Printer

Abstract

To provide a technique capable of avoiding resonance of a printing medium, without restricting the condition during use of a printer as much as possible.SOLUTION: A conveyance mechanism of a printer 1 has an inertia adjustment mechanism 70. The inertia adjustment mechanism 70 changes an inertia of a specific driven roller 12s. Thereby, a resonance frequency of a vibration system including the specific driven roller 12s can be changed. Accordingly, the resonance frequency can be deviated according to the condition during use of the printer 1. Thereby, the resonance of a printing medium can be avoided.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an inkjet printing apparatus. [Background technology]

[0002] A printing device that uses an inkjet printing system to print on the surface of a long, strip-shaped print medium while transporting the print medium in the longitudinal direction has been known. The printing device has a transport mechanism that includes multiple rollers that transport the print medium. The multiple rollers include a drive roller that is rotated by the power of a motor and a driven roller that rotates as the print medium moves.

[0003] A conventional printing device is described in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-37537 Summary of the Invention [Problem to be solved by the invention]

[0005] In this type of printing device, the print medium may resonate while being transported. Resonance of the print medium occurs when the natural frequency of the transport mechanism, which is determined by transport conditions such as the inertia of the driven roller, the material, thickness, and width of the print medium, and the length of the transport path, matches the frequency of the vibrations generated by the rotation of the roller. When the print medium resonates, the tension of the print medium fluctuates greatly. This can cause the ink ejection position on the print medium to shift, resulting in a decrease in print quality.

[0006] In order to avoid such resonance, conventionally, the printing device must be used under conditions in which the material, thickness, and width of the printing medium are such that resonance does not occur.

[0007] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a technique that can avoid resonance of a printing medium without restricting the conditions under which a printing device is used as much as possible. [Means for solving the problem]

[0008] In order to solve the above problem, the first invention of the present application is an inkjet printing device comprising a transport mechanism that transports a long strip of printing medium in a longitudinal direction, a head that ejects ink onto the printing medium transported by the transport mechanism, and a control unit that controls the transport mechanism and the head, wherein the transport mechanism has a drive roller that actively rotates by power output from a motor, a plurality of driven rollers that rotate passively as the printing medium moves, and an inertia adjustment mechanism that changes the inertia of a specific driven roller included in the plurality of driven rollers.

[0009] The second invention of the present application is a printing device of the first invention, wherein the control unit has table data indicating the usage conditions under which resonance occurs in the printing medium, and when the usage conditions of the printing device correspond to the usage conditions indicated in the table data, the inertia adjustment mechanism changes the inertia of the specific driven roller.

[0010] The third invention of the present application is a printing device of the first or second invention, wherein the transport mechanism has two of the drive rollers, and the specific driven roller is located between the two drive rollers in the transport path of the printing medium.

[0011] A fourth invention of the present application is a printing device according to any one of the first to third inventions, wherein the inertia adjustment mechanism has a flywheel and a switching mechanism that moves the flywheel between a retracted position away from the specific driven roller and a contact position in contact with the specific driven roller.

[0012] A fifth aspect of the present invention is the printing device of the fourth aspect, wherein the specific driven roller has an elastic roller that is elastically deformable, and the flywheel contacts the elastic roller at the contact position. [Effects of the Invention]

[0013] According to the first to fifth aspects of the present invention, the resonance frequency of the vibration system including the specific driven roller can be changed by changing the inertia of the specific driven roller. Therefore, the resonance frequency can be shifted depending on the conditions under which the printing device is used. This makes it possible to avoid resonance of the printing medium.

[0014] In particular, according to the second aspect of the present invention, when the printing device is used under conditions where resonance may occur, the inertia of the specific driven roller can be changed.

[0015] In particular, according to the third aspect of the present invention, it is possible to prevent the print medium from resonating between the two drive rollers.

[0016] In particular, according to the fourth aspect of the present invention, the inertia of the specific driven roller can be changed by bringing the flywheel into contact with the specific driven roller.

[0017] In particular, according to the fifth aspect of the present invention, the contact pressure of the flywheel with the specific driven roller can be changed gradually, thereby gradually changing the inertia of the specific driven roller. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 illustrates a configuration of a printing device. [Figure 2] FIG. 1 is a view of one head viewed from below. [Figure 3] FIG. 2 is a control block diagram of the printing apparatus. [Figure 4] 10 is a diagram showing the configuration of the vicinity of the end of the specific driven roller when the flywheel is in the retracted position. FIG. [Figure 5] FIG. 10 is a diagram showing the configuration of the vicinity of the end of the specific driven roller when the flywheel is in the contact position. [Figure 6] FIG. 10 is a diagram showing the structure of the specific driven roller and the inertia adjustment mechanism when the flywheel is in the retracted position. [Figure 7] FIG. 10 is a diagram showing the structure of the specific driven roller and the inertia adjustment mechanism when the flywheel is in the contact position. [Figure 8] FIG. 10 is a diagram illustrating an example of table data. [Figure 9] 10 is a flowchart showing a procedure for calculating a resonance occurrence condition. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] <1. Printer configuration> FIG. 1 is a diagram showing the configuration of a printing device 1 according to one embodiment of the present invention. This printing device 1 is a device that performs inkjet printing on a long, strip-shaped printing medium 9. The printing device 1 prints an image on the surface of the printing medium 9 by ejecting ink from multiple heads 21 toward the printing medium 9 while transporting the printing medium 9 in the longitudinal direction. The printing medium 9 may be printing paper or a resin film. As shown in FIG. 1, the printing device 1 includes a transport mechanism 10, a tension sensor 15, a printing unit 20, a drying unit 30, an inspection unit 40, and a control unit 50.

[0021] The transport mechanism 10 transports the print medium 9 along a predetermined transport path. The transport mechanism 10 of this embodiment has a plurality of drive rollers 11 and a plurality of driven rollers 12. The print medium 9 is stretched across the plurality of drive rollers 11 and the plurality of driven rollers 12 under tension.

[0022] The printing medium 9 is unwound from an unwinding roller (not shown) and transported along a transport path formed by multiple drive rollers 11 and multiple driven rollers 12. The multiple drive rollers 11 and multiple driven rollers 12 each rotate around an axis parallel to the width direction of the printing medium 9 (direction perpendicular and horizontal to the transport direction), thereby guiding the printing medium 9 downstream along the transport path. After transport, the printing medium 9 is collected by a take-up roller (not shown).

[0023] 1, the printing device 1 of this embodiment has a printing area A1, a drying area A2, and an inspection area A3 inside a housing 60. The transport mechanism 10 transports the print medium 9 inside the housing 60 from the printing area A1 through the drying area A2 to the inspection area A3.

[0024] Drive rollers 11 are arranged at multiple locations along the transport path. Each drive roller 11 has a cylindrical outer circumferential surface. The print medium 9 comes into contact with this outer circumferential surface of the drive roller 11. The drive roller 11 is connected to a motor 111. The drive roller 11 actively rotates due to the power output from the motor 111. This moves the print medium 9 downstream along the transport path.

[0025] In this embodiment, one of the multiple drive rollers 11 is arranged upstream of the printing unit 20 on the transport path. Hereinafter, this drive roller 11 will be referred to as the "first drive roller 11a." Another of the multiple drive rollers 11 is arranged downstream of the drying unit 30 on the transport path. Hereinafter, this drive roller 11 will be referred to as the "second drive roller 11b." No other drive roller 11 is arranged between the first drive roller 11a and the second drive roller 11b.

[0026] The driven rollers 12 are arranged at multiple locations on the transport path. The number of driven rollers 12 is greater than the number of drive rollers 11. A plurality of driven rollers 12 are arranged on the transport path between the first drive roller 11a and the second drive roller 11b. The driven rollers 12 have a cylindrical, hard outer surface. The printing medium 9 comes into contact with the outer surface of the driven roller 12. When the printing medium 9 is transported by the drive roller 11, the driven rollers 12 also rotate in accordance with the movement of the printing medium 9.

[0027] The tension sensor 15 is a sensor that detects the tension applied to the print medium 9. The tension sensor 15 is disposed on the conveyance path between the first drive roller 11a and the second drive roller 11b. The tension sensor 15 has a sensor roller 151 that contacts the print medium 9 and a load cell 152 connected to the sensor roller 151. The load cell 152 measures the load applied from the print medium 9 to the sensor roller 151. In this way, the tension sensor 15 detects the tension of the print medium 9. The tension sensor 15 then sends a detection signal indicating the tension of the print medium 9 to the control unit 50.

[0028] The printing unit 20 is a unit that ejects ink droplets (hereinafter referred to as "ink droplets") onto the print medium 9 transported by the transport mechanism 10. The printing unit 20 is provided in the printing area A1 inside the housing 60. In this embodiment, the printing unit 20 has four heads 21. The four heads 21 are arranged at intervals along the transport direction of the print medium 9. The print medium 9 is transported below the four heads 21 with the printing surface facing upward.

[0029] FIG. 2 is a view of one head 21 as viewed from below. In FIG. 2, the print medium 9 is indicated by an imaginary line (two-dot chain line). As shown enlarged in FIG. 2, the underside of the head 21 is provided with a plurality of nozzles 211 capable of ejecting ink droplets. In this embodiment, the plurality of nozzles 211 are arranged two-dimensionally in the transport direction and width direction on the underside of the head 21. The nozzles 211 are arranged with their positions shifted in the width direction. However, the plurality of nozzles 211 may also be arranged in a line along the width direction.

[0030] The four heads 21 eject ink droplets of different colors from multiple nozzles 211 toward the top surface of the print medium 9. For example, black, cyan, magenta, and yellow inks are ejected from the four heads 21, respectively. A multicolor image is formed on the surface of the print medium 9 by superimposing the monochromatic images formed by these ink colors.

[0031] The drying unit 30 is a unit that dries the ink on the print medium 9. The drying unit 30 is provided in the drying area A2 inside the housing 60. The drying unit 30 has multiple heaters 31. The heaters 31 blow heated hot air onto the print medium 9. This causes the solvent to evaporate from the ink on the print medium 9. As a result, the ink dries and becomes fixed on the print medium 9. However, the heaters 31 may also heat the ink by irradiating it with infrared rays, etc.

[0032] The inspection unit 40 is a unit that inspects the image printed on the print medium 9. The inspection unit 40 is provided in the inspection area A3 inside the housing 60. The inspection unit 40 has multiple cameras 41. The cameras 41 photograph the surface of the print medium 9 and transmit the obtained inspection images to the control unit 50. The control unit 50 inspects the quality of the image printed on the print medium 9 based on the inspection images received from the cameras 41.

[0033] The control unit 50 is an information processing device for controlling each unit within the printing device 1. Fig. 3 is a control block diagram of the printing device 1. As shown in Fig. 3, the control unit 50 is configured by a computer having a processor 501 such as a CPU, a memory 502 such as a RAM, and a storage unit 503 such as a hard disk drive. A computer program P for executing the printing process is stored in the storage unit 503.

[0034] 3, the control unit 50 is communicatively connected via wire or wirelessly to the above-mentioned multiple motors 111, tension sensor 15, four heads 21, multiple heaters 31, multiple cameras 41, and an air cylinder 722 (described later). The control unit 50 reads a computer program P from the storage unit 503 into the memory 502 and controls the above-mentioned components by operating the processor 501 in accordance with the computer program P. This allows the transport of the print medium 9 and the printing process to proceed.

[0035] <2. Structure to avoid resonance> In the printing device 1, the print medium 9 may resonate between the first drive roller 11a and the second drive roller 11b. Resonance of the print medium 9 occurs when the resonant frequency (natural frequency) of the transport mechanism 10, which is determined by transport conditions such as the inertia of the driven roller 12, the material of the print medium 9, the thickness and width of the print medium 9, and the length of the transport path, matches the frequency of vibrations generated by the rotation of the driven roller 12. When resonance occurs in the print medium 9, tension fluctuations in the print medium 9 increase. This can cause the ink ejection position on the print medium 9 to shift, resulting in reduced print quality.

[0036] Therefore, the transport mechanism 10 of this printing device 1 has an inertia adjustment mechanism 70 to avoid resonance of the print medium 9. The inertia adjustment mechanism 70 adjusts the inertia of one of the multiple driven rollers 12 arranged on the transport path between the first drive roller 11a and the second drive roller 11b. Hereinafter, the one driven roller 12 whose inertia is adjusted will be referred to as the "specific driven roller 12s."

[0037] 4 and 5 are diagrams showing the configuration near the end of the specific driven roller 12s. As shown in FIGS. 4 and 5, the specific driven roller 12s has an elastic roller 122. The elastic roller 122 is fixed to the end of the specific driven roller 12s. Therefore, when the specific driven roller 12s rotates, the elastic roller 122 also rotates. The elastic roller 122 has a cylindrical outer circumferential surface. The outer circumferential surface of the elastic roller 122 does not contact the print medium 9. The elastic roller 122 is made of elastically deformable rubber.

[0038] 6 and 7 are diagrams showing the structures of the specific driven roller 12s and the inertia adjustment mechanism 70. As shown in FIGS. 6 and 7, the inertia adjustment mechanism 70 has a flywheel 71 and a switching mechanism 72 that switches the position of the flywheel 71. The flywheel 71 is a disk-shaped rotating body. The flywheel 71 is supported rotatably around a rotation axis 710 that extends parallel to the rotation axis 120 of the specific driven roller 12s.

[0039] The flywheel 71 of this embodiment has a large diameter wheel 711 and a small diameter wheel 712. The outer diameter of the large diameter wheel 711 is larger than the outer diameter of the specific driven roller 12s. The outer diameter of the small diameter wheel 712 is smaller than the outer diameter of the large diameter wheel 711. The large diameter wheel 711 and the small diameter wheel 712 rotate together around the rotation axis 710.

[0040] The switching mechanism 72 has a lever 721 and an air cylinder 722. One end of the lever 721 rotatably supports the flywheel 71. The lever 721 is rotatable around a rotation shaft 720 located radially outward of the flywheel 71. The air cylinder 722 is disposed in a position where it can press the other end of the lever 721.

[0041] The air cylinder 722 moves the rod back and forth to rotate the lever 721, thereby moving the flywheel 71 between the retracted position shown in Figures 4 and 6 and the contact position shown in Figures 5 and 7. When the flywheel 71 is in the retracted position, the outer circumferential surface of the small diameter wheel 712 is separated from the outer circumferential surface of the elastic roller 122. When the flywheel 71 is in the contact position, the outer circumferential surface of the small diameter wheel 712 is in contact with the outer circumferential surface of the elastic roller 122.

[0042] Table data T is stored in the memory unit 503 of the control unit 50. FIG. 8 is a diagram showing an example of the table data T. The table data T is data indicating the operating conditions of the printing device 1 under which resonance of the printing medium 9 occurs (hereinafter referred to as "resonance occurrence conditions"). In the example of FIG. 8, the resonance occurrence conditions are described as combinations of the material of the printing medium 9, the thickness of the printing medium 9, the width of the printing medium 9, and the transport speed of the printing medium 9.

[0043] The resonance occurrence conditions are determined in advance by experiment, simulation, or calculation. A method for calculating the resonance occurrence conditions will be described later.

[0044] If the combination of the paper type, thickness, width, and conveyance speed of the print medium 9 does not satisfy any of the resonance occurrence conditions in the table data T, the control unit 50 positions the flywheel 71 in the retracted position by extending the rod of the air cylinder 722. In this case, the specific driven roller 12s rotates without contacting the flywheel 71.

[0045] On the other hand, if the combination of the paper type, thickness, and width of the print medium 9, and the conveyance speed of the print medium 9 satisfies any of the resonance occurrence conditions in the table data T, the control unit 50 moves the flywheel 71 from the retracted position to the contact position by pulling the rod of the air cylinder 722. This causes the small diameter wheel 712 of the flywheel 71 to contact the elastic roller 122 of the specific driven roller 12s. As a result, the inertia of the specific driven roller 12s increases. The specific driven roller 12s rotates while rotating the flywheel 71.

[0046] When the inertia of the specific driven roller 12s increases, the resonance frequency of the vibration system including the specific driven roller 12s decreases. Therefore, the resonance frequency can be shifted from the resonance frequency when the small diameter wheel 712 of the flywheel 71 is not in contact with the elastic roller 122 of the specific driven roller 12s. As a result, resonance of the print medium 9 can be prevented.

[0047] In this way, in the printing device 1 of this embodiment, the inertia of the specific driven roller 12s can be changed by bringing the flywheel 71 into contact with the specific driven roller 12s. This shifts the resonance frequency, making it possible to avoid resonance of the print medium 9. Therefore, printing can be performed without limiting the usage conditions of the printing device 1 and without generating resonance. As a result, print quality can be improved.

[0048] Furthermore, the printing device 1 may perform printing while gradually increasing the transport speed of the print medium 9 immediately after the start of the printing process. Also, the printing device 1 may perform printing while gradually decreasing the transport speed of the print medium 9 immediately before the end of the printing process. In these cases, a resonance occurrence condition may be temporarily met during the process of changing the transport speed. Even in such cases, the control unit 50 can bring the flywheel 71 into contact with the specific driven roller 12s only during the period when the resonance occurrence condition is met. This allows the transport speed of the print medium 9 to be changed while avoiding resonance of the print medium 9.

[0049] However, if the inertia of the specific driven roller 12s increases suddenly, a braking force may act on the specific driven roller 12s, potentially causing a temporary decrease in the transport speed of the print medium 9. Therefore, in this embodiment, the flywheel 71 is brought into contact with the outer circumferential surface of the elastic roller 122, which is elastically deformable, rather than with the hard surface of the specific driven roller 12s. This allows the contact pressure of the flywheel 71 against the specific driven roller 12s to be gradually increased. This allows the inertia of the specific driven roller 12s to be gradually increased. This prevents a temporary decrease in the transport speed of the print medium 9 when the flywheel 71 is switched from the retracted position to the contact position. Similarly, a temporary increase in the transport speed of the print medium 9 can be prevented when the flywheel 71 is switched from the contact position to the retracted position.

[0050] <3. How to calculate the operating conditions that cause resonance> As described above, the table data T defines the resonance occurrence conditions. These resonance occurrence conditions are determined by experiments or simulations, but can also be calculated by calculation. FIG. 9 is a flowchart showing the procedure for calculating the resonance occurrence conditions. The following calculation process may be performed by the control unit 50 or by a computer other than the control unit 50.

[0051] When calculating the resonance occurrence conditions, first, an equation of motion is established (step S1) for a vibration system consisting of the print medium 9 and the multiple driven rollers 12 between the first drive roller 11a and the second drive roller 11b. The equation of motion can be expressed, for example, by the following mathematical formula (1).

[0052]

number

[0053] The symbols in the above formula (1) represent the following: fi(t): whirling force due to eccentricity of the driven roller 12 Ji: Inertia of the driven roller 12 Ri: Radius of the driven roller 12 xi: Displacement of the contact point between the driven roller 12 and the printing medium 9 Ki: Spring constant of the printing medium

[0054] When the above formula (1) is organized in a matrix format from i=1 to i=n, ​​the following formula (2) is obtained (step S2).

[0055]

number

[0056] Here, since the displacement vector x is an oscillating solution, we can set it as x = φe^(-iωt). Substituting this into the above equation (2), we get the following equation (3).

[0057]

number

[0058] Furthermore, when the external force F(t) is 0, the above formula (3) can be expressed as the following formula (4).

[0059]

number

[0060] From this formula (4), the eigenvalues ​​of φ and ω are found (step S3). In order for formula (4) to have a solution other than φ=0, which represents a stationary state, the coefficient determinant must be 0, so the following formula (5) can be derived.

[0061]

number

[0062] When there are N degrees of freedom, N ω^2 values ​​that satisfy equation (5) are found. In this case, the smallest solution ω1 is the angular velocity corresponding to the primary natural frequency. Therefore, the primary natural frequency f1 is expressed by the following equation (6).

[0063]

number

[0064] This makes it possible to determine the primary natural frequency, i.e., the primary resonant frequency. The control unit 50 calculates the resonance occurrence conditions based on the calculated resonant frequency. For example, the control unit 50 sets the transport speed of the print medium 9 corresponding to the resonant frequency as the resonance occurrence condition. Then, the control unit 50 writes the resonance occurrence condition into the table data T. This allows the table data T to be created appropriately.

[0065] <4. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0066] In the above embodiment, the specific driven roller 12s is provided with an elastic roller 122, and the flywheel 71 is brought into contact with the elastic roller 122 to prevent a sudden change in inertia. However, it is not essential that the specific driven roller 12s has the elastic roller 122. A sudden change in inertia may be prevented by other methods.

[0067] For example, a powder clutch may be provided between the specific driven roller 12s and the flywheel 71. This allows the specific driven roller 12s and the flywheel 71 to be connected while allowing slippage between them, thereby preventing a sudden change in inertia.

[0068] Furthermore, a magnetic coupling may be provided between the specific driven roller 12s and the flywheel 71. In this case, by gradually bringing the flywheel 71 closer to the specific driven roller 12s, the torque transmitted between the specific driven roller 12s and the flywheel 71 can be gradually increased. As a result, a sudden change in inertia can be prevented.

[0069] Furthermore, a continuously variable transmission mechanism may be provided between the specific driven roller 12s and the flywheel 71. The continuously variable transmission mechanism may then be used to gradually change the rotation speed of the flywheel 71 relative to the specific driven roller 12s, thereby preventing abrupt changes in inertia.

[0070] In the above embodiment, the flywheel 71 is normally placed at the retracted position, and when a resonance occurrence condition is met, the flywheel 71 is moved from the retracted position to the contact position. However, the flywheel 71 may be normally placed at the contact position, and when a resonance occurrence condition is met in a vibration system including the flywheel 71, the flywheel 71 may be moved from the contact position to the retracted position.

[0071] Furthermore, the printing device 1 in the above embodiment is equipped with four heads 21. However, the number of heads 21 equipped in the printing device 1 may be one to three, or five or more. For example, the printing device 1 may be equipped with a head 21 that ejects ink of a special color in addition to inks of the colors C, M, Y, and K.

[0072] In addition, the specific driven roller 12s is not provided with the elastic roller 122, and the flywheel 71 is By contacting the hard outer peripheral surface of the driven roller 12s, the specific driven roller 12s The inertia of the

[0073] Furthermore, the elements appearing in the above-described embodiments and modifications may be combined as appropriate within the scope of not causing any contradiction. [Explanation of symbols]

[0074] 1:Printing device 9:Print media 10: Transport mechanism 11: Drive roller 11a: First driving roller 11b: Second driving roller 12: Driven roller 12s: Specific driven roller 15: Tension sensor 20:Printing Department 21: Head 30:Drying section 31: Heater 40: Inspection Department 41: Camera 50: Control unit 60: Housing 70: Inertia adjustment mechanism 71: Flywheel 72: Switching mechanism 122: Elastic roller 711: Large diameter wheels 712: Small diameter wheels 721: Lever 722: Air cylinder P: Computer Program T: Table data

Claims

1. An inkjet printing device, a transport mechanism that transports a long strip of printing medium in a longitudinal direction; a head that ejects ink onto the print medium transported by the transport mechanism; a control unit that controls the transport mechanism and the head; Equipped with The transport mechanism includes: a drive roller that actively rotates by power output from a motor; a plurality of driven rollers that rotate in accordance with the movement of the printing medium; an inertia adjustment mechanism that changes the inertia of a specific driven roller included in the plurality of driven rollers; A printing device comprising:

2. 2. The printing device according to claim 1, the control unit has table data indicating usage conditions under which resonance occurs in the print medium, When the use conditions of the printing device correspond to the use conditions shown in the table data, the inertia adjustment mechanism changes the inertia of the specific driven roller.

3. 3. The printing device according to claim 1, wherein: the transport mechanism has two of the drive rollers, The printing device, wherein the specific driven roller is located between two of the drive rollers in a transport path of the print medium.

4. 3. The printing device according to claim 1, wherein: The inertia adjustment mechanism includes: A flywheel and a switching mechanism that moves the flywheel between a retracted position away from the specific driven roller and a contact position in contact with the specific driven roller; A printing device comprising:

5. 5. The printing device according to claim 4, The specific driven roller has an elastic roller that is elastically deformable, The printing device, wherein the flywheel contacts the elastic roller at the contact position.

Images