Patent Description:
In the related art, a gear pump that transports an ultraviolet-curable ink is known as this type of gear pump (refer to PTL <NUM>).

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.

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.

PTL1: <CIT> describes a pump for a printing device using rotating elements to effect the pumping operation. <CIT> describes an ink pump for a printer capable of operating in a bidirectional manner. <CIT> discloses an electrical hydraulic actuation system that includes a motor-driven, reversible operation gear pump providing fluid under pressure to a rod and cylinder. <CIT> is also relevant.

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.

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.

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.

According to an aspect of the invention, there is provided a gear pump as defined in claim <NUM>.

According to another aspect of the invention, there is provided a printing apparatus as defined in claim <NUM>.

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.

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.

<FIG> is an explanatory diagram schematically illustrating the structure of the printing apparatus according to the embodiment. As shown in the drawing, the printing apparatus <NUM> is provided with a medium feed unit <NUM> that feeds a sheet-like printing medium P in a roll-to-roll format, a printing unit <NUM> that performs printing on the printing medium P being fed using the UV ink, an ink supply mechanism <NUM> that supplies the UV ink to the printing unit <NUM>, and an apparatus cover <NUM> 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.

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

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

The printing unit <NUM> includes a plurality of head units <NUM>, and is provided with an ink discharge unit <NUM> that discharges the UV ink onto the printing medium P, and a radiation unit <NUM> that causes the UV ink with which the printing medium P is coated to be cured through radiation of ultraviolet rays.

The plurality of head units <NUM> are provided lined up along the outer circumferential surface of the rotary drum <NUM>. The plurality of head units <NUM> 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 <NUM> is provided with a plurality of ink jet heads <NUM> (refer to <FIG>) to form one printing line in the axial direction of the rotary drum <NUM>. The plurality of ink jet heads <NUM> of each head unit <NUM> selectively discharge the UV ink with respect to the printing medium P supported on the outer circumferential surface of the rotary drum <NUM>. In so doing, a color image is formed on the printing medium P.

The radiation unit <NUM> is provided with a plurality of preliminary curing radiation devices <NUM> corresponding to the plurality of head units <NUM>, and a main curing radiation device <NUM> inserted in the feed path between the rotary drum <NUM> and the winding reel <NUM>. The plurality of preliminary radiation devices <NUM> are arranged so as to be alternately lined up one by one with the plurality of head units <NUM> along the outer circumferential surface of the rotary drum <NUM>. In this case, the preliminary radiation devices <NUM> are arranged on the downstream side in the feed direction of the printing medium P with respect to the corresponding head unit <NUM>. 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.

The main curing radiation device <NUM> is arranged further toward the downstream side than the preliminary curing radiation device <NUM> provided on the most downstream portion of the feed path. The main curing radiation device <NUM> radiates a greater accumulated amount of ultraviolet rays than the preliminary curing radiation device <NUM> 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 <NUM> and the main curing radiation device <NUM>.

The ink supply mechanism <NUM> is a mechanism that supplies UV ink to each ink jet head <NUM> (print head), and includes a plurality (by ink color) of ink supply systems <NUM> with respect to the plurality of types of UV ink.

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

The circulation flow path <NUM> includes an outward flow path 132a that leads to the plurality of ink jet heads <NUM> from the sub-tank <NUM>, and a return flow path 132b that leads to the sub-tank <NUM> from the plurality of inkjet heads <NUM>. A heat exchanger <NUM> and an outward manifold <NUM> that are connected to the circulation pump <NUM>, a filter <NUM>, and a heat source are inserted in the outward flow path 132a, and the plurality of ink jet heads <NUM> are connected in a branching manner to the outward manifold <NUM>. Similarly, a return manifold <NUM> is inserted in the return flow path 132b, and the plurality of ink jet heads <NUM> are connected in a converging manner to the return manifold <NUM>.

The UV ink in the circulation flow path <NUM> is raised to a predetermined temperature by the heat exchanger <NUM>, and is circulated by the circulation pump <NUM>. That is, the viscosity of the UV ink is adjusted by the temperature rise, and is supplied to the ink jet heads <NUM> in this state. Specifically, the UV ink is adjusted to a viscosity of <NUM> mPas at <NUM>, and is supplied to the plurality of inkjet heads <NUM> in a state where this viscosity (temperature) is maintained.

The circulation pump <NUM> is formed of the gear pump (<NUM>) 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 <NUM> does not drop below <NUM>. In so doing, the viscosity of the UV ink supplied to the ink jet head <NUM> is suppressed to a predetermined value (<NUM> mPas) and the ink discharge amount from each discharge nozzle of the inkjet head <NUM> is stabilized.

Next, the gear pump <NUM> that forms the circulation pump (<NUM>) will be described in detail with reference to <FIG>. Although, for the convenience of description, the upper side in the drawings is described as the upper side in the gear pump <NUM> in <FIG> and the lower side in the drawings as the lower side in the gear pump <NUM>, the arrangement directions of the actual gear pump <NUM> are not limited.

As shown in <FIG> and <FIG>, the gear pump <NUM> is formed of a power unit <NUM> and a pump unit <NUM>. The power unit <NUM> is provided with a motor <NUM> that is a power source and an output portion <NUM> that is linked to the main shaft 5a of the motor <NUM>. The pump unit <NUM> is provided with an input portion <NUM> that corresponds to the output portion <NUM>, a gear assembly <NUM> linked to the input portion <NUM>, and a pump casing <NUM> with a divided structure in which the input portion <NUM> and the gear assembly <NUM> are accommodated. Although described in detail later, the gear assembly <NUM> is formed by incorporating the driving gear <NUM>, the driven gear <NUM>, the driving gear shaft <NUM> and the driven gear shaft <NUM> into a bearing frame <NUM>.

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

That is, the rotation power of the motor <NUM> is transmitted to the driving gear shaft <NUM> in a non-contact manner via the outer magnet <NUM> and the inner magnet <NUM>. The input holder <NUM> is fixed by press-fitting or the like to the driving gear shaft <NUM>. The outer magnet <NUM> and the inner magnet <NUM> are formed by a permanent magnet such as a neodymium magnet.

The pump casing <NUM> has, in order from the motor <NUM> side, an upper casing <NUM>, an intermediate casing <NUM>, and a lower casing <NUM>, and these are bonded at the four corners thereof by screwing. The upper casing <NUM>, the intermediate casing <NUM>, and the lower casing <NUM> are bonded liquid-tight by an inner and outer double seal material <NUM> inserted between the end surfaces of one another. In so doing, a liquid-tight pump chamber <NUM> is formed in the pump casing <NUM>.

An intake port <NUM> is formed in one side surface of the intermediate casing <NUM>, and a discharge port <NUM> is formed in the other side surface (refer to <FIG>). The intake port <NUM> and the discharge port <NUM> 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 <NUM>. Although it goes without saying, the circulation flow path <NUM> (tube) is connected to the intake port <NUM> and the discharge port <NUM>.

The bearing frame <NUM> of the gear assembly <NUM> accommodated in the pump casing <NUM> is positioned on the inner circumferential surface 32a of the intermediate casing <NUM> (described in detail later). In this positioned state, the (tooth tips of) driving gear <NUM> and the driven gear <NUM> of the gear assembly <NUM> are opposite one another with a slight gap present on the inner circumferential surface 32a of the intermediate casing <NUM>. When the driving gear <NUM> and the driven gear <NUM> rotate, the UV ink (viscous fluid) that flows in from the intake port <NUM> 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 <NUM>.

A circular driving side upper concave portion <NUM> in which the driving side convex portion <NUM> of the bearing frame <NUM>, described later, is freely inserted and a circular driven side upper concave portion <NUM> in which a driven side convex portion <NUM> of the bearing frame <NUM>, described later, is freely inserted are formed on the inner side of the upper casing <NUM>. The outer side of the driving side upper concave portion <NUM> is projected in a circular shape, and the input portion <NUM> is accommodated in this part. A circular driving side upper shallow groove <NUM> is formed on the top surface of the driving side upper concave portion <NUM>, and one driving side thrust bearing <NUM>, described later, is mounted by press-fitting in the driving side upper shallow groove <NUM>. Similarly, a circular driven side upper shallow groove <NUM> is formed on the top surface of the driven side upper concave portion <NUM>, and one driven side thrust bearing <NUM>, described later, is mounted by press-fitting or the like in the driven side upper shallow groove <NUM>.

Similarly, a circular driving side lower concave portion <NUM> in which the driving side convex portion <NUM> of the bearing frame <NUM>, described later, is freely inserted and a circular driven side lower concave portion <NUM> in which the driven side convex portion <NUM> of the bearing frame <NUM>, described later, is freely inserted are formed on the inner side of the lower casing <NUM>. In this case also, a circular driving side lower shallow groove <NUM> is formed on the bottom surface of the driving side lower concave portion <NUM>, and the other driving side thrust bearing <NUM>, described later, is mounted by press-fitting or the like in the driving side lower shallow groove <NUM>. Similarly, a circular driven side lower shallow groove <NUM> is formed on the bottom surface of the driven side lower concave portion <NUM>, and the other driven side thrust bearing <NUM>, described later, is mounted by press-fitting or the like in the driven side lower shallow groove <NUM>.

As shown in <FIG>, <FIG>, and <FIG>, the gear assembly <NUM> includes a driving gear <NUM>, a driven gear <NUM> that meshes with the driving gear <NUM>, a driving gear shaft <NUM> to which the driving gear <NUM> is attached, a driven gear shaft <NUM> to which the driven gear <NUM> is attached, and a bearing frame <NUM> that rotatably supports the driving gear shaft <NUM> and rotatably supports the driven gear shaft <NUM>. The bearing frame <NUM> includes a frame main body <NUM>, a pair of driving side bearings <NUM> (driving side bearing portion) and a pair of driven side bearings <NUM> (driving side bearing portion) built into the frame main body <NUM>. Whereas the driving gear shaft <NUM> of the driving gear <NUM> is rotatably supported at both ends by the pair of driving side bearings <NUM>, the driven gear shaft <NUM> of the driven gear <NUM> is rotatably supported at both ends by the pair of driven side bearings <NUM>.

The frame main body <NUM> is integrally formed by a pair of bearing support portions <NUM> arranged so as to interpose the driving gear <NUM> and the driven gear <NUM> and a pair of connecting portions <NUM> that connect the pair of bearing support portions <NUM> on the outside (refer to <FIG>). Each bearing support portion <NUM> includes an elliptical flange portion <NUM>, and a circular driving side convex portion <NUM> and a circular driven side convex portion <NUM> that are provided so as to project from the flange portion <NUM>.

The driving side convex portion <NUM> is arranged on the same axis as the driving gear shaft <NUM> (and the driving gear <NUM>), and the semi-circular part of the driving gear <NUM> side of the flange portion <NUM> is arranged on the same axis as the driving gear shaft <NUM>. Similarly, the driven side convex portion <NUM> is arranged on the same axis as the driven gear shaft <NUM> (and the driven gear <NUM>), and the semi-circular part of the driven gear <NUM> side of the flange portion <NUM> is arranged on the same axis as the driven gear shaft <NUM>. Both semi-circular parts of the flange portion <NUM> are formed with a slightly larger diameter than the driving gear <NUM> and the driven gear <NUM>.

The driving side convex portion <NUM> and the driven side convex portion <NUM> in the upper side bearing support portion <NUM> are freely inserted in the driving side upper concave portion <NUM> and the driven side upper concave portion <NUM> of the upper casing <NUM> (refer to <FIG>). Similarly, the driving side convex portion <NUM> and the driven side convex portion <NUM> in the lower side bearing support portion <NUM> are freely inserted in the driving side lower concave portion <NUM> and the driven side lower concave portion <NUM> of the lower casing <NUM> (refer to <FIG>).

The pair of connecting portions <NUM> is integrally connected to the pair of flange portions <NUM>, and the pair of flange portions <NUM> and the pair of connecting portions <NUM> come in contact (internal contact) with the inner circumferential surface 32a of the intermediate casing <NUM> (refer to <FIG>). That is, the gear assembly <NUM> is mounted so as to mate with the inner side of the pump casing <NUM>. In so doing, the gear assembly <NUM> is immovably positioned in the pump casing <NUM>.

An inflow port <NUM> connected to the intake port <NUM> of the pump casing <NUM> is formed in one connecting portion <NUM> that is formed in a rectangular shape and an outflow port <NUM> that connects to the discharge port <NUM> is formed in the other connecting portion <NUM> (refer to <FIG>). The inflow port <NUM> and the outflow port <NUM> are formed in a circular shape with the same diameter as or a slightly larger diameter than the inner diameter of the intake port <NUM> and the discharge port <NUM>.

A driving side shaft hole <NUM> in which the driving gear shaft <NUM> is freely inserted is formed in the inner side of each of the driving side convex portion <NUM> and the flange portion <NUM>. The driving side shaft hole <NUM> 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 <NUM> is fixed so as to be press-fit to the fitting hole 78b (refer to <FIG>). That is, one driving side bearing <NUM> is fixed to the upper side fitting hole 78b and the other driving side bearing <NUM> is fixed to the lower side fitting hole 78b. The pair of driving side bearings <NUM> is arranged with a slight gap (gap in the axial direction) with respect to the driving gear <NUM>. The driving gear shaft <NUM> is rotatably supported at both ends on the pair of driving side bearings <NUM>.

Similarly, the driven side shaft hole <NUM> in which the driven gear shaft <NUM> is freely inserted is formed in the inner side of each of the driven side convex portion <NUM> and the flange portion <NUM>. Also in this case, the driven side shaft hole <NUM> 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 <NUM> is fixed so as to be press-fit to the fitting hole 79b (refer to <FIG>). That is, one driven side bearing <NUM> is fixed to the upper side fitting hole 79b and the other driven side bearing <NUM> is fixed to the lower side fitting hole 79b. The pair of driven side bearings <NUM> is arranged with a slight gap (gap in the axial direction) with respect to the driven gear <NUM>. The driven gear shaft <NUM> is rotatably supported at both ends on the pair of driven side bearings <NUM>.

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

The driving gear shaft <NUM> and the driven gear shaft <NUM> are formed with the same diameter, and the driving gear shaft <NUM> is formed longer than the driven gear shaft <NUM> by the amount attached to the input portion <NUM>. The driving gear shaft <NUM> is rotatably supported by the pair of driving side bearings <NUM> in the radial direction in the vicinity of the driving gear <NUM> attached thereto. The driving gear shaft <NUM> is rotatably supported by the pair of driving side thrust bearings <NUM> at both shaft end surfaces thereof. Similarly, the driven gear shaft <NUM> is rotatably supported by the pair of driven gear bearings <NUM> in the radial direction in the vicinity of the driven gear <NUM> attached thereto. The driven gear shaft <NUM> is rotatably supported by the pair of driven side thrust bearings <NUM> in the thrust direction at both shaft end surfaces thereof.

The driving side bearing <NUM> and the driven side bearing <NUM> 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 <NUM> and the driven side thrust bearing <NUM> are both formed in a disk shape, and formed with sufficiently larger diameter than the shaft diameter of the driving gear shaft <NUM> and the driven gear shaft <NUM>. The driving gear shaft <NUM>, the driven gear shaft <NUM>, the driving side bearing <NUM>, the driven side bearing <NUM>, the driving side thrust bearing <NUM> and the driven side thrust bearing <NUM> are formed of an alumina ceramic having chemical resistance and a suitable surface roughness.

The UV ink (ultraviolet-curable ink) transported by the gear pump <NUM> 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 <NUM> and the driving side bearing <NUM>, between the driven gear shaft <NUM> and the driven side bearing <NUM>, between the driving gear shaft <NUM> and the driving side thrust bearing <NUM>, and between the driven gear shaft <NUM> and the driven side thrust bearing <NUM>, 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 <NUM> or the driven gear shaft <NUM> locking (being unable to rotate) by the polymerization products generated through the curing.

In the embodiment, in addition to selecting the material so that fluid lubrication occurs between the driving gear shaft <NUM> and the driving side bearing <NUM>, between the driven gear shaft <NUM> and the driven side bearing <NUM>, between the driving gear shaft <NUM> and the driving side thrust bearing <NUM>, and between the driven gear shaft <NUM> and the driven side thrust bearing <NUM> to prevent excess heat generation, the dimensional relationship of the various sliding (lubricated) parts such as between the driving gear shaft <NUM> and the driving side bearing <NUM>, and between the driving gear shaft <NUM> and the driving side thrust bearing <NUM> is designed as follows.

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 <NUM> (journal bearing) to the shaft diameter D of the driving gear shaft <NUM> is <NUM> to <NUM>, and the ratio in the embodiment is designed to be width diameter ratio LID = <NUM>. Similarly, it is preferable that the width diameter ratio LID that is the ratio of the bearing length L of the driven side bearing <NUM> (journal bearing) to the shaft diameter D of the driven gear shaft <NUM> is <NUM> to <NUM>, and the ratio in the embodiment is designed to be a width diameter ratio LID = <NUM>.

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 <NUM> between the driving gear shaft <NUM> and the driving side bearing <NUM> (journal bearing) to the axial radius r of the driving gear shaft <NUM> is <NUM> to <NUM>, and the ratio in the embodiment is designed to be a clearance ratio c/r = <NUM>. Similarly, it is preferable that the clearance ratio c/r that is the ratio of the radial clearance c between the driven gear shaft <NUM> and the driven side bearing <NUM> (journal bearing) to the axial radius r of the driven gear shaft <NUM> is <NUM> to <NUM>, and the ratio in the embodiment is designed to be a clearance ratio c/r = <NUM>. It is preferable that the radial clearance c is <NUM> or more (for either, refer to <FIG>).

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 <NUM> and the driving side bearing <NUM>, and between the driven gear shaft <NUM> and the driven side bearing <NUM>, and the generation of frictional heat is suppressed.

Additionally, it is preferable that the clearance CLA1 between the end surface of the driving gear <NUM> and the opposed surface of each bearing support portion <NUM> (flange portion <NUM>) that opposes the end surface is <NUM> or more, and the clearance in the embodiment is designed to be a clearance CLA1 = <NUM>. Similarly, it is preferable that the clearance CLA2 between the end surface of the driven gear <NUM> and the opposed surface of each bearing support portion <NUM> (flange portion <NUM>) that opposes the end surface is <NUM> or more, and the clearance in the embodiment is designed to be clearance CLA2 = <NUM> (for either, refer to <FIG>).

It is preferable that the clearance CLB1 between the shaft end surface of the driving gear shaft <NUM> and the thrust bearing surface of the driving side thrust bearing <NUM> is <NUM> or more to <NUM> or less, and the clearance in the embodiment is designed to be a clearance CLB1 = <NUM>. Similarly, it is preferable that the clearance CLB2 between the shaft end surface of the driven gear shaft <NUM> and the thrust bearing surface of the driven side thrust bearing <NUM> is <NUM> or more to <NUM> or less, and the clearance in the embodiment is designed to be a clearance CLB2 = <NUM> (for either, refer to <FIG>).

By being designed in this way, fluid lubrication is created between the driving gear shaft <NUM> and the driving side thrust bearing <NUM>, and between the driven gear shaft <NUM> and the driven side thrust bearing <NUM>, and the generation of frictional heat is suppressed.

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

Furthermore, because a sufficient clearance is held between the end surface of the driving gear <NUM> (driven gear <NUM>) and the opposing surface of each bearing support portion <NUM>, and between the shaft end surface of the driving gear shaft <NUM> (driven gear shaft <NUM>) and the thrust bearing surface of the driving side thrust bearing <NUM> (driven side thrust bearing <NUM>) 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 <NUM>, it is possible to effectively prevent rotation locking of the gear pump <NUM>.

Claim 1:
A gear pump for transporting a fluid for a printing apparatus, and formed from a power unit (<NUM>) and a pump unit (<NUM>), wherein the power unit comprises a motor (<NUM>) that is a power source and an output portion (<NUM>) that is linked to a main shaft (5a) of the motor, and the pump unit (<NUM>) comprises:
an input portion (<NUM>) corresponding to the power unit output portion (<NUM>);
a pump casing (<NUM>) having a divided structure accommodating the input portion and a gear assembly (<NUM>); and
the gear assembly (<NUM>), which is linked to the input portion and which is accommodated in the pump casing,
wherein the gear assembly includes
a driving gear (<NUM>),
a driven gear (<NUM>) that meshes with the driving gear (<NUM>),
a driving gear shaft (<NUM>) to which the driving gear is attached,
a driven gear shaft (<NUM>) to which the driven gear is attached,
wherein the gear assembly further includes
a bearing frame (<NUM>) that rotatably supports the driving gear shaft and rotatably supports the driven gear shaft,
the bearing frame including
a frame main body (<NUM>),
a pair of driving side bearing portions (<NUM>) which is provided in the frame main body and which rotatably supports, using bearings (<NUM>) the driving gear shaft at both ends thereof, and
a pair of driven side bearing portions (<NUM>) which is provided in the frame main body and which rotatably supports, using bearings (<NUM>) the driven gear shaft at both ends thereof,
characterized in that the frame main body (<NUM>) is integrally formed by a pair of bearing support potions (<NUM>) arranged to interpose the driving gear (<NUM>) and driven gear (<NUM>), in which the driving side bearing portion and the driven side bearing portion are provided, and a pair of connecting portions (<NUM>) which connects the pair of bearing support portions (<NUM>) on the outside, and further wherein the bearing support portions include an elliptical flange portion (<NUM>), and a circular driving side convex portion (<NUM>) and a circular driven side convex portion (<NUM>) provided so as to project from the flange portion (<NUM>).