O6 may be displaced.

[0055] The plurality of nozzles N provided on the ejection surface FN are divided into a first nozzle row L1, a second nozzle row L2, a third nozzle row L3, and a fourth nozzle row L4. These nozzle rows are arranged at intervals in the order of the first nozzle row L1, the fourth nozzle row L4, the second nozzle row L2, and the third nozzle row L3 in the a1 direction.

[0056] Each of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 is a set of a plurality of nozzles N linearly arranged in the direction along the b axis. In this embodiment, the nozzle density in the direction along the b axis of each individual nozzle N included in each nozzle row is 300 npi (number of nozzles per inch). However, the present invention is not limited to this, and a lower nozzle density may be used, but from the viewpoints of printing quality and efficiency, a nozzle density of 25 npi or more is preferable. Also, in order to achieve such a nozzle density, the nozzles N may be arranged in a staggered pattern in each nozzle row. Here, the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 eject different types of ink. Specifically, the first nozzle row L1 ejects the first ink. The second nozzle row L2 ejects the second ink. The third nozzle row L3 ejects the third ink. The fourth nozzle row L4 ejects the fourth ink. Since each ink is ejected in the c2 direction under ideal conditions, the c2 direction can also be expressed as the ejection direction. Note that the arrangement of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 will be described in detail later with reference to FIGS. 5 and 6.

[0057] Although not shown, the head 3a has, for each nozzle N, a piezoelectric element as a driving element and a cavity for storing ink. Here, the piezoelectric element discharges ink from the nozzle corresponding to the cavity by changing the pressure in the cavity corresponding to the piezoelectric element. Such a head 3a can be obtained, for example, by bonding a plurality of substrates such as a silicon substrate appropriately processed by etching or the like with an adhesive or the like. Note that, as a driving element for discharging ink from the nozzle, instead of the piezoelectric element, a heater for heating the ink in the cavity may be used.

[0058] Ink is supplied to the above-described head 3a from an ink tank (not shown) via a first supply pipe 10a1, a second supply pipe 10a2, a third supply pipe 10a3, and a fourth supply pipe 10a4. Here, a pressure regulating valve 3b is interposed between each of the first supply pipe 10a1, the second supply pipe 10a2, the third supply pipe 10a3, and the fourth supply pipe 10a4 and the head 3a. The first supply pipe 10a1 is a flexible pipe that supplies the first ink to the head 3a. The second supply pipe 10a2 is a flexible pipe that supplies the second ink to the head 3a. The third supply pipe 10a3 is a flexible pipe that supplies the third ink to the head 3a. The fourth supply pipe 10a4 is a flexible pipe that supplies the fourth ink to the head 3a.

[0059] In the example shown in FIG. 3, the downstream ends of the first supply pipe 10a1, the second supply pipe 10a2, the third supply pipe 10a3, and the fourth supply pipe 10a4 are arranged in the order of the first supply pipe 10a1, the fourth supply pipe 10a4, the second supply pipe 10a2, and the third supply pipe 10a3 in the a1 direction. Here, the distance between the downstream end of the second supply pipe 10a2 or the fourth supply pipe 10a4 and the rotation axis O6 is smaller than the distance between the downstream end of the first supply pipe 10a1 or the third supply pipe 10a3 and the rotation axis O6.

[0060] The pressure adjustment valve 3b is a valve mechanism that opens and closes according to the pressure of the ink in the head 3a. By this opening and closing, even if the positional relationship between the head 3a and the ink tank (not shown above) changes, the pressure of the ink in the head 3a is maintained at a negative pressure within a predetermined range. For this reason, stabilization of the meniscus of the ink formed at the nozzles N of the head 3a is achieved. As a result, it is possible to prevent air bubbles from entering the nozzles N and ink from overflowing from the nozzles N. Further, the ink from the pressure adjustment valve 3b is appropriately distributed to a plurality of locations of the head 3a via a branch flow path (not shown). Here, the ink from the ink tank (not shown) is transferred into the first supply pipe 10a1, the second supply pipe 10a2, the third supply pipe 10a3, and the fourth supply pipe 10a4 at a predetermined pressure by using a pump, a head difference, or the like. Although not shown, the pressure adjustment valve 3b has a configuration for ink flow path and pressure adjustment for each type of ink so that the pressure of each of the four types of inks described above can be individually adjusted.

[0061] The energy emitting unit 3c emits energy such as light, heat, electron beam, or radiation for curing or solidifying the ink on the workpiece W. For example, when the ink has ultraviolet curability, the energy emitting unit 3c is composed of a light emitting element such as an LED (light emitting diode) that emits ultraviolet rays. Further, the energy emitting unit 3c may appropriately include optical components such as a lens for adjusting the emission direction or emission range of the energy.

[0062] Here, the energy emitting unit 3c includes an emission surface FL that emits the energy, and is arranged such that the emission surface FL faces the c2 direction. Further, as described above, since the rotation axis O6 intersects the ejection surface FN, the distance between each nozzle row and the rotation axis O6 is smaller than the distance between the emission surface FL and the rotation axis O6.

[0063] Note that the energy emitting unit 3c does not necessarily have to completely cure or solidify the ink on the work W. In this case, for example, the ink after the energy irradiation from the energy emitting unit 3c may be completely cured or solidified by the energy from a curing light source separately installed on the installation surface of the base 210 of the robot 2.

[0064] 1-3. Printing Operation of the Printing Apparatus FIG. 4 is a diagram for explaining the printing operation of the printing apparatus 1 according to the first embodiment. In FIG. 4, the case of printing on a predetermined region RP of the surface WF of the work W placed at a position in the X2 direction rather than the base 210 of the robot 2 as viewed in the direction along the Y axis is illustrated. Note that, as viewed in the direction along the X axis, the work W may be arranged at a position shifted in the Y1 direction or the Y2 direction with respect to the base 210 of the robot 2. Further, when the robot 2 is suspended from the ceiling, the work W and the base 210 may be arranged at positions overlapping each other as viewed in the direction along the Z axis.

[0065] In the printing operation, while the robot 2 changes the position and posture of the head 3a, the head 3a discharges ink. The change in the position and posture of the head 3a is performed based on the path information Da. Thereby, the head 3a moves along the movement path RU while maintaining a predetermined posture with respect to the surface WF. Note that the movement of the head 3a along the movement path RU may be performed a plurality of times for each discharge of each color of ink, or the discharge of all the inks may be performed in parallel during one movement of the head 3a along the movement path RU.

[0066] The movement path RU is a path from the position PS to the position PE. The position PS is a position in the X1 direction relative to the predetermined region RP when viewed in the Z2 direction. The position PE is a position in the X2 direction relative to the predetermined region RP when viewed in the Z2 direction. During the period until the head 3a reaches above the predetermined region RP from the position PS, the head 3a accelerates until it reaches a predetermined speed. During the period when the head 3a is positioned above the predetermined region RP, the head 3a moves at a constant speed at the said predetermined speed. During the period until the head 3a reaches the position PE from above the predetermined region RP, the head 3a decelerates so that it can stop at the position PE. Here, the predetermined region RP is a region extending from the position PR1 to the position PR2 along the movement path RU.

[0067] In the example shown in FIG. 4, the movement path RU is linear when viewed in the Z2 direction. The robot 2 linearly moves the head 3a along the movement path RU by operating three or more of the six joints 230, including the joints 230_2, 230_3, and 230_5, during the execution of the printing operation. Also, the robot 2 moves the head 3a in a direction away from the base 210. Here, the aforementioned a1 direction faces forward in the moving direction of the head 3a. Therefore, the energy emission unit 3c is positioned behind the head 3a in the moving direction of the head 3a. For this reason, energy from the energy emission unit 3c can be irradiated onto the ink that has just landed on the surface WF from the head 3a.

[0068] Here, when viewed in the direction along the X-axis and the workpiece W is disposed at a position overlapping the base 210, the movement path RU forms a straight line along the X-axis when viewed in the Z2 direction. Also, in this case, during the execution of the printing operation, the robot 2 performs the printing operation by operating three of the six joints 230. More specifically, during the execution of the printing operation, the robot 2 keeps the respective rotation axes of the joint 230_2, the joint 230_3, and the joint 230_5 parallel to the Y-axis and operates these joints 230. By operating these three joints 230, the head 3a can be stably moved along the movement path RU. In this case, it is not necessary to operate the joint 230_6. On the other hand, when viewed in the direction along the X-axis, the workpiece W is disposed at a position shifted in the Y1 direction or the Y2 direction with respect to the base 210, and the movement path RU forms a straight line along the X-axis when viewed in the Z2 direction, it is necessary to operate the joint 230_6 as the head 3a moves along the movement path RU in order to maintain the posture of the head 3a with respect to the moving direction, so that the effects described later due to the arrangement of the nozzle rows become prominent.

[0069] Note that the robot 2 may move the head 3a from the position PE to the position PS along the movement path RU in a direction approaching the base 210. In this case, printing is performed in a state where the posture of the head unit 3 is rotated 180° about the rotation axis O6 from the state shown in FIG. 4 so that the a1 direction faces forward in the moving direction of the head 3a.

[0070] Also, during the execution of the printing operation, since the aforementioned a1 direction faces forward in the moving direction of the head 3a, the first nozzle row L1, the fourth nozzle row L4, the second nozzle row L2, and the third nozzle row L3 are arranged in this order from the side closer to the base 210 to the side farther from the base 210.

[0071] 1-4. Arrangement of Nozzle Rows FIG. 5 is a schematic plan view for explaining the arrangement as a plurality of nozzle rows in the first embodiment. In FIG. 5, a view of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 as the plurality of nozzle rows in the c1 direction is shown. As described above, in the a1 direction, the first nozzle row L1, the fourth nozzle row L4, the second nozzle row L2, and the third nozzle row L3 are arranged in this order. In the example shown in FIG. 5, these nozzle rows are arranged at equal intervals. Note that the intervals between these nozzle rows do not have to be equal. Also, the lengths of these nozzle rows may be different from each other.

[0072] Here, when viewed in the direction along the rotation axis O6, the rotation axis O6 is located inside the region RN defined by the set of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4. The region RN can be represented as a quadrilateral with the smallest area surrounding all the nozzles N provided on the ejection surface FN. In the example shown in FIG. 5, since the lengths of these nozzle rows are equal to each other and both ends of these nozzle rows are aligned, the shape of the region RN is a rectangle. Note that the shape of the region RN only needs to be a quadrilateral and is not limited to a rectangle. For example, when each nozzle row extends in the same direction inclined with respect to the b axis, the shape of the region RN is a parallelogram. Also, both ends of these nozzle rows do not have to be aligned. That is, at least one of these nozzle rows may be displaced in the extending direction of the nozzle row.

[0073] In the example shown in FIG. 5, when viewed in the direction along the rotation axis O6, the rotation axis O6 is located between the second nozzle row L2 and the fourth nozzle row L4. Note that the position of the rotation axis O6 when viewed in the direction along the rotation axis O6 is not limited to the example shown in FIG. 5, and may be, for example, a position overlapping the second nozzle row L2 or the fourth nozzle row L4. However, among the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4, it is preferable that the second nozzle row L2 is the nozzle row closest to the center PC of the ejection surface FN or the rotation axis O6.

[0074] As understood from the above, when viewed in the direction along the rotation axis O6, the distance DN12 between the second nozzle row L2 and the rotation axis O6 is smaller than the distance DN11 between the first nozzle row L1 and the rotation axis O6, and is also smaller than the distance DN13 between the third nozzle row L3 and the rotation axis O6.

[0075] Similarly, the distance DN14 between the fourth nozzle row L4 and the rotation axis O6 is smaller than the distance DN11 between the first nozzle row L1 and the rotation axis O6, and is also smaller than the distance DN13 between the third nozzle row L3 and the rotation axis O6.

[0076] In the example shown in FIG. 5, the distance DN11 is equal to the distance DN13, and the distance DN12 is equal to the distance DN14. Note that the distance DN11 may be different from the distance DN13. Also, the distance DN12 may be different from the distance DN14.

[0077] FIG. 6 is a schematic side view for explaining the arrangement of a plurality of nozzle rows in the first embodiment. In FIG. 6, a view of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 as the plurality of nozzle rows in the b1 direction is shown.

[0078] Here, as shown in FIG. 6, the rotation axis O5 is orthogonal to the rotation axis O6. When viewed in the direction along the rotation axis O5, the distance DN22 between the second nozzle row L2 and the rotation axis O5 is smaller than the distance DN21 between the first nozzle row L1 and the rotation axis O5, and is also smaller than the distance DN23 between the third nozzle row L3 and the rotation axis O5.

[0079] Similarly, when viewed in the direction along the rotation axis O5, the distance DN24 between the fourth nozzle row L4 and the rotation axis O5 is smaller than the distance DN21 between the first nozzle row L1 and the rotation axis O5, and is also smaller than the distance DN23 between the third nozzle row L3 and the rotation axis O5.

[0080] In the example shown in FIG. 6, the distance DN21 is equal to the distance DN23, and the distance DN22 is equal to the distance DN24. Note that the distance DN21 may be different from the distance DN23. Also, the distance DN22 may be different from the distance DN24.

[0081] 1-5. Summary of the First Embodiment As described above, the printing apparatus 1 has the head 3a and the robot 2 that changes the position and orientation of the head 3a with respect to the work W. Here, the head 3a includes a first nozzle row L1 in which a plurality of nozzles N for discharging the first ink are arranged, and a second nozzle row L2 in which a plurality of nozzles N for discharging the second ink are arranged. The robot 2 has an arm portion 220 having a tip ET, a base end EB, and a plurality of joints 230, and a base portion 210 connected to the base end EB. The head 3a is supported by the tip ET. The lightness of the second ink is lower than that of the first ink. The plurality of joints 230 have a joint 230_6 which is an example of the "first joint". The joint 230_6 is the joint 230 closest to the tip ET among the plurality of joints 230. Further, the joint 230_6 is a rotation mechanism around a rotation axis O6 which is an example of the "first rotation axis".

[0082] Moreover, when viewed in the direction along the rotation axis O6, the distance DN12 between the second nozzle row L2 and the rotation axis O6 is smaller than the distance DN11 between the first nozzle row L1 and the rotation axis O6.

[0083] In the above printing apparatus 1, since the lightness of the second ink is lower than that of the first ink, the landing error of the second ink with respect to the work W is more noticeable than the landing error of the first ink with respect to the work W. That is, the second ink is more likely to cause a decrease in printing quality due to the landing error with respect to the work W than the first ink. Therefore, in order to improve the printing quality, when viewed in the direction along the rotation axis O6, the distance DN12 between the second nozzle row L2 and the rotation axis O6 is made smaller than the distance DN11 between the first nozzle row L1 and the rotation axis O6

[0084] More specifically, the joint 230_6 may be more likely to cause vibration of the arm 220 than other joints 230 due to insufficient holding force caused by the small rated output of the motor, backlash of the speed reducer, etc. Here, the larger the distance from the rotation axis O6 to the nozzle N, the larger the landing error of the ink due to this vibration. This is because the larger the distance from the rotation axis O6 to the nozzle N, the larger the moment around the rotation axis O6. Therefore, by making the distance DN12 smaller than the distance DN11, the influence of the moment on the second nozzle row L2 can be suppressed compared to the first nozzle row L1. As a result, the vibration of the second nozzle row L2 associated with the vibration of the joint 230_6 can be made smaller than the vibration of the first nozzle row L1. For this reason, the landing error of the second ink on the work W can be reduced.

[0085] As described above, motors 2a1 to 2a6 for driving the joints 230 are provided for each of the plurality of joints 230. Here, the rated output of the motor 2a6 for driving the joint 230_6 is smaller than the rated outputs of the motors 2a1 to 2a5 for driving the respective joints 230_1 to 230_5 excluding the joint 230_6 among the plurality of joints 230.

[0086] On the other hand, the vibration of the first nozzle row L1 associated with the vibration of the joint 230_6 is larger than the vibration of the second nozzle row L2. However, in the first nozzle row L1, the first ink with a less noticeable landing error compared to the second ink is used.

[0087] As described above, by improving the landing accuracy of the second ink, which is more likely to have a noticeable landing error, compared to the landing accuracy of the first ink, which is less likely to have a noticeable landing error, among the first ink and the second ink with different brightness levels from each other, it is possible to reduce the degradation of the printing quality due to the landing error of the ink on the work W as a whole. Therefore, the printing quality can be improved compared to a configuration where the distance DN12 is greater than or equal to the distance DN11.

[0088] In the present embodiment, as described above, the head 3a further includes a third nozzle row L3 in which a plurality of nozzles N for discharging a third ink are arranged. The lightness of the third ink is lower than that of the first ink and higher than that of the second ink. Moreover, when viewed in the direction along the rotation axis O6, the distance DN12 between the second nozzle row L2 and the rotation axis O6 is smaller than the distance DN13 between the third nozzle row L3 and the rotation axis O6. Furthermore, when viewed in the direction along the rotation axis O6, the second nozzle row L2 is positioned between the first nozzle row L1 and the third nozzle row L3. Therefore, even when the third ink is used in addition to the first ink and the second ink, it is possible to reduce a decrease in printing quality due to an ink landing error on the work W.

[0089] Also, in the present embodiment, as described above, the head 3a further includes a fourth nozzle row L4 in which a plurality of nozzles N for discharging a fourth ink are arranged. The lightness of the fourth ink is higher than that of the second ink and lower than that of the third ink. Moreover, when viewed in the direction along the rotation axis O6, the distance DN14 between the fourth nozzle row L4 and the rotation axis O6 is smaller than the distance DN11 between the first nozzle row L1 and the rotation axis O6 and smaller than the distance DN13 between the third nozzle row L3 and the rotation axis O6. Furthermore, when viewed in the direction along the rotation axis O6, the fourth nozzle row L4 is positioned between the first nozzle row L1 and the third nozzle row L3. Therefore, even when the fourth ink is used in addition to the first ink, the second ink, and the third ink, it is possible to reduce a decrease in printing quality due to an ink landing error on the work W.

[0090] Also, as described above, the plurality of joints 230 includes a joint 230_5 which is an example of a "second joint". The joint 230_5 is the joint among the plurality of joints 230 that is closest to the tip ET next to the joint 230_6. The joint 230_5 is a rotation mechanism around a rotation axis O5 which is an example of a "second rotation axis". The rotation axis O5 is an axis that intersects the rotation axis O6. Moreover, when viewed in the direction along the rotation axis O5, the distance DN22 between the second nozzle row L2 and the rotation axis O5 is smaller than the distance DN21 between the first nozzle row L1 and the rotation axis O5.

[0091] The joint 230_5 is more likely to cause the vibration of the arm portion 220 than the joint 230_6. Here, the larger the distance of the nozzle N from the rotation axis O5, the larger the landing error of the ink due to this vibration. This is because the larger the distance of the nozzle N from the rotation axis O5, the larger the moment around the rotation axis O5. Therefore, by making the distance DN22 smaller than the distance DN21, the influence of the moment on the second nozzle row L2 can be suppressed compared to the first nozzle row L1. As a result, the vibration of the second nozzle row L2 accompanying the vibration of the joint 230_5 can be made smaller than the vibration of the first nozzle row L1. For this reason, the landing error of the second ink on the work W can be reduced.

[0092] On the other hand, the vibration of the first nozzle row L1 accompanying the vibration of the joint 230_5 is larger than the vibration of the second nozzle row L2. However, in the first nozzle row L1, the first ink, for which the landing error is less noticeable compared to the second ink, is used. As a result, overall, the deterioration of the printing quality due to the landing error of the ink on the work W can be reduced. Note that the condition that the distance DN22 between the second nozzle row L2 and the rotation axis O5 is smaller than the distance DN21 between the first nozzle row L1 and the rotation axis O5 when viewed in the direction along the rotation axis O5 only needs to be satisfied during the execution of the printing operation, and does not necessarily need to be satisfied during the period when no liquid is discharged onto the work W. For example, the distance between the rotation axis O5 and each nozzle row may change due to the rotation of a joint closer to the tip ET than the joint 230_5, such as the joint 230_6.

[0093] As described above, the printing apparatus 1 further includes a flexible first supply pipe 10a1 for supplying the first ink to the first nozzle row L1 and a flexible second supply pipe 10a2 for supplying the second ink to the second nozzle row L2. A part of each of the first supply pipe 10a1 and the second supply pipe 10a2 is held by the arm portion 220. Moreover, it is preferable that the distance between the downstream end of the second supply pipe 10a2 and the rotation axis O6 is smaller than the distance between the downstream end of the first supply pipe 10a1 and the rotation axis O6. When the deformation of the second supply pipe 10a2 due to the operation of the robot 2 becomes large, the flow path resistance in the second supply pipe 10a2 fluctuates, which may cause poor ejection of the second ink. Therefore, by making the distance between the downstream end of the second supply pipe 10a2 and the rotation axis O6 smaller than the distance between the downstream end of the first supply pipe 10a1 and the rotation axis O6, the amount of deformation of the second supply pipe 10a2 due to the operation of the joint 230_6 can be made smaller than the amount of deformation of the first supply pipe 10a1. As a result, poor ejection of the second ink can be prevented.

[0094] Also, as described above, the printing apparatus 1 further includes an energy emission unit 3c. The energy emission unit 3c is supported at the tip ET and includes an emission surface FL that emits energy for curing each of the first ink and the second ink. Here, the head 3a includes a first nozzle row L1, a second nozzle row L2, a third nozzle row L3, and a fourth nozzle row L4 as a plurality of nozzle rows that eject ink. Moreover, when viewed in the direction along the rotation axis O6, the distances DN11, DN12, DN13, DN14 between each of the plurality of nozzle rows and the rotation axis O6 are smaller than the distance DL between the emission surface FL and the rotation axis O6. For this reason, the landing accuracy of the ink on the workpiece W can be improved as compared with a configuration in which the distances DN11, DN12, DN13, DN14 are equal to or greater than the distance DL. Here, the accuracy of the irradiation position of the energy from the emission surface FL to the workpiece W does not have to be higher than the landing accuracy, so there is no problem even if the distance DL is larger than the distances DN11, DN12, DN13, DN14.

[0095] Here, as described above, when viewed in the direction along the rotation axis O6, the rotation axis O6 is located inside the region RN defined by the set of the plurality of nozzle rows. For this reason, compared with a configuration in which the rotation axis O6 is located outside the region RN, the influence of the moment around the rotation axis O6 can be reduced, and as a result, the landing accuracy of the ink on the workpiece W can be improved.

[0096] More specifically, as described above, the head 3a has a discharge surface FN provided with a first nozzle row L1, a second nozzle row L2, a third nozzle row L3, and a fourth nozzle row L4 as four nozzle rows for discharging ink. Moreover, the second nozzle row L2 is the nozzle row closest to the center PC of the discharge surface FN among the four nozzle rows. For this reason, in a configuration in which the rotation axis O6 is brought closer to the center PC, the landing accuracy of the second ink on the workpiece W can be improved compared with a configuration in which another nozzle row is closest to the center PC. Note that the second nozzle row L2 may be the nozzle row closest to the center of the region RN among the four nozzle rows. Further, when the surface WF of the workpiece W is a convex curved surface, as shown in FIG. 6, while reducing the distance between each nozzle row and the surface WF, the distance PG2 between the second nozzle row L2 and the surface WF can be made smaller than the distance PG1 between the first nozzle row L1 and the surface WF. Therefore, in this case also, the landing accuracy of the second ink on the workpiece W can be improved at this point. Note that such an effect is not limited to the configuration of the present embodiment. For example, even in a configuration in which the position of the head 3a in the base coordinate system with reference to the position of the base 210 of the robot 2 is fixed and the robot 2 holds and moves the workpiece W at the tip of the arm portion 220, the same effect can be obtained. That is, in a configuration in which the relative position and posture of the workpiece W having the convex curved surface WF and the head 3a are changed during the execution of the printing operation, if the second nozzle row L2 is the nozzle row closest to the center PC of the discharge surface FN among the other nozzle rows, the landing accuracy of the second ink, for which the landing error is more likely to be conspicuous than that of the first ink, can be improved, and a decrease in the overall printing quality can be suppressed.

[0097] In this embodiment, as described above, the second ink is the ink with the lowest lightness among the inks ejected from the head 3a. Therefore, the printing quality can be suitably improved.

[0098] Furthermore, as described above, the second ink is black ink. Generally, among the inks of a plurality of colors used for full-color printing or the like, the ink with the lowest lightness is black ink. Therefore, by using black ink as the second ink, the printing quality of full-color printing or the like can be suitably improved.

[0099] In this embodiment, as described above, the first ink is the ink with the highest lightness among the inks ejected from the head 3a. Therefore, the printing quality can be suitably improved.

[0100] Furthermore, as described above, the first ink is yellow ink. Generally, among the inks of a plurality of colors used for full-color printing or the like, the ink with the highest lightness is yellow ink. Therefore, by using yellow ink as the first ink, the printing quality in full-color printing or the like can be suitably improved. In a configuration using five or more types of inks or the like, white ink may be used as the ink with the highest lightness. In this case, the first ink may be white ink.

[0101] 2. Second Embodiment Hereinafter, a second embodiment of the present invention will be described. For elements whose actions and functions are the same as those in the first embodiment in the forms exemplified below, the reference numerals used in the description of the first embodiment are reused, and the detailed description of each is appropriately omitted.

[0102] FIG. 7 is a schematic plan view for explaining the arrangement of a plurality of nozzle rows in the second embodiment. In FIG. 7, a view of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 as the plurality of nozzle rows in the c1 direction is shown. The head unit 3A of the present embodiment is the same as the head unit 3 of the first embodiment described above, except that the arrangement order of the second nozzle row L2 and the fourth nozzle row L4 is swapped. Specifically, in the a1 direction, the first nozzle row L1, the second nozzle row L2, the fourth nozzle row L4, and the third nozzle row L3 are arranged in this order. In the example shown in FIG. 7, these nozzle rows are arranged at equal intervals. Note that the intervals between these nozzle rows do not have to be equal intervals.

[0103] Even in the arrangement of the nozzle rows as described above, when viewed in the direction along the rotation axis O6, the distance DN12 between the second nozzle row L2 and the rotation axis O6 is smaller than the distance DN11 between the first nozzle row L1 and the rotation axis O6, and is also smaller than the distance DN13 between the third nozzle row L3 and the rotation axis O6.

[0104] Similarly, the distance DN14 between the fourth nozzle row L4 and the rotation axis O6 is smaller than the distance DN11 between the first nozzle row L1 and the rotation axis O6, and is also smaller than the distance DN13 between the third nozzle row L3 and the rotation axis O6.

[0105] In the example shown in FIG. 7, the distance DN11 is equal to the distance DN13, and the distance DN12 is equal to the distance DN14. Note that the distance DN11 may be different from the distance DN13. Also, the distance DN12 may be different from the distance DN14.

[0106] FIG. 8 is a schematic side view for explaining the arrangement of a plurality of nozzle rows in the second embodiment. In FIG. 8, a view of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 as the plurality of nozzle rows in the b1 direction is shown.

[0107] Here, as shown in FIG. 8, also in the present embodiment, when viewed in the direction along the rotation axis O5, the distance DN22 between the second nozzle row L2 and the rotation axis O5 is smaller than the distance DN21 between the first nozzle row L1 and the rotation axis O5, and is also smaller than the distance DN23 between the third nozzle row L3 and the rotation axis O5.

[0108] Similarly, when viewed in the direction along the rotation axis O5, the distance DN24 between the fourth nozzle row L4 and the rotation axis O5 is smaller than the distance DN21 between the first nozzle row L1 and the rotation axis O5, and is also smaller than the distance DN23 between the third nozzle row L3 and the rotation axis O5.

[0109] In the example shown in FIG. 8, the distance DN21 is equal to the distance DN23, and the distance DN22 is equal to the distance DN24. Note that the distance DN21 may be different from the distance DN23. Also, the distance DN22 may be different from the distance DN24.

[0110] Also, according to the above second embodiment, the printing quality can be improved.

[0111] 3. Third Embodiment Hereinafter, a third embodiment of the present invention will be described. For elements whose operations and functions are the same as those of the first embodiment in the forms exemplified below, the reference numerals used in the description of the first embodiment are reused, and the detailed descriptions thereof are appropriately omitted.

[0112] FIG. 9 is a perspective view showing a schematic configuration of a head unit 3B used in the third embodiment. This embodiment is the same as the first embodiment except that the head unit 3B is used instead of the head unit 3. As shown in FIG. 9, the head unit 3A has two energy emission units 3c. Of the two energy emission units 3c, one energy emission unit 3c is disposed at a position in the a1 direction with respect to the head 3a, and the other energy emission unit 3c is disposed at a position in the a2 direction with respect to the head 3a.

[0113] FIG. 10 is a diagram for explaining the movement paths RU1 and RU2 of the head 3a in the third embodiment. The movement path RU1 is a path from the position PS1 to the position PE1. The robot 2 moves the head 3a in a direction away from the base 210 along the movement path RU1. At this time, the a1 direction faces forward in the moving direction of the head 3a. The movement path RU2 is a path from the position PS2 to the position PE2. The robot 2 moves the head 3a in a direction approaching the base 210 along the movement path RU2. At this time, the a2 direction faces forward in the moving direction of the head 3a.

[0114] Here, although not shown, each of the position PS1 and the position PE2 is a position in the X1 direction with respect to a predetermined region RP when viewed in the Z2 direction. Each of the position PE1 and the position PS2, although not shown, is a position in the X2 direction with respect to the predetermined region RP when viewed in the Z2 direction.

[0115] Also according to the above-described third embodiment, the printing quality can be improved. In this embodiment, as described above, two energy emitting portions 3c are arranged via the head 3a. For this reason, printing can be performed in either a direction away from or approaching the base 210 with respect to the head 3a without rotating the head unit 3B by 180° around the rotation axis O6, and energy can be irradiated onto the ink immediately after landing on the workpiece W.

[0116] 4. Modification Each of the forms in the above examples can be variously modified. Specific modification modes applicable to each of the above forms are exemplified below. Note that two or more modes arbitrarily selected from the following examples can be appropriately combined within a range not conflicting with each other.

[0117] 4-1. Modification 1 In each of the above forms, a configuration in which the rotation axis O6 is located inside the region RN when viewed in the direction along the rotation axis O6 is exemplified, but the present invention is not limited to this configuration. Hereinafter, an example of a configuration in which the rotation axis O6 is located outside the region RN when viewed in the direction along the rotation axis O6 will be described.

[0118] FIG. 11 is a schematic side view for explaining the arrangement of a plurality of nozzle rows in Modification 1. In FIG. 11, a view of the first nozzle row L1, the second nozzle row L2, the third nozzle row L3, and the fourth nozzle row L4 as the plurality of nozzle rows in the b1 direction is shown. In the head unit 3C of this modification, the rotation axis O6 is located outside the region RN when viewed in the direction along the rotation axis O6. In the example shown in FIG. 11, the region RN is arranged at a position in the a1 direction with respect to the rotation axis O6.

[0119] Here, in the a1 direction, the second nozzle row L2, the fourth nozzle row L4, the third nozzle row L3, and the first nozzle row L1 are arranged in this order. In the example shown in FIG. 11, these nozzle rows are arranged at equal intervals. Note that the intervals between these nozzle rows do not have to be equal.

[0120] In the arrangement of the nozzle rows as described above, the distances from the rotation axis O6 when viewed in the direction along the rotation axis O6 are, in ascending order, the second nozzle row L2, the fourth nozzle row L4, the third nozzle row L3, and the first nozzle row L1. That is, in ascending order, the distances are DN12, DN14, DN13, and DN11.

[0121] Also, the distances from the rotation axis O5 when viewed in the direction along the rotation axis O5 are, in ascending order, the second nozzle row L2, the fourth nozzle row L4, the third nozzle row L3, and the first nozzle row L1. That is, in ascending order, the distances are DN22, DN24, DN23, and DN21.

[0122] Also according to the above Modification 1, since the distance DN12 is smaller than the distance DN11, the printing quality can be improved. Also, since the distance DN22 is smaller than the distance DN21, the printing quality can be improved in this respect as well.

[0123] 4-2. Modification 2 In the foregoing embodiment, among the plurality of nozzle rows, the nozzle row closest to the rotation axis O5 or the rotation axis O6 is the second nozzle row L2, and the nozzle row farthest from the rotation axis is the first nozzle row L1. Although this configuration is exemplified, the present invention is not limited to this configuration. The arrangement of the plurality of nozzle rows only needs to satisfy the condition that the second nozzle row L2 is arranged closer to the rotation axis O5 or the rotation axis O6 than the first nozzle row L1.

[0124] 4-3. Modification Example 3 In the foregoing embodiment, a configuration in which the ejection surface FN is orthogonal to the rotation axis O6 is exemplified. However, the present invention is not limited to this configuration, and any configuration may be adopted as long as the magnitude relationship between the rotation axis O6 and each nozzle row as described above is satisfied. For example, as long as such a magnitude relationship is satisfied, the ejection surface FN may be parallel to the rotation axis O6, or the ejection surface FN may be inclined with respect to the rotation axis O5 or the rotation axis O6.

[0125] 4-4. Modification Example 4 In the foregoing embodiment, a configuration in which printing is performed using four types of ink is exemplified. However, the present invention is not limited to this configuration, and any configuration may be adopted as long as the first ink and the second ink are used. The present disclosure can also be applied to configurations in which printing is performed using two, three, or five or more types of ink. Further, the first ink only needs to be an ink having a higher lightness than the second ink, and is not limited to yellow ink. Further, the second ink only needs to be an ink having a lower lightness than the first ink, and is not limited to black ink.

[0126] 4-5. Modification Example 5 In the foregoing embodiment, a configuration in which the energy emitting unit 3c is used is exemplified. However, the present invention is not limited to this configuration, and the energy emitting unit 3c may be omitted. In this case, for example, a separate means for emitting light for curing or solidifying the ink on the workpiece may be arranged outside the robot 2.

[0127] 4-6. Modification Example 6 In the foregoing embodiment, a configuration using a six-axis vertical multi-axis robot as the moving mechanism is exemplified, but the configuration is not limited thereto. The moving mechanism may be, for example, a vertical multi-axis robot with five or fewer axes or seven or more axes, or a horizontal multi-axis robot. Further, in addition to the rotating part constituted by the rotating mechanism, the arm part of the robot may have a telescopic mechanism, a linear motion mechanism, or the like. However, from the viewpoint of the balance between the printing quality in the printing operation and the degree of freedom of the operation of the robot in the non-printing operation, the robot is preferably a multi-axis robot with six or more axes.

[0128] 4-7. Variant 7 In the foregoing embodiment, a configuration using screwing or the like as a method for fixing the head to the robot is exemplified, but the configuration is not limited thereto. For example, 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.

Explanation of Reference Numerals

[0129] 1…Printing device, 2…Robot, 2a…Arm drive mechanism, 2a1…Motor, 2a2…Motor, 2a3…Motor, 2a4…Motor, 2a5…Motor, 2a6…Motor, 3…Head unit, 3A…Head unit, 3B…Head unit, 3C…Head unit, 3a…Head, 3b…Pressure regulating valve, 3c…Energy emitting part, 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, 10…Piping part, 10a1…First supply pipe, 10a2…Second supply pipe, 10a3…Third supply pipe, 10a4…Fourth supply pipe, 11…Wiring part, 210…Base, 220…Arm part, 221…Arm, 222…Arm, 223…Arm, 224…Arm, 225…Arm, 226…Arm, 230…Joint, 230_1…Joint, 230_2…Joint, 230_3…Joint, 230_4…Joint, 230_5…Joint (second joint), 230_6…Joint (first joint), CLK…Clock signal, CNG…Change signal, Com…Drive signal, D1…Output, D3…Signal, DL…Distance, DN11…Distance, DN12…Distance, DN13…Distance, DN14…Distance, DN21…Distance, DN22…Distance, DN23…Distance, DN24…Distance, Da…Route information, EB…Base end, ET…Tip end, FL…Emitting surface, FN…Ejection surface, Img…Printing data, L1…First nozzle row, L2…Second nozzle row, L3…Third nozzle row, L4…Fourth nozzle row, LAT…Latch signal, N…Nozzle, O1…Rotation axis, O2…Rotation axis, O3…Rotation axis, O4…Rotation axis, O5…Rotation axis (second rotation axis), O6…Rotation axis (first rotation axis), PC…Center, PD…Drive pulse, PE…Position, PE1…Position, PE2…Position, PG1…Distance, PG2…Distance, PR1…Position, PR2…Position, PS…Position, PS1…Position, PS2…Position, PTS…Timing signal, RN…Region, RP…Predetermined region, RU…Moving route, RU1…Moving route, RU2…Moving route, SI…Printing data signal, Sk1…Control signal, VBS…Offset potential, VHV…Power supply potential, W…Workpiece, WF…Surface, dCom…Waveform specifying signal.

Claims

1. A head including a first nozzle row in which a plurality of nozzles for discharging a first ink are arranged, and a second nozzle row in which a plurality of nozzles for discharging a second ink are arranged; An arm having a tip, a base end, and a plurality of joints, and a base portion connected to the base end, wherein the head is supported at the tip, and a robot for changing the position and orientation of the head with respect to a workpiece; The lightness of the second ink is lower than that of the first ink; The plurality of joints include a first joint that is the joint closest to the tip among the plurality of joints; The first joint is a rotation mechanism around a first rotation axis; When viewed in the direction along the first rotation axis, the distance between the second nozzle row and the first rotation axis is smaller than the distance between the first nozzle row and the first rotation axis; A printing apparatus.

2. The head further includes a third nozzle row in which a plurality of nozzles for discharging a third ink are arranged; The lightness of the third ink is lower than that of the first ink and higher than that of the second ink; When viewed in the direction along the first rotation axis, the distance between the second nozzle row and the first rotation axis is smaller than the distance between the third nozzle row and the first rotation axis; When viewed in the direction along the first rotation axis, the second nozzle row is located between the first nozzle row and the third nozzle row; The printing apparatus according to claim 1.

3. The head further includes a fourth nozzle row in which a plurality of nozzles for discharging a fourth ink are arranged; The lightness of the fourth ink is higher than that of the second ink and lower than that of the third ink; When viewed in the direction along the first rotation axis, the distance between the fourth nozzle row and the first rotation axis is smaller than the distance between the first nozzle row and the first rotation axis and smaller than the distance between the third nozzle row and the first rotation axis; When viewed in the direction along the first rotation axis, the fourth nozzle row is located between the first nozzle row and the third nozzle row; The printing apparatus according to claim 2.

4. The plurality of joints include a second joint that is the joint closer to the tip than the first joint among the plurality of joints; The second joint is a rotation mechanism around a second rotation axis that intersects the first rotation axis; When viewed in the direction along the second rotation axis, the distance between the second nozzle row and the second rotation axis is smaller than the distance between the first nozzle row and the second rotation axis; The printing apparatus according to any one of claims 1 to 3.

5. A flexible first supply pipe for supplying a first ink to the first nozzle row, And a flexible second supply pipe for supplying a second ink to the second nozzle row, A part of each of the first supply pipe and the second supply pipe is held by the arm portion, The distance between the downstream end of the second supply pipe and the first rotation axis is smaller than the distance between the downstream end of the first supply pipe and the first rotation axis, The printing apparatus according to any one of claims 1 to 4.

6. Further comprising an energy emitting unit including an emitting surface that is supported at the tip and emits energy for curing each of the first ink and the second ink, The head includes a plurality of nozzle rows that discharge ink, The plurality of nozzle rows include the first nozzle row and the second nozzle row, When viewed in the direction along the first rotation axis, the distance between each of the plurality of nozzle rows and the first rotation axis is smaller than the distance between the emitting surface and the first rotation axis, The printing apparatus according to any one of claims 1 to 5.

7. The head includes a plurality of nozzle rows that discharge ink, When viewed in the direction along the first rotation axis, the first rotation axis is located inside the region defined by the set of the plurality of nozzle rows, The printing apparatus according to any one of claims 1 to 6.

8. The head has a discharge surface provided with four nozzle rows that discharge ink, The four nozzle rows include the first nozzle row and the second nozzle row, The second nozzle row is the nozzle row closest to the center of the discharge surface among the four nozzle rows, The printing apparatus according to any one of claims 1 to 7.

9. The second ink is the ink with the lowest lightness among the inks discharged from the head, The printing apparatus according to any one of claims 1 to 8.

10. The second ink is black ink, The printing apparatus according to any one of claims 1 to 9.

11. The first ink is the ink with the highest lightness among the inks discharged from the head, The printing apparatus according to any one of claims 1 to 10.

12. The first ink is yellow ink or white ink, The printing apparatus according to any one of claims 1 to 11.

13. A motor for driving the joint is provided for each of the plurality of joints. The rated output of the motor for driving the first joint is smaller than the rated outputs of the motors for driving the respective joints other than the first joint among the plurality of joints. The printing apparatus according to any one of claims 1 to 12.

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