Inkjet recording device and coating method

Abstract

Provided are an inkjet recording device and a painting method with which it is possible to more reliably and efficiently suppress liquid dropping of ink landed onto an inclined surface. The inkjet recording device that performs painting by ejecting ink to an inclined surface of an object to be painted having the inclined surface inclined with respect to a horizontal surface is provided with: an ink ejection unit having a nozzle for ejecting ink; and a control unit. The control unit performs scan control to causing the ink to be ejected to the inclined surface from the nozzle of the ink ejection unit while causing the ink ejection unit and the inclined surface to relatively move in a prescribed scan direction. In the scan control, the control unit controls the ink ejection unit so that a liquid droplet amount of the ink landed per prescribed area of the inclined surface by one scan control becomes less than or equal to a maximum liquid droplet amount defined on the basis of an inclination angle of the inclined surface from a horizontal surface.

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording apparatus and a coating method. [Background technology]

[0002] Conventionally, there are inkjet recording devices that eject ink droplets from nozzles in an ink ejection unit onto a recording medium to form an image or the like on the recording medium. Such inkjet recording devices can also be used for coating industrial products, etc. Inkjet recording devices have the advantage that they can deposit a desired amount of ink at a desired position, which reduces ink waste compared to conventional spray coating, and also simplifies the coating process because masking is not required.

[0003] However, because there is an upper limit to the viscosity of ink that can be ejected from a nozzle, there is a problem that when coating on an inclined surface that is inclined relative to the horizontal, the ink that has landed is likely to drip due to gravity.In response to this, Patent Document 1 discloses a technology that suppresses ink dripping by keeping the atmospheric humidity low and promoting the evaporation of water in the ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-156088 Summary of the Invention [Problem to be solved by the invention]

[0005] However, within the viscosity range of ink typically used in inkjet recording devices, there are only limited cases in which dripping can be suppressed by adjusting the humidity of the atmosphere to promote drying. For example, if the inclination angle of the inclined surface exceeds a certain value or the viscosity of the ink is below a certain value, sufficient dripping suppression effect is often not achieved.

[0006] Furthermore, the likelihood of dripping depends on the inclination angle of the inclined surface on which the ink lands, and since it is difficult to flexibly change the humidity depending on the inclination angle, the above-mentioned conventional technology requires adjusting the humidity to match the largest inclination angle. Therefore, when the inclination angle of the inclined surface of the object to be coated is smaller than the assumed maximum inclination angle, there is a problem that measures to prevent dripping become excessive and inefficient.

[0007] An object of the present invention is to provide an inkjet recording apparatus and a coating method that can more reliably and efficiently prevent ink that has landed on an inclined surface from dripping. [Means for solving the problem]

[0008] In order to achieve the above object, the inkjet recording apparatus according to claim 1 comprises: An inkjet recording apparatus that discharges ink onto an inclined surface of an object to be coated, the inclined surface being inclined relative to a horizontal plane, an ink ejection unit having a nozzle for ejecting ink; A control unit; Equipped with The control unit performing scanning control to eject ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; In the scanning control, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area by one scanning control is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane. death , The ink ejection unit is controlled in the scanning control so that a maximum volume of ink droplets that lands per predetermined area on a first inclined surface having a first inclination angle is smaller than a maximum volume of ink droplets that lands per predetermined area on a second inclined surface having a second inclination angle that is smaller than the first inclination angle. . In order to achieve the above object, the inkjet recording apparatus according to claim 2 comprises: An inkjet recording apparatus that discharges ink onto an inclined surface of an object to be coated, the inclined surface being inclined relative to a horizontal plane, an ink ejection unit having a nozzle for ejecting ink; A control unit; Equipped with The control unit performing scanning control to eject ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; the scanning control controls the ink ejection unit so that the amount of ink droplets that land on a predetermined area of ​​the inclined surface in one scan control is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; The ink ejection unit is controlled in the scanning control so that the greater the inclination angle of the inclined surface, the smaller the maximum amount of ink droplets that land per predetermined area. In order to achieve the above object, the inkjet recording apparatus according to claim 3 comprises: An inkjet recording apparatus that discharges ink onto an inclined surface of an object to be coated, the inclined surface being inclined relative to a horizontal plane, an ink ejection unit having a nozzle for ejecting ink; A control unit; Equipped with The control unit performing scanning control to eject ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; the scanning control controls the ink ejection unit so that the amount of ink droplets that land on a predetermined area of ​​the inclined surface in one scan control is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; In the scanning control, when the inclination angle of the inclined surface is equal to or greater than a predetermined reference angle, the ink ejection position of the ink ejection unit is controlled so that ink droplets that have landed on the inclined surface do not coalesce.

[0009] Claim 4 The invention described in claim 1 Any one of ~3 In the inkjet recording apparatus described in The control unit determines the size of ink droplets to be ejected from the nozzles in the scan control based on the inclination angle of the inclined surface.

[0010] Claim 5 The invention described in claim 1 Any one of ~4 In the inkjet recording apparatus described in The control unit determines the maximum number of ink droplets to be landed per predetermined area in the scanning control based on the inclination angle of the inclined surface.

[0011] Claim 6 The invention described in claim 2 ~ 5 In the inkjet recording apparatus according to any one of the above items, the control unit controls the scanning so that a maximum volume of ink droplets that lands per predetermined area on the first inclined surface having a first inclination angle is smaller than a maximum volume of ink droplets that lands per predetermined area on the second inclined surface having a second inclination angle that is smaller than the first inclination angle. The aforementioned Controls the ink ejection unit.

[0012] Claim 7The invention described in claim 1 、3 ~ 6 In the inkjet recording apparatus according to any one of the above items, The control unit controls the ink ejection unit in the scanning control so that the maximum amount of ink droplets that land per predetermined area decreases as the inclination angle of the inclined surface increases.

[0013] Claim 8 The invention described in claims 1 to 7 In the inkjet recording apparatus according to any one of the above items, The control unit controls the ink ejection unit in the scanning control so that the speed of ink droplets ejected from the nozzle onto a first inclined surface having a first inclination angle is faster than the speed of ink droplets ejected from the nozzle onto a second inclined surface having a second inclination angle smaller than the first inclination angle.

[0014] Claim 9 The invention described in claims 1 to 8 In the inkjet recording apparatus according to any one of the above items, The control unit controls the ink ejection unit in the scanning control so that the speed of ink droplets ejected from the nozzles increases as the inclination angle of the inclined surface increases.

[0015] Claim 10 The invention described in claims 1 to 9 In the inkjet recording apparatus according to any one of the above items, The control unit acquiring inclination angle information relating to the inclination angle of the inclined surface specified in advance; In the scanning control, the ink ejection unit is controlled so that the amount of ink droplets that land per specified area of ​​the inclined surface by the scanning control is equal to or less than the maximum droplet amount corresponding to the inclination angle identified from the inclination angle information.

[0016] Claim 11 The invention described in claims 1 to 9In the inkjet recording apparatus according to any one of the above items, a detector for detecting the inclination angle of the inclined surface, In the scanning control, the control unit controls the ink ejection unit so that the amount of ink droplets that land per specified area of ​​the inclined surface by the scanning control is less than or equal to the maximum droplet amount corresponding to the inclination angle detected by the detection unit.

[0017] Claim 12 The invention described in claims 1 to 11 In the inkjet recording apparatus according to any one of the above items, a robot arm to which the ink ejection unit is attached, In the scanning control, the control unit operates the robot arm so that the ink ejection unit moves relative to the inclined surface in the scanning direction.

[0018] Claim 13 The invention described in claim 12 In the inkjet recording apparatus described in a pinning unit that increases the viscosity of ink that has landed on the inclined surface, The pinning unit is attached to the robot arm and moves relative to the inclined surface together with the ink ejection unit, and thickens the ink that is ejected from the ink ejection unit and lands on the inclined surface during the relative movement.

[0019] Claim 14 The invention described in claim 13 In the inkjet recording apparatus described in the ink ejection unit ejects ink from the nozzle, the ink being thickened by application of a predetermined amount of energy; The pinning portion imparts the predetermined energy to the ink that has landed on the inclined surface.

[0020] Claim 15 The invention described in claims 1 to 14 In the inkjet recording apparatus according to any one of the above items, the ink ejection unit has a nozzle row in which a plurality of the nozzles are arranged, In the scanning control, the control unit causes the nozzles to eject ink in a state in which the arrangement direction of the plurality of nozzles in the nozzle row is horizontal.

[0021] Claim 16 The invention described in claim 1 、2、4 ~ 15 In the inkjet recording apparatus according to any one of the above items, In the scanning control, when the inclination angle of the inclined surface is equal to or greater than a predetermined reference angle, the control unit controls the ink ejection position by the ink ejection unit so that ink droplets that have landed on the inclined surface do not coalesce.

[0022] Claim 17 The invention described in claims 1 to 16 In the inkjet recording apparatus according to any one of the above items, The ink ejection unit ejects ink onto the inclined surface at a temperature that is 10° C. or more higher than the temperature of the inclined surface.

[0023] Claim 18 The invention described in claims 1 to 17 In the inkjet recording apparatus according to any one of the above items, The ink ejection unit includes a viscosity adjusting unit that adjusts the viscosity of the ink ejected from the nozzles to within a viscosity range that allows the ink to be ejected from the nozzles.

[0024] Claim 19 The invention described in claim 18 In the inkjet recording apparatus described in The viscosity range is 200 cP or less.

[0025] Claim 20 The invention described in claim 18 or 19 In the inkjet recording apparatus described in The viscosity adjusting unit has an ink circulation mechanism that circulates ink through a path that includes the ink ejection unit.

[0026] Claim 21 The invention described in claim 18 ~ 20 In the inkjet recording apparatus according to any one of the above items, The viscosity adjusting unit has a heater that heats the ink.

[0027] Claim 22 The invention described in claims 1 to 21 In the inkjet recording apparatus according to any one of the above items, The ink ejection section ejects thixotropic ink from the nozzles.

[0028] Claim 23 The invention described in claims 1 to 22 In the inkjet recording apparatus according to any one of the above items, the inclined surface is a curved surface, The control unit determines the maximum amount of ink droplets that can land per predetermined area in a region of the curved surface where the ink lands, based on the inclination angle of the region.

[0029] Claim 24 The invention described in claims 1 to 23 In the inkjet recording apparatus according to any one of the above items, When the inclination angle of the inclined surface is 30° or more, the control unit controls the ink ejection unit so that the thickness of the ink in a liquid state that lands on the inclined surface by the scanning control is 10 μm or less.

[0030] Claim 25 The invention described in claims 1 to 24 In the inkjet recording apparatus according to any one of the above items, When the inclination angle of the inclined surface is 30° or more, the control unit controls the ink ejection unit so that the volume of the ink droplets ejected from the nozzles of the ink ejection unit onto the inclined surface is 1 pL or more and 50 pL or less.

[0031] In order to achieve the above object, claims 26 The invention of the coating method described in A coating method for coating an inclined surface of an object to be coated, the inclined surface being inclined with respect to a horizontal plane, by using an inkjet recording device equipped with an ink ejection unit having a nozzle for ejecting ink, the method comprising: a scanning step of ejecting ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; In the scanning step, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area in one scanning step is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane. death , In the scanning step, the ink ejection unit is controlled so that a maximum volume of ink droplets that lands per predetermined area on the first inclined surface having a first inclination angle is smaller than a maximum volume of ink droplets that lands per predetermined area on the second inclined surface having a second inclination angle that is smaller than the first inclination angle. . In order to achieve the above object, the coating method according to claim 27 comprises: A coating method for coating an inclined surface of an object to be coated, the inclined surface being inclined with respect to a horizontal plane, by using an inkjet recording device equipped with an ink ejection unit having a nozzle for ejecting ink, the method comprising: a scanning step of ejecting ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; in the scanning step, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area in one scanning step is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; In the scanning step, the ink ejection unit is controlled so that the maximum amount of ink droplets that land per predetermined area decreases as the inclination angle of the inclined surface increases. In order to achieve the above object, the coating method according to claim 28 comprises: A coating method for coating an inclined surface of an object to be coated, the inclined surface being inclined with respect to a horizontal plane, by using an inkjet recording device equipped with an ink ejection unit having a nozzle for ejecting ink, the method comprising: a scanning step of ejecting ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; in the scanning step, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area in one scanning step is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; In the scanning step, if the inclination angle of the inclined surface is equal to or greater than a predetermined reference angle, the ink ejection position of the ink ejection unit is controlled so that ink droplets that have landed on the inclined surface do not coalesce.

[0032] Claim 29 The invention described in claim Any one of items 26 to 28 In the coating method described in a functional liquid applying step of applying a functional liquid to the inclined surface, the functional liquid reacting with the ink ejected from the nozzles of the ink ejection unit to thicken the ink, In the scanning step, ink is ejected from the nozzles onto the inclined surface onto which the functional liquid has been applied. [Effects of the Invention]

[0033] According to the present invention, it is possible to more reliably and efficiently prevent ink that has landed on an inclined surface from dripping. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a side view showing the overall configuration of an inkjet recording apparatus. [Figure 2] FIG. 1 is a front view of an inkjet recording apparatus. [Figure 3] FIG. 2 is a diagram illustrating a configuration of a head unit. [Figure 4] FIG. 2 is a perspective view of an inkjet head. [Figure 5] FIG. 2 is a schematic cross-sectional view showing the internal configuration of an inkjet head. [Figure 6] FIG. 2 is an enlarged cross-sectional view showing the configuration of a head chip. [Figure 7] FIG. 2 is a schematic diagram illustrating the configuration of an ink circulation mechanism. [Figure 8] FIG. 2 is a diagram showing the tip of a robot arm. [Figure 9A] FIG. 4 is a diagram illustrating the inclination angle of an inclined surface. [Figure 9B] FIG. 4 is a diagram illustrating the inclination angle of an inclined surface. [Figure 10] FIG. 2 is a block diagram showing the main functional configuration of the inkjet printing apparatus. [Figure 11A] 10A and 10B are diagrams illustrating the scanning operation of the head unit when coating an inclined surface of a workpiece. [Figure 11B] 10A and 10B are diagrams illustrating the scanning operation of the head unit when coating an inclined surface of a workpiece. [Figure 12] 10A and 10B are diagrams showing examples of setting the size (volume) of ink droplets in a first droplet volume adjustment method. [Figure 13]10A and 10B are diagrams illustrating an example of setting the maximum number of ink droplets that land per predetermined area in the second droplet volume adjustment method. [Figure 14] 10 is a flowchart showing a control procedure for a painting process. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0036] Fig. 1 is a side view showing the overall configuration of an inkjet recording apparatus 1 according to an embodiment of the present invention, and Fig. 2 is a front view of the inkjet recording apparatus 1. In Figs. 1 and 2, the X-axis and Y-axis are parallel to the horizontal plane, and the Z-axis is perpendicular to the X-axis and Y-axis (i.e., parallel to the vertical direction).

[0037] The inkjet recording apparatus 1 includes a robot arm 20, a head unit 40 (ink ejection unit) held by the robot arm 20, and a chamber 2 that stores the robot arm 20, the head unit 40, and a workpiece W (see FIGS. 8, 10-12) as a coating target. The head unit 40 has multiple inkjet heads 41. Each inkjet head 41 is provided with multiple nozzles N (see FIG. 3) that eject ink. In this embodiment, a configuration in which the head unit 40 has six inkjet heads 41 is exemplified. However, the number of inkjet heads 41 included in the head unit 40 is not limited to six and can be changed appropriately depending on the coating width of the head unit 40, etc. Therefore, the number of inkjet heads 41 included in the head unit 40 may be seven or more or five or less, and one head unit 40 may have one inkjet head 41. The inkjet recording apparatus 1 can coat the surface of the workpiece W by ejecting ink from the nozzles N onto the workpiece W while moving the head unit 40 near the workpiece W using the robot arm 20. More specifically, when the workpiece W has an inclined surface S (see Figures 8, 9A and 9B) that is inclined relative to a horizontal plane (for example, when the workpiece W is a three-dimensional object), the inkjet recording device 1 can eject ink onto the inclined surface S to paint it.

[0038] [Robot arm] The robot arm 20 is a vertical multi-joint robot arm that includes a base 21 serving as a foundation, multiple arms 22 connected by joints 23, a drive motor (e.g., a servo motor) provided at each joint 23, and an encoder that detects the angle of the arm rotated or turned by each drive motor, and a head unit 40 is held at the tip of the multiple arms 22 connected by joints 23.

[0039] Each joint 23 is composed of either a swing joint that allows one end of the arm 22 to swing and pivots the other end, or a rotary joint that pivots the arm 22 itself so that it can rotate around its longitudinal direction. The robot arm 20 has six joints 23, and the head unit 40 at the tip of the robot arm 20 can be positioned at any position and can take any posture using the six axes. Therefore, the robot arm 20 can cause the head unit 40 to scan along any curve on the three-dimensional curved surface of the workpiece W to perform drawing.

[0040] In this embodiment, "scanning" (also referred to as "scanning operation") refers to ejecting ink from the nozzles N of the head unit 40 (inkjet head 41) onto the surface of the workpiece W while moving the head unit 40 relative to the workpiece W in a predetermined scanning direction. In one scan, the nozzle opening surface 41a of the head unit 40 (the surface on which the openings of the nozzles N of the inkjet head 41 are provided; see FIG. 3) does not face the same portion of the surface of the workpiece W more than once. By repeating this scan multiple times, the surface of the workpiece W is painted. In this embodiment, "painting" refers to coloring at least a portion of the surface of the workpiece W a predetermined color (which may include white or black) by one or more scans, and includes painting the area to be painted solid with one color or multiple colors, as well as forming (drawing) figures, letters, images, etc. on the area to be painted.

[0041] The robot arm 20 is not limited to a six-axis robot arm, but may have seven joints. In this case, redundant joints are created, and it becomes possible to position the inkjet head 41 at any position and to move the intermediate joints while allowing the inkjet head 41 to assume any posture, thereby making it possible to avoid interference with other objects around the robot arm 20. Therefore, the inkjet head 41 can be positioned at any position within a wider range and can assume any posture.

[0042] [Chamber] The chamber 2 is a storage room that stores the robot arm 20 and the workpiece W in a sealed state. A workbench 3 on which the workpiece W is placed is provided inside the chamber 2. The workbench 3 may be provided with a jig that holds the workpiece W in a predetermined position. The chamber 2 is sealed off from outside air, so the space inside the chamber 2 can be made dust-proof and moisture-proof.

[0043] [Head unit] FIG. 3 is a diagram showing the configuration of the head unit 40. As shown in FIG. In the following, the orientation of each part of the head unit 40 will be described using the x-axis and y-axis parallel to the nozzle opening surface 41a of the inkjet head 41 of the head unit 40, and the z-axis perpendicular to the nozzle opening surface 41a. Fig. 3 is a view of the head unit 40 as seen from the -z direction. The x-axis, y-axis, and z-axis are coordinate axes fixed to the head unit 40, and their orientations relative to the above-mentioned X-axis, Y-axis, and Z-axis change according to the operation of the robot arm 20.

[0044] The head unit 40 includes a plurality of inkjet heads 41 (six in this embodiment), each having a plurality of nozzles N. The head unit 40 includes a plate-shaped support portion 40a parallel to the xy plane, and six inkjet heads 41 fixed to the support portion 40a while fitting into through holes formed in the support portion 40a. Each inkjet head 41 is fixed to the support portion 40a with its nozzle opening surface 41a, where the openings of the nozzles N are provided, exposed from the through holes of the support portion 40a toward the -z direction. Therefore, the nozzle opening surface 41a of each inkjet head 41 faces the -z direction, and the nozzles N of the inkjet head 41 eject ink droplets in the -z direction. As described above, since the z axis is a coordinate axis fixed to the head unit 40, the "-z direction" may be oriented differently from the vertical downward direction (-Z direction) depending on the orientation of the head unit 40 in response to the operation of the robot arm 20.

[0045] In the inkjet head 41, a plurality of nozzles N are arranged at equal intervals in a predetermined arrangement direction (the x direction in FIG. 3) to form nozzle rows NL. In this embodiment, each inkjet head 41 has four nozzle rows NL. The positions of these nozzle rows NL in the x direction are shifted from each other so that the positions of the nozzles N in the x direction do not overlap. Note that the number of nozzle rows NL in one inkjet head 41 is not limited to four, and may be three or less, or five or more.

[0046] The six inkjet heads 41 in the head unit 40 are arranged in a staggered pattern so that the arrangement range of the nozzles N in the x direction is continuous. Therefore, the head unit 40 can paint over the arrangement range of the nozzles N included in the head unit 40 in the x direction in a single scan.

[0047] FIG. 4 is a perspective view of the inkjet head 41. As shown in FIG. The inkjet head 41 includes a housing 64 and an exterior member 65 that is fitted to the housing 64 at the bottom end thereof, and the main components are housed inside the housing 64 and the exterior member 65. The exterior member 65 is provided with an inlet 61 through which ink is supplied from the outside, and outlets 62 and 63 through which ink is discharged to the outside.

[0048] FIG. 5 is a schematic cross-sectional view showing the internal configuration of the inkjet head 41. As shown in FIG. The inkjet head 41 has a head chip 51 having a nozzle opening surface 41a, and an ink manifold 52 stacked on the +z direction side of the head chip 51. The ink manifold 52 has a common ink chamber 53 that communicates with an inlet 61. More specifically, the common ink chamber 53 has an upper layer 53a that communicates with the inlet 61 and a lower layer 53b that is separated from the upper layer 53a by a filter 54. The filter 54 allows ink to pass through and captures foreign matter and air bubbles that may be mixed in the ink. The upper layer 53a communicates with an outlet 62, and the lower layer 53b communicates with an outlet 63. Ink that flows in from the inlet 61 passes through the common ink chamber 53 and flows out of the inkjet head 41 from the outlets 62 and 63.

[0049] The head chip 51 is provided with an ink channel 511 that communicates with the lower layer 53b of the common ink chamber 53, and a nozzle N that communicates with the end of the ink channel 511 on the -z direction side. A portion of the ink that has flowed into the lower layer 53b of the common ink chamber 53 is supplied to the ink channel 511 and ejected from the nozzle N.

[0050] FIG. 6 is an enlarged cross-sectional view showing the configuration of head chip 51. As shown in FIG. 6 is a cross-sectional view of the area near one nozzle N of the head chip 51, viewed from the +x direction. The head chip 51 has a configuration in which a nozzle plate 51a, a flow path substrate 51b, and a pressure chamber substrate 51c are stacked in this order in the z direction.

[0051] The nozzle plate 51a is a plate-like member in which through holes that become the nozzles N are provided.

[0052] In the flow path substrate 51b and the pressure chamber substrate 51c, ink channels 511 and individual discharge flow paths 512 are formed. One ink channel 511 is provided for one nozzle N. The ink channel 511 penetrates the flow path substrate 51b and the pressure chamber substrate 51c in the z direction, with its upper end communicating with the lower layer 53b of the common ink chamber 53 and its lower end communicating with one nozzle N. Ink supplied to the common ink chamber 53 is supplied to the nozzle N via this ink channel 511.

[0053] The pressure chamber substrate 51c, which forms part of the wall surface of the ink channel 511, is made of a ceramic piezoelectric material. Examples of such piezoelectric materials include PZT (lead zirconate titanate), lithium niobate, barium titanate, lead titanate, and lead metaniobate. A drive electrode (not shown) is provided on the inner wall surface of the pressure chamber substrate 51c. When a voltage signal (drive signal) with a drive waveform is applied from a circuit unit (not shown) to the drive electrode, the side walls separating adjacent ink channels 511 undergo shear-mode displacement, causing fluctuations in the ink pressure within the ink channels 511. In response to this pressure fluctuation, ink within the ink channels 511 is ejected from the nozzles N. Note that, instead of the ink channels 511, air chambers without ink inflow paths may be provided at every other ink channel 511 formation position in the x direction in FIG. 5. This configuration prevents deformation of the partition walls of an ink channel 511 from affecting other ink channels 511. Hereinafter, the configuration including the ink channel 511, the nozzle N, and the above-mentioned drive electrode will also be referred to as the "ink ejection mechanism."

[0054] The size (volume) and velocity of ink droplets ejected from the nozzle N of the inkjet head 41 can be adjusted by changing the voltage magnitude and / or waveform pattern of the drive signal supplied to the drive electrode of the ink channel 511. For example, in a configuration in which ink is ejected by applying a drive signal including multiple pulse waveforms to the drive electrode, the size and velocity of the ejected ink can be adjusted by changing parameters such as the voltage magnitude of each pulse waveform, the duration of each pulse waveform, the time interval between pulse waveforms, and the number of pulse waveforms. For example, by shifting at least one of the above parameters from the optimal condition, it is possible to adjust the size and velocity of ink droplets ejected from the nozzle N, such as reducing the size or slowing the ink velocity. Alternatively, multiple drive signals with adjusted voltage magnitudes and application timings can be applied consecutively to the drive electrode, causing multiple ink droplets ejected from the nozzle N in response to each drive signal to coalesce and land on the workpiece W.

[0055] 6 has a horizontal portion 512a that branches off from the nozzle N-side end of the ink channel 511 and extends in the y direction, and a vertical portion 512b that bends in the +z direction from the end of the horizontal portion 512a and communicates with the common discharge channel 55. One individual discharge flow path 512 is provided for one ink channel 511. The horizontal portion 512a of the individual discharge flow path 512 is a groove provided on the surface of the plate-shaped flow path substrate 51b on the -z direction side, and the vertical portion 512b is a through-hole provided in the flow path substrate 51b and the pressure chamber substrate 51c.

[0056] The individual discharge flow paths 512 guide ink that has been supplied to the ink channels 511 but has not been ejected from the nozzles N to the common discharge flow path 55. The common discharge flow path 55 extends in the x direction and is connected to a plurality of individual discharge flow paths 512 that branch off from each ink channel 511. The common discharge flow path 55 is connected to either the outlet 62 or 63, and the ink that has flowed into the common discharge flow path 55 is discharged from the outlet 62 or 63 to the outside of the inkjet head 41.

[0057] In this way, in the inkjet head 41, a portion of the ink flowing in from the inlet 61 is ejected from the nozzle N, and the remaining ink is discharged from the outlets 62, 63 via the common ink chamber 53 or the individual discharge flow path 512. However, the configuration of the flow paths of the inkjet head 41 is not limited to the above. For example, the individual discharge flow path 512 and the common discharge flow path 55 may be omitted, and the ink flowing in from the inlet 61 may be guided to the outlets 62, 63 only via the common ink chamber 53. Alternatively, the common ink chamber 53 may not communicate with the outlets 62, 63, and the ink flowing in from the inlet 61 may be guided to the outlets 62, 63 only via the individual discharge flow path 512 and the common discharge flow path 55.

[0058] The ink flow from the inlet 61 of the inkjet head 41 to the outlets 62 and 63 can be generated by an ink circulation mechanism 8 that the inkjet recording apparatus 1 has.

[0059] [Ink circulation mechanism] FIG. 7 is a schematic diagram showing the configuration of the ink circulation mechanism 8. As shown in FIG. The ink circulation mechanism 8 includes a supply sub-tank 81, a reflux sub-tank 82, a main tank 83, ink flow paths 84 to 87, pumps 88 and 89, and the like. The supply sub-tank 81 stores ink to be supplied to the inkjet head 41. The supply sub-tank 81 is connected to the inlet 61 by an ink flow path . The reflux sub-tank 82 is connected to the outlets 62 and 63 by an ink flow path 85, and stores the ink discharged from the outlets 62 and 63. The supply sub-tank 81 and the return sub-tank 82 are connected by an ink flow path 86. A pump 88 provided in the ink flow path 86 allows ink to be returned from the return sub-tank 82 to the supply sub-tank 81. The main tank 83 stores ink to be supplied to the supply sub-tank 81. The main tank 83 is connected to the supply sub-tank 81 by an ink flow path 87. In addition, ink is supplied from the main tank 83 to the supply sub-tank 81 by a pump 89 provided in the ink flow path 87.

[0060] The supply sub-tank 81 is disposed at a position where its liquid level is higher than the nozzle opening surface 41a of the inkjet head 41. The return sub-tank 82 is disposed at a position where its liquid level is lower than the nozzle opening surface 41a. As a result, when the pressure inside the nozzle N (≈ atmospheric pressure) is taken as the reference pressure, the pressure at the inlet 61 is higher than the reference pressure by a pressure P1 due to a head difference, and the pressure at the outlets 62, 63 is lower than the reference pressure by a pressure P2 due to a head difference. This pressure difference between pressure P1 and pressure P2 causes ink to flow from the inlet 61 to the outlets 62, 63. By changing the position of the liquid level in each sub-tank, the pressure P1 and pressure P2 can be adjusted, thereby adjusting the ink flow rate.

[0061] Although the method of controlling the circulation of ink by the head difference has been described as an example of the ink circulation mechanism 8, it is of course possible to change it as appropriate as long as it is configured to generate a circulating flow of ink.

[0062] [ink] The ink used in the inkjet head 41 is not particularly limited as long as it can be ejected as droplets from the nozzle N. However, it is preferable for the ink to be thixotropic so that it quickly thickens after landing on the workpiece W. Thixotropy refers to the property of changing viscosity when shear is applied. When ink is thixotropic, shear forces are applied to the ink as it circulates through the narrow flow path of the ink circulation mechanism 8, causing the ink's viscosity to decrease to a certain value. On the other hand, when shear forces are no longer applied to the ink, such as when the circulation stops or when the ink is ejected from the nozzle N and lands on the workpiece W, the ink's viscosity changes (increases) to the viscosity before the shear forces were applied. This behavior can be achieved with dispersion-type inks containing polymer resin components or particles dispersed in the ink. When thixotropic ink is used, the ink thickens after landing on the workpiece W, thereby more effectively suppressing dripping.

[0063] For example, from the viewpoint of obtaining stable ejection (jetting) characteristics, it is preferable that the viscosity (25°C) at a shear rate of 1000 [1 / s] is 200 cP or less. Furthermore, from the viewpoint of obtaining appropriate thixotropy, it is preferable that the viscosity at a shear rate of 100 [1 / s] is greater than the viscosity at a shear rate of 1000 [1 / s], and that the viscosity at a shear rate of 10 [1 / s] is greater than the viscosity at a shear rate of 100 [1 / s]. The ink circulation mechanism 8 described above controls the average shear rate in the flow path (ink channel 511) communicating with the nozzle N to be 1000 [1 / s] or more and 10,000 [1 / s] or less during ink circulation.

[0064] The ink preferably contains an aqueous solvent (water-soluble solvent, water), a pigment, and a fixing resin, and particularly preferably contains a thixotropic agent. The ink preferably contains 3 to 10% by mass of pigment, 8 to 20% by mass of fixing resin, 10 to 30% by mass of water-soluble solvent, and 40 to 79% by mass of water. The ink preferably contains 6 to 30% by mass of solids. The term "solids of ink" refers to solid components that cannot be removed from the ink by drying at 100°C. The solids of ink are, for example, components other than the solvent, including the aqueous solvent.

[0065] In addition to the aqueous solvent, pigment, fixing resin, and thixotropy-imparting agent, the ink may contain any optional components that do not impair the thixotropy-related properties. Examples of optional components include a pigment dispersant and a surfactant.

[0066] Furthermore, the ink may contain a gelling agent. As for inks containing gelling agents, details are described in paragraphs 0027 to 0055 of International Publication WO2021 / 001937A1, and these can be applied.

[0067] Furthermore, the ink may contain an ultraviolet curing agent. Ink containing an ultraviolet curing agent is described in detail in paragraphs 0067 to 0129 of JP 2020-172043 A, and this can be applied.

[0068] Ink containing an ultraviolet curing agent may further contain an ultraviolet absorber. The ultraviolet absorber is not particularly limited, but examples of the ultraviolet absorber include those described in JP-A Nos. 57-74193, 57-87988, and 62-261476.

[0069] [Ink temperature adjustment section] The head unit 40 includes an ink temperature adjustment unit 43 (see FIG. 9 ) for adjusting the temperature of ink supplied to the nozzles N by heating it before ejection. The ink temperature adjustment unit 43 includes a heater 431 for heating the ink and a temperature detection element 432 for detecting the temperature of the heated ink. The heater 431 is provided in a position where it can heat the ink in the ink circulation flow path or tank. The temperature detection element 432 is provided near the heater 431 or closer to the nozzles N than the heater 431 in the ink circulation direction, and detects the temperature of the ink supplied to the nozzles N. The output of the heater 431 is controlled based on the temperature detection result by the temperature detection element 432 so that the ink reaches a predetermined temperature. This allows the ink to be adjusted to an appropriate target temperature immediately before being ejected from the nozzles N. Because the viscosity of ink is temperature-dependent (usually, the lower the temperature, the higher the viscosity), adjusting the temperature of the ink with the ink temperature adjustment unit 43 allows the viscosity of the ink to be adjusted within a desired viscosity range. The target temperature is determined so that the viscosity of the ink at the target temperature is a viscosity (for example, 200 cP or less) that allows the ink to be appropriately ejected as droplets from the nozzle N at the shear speed during ink circulation.

[0070] In this way, the viscosity of the ink ejected from the nozzles N is adjusted by increasing the shear rate caused by the ink circulation mechanism 8 circulating the ink in a circulation path including the inkjet head 41, and by heating the ink by the ink temperature adjustment unit 43. Therefore, in this embodiment, the ink circulation mechanism 8, the inkjet head 41, and the ink temperature adjustment unit 43 form a "viscosity adjustment unit 70" (see FIG. 10). This viscosity adjustment unit 70 adjusts the viscosity of the ink ejected from the nozzles N of the head unit 40 to within a viscosity range that allows ejection from the nozzles N. This viscosity range is, for example, 200 cP or less.

[0071] [Pinning section] FIG. 8 is a diagram showing the tip of the robot arm 20. As shown in FIG. As shown in FIG. 8, a pinning unit 31 and a workpiece detection unit 32 (detection unit) are attached to the tip of the arm 22 of the robot arm 20 near the head unit 40.

[0072] The inkjet head 41 of the head unit 40 of this embodiment ejects ultraviolet-curable ink that thickens when exposed to ultraviolet light (a predetermined energy). The pinning unit 31 moves relative to the inclined surface S together with the head unit 40, and irradiates ultraviolet light onto the ink that has been ejected from the inkjet head 41 and landed on the surface of the workpiece W. That is, the pinning unit 31 thickens the ink that has been ejected from the head unit 40 and landed on the inclined surface S while the head unit 40 is moving relative to the inclined surface S. As a result, the ink that has landed on the surface of the workpiece W thickens immediately after landing, thereby suppressing ink dripping. The pinning unit 31 may emit excimer light in the ultraviolet wavelength range.

[0073] The pinning unit 31 has a determined ultraviolet irradiation range (particularly, an irradiation range in the x direction) so that it can irradiate ultraviolet rays onto ink ejected from all of the nozzles N provided in the inkjet head 41 of the head unit 40. The pinning unit 31 may be disposed at the tip of the robot arm 20, upstream of the head unit 40 in the scanning direction D. This allows ultraviolet rays to be sequentially irradiated onto ink ejected from the head unit 40 from the upstream side of the head unit 40. In FIG. 8, the landing position P of the ink from the head unit 40 and the irradiation position of ultraviolet rays by the pinning unit 31 coincide with each other, but this is not limiting, and the irradiation position of ultraviolet rays by the pinning unit 31 may be upstream of the landing position P in the scanning direction D.

[0074] Although the pinning unit 31 has been exemplified as one that irradiates ultraviolet rays, the pinning unit 31 is not limited to this, and may instead impart any energy to the ink that is capable of thickening the ink. For example, when ink is used that thickens when heated by evaporating the solvent, the pinning unit 31 may transfer (impart) heat as a predetermined energy to the ink by convection or radiation. In this case, the pinning unit 31 may include, for example, one or more hot air generators, infrared heaters, or halogen lamps. In this case, the ink can be heated by the pinning unit 31 to evaporate the solvent and thicken the ink. Furthermore, the pinning unit 31 may be attached to a robot arm 20 separate from the robot arm 20 to which the head unit 40 is attached. In this case, the same effect can be obtained by operating the robot arms 20 in synchronization.

[0075] [Work detection unit] The workpiece detection unit 32 shown in FIG. 8 will be described. The workpiece detection unit 32 detects the inclination angle θ of the inclined surface S of the workpiece W from a horizontal plane (more specifically, the inclination angle θ of the landing position P of the ink ejected from the inkjet head 41 on the inclined surface S). The workpiece detection unit 32 can detect the inclination angle θ, for example, by calculating the results of a laser displacement sensor. Specifically, the workpiece detection unit 32 can be provided with a light-emitting unit that emits a laser and a light-receiving unit that receives reflected light of the laser light emitted by the light-emitting unit, and the inclination angle θ of the inclined surface S can be determined from the relationship between the laser emission direction of the light-emitting unit and the light-receiving position of the light-receiving unit. The workpiece detection unit 32 detects the relative angle of the inclined surface S based on its own orientation (the laser emission direction). Therefore, by using information about the orientation of the workpiece detection unit 32 at that time (i.e., the orientation of the arm 22), the inclination angle θ of the inclined surface S can be converted into the inclination angle θ of the inclined surface S from a horizontal plane. The method for detecting the inclination angle θ by the workpiece detection unit 32 is not limited to the above, and may be, for example, a method for detecting the inclination degree by calculation from the image processing results of an image of the inclined surface S captured by a camera. Furthermore, the workpiece detection unit 32 may further detect the distance d from the nozzle opening surface 41a of the inkjet head 41 to the workpiece W.

[0076] In this embodiment, the inclination angle θ of the inclined surface S of the workpiece W is within the range of 0°<θ≦90°. Therefore, when the normal vector of the inclined surface S of the workpiece W has a −Z direction component (when the inclined surface S faces downward), the inclination angle θ is set to the acute angle formed by the horizontal plane (XY plane) and the inclined surface S, as shown in FIG. 9A. Furthermore, when the inclined surface S is a curved surface, the inclination angle θ is set to the acute angle formed by the tangent plane Sa of the inclined surface S at a portion of the inclined surface S that faces the nozzle opening surface 41a of the head unit 40 (for example, at the impact position P) and the horizontal plane, as shown in FIG. 9B.

[0077] It should be noted that the workpiece detection unit 32 is not an essential component of the inkjet recording apparatus 1. For example, if workpiece shape data 141 (see FIG. 9) representing the three-dimensional surface shape of the workpiece W is acquired and the coordinates of the surface of the workpiece W can be expanded into the coordinate system of the robot arm 20, the inclination angle θ of the inclined surface S and the distance d from the nozzle opening surface 41a to the workpiece W can be determined based on the surface position coordinates of the workpiece W. The workpiece shape data 141 corresponds to "inclination angle information relating to the inclination angle of the inclined surface S that has been determined in advance." It should be noted that the inclination angle θ and the distance d may be determined using both the coordinates of the surface of the workpiece W expanded into the coordinate system of the robot arm 20 and the detection results by the workpiece detection unit 32.

[0078] FIG. 10 is a block diagram showing the main functional configuration of the inkjet recording apparatus 1. As shown in FIG. The inkjet recording apparatus 1 includes a control unit 10, a robot arm 20 having an arm control unit 24 and a drive motor 25, a pinning unit 31, a workpiece detection unit 32, a coating surface cooling unit 33, a communication unit 34, a head unit 40 having an inkjet head 41, a head control unit 42, and an ink temperature adjustment unit 43, and an ink circulation mechanism 8, and these components are connected by a bus 90. The inkjet head 41, the ink temperature adjustment unit 43, and the ink circulation mechanism 8 form a viscosity adjustment unit 70. The components that have already been described will not be described below.

[0079] The control unit 10 includes a central processing unit (CPU) 11, a random access memory (RAM) 12, a read-only memory (ROM) 13, and a storage unit 14. The control unit 10 controls the overall operation of each unit of the inkjet recording apparatus 1 by having the CPU 11 execute various processes according to a program 131. For example, to paint the inclined surface S of the workpiece W, the control unit 10 executes scanning control to eject ink from the nozzles N of the head unit 40 onto the inclined surface S while moving the head unit 40 and the inclined surface S relatively in a predetermined scanning direction. The control unit 10 also repeats the above scanning control for each relative movement to paint a specified area of ​​the inclined surface S. Note that while FIG. 10 illustrates the control unit 10 having one CPU 11, this is merely an example, and the control unit 10 may have two or more circuit elements, such as CPUs, that perform arithmetic processing. In this case, multiple circuit elements may participate in a common process, or multiple circuit elements may independently execute different processes in parallel.

[0080] The CPU 11 reads out various control programs 131 and setting data stored in the ROM 13, stores them in the RAM 12, and executes the programs to perform various arithmetic processing.

[0081] The RAM 12 provides a working memory space for the CPU 11 and stores temporary data. The RAM 12 may include a non-volatile memory.

[0082] The ROM 13 is a non-transitory recording medium readable by the CPU 11 as a computer, and stores various control programs 131 and setting data executed by the CPU 11. Note that the ROM 13 may be replaced by a rewritable non-volatile memory such as a flash memory.

[0083] The storage unit 14 is a non-transitory recording medium readable by the CPU 11 as a computer, and stores workpiece shape data 141 representing the three-dimensional surface shape of the workpiece W, job data 142 relating to a painting job (painting command), and the like, which are input from an external device via the communication unit 34. The workpiece shape data 141 may be in any data format as long as it can identify the arrangement of the inclined surfaces S of the workpiece W and the inclination angle θ of each inclined surface S. The job data 142 is data specifying the painting area and painting color (painting density) of the workpiece W, for example. The job data 142 may include, for example, image data of a painting image corresponding to the painting area, and the image data may include gradation data (painting density data) for each pixel of the painting image. An HDD (Hard Disk Drive), for example, is used as the storage unit 14.

[0084] The drive motor 25 of the robot arm 20 is, for example, a servo motor provided at each joint 23. The arm control unit 24 operates the drive motor 25 in accordance with a control signal sent from the control unit 10, and changes the angle of the arm 22 connected to the joint 23.

[0085] The pinning unit 31 irradiates the ink that has landed on the surface of the workpiece W with ultraviolet light in response to a control signal sent from the control unit 10, thereby hardening (thickening) the ink.

[0086] The workpiece detection unit 32 detects the inclination angle θ of the inclined surface S of the workpiece W and the distance d to the inclined surface S in response to a control signal transmitted from the control unit 10, and outputs data relating to the detection results to the control unit 10.

[0087] The coating surface cooling unit 33 uses a predetermined method to lower the temperature of the surface to be coated (for example, the inclined surface S) of the workpiece W. The method for lowering the temperature by the coating surface cooling unit 33 is not particularly limited, but may be, for example, cooling the inclined surface S with a cooling device, bringing a low-temperature member into contact with the inclined surface S via a member with good thermal conductivity, or blowing air that is cooler than the air temperature inside the chamber 2 onto the surface of the workpiece W.

[0088] The communication unit 34 is a communication interface that controls data communication with external devices. The communication interface may include one or more devices that are compatible with various communication protocols, such as a LAN board or LAN card. The communication unit 34 acquires work shape data 141, job data 142, etc. from external devices under the control of the control unit 10, and also transmits status information, etc. to the external devices.

[0089] The head control unit 42 of the head unit 40 outputs a drive signal to a drive electrode of an ink ejection mechanism at an appropriate timing for the inkjet head 41 based on the control signal and image data of the painted image sent from the control unit 10. The configuration of the head control unit 42 is not particularly limited, but can include, for example, a drive waveform generation unit that generates a drive waveform pattern in accordance with the control signal and image data sent from the control unit 10, a DAC that converts the drive waveform pattern into an analog drive waveform, and an amplifier circuit that amplifies the analog drive waveform to generate a drive signal.

[0090] The ink temperature adjustment section 43 of the head unit 40 adjusts the temperature of the ink inside the head unit 40 based on a control signal sent from the control section 10. Specifically, the ink temperature adjustment section 43 operates the heater 431 to heat the ink under the control of the control section 10, and outputs data related to the detection result of the ink temperature by the temperature detection element 432 to the control section 10. Based on the detection result by the temperature detection element 432, the control section 10 controls the heater 431 so that the ink is heated to a predetermined temperature.

[0091] The ink circulation mechanism 8 performs an ink delivery operation using pumps 88 and 89 based on a control signal sent from the control unit 10 , and circulates the ink through a circulation path passing through the inkjet head 41 .

[0092] [Operation of inkjet recording device] Next, the operation of the inkjet recording apparatus 1 will be described, focusing on the operation when coating the inclined surface S of the workpiece W.

[0093] 11A and 11B are diagrams showing the scanning operation of the head unit 40 when coating an inclined surface S of a workpiece W. Figures 11A and 11B are diagrams illustrating one inkjet head 41 extracted from the head unit 40 performing a scanning operation on an inclined surface S inclined at an inclination angle θ with respect to the horizontal plane (XY plane), with Fig. 11A being a view from the -Y direction and Fig. 11B being a view from the +X direction.

[0094] As described above, this scanning operation is performed by the control unit 10 executing the scan control. In the scan control, the control unit 10 operates the robot arm 20 so that the head unit 40 moves relative to the inclined surface S in a predetermined scanning direction D. The control unit 10 also ejects ink droplets from the nozzles N of the head unit 40, which is moving relative to the inclined surface S, at appropriate timing according to the image data (job data 142) of the painting job, causing the ink droplets to land on the inclined surface S. The control unit 10 repeatedly executes the scan control while changing the target range of the scanning operation (the range of the inclined surface S that the nozzle opening surface 41a of the inkjet head 41 faces during the scanning operation) as necessary so that the range specified in the painting job is painted with the specified density. Furthermore, if a single scanning operation of the head unit 40 under scan control is unable to paint with the specified density, the control unit 10 causes second and subsequent scanning operations to be performed on the same range of the inclined surface S, thereby applying ink overlays. When multiple scanning operations are performed on the same area of ​​the inclined surface S, it is preferable to start the next scanning operation after the ink that landed in the previous scanning operation has thickened and solidified.

[0095] [Head unit orientation and scanning direction during scanning operation] The orientation of the head unit 40 and the scanning direction D during the scanning operation are determined based on the shape of the inclined surface S. For example, during scanning operation, the head unit 40 preferably ejects ink from the nozzles N in a state where the arrangement direction of each nozzle row NL in the inkjet head 41 is horizontal. This makes it possible to suppress variations in the ejection state between different nozzles N included in one nozzle row NL due to differences in head pressure (differences in ink pressure due to differences in the height of the nozzles N). FIG. 11 illustrates a state where the nozzle rows NL are parallel to the Y direction. Here, the horizontal arrangement direction of the nozzle rows NL includes not only a case where the arrangement direction of the nozzle rows NL is completely horizontal, but also a state that can be considered equivalent to the case where the arrangement direction of the nozzle rows NL is horizontal. The "state that can be considered equivalent to the case where the arrangement direction of the nozzle rows NL is horizontal" refers to, for example, a state where differences in the ejection state (variations in liquid volume and speed) due to differences in head pressure between different nozzles N included in the nozzle row NL can be ignored (a state where the effect on coating density is not visible). The scanning direction D is a direction intersecting the arrangement direction of the nozzle row NL (usually a direction perpendicular to the arrangement direction of the nozzle row NL). For example, as shown in Figures 11A and 11B, the scanning direction D is a direction going down the slope along the inclined surface S. Alternatively, the scanning direction D may be a direction going up the slope along the inclined surface S.

[0096] Furthermore, during the scanning operation, it is preferable that the nozzle opening surface 41a of the inkjet head 41 is parallel to the inclined surface S. This makes the distance between each nozzle row NL and the inclined surface S uniform, and the ink flight distance and flight time can be made uniform between different nozzle rows NL, thereby improving the coating quality.

[0097] The control unit 10 controls the operation of the robot arm 20 in the scanning control so that the orientation of the head unit 40 (inkjet head 41) and the scanning direction D in the scanning operation are as described above.

[0098] [Adjust ink droplet volume based on tilt angle] Generally, when ink droplets are landed on an inclined surface S, the liquid ink immediately after landing tends to fall along the inclined surface S due to gravity, which can cause dripping depending on the inclination angle θ of the inclined surface S, the viscosity of the ink, and the amount of droplets that land. Here, dripping refers to the phenomenon in which a portion of the landed ink flows from the landing position along the inclined surface S in a direction that has a vertically downward component.

[0099] To prevent such dripping, the control unit 10 controls the head unit 40 so that the amount of ink droplets landing per predetermined area on the inclined surface S in one scan control (i.e., in one scanning operation) is equal to or less than the maximum droplet amount Vmax determined based on the inclination angle θ of the inclined surface S from the horizontal plane. The maximum droplet amount Vmax corresponding to a certain inclination angle θ is determined within a range in which dripping does not occur on the inclined surface S with that inclination angle θ.

[0100] More specifically, the maximum droplet volume Vmax is determined based on the tilt angle θ, for example, as follows: That is, the maximum droplet volume Vmax1 of ink that lands per predetermined area on a first inclined surface S1 having a first inclination angle θ1 is determined to be smaller than the maximum droplet volume Vmax2 of ink that lands per predetermined area on a second inclined surface S2 having a second inclination angle θ2 that is smaller than the first inclination angle θ1. From another perspective, when the inclination angle θ from 0° to 90° is divided into multiple angle ranges, the maximum droplet volume Vmax is determined for each angle range so that the larger the inclination angle θ, the smaller the maximum droplet volume Vmax. Alternatively, the maximum droplet volume Vmax may be determined according to the inclination angle θ so that the larger the inclination angle θ of the inclined surface S, the smaller the maximum droplet volume Vmax of ink that lands per predetermined area.

[0101] Methods for adjusting the amount of ink droplets landing per specified area on an inclined surface S having an inclination angle θ to be equal to or less than the maximum droplet amount Vmax based on the inclination angle θ include, for example, the following first droplet amount adjustment method and second droplet amount adjustment method.

[0102] [First droplet volume adjustment method] The first droplet volume adjustment method is a method in which the size (volume) of ink droplets ejected from nozzles N during scan control is determined based on the inclination angle θ of inclined surface S. As described above, the size of ink droplets ejected from nozzles N can be changed, for example, by adjusting the magnitude of the voltage of the drive signal supplied to the drive electrode of the ink ejection mechanism and / or the waveform pattern of the drive signal. Alternatively, a method in which multiple ink droplets are ejected from nozzles N and coalesce while the ink is flying or before it thickens after landing, and the number of droplets to be coalesced can be changed, may also be used.

[0103] 12 is a diagram showing an example of setting the size (volume) of ink droplets in the first droplet volume adjustment method. The setting contents are stored in the storage unit 14 as setting data. In the example shown in FIG. 12, when the inclination angle θ of the inclined surface S is greater than 0° and less than 30°, the size of the ejected ink droplets is set to "large (75 pL)". Furthermore, when the inclination angle θ of the inclined surface S is equal to or greater than 30° and less than 60°, the size of the ink droplets ejected is set to "medium (50 pL)". Furthermore, when the inclination angle θ of the inclined surface S is equal to or greater than 60° and equal to or less than 90°, the size of the ejected ink droplets is set to "small (25 pL)". The size of the ink droplets ejected onto a coating surface with an inclination angle θ of 0° (i.e., horizontal) may be "large (75 pL)", as in the case where the inclination angle θ is greater than 0° and less than 30°, or may be even larger (e.g., extra-large (100 pL)). In particular, when the inclination angle θ of the inclined surface S is 30° or more, it is preferable that the volume of the ink droplets ejected from the nozzles N be 1 pL or more and 50 pL or less. Furthermore, it is more preferable that the volume of the ink droplets be 2 pL or more and 40 pL or less, and even more preferable that the volume be 3 pL or more and 30 pL or less.

[0104] In this way, the size of the ink droplets is determined for each angle range of the tilt angle θ so that the ink droplets become smaller as the angle range of the tilt angle θ increases. The droplet sizes in the right column of Fig. 12 are determined so as to satisfy the condition that, for example, when ink droplets of the sizes in the right column are ejected onto all ink ejection possible positions (landing positions) during a scanning operation for an inclined surface S within the angle range of the tilt angle θ shown in the left column, "the amount of ink droplets landing per specified area of ​​the inclined surface S is equal to or less than the maximum droplet volume Vmax."

[0105] When the first droplet volume adjustment method is used, the control unit 10 identifies the inclination angle θ of the inclined surface S to be coated based on the workpiece shape data 141 or the detection results of the workpiece detection unit 32. Then, the control unit 10 references the settings shown in FIG. 12 and changes the voltage magnitude of the drive signal supplied to the ink discharge mechanism and / or the waveform pattern of the drive signal so that ink is discharged from the nozzle N with a droplet size corresponding to the angle range to which the identified inclination angle θ belongs. The control unit 10 supplies the drive signal to the ink discharge mechanism with the changed settings, causing ink to be discharged from the nozzle N. The control unit 10 also varies the size of the ink droplets discharged from the nozzle N of a given head unit 40 (and therefore the maximum amount of ink droplets that can land per specified area) depending on the inclination angle θ of the inclined surface S to be coated. This allows a single head unit 40 to coat multiple inclined surfaces S with different inclination angles θ without dripping. This makes it possible to simplify the device configuration and control, and reduce costs.

[0106] The droplet size setting values ​​shown in FIG. 12 are merely examples and are not limited to these. The likelihood of dripping varies depending on various factors, such as the physical properties of the ink, the physical properties and surface condition of the inclined surface S, and the environment surrounding the inclined surface S (temperature, humidity, etc.). Therefore, the droplet size setting values ​​in FIG. 12 may be appropriately determined depending on these factors. The width of each angle range is not limited to 30° and can be changed as appropriate. The size of the ink droplets may be determined so that the thickness of the ink in a liquid state after landing on the inclined surface S is a predetermined value or less. For example, when the inclination angle θ is 30° or greater, it is preferable to determine the size of the ink droplets so that the thickness of the ink in a liquid state after landing on the inclined surface S in one scan control is 10 μm or less. It is more preferable to determine the size of the ink droplets so that the thickness is 5 μm or less, and even more preferable to determine the size of the ink droplets so that the thickness is 3 μm or less.

[0107] [Second droplet volume adjustment method] The second droplet volume adjustment method is a method in which the maximum number of ink droplets that are to land per predetermined area during scan control is determined based on the inclination angle θ of the inclined surface S.

[0108] 13 is a diagram showing an example of setting the maximum number of ink droplets that are to land per specified area in the second droplet volume adjustment method. This setting content is stored in the storage unit 14 as setting data. In the example shown in FIG. 13, the maximum number of pixels onto which ink is ejected (hereinafter referred to as the "maximum number of ejection pixels") among a unit pixel group consisting of nine pixels arranged in three rows and three columns is determined for each angle range of the tilt angle θ. Here, each pixel constituting the unit pixel group corresponds to an area on the inclined surface S onto which ink is ejected and landed, corresponding to one pixel data in the image data of the job data 142. The area of ​​the unit pixel group corresponds to the "predetermined area." Furthermore, when one ink droplet is ejected per pixel, the maximum number of ejection pixels corresponds to the "maximum number of ink droplets to land per predetermined area." Note that although ink that lands on the inclined surface S spreads in a roughly circular shape, in FIG. 13, the area of ​​each pixel is represented as a square for convenience. Furthermore, the configuration of the unit pixel group is not limited to nine pixels arranged in three rows and three columns, but can be any configuration, such as four pixels arranged in two rows and two columns, or 16 pixels arranged in four rows and four columns.

[0109] 13, when the inclination angle θ of the inclined surface S is greater than 0° and less than 30°, the maximum number of ejection pixels in the unit pixel group is 9. That is, in this case, as shown in the rightmost column in FIG. 13, ink is ejected onto all pixels included in the unit pixel group. Furthermore, when the inclination angle θ of the inclined surface S is equal to or greater than 30° and less than 60°, the maximum number of discharge pixels in the unit pixel group is set to 5. In this case, ink is discharged onto pixels forming a checkerboard pattern within the unit pixel group, as shown in the rightmost column of FIG. Furthermore, when the inclination angle θ of the inclined surface S is between 60° and 90°, the maximum number of ejected pixels in the unit pixel group is 3. In this case, as shown in the rightmost column of Fig. 13, for example, ink is ejected so that the number of ejected pixels per row and per column in the unit pixel group is one pixel. When ink is ejected onto a painted surface with an inclination angle θ of 0° (that is, a horizontal surface), the maximum number of ejection pixels is 9 pixels.

[0110] In this way, the maximum number of ejection pixels is determined for each angle range of the tilt angle θ so that the maximum number of ink droplets that land decreases as the angle range of the tilt angle θ increases. For example, the maximum number of ejection pixels in Fig. 13 is determined so as to satisfy the condition that "the amount of ink droplets that land per specified area of ​​the inclined surface S is equal to or less than the maximum droplet amount Vmax" when ink droplets of a specified size are ejected onto the pixels of the maximum number of ejection pixels per unit pixel group for the inclined surface S within the angle range of the tilt angle θ shown in the leftmost column.

[0111] Furthermore, when the inclination angle θ of the inclined surface S is equal to or greater than a predetermined reference angle, it is preferable to control the ink ejection position so that ink droplets that land on the inclined surface S do not coalesce. When the ink droplets coalesce, they form larger droplets on the inclined surface S, which makes them more susceptible to dripping. Therefore, when the inclination angle θ is large (equal to or greater than the reference angle), preventing ink from coalescing on the inclined surface S can effectively suppress dripping. The reference angle is not particularly limited, but can be determined depending on the physical properties of the ink, the physical properties and surface condition of the inclined surface S, the environment surrounding the inclined surface S, and the like, and may be, for example, 30°. To prevent ink droplets from coalescing, if the area where the landed ink droplets spread is a circle with a diameter r, the ink droplets should be determined so that the distance between the ink droplets (the centers of the wetting and spreading area) is greater than 2r.

[0112] When the second droplet volume adjustment method is used, the control unit 10 identifies the inclination angle θ of the inclined surface S based on the workpiece shape data 141 or the detection results of the workpiece detection unit 32. Then, the control unit 10 references the settings shown in FIG. 13 and acquires the maximum number of ejection pixels corresponding to the angle range to which the identified inclination angle θ belongs. The control unit 10 adjusts the timing of ink ejection from each nozzle N so that the number of pixels ejected per unit pixel does not exceed the maximum number of ejection pixels. For example, by applying mask pattern data of a mask pattern corresponding to the maximum number of ejection pixels to the image data of the job data 142, mask image data is generated in which some of the pixel data is changed to pixel data corresponding to non-ejection of ink, and ink is ejected from each nozzle N based on this mask image data. When performing two or more scans on the same area of ​​the inclined surface S, it is preferable to determine the mask pattern so that the masked portions of the mask pattern data applied in each scan are complementary. Furthermore, the control unit 10 varies the maximum number of ink droplets (maximum ink droplet volume) that are landed per predetermined area by one head unit 40 according to the inclination angle θ of the inclined surface S to be coated.

[0113] The set value of the maximum number of ejection pixels and the positions of the ejection pixels shown in FIG. 13 are merely examples and are not limited to these. They may be appropriately determined depending on factors such as the physical properties of the ink, the physical properties and surface condition of the inclined surface S, and the environment surrounding the inclined surface S (temperature, humidity, etc.). The width of each angle range is not limited to 30° and can be changed as appropriate. The set value of the maximum number of ejection pixels may be determined so that the thickness of the ink in a liquid state that has landed on the inclined surface S is equal to or less than a predetermined value. For example, when the inclination angle θ is 30° or greater, it is preferable to set the set value of the maximum number of ejection pixels so that the thickness of the ink in a liquid state that has landed on the inclined surface S in one scan control is equal to or less than 10 μm. It is more preferable to set the set value of the maximum number of ejection pixels so that the thickness is equal to or less than 5 μm, and even more preferable to set the set value of the maximum number of ejection pixels so that the thickness is equal to or less than 3 μm.

[0114] Furthermore, the first droplet volume adjustment method and the second droplet volume adjustment method may be combined. That is, the size of the ink droplets ejected from the nozzles N and the maximum number of ink droplets that land per specified area may be set for each range of the tilt angle θ.

[0115] Adjust ink speed based on tilt angle When ink is ejected onto the inclined surface S, the speed of the ink droplets ejected from the nozzles N may be adjusted based on the inclination angle θ of the inclined surface S. The adjustment of the ink droplet speed may be combined with either the first droplet volume adjustment method or the second droplet volume adjustment method. More specifically, the velocity of ink droplets is determined based on the tilt angle θ, for example, as follows: That is, the velocity of ink droplets is determined so that the velocity of ink droplets ejected from a nozzle N onto a first inclined surface S1 having a first tilt angle θ1 is faster than the velocity of ink droplets ejected from a nozzle N onto a second inclined surface S2 having a second tilt angle θ2 that is smaller than the first tilt angle θ1. From another perspective, when the tilt angle θ from 0° to 90° is divided into a plurality of angle ranges, the velocity of ink droplets is determined for each angle range so that the velocity of ink droplets increases as the tilt angle θ increases. Alternatively, the velocity of ink droplets may be determined so that the velocity of ink droplets ejected from a nozzle N increases as the tilt angle θ of the inclined surface S increases.

[0116] By increasing the ink speed, the height of the ink from the inclined surface S after landing is reduced, making it less likely for dripping to occur. Furthermore, with the first droplet volume adjustment method, the size of the ejected ink droplets becomes smaller depending on the magnitude of the inclination angle θ, and the ink flight path is more likely to vary due to air resistance and air currents, making it difficult to land the ink in the desired position. However, by increasing the ink speed, it is possible to suppress variation in the flight path, making it possible to reliably land the ink in the desired position.

[0117] [How to paint curved, inclined surfaces S] The inkjet recording apparatus 1 of this embodiment can also paint the inclined surface S when the inclined surface S is a curved surface. When the inclined surface S is a curved surface, the orientation of the head unit 40 (the angle of the arm 22 of the robot arm 20) is adjusted each time during the scanning operation in accordance with the shape of the curved surface so that the nozzle opening surface 41a of the head unit 40 directly faces the curved surface of the inclined surface S.

[0118] Furthermore, when the inclined surface S is a curved surface, the control unit 10 determines the maximum volume Vmax of ink droplets that can be landed per specified area in the region based on the inclination angle of the region of the curved surface where the ink will land. Here, the size of the region can be determined as appropriate, but it is preferable to make the size smaller as the curvature of the curved surface increases so that the maximum volume Vmax of ink droplets matches the shape of the curved surface as much as possible.

[0119] [Ink temperature and viscosity adjustment] Prior to the start of scan control, the temperature and viscosity of the ink ejected from the nozzles N of the head unit 40 are adjusted. The temperature of the ink is adjusted, for example, by an ink temperature adjustment unit 43 included in the head unit 40. Furthermore, heaters for heating the ink may be provided outside the head unit 40, for example, in the supply sub-tank 81, the reflux sub-tank 82, the main tank 83, and at least some of the ink flow paths 84 to 87 shown in FIG.

[0120] The temperature of the ink ejected from the nozzle N is preferably 10°C or more higher than the temperature of the inclined surface S. This makes it less likely for the ink to drip because it is rapidly cooled and thickened when it lands on the inclined surface S. In other words, since it is preferable for the temperature of the inclined surface S to be 10°C or more lower than the temperature of the ink at the time of ejection, the temperature of the inclined surface S may be lowered by the coating surface cooling unit 33 in addition to or instead of heating the ink.

[0121] The viscosity of ink typically decreases as the ink temperature increases. Furthermore, because the ink in this embodiment is thixotropic, shear forces are applied to the ink as it circulates through the narrow passages in the ink circulation mechanism 8, which also reduces the ink viscosity. To more effectively adjust the viscosity, a viscosity-adjusting configuration (e.g., a static mixer) or device (e.g., an agitator) may be provided in the ink flow path of the ink circulation mechanism 8. These various viscosity adjustment methods may be used alone or in combination. A more preferred configuration is one in which the ink viscosity is reduced to a certain degree using an agitator in a tank in the ink circulation mechanism 8, and then the ink is circulated within the ink circulation mechanism 8. Furthermore, the ink is heated in the head unit 40 or the like to stabilize the ink temperature at a desired temperature, allowing the ink to be supplied to the head and ejected without significantly changing the viscosity adjusted in the tank. This configuration is preferred because it allows for stable adjustment of the ink viscosity.

[0122] [Application of primer ink] It is preferable to apply a primer ink (functional liquid) in advance to the inclined surface S of the workpiece W, which reacts with the ink ejected from the nozzles N of the head unit 40 to thicken the ink. The method for applying the primer ink is not particularly limited, but it may be applied by various application methods such as screen printing, or it may be applied by ejecting the primer ink from the head unit 40 of the inkjet recording device 1. By ejecting ink onto the inclined surface S to which the primer ink has been applied, the ink undergoes a coagulation reaction after landing, causing a sudden increase in viscosity, making it possible to more effectively suppress dripping.

[0123] [Painting process control procedure by the control unit] Next, a control procedure for the coating process for coating the workpiece W by the above operation will be described. FIG. 14 is a flowchart showing the control procedure for the painting process. The painting process is executed when the control unit 10 receives job data 142 related to a painting job from an external device via the communication unit 34. Furthermore, before the start of the painting process, a functional liquid application step of applying a primer ink to the inclined surface S of the workpiece W may be executed.

[0124] When the coating process starts, the control unit 10 starts adjusting the temperature and viscosity of the ink (step S101). Here, the control unit 10 operates the pumps 88 and 89 of the ink circulation mechanism 8 to start circulating the ink, and causes the ink temperature adjustment unit 43 to start heating the ink.

[0125] The control unit 10 determines whether the temperature and viscosity of the ink are within the appropriate range (step S102), and if it is determined that they are not within the appropriate range ("NO" in step S102), it executes the processing of step S102 again.

[0126] If it is determined that the temperature and viscosity of the ink are within the appropriate range ("YES" in step S102), the control unit 10 supplies a control signal to the arm control unit 24 to operate the robot arm 20 and move the head unit 40 to the scanning start position (step S103).

[0127] The control unit 10 acquires the inclination angle θ of the inclined surface S of the workpiece W (step S104). Here, if workpiece shape data 141 representing the three-dimensional surface shape of the workpiece W is stored in advance in the storage unit 14, the control unit 10 identifies the inclination angle θ of the inclined surface S by referring to the workpiece shape data 141. Furthermore, if there is no workpiece shape data 141, the control unit 10 identifies the inclination angle θ of the inclined surface S based on the detection result by the workpiece detection unit 32.

[0128] Based on the tilt angle θ identified in step S104, the control unit 10 determines the size of ink droplets to be ejected from the nozzles N of the head unit 40, the velocity of the ink droplets, and the pixel positions at which the droplets are to be ejected (step S105). For example, when using the first droplet volume adjustment method, the control unit 10 refers to the setting data shown in FIG. 12 and identifies the size of ink droplets corresponding to the tilt angle θ of the inclined surface S. When using the second droplet volume adjustment method, the control unit 10 refers to the setting data shown in FIG. 13 and identifies the maximum number of ink droplet ejection pixels and the positions of the ejection pixels corresponding to the tilt angle θ of the inclined surface S. Furthermore, mask pattern data corresponding to the identified positions of the ejection pixels is applied to the image data of the job data 142 to generate mask image data.

[0129] The control unit 10 transmits a control signal to the pinning unit 31 to start the operation of the pinning unit 31 (step S106). In this embodiment, the control unit 10 starts the pinning unit 31 irradiating ultraviolet light.

[0130] The control unit 10 supplies a control signal to the arm control unit 24 to operate the robot arm 20, and starts the relative movement between the head unit 40 and the inclined surface S of the workpiece W (step S107).

[0131] The control unit 10 ejects ink from the nozzle N at a predetermined ejection position on the inclined surface S (step S108). More specifically, the control unit 10 outputs a control signal to the head control unit 42 based on the image data of the job data 142 or the above-mentioned mask image data, and causes the head control unit 42 to supply a drive signal to the ink ejection mechanism of the inkjet head 41 at an appropriate timing (the timing when the nozzle N faces the ejection position on the inclined surface S).

[0132] The control unit 10 determines whether the head unit 40 has moved to the scanning end position (step S109), and if it is determined that the head unit 40 has not moved to the scanning end position ("NO" in step S109), the process returns to step S108.

[0133] If it is determined that the head unit 40 has moved to the scan end position ("YES" in step S109), the control unit 10 causes the pinning unit 31 to end the ultraviolet ray irradiation operation (step S110).

[0134] The control unit 10 determines whether painting of the workpiece W specified by the painting job has been completed (step S111). If it is determined that painting of the workpiece W has not been completed ("NO" in step S111), the control unit 10 moves the head unit 40 to the next scanning start position (step S112) and returns the process to step S104 to perform the next scanning operation. Steps S104 to S110 correspond to the "scanning step," and the control by the control unit 10 in this scanning step corresponds to the "scanning control." If it is determined that painting of the workpiece W is complete ("YES" in step S111), the control unit 10 ends the painting process.

[0135] [Effects of the embodiment] As described above, the inkjet recording apparatus 1 according to this embodiment ejects ink onto the inclined surface S of a workpiece W, which has an inclined surface S inclined relative to a horizontal plane, and includes a head unit 40 having nozzles N for ejecting ink, and a control unit 10. The control unit 10 controls the head unit 40 to eject ink from the nozzles N of the head unit 40 onto the inclined surface S while moving the head unit 40 and the inclined surface S relative to each other in a predetermined scanning direction. The control unit 10 controls the head unit 40 so that the volume of ink droplets landing per unit area of ​​the inclined surface S during each scan is equal to or less than the maximum droplet volume Vmax determined based on the inclination angle θ of the inclined surface S from the horizontal plane. This effectively prevents ink dripping even when ink within a viscosity range typically used in the inkjet recording apparatus 1 (e.g., 200 cP or less) is used. In other words, since there is no need to use special high-viscosity ink to prevent dripping, stable ink ejection can be achieved while preventing dripping. Furthermore, it is possible to suppress dripping by setting a relatively small maximum droplet volume Vmax for inclined surfaces S with a large inclination angle θ, while setting a relatively large maximum droplet volume Vmax for inclined surfaces S with a small inclination angle θ, improving coating efficiency and productivity. This avoids excessive dripping countermeasures, allowing for efficient coating. Furthermore, the use of an inkjet system minimizes ink scattering compared to spray coating, thereby reducing ink waste. Furthermore, since it is possible to paint by having the ink land only on the desired areas, manual work such as masking non-painted areas is no longer necessary, enabling highly productive coating. In this way, according to this embodiment, it is possible to more reliably and efficiently suppress dripping of ink that has landed on the inclined surface S, resulting in a high-quality coated object with a uniform film thickness and little unevenness.

[0136] Furthermore, when the first droplet volume adjustment method is used, the control unit 10 determines the size of the ink droplets ejected from the nozzles N during scan control based on the inclination angle θ of the inclined surface S. This makes it possible to keep the volume of ink droplets landing per specified area equal to or less than the maximum droplet volume Vmax.

[0137] Furthermore, when the second droplet volume adjustment method is used, the control unit 10 determines the maximum number of ink droplets that are to land per predetermined area during scan control based on the inclination angle θ of the inclined surface S. This allows the volume of ink droplets that land per predetermined area to be equal to or less than the maximum droplet volume Vmax, regardless of the size of the ink being ejected.

[0138] Furthermore, the control unit 10 controls the head unit 40 in the scan control so that the maximum volume Vmax1 of ink droplets that land per predetermined area on the first inclined surface S1 having the first inclination angle θ1 is smaller than the maximum volume Vmax2 of ink droplets that land per predetermined area on the second inclined surface S2 having the second inclination angle θ2 that is smaller than the first inclination angle θ1. This adjusts the maximum volume Vmax of ink droplets according to the magnitude of the inclination angle θ of the inclined surface S, thereby making it possible to suppress dripping regardless of the magnitude of the inclination angle θ.

[0139] Furthermore, the control unit 10 controls the head unit 40 in the scan control so that the maximum volume Vmax of ink droplets that land per specified area decreases as the inclination angle θ of the inclined surface S increases. This adjusts the maximum volume Vmax of ink droplets according to the magnitude of the inclination angle θ of the inclined surface S, thereby making it possible to suppress dripping regardless of the magnitude of the inclination angle θ.

[0140] Furthermore, the control unit 10 controls the head unit 40 in the scan control so that the velocity of ink droplets ejected from the nozzles N toward the first inclined surface S1 having the first inclination angle θ1 is faster than the velocity of ink droplets ejected from the nozzles N toward the second inclined surface S2 having the second inclination angle θ2 that is smaller than the first inclination angle θ1. By increasing the ink velocity when the inclination angle θ is large, the height of the ink from the inclined surface S after landing is reduced, making it less likely for the ink to drip. Furthermore, when the ink droplets are made smaller depending on the magnitude of the inclination angle θ, the ink flight path is more likely to vary due to air resistance and air currents, making it difficult to land the ink at the desired position. However, by increasing the ink velocity, the variation in the ink flight path can be suppressed, ensuring that the ink can land at the desired position.

[0141] Furthermore, the control unit 10 controls the head unit 40 in the scan control so that the velocity of ink droplets ejected from the nozzles N increases as the inclination angle θ of the inclined surface S increases. This adjusts the ink velocity according to the magnitude of the inclination angle θ of the inclined surface S, making it possible to suppress dripping regardless of the magnitude of the inclination angle θ and to ensure that the ink hits the desired position.

[0142] The control unit 10 also acquires work shape data 141 as inclination angle information relating to a pre-specified inclination angle θ of the inclined surface S, and controls the head unit 40 in the scan control so that the amount of ink droplets that land per predetermined area of ​​the inclined surface S by the scan control is equal to or less than the maximum droplet amount corresponding to the inclination angle θ specified from the work shape data 141. This makes it possible to easily specify the inclination angle θ of the inclined surface S.

[0143] The control unit 10 also includes a workpiece detection unit 32 that detects the inclination angle θ of the inclined surface S, and controls the head unit 40 during scanning control so that the amount of ink droplets that land per predetermined area of ​​the inclined surface S due to the scanning control is equal to or less than the maximum droplet amount corresponding to the inclination angle θ detected by the workpiece detection unit 32. This makes it possible to identify the inclination angle θ of the inclined surface S on the spot.

[0144] Furthermore, the inkjet recording apparatus 1 includes a robot arm 20 to which a head unit 40 is attached, and the control unit 10, in scanning control, operates the robot arm 20 so that the head unit 40 moves relative to the inclined surface S in the scanning direction. This makes it possible to efficiently position the nozzle opening surface 41a of the head unit 40 opposite the inclined surface S of the workpiece W, which is a three-dimensional object, and improves productivity.

[0145] Furthermore, the inkjet recording apparatus 1 is equipped with a pinning unit 31 that thickens the ink that has landed on the inclined surface S. The pinning unit 31 is attached to the robot arm 20 and moves relative to the inclined surface S together with the head unit 40, thickening the ink that has been ejected from the head unit 40 and landed on the inclined surface S during the relative movement. This allows the ink to be thickened quickly immediately after it has landed on the inclined surface S, making it possible to more reliably prevent dripping.

[0146] Furthermore, the head unit 40 ejects ink from the nozzles N, which thickens when a predetermined amount of energy is applied, and the pinning unit 31 applies the energy to the ink that has landed on the inclined surface S. This allows the ink to thicken quickly immediately after landing on the inclined surface S.

[0147] The head unit 40 also has a nozzle row NL in which multiple nozzles N are arranged, and the control unit 10, during scan control, ejects ink from the nozzles N while the arrangement direction of the multiple nozzles N in the nozzle row NL is horizontal. This reduces the head pressure difference between each nozzle N in the nozzle row NL, enabling stable ejection with little variation. In addition, the ink ejection conditions (droplet volume, ejection speed) can be changed for each nozzle row NL, making it easier to control the ejection conditions.

[0148] Furthermore, in the scanning control, when the tilt angle θ of the inclined surface S is equal to or greater than a predetermined reference angle, the control unit 10 controls the ink ejection position by the head unit 40 so that ink droplets that have landed on the inclined surface S do not coalesce. This makes it possible to eliminate connections between ink droplets (dots) in the vertical direction (the direction in which dripping occurs) on the inclined surface S, thereby making it more difficult for dripping to occur.

[0149] Furthermore, the head unit 40 ejects ink onto the inclined surface S at a temperature that is 10° C. or more higher than the temperature of the inclined surface S. This causes the ink to cool rapidly and thicken after landing, making it less likely to drip.

[0150] The inkjet recording device 1 also includes a viscosity adjusting unit 70 that adjusts the viscosity of the ink ejected from the nozzles N of the head unit 40 to within a viscosity range that allows ink to be ejected from the nozzles N. Although there is an upper limit to the viscosity of the ink that can be ejected from the nozzles N of the head unit 40, providing the viscosity adjusting unit 70 allows the viscosity of the ink to be adjusted to be equal to or lower than the upper limit viscosity, thereby enabling stable ejection.

[0151] Furthermore, by setting the viscosity range to 200 cP or less, stable ink ejection from the nozzles N of the head unit 40 becomes possible.

[0152] The viscosity adjustment unit 70 also has an ink circulation mechanism 8 that circulates the ink in a path that includes the head unit 40. By circulating the ink, the viscosity of the ink can be stably maintained at a viscosity that allows it to be ejected from the nozzles N of the head unit 40.

[0153] The viscosity adjusting unit 70 also has a heater 431 that heats the ink. This makes it possible to adjust the viscosity of the ink to a level that allows it to be ejected from the nozzles N of the head unit 40. Furthermore, the temperature difference between the temperature of the ink and the temperature of the inclined surface S can be easily controlled.

[0154] Furthermore, the head unit 40 ejects thixotropic ink from the nozzles N. When the ink has thixotropy, it is no longer subjected to shear force after landing on the inclined surface S, and therefore the ink tends to thicken. This makes it even less likely for the ink to drip.

[0155] Furthermore, the inclined surface S is a curved surface, and the control unit 10 determines the maximum amount of ink droplets that can land per specified area in the region on the curved surface based on the inclination angle θ of the region where the ink lands. This makes it possible to effectively suppress dripping even on the inclined surface S where the inclination angle θ varies depending on the position.

[0156] Furthermore, when the inclination angle θ of the inclined surface S is 30° or more, the control unit 10 controls the head unit 40 by scanning control so that the thickness of the ink in a liquid state that lands on the inclined surface S is 10 μm or less. This makes it possible to effectively suppress dripping.

[0157] Furthermore, when the inclination angle θ of the inclined surface S is 30° or more, the control unit 10 controls the head unit 40 so that the volume of the ink droplets ejected from the nozzles N of the head unit 40 onto the inclined surface S is 1 pL or more and 50 pL or less. This makes it possible to effectively suppress dripping.

[0158] Furthermore, the coating method according to this embodiment performs a scanning step in which ink is ejected from the nozzles N of the head unit 40 onto the inclined surface S while moving the head unit 40 and the inclined surface S relatively in a predetermined scanning direction, and in the scanning step, the head unit 40 is controlled so that the amount of ink droplets landing per predetermined area on the inclined surface S in one scanning step is equal to or less than a maximum droplet amount determined based on the inclination angle θ of the inclined surface S from the horizontal plane. This makes it possible to more reliably and efficiently suppress dripping of ink that has landed on the inclined surface S.

[0159] The coating method also includes a functional liquid application step of applying primer ink to the inclined surface S as a functional liquid that reacts with ink ejected from the nozzles N of the head unit 40 to thicken the ink, and in the scanning step, ink is ejected from the nozzles N onto the inclined surface S to which the primer ink has been applied. This allows the ink to thicken quickly immediately after landing on the inclined surface S, making it possible to more reliably prevent dripping.

[0160] [others] The present invention is not limited to the above-described embodiment and modifications, and various modifications are possible. For example, in the above embodiment, the head unit 40 is moved in the scan control to move the head unit 40 and the inclined surface S relative to each other, but this is not limiting, and the head unit 40 and the inclined surface S may be moved relative to each other by moving the inclined surface S (workpiece W). Furthermore, the head unit 40 and the inclined surface S may be moved relative to each other by moving both.

[0161] Furthermore, if, at a certain point during a scanning operation, the area to be painted by one head unit 40 includes areas with different tilt angles θ, the amount of ink droplets ejected (the size of the ink droplets and / or the maximum number of ink droplets ejected) for each inkjet head 41 or each nozzle N of the head unit 40 may be made different depending on the tilt angle θ of the area to be painted.

[0162] Furthermore, the inkjet recording apparatus 1 may be provided with a plurality of head units 40, and each head unit 40 may be attached to a different robot arm 20.

[0163] Furthermore, color coating may be performed by providing a plurality of head units 40 that eject ink of different colors, and performing a scanning operation with each of the plurality of head units 40 over the same area of ​​the inclined surface S. Furthermore, one head unit 40 may be provided with an inkjet head 41 that ejects ink of a plurality of different colors, and coating of a plurality of colors may be performed with a single scanning operation.

[0164] Furthermore, ink may be ejected from the nozzles N without being based on the image data of the job data 142. For example, during the period in which the head unit 40 moves relative to the inclined surface S, a drive signal may be supplied to the ink ejection mechanism at a predetermined frequency to eject ink from the nozzles N while the head unit 40 is facing the area to be painted, and during the period in which the head unit 40 is not facing the area to be painted, the supply of the drive signal may be stopped to prevent ink from being ejected from the nozzles N. The positional relationship between the head unit 40 and the inclined surface S may be determined, for example, based on the coordinates of the surface of the workpiece W expanded in the coordinate system of the robot arm 20 based on the workpiece shape data 141, or may be determined based on the detection results by the workpiece detection unit 32.

[0165] Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents. [Industrial Applicability]

[0166] The present invention can be used in an inkjet recording apparatus and a coating method. [Explanation of symbols]

[0167] 1. Inkjet recording device 2 chambers 8 Ink circulation mechanism 10 Control Unit 11 CPU 12 RAM 13 ROM 131 Programs 14 Storage section 141 Work shape data (tilt angle information) 142 Job Data 20 Robot Arm 21 Base 22 Arm 23 Joints 24 Arm control unit 25 drive motor 31 Pinning section 32 Work detection unit (detection unit) 33 Cooling painted surface area 34 Communications Department 40 Head unit (ink ejection unit) 41 Inkjet head 41a Nozzle opening surface 42 Head control unit 43 Ink temperature adjustment unit 431 Heater 432 Temperature detection element 51 Head Chip 511 Ink Channel 512 Individual discharge flow path 52 Ink manifold 53 Common ink chamber 54 filters 55 Common discharge flow path 61 Inlet 62, 63 Outlets 64 cabinet 65 Exterior materials 70 Viscosity adjustment section D Scanning direction N nozzle NL nozzle row S inclined plane W Work (painting object) θ Tilt angle

Claims

1. An inkjet recording apparatus that discharges ink onto an inclined surface of an object to be coated, the inclined surface being inclined relative to a horizontal plane, an ink ejection unit having a nozzle for ejecting ink; A control unit; Equipped with The control unit performing scanning control to eject ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; the scanning control controls the ink ejection unit so that the amount of ink droplets that land on the inclined surface per predetermined area in one scan control is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; controlling the ink ejection unit in the scanning control so that a maximum volume of ink droplets that land on the first inclined surface having a first inclination angle per predetermined area is smaller than a maximum volume of ink droplets that land on the second inclined surface having a second inclination angle smaller than the first inclination angle per predetermined area; Inkjet recording device.

2. An inkjet recording device that discharges ink onto an inclined surface of an object to be coated, the inclined surface being inclined relative to a horizontal plane, an ink ejection unit having a nozzle for ejecting ink; A control unit; Equipped with The control unit performing scanning control to eject ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; the scanning control controls the ink ejection unit so that the amount of ink droplets that land on the inclined surface per predetermined area in one scan control is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; the ink ejection unit is controlled in the scanning control so that the maximum amount of ink droplets that land per predetermined area decreases as the inclination angle of the inclined surface increases. Inkjet recording device.

3. An inkjet recording device that discharges ink onto an inclined surface of an object to be coated, the inclined surface being inclined relative to a horizontal plane, an ink ejection unit having a nozzle for ejecting ink; A control unit; Equipped with The control unit performing scanning control to eject ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; the scanning control controls the ink ejection unit so that the amount of ink droplets that land on the inclined surface per predetermined area in one scan control is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; In the scanning control, when the inclination angle of the inclined surface is equal to or greater than a predetermined reference angle, the ink ejection position of the ink ejection unit is controlled so that ink droplets that have landed on the inclined surface do not coalesce. Inkjet recording device.

4. 4. The inkjet recording apparatus according to claim 1, wherein the control unit determines the size of ink droplets to be ejected from the nozzles in the scanning control based on the inclination angle of the inclined surface.

5. 5. The inkjet recording apparatus according to claim 1, wherein the control unit determines a maximum number of ink droplets to be landed per predetermined area in the scanning control based on the inclination angle of the inclined surface.

6. The inkjet recording device of any one of claims 2 to 5, wherein the control unit controls the ink ejection unit in the scanning control so that the maximum amount of ink droplets that land per specified area on a first inclined surface having a first inclination angle is smaller than the maximum amount of ink droplets that land per specified area on a second inclined surface having a second inclination angle that is smaller than the first inclination angle.

7. The inkjet recording device according to any one of claims 1, 3 to 6, wherein the control unit controls the ink ejection unit in the scanning control so that the maximum amount of ink droplets that land per specified area becomes smaller as the inclination angle of the inclined surface becomes larger.

8. An inkjet recording device according to any one of claims 1 to 7, wherein the control unit controls the ink ejection unit in the scanning control so that the speed of ink droplets ejected from the nozzles onto a first inclined surface having a first inclination angle is faster than the speed of ink droplets ejected from the nozzles onto a second inclined surface having a second inclination angle smaller than the first inclination angle.

9. The inkjet recording device according to any one of claims 1 to 8, wherein the control unit controls the ink ejection unit in the scanning control so that the speed of ink droplets ejected from the nozzles increases as the inclination angle of the inclined surface increases.

10. The control unit acquiring inclination angle information relating to the inclination angle of the inclined surface specified in advance; In the scanning control, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area by the scanning control is equal to or less than the maximum amount of ink droplets that corresponds to the inclination angle identified from the inclination angle information. The inkjet recording apparatus according to any one of claims 1 to 9.

11. a detector for detecting the inclination angle of the inclined surface, the control unit controls the ink ejection unit so that the amount of ink droplets that land on the inclined surface per predetermined area by the scanning control is equal to or less than the maximum droplet amount corresponding to the inclination angle detected by the detection unit. The inkjet recording apparatus according to any one of claims 1 to 9.

12. a robot arm to which the ink ejection unit is attached, the control unit, in the scanning control, operates the robot arm so that the ink discharge unit moves relative to the inclined surface in the scanning direction. The inkjet recording apparatus according to any one of claims 1 to 11.

13. a pinning unit that increases the viscosity of ink that has landed on the inclined surface, the pinning unit is attached to the robot arm and moves relative to the inclined surface together with the ink ejection unit, and thickens ink that is ejected from the ink ejection unit and lands on the inclined surface during the relative movement. The inkjet recording apparatus according to claim 12.

14. the ink ejection unit ejects ink from the nozzle, the ink being thickened by application of a predetermined amount of energy; the pinning unit imparts the predetermined energy to the ink that has landed on the inclined surface; The inkjet recording apparatus according to claim 13.

15. the ink ejection unit has a nozzle row in which a plurality of the nozzles are arranged, the control unit, in the scanning control, causes the nozzles to eject ink in a state in which the arrangement direction of the plurality of nozzles in the nozzle row is horizontal; The inkjet recording apparatus according to any one of claims 1 to 14.

16. The inkjet recording device according to any one of claims 1, 2, and 4 to 15, wherein, in the scanning control, when the inclination angle of the inclined surface is equal to or greater than a predetermined reference angle, the control unit controls the ink ejection position of the ink ejection unit so that ink droplets landing on the inclined surface do not coalesce.

17. 17. The inkjet recording apparatus according to claim 1, wherein the ink ejection section ejects onto the inclined surface ink at a temperature that is 10° C. or more higher than the temperature of the inclined surface.

18. 18. The inkjet recording apparatus according to claim 1, further comprising a viscosity adjusting unit that adjusts the viscosity of the ink ejected from the nozzles of the ink ejection unit to within a viscosity range that allows the ink to be ejected from the nozzles.

19. 19. The inkjet recording apparatus according to claim 18, wherein the viscosity range is 200 cP or less.

20. 20. The inkjet recording apparatus according to claim 18, wherein the viscosity adjusting section has an ink circulation mechanism that circulates ink through a path including the ink ejection section.

21. 21. The inkjet recording apparatus according to claim 18, wherein the viscosity adjusting section has a heater that heats the ink.

22. 22. The inkjet recording apparatus according to claim 1, wherein the ink ejection section ejects ink having thixotropy from the nozzles.

23. the inclined surface is a curved surface, the control unit determines the maximum amount of ink droplets to be landed per predetermined area in the region on the curved surface based on an inclination angle of the region on which the ink is to be landed. The inkjet recording apparatus according to any one of claims 1 to 22.

24. An inkjet recording device according to any one of claims 1 to 23, wherein the control unit controls the ink ejection unit so that the thickness of the ink in a liquid state that lands on the inclined surface by the scanning control is 10 μm or less when the inclination angle of the inclined surface is 30° or more.

25. An inkjet recording device according to any one of claims 1 to 24, wherein the control unit controls the ink ejection unit so that the volume of ink droplets ejected from the nozzles of the ink ejection unit onto the inclined surface is 1 pL or more and 50 pL or less when the inclination angle of the inclined surface is 30° or more.

26. A coating method for coating an inclined surface of an object to be coated, the inclined surface being inclined with respect to a horizontal plane, by using an inkjet recording device equipped with an ink ejection unit having a nozzle for ejecting ink, the method comprising: a scanning step of ejecting ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; in the scanning step, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area in one scanning step is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; In the scanning step, the ink ejection unit is controlled so that a maximum volume of ink droplets that lands per predetermined area on the first inclined surface having a first inclination angle is smaller than a maximum volume of ink droplets that lands per predetermined area on the second inclined surface having a second inclination angle that is smaller than the first inclination angle. Painting method.

27. ​​A coating method for coating an object having an inclined surface inclined relative to a horizontal plane by ejecting ink onto the inclined surface using an inkjet recording device equipped with an ink ejection unit having a nozzle for ejecting ink, comprising: a scanning step of ejecting ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; in the scanning step, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area in one scanning step is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; In the scanning step, the ink ejection unit is controlled so that the maximum amount of ink droplets that land per predetermined area decreases as the inclination angle of the inclined surface increases. Painting method.

28. A coating method for coating an object having an inclined surface inclined relative to a horizontal plane by ejecting ink onto the inclined surface using an inkjet recording device equipped with an ink ejection unit having a nozzle for ejecting ink, comprising: a scanning step of ejecting ink from the nozzles of the ink ejection unit onto the inclined surface while moving the ink ejection unit and the inclined surface relatively in a predetermined scanning direction; in the scanning step, the ink ejection unit is controlled so that the amount of ink droplets that land on the inclined surface per predetermined area in one scanning step is equal to or less than a maximum droplet amount determined based on the inclination angle of the inclined surface from a horizontal plane; In the scanning step, when the inclination angle of the inclined surface is equal to or greater than a predetermined reference angle, the ink ejection position of the ink ejection unit is controlled so that ink droplets that have landed on the inclined surface do not coalesce. Painting method.

29. a functional liquid applying step of applying a functional liquid to the inclined surface, the functional liquid reacting with the ink ejected from the nozzles of the ink ejection unit to thicken the ink, In the scanning step, ink is ejected from the nozzles onto the inclined surface to which the functional liquid has been applied. The coating method according to any one of claims 26 to 28.

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