Printing apparatus and control method therefor

Abstract

To provide a printing apparatus for performing printing on an outer peripheral surface of a printing medium having a columnar, truncated conical, or conical outer shape, the printing apparatus being capable of securing print quality of the body to be printed even when printing a plurality of ink layers on the outer peripheral surface of the body to be printed while rotating the body to be printed.SOLUTION: A control unit of a printing apparatus executes any one of the following controls: motor rotation speed control that calculates the number of ink layers L1, L2 printed on the outer peripheral surface of the printing medium 2 during printing on the printing medium 2, and controls the rotation speed of the motor based on the number of ink layers L1, L2; ink ejection speed control that controls the ink ejection speed from the nozzle by the ejection energy generating element based on the number of ink layers L1, L2; and ink ejection timing control that controls the timing of ink ejection from the nozzles by the ejection energy generating elements based on the number of ink layers L1, L2.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a printing apparatus for printing on the outer peripheral surface of a printing medium having a cylindrical, truncated conical or conical outer shape, and also to a method for controlling the printing apparatus. [Background technology]

[0002] Conventionally, there has been known a printing device for printing using ultraviolet-curable ink on the outer peripheral surface of a printing medium having a cylindrical, truncated cone, or conical outer shape (see, for example, Patent Document 1). The printing device described in Patent Document 1 includes an inkjet head that ejects ink toward the outer peripheral surface of the printing medium, an ultraviolet irradiation device that cures the ink ejected onto the outer peripheral surface of the printing medium, a stage having a table on which the ultraviolet irradiation device is placed, a carriage drive mechanism that moves a carriage on which the inkjet head is mounted in the main scanning direction, a stage drive mechanism that moves the stage in the sub-scanning direction, and a table lifting mechanism that raises and lowers the table.

[0003] In the printing device described in Patent Document 1, the ultraviolet irradiation device is equipped with a rotation mechanism that holds the print medium and rotates the print medium around its axis. The rotation mechanism includes a first rotating unit that holds one end of the print medium, a second rotating unit that holds the other end of the print medium, a motor for rotating the print medium, and a power transmission mechanism that connects the first rotating unit to the motor. In the printing device described in Patent Document 1, while the print medium is rotated by the rotation mechanism, ink is ejected from an inkjet head that is stopped in a fixed position to print on the outer peripheral surface of the print medium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-88834 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have been studying printing multiple ink layers on the outer peripheral surface of a substrate using the printing device described in Patent Document 1. According to the studies of the present inventors, it has become clear that if multiple ink layers are printed on the outer peripheral surface of a substrate while the substrate is being rotated using the printing device described in Patent Document 1, there is a risk that the printing accuracy of the substrate may decrease.

[0006] Therefore, an object of the present invention is to provide a printing device for printing on the outer peripheral surface of a printing substrate having a cylindrical, truncated conical, or conical outer shape, which can ensure the print quality of the printing substrate even when printing multiple ink layers on the outer peripheral surface of the printing substrate while rotating the printing substrate.Another object of the present invention is to provide a printing device control method for printing on the outer peripheral surface of a printing substrate having a cylindrical, truncated conical, or conical outer shape, which can ensure the print quality of the printing substrate even when printing multiple ink layers on the outer peripheral surface of the printing substrate while rotating the printing substrate. [Means for solving the problem]

[0007] In order to solve the above problems, the inventors of the present application conducted various studies and found that when printing multiple ink layers on the outer peripheral surface of a substrate while the substrate is rotated, the outer diameter of the substrate including the ink layers varies depending on the number of ink layers already printed on the outer peripheral surface of the substrate, and the circumferential speed (speed in the circumferential direction of the substrate) of the portion where ink ejected from the inkjet head lands varies. Therefore, when printing multiple ink layers on the outer peripheral surface of a substrate while the substrate is rotated, the landing position of the ink may be shifted in the circumferential direction of the substrate depending on the number of ink layers already printed on the outer peripheral surface of the substrate.

[0008] Furthermore, as a result of various studies, the inventors of the present application have come to the knowledge that, since the outer diameter of the print substrate, including the ink layers, varies depending on the number of printed ink layers printed on the outer peripheral surface of the print substrate, and this varies the distance between the area where the ink ejected from the inkjet head lands and the ink ejection surface of the inkjet head, when printing multiple ink layers on top of each other on the outer peripheral surface of the print substrate while rotating the print substrate, the ink landing position in the circumferential direction of the print substrate may be shifted depending on the number of printed ink layers printed on the outer peripheral surface of the print substrate.The inventors have also come to the knowledge that this shift in the ink landing position may result in a decrease in printing accuracy on the print substrate.

[0009] The printing device of the present invention is based on this new finding, and is a printing device for printing by overlapping a plurality of ink layers on the outer peripheral surface of a printing medium having a cylindrical, truncated conical or conical outer shape, and is provided with a rotation mechanism that holds the printing medium and rotates the printing medium around its axis as the center of rotation, an inkjet head that is disposed above the printing medium and ejects ink toward the outer peripheral surface of the printing medium, and a control unit that controls the printing device, wherein the inkjet head is formed with a plurality of nozzles that eject ink, and the inkjet head is provided with a plurality of ejection energy generating elements for ejecting ink from each of the plurality of nozzles, and the rotation mechanism is provided with a drive source and and a power transmission mechanism for transmitting the power of the motor to the substrate, and the substrate is rotated when printing is performed on it, and the control unit calculates the number of ink layers printed on the outer peripheral surface of the substrate when printing is performed on it, and performs at least one of the following controls: motor rotation speed control, which calculates the number of ink layers printed on the outer peripheral surface of the substrate and controls the rotation speed of the motor based on the calculated number of ink layers; ink ejection speed control, which controls the ejection speed of ink from the nozzles by the ejection energy generating element based on the calculated number of ink layers; and ink ejection timing control, which controls the timing of ink ejection from the nozzles by the ejection energy generating element based on the calculated number of ink layers.

[0010] Furthermore, based on this new finding, a method for controlling a printing device of the present invention is a printing device for printing by overlapping a plurality of ink layers on the outer peripheral surface of a printing medium having a cylindrical, truncated conical or conical outer shape, the printing device comprising: a rotation mechanism for holding the printing medium and rotating the printing medium around the axis of the printing medium as the center of rotation; and an inkjet head disposed above the printing medium and ejecting ink toward the outer peripheral surface of the printing medium, the inkjet head having a plurality of nozzles for ejecting ink, the inkjet head having a plurality of ejection energy generating elements for ejecting ink from each of the plurality of nozzles; the rotation mechanism comprising a motor as a drive source; and a power transmission mechanism for transmitting the power of the ink jet head to the print medium, and a control method for rotating the print medium when printing on the print medium, the control method comprising the steps of: calculating the number of ink layers printed on the outer peripheral surface of the print medium when printing on the print medium; and executing at least one of the following controls: motor rotation speed control, which calculates the number of ink layers printed on the outer peripheral surface of the print medium and controls the rotation speed of the motor based on the calculated number of ink layers; ink ejection speed control, which controls the ink ejection speed from the nozzles by the ejection energy generating element based on the calculated number of ink layers; and ink ejection timing control, which controls the timing of ink ejection from the nozzles by the ejection energy generating element based on the calculated number of ink layers.

[0011] In the present invention, when printing on a substrate, at least one of the following control operations is performed: motor rotation speed control, which calculates the number of ink layers printed on the outer peripheral surface of the substrate and controls the motor rotation speed based on the calculated number of ink layers; ink ejection speed control, which controls the ink ejection speed from the nozzles by the ejection energy generating elements based on the calculated number of ink layers; and ink ejection timing control, which controls the ink ejection timing from the nozzles by the ejection energy generating elements based on the calculated number of ink layers. Therefore, in the present invention, it is possible to suppress deviations in the ink landing position in the circumferential direction of the substrate, regardless of the number of ink layers already printed on the outer peripheral surface of the substrate. Therefore, in the present invention, it is possible to ensure the print quality of the substrate, even when multiple ink layers are printed on top of each other on the outer peripheral surface of the substrate while the substrate is rotating.

[0012] In the present invention, it is preferable that the control unit executes all of the motor rotation speed control, ink ejection speed control, and ink ejection timing control, or executes two controls arbitrarily selected from the motor rotation speed control, ink ejection speed control, and ink ejection timing control. This configuration effectively suppresses deviations in the ink landing position in the circumferential direction of the print substrate, regardless of the number of ink layers already printed on the outer peripheral surface of the print substrate. Therefore, it is possible to improve the print quality of the print substrate, even when printing multiple ink layers on the outer peripheral surface of the print substrate while rotating the print substrate.

[0013] In the present invention, for example, the ejection energy generating element is a piezoelectric element, and the control unit controls the voltage applied to the piezoelectric element in ink ejection speed control. Also, in the present invention, for example, the rotation mechanism includes an encoder for detecting the rotation position and rotation speed of the motor or the print medium, and the control unit generates an ejection trigger signal for starting ink ejection from the nozzles based on the output signal of the encoder when printing on the print medium, and controls the ink ejection start time from the point in time when the ejection trigger signal is generated in ink ejection timing control.

[0014] In the present invention, the printing device preferably includes an ultraviolet irradiator that irradiates ultraviolet rays toward the outer peripheral surface of the substrate to which ink is adhered, the ink layer is made of ultraviolet-curable ink, multiple ink layers with different ultraviolet transmittances are superimposed on the outer peripheral surface of the substrate, the control unit stores the ultraviolet transmittance of each of the multiple ink layers in advance, and print data for printing on the substrate is input, and the control unit ejects ink from the inkjet head based on the ultraviolet transmittances of the ink layers stored in the control unit and the print data so that the ultraviolet transmittance of the ink layer located on the outer peripheral side of the substrate is higher than the ultraviolet transmittance of the ink layer located on the inner peripheral side of the substrate.

[0015] With this configuration, after printing the ink layer located on the outer periphery of the substrate, when the ultraviolet irradiator irradiates ultraviolet light toward the surface of this ink layer, it is possible for the ultraviolet light to reach the ink layer located on the inner periphery of the substrate. Therefore, even if the time for irradiating ultraviolet light toward the surface of this ink layer after printing the ink layer located on the inner periphery of the substrate is shortened, it is possible to ensure the cumulative amount of ultraviolet light irradiated onto this ink layer and cure this ink layer. As a result, it is possible to shorten the printing time of the substrate. [Effects of the Invention]

[0016] As described above, in the present invention, in a printing device for printing on the outer surface of a substrate having a cylindrical, truncated cone, or conical outer shape, it is possible to ensure the printing quality of the substrate, even when printing multiple ink layers on the outer surface of the substrate while rotating the substrate. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a front view illustrating a configuration of a printing apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram illustrating the configuration of the printing apparatus shown in FIG. [Figure 3] FIG. 2A is a bottom view of the inkjet head and carriage shown in FIG. 1, and FIG. 2B is a bottom view for explaining the configuration of the inkjet head shown in FIG. [Figure 4] FIG. 2 is a front view for explaining the configuration of the ultraviolet irradiation device shown in FIG. [Figure 5] FIG. 5 is a side view for explaining the configuration of the rotation mechanism shown in FIG. [Figure 6] FIG. 5 is a side view for explaining the configuration of the rotation mechanism shown in FIG. [Figure 7] 2 is a schematic diagram for explaining a cross section of a printing medium after printing by the printing device shown in FIG. 1. FIG. [Figure 8] 2 is a schematic diagram for explaining the vertical distance between the portion where ink ejected from the inkjet head shown in FIG. 1 lands and the ink ejection surface of the inkjet head. FIG. [Figure 9] 4 is a timing chart for explaining the timing of ejecting ink when printing on a print medium using the printing device shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] (Overall configuration of the printing device) Fig. 1 is a front view illustrating the configuration of a printing device 1 according to an embodiment of the present invention. Fig. 2 is a block diagram illustrating the configuration of the printing device 1 shown in Fig. 1. Fig. 3(A) is a bottom view of the inkjet head 3 and carriage 7 shown in Fig. 1, and Fig. 3(B) is a bottom view illustrating the configuration of the inkjet head 3 shown in Fig. 3(A).

[0020] The printing device 1 of this embodiment is a device for printing on the outer peripheral surface of a printing substrate 2 having a cylindrical, truncated conical, or conical outer shape, and is, for example, a commercial inkjet printer. The printing device 1 prints on the outer peripheral surface of the printing substrate 2 using ultraviolet-curable ink. The printing substrate 2 is formed, for example, in a cylindrical shape. That is, the printing substrate 2 is formed in a cylindrical, truncated conical, or conical cylindrical shape. The printing substrate 2 is also formed, for example, from resin. The printing device 1 is capable of printing on multiple types of printing substrates 2 with different outer diameters and lengths.

[0021] The printing device 1 is equipped with inkjet heads 3 (hereinafter referred to as "heads 3") that eject ultraviolet-curable ink toward the outer peripheral surface of the print medium 2. The printing device 1 of this embodiment is equipped with multiple heads 3. Specifically, the printing device 1 is equipped with four heads 3. The printing device 1 also includes an ultraviolet irradiation device 4 for curing the ink ejected onto the outer peripheral surface of the print medium 2, a stage 6 having a table 5 on which the ultraviolet irradiation device 4 is placed, a carriage 7 on which the multiple heads 3 are mounted, a Y-bar 8 that holds the carriage 7 so that it can move in the main scanning direction, and a main frame 9 that holds the stage 6 so that it can move up and down (vertical direction) and in a sub-scanning direction that is perpendicular to the main scanning direction.

[0022] The printing device 1 also includes a carriage drive mechanism 11 that moves the carriage 7 relative to the Y bar 8 in the main scanning direction, a stage drive mechanism 12 that moves the stage 6 relative to the main frame 9 in the sub-scanning direction, a table lifting mechanism 13 that raises and lowers the table 5, and a control unit 14 for controlling the printing device 1. The carriage drive mechanism 11 includes, for example, a motor 15 as a drive source and a power transmission mechanism such as a belt and pulleys that transmits the power of the motor 15 to the carriage 7. The stage drive mechanism 12 includes, for example, a motor as a drive source and a power transmission mechanism such as a belt and pulleys that transmits the power of the motor to the stage 6. The table lifting mechanism 13 includes, for example, a motor as a drive source and a power transmission mechanism such as a ball screw that transmits the power of the motor to the table 5.

[0023] In the following description, the sub-scanning direction (X direction in Fig. 1, etc.) is the front-to-rear direction, and the main scanning direction (Y direction in Fig. 1, etc.) is the left-to-right direction. In the following description, the X1 direction side in Fig. 5, etc., which is one side of the front-to-rear direction, is the "front" side, the X2 direction side in Fig. 5, etc., which is the opposite side, is the "rear" side, the Y1 direction side in Fig. 4, etc., which is one side of the left-to-right direction, is the "right" side, and the Y2 direction side in Fig. 2, etc., which is the opposite side, is the "left" side.

[0024] The upper surface of the table 5 is a plane perpendicular to the vertical direction. The ultraviolet irradiation device 4 placed on the table 5 is arranged below the head 3. The print medium 2 is held by the ultraviolet irradiation device 4 and arranged below the head 3. In other words, the head 3 is arranged above the print medium 2. The head 3 ejects ink downward. The ink ejected by the head 3 lands on the outer peripheral surface of the print medium 2 at the upper end of the print medium 2.

[0025] The head 3 is formed with a plurality of nozzles 3a that eject ink. Specifically, the large number of nozzles 3a are formed on the bottom surface of the head 3. The bottom surface of the head 3 serves as an ink ejection surface 3c on which the large number of nozzles 3a are formed. On the ink ejection surface 3c, a nozzle row 3b is formed from the large number of nozzles 3a that are arranged in the sub-scanning direction (front-back direction). On the ink ejection surface 3c, a plurality of nozzle rows 3b that are arranged in the main scanning direction (left-right direction) are formed. The head 3 is equipped with a plurality of piezoelectric elements (piezo elements) 16 that cause ink to be ejected from each of the plurality of nozzles 3a. In this embodiment, the piezoelectric elements 16 are ejection energy generating elements.

[0026] As shown in Figure 3(A), for example, three of the four heads 3 mounted on the carriage 7 are arranged at the same position in the front-to-rear direction and are aligned in the left-to-right direction. The remaining head 3 is arranged at a position offset from the other three heads 3 in the front-to-rear direction. Three of the four heads 3 eject color inks, and the remaining head 3 ejects white ink. The viscosity of the white ink is higher than the viscosity of the color inks.

[0027] A motor 15 and a plurality of piezoelectric elements 16 are electrically connected to the control unit 14. A PC (personal computer) 18 is also electrically connected to the control unit 14. The PC 18 generates print data for printing on the print substrate 2. When printing on the print substrate 2, the print data generated by the PC 18 is sent from the PC 18 to the control unit 14. In other words, when printing on the print substrate 2, the print data sent from the PC 18 is input to the control unit 14.

[0028] (Configuration of ultraviolet irradiation device) Fig. 4 is a front view for explaining the configuration of the ultraviolet irradiation device 4 shown in Fig. 1. Figs. 5 and 6 are side views for explaining the configuration of the rotation mechanism 21 shown in Fig. 4.

[0029] The ultraviolet irradiation device 4 includes a rotation mechanism 21 that holds the substrate 2 and rotates it around its axis, an ultraviolet irradiator 22 that irradiates ultraviolet rays toward the outer peripheral surface of the substrate 2 to which ink is attached, and a cover 23 that covers the rotation mechanism 21 and the ultraviolet irradiator 22 from above. The cover 23 has an opening 23a through which the upper end of the substrate 2 is positioned. The ultraviolet irradiation device 4 is placed on the table 5 so that the axis of the substrate 2 coincides with the front-to-rear direction when viewed from above. In other words, the axis of the substrate 2 coincides with the front-to-rear direction when viewed from above. The nozzle row 3b that ejects ink toward the substrate 2 during printing is positioned directly above the substrate 2.

[0030] The rotation mechanism 21 rotates the print substrate 2 when printing on the print substrate 2. In this embodiment, printing is performed on the print substrate 2 while the rotation mechanism 21 rotates the print substrate 2 with the carriage 7 stopped at a fixed position. When printing on the print substrate 2, the rotation mechanism 21 rotates the print substrate 2, for example, counterclockwise when viewed from the front. Also, in this embodiment, the length of the print substrate 2 (length in the axial direction) is longer than the width of the head 3 in the front-to-rear direction. Therefore, when printing on the print substrate 2, the table 5 is moved in stages in the front-to-rear direction (sub-scanning direction). The length of the print substrate 2 may be equal to the width of the head 3 in the front-to-rear direction, or may be shorter than the width of the head 3 in the front-to-rear direction.

[0031] The rotation mechanism 21 includes a motor 25 as a drive source and a power transmission mechanism 26 for transmitting the power of the motor 25 to the printing medium 2. The rotation mechanism 21 also includes a first rotating unit 27 that holds one end of the printing medium 2, a first holding unit 28 that rotatably holds the first rotating unit 27, a second rotating unit 29 that holds the other end of the printing medium 2, a second holding unit 30 that rotatably holds the second rotating unit 29, a rotating frame 31 to which the first holding unit 28 and the second holding unit 30 are attached, and an encoder 32 for detecting the rotational position and rotational speed of the printing medium 2. The motor 25 and the encoder 32 are electrically connected to the control unit 14. Note that the power transmission mechanism 26 and other components are not shown in FIG. 4.

[0032] The first rotating unit 27 and the second rotating unit 29 rotate together with the substrate 2. The first rotating unit 27 holds the rear end of the substrate 2, and the second rotating unit 29 holds the front end of the substrate 2. The power transmission mechanism 26 connects the first rotating unit 27 to the motor 25. The power transmission mechanism 26 includes a gear train 33. The gear train 33 includes a drive gear fixed to the output shaft of the motor 25 and a driven gear fixed to the first rotating unit 27. The encoder 32 is connected to the rear end of the first rotating unit 27. The second holding unit 30 is movable in the direction of the axis of the substrate 2. In this embodiment, the positions of the second rotating unit 29 and the second holding unit 30 in the direction of the axis of the substrate 2 are adjusted depending on the length of the substrate 2. The power transmission mechanism 26 may also be configured using pulleys, belts, etc.

[0033] The rotating frame 31 is rotatable relative to a lower frame 34 that constitutes the bottom surface of the ultraviolet irradiation device 4, with the left-right direction as the axis of rotation. The rotating frame 31 is also rotatable relative to the lower frame 34, with the rear end of the rotating frame 31 as the rotation center. In this embodiment, by rotating the rotating frame 31 relative to the lower frame 34, it is possible to adjust the inclination of the rotation mechanism 21 relative to the horizontal direction when viewed from the left-right direction. In other words, by rotating the rotating frame 31 relative to the lower frame 34, it is possible to adjust the inclination of the axis of the printing medium 2 relative to the horizontal direction.

[0034] In this embodiment, when printing on a printing substrate 2 having a cylindrical outer shape, the direction of the axis of the printing substrate 2 coincides with the front-to-rear direction (see FIG. 5). On the other hand, when printing on a printing substrate 2 having a truncated cone or conical outer shape, the direction of the axis of the printing substrate 2 is inclined with respect to the front-to-rear direction (see FIG. 6). In other words, the inclination of the rotation mechanism 21 is adjusted when printing on the outer peripheral surface of a printing substrate 2 having a truncated cone or conical outer shape. Specifically, the inclination of the rotation mechanism 21 is adjusted so that the top end of the printing substrate 2 is parallel to the front-to-rear direction.

[0035] The ultraviolet irradiator 22 includes an LED substrate on which numerous LED chips that emit ultraviolet light are mounted. The ultraviolet irradiator 22 is disposed to the left of the substrate 2. The ultraviolet irradiator 22 irradiates the substrate 2 with ultraviolet light from the left side immediately after ink has been ejected onto it. In this embodiment, the vertical position of the ultraviolet irradiator 22 is adjustable. The horizontal position of the ultraviolet irradiator 22 and the inclination of the ultraviolet irradiator 22 relative to the axis of the substrate 2 when viewed from the vertical direction are also adjustable. In this embodiment, when printing on a substrate 2 having a cylindrical outer shape, the ultraviolet irradiator 22 is installed so that the ultraviolet light emission surface of the ultraviolet irradiator 22 is parallel to the front-to-back direction. When printing on a substrate 2 having a truncated cone or conical outer shape, the inclination of the ultraviolet irradiator 22 is adjusted so that the ultraviolet light emission surface of the ultraviolet irradiator 22 is parallel to the left edge of the substrate 2.

[0036] (Printing device control method) Fig. 7 is a schematic diagram illustrating a cross section of the print medium 2 after printing by the printing device 1 shown in Fig. 1. Fig. 8 is a schematic diagram illustrating the vertical distance between the portion where ink ejected from the head 3 shown in Fig. 1 lands and the ink ejection surface 3c of the head 3. Fig. 9 is a timing chart illustrating the ink ejection timing when printing is performed on the print medium 2 by the printing device 1 shown in Fig. 1.

[0037] As described above, when printing is performed on the print substrate 2 by the printer 1, print data sent from the PC 18 is input to the control unit 14. The control unit 14 performs printing on the print substrate 2 based on the input print data. The printer 1 of this embodiment prints a plurality of ink layers L1, L2 on top of each other on the outer peripheral surface of the print substrate 2. The ink layers L1, L2 are made of ultraviolet-curable ink.

[0038] For simplicity of explanation, the following describes an example of a control method for the printing device 1 when two ink layers L1 and L2 are printed on the outer peripheral surface of the substrate 2 in this order from the inner periphery to the outer periphery of the substrate 2. However, three or more ink layers may be printed on the outer peripheral surface of the substrate 2. When the printing area of ​​an image or the like to be printed on the outer peripheral surface of the substrate 2 is large, multiple ink layers L1 and L2 are printed on the outer peripheral surface of the substrate 2. In this case, for example, the ink layer L1 is a so-called solid white lower layer made of white ink.

[0039] When printing on the print medium 2, the control unit 14 generates an ejection trigger signal for starting the ejection of ink from the nozzle 3a of the head 3 based on the output signal of the encoder 32 (see FIG. 9). Specifically, the control unit 14 generates the ejection trigger signal when the count number of encoder pulses reaches a predetermined value. The control unit 14 also transmits a drive signal to the piezoelectric element 16 for ejecting ink from the nozzle 3a based on the ejection trigger signal. Specifically, the control unit 14 transmits a drive signal to the piezoelectric element 16 for ejecting one dot of ink from the nozzle 3a based on the ejection trigger signal, thereby ejecting ink from the nozzle 3a.

[0040] As described above, in this embodiment, the carriage 7 is stopped at a fixed position, and the print substrate 2 is rotated while multiple ink layers L1, L2 are printed on the outer peripheral surface of the print substrate 2 in an overlapping manner. When two ink layers L1, L2 are printed on the outer peripheral surface of the print substrate 2 in an overlapping manner, the outer diameter of the print substrate 2, including the ink layers L1, L2, varies depending on the number of ink layers L1, L2 already printed on the outer peripheral surface of the print substrate 2. Furthermore, if the outer diameter of the print substrate 2, including the ink layers L1, L2, varies, when the print substrate 2 is rotated at a constant rotational speed, the circumferential speed (the speed in the circumferential direction of the print substrate 2) of the portion where the ink ejected from the head 3 lands will vary.

[0041] For example, as shown in Figure 8, if a portion of the outer surface of the substrate 2 where ink ejected from the head 3 lands when no ink layer is printed on the outer surface of the substrate 2 is designated as landing portion P1, and if only ink layer L1 is printed on the outer surface of the substrate 2 where ink ejected from the head 3 lands is designated as landing portion P2, the circumferential speed of landing portion P2 when the substrate 2 is rotated at a constant rotational speed will be faster than the circumferential speed of landing portion P1.

[0042] Furthermore, when two ink layers L1, L2 are printed on top of each other on the outer peripheral surface of the print substrate 2, the outer diameter of the print substrate 2 including the ink layers L1, L2 varies depending on the number of ink layers L1, L2 already printed on the outer peripheral surface of the print substrate 2, and therefore the distance between the landing portions P1, P2 and the ink ejection surface 3c of the head 3 varies. In other words, the distance D1 between the landing portion P1 and the ink ejection surface 3c is longer than the distance D2 between the landing portion P2 and the ink ejection surface 3c.

[0043] Therefore, when printing two ink layers L1 and L2 on top of each other on the outer peripheral surface of the substrate 2 while rotating the substrate 2, if the substrate 2 is rotated at a constant rotational speed, ink is ejected from the nozzle 3a at a constant speed, and the time from the generation of the ejection trigger signal to the ejection of ink from the nozzle 3a (i.e., the timing of ink ejection from the nozzle 3a) is kept the same, the ink landing position when printing ink layer L1 and the ink landing position when printing ink layer L2 will be shifted in the circumferential direction of the substrate 2.

[0044] In this embodiment, in order to suppress deviation in the ink landing position, when printing on the print substrate 2, the control unit 14 first calculates the number of ink layers L1, L2 printed on the outer peripheral surface of the print substrate 2. For example, the control unit 14 calculates the number of printed ink layers L1, L2 printed on the outer peripheral surface of the print substrate 2 based on at least one of the following data: the amount of rotation of the print substrate 2 calculated based on the detection result of the encoder 32, the print data input to the control unit 14, and the number of drive signals sent to the piezoelectric element 16 (i.e., the number of times the piezoelectric element 16 is driven (the number of times ink is ejected from the nozzle 3a)).

[0045] The control unit 14 also performs at least one of the following controls: motor rotation speed control, which controls the rotation speed of the motor 25 based on the calculated number of ink layers L1, L2 (i.e., in accordance with the number of ink layers L1, L2 overlapping on the outer peripheral surface of the print medium 2); ink ejection speed control, which controls the ink ejection speed from the nozzles 3a by the piezoelectric elements 16 based on the calculated number of ink layers L1, L2; and ink ejection timing control, which controls the ink ejection timing from the nozzles 3a by the piezoelectric elements 16 based on the calculated number of ink layers L1, L2. In this embodiment, the control unit 14 performs all of the motor rotation speed control, ink ejection speed control, and ink ejection timing control.

[0046] In controlling the motor rotation speed, the control unit 14 changes the rotation speed of the motor 25 when printing ink layer L1 and when printing ink layer L2. That is, in controlling the motor rotation speed, the control unit 14 changes the rotation speed of the motor 25 depending on which ink layer L1 or L2 is being printed. Specifically, the control unit 14 makes the rotation speed of the motor 25 when printing ink layer L2 slower than the rotation speed of the motor 25 when printing ink layer L1. That is, the control unit 14 makes the rotation speed of the print substrate 2 when printing ink layer L2 slower than the rotation speed of the print substrate 2 when printing ink layer L2.

[0047] In ink ejection speed control, the control unit 14 controls the voltage applied to the piezoelectric element 16, thereby controlling the ink ejection speed from the nozzle 3a by the piezoelectric element 16. Furthermore, in ink ejection speed control, the control unit 14 changes the ink ejection speed when printing the ink layer L1 and the ink ejection speed when printing the ink layer L2. That is, in ink ejection speed control, the control unit 14 changes the ink ejection speed depending on which ink layer L1 or L2 is being printed. Specifically, the control unit 14 makes the ink ejection speed when printing the ink layer L2 slower than the ink ejection speed when printing the ink layer L1.

[0048] In ink ejection timing control, the control unit 14 controls the timing of ink ejection from the nozzle 3a by controlling the ink ejection start time from the time the ejection trigger signal is generated. Also, in ink ejection timing control, the control unit 14 changes the ink ejection timing when printing the ink layer L1 and the ink ejection timing when printing the ink layer L2. That is, in ink ejection timing control, the control unit 14 changes the ink ejection timing depending on which ink layer L1 or L2 is being printed. Specifically, the control unit 14 delays the ink ejection timing when printing the ink layer L2 compared to the ink ejection timing when printing the ink layer L1.

[0049] As described above, for example, two ink layers L1 and L2 are printed on the outer peripheral surface of the print substrate 2. In this embodiment, the ultraviolet-curable ink constituting ink layer L1 has a different ultraviolet transmittance from the ultraviolet-curable ink constituting ink layer L2. That is, multiple ink layers L1 and L2 with different ultraviolet transmittances are stacked on top of each other on the outer peripheral surface of the print substrate 2. Specifically, the ultraviolet transmittance of the upper ink layer L2 (on the outer peripheral side) is higher than the ultraviolet transmittance of the lower ink layer L1 (on the inner peripheral side).

[0050] The control unit 14 stores in advance the ultraviolet transmittance of each of the ink layers L1 and L2. That is, the control unit 14 stores in advance the ultraviolet transmittance of the ink constituting the ink layer L1 and the ultraviolet transmittance of the ink constituting the ink layer L2. When printing on the substrate 2, the control unit 14 ejects ink from the head 3 based on the ultraviolet transmittances of the ink layers L1 and L2 stored in the control unit 14 and the print data input to the control unit 14 so that the ultraviolet transmittance of the ink layer L2 arranged on the outer periphery of the substrate 2 is higher than the ultraviolet transmittance of the ink layer L1 arranged on the inner periphery of the substrate 2.

[0051] When printing the ink layer L1, the control unit 14 moves the carriage 7 and the head 3 so that the nozzles 3a that eject the ink that makes up the ink layer L1 are positioned directly above the print substrate 2. When printing the ink layer L2, the control unit 14 moves the carriage 7 and the head 3 so that the nozzles 3a that eject the ink that makes up the ink layer L2 are positioned directly above the print substrate 2.

[0052] (Main effect of this form) As described above, in this embodiment, the control unit 14 calculates the number of ink layers L1, L2 printed on the outer peripheral surface of the print substrate 2 during printing on the print substrate 2, and controls the motor rotation speed, ink ejection speed, and ink ejection timing based on the calculation results of the number of ink layers L1, L2. Therefore, in this embodiment, it is possible to suppress deviations in the ink landing positions in the circumferential direction of the print substrate 2, regardless of the number of printed ink layers L1, L2 printed on the outer peripheral surface of the print substrate 2. Therefore, in this embodiment, it is possible to ensure the print quality of the print substrate 2 even when multiple ink layers L1, L2 are printed on top of each other on the outer peripheral surface of the print substrate 2 while the print substrate 2 is rotating.

[0053] In particular, in this embodiment, the control unit 14 executes all of the motor rotation speed control, ink ejection speed control, and ink ejection timing control during printing on the print substrate 2, making it possible to effectively suppress deviations in the ink landing position in the circumferential direction of the print substrate 2, regardless of the number of ink layers L1, L2 printed on the outer peripheral surface of the print substrate 2. Therefore, in this embodiment, it is possible to improve the print quality of the print substrate 2, even when printing multiple ink layers L1, L2 on top of each other on the outer peripheral surface of the print substrate 2 while rotating the print substrate 2.

[0054] In this embodiment, the control unit 14 prints on the substrate 2 by ejecting ink from the head 3 so that the UV transmittance of the ink layer L2, which is located on the outer periphery of the substrate 2, is higher than the UV transmittance of the ink layer L1, which is located on the inner periphery of the substrate 2, based on the UV transmittances of the ink layers L1 and L2 stored in the control unit 14 and the printing data input to the control unit 14. Therefore, in this embodiment, after printing the ink layer L2, when the UV irradiator 22 irradiates the surface of the ink layer L2 with UV light, the UV light can reach the ink layer L1, which is located on the inner periphery of the substrate 2. Therefore, in this embodiment, even if the UV irradiator 22 irradiates the surface of the ink layer L1 with UV light for a shorter period of time after printing the ink layer L1, which is located on the inner periphery of the substrate 2, the cumulative amount of UV light irradiated on the ink layer L1 can be ensured, thereby curing the ink layer L1. As a result, in this embodiment, the printing time for the substrate 2 can be shortened.

[0055] (Other embodiments) The above-described embodiment is one example of a preferred embodiment of the present invention, but the present invention is not limited to this embodiment and various modifications can be made without departing from the spirit of the present invention.

[0056] In the above-described embodiment, the control unit 14 may execute two controls arbitrarily selected from motor rotation speed control, ink ejection speed control, and ink ejection timing control when printing on the print substrate 2. Also, in the above-described embodiment, the control unit 14 may execute only one of motor rotation speed control, ink ejection speed control, and ink ejection timing control when printing on the print substrate 2. Even in these cases, it is possible to suppress deviations in the ink landing positions in the circumferential direction of the print substrate 2, regardless of the number of printed ink layers L1, L2 printed on the outer peripheral surface of the print substrate 2.

[0057] In the embodiment described above, the rotation mechanism 21 may be provided with an encoder for detecting the rotation position and rotation speed of the motor 25, instead of the encoder 32. In this case, the control unit 14 calculates the number of printed ink layers L1, L2 printed on the outer peripheral surface of the printing medium 2, for example, based on the amount of rotation of the motor 25 calculated based on the detection result of the encoder during printing on the printing medium 2.

[0058] In the above-described embodiment, the ultraviolet transmittance of the ink layer L2 may be lower than the ultraviolet transmittance of the ink layer L1, and the control unit 14 may perform printing on the substrate 2 by ejecting ink from the head 3 so that the ultraviolet transmittance of the ink layer L2 arranged on the outer periphery of the substrate 2 is lower than the ultraviolet transmittance of the ink layer L1 arranged on the inner periphery of the substrate 2. Furthermore, in the above-described embodiment, the ultraviolet transmittance of the ink layer L2 and the ultraviolet transmittance of the ink layer L1 may be equal.

[0059] In the above-described embodiment, if only printing on a substrate 2 having a fixed outer diameter is performed by the printing device 1, the vertical position of the ultraviolet irradiator 22 does not have to be adjustable. Also, in the above-described embodiment, if only printing on a substrate 2 having a cylindrical outer shape is performed by the printing device 1, the inclination of the rotation mechanism 21 relative to the horizontal when viewed from the left and right does not have to be adjustable, and the inclination of the ultraviolet irradiator 22 relative to the axis of the substrate 2 when viewed from the top and bottom does not have to be adjustable.

[0060] In the above-described embodiment, the ultraviolet irradiation device 4 may be placed on the table 5 so that the direction of the axis of the print medium 2 when viewed from the top-bottom direction coincides with the left-right direction. Also, in the above-described embodiment, the ultraviolet irradiator 22 may be disposed below the print medium 2. Furthermore, in the above-described embodiment, the printing apparatus 1 may be provided with a Y-bar drive mechanism that moves the Y-bar 8 in the sub-scanning direction instead of the stage drive mechanism 12. Also, in the above-described embodiment, the ejection energy generating element for ejecting ink from the nozzle 3a may be a heater (heat generating element). Also, in the above-described embodiment, the printing apparatus 1 may have only one head 3. [Explanation of symbols]

[0061] 1 Printing device 2 Printing material 3 heads (inkjet heads) 3a nozzle 14 Control Unit 16 Piezoelectric element (ejection energy generating element) 21 Rotation mechanism 22 Ultraviolet irradiator 25 motor 26 Power transmission mechanism 32 Encoder L1, L2 ink layers

Claims

1. A printing device for printing by overlapping a plurality of ink layers on the outer peripheral surface of a printing object having a cylindrical, truncated conical or conical outer shape, a rotation mechanism that holds the medium to be printed and rotates the medium around an axis of the medium, an inkjet head that is disposed above the medium to be printed and ejects ink toward the outer peripheral surface of the medium, and a control unit that controls the printing device; The inkjet head is formed with a plurality of nozzles for ejecting ink, the inkjet head includes a plurality of ejection energy generating elements for ejecting ink from each of the plurality of nozzles; the rotation mechanism includes a motor as a drive source and a power transmission mechanism for transmitting power of the motor to the printing medium, and rotates the printing medium when printing is performed on the printing medium; The control unit calculates the number of ink layers printed on the outer peripheral surface of the substrate when printing on the substrate, and performs at least one of the following controls: motor rotation speed control, which controls the rotation speed of the motor based on the calculated number of ink layers; ink ejection speed control, which controls the ink ejection speed from the nozzle by the ejection energy generating element based on the calculated number of ink layers; and ink ejection timing control, which controls the timing of ink ejection from the nozzle by the ejection energy generating element based on the calculated number of ink layers.

2. 2. The printing device according to claim 1, wherein the control unit executes all of the motor rotation speed control, the ink ejection speed control, and the ink ejection timing control, or executes two controls arbitrarily selected from the motor rotation speed control, the ink ejection speed control, and the ink ejection timing control.

3. the ejection energy generating element is a piezoelectric element, 3. The printing apparatus according to claim 1, wherein the control unit controls the voltage applied to the piezoelectric element in the ink ejection speed control.

4. the rotation mechanism includes an encoder for detecting the rotation position and rotation speed of the motor or the printing medium; The printing device according to claim 1 or 2, characterized in that, when printing on the printing medium, the control unit generates an ejection trigger signal for starting ink ejection from the nozzle based on the output signal of the encoder, and in the ink ejection timing control, controls the ink ejection start time from the point in time when the ejection trigger signal is generated.

5. an ultraviolet irradiator that irradiates ultraviolet rays toward the outer peripheral surface of the printing medium on which ink is attached; the ink layer is made of ultraviolet curable ink, On the outer peripheral surface of the printing medium, a plurality of ink layers each having a different ultraviolet transmittance are superimposed, The control unit stores in advance the ultraviolet transmittance of each of the plurality of ink layers, and receives print data for printing on the print medium, 3. The printing device according to claim 1, wherein the control unit ejects ink from the inkjet head so that the ultraviolet transmittance of the ink layer arranged on the outer periphery of the substrate is higher than the ultraviolet transmittance of the ink layer arranged on the inner periphery of the substrate, based on the ultraviolet transmittance of the ink layer stored in the control unit and the printing data.

6. A printing device for printing by overlapping a plurality of ink layers on the outer peripheral surface of a printing medium having a cylindrical, truncated conical or conical outer shape, the printing device comprising: a rotation mechanism that holds the printing medium and rotates the printing medium around the axis of the printing medium as the center of rotation; and an inkjet head that is disposed above the printing medium and ejects ink toward the outer peripheral surface of the printing medium, the inkjet head having a plurality of nozzles that eject ink and a plurality of ejection energy generating elements for ejecting ink from each of the plurality of nozzles, the rotation mechanism comprising a motor as a drive source and a power transmission mechanism that transmits the power of the motor to the printing medium, and a control method for a printing device that rotates the printing medium when printing on the printing medium, the method comprising: A control method for a printing device, characterized by performing at least one of the following controls: motor rotation speed control, which calculates the number of ink layers printed on the outer peripheral surface of the print medium during printing, and controls the rotation speed of the motor based on the calculated number of ink layers; ink ejection speed control, which controls the ink ejection speed from the nozzle by the ejection energy generating element based on the calculated number of ink layers; and ink ejection timing control, which controls the timing of ink ejection from the nozzle by the ejection energy generating element based on the calculated number of ink layers.

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