Medium transport device and printer

Abstract

To provide a medium transport device which achieves reduction of fluctuation of tension applied to a medium, and to provide a printer.SOLUTION: A medium transport device 100 includes: a medium support part 101 which supports a transported medium M; a take-up part 109 which takes up the medium M; a tension bar 103 which applies tension to the medium M between the medium support part 101 and the take-up part 109; an arm part 105 which supports the tension bar 103 at one end; a rotation part 107 which rotatably supports the other end of the arm part 105; and a power source 106 which applies a force for rotating the arm part 105. The power source 106 applies the force to the arm part 105 so that an amount of change of a moment has a sign opposite to that of an amount of change of a moment Wm generated by self-weights of the tension bar 103 and the arm part 105.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a medium transport device and a printing device. [Background technology]

[0002] Conventionally, there have been known media transport devices that wind continuous form media, such as roll paper, onto a roll body. Some of these devices are equipped with a tension bar to improve the media winding accuracy. For example, Patent Document 1 discloses a printing device that applies tension to the media by swinging a swing arm. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-268824 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the device described in Patent Document 1 had a problem in that the tension applied to the medium was prone to fluctuation. Specifically, when the swing arm swings under its own weight, the roll paper (the medium) is bent in a U-shape, applying tension. In other words, the strength of the applied tension depended on the mass of the swing arm and the tension bar. As a result, the degree of bending of the roll paper changed depending on the position of the swing arm during the swing process, making the tension prone to fluctuation. When the tension fluctuated, winding accuracy could decrease, potentially causing problems such as misalignment. In other words, there was a need for a media transport device that reduced the fluctuation in tension applied to the medium. [Means for solving the problem]

[0005] The medium transport device comprises a medium support section that supports the medium to be transported, a winding section that winds up the medium, a tension bar that applies tension to the medium between the medium support section and the winding section, an arm section that supports the tension bar at one end, a rotating section that rotatably supports the other end of the arm section, and a power source that applies a force to rotate the arm section, and is characterized in that the power source applies the force to the arm section so that the amount of change in moment due to the weight of the tension bar and the arm section is opposite in sign to the amount of change in moment.

[0006] The printing device comprises a printing unit that prints on a medium, a medium support unit that supports the medium being transported, a winding unit that winds up the medium, a tension bar that applies tension to the medium between the medium support unit and the winding unit, an arm unit that supports the tension bar at one end, a rotating unit that rotatably supports the other end of the arm unit, and a power source that applies a force to rotate the arm unit, and is characterized in that the power source applies the force to the arm unit so that the amount of change in moment due to the weight of the tension bar and the arm unit is opposite in sign to the amount of change. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a printing apparatus according to a first embodiment. [Figure 2] FIG. 1 is a perspective view showing the appearance of a printing apparatus. [Figure 3] FIG. 2 is a side view showing the configuration of a power source, a rotating unit, an arm unit, and the like. [Figure 4] FIG. 1 is a perspective view showing the arrangement of a power source, a rotating unit, an arm unit, and the like. [Figure 5] 6 is a graph showing the relationship between the operating angle of the arm and various moments. [Figure 6] FIG. 10 is a schematic diagram showing the configuration of a rotating section, a power source, and the like according to a second embodiment. [Figure 7] 6 is a graph showing the relationship between the operating angle of the arm and various moments. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the following embodiments, a medium transport device and a printing device equipped with the medium transport device are illustrated and described with reference to the drawings. The printing device in the following embodiment is a large-format printer that prints on continuous form sheets. Note that the medium transport device of the present invention is not limited to being equipped in a printing device, and the printing device of the present invention is not limited to the following configuration.

[0009] In the following figures, X, Y, and Z axes are used as mutually orthogonal coordinate axes, with the direction indicated by each arrow being the + direction and the direction opposite the + direction being the - direction. When the printing device is installed on a horizontal surface, the -Z direction is the vertical direction. In the following explanation, the +Z direction is referred to as the upward direction and the -Z direction is referred to as the downward direction. In the following figures, the sizes of the components are different from their actual sizes for the sake of convenience.

[0010] 1. First embodiment As shown in Figure 1, the printing device 1 according to this embodiment includes a structural member 10, a feeding unit 20, medium support members 30 and 50, a transport unit 40, a printing unit 60, a blower unit 80, a medium transport device 100, and a housing (not shown). The printing device 1 also includes a control unit (not shown). The control unit comprehensively controls the operation of each component of the printing device 1, including the medium transport device 100. The medium transport device 100 is an example of a medium transport device of the present invention.

[0011] For convenience of illustration, a housing that houses the printing unit 60 and the like is omitted from Fig. 1. In the following description of Fig. 1, unless otherwise specified, the state viewed from the -X direction will be described.

[0012] The printing device 1 produces printed matter by applying ink to a medium M, which is a continuous form sheet. In the printing device 1, the medium M is unwound from a roll R1, which is an original roll, to become a printed matter, and the printed matter is then wound up into a roll R2.

[0013] The control unit includes hardware such as a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The control unit controls the printing device 1 by executing a predetermined control program using the CPU. The ROM is a non-volatile storage device that stores the control program executed by the CPU and data processed by the control program. The RAM forms the CPU's work area. The CPU loads the control program read from the ROM or the like into the RAM, and executes the loaded control program to control the printing device 1.

[0014] The path along which the medium M moves from when it is unwound from the roll R1 until it is wound up as the roll R2 is referred to as the transport path. In FIG. 1, the transport path is indicated by a dashed line. In the transport path, the original web side of the medium M is also referred to as the upstream side, and the side along which the medium M and printed matter travel is also referred to as the downstream side. In the transport path, from upstream to downstream, the following are arranged in this order: a payout unit 20, a medium support member 30, a transport unit 40, a medium support member 50, a printing unit 60, a medium transport device 100, and a blower unit 80. In the transport path, the direction along which the medium M travels from upstream to downstream is also referred to as the transport direction.

[0015] The structural member 10 is a frame that supports the above-mentioned components of the printing device 1. The structural member 10 is made by assembling a plurality of sheet metal members, tubular members, etc. Casters, installation members, etc. may be arranged on the portion of the structural member 10 that comes into contact with the floor below.

[0016] The unwinding unit 20 includes a roll body holding unit 21. The unwinding unit 20 is disposed in the -Y direction below the printing device 1. The roll body holding unit 21 supports the roll body R1 so that it can rotate about an axis along the X axis. The medium M is pulled by the transport unit 40 and unwound from the roll body R1 and supplied downstream. The roll body R1 is detachable from the printing device 1. The medium M is transported by the transport unit 40 from the roll body holding unit 21 in a substantially upward direction and advances to the medium support member 30.

[0017] The medium M is appropriately selected depending on the type of ink to be applied to the medium M and the purpose of the printed matter. In the printing device 1, so-called soft solvent ink is used as the ink, and therefore a polyvinyl chloride sheet or the like is used as the medium M.

[0018] The medium support member 30 has a curved surface that is approximately arc-shaped, and supports the medium M being transported. The transport direction of the medium M is changed from a substantially upward direction to a substantially +Y direction by the curved surface of the medium support member 30. The medium M is transported while sliding in contact with the curved surface of the medium support member 30. The medium M proceeds from the medium support member 30 to the transport section 40.

[0019] Although not shown in the drawings, the medium support member 30 has a built-in electric heater that heats the medium M. The electric heater preheats the medium M before ink is applied to it. This improves the fixability and solubility of the ink on the medium M.

[0020] The transport unit 40 includes transport rollers 41 and 42. The transport rollers 41 and 42 form a pair, with their sides in contact with each other. The transport roller 41 is disposed below the transport path, and the transport roller 42 is disposed above the transport path. The transport rollers 41 and 42 each rotate around an axis along the X-axis.

[0021] The transport roller 41 is driven to rotate by a drive motor (not shown). The transport roller 42 is a driven roller, and rotates in the opposite direction to the transport roller 41 as the transport roller 41 rotates. When the transport roller 41 rotates counterclockwise, the transport roller 42 rotates clockwise. As a result, the medium M is sandwiched between the transport rollers 41 and 42 and transported downstream. The medium M then advances to the medium support member 50.

[0022] The medium support member 50 is a member that constitutes a so-called platen. The upper surface of the medium support member 50 is along the XY plane and supports the medium M. In the medium support member 50, the transport direction of the medium M is the +Y direction. The surface of the medium M facing upward is the printing surface.

[0023] Although not shown in the figures, the medium support member 50 has a built-in electric heater that heats the medium M. The electric heater heats the medium M when the ink is applied to it. This improves the fixability and solubility of the ink on the medium M, and also makes it easier for volatile components such as solvents contained in the ink to volatilize.

[0024] The printing unit 60 prints on the medium M. The printing unit 60 includes a head 61 and a carriage 62. The printing unit 60 is disposed above the medium support member 50. The carriage 62 is supported above the structural member 10 so as to be capable of reciprocating movement along the X axis. The reciprocating movement is driven by a carriage motor (not shown). The carriage 62 supports the head 61 above the medium support member 50.

[0025] The head 61 deposits ink on the printing surface of the medium M supported on the upper surface of the medium support member 50. The head 61 moves back and forth along the X axis together with the carriage 62 within a range that includes the area that faces the medium support member 50 in the vertical direction.

[0026] Although not shown in the figure, a nozzle surface is arranged on the downward-facing surface of the head 61. Multiple nozzle rows are provided on the nozzle surface. Each nozzle row is made up of multiple nozzles that eject ink. Ink of each color, such as black, cyan, yellow, and magenta, is supplied to each nozzle row individually from an ink storage container (not shown). Each color ink is ejected from each nozzle row toward the printing surface of the medium M.

[0027] As described above, the ink used in the printing device 1 is soft solvent ink. Soft solvent ink is, for example, a solvent ink that does not contain intentionally added water and contains a glycol ether-based solvent, a lactone-based solvent, or the like as the main solvent. Note that the ink ejected by the head 61 may also contain a treatment liquid and a clear ink that does not contain a colorant.

[0028] On the medium support member 50, the head 61 moves back and forth along the X axis together with the carriage 62 while the medium M is transported in the +Y direction. At this time, ink is applied to the printing surface of the medium M at any timing, thereby printing images such as pictures, photographs, text, and patterns on the medium M. The medium M on which the printing has been performed is pulled by the medium transport device 100 and proceeds downstream to the medium transport device 100 and the air blower 80.

[0029] The medium conveying device 100 includes a medium support unit 101, a heating unit 102, a tension bar 103, an arm unit 105, a rotating unit 107, a winding unit 109, and a power source 106, which will be described later.

[0030] Each component of the medium transport device 100 is supported by a structural member 10 and is arranged in the +Y direction of the printing device 1. In the medium transport device 100, the medium support unit 101, tension bar 103, and winding unit 109 are arranged in the above order in the transport direction.

[0031] The medium support part 101 has a curved surface that serves as a surface for supporting the medium M, and supports the medium M being transported. The curved surface of the medium support part 101 faces substantially upward within the medium support part 101. The medium M is transported while sliding in contact with the curved surface of the medium support part 101. In the direction along the X axis, the length of the curved surface of the medium support part 101 is longer than the length of the medium M. The transport direction of the medium M is changed from the +Y direction to the +Y direction and slightly downward by the curved surface of the medium support part 101.

[0032] The medium support unit 101 has a pair of side walls 101p. The side walls 101p are respectively arranged at the end of the medium support unit 101 in the +X direction and the end in the -X direction. Each side wall 101p is a substantially plate-shaped member and is formed, for example, from sheet metal. Each side wall 101p includes a surface that extends along the YZ plane and intersects with the curved surface of the medium support unit 101.

[0033] The medium support unit 101 has a heating unit 102. The heating unit 102 is an electric heater. The heating unit 102 heats the medium M supported on the curved surface of the medium support unit 101. The heating unit 102 is disposed inside the curved surface of the medium support unit 101. By applying heat, the heating unit 102 promotes the evaporation of volatile components contained in ink adhered to the medium M. This makes it possible to prevent ink components from adhering to other locations when the medium M is wound onto the roll R2 in the winding unit 109.

[0034] The air blowing unit 80 blows air onto the printing surface of the medium M to assist in the evaporation of the volatile components. The air blowing unit 80 is supported by the structural member 10 above the transport path of the medium support unit 101. The air blowing unit 80 blows air over the entire range of the medium M along the X-axis.

[0035] Heating by the heating unit 102 and air blowing by the air blowing unit 80 promotes drying of the ink attached to the medium M. This allows the downstream winding unit 109 to wind up the medium M. The medium M is pulled and transported by the winding unit 109 and advances to the tension bar 103.

[0036] The tension bar 103 applies tension to the medium M between the medium support unit 101 and the winding unit 109 in the transport path. The tension bar 103 is a substantially cylindrical member, and the longitudinal direction of the cylinder is arranged along the X axis. The -X direction end and +X direction end of the tension bar 103 are each supported by arm units 105. The tension bar 103 is supported by the pair of arm units 105 and protrudes slightly downward in the +Y direction from the medium support unit 101.

[0037] If the tension bar 103 were not included, the medium M would proceed from the +Y end of the medium support unit 101 to the winding unit 109 located substantially below. In contrast, in the printing device 1, the tension bar 103 protrudes downward from the medium support unit 101 and slightly in the +Y direction. Therefore, the medium M is transported while being pushed substantially in the +Y direction by the tension bar 103. As a result, the medium M is wound up by the winding unit 109 while tension is applied to it.

[0038] The surface of the tension bar 103, which corresponds to the side of the cylinder, is formed smoothly with relatively low friction resistance. Therefore, the medium M slides along the side of the tension bar 103 even while tension is being applied. The side of the cylinder of the tension bar 103 may be covered with a sheet-like member to prevent direct contact with the medium M. The tension bar 103 does not rotate relative to the arm portion 105.

[0039] Each arm 105 is a generally rod-shaped member. When the tension bar 103 is in a functional state, each arm 105 supports the tension bar 103 at one end substantially in the +Y direction. The other end of each arm 105 substantially in the -Y direction is rotatably supported by a rotating portion 107.

[0040] In a plan view from above, the length, which is the distance between one end and the other end of each arm portion 105, is shorter than the length along the transport direction of the medium support portion 101. Therefore, the arm portion 105 and the like are relatively small in size.

[0041] The rotating units 107 are arranged corresponding to the respective arm units 105. More specifically, the rotating units 107 are provided on the +X direction side wall 101p and the -X direction side wall 101p of the medium support unit 101. This makes it difficult for the rotating units 107 to interfere with the medium M, allowing the medium conveying device 100 to be made smaller.

[0042] Here, the rotating unit 107 is not limited to being disposed on the side wall 101p. The rotating unit 107 may also be disposed on the structural member 10. Specifically, for example, the rotating unit 107 may be disposed near the lower side of the structural member 10. In this case, the arm unit 105 is extended to apply tension to the medium M between the medium support unit 101 and the winding unit 109.

[0043] Each rotating unit 107 rotates clockwise and counterclockwise around the vicinity of the other end of the arm unit 105 as a rotation center due to the force applied by the power source 106 (described later). One end of each arm unit 105 rotates clockwise and counterclockwise while supporting the tension bar 103. This changes the position of the tension bar 103, particularly the protruding distance from the medium support unit 101 in the +Y direction, thereby adjusting the strength of the tension applied to the medium M. Specifically, when the tension bar 103 rotates clockwise, the protruding distance of the tension bar 103 from the medium support unit 101 in the +Y direction increases, and the medium M is pushed in the +Y direction, applying strong tension. On the other hand, when the tension bar 103 rotates counterclockwise, the protruding distance of the tension bar 103 from the medium support unit 101 in the +Y direction decreases, and the force pushing the medium M in the +Y direction weakens, reducing the applied tension.

[0044] Each rotating unit 107 is provided at a position closer to the downstream end (+Y direction end) of the medium support unit 101 than to the upstream end (-Y direction end) of the medium support unit 101 with respect to the transport direction of the medium M. This reduces the length of the arm unit 105 compared to when each rotating unit 107 is provided closer to the upstream end of the medium support unit 101.

[0045] The conveying direction of the medium M is changed from a downward direction in the +Y direction to a downward direction in the −Y direction by the tension bar 103. The medium M passes through the tension bar 103 and advances to the winding section 109.

[0046] The winding unit 109 winds the medium M onto the roll R2. The winding unit 109 includes a roll holder 109a. The winding unit 109 is disposed in the +Y direction below the printing device 1. The roll holder 109a rotates counterclockwise by the rotational drive of a drive motor (not shown), and winds the medium M onto the roll R2. At this time, the roll R2 rotates around an axis along the X axis.

[0047] When the medium M is wound onto the roll R2, the tension applied by the tension bar 103 improves the winding accuracy. As a result, misalignment of both ends of the medium M along the X axis is reduced, resulting in a roll R2 with both ends relatively aligned. In addition, the applied tension reduces gaps between the stacked pieces of medium M, resulting in a dense roll R2. There is an appropriate range for the strength of the tension applied to the medium M. The tension is set appropriately depending on the type and dimensions of the medium M, etc.

[0048] As a result of the above, the medium M, which is the printed matter, becomes the roll R2. The roll R2 can be removed from the printing device 1 in approximately the +Y direction.

[0049] As shown in Fig. 2, side walls 101p are disposed at the -X direction end and the +X direction end of the medium support unit 101. A rotating unit 107, an arm unit 105, and a power source 106 (not shown) are disposed on each side wall 101p. The tension bar 103 is supported at both ends along the X axis by the arm unit 105. Note that other components of the printing device 1, including the housing and printing unit 60, are not shown in Fig. 2.

[0050] As shown in Fig. 3, a power source 106 is attached to the rotating unit 107. The rotating unit 107 has gears 107a and 107b as a reducer. Note that Fig. 3 shows the -X direction side wall 101p of the medium conveying device 100 as viewed from the -X direction. On the +X direction side wall 101p of the medium conveying device 100, each component is also arranged symmetrically with respect to a plane along the YZ plane.

[0051] In the following explanation, the configuration on the -X direction side will be explained as a representative example, and an explanation of the configuration on the +X direction side will be omitted. In addition, in the following explanation of Figures 3 and 4, the state viewed from the -X direction will be described unless otherwise specified.

[0052] The power source 106 applies a force that rotates the arm unit 105. The power source 106 is disposed outside the side wall 101p on the -X direction side, that is, on the -X direction side. This makes it less likely for the medium M to interfere with the power source 106, allowing the medium conveyance device 100 to be made more compact. Furthermore, because the power source 106 is disposed outside the side wall 101p, the power source 106 can be easily adjusted or replaced.

[0053] The power source 106 is a spring. Examples of springs include a coil spring, a torsion spring, and a leaf spring. In this embodiment, a coil spring is used as the spring of the power source 106. By using a spring as the power source 106, a rotational force is applied to the arm portion 105 by the elasticity of the spring. This eliminates the need for a drive mechanism such as an electric motor, and the power source 106 can be configured simply and inexpensively.

[0054] One end of the power source 106 is attached to the gear 107a through an opening (not shown) in the side wall 101p, and the other end of the power source 106 is attached to the side wall 101p through a support member 106a.

[0055] Power source 106 is not limited to a spring as long as it can impart a rotational force to arm portion 105. For example, a damper, a spring, an electric motor, etc. can be used as power source 106.

[0056] Gears 107a and 107b are arranged inside sidewall 101p on the -X direction side, i.e., on the +X direction side. By arranging gears 107a and 107b inside sidewall 101p, it is possible to reduce the number of components arranged outside sidewall 101p, and to prevent the length of medium conveying device 100 in the X direction from increasing. Gears 107a and 107b are supported by sidewall 101p so as to be rotatable about axes along the X axis. Gears 107a and 107b are arranged adjacent to each other in the direction along the Y axis and mesh with each other.

[0057] Gear 107b penetrates side wall 101p and is directly connected to the other end of arm 105 in the approximately -Y direction when tension bar 103 is in a functional state. Gear 107b is driven by the rotation of gear 107a and rotates about a central axis AR along the X axis. Arm 105 rotates with the rotation of gear 107b, with the central axis AR as a fulcrum. The rotation of arm 105 causes the tension bar 103 to swing like a pendulum, with the central axis AR as a fulcrum.

[0058] A locking member 101s and stoppers 108a and 108b are provided on the outside of side wall 101p on the -X direction side, i.e., on the -X direction side. Locking member 101s is disposed corresponding to one end of power source 106. Stoppers 108a and 108b are disposed corresponding to arm portion 105. Note that components such as power source 106 disposed on the outside of side wall 101p may be covered with a cover.

[0059] When the gear 107a rotates counterclockwise, the locking member 101s comes into contact with one end of the power source 106. This restricts the gear 107a from rotating further counterclockwise.

[0060] The stoppers 108a and 108b restrict the rotation of the arm unit 105 from exceeding a certain range. Specifically, the stopper 108a comes into contact with the arm unit 105 when the arm unit 105 is rotated counterclockwise by a large amount to store the arm unit 105 below the medium support unit 101. This restricts the arm unit 105 from rotating counterclockwise any further. For example, the above-described storing operation of the arm unit 105 is performed when, for example, the roll R2 (not shown) is removed from the printing device 1.

[0061] Stopper 108b restricts clockwise rotation of arm portion 105. When arm portion 105 rotates clockwise, arm portion 105 and stopper 108b come into contact with each other. This restricts further clockwise rotation of arm portion 105. Note that FIG. 3 shows a state in which arm portion 105 and stopper 108b come into contact with each other.

[0062] As shown in FIG. 4, when the tension bar 103 is in a functioning state, the power source 106 attempts to contract in the direction of the white arrow. This urges the gear 107a to rotate counterclockwise. Because the gears 107a and 107b are meshed, the rotational driving force of the gear 107a is transmitted to the gear 107b, causing the gear 107b to rotate clockwise. In conjunction with the rotation of the gear 107b, the arm 105 rotates clockwise around the central axis AR as a fulcrum. That is, the power source 106 imparts a rotational force to the arm 105 via the gears 107a and 107b, which are reducers.

[0063] 4, arm portion 105 is in a state where it is almost in contact with stopper 108b. For convenience in explaining the function of each component, the rotation directions of gears 107a and 107b and arm portion 105 are indicated by arrows, but arm portion 105 does not rotate clockwise from the state in FIG.

[0064] When the tension bar 103 is in a functional state, the arm 105 rotates clockwise, causing one end of the arm 105 in the approximately +Y direction to be raised upward. As a result, the medium M (not shown) is pushed in the approximately +Y direction by the tension bar 103, and tension is applied to the medium M.

[0065] The strength of the tension applied to the medium M is adjusted by the elastic coefficient of the power source 106, the reduction ratio of the gears 107a and 107b, the length of the arm portion 105, the mass of the arm portion 105 and the tension bar 103, and the like.

[0066] Here, the tension applied to the medium M will be described with reference to Figure 5. Figure 5 shows the relationship between the rotation angle of the arm unit 105 and various moments. In Figure 5, the horizontal axis represents the operating angle [deg], which is the rotation angle of the arm unit 105, and the vertical axis represents the magnitude of the moment [Nmm]. M on the vertical axis is a positive numerical value, and is the same numerical value as Figure 7, which will be described later.

[0067] The moment Wm is a moment due to the weight of the tension bar 103 and the arm portion 105. The moment Pm is a moment of the force applied by the power source 106. The moment Sm is a composite moment obtained by adding the moment Wm and the moment Pm together.

[0068] The rotation angle of the arm unit 105 is the rotation angle of the arm unit 105 with the central axis AR as the fulcrum. When the medium conveying device 100 is viewed from the -X direction, the position corresponding to 9 o'clock is set as the reference angle of 0 degrees, with a clockwise direction being a positive rotation angle and a counterclockwise direction being a negative rotation angle.

[0069] In a configuration without a power source, in other words, in a configuration in which tension is applied to the medium only by the weight of the tension bar and arm, the moment of the tension bar varies depending on the rotation angle of the arm.

[0070] The tension applied to the medium M is determined by the moment of the tension bar. Therefore, if the moment of the tension bar fluctuates, the tension applied to the medium also fluctuates. Fluctuations in tension can easily reduce the accuracy of winding the medium and can cause winding misalignment.

[0071] In response to this, the medium conveying device 100 reduces fluctuations in the moment of the tension bar 103 using the power source 106. Specifically, in FIG. 5, the moment Wm fluctuates by more than M / 2 when the operating angle of the arm unit 105 is in the range of -150 degrees to -20 degrees. The power source 106 applies a force that rotates the arm unit 105 so that the amount of change in the moment Wm due to the weight of the tension bar 103 and the arm unit 105 is opposite in sign to the amount of change in the moment Wm. In FIG. 5, the amount of change in the moment Wm is negative as the operating angle of the arm unit 105 moves from -150 degrees to -20 degrees, and the amount of change in the moment Pm is positive. The amounts of change in the moments Wm and Pm have opposite signs. At least, the fluctuation trends of the moments Wm and Pm include line segments with opposite signs of change within the range of the operating angle of the arm unit 105 when the tension bar 103 swings. In this embodiment, the moment Wm is a negative value, and the power source 106 applies a force to apply tension to the medium M. However, regardless of whether the moment Wm is a positive or negative value, the fluctuation of the moment Sm is reduced by adding the moment Pm.

[0072] Specifically, in the medium conveying device 100, the moment Sm, which is the resultant moment of the moments Wm and Pm, becomes the moment of the tension bar 103. The moment Pm is out of phase with the moment Wm and has an opposite sign of change. The moment Pm acts to cancel out fluctuations in the moment Wm. Therefore, fluctuations in the moment Sm are minor compared to fluctuations in the moment Wm. This reduces fluctuations in the moment of the tension bar 103, and thus reduces fluctuations in the tension applied to the medium M.

[0073] Furthermore, because the rotating unit 107 has gears 107a and 107b as reducers, it is easy to adjust the moment Pm to correspond to fluctuations in the moment Wm. Furthermore, if the moments Wm and Pm are adjusted to have an antiphase relationship, fluctuations in the moment Sm are eliminated, and a constant tension can be applied to the medium M. However, even if the moments Wm and Pm cannot be perfectly antiphased, by reversing the sign of the change, it is possible to reduce fluctuations in the moment Sm and thus fluctuations in the tension applied to the medium M.

[0074] According to this embodiment, the following effects can be obtained.

[0075] This reduces fluctuations in the tension applied to the medium M. Specifically, in this embodiment, the tension applied to the medium M depends on moment Sm, which is the sum of moment Wm and moment Pm. Because moment Wm depends on the rotation angle of the arm unit 105, moment Wm also changes when the rotation angle changes. In contrast, moment Pm has the opposite sign of change to moment Wm, thereby suppressing fluctuations in moment Wm. Therefore, moment Sm does not fluctuate as much as moment Wm, and fluctuations in moment Sm are suppressed even when the rotation angle of the arm unit 105 changes. This reduces fluctuations in the tension applied to the medium M even when the rotation angle of the arm unit 105 changes. Therefore, it is possible to provide a medium conveying device 100 and a printing device 1 that reduce fluctuations in the tension applied to the medium M.

[0076] 2. Second embodiment The printing device and medium transport device of this embodiment are different from the printing device 1 and medium transport device 100 of the above embodiment in that the configuration of the rotating unit 107 is changed. The same reference numerals are used for configurations similar to those of the printing device 1 and medium transport device 100, and duplicated explanations will be omitted.

[0077] As shown in Fig. 6, the medium conveying device of this embodiment includes a tension bar 103, an arm unit 105, a rotating unit 207, and a power source 106. Although not shown, the medium conveying device of this embodiment also includes a medium support unit 101 and a winding unit 109. Note that the description of Fig. 6 will be given from the perspective of the -X direction unless otherwise specified.

[0078] The medium conveying device of this embodiment differs from the first embodiment in that it includes a pair of rotating parts 207 instead of the pair of rotating parts 107. Each rotating part 207 has a substantially rod-shaped branch part 207a and does not have a reducer.

[0079] One end, which is the base of branch portion 207a, is rotatable about central axis AR and is directly connected to arm portion 105. Rotating portion 207 rotatably supports arm portion 105. When branch portion 207a rotates, arm portion 105 also rotates in conjunction with it. The angle formed between branch portion 207a and arm portion 105 is approximately 100 degrees, and this angle remains constant. A power source 106 is attached to the other end, which is the tip of branch portion 207a.

[0080] One end of the power source 106 is attached to a side wall 101p (not shown), and the other end is attached to the tip of the branch portion 207a. A contraction force acts on the power source 106 from the other end toward the one end, and this contraction force applies a rotational force to the rotating portion 207.

[0081] A biasing force indicated by the white arrow is applied to the branch portion 207a by the power source 106. This force causes the branch portion 207a and the arm portion 105 to rotate clockwise. Then, the tension bar 103 is displaced so as to protrude from the medium support portion 101 in approximately the +Y direction, and tension is applied to the medium M.

[0082] 7 is a graph showing the relationship between the rotation angle of the arm unit 105 in the medium conveying device of this embodiment and each moment. The horizontal and vertical axes of the graph represent the same variables as in FIG. 5. However, the numerical values and scales are different.

[0083] As shown in Fig. 7, in this embodiment as well, the moment of the tension bar 103 is moment Sm, which is the resultant moment of moments Wm and Pm. The moment due to the weight of the tension bar 103 and the arm portion 105 is moment Wm. In Fig. 7, moment Wm fluctuates by approximately M / 4 when the operating angle of the arm portion 105 is in the range of -70 degrees to -30 degrees.

[0084] In contrast, in this embodiment, the moment Pm from the power source 106 is taken into account. Because the sign of the change in the moment Pm is opposite to that of the moment Wm, the fluctuation in the moment Sm is reduced. In this embodiment, the moment Wm is a negative value, and tension is applied to the medium M by the power source 106 applying a force. However, regardless of whether the moment Wm is a positive or negative value, the fluctuation in the moment Sm is reduced by adding the moment Pm.

[0085] According to this embodiment, it is possible to obtain the same effects as the above-described embodiment, and also to have a simple configuration without a reducer. [Explanation of symbols]

[0086] 1...printing device, 60...printing unit, 100...medium transport device, 101...medium support unit, 101p...side wall, 103...tension bar, 105...arm unit, 106...power source, 107...rotating unit, 107a, 107b...gears as reducers, 109...winding unit, M...medium, Wm...moment due to own weight.

Claims

1. a medium support section that supports the medium to be transported; a winding unit that winds up the medium; a tension bar that applies tension to the medium between the medium support unit and the winding unit; an arm portion that supports the tension bar at one end; a rotation portion that rotatably supports the other end of the arm portion; a power source that applies a force that rotates the arm portion, The medium transport device is characterized in that the power source applies the force to the arm portion so that the amount of change in moment due to the tension bar and the arm portion's own weight is opposite in sign to the amount of change in moment.

2. The media transport device of claim 1 , wherein the power source is a spring.

3. the rotating part has a reducer, The medium transport device according to claim 1 , wherein the power source applies the force to the arm portion via the reducer.

4. the medium support portion has a sidewall including a surface that intersects with a surface that supports the medium; The medium transport device according to claim 1 , wherein the rotating portion is provided on the side wall.

5. The media transport device of claim 4 , wherein the power source is disposed outside the side wall.

6. a printing unit that prints on the medium; a medium support section that supports the medium to be transported; a winding unit that winds up the medium; a tension bar that applies tension to the medium between the medium support unit and the winding unit; an arm portion that supports the tension bar at one end; a rotation portion that rotatably supports the other end of the arm portion; a power source that applies a force that rotates the arm portion, a power source that applies a force to the arm portion such that the force has a sign opposite to a sign of a change in moment due to the tension bar and the arm portion's own weight;

Images