Gear pump and printing apparatus provided with same

Abstract

The present invention relates to a gear pump or the like able to effectively prevent excess heat generation between a gear shaft and a journal bearing. A gear pump (1) that lubricates gear shafts (14, 15) on which gears (12, 13) are attached and journal bearings (62, 63) that rotatably support the gear shafts (14, 15) with an ultraviolet-curable ink that is a transport target, in which a width diameter ratio that is a ratio of a bearing length of the journal bearings (62, 63) to the shaft diameter of the gear shafts (14, 15) is 0.5 to 2.0, and a clearance ratio that is a ratio of a radial clearance between the gear shafts (14, 15) and the journal bearings (62, 63) to the shaft radius of the gear shafts (14, 15) is 0.0009 to 0.01.

Description

[Technical Field]

[0001] The present invention relates to a gear pump that transports a viscous fluid and printing apparatus provided with the same.[Background Art]

[0002] In the related art, a gear pump that transports an ultraviolet-curable ink is known as this type of gear pump (refer to PTL 1).

[0003] The gear pump is provided with a drive shaft that inputs the power from a motor via a power transmission mechanism, a driving gear attached to the drive shaft, a driven gear that meshes with the driving gear, and a fixed shaft that rotatably supports the driven gear. The gear pump is provided with a case (pump chamber) that has a suction port and a discharge port, and that accommodates the driving gear and the driven gear along with the drive shaft and the fixed shaft.

[0004] Meanwhile, a controller that controls the motor alternately executes reverse driving and forward driving of the motor a plurality of times whenever a threshold time elapses after the motor starts forward driving. The driving and driven gears are helical gears and reverse driving and forward driving are alternately performed so that the thrust force alternately works in the forward and reverse directions and the drive shaft and the driven gear move slightly, as appropriate, in the axial direction. In so doing, ink that lubricates between the driving gear and a first bearing portion that supports the driving gear and ink that lubricates between the driven gear and the fixed shaft that supports the driven gear flow. Although the ultraviolet-curable ink undergoes a polymerization reaction and is cured induced by heat or the like, the curing of the ink is suppressed by the flow, and fixing of the drive shaft and driven gear is prevented.[Citation List][Patent Literature]

[0005] PTL1: JP-A-2012-21516 describes a pump for a printing device using rotating elements to effect the pumping operation. US2011 / 148957 describes an ink pump for a printer capable of operating in a bidirectional manner. WO 2015 / 026850 discloses an electrical hydraulic actuation system that includes a motor-driven, reversible operation gear pump providing fluid under pressure to a rod and cylinder. EP 1988290 is also relevant.[Summary of Invention][Technical Problem]

[0006] In the gear pump of the related art, a problem arises in that not only does the control of the motor become complicated, but also the transport of the ultraviolet-curable ink that is the original function becomes unstable due to the forward and reverse driving.

[0007] The relationship between the drive shaft and the first bearing portion and the relationship between the driven gear and the fixed shaft are included in the relationship between the shaft and the bearing in a relative sense. Therefore, as long as the clearance between the shaft and the bearing is made suitable, it is thought that heat generation at those parts is suppressed, and curing of the ultraviolet-curable ink is prevented.

[0008] Accordingly, it is an object of the present invention to provide a gear pump that is able to effectively prevent excess heat generation between the gear shaft and the journal bearing, and a printing apparatus provided with the same.[Solution to Problem]

[0009] According to an aspect of the invention, there is provided a gear pump as defined in claim 1.

[0010] According to another aspect of the invention, there is provided a printing apparatus as defined in claim 8.

[0011] According to the configuration, because transport of the ultraviolet-curable ink can be stably performed with the circulation pump, printing on the printing medium can be stably performed by the print head. The maintenance frequency of the gear pump (circulation pump) can be extremely suppressed.[Brief Description of Drawings]

[0012] Fig. 1 is an explanatory diagram schematically illustrating a structure of a printing apparatus according to an embodiment. Fig. 2 is a system diagram of an ink supply system in the printing apparatus. Fig. 3 is a cross-sectional view of a gear pump according to the embodiment. Fig. 4A is a plan view of a pump unit in the gear pump. Fig. 4B is an enlarged cross-sectional view taken along line IVB-IVB in Fig. 4A. Fig. 4C is a diagram illustrating dimensional and distance relationships between a driving gear shaft and a driving side bearing. Fig. 5 is a perspective view of a gear assembly. Fig. 6 is a perspective view of a bearing frame (frame main body). [Description of Embodiment]

[0013] Below, the gear pump and printing apparatus to which the gear pump is mounted according to an embodiment of the invention will be described with reference to the attached drawings. The printing apparatus performs printing by feeding a set printing medium in a roll-to-roll format, and discharging an ultraviolet-curable ink (below, referred to as a "UV ink") to the printing medium being fed with an ink jet method. The gear pump is incorporated into the ink supply system of the printing apparatus as a circulation pump.(Structure of Printing Apparatus)

[0014] Fig. 1 is an explanatory diagram schematically illustrating the structure of the printing apparatus according to the embodiment. As shown in the drawing, the printing apparatus 100 is provided with a medium feed unit 101 that feeds a sheet-like printing medium P in a roll-to-roll format, a printing unit 102 that performs printing on the printing medium P being fed using the UV ink, an ink supply mechanism 103 that supplies the UV ink to the printing unit 102, and an apparatus cover 104 that accommodates these internal devices. The material of the printing medium P is not particularly limited, and various printing media such as paper or film-based media are used.

[0015] The medium feed unit 101 is provided with a delivery reel 111 that delivers the printing medium P that is wound in a roll shape, a rotary drum 112 that performs feeding while holding the delivered printing medium P in order to perform printing, a winding reel 113 that winds up the printing medium P fed out from the rotary drum 112 into a roll shape, and a plurality of rollers 114 that regulate (path modification) the feed path of the printing medium with the rotary drum 112 as a center.

[0016] The printing medium P is fed so as to be held by frictional force to the outer circumferential surface of the rotary drum 112, and to move around by rotation of the rotary drum 112. The printing unit 102 is opposite a portion of the outer circumferential surface of the rotary drum 112, and discharges (prints) the UV ink onto the printing medium P being sent out based on the printing data. That is, the rotary drum 112 serves as a platen in the printing unit 102.

[0017] The printing unit 102 includes a plurality of head units 117, and is provided with an ink discharge unit 116 that discharges the UV ink onto the printing medium P, and a radiation unit 118 that causes the UV ink with which the printing medium P is coated to be cured through radiation of ultraviolet rays.

[0018] The plurality of head units 117 are provided lined up along the outer circumferential surface of the rotary drum 112. The plurality of head units 117 have a one-to-one correspondence to a plurality of types (for example, the four colors of C-M-Y-K) of UV inks. Each color of head unit 117 is provided with a plurality of ink jet heads 120 (refer to Fig. 2) to form one printing line in the axial direction of the rotary drum 112. The plurality of ink jet heads 120 of each head unit 117 selectively discharge the UV ink with respect to the printing medium P supported on the outer circumferential surface of the rotary drum 112. In so doing, a color image is formed on the printing medium P.

[0019] The radiation unit 118 is provided with a plurality of preliminary curing radiation devices 121 corresponding to the plurality of head units 117, and a main curing radiation device 122 inserted in the feed path between the rotary drum 112 and the winding reel 113. The plurality of preliminary radiation devices 121 are arranged so as to be alternately lined up one by one with the plurality of head units 117 along the outer circumferential surface of the rotary drum 112. In this case, the preliminary radiation devices 121 are arranged on the downstream side in the feed direction of the printing medium P with respect to the corresponding head unit 117. When the UV ink is discharged on to the printing medium P, the UV ink is irradiated with ultraviolet rays directly after being deposited on the printing medium P, and preliminary curing is performed. In so doing, spreading of the dots of UV inks and mixing of the colors are suppressed.

[0020] The main curing radiation device 122 is arranged further toward the downstream side than the preliminary curing radiation device 121 provided on the most downstream portion of the feed path. The main curing radiation device 122 radiates a greater accumulated amount of ultraviolet rays than the preliminary curing radiation device 121 with respect to the printing medium P on which discharge of the UV ink and preliminary curing are performed. In so doing, the UV ink deposited on the printing medium P is completely cured and is fixed to the printing medium P. It is possible for a light emitting diode (LED) lamp, a high pressure mercury lamp, or the like that radiates ultraviolet rays to be used in the preliminary curing radiation device 121 and the main curing radiation device 122.(Configuration of Ink Supply System)

[0021] The ink supply mechanism 103 is a mechanism that supplies UV ink to each ink jet head 120 (print head), and includes a plurality (by ink color) of ink supply systems 130 with respect to the plurality of types of UV ink.

[0022] As shown in Fig. 2, each ink supply system 130 is provided with a sub-tank 131 connected to a main tank, not shown, and a circulation flow path 132 that connects the sub-tank 131 and the plurality of ink jet heads 120. In the sub-tank 131, the UV ink is replenished from the main tank and the liquid level in the sub-tank 131 is held constant. The sub-tank 131 is arranged at a height at which the water head difference between the liquid level of the sub-tank 131 and the nozzle surface of the inkjet head 120 becomes a predetermined value. In so doing, the UV ink is supplied to each inkjet head 120 at a predetermined water head pressure.

[0023] The circulation flow path 132 includes an outward flow path 132a that leads to the plurality of ink jet heads 120 from the sub-tank 131, and a return flow path 132b that leads to the sub-tank 131 from the plurality of inkjet heads 120. A heat exchanger 143 and an outward manifold 144 that are connected to the circulation pump 141, a filter 142, and a heat source are inserted in the outward flow path 132a, and the plurality of ink jet heads 120 are connected in a branching manner to the outward manifold 144. Similarly, a return manifold 146 is inserted in the return flow path 132b, and the plurality of ink jet heads 120 are connected in a converging manner to the return manifold 146.

[0024] The UV ink in the circulation flow path 132 is raised to a predetermined temperature by the heat exchanger 143, and is circulated by the circulation pump 141. That is, the viscosity of the UV ink is adjusted by the temperature rise, and is supplied to the ink jet heads 120 in this state. Specifically, the UV ink is adjusted to a viscosity of 8 mPas at 40°C, and is supplied to the plurality of inkjet heads 120 in a state where this viscosity (temperature) is maintained.

[0025] The circulation pump 141 is formed of the gear pump (1) that has low pressure fluctuations, and causes the UV ink to be supplied at a predetermined flow rate so that the UV ink supplied to the inkjet head 120 does not drop below 40°C. In so doing, the viscosity of the UV ink supplied to the ink jet head 120 is suppressed to a predetermined value (8 mPas) and the ink discharge amount from each discharge nozzle of the inkjet head 120 is stabilized.(Structure of Gear Pump)

[0026] Next, the gear pump 1 that forms the circulation pump (141) will be described in detail with reference to Figs. 3 to 6. Although, for the convenience of description, the upper side in the drawings is described as the upper side in the gear pump 1 in Figs. 3 to 6 and the lower side in the drawings as the lower side in the gear pump 1, the arrangement directions of the actual gear pump 1 are not limited.

[0027] As shown in Figs. 3 and 4, the gear pump 1 is formed of a power unit 2 and a pump unit 3. The power unit 2 is provided with a motor 5 that is a power source and an output portion 6 that is linked to the main shaft 5a of the motor 5. The pump unit 3 is provided with an input portion 7 that corresponds to the output portion 6, a gear assembly 8 linked to the input portion 7, and a pump casing 9 with a divided structure in which the input portion 7 and the gear assembly 8 are accommodated. Although described in detail later, the gear assembly 8 is formed by incorporating the driving gear 12, the driven gear 13, the driving gear shaft 14 and the driven gear shaft 15 into a bearing frame 11.

[0028] The output portion 6 includes a cap-like output holder 21 linked to the main shaft 5a of the motor 5, and an outer magnet 22 provided on the inner circumferential surface of the output holder 21. Meanwhile, the input portion 7 includes a block-like input holder 24 fixed to the shaft end portion of the driving gear shaft 14 and an inner magnet 25 mounted so as to be embedded in the input holder 24. The output portion 6 (outer magnet 22) and the input portion 7 (inner magnet 25) form a so-called magnetic coupling, and the magnetic force of the outer magnet 22 that rotates due to the rotation of the motor 5 is received, and the inner magnet 25 rotates.

[0029] That is, the rotation power of the motor 5 is transmitted to the driving gear shaft 14 in a non-contact manner via the outer magnet 22 and the inner magnet 25. The input holder 24 is fixed by press-fitting or the like to the driving gear shaft 14. The outer magnet 22 and the inner magnet 25 are formed by a permanent magnet such as a neodymium magnet.

[0030] The pump casing 9 has, in order from the motor 5 side, an upper casing 31, an intermediate casing 32, and a lower casing 33, and these are bonded at the four corners thereof by screwing. The upper casing 31, the intermediate casing 32, and the lower casing 33 are bonded liquid-tight by an inner and outer double seal material 34 inserted between the end surfaces of one another. In so doing, a liquid-tight pump chamber 35 is formed in the pump casing 9.

[0031] An intake port 41 is formed in one side surface of the intermediate casing 32, and a discharge port 42 is formed in the other side surface (refer to Fig. 4A). The intake port 41 and the discharge port 42 are formed in the shape of a coupling that is able to connect to a tube, and are provided so as to project from the side surfaces of the intermediate casing 32. Although it goes without saying, the circulation flow path 132 (tube) is connected to the intake port 41 and the discharge port 42.

[0032] The bearing frame 11 of the gear assembly 8 accommodated in the pump casing 9 is positioned on the inner circumferential surface 32a of the intermediate casing 32 (described in detail later). In this positioned state, the (tooth tips of) driving gear 12 and the driven gear 13 of the gear assembly 8 are opposite one another with a slight gap present on the inner circumferential surface 32a of the intermediate casing 32. When the driving gear 12 and the driven gear 13 rotate, the UV ink (viscous fluid) that flows in from the intake port 41 flows so that the flow is divided to substantially half flow into the slight gap, and the flows merge to flow out from the discharge port 42.

[0033] A circular driving side upper concave portion 44 in which the driving side convex portion 72 of the bearing frame 11, described later, is freely inserted and a circular driven side upper concave portion 45 in which a driven side convex portion 73 of the bearing frame 11, described later, is freely inserted are formed on the inner side of the upper casing 31. The outer side of the driving side upper concave portion 44 is projected in a circular shape, and the input portion 7 is accommodated in this part. A circular driving side upper shallow groove 46 is formed on the top surface of the driving side upper concave portion 44, and one driving side thrust bearing 81, described later, is mounted by press-fitting in the driving side upper shallow groove 46. Similarly, a circular driven side upper shallow groove 47 is formed on the top surface of the driven side upper concave portion 45, and one driven side thrust bearing 82, described later, is mounted by press-fitting or the like in the driven side upper shallow groove 47.

[0034] Similarly, a circular driving side lower concave portion 51 in which the driving side convex portion 72 of the bearing frame 11, described later, is freely inserted and a circular driven side lower concave portion 52 in which the driven side convex portion 73 of the bearing frame 11, described later, is freely inserted are formed on the inner side of the lower casing 33. In this case also, a circular driving side lower shallow groove 53 is formed on the bottom surface of the driving side lower concave portion 51, and the other driving side thrust bearing 81, described later, is mounted by press-fitting or the like in the driving side lower shallow groove 53. Similarly, a circular driven side lower shallow groove 54 is formed on the bottom surface of the driven side lower concave portion 52, and the other driven side thrust bearing 82, described later, is mounted by press-fitting or the like in the driven side lower shallow groove 54.(Structure of Gear Assembly)

[0035] As shown in Figs. 4B, 5, and 6, the gear assembly 8 includes a driving gear 12, a driven gear 13 that meshes with the driving gear 12, a driving gear shaft 14 to which the driving gear 12 is attached, a driven gear shaft 15 to which the driven gear 13 is attached, and a bearing frame 11 that rotatably supports the driving gear shaft 14 and rotatably supports the driven gear shaft 15. The bearing frame 11 includes a frame main body 61, a pair of driving side bearings 62 (driving side bearing portion) and a pair of driven side bearings 63 (driving side bearing portion) built into the frame main body 61. Whereas the driving gear shaft 14 of the driving gear 12 is rotatably supported at both ends by the pair of driving side bearings 62, the driven gear shaft 15 of the driven gear 13 is rotatably supported at both ends by the pair of driven side bearings 63.

[0036] The frame main body 61 is integrally formed by a pair of bearing support portions 65 arranged so as to interpose the driving gear 12 and the driven gear 13 and a pair of connecting portions 66 that connect the pair of bearing support portions 65 on the outside (refer to Fig. 6). Each bearing support portion 65 includes an elliptical flange portion 71, and a circular driving side convex portion 72 and a circular driven side convex portion 73 that are provided so as to project from the flange portion 71.

[0037] The driving side convex portion 72 is arranged on the same axis as the driving gear shaft 14 (and the driving gear 12), and the semi-circular part of the driving gear 12 side of the flange portion 71 is arranged on the same axis as the driving gear shaft 14. Similarly, the driven side convex portion 73 is arranged on the same axis as the driven gear shaft 15 (and the driven gear 13), and the semi-circular part of the driven gear 13 side of the flange portion 71 is arranged on the same axis as the driven gear shaft 15. Both semi-circular parts of the flange portion 71 are formed with a slightly larger diameter than the driving gear 12 and the driven gear 13.

[0038] The driving side convex portion 72 and the driven side convex portion 73 in the upper side bearing support portion 65 are freely inserted in the driving side upper concave portion 44 and the driven side upper concave portion 45 of the upper casing 31 (refer to Fig. 4B). Similarly, the driving side convex portion 72 and the driven side convex portion 73 in the lower side bearing support portion 65 are freely inserted in the driving side lower concave portion 51 and the driven side lower concave portion 52 of the lower casing 33 (refer to Fig. 4B).

[0039] The pair of connecting portions 66 is integrally connected to the pair of flange portions 71, and the pair of flange portions 71 and the pair of connecting portions 66 come in contact (internal contact) with the inner circumferential surface 32a of the intermediate casing 32 (refer to Fig. 4B). That is, the gear assembly 8 is mounted so as to mate with the inner side of the pump casing 9. In so doing, the gear assembly 8 is immovably positioned in the pump casing 9.

[0040] An inflow port 75 connected to the intake port 41 of the pump casing 9 is formed in one connecting portion 66 that is formed in a rectangular shape and an outflow port 76 that connects to the discharge port 42 is formed in the other connecting portion 66 (refer to Fig. 6). The inflow port 75 and the outflow port 76 are formed in a circular shape with the same diameter as or a slightly larger diameter than the inner diameter of the intake port 41 and the discharge port 42.

[0041] A driving side shaft hole 78 in which the driving gear shaft 14 is freely inserted is formed in the inner side of each of the driving side convex portion 72 and the flange portion 71. The driving side shaft hole 78 includes an upper side (front side) guide hole 78a and a lower side (rear side) fitting hole 78b that connects to the guide hole 78a, and the driving side bearing 62 is fixed so as to be press-fit to the fitting hole 78b (refer to Fig. 4B). That is, one driving side bearing 62 is fixed to the upper side fitting hole 78b and the other driving side bearing 62 is fixed to the lower side fitting hole 78b. The pair of driving side bearings 62 is arranged with a slight gap (gap in the axial direction) with respect to the driving gear 12. The driving gear shaft 14 is rotatably supported at both ends on the pair of driving side bearings 62.

[0042] Similarly, the driven side shaft hole 79 in which the driven gear shaft 15 is freely inserted is formed in the inner side of each of the driven side convex portion 73 and the flange portion 71. Also in this case, the driven side shaft hole 79 includes an upper side (front side) guide hole 79a and a lower side (rear side) fitting hole 79b that connects to the guide hole 79a, and the driven side bearing 63 is fixed so as to be press-fit to the fitting hole 79b (refer to Fig. 4B). That is, one driven side bearing 63 is fixed to the upper side fitting hole 79b and the other driven side bearing 63 is fixed to the lower side fitting hole 79b. The pair of driven side bearings 63 is arranged with a slight gap (gap in the axial direction) with respect to the driven gear 13. The driven gear shaft 15 is rotatably supported at both ends on the pair of driven side bearings 63.

[0043] The driving gear 12 and the driven gear 13 are parts that exhibit a pumping action in the gear pump 1 and both are formed of spur gears. The driving gear 12 is fixed (attached) on the driving side bearing 62 by press-fitting. The driving gear 12 is arranged with a slight gap (clearance CLA1, described later) between the pair of bearing support portions 65. Similarly, the driven gear 13 is fixed (attached) to the driven side bearing 63 by press-fitting. The driven gear 13 is arranged with a slight gap (clearance CLA2, described later) between the pair of bearing support portions 65. The driving gear 12 and the driven gear 13 are formed of polyethylene terephthalate (PET) having chemical resistance and a suitable surface roughness.

[0044] The driving gear shaft 14 and the driven gear shaft 15 are formed with the same diameter, and the driving gear shaft 14 is formed longer than the driven gear shaft 15 by the amount attached to the input portion 7. The driving gear shaft 14 is rotatably supported by the pair of driving side bearings 62 in the radial direction in the vicinity of the driving gear 12 attached thereto. The driving gear shaft 14 is rotatably supported by the pair of driving side thrust bearings 81 at both shaft end surfaces thereof. Similarly, the driven gear shaft 15 is rotatably supported by the pair of driven gear bearings 63 in the radial direction in the vicinity of the driven gear 13 attached thereto. The driven gear shaft 15 is rotatably supported by the pair of driven side thrust bearings 82 in the thrust direction at both shaft end surfaces thereof.

[0045] The driving side bearing 62 and the driven side bearing 63 are both formed in a cylindrical shape, and are formed of a journal bearing that receives a load in the radial direction. The driving side thrust bearing 81 and the driven side thrust bearing 82 are both formed in a disk shape, and formed with sufficiently larger diameter than the shaft diameter of the driving gear shaft 14 and the driven gear shaft 15. The driving gear shaft 14, the driven gear shaft 15, the driving side bearing 62, the driven side bearing 63, the driving side thrust bearing 81 and the driven side thrust bearing 82 are formed of an alumina ceramic having chemical resistance and a suitable surface roughness.

[0046] The UV ink (ultraviolet-curable ink) transported by the gear pump 1 of the embodiment has the characteristic of undergoing a polymerization reaction to be cured due to a temperature rise, in addition to irradiation of ultraviolet rays. In particular, in the UV ink that lubricates between the driving gear shaft 14 and the driving side bearing 62, between the driven gear shaft 15 and the driven side bearing 63, between the driving gear shaft 14 and the driving side thrust bearing 81, and between the driven gear shaft 15 and the driven side thrust bearing 82, there is concern of the UV ink undergoing a polymerization reaction and curing through excess heat generation (frictional heat) occurring due to the shaft and the bearing coming into contact, and the rotation of the driving gear shaft 14 or the driven gear shaft 15 locking (being unable to rotate) by the polymerization products generated through the curing.

[0047] In the embodiment, in addition to selecting the material so that fluid lubrication occurs between the driving gear shaft 14 and the driving side bearing 62, between the driven gear shaft 15 and the driven side bearing 63, between the driving gear shaft 14 and the driving side thrust bearing 81, and between the driven gear shaft 15 and the driven side thrust bearing 82 to prevent excess heat generation, the dimensional relationship of the various sliding (lubricated) parts such as between the driving gear shaft 14 and the driving side bearing 62, and between the driving gear shaft 14 and the driving side thrust bearing 81 is designed as follows.

[0048] That is, it is preferable that the width diameter ratio LID that is the ratio of the bearing length L of the driving side bearing 62 (journal bearing) to the shaft diameter D of the driving gear shaft 14 is 0.5 to 2.0, and the ratio in the embodiment is designed to be width diameter ratio LID = 0.796. Similarly, it is preferable that the width diameter ratio LID that is the ratio of the bearing length L of the driven side bearing 63 (journal bearing) to the shaft diameter D of the driven gear shaft 15 is 0.5 to 2.0, and the ratio in the embodiment is designed to be a width diameter ratio LID = 0.796.

[0049] It is preferable that the clearance ratio c / r that is the ratio of the clearance (radial clearance) c in the axial radial direction of the driving gear shaft 14 between the driving gear shaft 14 and the driving side bearing 62 (journal bearing) to the axial radius r of the driving gear shaft 14 is 0.0009 to 0.01, and the ratio in the embodiment is designed to be a clearance ratio c / r = 0.005. Similarly, it is preferable that the clearance ratio c / r that is the ratio of the radial clearance c between the driven gear shaft 15 and the driven side bearing 63 (journal bearing) to the axial radius r of the driven gear shaft 15 is 0.0009 to 0.01, and the ratio in the embodiment is designed to be a clearance ratio c / r = 0.005. It is preferable that the radial clearance c is 1.7 µm or more (for either, refer to Fig. 4C).

[0050] By designing the width diameter ratio LID and the clearance ratio c / r in this way, fluid lubrication is created between the driving gear shaft 14 and the driving side bearing 62, and between the driven gear shaft 15 and the driven side bearing 63, and the generation of frictional heat is suppressed.

[0051] Additionally, it is preferable that the clearance CLA1 between the end surface of the driving gear 12 and the opposed surface of each bearing support portion 65 (flange portion 71) that opposes the end surface is 50 µm or more, and the clearance in the embodiment is designed to be a clearance CLA1 = 100 µm. Similarly, it is preferable that the clearance CLA2 between the end surface of the driven gear 13 and the opposed surface of each bearing support portion 65 (flange portion 71) that opposes the end surface is 50 µm or more, and the clearance in the embodiment is designed to be clearance CLA2 = 100 µm (for either, refer to Fig. 4B).

[0052] It is preferable that the clearance CLB1 between the shaft end surface of the driving gear shaft 14 and the thrust bearing surface of the driving side thrust bearing 81 is 1.7 µm or more to 2500 µm or less, and the clearance in the embodiment is designed to be a clearance CLB1 = 50 µm. Similarly, it is preferable that the clearance CLB2 between the shaft end surface of the driven gear shaft 15 and the thrust bearing surface of the driven side thrust bearing 82 is 1.7 µm or more to 2500 µm or less, and the clearance in the embodiment is designed to be a clearance CLB2 = 50 µm (for either, refer to Fig. 4B).

[0053] By being designed in this way, fluid lubrication is created between the driving gear shaft 14 and the driving side thrust bearing 81, and between the driven gear shaft 15 and the driven side thrust bearing 82, and the generation of frictional heat is suppressed.(Action and Effects)

[0054] As above, according to the gear pump 1 of the embodiment, the width diameter ratio of the driving side bearing 62 to the driving gear shaft 14 and width diameter ratio of the driven side bearing 63 to the driven gear shaft 15 are each made LID = 0.5 to 2.0. The clearance ratio between the driving gear shaft 14 and the driving side bearing 62 and the clearance ratio between the driven gear shaft 15 and the driven side bearing 63 are each made c / r = 0.0009 to 0.01. In so doing, the driving gear shaft 14 (driven gear shaft 15) and the driving side bearing 62 (driven side bearing 63) are prevented from coming into contact, such as partial contact. Accordingly, heat generation from the sliding parts (lubricated parts) between the driving gear shaft 14 (driven gear shaft 15) and the driving side bearing 62 (driven side bearing 63) is suppressed, and curing of the UV ink that functions as a lubricating oil is prevented.

[0055] Furthermore, because a sufficient clearance is held between the end surface of the driving gear 12 (driven gear 13) and the opposing surface of each bearing support portion 65, and between the shaft end surface of the driving gear shaft 14 (driven gear shaft 15) and the thrust bearing surface of the driving side thrust bearing 81 (driven side thrust bearing 82) that are the sliding parts (lubricated parts) between the members, it is possible for heat generation due to members coming in contact with each other to be suppressed, and to prevent curing of the UV ink that functions as a lubricating oil in these parts. In this way, because it is possible to prevent curing of the UV ink in each of the sliding parts (lubricated parts) of the gear pump 1, it is possible to effectively prevent rotation locking of the gear pump 1.

[0056] In the embodiment, although the driving side bearing 62 and the driven side bearing 63 are formed separate to the frame main body 61, these members may be formed integrally to the frame main body 61. That is, the pair of driving side bearing portions and the pair of driven side bearing portions may be formed in the bearing frame 11.Reference Signs List

[0057] 1 gear pump 3 pump unit 8 gear assembly 9 pump casing 11 bearing frame 12 driving gear 13 driven gear 14 driving gear shaft 15 driven gear shaft 41 intake port 42 discharge port 61 frame main body 62 driving side bearing 63 driven side bearing 65 bearing support portion 66 connecting portion 75 inflow port 76 outflow port 78 driving side shaft hole 79 driven side shaft hole 81 driving side thrust bearing 82 driven side thrust bearing 100 printing apparatus 101 medium feed unit 102 printing unit 103 ink supply mechanism 120 inkjet head 130 ink supply system 132 circulation flow path 141 circulation pump P printing medium

Claims

1. A gear pump for transporting a fluid for a printing apparatus, and formed from a power unit (2) and a pump unit (3), wherein the power unit comprises a motor (5) that is a power source and an output portion (6) that is linked to a main shaft (5a) of the motor, and the pump unit (3) comprises: an input portion (7) corresponding to the power unit output portion (6); a pump casing (9) having a divided structure accommodating the input portion and a gear assembly (8); and the gear assembly (8), which is linked to the input portion and which is accommodated in the pump casing, wherein the gear assembly includes a driving gear (12), a driven gear (13) that meshes with the driving gear (12), a driving gear shaft (14) to which the driving gear is attached, a driven gear shaft (15) to which the driven gear is attached, wherein the gear assembly further includes a bearing frame (11) that rotatably supports the driving gear shaft and rotatably supports the driven gear shaft, the bearing frame including a frame main body (61), a pair of driving side bearing portions (62) which is provided in the frame main body and which rotatably supports, using bearings (62) the driving gear shaft at both ends thereof, and a pair of driven side bearing portions (63) which is provided in the frame main body and which rotatably supports, using bearings (63) the driven gear shaft at both ends thereof, characterized in that the frame main body (61) is integrally formed by a pair of bearing support potions (65) arranged to interpose the driving gear (12) and driven gear (13), in which the driving side bearing portion and the driven side bearing portion are provided, and a pair of connecting portions (66) which connects the pair of bearing support portions (65) on the outside, and further wherein the bearing support portions include an elliptical flange portion (71), and a circular driving side convex portion (72) and a circular driven side convex portion (73) provided so as to project from the flange portion (71).

2. The gear pump according to Claim 1, wherein each of the driving side bearing portions (62) and the driven side bearing portion (63) is formed in a cylindrical shape, and of a journal bearing which is separate from the frame main body, and arranged to receive a load in a radial direction, wherein the driving gear shaft (14) is rotatably supported by a pair of driving side thrust bearings (81) at both shaft end surfaces thereof, wherein the driven gear shaft (15) is rotatably supported by a pair of driven side thrust bearings (82) at both shaft end surfaces thereof, and wherein the pair of driving side thrust bearings and the pair of driven side thrust bearings are both formed in a disk shape, and are formed with a larger diameter than a shaft diameter of the driving gear shaft and the driven gear shaft.

3. The gear pump according to Claim 2, wherein each of the driving gear shaft (14), the driven gear shaft (15), the driving side bearing portion (62), and the driven side bearing portion (63), the pair of driving side thrust bearings (81) and the pair of driven side thrust bearings (82) is formed of an alumina ceramic having chemical resistance and a suitable surface roughness.

4. The gear pump according to claim 1, wherein a clearance between an end surface of the driving gear (12) and an opposed surface of each bearing support portion (65) that opposes the end surface is 50 µm or more, and wherein a clearance between an end surface of the driven gear (13) and an opposed surface of each bearing support portion (65) that opposes the end surface is 50 µm or more.

5. The gear pump according to Claim 4, wherein each of the driving gear (12) and the driven gear (13) is formed of polyethylene terephthalate having chemical resistance and a suitable surface roughness.

6. The gear pump according to claim 1, wherein each of the connecting portions (66) is formed in a rectangular shape, and one of the connecting portions includes an inflow port (75) that connects to an intake port (41) of the pump casing and the other one of the connecting portions includes an outflow port (76) that connects to a discharge port (42) of the pump casing, wherein the inflow port and the outflow port are formed in a circular shape with the same diameter as or a larger diameter than an inner diameter of the intake port and the discharge port.

7. The gear pump according to claim 1, wherein the fluid is an ultraviolet-curable ink.

8. A printing apparatus comprising: a print head (120) that performs printing by discharging an ultraviolet-curable ink to a printing medium; a circulation flow path that supplies the ultraviolet-curable ink to the print head; and a circulation pump (141) inserted in the circulation flow path, wherein the circulation pump (141) is formed of the gear pump according to Claim 7.

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