Printer and maintenance method

Abstract

To resolve temporal elongation of a resin sheet.SOLUTION: A printer 1 includes a printing drum 60 and a heater 81. The printing drum 60 has a heat shrinkable resin sheet 65e on its outer peripheral surface 62. The printing drum 60 has a tension adjustment mechanism of tensioning the resin sheet 65e on the outer peripheral surface 62 and relaxing the tension of the resin sheet 65e. The heater 81 heats the outer peripheral surface 62 of the printing drum 60. The tension adjustment mechanism relaxes the tension of the resin sheet 65e, and then the heater 81 heats the outer peripheral surface 62 of the printing drum 60. The outer peripheral surface 62 of the printing drum 60 is heated, and then the tension adjustment mechanism tensions the resin sheet 65e on the outer peripheral surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a printing apparatus and a maintenance method. [Background technology]

[0002] Patent documents 1 to 4 disclose a printing device including a printing drum and a print head. The print drum adsorbs a sheet to be printed on its outer circumferential surface. When the print drum rotates, the sheet to be printed passes between the outer circumferential surface of the print head and the print head in the circumferential direction. The print head prints an image on the sheet to be printed that is fed by the print drum.

[0003] The printing drum has a perforated sheet on its outer periphery, and the perforated sheet has a number of suction holes penetrating from its front to its back. A vacuum is connected to the printing drum, and negative pressure is generated in the suction holes by the vacuum, so that the sheet to be printed is attracted to the perforated sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-1198 A [Patent Document 2] Japanese Patent Application Publication No. 10-175338 [Patent Document 3] JP 2009-279795 A [Patent Document 4] JP 2011-178547 A Summary of the Invention [Problem to be solved by the invention]

[0005] Since the porous sheet is stretched over the outer circumferential surface of the printing drum, the porous sheet stretches over time due to tension. The stretching of the porous sheet over time causes wrinkles to form on the porous sheet. When wrinkles form on the porous sheet, the distance between the print head and the sheet to be printed, which is attracted to the porous sheet, becomes narrower than the appropriate value, resulting in poor quality of the printed image. Therefore, the technique disclosed in this specification aims to eliminate the elongation over time of a resin sheet such as a porous sheet. [Means for solving the problem]

[0006] In order to solve the above problems, this specification discloses a printing apparatus and a maintenance method. The printing device includes a print drum and a heater. The print drum has a heat-shrinkable resin sheet on its outer peripheral surface, and has a tension adjustment mechanism that stretches the resin sheet over the outer peripheral surface and releases the tension of the resin sheet. The heater heats the outer peripheral surface of the print drum. After the tension adjustment mechanism releases the tension of the resin sheet, the heater heats the outer peripheral surface of the print drum. After the outer peripheral surface of the print drum is heated, the tension adjustment mechanism stretches the resin sheet over the outer peripheral surface.

[0007] The maintenance method includes a relaxation step, a heating step, and a tensioning step. The relaxation step is a step of loosening the tension of a heat-shrinkable resin sheet stretched over the outer peripheral surface of a printing drum. The heating step is a step of heating the resin sheet loosened by the relaxation step, thereby thermally shrinking the resin sheet. The tensioning step is a step of stretching the resin sheet over the outer peripheral surface of the printing drum after the heating step. Effect of the Invention

[0008] The technology disclosed in this specification contributes to eliminating elongation of the resin sheet over time and tensioning the resin sheet to the outer circumferential surface of the printing drum. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 shows a printing device. [Diagram 2] FIG. 2 shows the components of a printing device. [Diagram 3] FIG. 3 shows the inside of the main body of the printing device. [Figure 4] FIG. 4 shows an enlarged view of region IV in FIG. [Diagram 5] FIG. 5 shows the relationship between the temperature and the shrinkage rate of the resin sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described with reference to the drawings. The features and technical effects of the embodiments will be understood from the following detailed description and drawings. However, the scope of the present invention is not limited to the embodiments disclosed below. The drawings are provided for illustrative purposes only, and therefore the scope of the present invention is not limited to the illustrations in the drawings.

[0011] <<Printing device>> Fig. 1 is a side view that shows a schematic configuration of the printing device 1. Fig. 2 is a block diagram of the printing device 1.

[0012] The printing apparatus 1 is a sheet-fed on-demand printer. The printing apparatus 1 includes a feeder 10, a printing apparatus main body 30, a delivery 20, and a control unit 79.

[0013] A plurality of sheets to be printed 99 are stored in a stacked state in the feeder 10. The feeder 10 feeds the stacked sheets to be printed 99 one by one to the printing device main body 30. The front ends of the sheets to be printed 99 fed by the feeder 10 face forward in the traveling direction. The sheets to be printed 99 are also referred to as recording media or media.

[0014] The feeder 10 has a paper feed tray 11, a separator 12, and a feeder board 13. The paper feed tray 11 supports the print sheets 99 from below a plurality of stacked print sheets 99. The paper feed tray 11 is provided so as to be movable up and down. The vertical position of the paper feed tray 11 is determined by the number of print sheets 99 placed on the paper feed tray 11, and the paper feed tray 11 rises as the number of print sheets 99 on the paper feed tray 11 decreases. The separator 12 is provided above the paper feed tray 11. The separator 12 takes out the print sheets 99 on the paper feed tray 11 one by one from the top of them to the feeder board 13. The feeder board 13 is provided between the separator 12 and an intake port of the printing device main body 30. The feeder board 13 has, for example, an endless belt conveyor or the like. The feeder board 13 transports the printing sheet 99 removed by the separator 12 to an inlet of the printing device main body 30 .

[0015] The printing device main body 30 prints an image on the sheet fed by the feeder 10, and discharges the printed sheet 99 to the delivery 20. The printing device main body 30 will be described in detail later.

[0016] The delivery 20 stacks and stores the print sheets 99 printed by the printing device main body 30. The delivery 20 has a discharger 21 and a paper output tray 22. The discharger 21 is arranged from the discharge port of the printing device main body 30 to the paper output tray 22. The discharger 21 has, for example, an endless belt conveyor or the like. The discharger 21 transports the print sheets 99 printed by the printing device main body 30 to the paper output tray 22. The print sheets 99 transported by the discharger 21 are placed in a stack on top of the paper output tray 22.

[0017] The control unit 79 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a driving circuit, etc. The control unit 79 controls the entire printing apparatus 1.

[0018] <<Printing device body>> The printing device main body 30 has a print head 31, a transport device 40, an ultraviolet irradiator 50, a temperature sensor 71, a paper float detector 72, an inspector 73, a heater 81, and actuators 86-88.

[0019] The conveying device 40 conveys the print sheet 99 supplied from the feeder board 13 of the feeder 10 to the discharger 21 of the delivery 20. The conveying device 40 inverts the print sheet 99 while conveying it, as necessary.

[0020] The transport device 40 includes a swing arm 41, a transport drum 42, a printing drum 60, a transport drum 44, a selection drum 45, a transport drum 46, an inverting drum 47, a swing arm 48, and a drive device 85. The drum is also called a body, a cylinder, or a roller.

[0021] The rotation axes of the transport drum 42, the print drum 60, the transport drum 44, the selection drum 45, the transport drum 46, and the reversing drum 47 are arranged parallel to one another. The transport drum 42, the temperature sensor 71, the paper float detector 72, the print head 31, the ultraviolet irradiator 50, the transport drum 44, the heater 81, the reversing drum 47, and the swing arm 48 are arranged in this order on the outside of the outer circumferential surface 62 of the print drum 60 in the direction of forward rotation of the print drum 60. The direction of forward rotation of the print drum 60 is indicated by an arrow 96 in the figure. Hereinafter, the axial direction refers to a direction parallel to the rotation axis of the print drum 60, the circumferential direction refers to a direction around the rotation axis of the print drum 60, and the radial direction refers to a direction perpendicular to the rotation axis of the print drum 60.

[0022] The transport drum 42, the printing drum 60, the transport drum 44, the selection drum 45, the transport drum 46, and the reversing drum 47 are connected to a drive device 85. The drive device 85 rotates and drives the swing arm 41, the transport drum 42, the printing drum 60, the transport drum 44, the selection drum 45, the transport drum 46, the reversing drum 47, and the swing arm 48. The drive device 85 has one or more motors and a transmission mechanism. The transmission mechanism transmits the power of the motor to the swing arm 41, the transport drum 42, the printing drum 60, the transport drum 44, the selection drum 45, the transport drum 46, the reversing drum 47, and the swing arm 48. The transmission mechanism is, for example, a gear transmission mechanism or a wrapping transmission mechanism. The rotation direction of the transport drum 42, the transport drum 44, the transport drum 46, and the reversing drum 47 is opposite to the rotation direction of the printing drum and the selection drum 45. In FIG. 1, the transport drum 42, the transport drum 44, the transport drum 46 and the reversing drum 47 rotate clockwise, and the printing drum and the selection drum 45 rotate counterclockwise.

[0023] The swing arm 41 is disposed near an end of the feeder board 13. The swing arm 41 scoops up the sheet to be printed 99 transported by the feeder board 13 from the feeder board 13 to the transport drum 42. As a result, the sheet to be printed 99 is wound around the outer circumferential surface of the transport drum 42.

[0024] The transport drum 42 is disposed between the swing arm 41 and the printing drum 60. The transport drum 42 is adjacent to the outer peripheral surface 62 of the printing drum 60. The transport drum 42 has a gripper 42a on its outer periphery. The rotational motion of the transport drum 42 is converted into the motion of the gripper 42a by, for example, a cam. The motion of the gripper 42a refers to the action of holding and releasing the printing sheet 99. The transport drum 42 holds the front end of the printing sheet 99 picked up by the swing arm 41 with the gripper 42a, and sends the printing sheet 99 from the feeder board 13 to the printing drum 60 while winding it up. The gripper is also called a claw mechanism, a claw device, a gripping mechanism, a gripping device, or a fastener.

[0025] The transport drum 42 preheats the sheet to be printed 99. That is, the transport drum 42 has a heater 42b, and the heater 42b heats the sheet to be printed 99. Since the outer circumferential surface of the transport drum 42 is close to the outer circumferential surface 62 of the printing drum 60, the printing drum 60 is heated by the heat of the heater 42b.

[0026] The printing drum 60 is disposed between the transport drum 42 and the transport drum 44. The rotation axis of the printing drum 60 is located above the rotation axes of the transport drums 42, 44. The printing drum 60 has three grippers 61 on the inside near its outer circumferential surface 62. These grippers 61 are arranged in the circumferential direction at an equal pitch. The pitch of these grippers 61 is equal to the circumferential lengths of the transport drum 42, the transport drum 44, the selection drum 45, and the transport drum 46. The circumferential length of the printing drum 60 is set to a length that allows three printed sheets 99 to be held simultaneously on the outer periphery of the printing drum 60 without overlapping.

[0027] The number of grippers 61 is not limited to three, and may be one or two, or may be four or more. Even if the number of grippers 61 changes, the pitch of the grippers 61 does not change, and the diameter of the printing drum 60 increases as the number of grippers 61 increases. If the number of grippers 61 on the printing drum 60 is n, one cycle is defined as a period in which the printing drum 60 rotates 1 / n. In this embodiment, since the printing drum 60 has three grippers 61, one cycle is a period in which the printing drum 60 rotates 1 / 3. n is also the number of mounting bases 65 that the printing drum 60 has on its outer periphery, which will be described later. n is also the number of slots 67 that the printing drum 60 has on its outer periphery, which will be described later.

[0028] The rotational motion of the printing drum 60 is converted into the motion of the gripper 61 by, for example, a cam. The motion of the gripper 61 refers to the action of holding and releasing the sheet to be printed 99. Every time the transport drum 42 rotates once, one of the grippers 61 of the printing drum 60 approaches the gripper 42a of the transport drum 42. Therefore, when the sheet to be printed 99 is transferred from the transport drum 42 to the printing drum 60, the gripper 42a of the transport drum 42 releases the front end of the sheet to be printed 99, and the gripper 61 adjacent thereto holds the front end of the sheet to be printed 99. The printing drum 60 holds the front end of the sheet to be printed 99 transported by the transport drum 42 by the gripper 61, and sends the sheet to be printed 99 to the transport drum 44 while winding it up from the transport drum 42.

[0029] As shown by the dashed arrow, a region 97 from the transport drum 42 to the transport drum 44 along the outer peripheral surface 62 of the printing drum 60 in the forward rotation direction of the printing drum 60 is a path along which the printing drum 60 sends the sheet to be printed 99. In this region 97, the sheet to be printed 99 is attracted to the outer peripheral surface 62 of the printing drum 60 by the suction function of the printing drum 60. As shown by the dashed arrow, in a region 98 from the transport drum 44 to the transport drum 42 along the outer peripheral surface 62 of the printing drum 60 in the forward rotation direction of the printing drum 60, the printing drum 60 does not exert its suction function. The forward rotation direction of the printing drum 60 is also forward in the direction of travel of the sheet to be printed 99 transported by the printing drum 60. The printing drum 60 and its suction function will be described in detail later.

[0030] The sheet to be printed 99 transported in the circumferential direction by the printing drum 60 is printed on by the print head 31. Then, the sheet to be printed 99 is exposed to ultraviolet rays by the ultraviolet irradiator 50. Then, the sheet to be printed 99 is transferred from the printing drum 60 to the transport drum 44.

[0031] The print head 31 is disposed in the path of the sheet to be printed 99 transported by the print drum 60 from the transport drum 42 to the transport drum 44, i.e., in an area 97, outside the print drum 60. Specifically, the print head 31 is disposed at a position away from the transport drum 42 in the forward rotation direction of the print drum 60, facing from the outside of the print drum 60 toward the outer circumferential surface 62 of the print drum 60. When the sheet to be printed 99 passes between the print head 31 and the print drum 60 in the circumferential direction, the print head 31 forms an image on the sheet to be printed 99.

[0032] The print head 31 has a plurality of inkjet heads 32-35. The inkjet heads 32-35 are disposed outside the print drum 60, facing the outer circumferential surface 62 of the print drum 60, and are arranged at intervals in the circumferential direction. The inkjet heads 32-35 form an image on the print sheet 99 by ejecting ink toward the print sheet 99 attached to the outer circumferential surface 62 of the print drum 60. The inkjet heads 32-35 eject ink of different colors. The inkjet heads 32, 33, 34, 35 eject yellow, magenta, cyan, and black inks, respectively. In addition to the inkjet heads 32-35, the print head 31 may have inkjet heads that eject light cyan and light magenta inks, respectively.

[0033] The ink supplied from the ink tank to the inkjet heads 32 to 35 is heated by an ink heater. The temperature of the heated ink is, for example, 80°C.

[0034] The inkjet heads 32-35 are provided so as to be movable in the axial or radial direction of the print drum 60 between the printable position and the retracted position by a guide mechanism. When the inkjet heads 32-35 are located at the printable position, the inkjet heads 32-35 are disposed on the outer side of the print drum 60 of the conveying device 40, facing the outer circumferential surface of the print drum 60, as described above. When the inkjet heads 32-35 are located at the retracted position, the inkjet heads 32-35 are spaced apart from the outer circumferential surface of the print drum 60. When the inkjet heads 32-35 are located at the retracted position, the distance from the inkjet heads 32-35 to the outer circumferential surface of the print drum 60 is greater than the distance from the inkjet heads 32-35 to the outer circumferential surface of the print drum 60 when the inkjet heads 32-35 are located at the printable position. The print head 31 may be moved manually between the printable position and the retracted position. The actuator 86 may drive the print head 31 to move the print head 31 between the printable position and the retracted position. The actuator 86 may be controlled by the control unit 79.

[0035] Note that the print head 31 may have a laser printer type head that forms yellow, magenta, cyan, and black images, respectively, on the printing sheet 99, instead of the inkjet heads 32 to 35. The laser printer type head has a photosensitive drum, a scanning laser beam irradiator that forms a latent image on the outer circumferential surface of the photosensitive drum, and a toner drum that makes the latent image visible by adhering toner to the photosensitive drum. Furthermore, the print head 31 may have, instead of the inkjet heads 32 to 35, thermal heads of a thermal transfer type that form yellow, magenta, cyan and black images on the print-receiving sheet 99, respectively.

[0036] The ultraviolet irradiator 50 is disposed outside the printing drum 60 in the path of the sheet to be printed 99 transported by the printing drum 60 from the inkjet head 35 to the transport drum 44. Specifically, the ultraviolet irradiator 50 is disposed at a position away from the inkjet head 35 in the forward rotation direction of the printing drum 60, from the outside of the printing drum 60 toward the outer circumferential surface of the printing drum 60. When the sheet to be printed 99 passes between the ultraviolet irradiator 50 and the printing drum 60 in the circumferential direction, the ink adhering to the sheet to be printed 99 is exposed to ultraviolet light emitted from the ultraviolet irradiator 50, whereby the image is fixed to the sheet to be printed 99.

[0037] The ultraviolet irradiator 50 emits ultraviolet light radially inward. The ultraviolet irradiator 50 irradiates the print-receiving sheet 99 with ultraviolet light to harden the ink adhered to the print-receiving sheet 99, thereby fixing the ink to the print-receiving sheet 99.

[0038] The ultraviolet energy of the ultraviolet irradiator 50 heats the outer peripheral surface 62 of the print drum 60. Therefore, the ultraviolet irradiator 50 is also a radiant heater that heats the outer peripheral surface 62 of the print drum 60 by irradiating ultraviolet rays. The ultraviolet irradiator 50 may be provided so as to be movable in the radial direction so as to approach or move away from the outer peripheral surface 62 of the print drum 60. The position of the ultraviolet irradiator 50 when the ultraviolet irradiator 50 approaches the outer peripheral surface 62 of the print drum 60 is called a first approach position. The position of the ultraviolet irradiator 50 when the ultraviolet irradiator 50 moves away from the outer peripheral surface 62 of the print drum 60 is called a first separated position. When the ultraviolet irradiator 50 is disposed at the first approach position, the outer peripheral surface 62 of the print drum 60 is efficiently heated and the outer peripheral surface 62 of the print drum 60 becomes hot. The ultraviolet irradiator 50 may be manually moved between the first approach position and the first separated position. The actuator 87 may drive the print head 31 to move the ultraviolet irradiator 50 between the first close position and the first distant position. The actuator 87 may be controlled by the control unit 79.

[0039] The transport drum 44 is disposed on the opposite side of the transport drum 42 with respect to the printing drum 60. The transport drum 44 is close to the outer peripheral surface 62 of the printing drum 60. The transport drum 44 has a gripper 44a on the inside near its outer peripheral surface. The rotational motion of the transport drum 44 is converted into the motion of the gripper 44a by, for example, a cam. The motion of the gripper 44a refers to the action of holding and releasing the printed sheet 99. As in the case of the transport drum 42, the gripper 44a of the transport drum 44 comes close to one of the grippers 61 of the printing drum 60 every time the transport drum 44 rotates once. The transport drum 44 holds the front end of the printed sheet 99 transported by the printing drum 60 by the gripper 44a, and sends the printed sheet 99 from the printing drum 60 to the selection drum 45 while winding it up.

[0040] The selection drum 45 is disposed below the transport drum 44 in close proximity to the transport drum 44. The selection drum 45 has a gripper 45a on the inside near its outer circumferential surface. The rotational motion of the selection drum 45 is converted into the motion of the gripper 45a by, for example, a cam. The motion of the gripper 45a refers to the action of holding and releasing the printed sheet 99. Every time the selection drum 45 rotates once, the gripper 45a of the selection drum 45 approaches the gripper 44a of the transport drum 44. The selection drum 45 holds the front end of the printed sheet 99 transported by the transport drum 44 with the gripper 45a, and sends the printed sheet 99 to the transport drum 46 or the reversing drum 47 while winding it up from the transport drum 44.

[0041] The transport drum 46 is disposed adjacent to the selection drum 45 and the discharger 21. The transport drum 46 is disposed on the opposite side of the printing drum 60 with respect to the selection drum 45 and the transport drum 44. The transport drum 46 has a gripper 46a on the inside near its outer circumferential surface. The rotational movement of the transport drum 46 is converted into the movement of the gripper 46a by, for example, a cam. The movement of the gripper 46a refers to the action of holding and releasing the printed sheet 99. The reversing drum 47 is arranged under the printing drum 60 in the vicinity of the selection drum 45. The reversing drum 47 is arranged on the opposite side of the selection drum 45 from the transport drum 46 and the discharger 21. The rotational movement of the reversing drum 47 is converted into the movement of the gripper 47a, for example by a cam. The movement of the gripper 47a refers to the action of holding and releasing the printed sheet 99. The circumference of the reversing drum 47 is twice the circumference of the transport drums 42, 44, 46 and the selection drum 45. The swing arm 48 is arranged between the reversing drum 47 and the transport drum 42 in the vicinity of the printing drum 60.

[0042] Every time the selection drum 45 rotates once, the gripper 45 a of the selection drum 45 approaches the gripper 46 a of the transport drum 46 , and then the gripper 45 a of the selection drum 45 approaches the gripper 47 a of the reversing drum 47 .

[0043] When discharging the printed sheet 99 transported by the selection drum 45, the gripper 45a of the selection drum 45 releases the leading end of the printed sheet 99, and the gripper 46a of the transport drum 46 adjacent thereto holds the leading end of the printed sheet 99. Therefore, the transport drum 46 holds the leading end of the printed sheet 99 transported by the selection drum 45 with the gripper 46a, and sends the printed sheet 99 to the discharger 21 while winding it up from the selection drum 45. The printed sheet 99 is discharged by the discharger 21.

[0044] In the case of inverting the front and back sides of the sheet to be printed 99 conveyed by the selection drum 45, the gripper 45a of the selection drum 45 releases the front end of the sheet to be printed 99, and the gripper 47a of the reversing drum 47 adjacent thereto holds the front end of the sheet to be printed 99. Therefore, the reversing drum 47 holds the front end of the sheet to be printed 99 conveyed by the selection drum 45 with the gripper 47a, and winds up the sheet to be printed 99 from the selection drum 45. When the sheet to be printed 99 is wound up on the reversing drum 47, the front and back sides of the sheet to be printed 99 are inverted. When the rear end of the sheet to be printed 99 comes close to the swing arm 48, the swing arm 48 transfers the rear end of the sheet to be printed 99 from the reversing drum 47 to one of the grippers 61 of the printing drum 60, and the gripper 47a of the reversing drum 47 releases the front end of the sheet to be printed 99. Therefore, the printing drum 60 holds the rear end of the sheet to be printed 99 with the gripper 61, and sends the sheet to be printed 99 to the transport drum 44 while winding it up from the reversing drum 47. The sheet to be printed 99 passes from the printing drum 60 sequentially through the transport drum 44, the selection drum 45, and the transport drum 46, and is discharged by the discharger 21. When the sheet to be printed 99 passes between the inkjet heads 32 to 35 and the printing drum 60 in the circumferential direction, the inkjet heads 32 to 35 discharge ink onto the sheet to be printed 99, whereby the back side of the sheet to be printed 99 is printed.

[0045] The selection drum 45 is spaced diagonally downward from the printing drum 60, and a space 90 exists between the selection drum 45 and the printing drum 60. This space 90 is surrounded by the selection drum 45 and the printing drum 60, as well as the transport drum 44 and the reversing drum 47. This space 90 is located on the transport drum 44 side of the region 98. This space 90 is located below the printing drum 60. A heater 81 is disposed in this space 90. The heater 81 may be provided in the internal space 66 of the printing drum 60 and heat the outer peripheral surface 62 of the printing drum 60 from inside the printing drum 60.

[0046] The heater 81 faces the outer peripheral surface 62 of the print drum 60 in the space 90. The heater 81 is configured as a convection heater, a radiation heater, or a contact heater. The convection heater has a heat source and a fan, and the fan generates a convection current from the heat source toward the outer peripheral surface 62 of the print drum 60. The radiation heater radiates electromagnetic waves to the outer peripheral surface 62 of the print drum 60 to heat the outer peripheral surface 62 of the print drum 60. The radiation heater is, for example, an infrared heater. The contact heater is in contact with the outer peripheral surface 62 of the print drum 60 and heats the outer peripheral surface 62 of the print drum 60 by thermal conduction. The temperature of the outer peripheral surface 62 of the print drum 60 is controlled by controlling the heater 81. When the heater 81 is a convection heater or a radiation heater, the heater 81 may be provided so as to be movable in the radial direction so as to approach or move away from the outer peripheral surface 62 of the print drum 60. The position of the heater 81 when the heater 81 approaches the outer peripheral surface 62 of the print drum 60 is referred to as the second proximity position. The position of the heater 81 when the heater 81 moves away from the outer peripheral surface 62 of the print drum 60 is referred to as the second separated position. When the heater 81 is disposed at the second proximity position, the outer peripheral surface 62 of the print drum 60 is efficiently heated and the outer peripheral surface 62 of the print drum 60 becomes hot. The heater 81 may be manually moved between the second proximity position and the second separated position. The actuator 88 may drive the print head 31 to move the heater 81 between the second proximity position and the second separated position. The actuator 88 may be controlled by the control unit 79.

[0047] The temperature sensor 71 is disposed outside the printing drum 60 at a position away from the transport drum 42 in the forward rotation direction of the printing drum 60. The temperature sensor 71 is disposed between the transport drum 42 and the inkjet head 32 in the circumferential direction. The temperature sensor 71 detects the temperature of the printing sheet 99 attached to the outer circumferential surface of the printing drum 60, and outputs a signal indicating the detected temperature of the printing sheet 99 to the control unit 79. The temperature sensor 71 detects the temperature of the outer circumferential surface 62 of the printing drum 60, and outputs a signal indicating the detected temperature of the printing sheet 99 to the control unit 79. The temperature sensor 71 may be a contact type temperature sensor that contacts the outer circumferential surface of the printing drum 60 or the printing sheet 99, or may be a non-contact type temperature sensor that is separated from the outer circumferential surface of the printing drum 60 or the printing sheet 99.

[0048] The paper float detector 72 is disposed outside the print drum 60, at a position away from the inkjet head 32 in the opposite direction of the forward rotation of the print drum 60. The paper float detector 72 is disposed between the transport drum 42 and the inkjet head 32 in the circumferential direction. If the paper float detector 72 detects that the printed sheet 99 passing the position of the paper float detector 72 has floated from the outer circumferential surface 62 of the print drum 60, it outputs a detection signal of, for example, a high level to the control unit 79. If the paper float detector 72 does not detect the floating of the printed sheet 99, it outputs a non-detection signal of, for example, a low level to the control unit 79. The paper float detector 72 is composed of, for example, a light sensor, an image sensor, a proximity sensor, a contact switch, a contact sensor, a magnetic sensor, or the like.

[0049] The inspector 73 is disposed outside the print drum 60 at a position away from the ultraviolet irradiator 50 in the direction of forward rotation of the print drum 60. The inspector 73 is disposed between the ultraviolet irradiator 50 and the transport drum 44 in the circumferential direction. The inspector 73 detects the printable sheet 99 and its print quality after printing. The inspector 73 detects the condition and goodness of the print drum 60. The inspector 73 is composed of a linear image sensor such as a CIS (Contact Image Sensor). The CIS has an LED illuminator, an equal-magnification imaging optical system, and a linear imaging element that are assembled together.

[0050] <<Printing drum>> The print drum 60 will be described in detail with reference to Figures 3 and 4. Figure 3 is a side view that shows a schematic view of the inside of the main body of the printing apparatus. Figure 4 is an enlarged view of an area IV in Figure 3.

[0051] In addition to the three grippers 61, the print drum 60 has a shaft 63, two flanges 64, and three mounting bases 65. Note that in Figures 3 and 4, one of the flanges 64 is shown, and the other flange 64 is not shown.

[0052] The shaft 63 extends in the axial direction. The shaft 63 is connected to a driving device 85 and is driven to rotate by the driving device 85. The flanges 64 are attached to the shaft 63 in parallel to each other with a gap in the axial direction. The flanges 64 are provided in a disk shape so as to extend radially and circumferentially from the shaft 63. The flanges 64 are made of, for example, a metal. Since the flanges 64 are large, the heat capacity of the flanges 64 is large. In particular, the heat capacity of the flanges 64 is larger than that of the mounting base 65. The mounting bases 65 are shaped like arcuate columns. The mounting bases 65 are arranged at intervals in the circumferential direction around the shaft 63. The mounting bases 65 are bridged between the outer periphery of one flange 64 and the outer periphery of the other flange 64, and are attached to these flanges 64. The outer periphery of the mounting bases 65 forms the outer periphery 62 of the printing drum 60.

[0053] The mounting table 65 has a hollow 65a on the inside thereof, and has a number of suction holes 65b on the outer periphery that communicate with the hollow 65a. These suction holes 65b are distributed around the entire outer periphery of the mounting table 65. The hollow 65a of the mounting table 65 is connected to a vacuum. The vacuum sucks air from the hollow 65a, generating a suction force in the suction holes 65b. As a result, the printing sheet 99 is adsorbed to the outer periphery of the mounting table 65. Note that one printing sheet 99 is adsorbed per one mounting table 65.

[0054] The printing drum 60 has an internal space 66 on its inside. The internal space 66 is surrounded by the mounting base 65 and the flange 64. The printing drum 60 has a slot 67 between adjacent mounting bases 65 in the circumferential direction. The internal space 66 communicates with the outside of the printing drum 60 through the slot 67.

[0055] The three grippers 61 are attached to a mounting base 65 or flange 64 within three slots 67, respectively.

[0056] The mounting base 65 has a box body 65c, a metal sheet 65d, a resin sheet 65e, a front holder 65f, rear holders 65g and 65h, an actuator 65i, and a guide 65j. The mechanism having the holder 65f, the holder 65h, and the guide 65j is a tension adjustment mechanism that adjusts the tension of the resin sheet 65e.

[0057] The box body 65c is shaped like a circular arc column. The box body 65c has a hollow 65a on the inside that is recessed from the outer periphery of the box body 65c, and the hollow 65a opens at the outer periphery of the box body 65c. Three box bodies 65c are arranged at intervals on the radially outer side of the shaft 63, and these box bodies 65c are attached to the flanges 64 by bridging between the outer periphery of one flange 64 and the outer periphery of the other flange 64. A front end 65c1 of the box body 65c in the circumferential direction faces the direction of forward rotation of the print drum 60. A rear end 65c2 of the box body 65c in the circumferential direction faces the opposite direction of the forward rotation of the print drum 60.

[0058] The front holder 65f is disposed between adjacent box bodies 65c. The front holder 65f is attached to the box body 65c or the flange 64 along the front end 65c1 of the box body 65c. The front holder 65f clamps and holds the front ends of the metal sheet 65d and the resin sheet 65e to the front end 65c1 of the box body 65c.

[0059] The rear retainer 65g is disposed between adjacent box bodies 65c. The retainer 65g is attached to the box body 65c or the flange 64 along the rear end 65c2 of the box body 65c. The retainer 65g clamps and holds the rear end of the metal sheet 65d, and fixes the rear end of the metal sheet 65d to the rear end 65c2 of the box body 65c.

[0060] The rear retainer 65h is disposed between adjacent box bodies 65c. The rear retainer 65h is provided along the rear end 65c2 of the box body 65c. The retainer 65h is attached to the box body 65c or the flange 64 via a guide 65j or the like. The retainer 65h is guided by the guide 65j. The retainer 65h moves away from the rear end 65c2 of the box body 65c along the guide 65j in the direction opposite to the forward rotation of the print drum 60, and moves toward the rear end 65c2 of the box body 65c along the guide 65j in the direction of the forward rotation of the print drum 60. The retainer 65h clamps and holds the rear end of the resin sheet 65e.

[0061] The actuator 65i is disposed between adjacent box bodies 65c. The actuator 65i is attached to the box body 65c or the flange 64. The actuator 65i is connected to the holder 65h. The actuator 65i drives the holder 65h so as to move the holder 65h along the guide 65j. The actuator 65i includes a motor, an electromagnetic solenoid, a hydraulic cylinder, a pneumatic cylinder, or the like.

[0062] The metal sheet 65d is attached to the outer periphery of the box body 65c so as to cover the hollow 65a of the box body 65c. The metal sheet 65d has a number of holes penetrating from the front to the back of the metal sheet 65d. The front and rear ends of the metal sheet 65d are held by the holders 65f and 65g, respectively, so that the metal sheet 65d is attached to the outer periphery of the box body 65c in a taut state. The metal sheet 65d is bent into a cylindrical surface shape along the outer periphery of the box body 65c.

[0063] The resin sheet 65e is placed on the metal sheet 65d and attached to the outer periphery of the box body 65c so as to cover the hollow 65a of the box body 65c. The resin sheet 65e has a number of holes penetrating from the front to the back of the resin sheet 65e. The front and rear ends of the resin sheet 65e are held by the holders 65f and 65h, respectively, so that the resin sheet 65e is attached to the outer periphery of the box body 65c in a taut state. The resin sheet 65e is bent into a cylindrical surface shape along the outer periphery of the box body 65c. When the holder 65h is driven by the actuator 65i and the holder 65h approaches the rear end 65c2 of the box body 65c, the resin sheet 65e relaxes. When the holder 65h is driven by the actuator 65i and the holder 65h moves away from the rear end 65c2 of the box body 65c, the resin sheet 65e becomes taut.

[0064] The metal sheet 65d and the resin sheet 65e form the outer periphery of the mounting base 65. Holes in the metal sheet 65d and the resin sheet 65e form suction holes 65b.

[0065] The resin sheet 65e is made of a heat-shrinkable resin such as fluorinated ethylene propylene (FEP) or perfluoroalkoxy alkane (PFA). Specifically, the resin sheet 65e is made of tetrafluoroethylene-hexafluoropropylene copolymer resin or tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin. FIG. 5 is a graph showing the heat shrinkage characteristics of FEP and PFA used in the resin sheet 65e. As is clear from FIG. 5, when the temperature of the resin sheet 65e is about 40 degrees, the resin sheet 65e hardly shrinks. The higher the temperature of the resin sheet 65e, the higher the shrinkage rate of the resin sheet 65e.

[0066] <<Printing operation of the printing device>> The printing device 1 configured as above performs printing operations under the control of the control unit 79 as follows.

[0067] Before the printing device 1 performs a printing operation, the control unit 79 stops the heater 81 and the driving device 85. Therefore, the heater 81 does not generate heat, and the swing arm 41, the transport drum 42, the printing drum 60, the transport drum 44, the selection drum 45, the transport drum 46, the reversing drum 47, and the swing arm 48 are stopped. Before the printing device 1 performs a printing operation, the inkjet heads 32 to 35 are disposed in printable positions. Before the printing device 1 performs a printing operation, the ultraviolet irradiator 50 and the heater 81 are disposed in the first and second separated positions, respectively. Before the printing device 1 performs a printing operation, the holder 65h is separated from the rear end 65c2 of the box body 65c, and the resin sheet 65e is stretched.

[0068] When an external device such as a personal computer transfers print job data to the control unit 79, the control unit 79 activates the drive unit 85, the vacuum, and the delivery 20. Then, the drive unit 85 drives the swing arm 41, the transport drum 42, the printing drum 60, the transport drum 44, the selection drum 45, the transport drum 46, the reversing drum 47, and the swing arm 48. During the rotation of the printing drum 60, the mounting table 65 passing through an area 97 generates a suction force on its outer circumferential surface by the vacuum, and the mounting table 65 passing through an area 98 is disconnected from the vacuum and does not generate a suction force.

[0069] Next, the control unit 79 drives the heater 42b, the heater 81, and the ultraviolet irradiator 50. Then, the temperature of the transport drum 42 rises to the first target temperature by the heat of the heater 42b. The temperature of the outer peripheral surface of the print drum 60, i.e., the resin sheet 65e, rises to the first target temperature by the heat of the heater 42b, the heater 81, and the ultraviolet irradiator 50. At this time, the control unit 79 controls the heater 81 based on the temperature detected by the temperature sensor 71, thereby maintaining the temperature of the outer peripheral surface of the print drum 60 at the first target temperature. The first target temperature is lower than the temperature of the ink. The first target temperature is a temperature that hardly causes thermal shrinkage in the resin sheet 65e, for example, 40°C.

[0070] Next, the control unit 79 controls the feeder 10 to perform a feeding operation of the print sheet 99, and the feeder 10 periodically feeds the print sheet 99 to the printing device main body 30. For example, when the print job data includes data indicating single-sided printing, the period during which the feeder 10 feeds one print sheet 99 is equal to the period of one cycle, and when the print job data includes data indicating double-sided printing, the period during which the feeder 10 feeds one print sheet 99 is equal to twice the period of one cycle.

[0071] When the sheet to be printed 99 is sent to the printer body 30 by the feeder 10, the swing arm 41 scoops up the sheet to be printed 99 from the feeder board 13 to the transport drum 42, and then the transport drum 42 holds the front end of the sheet to be printed 99 with the gripper 42a and sends the sheet to the printing drum 60 while winding it up. When the sheet to be printed 99 is in contact with the outer circumferential surface of the transport drum 42, the sheet to be printed 99 is heated by the heater 42b of the transport drum 42. Thereafter, the printing drum 60 holds the front end of the sheet to be printed 99 with one of the grippers 61, and the mounting table 65 next to the gripper 61 adsorbs the sheet to be printed 99 to the outer circumferential surface of the mounting table 65. The printing drum 60 sends the sheet to be printed 99 from the transport drum 42 to the inkjet heads 32 to 35 and then to the transport drum 44. When the printing sheet 99 is adsorbed to the outer periphery of the mounting table 65, the printing sheet 99 is heated by the heat of the mounting table 65, and the temperature of the printing sheet 99 becomes approximately the first target temperature (for example, 40° C.).

[0072] If the printed sheet 99 floats from the outer periphery of the mounting table 65, the printed sheet 99 will be detected by the paper float detector 72 before it reaches the inkjet head 32. If this happens, the control unit 79 receives a detection signal from the paper float detector 72, which triggers the control unit 79 to make an emergency stop of the drive device 85. As a result, the printed sheet 99 does not hit the inkjet heads 32 to 35. If the printed sheet 99 is properly attached to the outer periphery of the mounting table 65, the printed sheet 99 will not be detected by the paper float detector 72, and the operation of the drive device 85 will continue.

[0073] When the sheet to be printed 99 passes between the inkjet heads 32-35 and the printing drum 60 in the circumferential direction, the control unit 79 controls the inkjet heads 32-35 in accordance with the print job data. As a result, the inkjet heads 32-35 eject ink onto the front surface of the sheet to be printed 99, and an image is formed on the front surface of the sheet to be printed 99. Thereafter, the transport drum 44 holds the front end of the sheet to be printed 99 with the gripper 44a, and sends the sheet to be printed 99 to the selection drum 45 while winding it up.

[0074] When the print job data includes data for single-sided printing, the selection drum 45 holds the leading end of the printed sheet 99 transported by the transport drum 44 with the gripper 45a, and sends the printed sheet 99 to the transport drum 46 while winding it up. Thereafter, the transport drum 46 holds the leading end of the printed sheet 99 with the gripper 46a, and sends the printed sheet 99 to the discharge device 21 while winding it up. Thereafter, the discharge device 21 transports the printed sheet 99 to the paper output tray 22.

[0075] When the print job data includes data for double-sided printing, the selection drum 45 holds the leading end of the sheet to be printed 99 conveyed by the conveying drum 44 with the gripper 45a, and sends the sheet to be printed 99 to the reversing drum 47 while winding it up. Thereafter, the reversing drum 47 holds the leading end of the sheet to be printed 99 with the gripper 47a, and winds up the sheet to be printed 99 from the selection drum 45. At that time, the sheet to be printed 99 is turned over. Thereafter, the swing arm 48 transfers the trailing end of the sheet to be printed 99 from the reversing drum 47 to one of the grippers 61 of the printing drum 60, and the printing drum 60 holds the trailing end of the sheet to be printed 99 with the gripper 61, and sends the sheet to be printed 99 from the reversing drum 47 to the conveying drum 44 while winding it up. When the print sheet 99 passes between the inkjet heads 32-35 and the printing drum 60 in the circumferential direction, the control unit 79 controls the inkjet heads 32-35 in accordance with the print job data, whereby the inkjet heads 32-35 eject ink onto the rear surface of the print sheet 99, forming an image on the rear surface of the print sheet 99. The print sheet 99 passes from the printing drum 60 sequentially through the transport drum 44, the selection drum 45, and the transport drum 46, and is discharged by the discharger 21.

[0076] The control unit 79 continuously operates the drive unit 85, the vacuum and the delivery 20, and causes the feeder 10 to perform a periodic feeding operation, whereby single-sided or double-sided printing is performed on a plurality of printing sheets 99.

[0077] When the number of print sheets 99 corresponding to the number data included in the print job data has been fed by the feeder 10, the control unit 79 stops the feeding operation of the feeder 10. Thereafter, when single-sided or double-sided printing on the last print sheet 99 is completed and the last print sheet 99 is discharged by the discharger 21, the control unit 79 stops the supply of power to the heaters 42b, 81, thereby causing the heaters 42b, 81 to stop generating heat. Furthermore, the control unit 79 turns off the ultraviolet irradiator 50.

[0078] Thereafter, when the control unit 79 stops the drive device 85, the transport drum 42, the printing drum 60, the transport drum 44, the selection drum 45, the transport drum 46, the reversing drum 47, and the swing arm 48 stop. Furthermore, the control unit 79 stops the vacuum and the delivery 20.

[0079] <<Stretching of resin sheet>> Since the resin sheet 65e is taut, the resin sheet 65e stretches over time. When the printing device 1 performs printing operations many times, creep occurs in the resin sheet 65e, and the resin sheet 65e stretches over time due to heat and tension. The stretching of the resin sheet 65e causes wrinkles in the resin sheet 65e. If wrinkles occur in the resin sheet 65e, the printed sheet 99 will float from the outer circumferential surface of the printing drum 60 during the printing operation of the printing device 1. Therefore, the printing device 1, and particularly the printing drum 60, are maintained by operating the printing device 1 as follows to eliminate the stretching of the resin sheet 65e.

[0080] <<Operation and maintenance of printing equipment to eliminate stretching of resin sheets>> When the user gives a command to the control unit 79 using an input device such as a push button switch or a touch panel, the printing device 1 operates as follows. Alternatively, in an inspection mode or the like that does not involve printing, if the inspector 73 detects wrinkles in the resin sheet 65e while the print drum 60 is rotating, the printing device 1 operates as follows. Alternatively, in an inspection mode or the like that does not involve printing, if the paper floating detector 72 detects wrinkles in the resin sheet 65e while the print drum 60 is rotating, the printing device 1 operates as follows. The following operations contribute to the maintenance of the printing device 1, and in particular the print drum 60.

[0081] The control unit 79 controls the actuator 65i, which causes the actuator 65i to move the holder 65h closer to the rear end 65c2 of the box body 65c. This causes the resin sheet 65e to relax. Alternatively, the user may manually move the holder 65h closer to the rear end 65c2 of the box body 65c to relax the resin sheet 65e.

[0082] The control unit 79 controls the actuator 86, which then retracts the inkjet heads 32 to 35 to the retracted position. Alternatively, the user may manually retract the inkjet heads 32 to 35 to the retracted position.

[0083] The control unit 79 controls the actuator 87, which moves the ultraviolet irradiator 50 closer to the outer circumferential surface 62 of the print drum 60, thereby positioning the ultraviolet irradiator 50 at the first proximity position. Note that the user may manually move the ultraviolet irradiator 50 closer to the outer circumferential surface 62 of the print drum 60.

[0084] The control unit 79 controls the actuator 88, which moves the heater 81 closer to the outer circumferential surface 62 of the print drum 60 and positions the heater 81 at the second proximity position. Alternatively, the user may manually move the heater 81 closer to the outer circumferential surface 62 of the print drum 60.

[0085] Next, the control unit 79 controls the drive device 85, and the print drum 60 is rotated and driven by the drive device 85. The rotation speed of the print drum 60 at this time is lower than the rotation speed of the print drum during printing. While the print drum 60 is rotating, the control unit 79 ignores the signal of the paper lift detector 72. In other words, even if wrinkles or sagging of the resin sheet 65e are detected by the paper lift detector 72, the control unit 79 ignores it and continues to operate the drive device 85. Since the inkjet heads 32-35 are retracted to the retracted position, the resin sheet 65e does not come into contact with the inkjet heads 32-35 even if the resin sheet 65e is relaxed.

[0086] Next, the control unit 79 drives the heater 42b, the heater 81, and the ultraviolet irradiator 50. Then, the temperature of the transport drum 42 rises due to the heat from the heater 42b. The outer peripheral surface of the print drum 60 rises due to the heat from the heater 42b, the heater 81, and the ultraviolet irradiator 50. Because the ultraviolet irradiator 50 and the heater 81 are located at the first proximity position and the second proximity position, respectively, the outer peripheral surface of the print drum 60 is efficiently heated and tends to reach a high temperature.

[0087] Here, the control unit 79 controls at least one of the heater 42b, the heater 81, and the ultraviolet irradiator 50 based on the temperature detected by the temperature sensor 71, thereby maintaining the temperature of the outer circumferential surface of the print drum 60 at the second target temperature. For example, if the temperature detected by the temperature sensor 71 exceeds an upper limit value higher than the second target temperature, the control unit 79 reduces the output power of at least one of the heater 42b, the heater 81, and the ultraviolet irradiator 50. For example, if the temperature detected by the temperature sensor 71 falls below a lower limit value lower than the second target temperature, the control unit 79 increases the output power of at least one of the heater 42b, the heater 81, and the ultraviolet irradiator 50.

[0088] Furthermore, the control unit 79 controls the speed of the drive device 85 and the print drum 60 based on the temperature detected by the temperature sensor 71, thereby maintaining the outer peripheral surface of the print drum 60 at the second target temperature. For example, if the temperature detected by the temperature sensor 71 exceeds an upper limit value that is higher than the second target temperature, the control unit 79 reduces the speed of the drive device 85 and the print drum 60. For example, if the temperature detected by the temperature sensor 71 falls below a lower limit value that is lower than the second target temperature, the control unit 79 increases the speed of the drive device 85 and the print drum 60. Such control by the control unit 79 contributes to maintaining the temperature of the outer peripheral surface 62 of the print drum 60 at the second target temperature.

[0089] The second target temperature is a temperature that causes thermal shrinkage in the resin sheet 65e. The second target temperature is equal to or higher than the temperature of the ink during printing. The second target temperature is higher than the first target temperature. The second target temperature is, for example, 80 to 200°C, preferably 100 to 200°C, and more preferably 120°C.

[0090] As described above, the tension of the resin sheet 65e is released and the resin sheet 65e is heated, whereby the resin sheet 65e undergoes thermal contraction.

[0091] After the resin sheet 65e has thermally shrunk, the control unit 79 stops the power supply to the heaters 42b, 81, thereby stopping the heat generation of the heaters 42b, 81. Furthermore, the control unit 79 turns off the ultraviolet irradiator 50.

[0092] Next, the control unit 79 controls the actuator 65i, causing the actuator 65i to move the holder 65h away from the rear end 65c2 of the box body 65c. This causes the resin sheet 65e to become taut, and wrinkles in the resin sheet 65e are eliminated. When wrinkles in the resin sheet 65e are no longer detected by the inspector 73 while the actuator 65i is in operation, the control unit 79 stops the actuator 65i. Note that the user may manually move the holder 65h away from the rear end 65c2 of the box body 65c to taut the resin sheet 65e.

[0093] Subsequently, when the control unit 79 stops the drive device 85, the printing drum 60 stops.

[0094] Next, the control unit 79 controls the actuator 87 to move the ultraviolet irradiator 50 away from the outer circumferential surface 62 of the print drum 60 and position the ultraviolet irradiator 50 at the first separated position. Note that the user may manually move the ultraviolet irradiator 50 away from the outer circumferential surface 62 of the print drum 60.

[0095] The control unit 79 controls the actuator 88, which moves the heater 81 away from the outer circumferential surface 62 of the print drum 60 to position the heater 81 at the second separated position. Note that the user may manually move the heater 81 away from the outer circumferential surface 62 of the print drum 60.

[0096] The control unit 79 controls the actuator 86, which then moves the inkjet heads 32 to 35 to the printable positions. Alternatively, the user may manually move the inkjet heads 32 to 35 to the printable positions.

[0097] <<Summary>> As described above, the printing device 1 includes the printing drum 60, the heater 81, the ultraviolet irradiator 50, and the heater 42b. The printing drum 60 has a heat-shrinkable resin sheet 65e on the outer peripheral surface 62 of the printing drum 60. The printing drum 60 includes a tension adjustment mechanism having a holder 65f, a holder 65h, an actuator 65i, and a guide 65j in a slot 67 on the outer peripheral surface 62. After the tension of the resin sheet 65e is loosened by the tension adjustment mechanism, the outer peripheral surface 62 of the printing drum 60 is heated by at least one of the heater 81, the ultraviolet irradiator 50, and the heater 42b. Then, thermal contraction occurs in the resin sheet 65e, and the stretch of the resin sheet 65e is eliminated. After the outer peripheral surface 62 of the printing drum 60 is heated, the resin sheet 65e is tensioned by the tension adjustment mechanism, and wrinkles in the resin sheet 65e are eliminated.

[0098] The resin sheet 65e thermally shrinks during maintenance of the print drum 60. Therefore, even if maintenance of the print drum 60 is performed multiple times, the movable range of the holder 65h is ensured, and the resin sheet 65e can be loosened and tensioned multiple times by the reciprocating movement of the holder 65h.

[0099] When the resin sheet 65e is heated, the tension of the resin sheet 65e is relaxed by the tension adjustment mechanism, which suppresses the extension of the resin sheet 65e softened by heating.

[0100] When the outer peripheral surface 62 of the printing drum 60 is heated by at least one of the heater 81, the ultraviolet irradiator 50, and the heater 42b after the tension of the resin sheet 65e has been loosened by the tension adjustment mechanism, the printing drum 60 is rotationally driven by the drive device 85. This contributes to the resin sheet 65e being heated uniformly overall and thermally shrinking uniformly overall.

[0101] During maintenance of the print drum 60, the control unit 79 ignores the signal from the paper float detector 72 and continues operation of the drive device 85. Therefore, even if wrinkles or sagging of the resin sheet 65e are detected by the paper float detector 72 during maintenance of the print drum 60, the maintenance of the print drum 60 continues.

[0102] During maintenance of the print drum 60, the control unit 79 controls the speed of the drive device 85 based on the temperature detected by the temperature sensor 71. Therefore, the temperature of the resin sheet 65e is controlled to be a constant temperature at an appropriate second target temperature.

[0103] During maintenance of the print drum 60, the control unit 79 controls at least one of the heater 81, the ultraviolet irradiator 50, and the heater 42b based on the temperature detected by the temperature sensor 71. Therefore, the temperature of the resin sheet 65e is controlled to be a constant temperature at an appropriate second target temperature.

[0104] The heater 81 is used to heat the outer peripheral surface 62 of the print drum 60 in order to improve the quality of the printed image during printing. The heater 81 is used to heat the outer peripheral surface 62 of the print drum 60 in order to thermally shrink the resin sheet 65e during maintenance. Because the heater 81 is used for both of these purposes, the number of parts in the printing device 1 does not increase.

[0105] The ultraviolet irradiator 50 is used for fixing and curing the ink during printing. The ultraviolet irradiator 50 is also used for heating the outer peripheral surface 62 of the print drum 60 for the purpose of thermally shrinking the resin sheet 65e during maintenance. Because the ultraviolet irradiator 50 is used for both of these purposes, the number of parts of the printing device 1 does not increase.

[0106] The heater 42b is used to heat the print sheet 99 in order to improve the quality of the printed image during printing. The heater 42b is used to heat the outer circumferential surface 62 of the print drum 60 in order to thermally shrink the resin sheet 65e during maintenance. Because the heater 42b is used for both of these purposes, the number of parts in the printing device 1 does not increase.

[0107] During printing, the ultraviolet irradiator 50 is located at the first separated position. During maintenance, the ultraviolet irradiator 50 approaches the outer peripheral surface 62 of the print drum 60 from the first separated position. Therefore, the outer peripheral surface 62 of the print drum 60 is efficiently heated during maintenance, and the temperature of the outer peripheral surface 62 of the print drum 60 during maintenance becomes higher than the temperature of the outer peripheral surface 62 of the print drum 60 during printing.

[0108] During printing, the heater 81 is located at the second separated position. During maintenance, the heater 81 approaches the outer peripheral surface 62 of the print drum 60 from the second separated position. Therefore, the outer peripheral surface 62 of the print drum 60 is efficiently heated during maintenance, and the temperature of the outer peripheral surface 62 of the print drum 60 during maintenance becomes higher than the temperature of the outer peripheral surface 62 of the print drum 60 during printing.

[0109] During printing, the inkjet heads 32-35 are located in the printable position. During maintenance, the inkjet heads 32-35 move from the printable position to the retracted position, and thereby the inkjet heads 32-35 move away from the outer circumferential surface 62 of the print drum 60. Therefore, even if the resin sheet 65e is bent during maintenance, the resin sheet 65e does not come into contact with the inkjet heads 32-35.

[0110] <<Modifications>> The following describes modifications from the above embodiment. Some of the modifications described below may be combined and used.

[0111] (1) In the above embodiment, the number of grippers 61, the number of mounting bases 65, and the number of slots 67 are 3. In contrast, the number of grippers 61, the number of mounting bases 65, and the number of slots 67 may be 1 or 2, or may be 4 or more. Even if the number of grippers 61 and mounting bases 65 changes, the pitch of the grippers 61 and the circumferential length of the mounting bases 65 do not change, and the diameter of the printing drum 60 increases as the number of grippers 61 increases.

[0112] (2) In the above embodiment, three rectangular resin sheets 65e are stretched over the outer circumferential surface 62 of the print drum 60. Alternatively, one tubular resin sheet may be stretched over the outer circumferential surface 62 of the print drum 60. In this case, an adjustment mechanism for adjusting the position of the box body 65c in the radial direction is attached between the box body 65c and the flange 64. When the position of the box body 65c is adjusted radially inward by the adjustment mechanism, the tension of the resin sheets is relaxed. When the position of the box body 65c is adjusted radially outward by the adjustment mechanism, the resin sheets are stretched. In addition, the resin sheets have openings at positions overlapping with the slots 67. [Explanation of symbols]

[0113] 1 Printing device 32-35 Inkjet head 42b Heater 50 UV irradiator 60 Printing drums 61 Gripper 62 Outer surface 65e Resin sheet 65g holder 65h retainer 65i Actuator 65j Guide 71 Temperature Sensor 72 Paper lift detector 73 Inspection Equipment 79 Control Unit 81 Heater 85 Drive unit 86-88 Actuator 99 Printed Sheets

Claims

1. a printing drum having a heat-shrinkable resin sheet on its outer peripheral surface, the printing drum having a tension adjustment mechanism for stretching the resin sheet on the outer peripheral surface and loosening the tension of the resin sheet; a heater for heating the outer peripheral surface of the printing drum; Equipped with After the tension adjustment mechanism releases the tension of the resin sheet, the heater heats the outer circumferential surface of the printing drum, After the outer peripheral surface of the printing drum is heated, the tension adjustment mechanism tensions the resin sheet on the outer peripheral surface. Printing device.

2. The printing apparatus further includes a drive device that drives the printing drum to rotate, When the heater heats the outer circumferential surface of the printing drum after the tension adjustment mechanism releases the tension of the resin sheet, the drive device drives the printing drum to rotate. The printing device of claim 1 .

3. a lift detector that detects whether the sheet that is attracted to the outer peripheral surface of the printing drum during printing has lifted from the outer peripheral surface of the printing drum; a control unit that operates the drive device during printing and stops the drive device when the lift detector detects lifting of the sheet; Equipped with When the heater heats the outer peripheral surface of the printing drum after the tension adjustment mechanism releases the tension of the resin sheet, the control unit ignores the signal from the float detector and continues to operate the drive device. The printing device according to claim 2 .

4. a print head that is movable between a printable position facing the outer circumferential surface of the printing drum and a retreated position that is farther from the outer circumferential surface of the printing drum than the printable position; Further comprising: During printing, the print head is disposed at the printable position, When the heater heats the outer circumferential surface of the printing drum after the print head has been moved to the retracted position and the tension adjustment mechanism has released the tension of the resin sheet, the drive device drives the printing drum to rotate.

4. The printing device according to claim 2 or 3.

5. a temperature sensor for detecting the outer peripheral surface of the printing drum; When the heater heats the outer peripheral surface of the printing drum after the tension adjustment mechanism releases the tension of the resin sheet, the control unit controls the speed of the driving device based on the temperature detected by the temperature sensor. The printing device according to claim 3 .

6. The heater is a convection heater, a radiation heater, or a contact heater. The printing device of claim 1 .

7. The heater is an ultraviolet irradiator. The printing device of claim 1 .

8. The ultraviolet irradiator is used to harden the ink attached to the sheet adsorbed on the outer peripheral surface of the printing drum during printing. The printing device according to claim 7.

9. The heater is used to heat a transport drum that is adjacent to the outer periphery of the printing drum and that winds the sheet around the printing drum. The printing device of claim 1 .

10. The heater heats the outer peripheral surface of the printing drum during printing, The heater is a convection heater or a radiation heater, The position of the heater when the heater heats the outer peripheral surface of the printing drum after the tension adjustment mechanism loosens the tension of the resin sheet is closer to the outer peripheral surface of the printing drum than the position of the heater during printing. The printing device of claim 1 .

11. The heater heats the outer peripheral surface of the printing drum during printing. The printing device of claim 1 .

12. The temperature of the outer circumferential surface of the printing drum heated by the heater after the tension adjustment mechanism loosens the tension of the resin sheet is higher than the temperature of the outer circumferential surface of the printing drum heated by the heater during printing. The printing device of claim 11.

13. The tension adjustment mechanism is manual or automatic. The printing device of claim 1 .

14. The temperature of the outer circumferential surface of the printing drum heated by the heater after the tension adjustment mechanism loosens the tension of the resin sheet is higher than the temperature of ink ejected by the print head during printing. The printing device of claim 1 .

15. A temperature sensor for detecting the outer circumferential surface of the printing drum The printing device of claim 1 .

16. a control unit that controls the heater based on a temperature detected by the temperature sensor when the heater heats the outer peripheral surface of the printing drum after the tension adjustment mechanism releases the tension of the resin sheet. The printing device of claim 15 further comprising:

17. a relaxation step of relaxing the tension of a heat-shrinkable resin sheet provided and stretched on the outer peripheral surface of the printing drum; a heating step of thermally shrinking the resin sheet by heating the resin sheet relaxed in the relaxation step; a tensioning step of tensioning the resin sheet on an outer circumferential surface of the printing drum after the heating step; Maintenance methods including.

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