Ink jet image forming device

Abstract

To provide an ink jet image forming device capable of performing high-quality printing on an object of a three-dimensional shape to be drawn.SOLUTION: An image forming device 100 comprises: an ink discharge unit 1 that discharges ink drops toward an object 7 to be drawn; a drive unit 3 that moves the ink discharge unit 1 relative to the object 7 to be drawn; and a control unit 5 that sets the relative moving speed of the ink discharge unit 1 by the drive unit 3 so as to set the landing angle of the ink drops with respect to the slope of the object 7 to be drawn equal to or higher than a prescribed angle at the target landing position of the ink drops on the object 7 to be drawn on the basis of three-dimensional shape data of the object 7 to be drawn.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to inkjet imaging devices. [Background technology]

[0002] 2. Description of the Related Art There is known an inkjet type image forming apparatus that forms an image on a target by ejecting ink droplets from nozzles of an inkjet head (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-35025 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, with the widespread use of such inkjet image forming devices, the applications of such devices have expanded from flat printing to three-dimensional printing, which involves printing on uneven materials. This involves printing on the surfaces of solid objects having various three-dimensional shapes.

[0005] When printing three-dimensional shapes using an inkjet image forming device, the landing position of the ink droplets is prone to misalignment, and the ink droplets have difficulty landing on inclined surfaces that are close to vertical on the three-dimensional object (i.e., inclined surfaces that are close to perpendicular to the stage), resulting in poor image quality such as unpainted areas and streaks in the image formed on the object.

[0006] Patent Document 1 describes a technique for changing the ejection timing (frequency) according to the inclination angle of the inclined surface when ejecting ink onto a three-dimensional object. However, the conventional technique described in Patent Document 1 can adjust the density of the image formed on the object, but cannot land ink droplets on places on the object where it is difficult to land ink droplets.

[0007] The present invention has been made in consideration of the above problems, and has an object to provide an ink-jet type image forming apparatus capable of performing high-quality printing on a drawing target having a three-dimensional shape. [Means for solving the problem]

[0008] The main object of the present invention to solve the above-mentioned problems is to An inkjet image forming apparatus for forming an image on a drawing target having a three-dimensional shape, an ink ejection unit that ejects ink droplets toward the drawing object; a drive unit that moves the ink ejection unit relative to the drawing object; a control unit that sets a relative movement speed of the ink ejection unit caused by the drive unit based on three-dimensional shape data of the drawing object so that an impact angle of the ink droplet with respect to an inclined surface of the drawing object is equal to or greater than a predetermined angle at a target impact position of the ink droplet on the drawing object; The image forming apparatus includes: Effect of the Invention

[0009] The image forming apparatus according to the present invention is capable of performing high-quality printing on an object having a three-dimensional shape. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] A diagram showing the ink ejection section (i.e., the print head section) viewed obliquely from below. [Diagram 3] FIG. 1 is a schematic diagram illustrating a configuration of a control system of an image forming apparatus according to an embodiment of the present invention. [Figure 4] FIG. 1 is a functional block diagram of an image forming apparatus according to an embodiment of the present invention. [Diagram 5] A diagram for explaining a method for calculating the landing angle of an ink droplet with respect to the inclined surface of the drawing object (the inclined surface on the front side of the convex portion). [Figure 6]A diagram for explaining a method for calculating the landing angle of an ink droplet with respect to the inclined surface of an object (the inclined surface on the rear side of a convex portion) [Figure 7] The results of an experiment verifying the adhesion state of ink droplets to the target landing position on the drawing object, depending on the landing angle of the ink droplets. [Figure 8] A table summarizing the threshold ink droplet landing angle when the ink droplet adheres well to the target landing position on the drawing object (the inclined surface on the front side of the convex part). [Figure 9A] A table showing the estimated landing angles of ink droplets when the inclination angle of the inclined surface of the drawing object at the target landing position and the relative movement speed of the drive unit are different. [Figure 9B] A table summarizing the evaluation results of the adhesion state of ink droplets when the inclination angle of the inclined surface of the drawing object at the target landing position and the relative movement speed of the drive unit are different. [Figure 10] A graph plotting the evaluation results of the tables in FIG. 9A and FIG. 9B. [Figure 11] A table summarizing the threshold ink droplet landing angle when the ink droplet adheres well to the target landing position on the drawing object (the inclined rear surface of the convex part). [Figure 12A] A table showing the estimated landing angles of ink droplets when the inclination angle of the inclined surface of the drawing object at the target landing position and the relative movement speed of the drive unit are different. [Figure 12B] A table summarizing the evaluation results of the adhesion state of ink droplets when the inclination angle of the inclined surface of the drawing object at the target landing position and the relative movement speed of the drive unit are different. [Figure 13] A graph plotting the evaluation results in the tables of FIGS. 12A and 12B. [Figure 14A] FIG. 13 is a diagram showing a preferred setting mode for the relative movement speed of the ink ejection unit. [Figure 14B] FIG. 13 is a diagram showing a preferred setting mode for the relative movement speed of the ink ejection unit. [Figure 15] FIG. 13 is a diagram showing a preferred control mode of the control unit for appropriately controlling the relative movement speed of the ink ejection unit. [Figure 16]FIG. 1 is a flowchart showing an example of an operation of an image forming apparatus. [Figure 17] FIG. 11 is a diagram showing a control mode of an ink ejection unit and a drive unit by a control unit according to a first modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functions are designated by the same reference numerals, and redundant description will be omitted.

[0012] <Overall configuration of image forming apparatus> First, a configuration of an inkjet type image forming apparatus 100 (hereinafter, simply referred to as "image forming apparatus 100") according to one embodiment of the present invention will be described with reference to Figures 1 to 4. Note that this image forming apparatus 100 is an image forming apparatus that performs printing on a drawing target having a three-dimensional shape.

[0013] The target object on which the image is formed by the image forming apparatus 100 may be any of a variety of objects, such as paper, fabric, or resin material, on whose surface the ink can be fixed.

[0014] FIG. 1 is a diagram showing the device configuration of an image forming apparatus 100. FIG. 2 is a diagram showing the ink ejection unit 1 (i.e., print head unit H) as viewed obliquely from below. FIG. 3 is a schematic diagram showing the configuration of a control system of the image forming apparatus 100. FIG. 4 is a functional block diagram of the image forming apparatus 100. Here, three mutually orthogonal axes (X-axis, Y-axis, Z-axis) are defined as shown in FIG. 1. The Z-axis direction corresponds to the vertically upward direction, and the X-axis and Y-axis directions correspond to horizontal directions perpendicular to the vertically upward direction.

[0015] The image forming apparatus 100 includes an ink ejection unit 1, a shape measurement unit 2, a drive unit 3, a control unit 5, and an external input / output unit 6 (see FIG. 3).

[0016] <Drive unit 3> The drive unit 3 moves the ink discharge unit 1 relatively to the drawing target 7. Specifically, the drive unit 3 has an X-direction drive unit 31 and a Y-direction drive unit 32.

[0017] In the image forming apparatus 100, a Y-direction driving unit 32 is built in a table 41, and a drawing object 7 is fixed on a turntable 341 attached to the Y-direction driving unit 32. That is, the turntable 341 serves as a stage on which the drawing object 7 is placed.

[0018] Here, an object having a convex portion on its surface is illustrated as an example of the drawing object 7. The method of fixing the drawing object 7 to the turntable 341 may be appropriately selected according to the shape of the object, but it may be possible to fix the drawing object 7 by clamping both ends of the object 7 like a vice, to hold down the non-printing portion with a spring presser, or, in the case where the contact surface of the drawing object 7 with the turntable 341 is relatively large as in this example, to attach the object with adhesive tape or the like.

[0019] Furthermore, image forming apparatus 100 is provided with a table 41 that is placed horizontally relative to the floor surface and two stands 42 that extend vertically. As shown in Fig. 1, one end of each of these two stands 42 is attached to table 41, and the other end supports X-direction drive unit 31. X-direction drive unit 31 holds print head unit H at its output portion and moves print head unit H linearly in the X direction.

[0020] In this way, the image forming apparatus 100 has drive units 3 for each direction (X direction, Y direction) including the X-direction drive unit 31 and the Y-direction drive unit 32, and by combining the operations of the drive units 3 for each of these directions, it becomes possible to move the ink ejection unit 1 and the shape measurement unit 2 relative to the object to be drawn 7.

[0021] The drive unit 3 may have a Z-direction drive unit that moves the print head unit H along the Z direction relative to the drawing object 7. The drive unit 3 may also have an R-direction drive unit that enables the print head unit H to rotate about the Z axis relative to the drawing object 7.

[0022] <Ink ejection section 1> In the print head section H, an ink ejection section 1 and a shape measuring section 2 are integrally disposed.

[0023] As shown in FIG. 2, the ink ejection section 1 has an ink ejection head section 11 and an ink storage section 12. The ink ejection head section 11 has a C ink ejection head section 111 that ejects C (cyan) ink, an M ink ejection head section 112 that ejects M (magenta) ink, a Y ink ejection head section 113 that ejects Y (yellow) ink, and a K ink ejection head section 114 that ejects K (black) ink. Furthermore, each of the color-specific ink ejection head sections 111, 112, 113, and 114 relating to these four colors (CMYK) has a plurality of C (cyan) ink ejection nozzles 111N, M (magenta) ink ejection nozzles 112N, Y (yellow) ink ejection nozzles 113N, and K (black) ink ejection nozzles 114N, respectively, and ejects ink of the corresponding color among the four colors (CMYK). Here, these nozzles are illustrated as being arranged in a row for each color.

[0024] On the other hand, the ink storage unit 12 is provided with a C ink storage unit 121, an M ink storage unit 122, a Y ink storage unit 123, and a K ink storage unit 124 (see FIG. 3). Although not shown in FIGS. 1 and 2, these colored ink storage units 121, 122, 123, and 124 are built into the ink storage unit 12. Each of the ink ejection nozzles 111N-114N receives ink of a corresponding color from each of the colored ink storage units 121-124 that store ink of that color, and selectively ejects the ink onto the drawing object 7. In this way, printing (coloring) is performed on the surface of the drawing object 7.

[0025] The types of ink are not limited to the above, and are appropriately combined depending on the color and properties of the ink required to color the surface of the drawing object 7. When performing color printing, it is sufficient to provide a number of different types of color-specific ink ejection heads according to the required colors and a number of color-specific ink storage tanks for storing each color ink. For example, a combination of one or more of the four colors C, M, Y, and K may be used, or a combination of R (red), G (green), and B (blue) may be used. In addition, inks containing mixed colors or glitter pigments may be used, and the types of inks prepared from these inks may be increased or decreased as necessary, or the order of arrangement may be changed. In addition, when performing monochromatic printing (when the ink is monochromatic), it is sufficient to have one or more ink ejection nozzles and ink storage tanks. In addition, special color inks such as white ink and metal ink, and functional inks used for industrial purposes may be used.

[0026] <Shape measurement section 2> The shape measuring unit 2 is, for example, composed of a known optical displacement sensor having a light-projecting unit 21 and a light-receiving unit 22. Laser light is emitted downward in the Z-axis direction from the light-projecting unit 21, and the light diffused and reflected from the surface of the object 7 is received by the light-receiving unit 22 equipped with a line sensor, lens, etc., and the distance in the Z-axis direction from the shape measuring unit 2 to the surface of the object 7 can be determined by a triangulation method.

[0027] The shape measuring unit 2 is disposed integrally with the ink ejection unit 1 in the print head unit H, and is controlled by the drive unit 3 so as to move relative to the object 7 to be drawn. The shape measuring unit 2 is controlled to move so as to scan within the XY plane (i.e., the X and Y directions) under the operation of the drive unit 3, for example, and measures the distance in the Z-axis direction at each point (X, Y). The shape measuring unit 2 then measures the distance in the Z-axis direction from the shape measuring unit 2 to the surface of the object 7 to be drawn at multiple points (X, Y) in the XY plane, thereby measuring the three-dimensional shape of the object 7 to be drawn.

[0028] Although an example has been described here in which the shape measuring unit 2 is configured as a reflective optical sensor, the shape measuring unit 2 is not limited to this and other optical sensors, contact sensors, ultrasonic sensors, etc. may also be used.

[0029] <External input / output section 6> The external input / output unit 6 is provided inside the main body as a part of the main body of the image forming apparatus 100 and / or separately outside the main body, and has a function as an interface with an operator of the image forming apparatus 100 (see FIG. 3). That is, the external input / output unit 6 has a display unit (output unit) such as a monitor and a lamp, and an input unit such as a keyboard, a teaching pendant, and an emergency stop button, and is used to input signals to start and stop printing, to display the contents of a trouble that occurs, to perform an emergency stop at that time, and to rewrite the contents of the memory 55. These signals are transmitted and received through an internal bus or the like that mutually connects the external input / output unit 6 with the CPU 54, the memory 55, and the controllers 511, 521, and 531, as shown in FIG. 3.

[0030] <Control unit 5> The control unit 5 has an ink ejection controller 511, an ink ejection driver 512, a shape measurement controller 521, a shape measurement driver 522, a drive controller 531, a drive driver 532, a CPU 54, a semiconductor memory 55 such as a ROM or a RAM, and an auxiliary storage unit 56 (see FIG. 3). The control unit 5 is provided, for example, inside the main body of the image forming apparatus 100 or separately outside the main body (not shown in FIG. 1).

[0031] The semiconductor memory 55 (hereinafter also simply referred to as "memory") and / or auxiliary storage unit 56 (e.g., a hard disk drive) stores software programs (hereinafter also simply referred to as "programs") that control the timing of ink ejection of each color from the ink ejection unit 1, the measurement operation of the shape measurement unit 2, and the drive control of the drive unit 3, as well as a program for creating three-dimensional shape data from distance information obtained by the shape measurement unit 2, a program for matching image data to this, and a program for planning a printing procedure based on these data. The semiconductor memory 55 also stores necessary data such as a geometric position correction table between each ink ejection nozzle and the shape measurement unit 2, a relative movement speed correction table, and an ink ejection timing correction table.

[0032] The CPU 54 executes a program that stores printing procedures, and performs sequential processing based on the data in the memory 55, thereby outputting control signals to the controllers 511, 521, and 531. The controllers 511, 521, and 531 process the respective control signals, and send signals to the drivers 512, 522, and 532 to actually drive the respective operating units, that is, the ink discharge unit 1, the shape measurement unit 2, and the drive unit 3. The drivers 512, 522, and 532 drive the respective operating units 1 to 3 in response to the control signals.

[0033] Furthermore, signals are sent from each operating section, namely the ink discharge section 1, the shape measurement section 2, and the drive section 3, to the controllers 511, 521, and 531 via the drivers 512, 522, and 532 as necessary. Based on these signals and the data in the memory 55, the CPU 54 feeds back new control signals to each controller, or stores them as data.

[0034] The control unit 5 performs the functions of an operation content determination unit 5A and a printing operation control unit 5B by executing the corresponding programs in the CPU 54. The operation content determination unit 5A determines the operation content of the ink discharge unit 1 and the operation content of the drive unit 3 based on the three-dimensional shape data acquired using the shape measurement unit 2, and the printing operation control unit 5B performs the printing operation by controlling the operation of the ink discharge unit 1 and the operation of the drive unit 3 in accordance with the operation content determined by the operation content determination unit 5A.

[0035] <Details of control by control unit 5> 5 and 6, a description will be given of a control mode performed by the control unit 5 according to this embodiment for causing ink droplets to land on the inclined surface of the drawing target 7. For ease of explanation, this embodiment uses, as the drawing target 7, an object having a hemispherical convex portion 71 formed on its surface.

[0036] <Method of deriving the landing angle of ink droplets> First, we will explain how the angle Δ between the flight direction of the ink droplet and the inclined surface of the drawing object 7 (convex portion 71) (hereinafter referred to as the "ink droplet landing angle Δ") changes depending on the relative movement speed Vs of the ink ejection section 1.

[0037] 5 and 6 are diagrams for explaining a method for calculating the landing angle Δ of an ink droplet. Fig. 5 shows a method for calculating the landing angle Δ when an ink droplet lands on the front-side inclined surface of a convex portion 71 (the inclined surface of the hemispherical inclined surface of the convex portion 71 that is on the front side as viewed from the position of the ink ejection portion 1 when ejecting ink; the same applies below). Fig. 6 shows a method for calculating the landing angle Δ when an ink droplet lands on the rear-side inclined surface of a convex portion 71 on the surface of an object 7 to be drawn (the inclined surface of the hemispherical inclined surface of the convex portion 71 that is on the rear side as viewed from the position of the ink ejection portion 1 when ejecting ink; the same applies below).

[0038] 5 and 6 show a state in which the ink discharge unit 1 moves from the plus X direction to the minus X direction as the X-direction drive unit 31 is driven. That is, here, drawing on the drawing target 7 is performed by discharging ink from the ink discharge unit 1 while the ink discharge unit 1 moves in the minus X direction. In Figs. 5 and 6, the inclined surface on the plus X direction side of the convex portion 71 corresponds to the "front side inclined surface" (i.e., the inclined surface on the front side as seen from the ink discharge unit 1), and the inclined surface on the minus X direction side of the convex portion 71 corresponds to the "rear side inclined surface" (i.e., the inclined surface on the rear side as seen from the ink discharge unit 1).

[0039] In recent image forming devices, the demand for high-speed printing has led to a configuration in which ink is discharged while the drawing target is being moved. In response to the same demand, the control unit 5 according to this embodiment also causes the ink discharge unit 1 to perform a discharge operation while moving the ink discharge unit 1 relative to the drawing target 7 by the drive unit 3.

[0040] Therefore, when viewed from the object to be drawn 7, the flight direction θ' (where θ' represents the inclination angle with respect to the vertical downward direction; the same applies below) of the ink droplets ejected from the ink ejection unit 1 is the direction of the resultant vector of the ejection velocity component Vd (i.e., the velocity component in the Z direction) of the ink droplets ejected from the ink ejection unit 1 and the relative movement velocity component Vs of the ink ejection unit 1 (i.e., the movement velocity of the print head unit H by the X-direction drive unit 31 and / or the movement velocity of the object to be drawn 7 by the Y-direction drive unit 32) (see vectors in Figures 5 and 6).

[0041] The landing angle Δ of the ink droplet with respect to the inclined surface of the drawing target 7 (the convex portion 71) is calculated from the flight direction θ' of the ink droplet and the inclination angle θ of the inclined surface of the convex portion 71 (where θ represents the inclination angle with respect to the vertical upward direction; the same applies below) (in Figs. 5 and 6, Px on the inclined surface of the convex portion 71 represents the landing position of the ink droplet). Specifically, as in Fig. 5, when the ink droplet is landed on the front side inclined surface of the convex portion 71, the landing angle Δ of the ink droplet is calculated by θ+θ'. On the other hand, as in Fig. 6, when the ink droplet is landed on the rear side inclined surface of the convex portion 71, the landing angle Δ of the ink droplet is calculated by θ-θ'. The inclination angle θ of the inclined surface of the convex portion 71 can be calculated based on, for example, the three-dimensional shape data of the drawing target 7 generated by the shape measuring unit 2 described above.

[0042] In this way, the landing angle Δ when the ink droplets ejected from the ink ejection unit 1 land on the inclined surface of the drawing object 7 is determined by the flight direction θ' of the ink droplets and the inclination angle θ of the inclined surface of the convex portion 71. In this case, the only parameter that can be substantially changed in order to adjust the landing angle Δ is the relative movement speed Vs of the ink ejection unit 1 caused by the drive unit 3.

[0043] From this viewpoint, the control unit 5 according to this embodiment, when performing a discharge operation from the ink discharge unit 1, appropriately controls the relative movement speed Vs of the ink discharge unit 1 so that the landing angle Δ of the ink droplets with respect to the inclined surface of the drawing target 7 is equal to or greater than a predetermined angle. That is, based on information on the inclination of the surface of the drawing target 7 contained in the three-dimensional shape data of the drawing target 7 (i.e., the measurement result of the shape measurement unit 2), the control unit 5 performs a discharge operation from the ink discharge unit 1 in a state in which the relative movement speed Vs of the ink discharge unit 1 is controlled so that the landing angle Δ of the ink droplets with respect to the inclined surface of the drawing target 7 (i.e., the angle formed by the flight direction of the ink droplets with respect to the inclined surface of the drawing target 7) is equal to or greater than a predetermined angle at the target landing position of the ink droplets on the drawing target 7.

[0044] In addition, here, the "target landing positions of ink droplets on the drawing object 7" refers to the target positions of drawing on the drawing object 7. The target landing positions of ink droplets on the drawing object 7 are set, for example, based on image data of the drawing object, and typically, a plurality of target landing positions are set on the drawing object 7.

[0045] <<About the verification experiment conducted when deriving the appropriate ink droplet landing angle>> However, according to verification experiments by the inventors of the present application, whether or not the ink droplets discharged from the ink discharge unit 1 can land and adhere to the target landing position on the drawing target 7 basically depends on the landing angle Δ of the ink droplets. That is, there is a threshold value for the landing angle Δ of the ink droplets with respect to the inclined surface of the drawing target 7, and this angle is "10°" according to the results of the verification experiments by the inventors of the present application.

[0046] Specifically, when the landing angle Δ of the ink droplets is 10° or more, the ink droplets discharged from the ink discharge unit 1 land on the target landing position on the drawing object 7 and adhere to that position, and when the landing angle Δ of the ink droplets is less than 10°, the ink droplets discharged from the ink discharge unit 1 cannot land on the target landing position on the drawing object 7, or even if they land, they do not adhere to the target landing position and spread to a position away from the target landing position. The threshold value of the landing angle Δ is approximately 10° in the specifications of a typical inkjet image forming device, although it varies somewhat depending on the type of ink, the size of the ink droplets, and the surface condition (e.g., adhesion) of the drawing object 7, and the adhesion state of the ink droplets to the target landing position on the drawing object 7 changes greatly depending on whether the landing angle Δ of the ink droplets with respect to the inclined surface of the drawing object 7 is 10° or more or less than 10°.

[0047] 7 to 13 show the results of an experiment verifying the adhesion state of ink droplets at the target landing positions on the drawing target 7, depending on the landing angle Δ of the ink droplets.

[0048] In this verification experiment, the adhesion state of ink droplets at the target landing position on the drawing target 7 was verified when the relative movement speed Vs of the ink discharge unit 1 was changed to various settings. Here, the drawing target 7 to be tested had a hemispherical convex portion 71 on its surface as shown in FIG. 7. The relative movement speed Vs of the ink discharge unit 1 used in the test was five patterns: "6 m / min", "12 m / min", "25.5 m / min", "51 m / min", and "70 m / min". In this verification experiment, attention was paid to the adhesion state of ink droplets on the front side inclined surface and rear side inclined surface of the convex portion 71.

[0049] Each camera image in Figure 7 is a camera image capturing the state of ink droplets adhering to the target landing position on the workpiece 7 under conditions where the relative movement speed Vs of the ink ejection section 1 is different. Each camera image in the upper column of Figure 7 is a camera image capturing the front side inclined surface of the convex portion 71, and each camera image in the lower column of Figure 7 is a camera image capturing the rear side inclined surface of the convex portion 71.

[0050] In the upper and lower diagrams of Fig. 7, the width of the areas where no ink droplets are attached in front of and behind the convex portion 71 are indicated by dotted lines. Note that the ends of the front-side inclined surface and the rear-side inclined surface of the hemispherical convex portion 71 become more perpendicular to the XY plane, so that the landing angle Δ of the ink droplets approaches zero degrees. Therefore, in each camera image of Fig. 7, there are areas where no ink droplets are attached (areas where white streaks are formed) at the ends of the convex portion 71.

[0051] 7, it can be seen that the slower the relative movement speed Vs of the ink ejection section 1 (i.e., the left camera image in the upper column of FIG. 7), the larger the ink-unattached area is formed on the front inclined surface of the convex section 71. This is presumably because, as described above, the slower the relative movement speed Vs of the ink ejection section 1, the smaller the landing angle Δ of the ink droplets on the front inclined surface of the convex section 71 becomes.

[0052] 8 is a table summarizing the ink droplet landing angle Δ that is the threshold when ink droplets are satisfactorily deposited at the target landing position on the drawing object 7 (the front-side inclined surface of the convex portion 71). In this verification experiment, the ink droplet landing angle Δ that is the threshold when ink droplets are satisfactorily deposited at the target landing position on the drawing object 7 was derived by identifying the upper end positions of the ink non-deposited areas on the front-side inclined surface and the back-side inclined surface of the convex portion 71 from each camera image (i.e., the maximum value of the inclination angle θ of the inclined surface of the convex portion 71 where ink is not deposited).

[0053] 9A and 9B are original data used to derive the table of FIG. 8, and are tables summarizing evaluation results of the adhesion state of ink droplets when the inclination angle θ of the inclined surface of the object 7 to be drawn at the target landing position and the relative movement speed Vs of the drive unit 3 are different. The table of FIG. 9A shows estimated values ​​of the landing angle Δ of ink droplets under each condition calculated from the inclination angle θ of the inclined surface of the object 7 to be drawn at the target landing position and the relative movement speed Vs of the drive unit 3. The table of FIG. 9B shows evaluation results under each condition, with "x" representing a state in which ink droplets did not adhere (land) at the target landing position on the object 7 to be drawn, and "◯" and "◎" representing a state in which ink droplets adhere (land) at the target landing position on the object 7 to be drawn. However, the evaluation item "○" indicates that the ink droplets were deposited in an elliptical shape rather than a perfect circle at the target landing position on the drawing object 7 (i.e., there was some wetting and spreading), and the evaluation item "◎" indicates that the ink droplets were deposited in a perfect circle at the target landing position on the drawing object 7. In other words, in terms of image quality after printing, the image formed under the conditions of the evaluation item "◎" is better than the image formed under the conditions of the evaluation item "○".

[0054] Figure 10 is a graph plotting the evaluation results in the tables of Figures 9A and 9B. The values ​​added to each plot in Figure 10 are the values ​​of the inclination angle at each landing position.

[0055] From Figures 8 to 10, it can be seen that when the ink droplet landing angle Δ is 10° or more, the adhesion condition of the ink droplets at the target landing position on the surface of the object to be drawn 7 is relatively good, but the adhesion condition changes when the ink droplet landing angle Δ reaches the boundary of 10°, and when the ink droplet landing angle Δ is less than 10°, the adhesion condition of the ink droplets at the target landing position on the surface of the object to be drawn 7 deteriorates significantly.

[0056] The same can be seen from the diagrams in the lower column of Fig. 7 and Figs. 11 to 13 regarding the inclined rear surface of the convex portion 71. That is, in the diagrams in the lower column of Fig. 7, the greater the relative movement speed Vs of the ink ejection portion 1 (i.e., the right camera image in the lower column of Fig. 7), the greater the ink-unattached area formed on the inclined rear surface of the convex portion 71. This is presumably because, as described above, on the inclined rear surface of the convex portion 71, the greater the relative movement speed Vs of the ink ejection portion 1, the smaller the landing angle Δ of the ink droplets becomes.

[0057] FIG. 11 is a table showing the ink droplet landing angle Δ that is the threshold value when the ink droplet is satisfactorily deposited on the target landing position on the drawing target 7 (the rear inclined surface of the convex portion 71).

[0058] 12A and 12B are original data used to derive the table of FIG. 11, and are tables summarizing evaluation results of the adhesion state of ink droplets when the inclination angle θ of the inclined surface of the object to be drawn 7 at the target landing position and the relative movement speed Vs in the drive unit 3 are different. The table of FIG. 12A shows estimated values ​​of the landing angle Δ of ink droplets under each condition calculated from the inclination angle θ of the inclined surface of the object to be drawn 7 at the target landing position and the relative movement speed Vs in the drive unit 3. The table of FIG. 12B shows evaluation results under each condition, with "x" representing a state in which ink droplets did not adhere (land) at the target landing position on the object to be drawn 7 and "o" representing a state in which ink droplets did adhere (land) at the target landing position on the object to be drawn 7.

[0059] Figure 13 is a graph plotting the evaluation results in the tables of Figures 12A and 12B. The values ​​added to each plot in Figure 13 are the values ​​of the inclination angle at each landing position.

[0060] From Figures 11 to 13, it can be seen that even on the rear inclined surface of the convex portion 71, when the ink droplet landing angle Δ is 10° or more, the adhesion condition of the ink droplets at the target landing position on the surface of the object to be drawn 7 is relatively good, but the adhesion condition changes when the ink droplet landing angle Δ reaches 10°, and when the ink droplet landing angle Δ is less than 10°, the adhesion condition of the ink droplets at the target landing position on the surface of the object to be drawn 7 deteriorates significantly.

[0061] <Specific control mode of the control unit 5> The control unit 5 in this embodiment is designed based on the above experimental results, and performs the ejection operation from the ink ejection unit 1 while controlling the relative movement speed Vs of the ink ejection unit 1 so that the landing angle Δ of the ink droplet with respect to the inclined surface of the drawing object 7 is 10° or more at the target landing position of the ink droplet on the drawing object 7 based on the three-dimensional shape data of the drawing object 7.

[0062] Specifically, the control unit 5 (operation content determination unit 5A) calculates the landing angle Δ of ink droplets at all target landing positions on the drawing target 7, assuming that the relative movement speed Vs by the driving unit 3 (for example, the driving unit 3 that drives in the Y direction) is set to a reference value (for example, 25.5 m / min) in advance in order to formulate an operation plan for the driving unit 3 and the ink discharge unit 1. Then, for example, for a target landing position (hereinafter referred to as a "target landing position requiring caution") where the landing angle Δ is less than 10° among all the target landing positions on the drawing target 7, the control unit 5 sets the operation content so that the relative movement speed Vs of the ink discharge unit 1 when performing a discharge operation from the ink discharge unit 1 to the target landing position requiring caution is changed (increased or decreased) from the reference value so that the landing angle Δ is 10° or more. That is, the control unit 5 changes the relative movement speed Vs of the ink discharge unit 1 according to the position of the target landing position on the surface of the drawing target 7 to be drawn.

[0063] Incidentally, the closer the ink droplet landing angle Δ is to 90°, the easier it is for the ink droplets to land on the inclined surface of the drawing object 7. However, if the relative movement speed Vs of the ink discharge unit 1 is set excessively large in order to bring the ink droplet landing angle Δ closer to 90°, other problems will arise, such as the ink droplets formed on the drawing object 7 becoming too wide, so the relative movement speed Vs of the ink discharge unit 1 must be appropriately controlled. In other words, it is preferable to set the relative movement speed Vs of the ink discharge unit 1 to be close to a reference value.

[0064] From this viewpoint, when the control unit 5 (operation content determination unit 5A) changes the setting of the relative movement speed Vs when ink is discharged to the target landing position requiring attention, it is preferable to change the setting of the relative movement speed Vs so that the landing angle Δ of the ink droplets is 10° or more and 20° or less. This makes it possible to prevent the relative movement speed Vs of the ink discharge unit 1 from being set excessively large with respect to the reference value. At this time, the control unit 5 may derive an appropriate relative movement speed Vs of the ink discharge unit 1 based on, for example, the inclination angle θ of the inclined surface of the drawing target 7 at the target landing position requiring attention and the ink discharge speed Vd of the ink discharged from the ink discharge unit 1 so that the landing angle Δ of the ink droplets becomes the target landing angle (for example, 15°). The method of deriving the appropriate relative movement speed Vs of the ink discharge unit 1 may be, for example, a method using a data table prepared in advance, or a method of calculating by an arithmetic formula using the following formula (1) or formula (2). Vs=Vd×tan(θ+θ'-θ)...Equation (1) (However, this applies when ink droplets are caused to land on the front inclined surface of the protrusion 71.) Vs=Vd×tan(θ-(θ-θ'))...Equation (2) (However, this applies when ink droplets are caused to land on the inclined surface on the rear side of the convex portion 71.)

[0065] Figures 14A and 14B are figures showing preferred setting modes for the relative movement speed Vs of the ink ejection portion 1, where Figure 14A shows a setting mode for causing ink droplets to land (adhere) on the front side inclined surface of the convex portion 71, and Figure 14B shows a setting mode for causing ink droplets to land (adhere) on the rear side inclined surface of the convex portion 71.

[0066] Here, it is preferable that the control unit 5 (operation content determination unit 5A) sets the relative movement speed Vs of the ink ejection unit 1 to be greater than a reference value when ejecting ink to a target landing position on the front inclined surface of the convex portion 71 (typically, the above-mentioned target landing position requiring caution) (see Figure 14A), and sets the relative movement speed Vs of the ink ejection unit 1 to be smaller than the reference value when ejecting ink to a target landing position on the rear inclined surface of the convex portion 71 (typically, the above-mentioned target landing position requiring caution) (see Figure 14B).

[0067] 5, when ink droplets are caused to land on the front-side inclined surface of the convex portion 71 on the surface of the drawing object 7, a larger landing angle Δ(=θ+θ') of the ink droplets can be ensured by increasing the relative movement speed Vs of the ink ejection unit 1, due to the relationship between the movement direction of the ink ejection unit 1 and the inclination direction of the inclined surface of the convex portion 71. Similarly, when ink droplets are caused to land on the rear-side inclined surface of the convex portion 71 on the surface of the drawing object 7, a larger landing angle Δ(=θ-θ') of the ink droplets can be ensured by decreasing the relative movement speed Vs of the ink ejection unit 1, as described with reference to FIG.

[0068] FIG. 15 is a diagram showing a preferred control mode of the control unit 5 for appropriately controlling the relative movement speed Vs of the ink discharge unit 1. As shown in FIG.

[0069] It is preferable that the control unit 5 (operation content determination unit 5A) formulates an operation plan for the drive unit 3 and the ink ejection unit 1 so as to form an image by moving the ink ejection unit 1 back and forth relative to the object to be drawn 7 in a multi-pass manner, as shown in FIG. 15, and to change the relative movement speed Vs of the ink ejection unit 1 for each pass and change the target impact position on the object to be drawn 7 to which ink is ejected in accordance with the relative movement speed Vs.

[0070] For example, when drawing one line on the drawing target 7, the control unit 5 (operation content determination unit 5A) performs a scanning pass with the relative movement speed Vs of the ink discharge unit 1 set to a reference value, and a scanning pass with the relative movement speed Vs of the ink discharge unit 1 set to a relative movement speed Vs greater than the reference value. The control unit 5 then formulates an operation plan for the drive unit 3 and the ink discharge unit 1 so that when ink droplets are discharged to a normal target landing position (here, this means a target landing position that does not correspond to a target landing position requiring attention. For example, the R1 area in FIG. 15), ink is discharged while scanning with the relative movement speed Vs of the ink discharge unit 1 set to the reference value, and when ink droplets are discharged to a target landing position requiring attention (for example, the R2 area in FIG. 15), ink is discharged while scanning with the relative movement speed Vs of the ink discharge unit 1 set to a value greater than the reference value.

[0071] This makes it possible to change the relative movement speed Vs of the ink ejection unit 1 midway through one pass, thereby preventing the spacing between ink droplets formed on the drawing object 7 from changing midway through the same line.

[0072] It is preferable that the control unit 5 (operation content determination unit 5A) corrects the ejection mode of the ink droplets ejected from the ink ejection unit 1 based on the relative movement speed Vs of the ink ejection unit 1.

[0073] As described above, when the relative movement speed Vs of the ink discharge unit 1 is changed, there is a risk that the interval of ink formed on the drawing target 7 (i.e., image resolution) will not satisfy the user's required specifications. From this viewpoint, when the control unit 5 (operation content determination unit 5A) makes the relative movement speed Vs of the ink discharge unit 1 greater than a reference value, for example, it is preferable that the control unit 5 (operation content determination unit 5A) increases the amount of ink droplets discharged from the ink discharge unit 1 per time or increases the discharge frequency of ink droplets discharged from the ink discharge unit 1. Such operation correction of the ink discharge unit 1 can be realized, for example, by preparing table data in advance so that the discharge mode of ink droplets discharged from the ink discharge unit 1 corresponds to the relative movement speed Vs of the ink discharge unit 1.

[0074] At this time, the control unit 5 may change the setting of the ejection frequency of ink ejected from the ink ejection unit 1 according to the inclination angle θ of the inclined surface of the object 7 so that the distribution of ink dots formed on the object 7 becomes uniform on each inclined surface of the object 7. Please refer to publicly known techniques such as Patent Document 1 for a method of changing the setting of the ejection frequency of ink ejected from the ink ejection unit 1 according to the inclination angle θ of the inclined surface of the object 7.

[0075] <Operation of Image Forming Apparatus 100> 16 is a diagram showing an example of a flowchart illustrating the operation of the image forming apparatus 100. For example, this operation is realized by the control unit 5 executing the operation in accordance with a computer program.

[0076] In step S1, the control unit 5 first checks whether or not three-dimensional shape data of the drawing target 7 exists in the memory 55. If three-dimensional shape data of the drawing target 7 exists (step S1: YES), the control unit 5 advances the process to step S3, and if three-dimensional shape data of the drawing target 7 does not exist (step S1: NO), the control unit 5 advances the process to step S2.

[0077] In step S2, the control unit 5 causes the shape measuring unit 2 (for example, laser measurement) to actually measure the outer shape of the drawing target object 7, and generates three-dimensional shape data.

[0078] At this time, the control unit 5 controls, for example, the X-direction drive unit 31 and the Y-direction drive unit 32 to move the shape measurement unit 2 provided in the print head unit H so as to scan a predetermined range (X-direction and Y-direction) of the drawing target of the drawing target 7. Simultaneously with this scanning operation, the control unit 5 causes the shape measurement unit 2 to measure the distance (i.e., the Z-direction distance) from the shape measurement unit 2 to the laser irradiation position on the surface of the drawing target 7. The detection value obtained by this distance measurement operation is stored in the memory 55. In this manner, the control unit 5 creates three-dimensional shape data of the drawing target 7.

[0079] Next, the control unit 5 sequentially executes the processes from steps S3 to S8 (for example, executes a loop process in which the variable i of the target landing position to be processed is sequentially incremented) in order to set an appropriate relative movement speed Vs of the ink ejection unit 1 when ejecting ink to each of the target landing positions of the ink droplets set on the drawing target 7. Note that the target landing positions of the ink droplets on the drawing target 7 are set based on, for example, image data of the drawing target, and typically, a plurality of target landing positions are set on the drawing target 7.

[0080] In step S3, the control unit 5 calculates the inclination angle θ at the target impact position on the surface of the object to be drawn 7 based on the Z-direction data of the three-dimensional shape data of the object to be drawn 7 (i.e., the distance from the shape measurement unit 2 to the laser irradiation position at each position on the surface of the object to be drawn 7).

[0081] In step S4, the control unit 5 virtually sets the relative movement speed Vs of the ink ejection unit 1 to a reference value, and calculates the flight direction θ' of the ink droplets (i.e., the angle of the flight vector with respect to the vertical downward direction) based on the relative movement speed Vs of the ink ejection unit 1 at this time and the ink ejection speed Vd ejected from the ink ejection unit 1.

[0082] In step S5, the control unit 5 calculates the angle of the flight direction of the ink droplets with respect to the inclined surface of the drawing object 7 at the target landing position (i.e., the landing angle Δ of the ink droplets). At this time, the control unit 5 calculates the landing angle Δ of the ink droplets with respect to the surface of the drawing object 7 at the target landing position (i.e., the angle of the flight direction of the ink droplets with respect to the surface of the drawing object 7) based on, for example, the flight direction θ' of the ink droplets calculated in step S4 and the inclination angle θ of the target landing position of the surface of the drawing object 7 calculated in step S3. For example, as described above with reference to Figs. 5 and 6, the control unit 5 calculates the landing angle Δ of the ink droplets by θ+θ' when ejecting ink to a target landing position that exists on the front side inclined surface of the convex portion 71, and by θ-θ' when ejecting ink to a target landing position that exists on the rear side inclined surface of the convex portion 71.

[0083] In step S6, the control unit 5 determines whether the landing angle Δ of the ink droplet with respect to the surface of the drawing object 7 at the target landing position is 10° or more. If the landing angle Δ of the ink droplet is 10° or more (step S6: YES), the control unit 5 advances the process to step S8, and if the landing angle Δ of the ink droplet is less than 10° (step S6: NO), the control unit 5 advances the process to step S7.

[0084] In step S7, the control unit 5 changes the relative movement speed Vs of the ink discharge unit 1 from the reference value, and returns to step S6 to recalculate the landing angle Δ of the ink droplet with respect to the surface of the drawing target 7 at the target landing position.

[0085] At this time, the control unit 5 increases the relative movement speed Vs of the ink discharge unit 1 from the reference value when ink is discharged to a target landing position on the front side inclined surface of the convex portion 71, for example, and decreases the relative movement speed Vs from the reference value when ink is discharged to a target landing position on the rear side inclined surface of the convex portion 71. At this time, the control unit 5 changes (increases or decreases) the relative movement speed Vs of the ink discharge unit 1 in increments of 5 m / min, for example, recalculates the landing angle Δ of the ink droplets, and repeats the process of changing the relative movement speed Vs of the ink discharge unit 1 until the landing angle Δ of the ink droplets becomes 10° or more. As a result, the setting of the relative movement speed Vs of the ink discharge unit 1 is typically changed so that the landing angle Δ of the ink droplets is 10° or more and 20° or less, and at this time, the relative movement speed Vs of the ink discharge unit 1 is changed to a speed close to the reference value.

[0086] In step S8, the control unit 5 determines the relative movement speed Vs of the drive unit 3 when discharging ink to the target landing position. That is, the control unit 5 determines the relative movement speed Vs of the ink discharge unit 1 to be the reference value or the value changed in step S7.

[0087] In this way, the control unit 5 executes the processes of steps S3 to S8 for each target landing position, sets the relative movement speed Vs of the ink discharge unit 1 for all target landing positions, and then proceeds to the next step S9.

[0088] In step S9, the control unit 5 determines whether or not the user has set the density correction to be performed. If the density correction has been set to be performed (step S9: YES), the control unit 5 proceeds to step S10. If the density correction has not been set to be performed (step S9: NO), the control unit 5 proceeds to step S11.

[0089] In step S10, the control unit 5 corrects the ejection interval of the ink droplets ejected from the ink ejection unit 1 and / or corrects the volume of the ink droplets.

[0090] At this time, the control unit 5 corrects the ejection mode of the ink droplets ejected from the ink ejection unit 1 based on the relative movement speed Vs of the ink ejection unit 1 caused by the drive unit 3. The ejection mode of the ink droplets to be corrected is, for example, the ejection amount of ink droplets ejected from the ink ejection unit 1 per time, or the ejection frequency of ink droplets ejected from the ink ejection unit 1. For example, when the control unit 5 makes the relative movement speed Vs of the ink ejection unit 1 greater than a reference value, the control unit 5 increases the ejection amount of ink droplets ejected from the ink ejection unit 1 per time, or increases the ejection frequency of ink droplets ejected from the ink ejection unit 1.

[0091] In step S11, the control unit 5 formulates an operation plan for the ink ejection unit 1 and the drive unit 3 so as to achieve the set conditions (relative movement speed Vs of the ink ejection unit 1, ink droplet ejection pattern), and starts printing on the object 7 to be drawn.

[0092] During printing, the control unit 5 moves the print head unit H a predetermined distance from left (-X) to right (+X) along the X-axis direction, and causes the ink discharge unit 1 to discharge ink at each position. At this time, the control unit 5, for example, when drawing one line along the X-axis direction, as described above in FIG. 15, forms an image by moving the ink discharge unit 1 back and forth (for example, back and forth along the X-axis direction) relative to the drawing target 7 using a multi-pass method. The control unit 5 then changes the relative movement speed Vs of the ink discharge unit 1 for each pass, and changes the target landing position on the drawing target 7 to which ink is discharged in accordance with the relative movement speed Vs.

[0093] When the control unit 5 has completed drawing one line, it moves the print head unit H a predetermined distance in the +Y direction to a position to draw the next line, and then moves it again a predetermined distance from left (-X) to right (+X) along the X-axis direction.

[0094] The control unit 5 repeats this operation to perform drawing on a predetermined range on the drawing target 7.

[0095] [effect] As described above, the image forming apparatus 100 according to the present embodiment has the following features: an ink ejection unit 1 that ejects ink droplets toward a drawing target 7 having a three-dimensional shape; A drive unit 3 that moves the ink discharge unit 1 relative to the drawing target 7; a control unit (5) that sets the relative movement speed of the ink discharge unit (1) caused by the drive unit (3) so that the landing angle of the ink droplets with respect to the inclined surface of the drawing object (7) is equal to or greater than a predetermined angle at the target landing position of the ink droplets on the drawing object (7) based on three-dimensional shape data of the drawing object (7); Equipped with.

[0096] Therefore, the image forming apparatus 100 according to this embodiment makes it possible to land ink even on parts of the drawing target 7 where the inclination of the inclined surface is large and where it is difficult for ink to land. This makes it possible to prevent the occurrence of unpainted areas in the drawing target 7 and improve the quality of the image formed on the drawing target 7.

[0097] Furthermore, the image forming apparatus 100 according to this embodiment is also useful in that it does not require an arm or the like for changing the holding angle of the drawing object 7 so that the ink can land more easily on the drawing object 7.

[0098] <Variation 1> FIG. 17 is a diagram showing a control mode of the ink ejection unit 1 and the drive unit 3 by the control unit 5 according to the first modification.

[0099] As described above, due to the relationship of the flight direction θ' of the ink droplets with respect to the inclined surface of the drawing target 7, a larger landing angle Δ of the ink droplets can usually be ensured when the ink droplets are landed at the target landing position on the front side inclined surface of the convex portion 71 on the surface of the drawing target 7 than when the ink droplets are landed at the target landing position on the rear side inclined surface of the convex portion 71 on the surface of the drawing target 7 (see Figs. 5 and 6). Therefore, when the ink droplets are landed on the front side inclined surface of the convex portion 71, it is possible to land the ink droplets at the target landing position more easily than when the ink droplets are landed on the rear side inclined surface of the convex portion 71.

[0100] From this viewpoint, the control unit 5 in the modified example controls the drive unit 3 to move the ink ejection unit 1 back and forth relative to the drawing object 7, and changes the target landing position of the object onto which ink is to be ejected between the forward and return paths so that ink is ejected when the target landing position is on the front inclined surface of the convex portion 71 as viewed from the ink ejection unit 1 during ink ejection.

[0101] For example, the control unit 5 causes the ink discharge unit 1 to perform a discharge operation for a target landing position in region R3 on the minus X-direction side of the convex portion 71 when the ink discharge unit 1 is moved in the plus X-direction relative to the drawing object 7, and causes the ink discharge unit 1 to perform a discharge operation for a target landing position in region R4 on the plus X-direction side of the convex portion 71 when the ink discharge unit 1 is moved in the minus X-direction relative to the drawing object 7.

[0102] This makes it possible to more reliably cause the ink droplets to land (or adhere) to the target landing positions on the drawing target 7.

[0103] <Variation 2> When ensuring that ink lands (adheres) on each inclined surface of the convex portion 71, it may be preferable not only to eject ink from the ink ejection unit 1 onto the inclined surfaces of the convex portion 71 on the positive and negative sides in the X-axis direction, but also to eject ink from the ink ejection unit 1 onto the inclined surfaces of the convex portion 71 on the positive and negative sides in the Y-axis direction.

[0104] From this perspective, the image forming apparatus 100 according to this modified example is capable of not only drawing on the object to be drawn 7 while moving the ink ejection unit 1 along the X-axis direction, but also drawing on the object to be drawn 7 while moving the ink ejection unit 1 along the Y-axis direction.

[0105] The drive unit 3 in this modified example is configured to be able to move the ink ejection unit 1 relative to the drawing object 7 along the mutually perpendicular X-axis and Y-axis directions, and to be able to change the setting of the relative movement speed Vs of the ink ejection unit 1.

[0106] Similarly, when relatively moving the ink discharge unit 1 along the Y-axis direction, the control unit 5 according to this modification sets an appropriate relative movement speed Vs of the ink discharge unit 1 so that the landing angle Δ of the ink droplets is 10° or more for each target landing position of the ink droplets set on the drawing target 7. Then, the control unit 5 performs drawing on the drawing target 7 while moving the ink discharge unit 1 along the Y-axis direction at the relative movement speed Vs.

[0107] This makes it possible to more reliably cause the ink droplets to land (or adhere) to the target landing positions on the drawing target 7.

[0108] <Variation 3> In the above embodiment, the control unit 5 actually measures the outer shape of the drawing target 7 using the shape measurement unit 2 (for example, laser measurement) to generate three-dimensional shape data. However, the three-dimensional shape data may be generated based on three-dimensional model data of the drawing target 7 previously acquired from outside.

[0109] At this time, when the control unit 5 has previously acquired three-dimensional model data of the drawing target 7 (for example, polygon data of the drawing target 7) from the outside, the control unit 5 may generate three-dimensional shape data from the three-dimensional model data. In this case, the process of actually measuring the outer shape of the drawing target 7 in step S2 may be unnecessary.

[0110] Although the specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Industrial Applicability]

[0111] The image forming apparatus according to the present invention is capable of performing high-quality printing on an object having a three-dimensional shape. [Explanation of symbols]

[0112] 100 Image forming device 1 Ink ejection section 2 Shape measurement section 3 Drive unit 5. Control section 6 External input / output section 7 Object to be drawn

Claims

1. An inkjet image forming apparatus for forming an image on a drawing target having a three-dimensional shape, an ink ejection unit that ejects ink droplets toward the drawing object; a drive unit that moves the ink ejection unit relative to the drawing object; a control unit that sets a relative movement speed of the ink ejection unit caused by the drive unit based on three-dimensional shape data of the drawing object so that an impact angle of the ink droplet with respect to an inclined surface of the drawing object is equal to or greater than a predetermined angle at a target impact position of the ink droplet on the drawing object; An image forming apparatus comprising:

2. The predetermined angle is 10 degrees. The image forming apparatus according to claim 1 .

3. the control unit calculates the landing angle of the ink droplet at the target landing position on the assumption that the relative movement speed of the ink ejection unit is set to a reference value based on three-dimensional shape data of the drawing object, and if the landing angle is less than 10°, changes the setting of the relative movement speed so that the landing angle is equal to or greater than 10° and equal to or less than 20°. The image forming apparatus according to claim 2 .

4. the control unit changes and sets the relative movement speed based on an inclination angle of an inclined surface of the drawing object at the target landing position, the inclination angle being determined from the three-dimensional shape data, and an ink ejection speed of the ink ejection unit, so that the landing angle of the ink droplet becomes a target landing angle. The image forming apparatus according to claim 1 .

5. The apparatus further includes a shape measuring unit for measuring a three-dimensional shape of the object to be drawn. The image forming apparatus according to claim 1 .

6. the target landing positions of the ink droplets are set at a plurality of locations on the drawing target, The control unit changes the relative movement speed when ejecting ink to the target landing position in accordance with a position of the target landing position on the drawing object. The image forming apparatus according to claim 1 .

7. the object to be drawn includes a convex portion, When the target landing position is on the front side inclined surface of the convex portion as viewed from the ink ejection portion during ink ejection, the control unit increases the relative movement speed when ejecting ink to the target landing position from a reference value, and when the target landing position is on the rear side inclined surface of the convex portion, decreases the relative movement speed when ejecting ink to the target landing position from a reference value. The image forming apparatus according to claim 6.

8. the object to be drawn includes a convex portion, The control unit controls the drive unit to reciprocate the ink ejection unit relative to the drawing object, and changes the target landing position of the object onto which ink is ejected between the forward path and the return path so that ink is ejected when the target landing position is on the front side inclined surface of the convex portion as viewed from the ink ejection unit during ink ejection. The image forming apparatus according to claim 6.

9. The control unit controls the drive unit to reciprocate the ink ejection unit relative to the drawing object in a multi-pass system, changes the relative movement speed of the ink ejection unit caused by the drive unit for each pass, and changes the target landing position of the object onto which ink is ejected in accordance with the relative movement speed. The image forming apparatus according to claim 6.

10. The drive unit is configured to be able to move the ink ejection unit relative to the drawing object along first and second directions that are perpendicular to each other, and to change the setting of the relative movement speed of the ink ejection unit. The image forming apparatus according to claim 1 .

11. The control unit corrects a discharge state of the ink droplets discharged from the ink discharge unit based on the relative movement speed of the ink discharge unit. The image forming apparatus according to claim 1 .

12. The ejection mode of the ink droplets includes an ejection amount of the ink droplets ejected from the ink ejection unit at one time. The image forming apparatus according to claim 11.

13. The ejection mode of the ink droplets includes an ejection frequency of the ink droplets ejected from the ink ejection unit. The image forming apparatus according to claim 11.

Images