JP2011206121A - Fluid dynamic pressure bearing device for dental handpiece, and dental handpiece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid dynamic pressure bearing device for a dental handpiece and a dental handpiece, capable of eliminating the rolling sound and capable of being maintenance-free.SOLUTION: In the fluid dynamic pressure bearing device 10 for the dental handpiece, a cutting tool is attached and a rotating shaft driven by a turbine is rotatably supported at a case by a pair of bearing parts. The fluid dynamic pressure bearing device 10 includes: an outer member 20 including a radial bearing surface 29R and thrust bearing surfaces 23T and 23T formed at both ends of the radial bearing surface; and an inner member 11 disposed on the inside of the outer member 20, including a radial bearing surface 12R and thrust bearing surfaces 13T and 13T opposing the radial bearing surface 29R and thrust bearing surfaces 23T and 23T, respectively. A radial bearing gap R is formed between the radial bearing surfaces 29R and 12R of the outer member 20 and inner member 11 respectively, and a thrust bearing gap T is formed between the thrust bearing surfaces 23T and 13T. Lubricant oil is interposed in these bearing gaps R and T.

Description

  The present invention relates to a fluid dynamic pressure bearing device for a dental handpiece and a dental handpiece, in which a cutting tool is attached and a rotating shaft driven by a turbine is rotatably supported by a case.

  The dental handpiece is generally of a type in which a cutting tool is attached to the tip of a rotating shaft, driven by an air turbine, and both axial sides of the rotating shaft to which the turbine is attached are supported by a pair of rolling bearings ( For example, Patent Document 1).

  On the other hand, a fluid dynamic pressure bearing is provided between the journal portion of the rotating shaft and the case. There is an example in which a configuration supported by the above has been tried (Patent Document 2).

JP-A-8-173453 Japanese Patent Laid-Open No. 6-292689

By the way, in the type supported by the rolling bearing of Patent Document 1, as a problem of the rolling bearing, lubricating oil is reduced by reducing rolling noise during high-speed rotation exceeding 300,000 revolutions per minute or by sterilization treatment exposed to a high-temperature and high-humidity atmosphere. Flows out and must be used while replenishing the lubricating oil each time, and there is a high demand for maintenance-free.

  In the handpiece of Patent Document 2, a turbine is provided at the rear end portion of the rotating shaft, a thrust bearing is formed at the center portion of the side surface of the turbine and the receiving portion center portion facing the turbine, and between the journal portion of the rotating shaft and the case. The structure is supported by a fluid dynamic pressure bearing provided, and has a special dedicated structure as a bearing structure for the handpiece. Therefore, there are problems in terms of assembly workability and manufacturing cost.

  An object of the present invention is to provide a fluid dynamic pressure bearing device and a dental handpiece for a dental handpiece that eliminates rolling noise and realizes maintenance-free by paying attention to the configuration of a fluid dynamic pressure bearing device for a dental handpiece. There is to do.

As a result of various studies on the above problems, the inventors of the present application have arrived at the following new idea, and together with these, the present invention could be achieved.
(1) As a dental handpiece, construct a highly versatile fluid dynamic pressure bearing device of the same size as a rolling bearing. (2) The inner member with a radial bearing surface and a thrust bearing surface is made of sintered metal. (3) Forming an outer member having a radial bearing surface and a thrust bearing surface by pressing a plate material. (4) Resin injection molded product using the inner member as an insert part as the outer member. To do

  The present invention is a fluid dynamic pressure bearing device for a dental handpiece in which a cutting tool is attached and a rotating shaft driven by a turbine is rotatably supported on a case by a pair of bearing portions, and the fluid dynamic pressure bearing device includes: A radial bearing surface and an outer member having a thrust bearing surface formed at both ends thereof, and a radial bearing surface and a thrust bearing surface which are arranged inside the outer member and face the radial bearing surface and the thrust bearing surface, respectively. A radial bearing gap between the radial bearing surfaces of the outer member and the inner member and a thrust bearing gap between the thrust bearing surfaces, and lubricating oil is interposed in these bearing gaps. The outer member has an outer peripheral surface attached to a case, and the inner member has an inner peripheral surface attached to a rotating shaft. Is shall. With the configuration as described above, the number of parts is small, and it can be manufactured with high accuracy and low cost, and it is excellent in quietness. Moreover, since it can be formed in the same size as the rolling bearing, it is highly versatile, excellent in handling and maintenance-free.

  Further, by forming a dynamic pressure groove on at least one of the radial bearing surface and the thrust bearing surface of the inner member, the rotating shaft can be supported in a non-contact manner by the dynamic pressure action of the lubricating oil, and excellent in quietness. .

  Further, when the inner member is formed of sintered metal, the plastic flow at the time of rolling the dynamic pressure groove on the radial bearing surface of the inner member can be absorbed by the inner pores of the sintered metal. For this reason, the rise of the surface due to plastic flow is suppressed, and the dynamic pressure grooves can be formed with high accuracy.

  Dental handpieces are operated at high speeds exceeding 300,000 revolutions per minute. Since the inner member made of a sintered body that is attached to the rotating shaft and the fastening allowance needs to withstand the acting hoop stress, the material of the metal sintered body constituting the inner member has a tensile allowable stress of 100 MPa or more. It is desirable to have.

  If the sintered body is made of ceramics, the weight can be reduced, which is advantageous for high-speed operation.

  On the other hand, when the outer member is formed of two members, a first outer member and a second outer member, and the longitudinal cross-sectional shapes of these two members are both substantially L-shaped, The fitting length between the side member and the second outer member can be secured, and the accuracy and the coupling state can be improved.

  A dynamic pressure groove is formed by press working on at least one of the inner side surface of the first outer member in the radial direction and the inner side surface of the second outer member in the radial direction. In this case, when the first outer member and the second outer member are formed from the plate material by press working, the dynamic pressure grooves are formed by press working, so that the dynamic pressure grooves can be formed with high accuracy and efficiency. .

  The first outer member and the second outer member are made of stainless steel material, are fitted at least on the inner side, and the second outer member having a radial bearing surface on the inner periphery is made of SUS430. Even when exposed to a high humidity atmosphere during sterilization, it has excellent corrosion resistance, is suitable for press work, and has good wear resistance.

  Further, the outer member can be a resin injection molded product using the inner member as an insert part. In this case, the number of parts and the number of assembly steps can be reduced.

  Since the thrust bearing surface of the outer member is peeled off from the inner member by forming shrinkage in the axial direction of the resin molding portion of the outer member, the thrust bearing gap is formed, so that the clearance can be easily set. Furthermore, the outer member is provided with a metal core, and the outer member is injection-molded with resin using the inner member and the metal core arranged on the outer diameter side of the inner member as an insert part, thereby increasing the gap. It becomes possible to set the accuracy.

  Lubricating oil that fills the bearing gap should not affect the human body. Use one that meets the NSF H1 standard, which is the standard of the International Health Science Foundation (NSF). And the lubricating oil which uses poly alpha olefin (PAO) as base oil is desirable from heat resistance and water resistance.

  A damper mechanism is provided between the case of the handpiece and the outer member of the fluid dynamic pressure device. A mesh spring or the like is used as a damper mechanism. With this damper mechanism, it is possible to reduce the load and vibration during treatment.

  A vent hole is provided for communicating the turbine housing space of the case with the outside. This vent hole can prevent the lubricating oil of the fluid dynamic bearing device from being pushed out due to the pressure rise in the turbine housing space when pressurized air is supplied to drive the turbine.

  On the cutting tool mounting side of the rotary shaft, a seal member is provided on the inner peripheral surface of the case, and this seal member is brought into contact with the outer peripheral surface of the rotary shaft. As the seal member, a felt in which wax (lubricating oil) is impregnated is suitable. Thus, by providing a separate seal mechanism from the fluid dynamic bearing device, leakage of the lubricating oil can be further prevented.

  According to the fluid dynamic pressure bearing device for a dental handpiece of the present invention, the number of parts is small, it can be manufactured with high accuracy and at low cost, and it is excellent in quietness. In addition, since it can be formed in the same size as the rolling bearing, it is highly versatile and excellent in handling, and maintenance-free of the fluid dynamic pressure bearing device and thus maintenance-free of the handpiece can be realized.

It is an external view of a dental handpiece. It is a longitudinal cross-sectional view of the dental handpiece incorporating the fluid dynamic bearing device of the first embodiment of the present invention. It is a longitudinal cross-sectional view of the fluid dynamic pressure bearing apparatus of the 1st Embodiment of this invention. It is the front view and side view which show the dynamic pressure groove formed in the inward member. It is the longitudinal cross-sectional view which expanded the principal part of FIG. It is a longitudinal cross-sectional view of the fluid dynamic pressure bearing apparatus of the modification of 1st Embodiment. It is a longitudinal cross-sectional view which shows another modification of 1st Embodiment. It is a longitudinal cross-sectional view of another embodiment of the dental handpiece of the present invention. It is a longitudinal cross-sectional view of the dental handpiece incorporating the fluid dynamic bearing device according to the second embodiment of the present invention. It is a longitudinal cross-sectional view of the fluid dynamic pressure bearing apparatus of 2nd Embodiment. It is the longitudinal cross-sectional view which expanded the principal part of FIG. It is a front view which shows the dynamic pressure groove formed in the inward member of 2nd Embodiment. It is a longitudinal cross-sectional view which shows the modification of 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an external view of a handpiece in which a fluid dynamic bearing device according to an embodiment of the present invention is incorporated. The dental handpiece 1 accommodates a rotating shaft in the case 4 of the head 3 provided at the tip of the grip portion 2. The cutting tool 5 is attached to the rotating shaft, pressurized air is supplied from the air supply pipe at the other end, and the cutting tool 5 is rotationally driven by a turbine (not shown) attached to the rotating shaft.

  FIG. 2 is a longitudinal sectional view of a portion of the case 4 in FIG. Based on this figure, the hydrodynamic bearing device 10 for a dental handpiece according to the first embodiment of the present invention will be described. FIG. 2 shows the inside of the case 4 of the handpiece 1. The turbine 7 is attached to a substantially central portion of the rotary shaft 8, and between the inner peripheral surfaces 4 a and 9 a of the case 4 and the lid member 9 and the outer peripheral surface 8 a of the rotary shaft 8 at both axial positions of the turbine 7. The fluid dynamic pressure bearing devices 10, 10 are incorporated in the rotary shaft 8, and the rotary shaft 8 is rotatably supported with respect to the case 4. Specifically, shoulder surfaces 4b and 9b are provided on the back side of the inner peripheral surfaces 4a and 9a of the case 4 and the lid member 9, and end portions of the fluid dynamic bearing devices 10 and 10 are provided on the shoulder surfaces 4b and 9b. It is built in the state where it touched. The outer peripheral surface 27 and the inner peripheral surface 11a of the fluid dynamic bearing devices 10 and 10 are assembled by light press-fitting into the inner peripheral surfaces 4a and 9a of the case 4 and the lid member 9 and the outer peripheral surface 8a of the rotary shaft 8, and are made of adhesive. Fixed. A large-diameter inner peripheral surface 4b is formed at substantially the center of the case 4, and the turbine 7 is accommodated in the internal space 4c. Pressurized air is sprayed from the air supply pipe 6 provided in the head 3 to the turbine 7 to drive the turbine 7. A cutting tool (not shown) is attached to the tip of the rotating shaft 8.

  Based on FIG. 3, the structure of the fluid dynamic bearing device 10 of this embodiment is demonstrated. As shown in FIG. 3, the fluid dynamic bearing device 10 includes an inner member 11 and an outer member 20 that rotatably supports the inner member 11. The inner member 11 has an inner peripheral surface 11 a fitted and fixed to the outer peripheral surface 8 a of the rotary shaft 8, and the outer member 20 is attached with the outer peripheral surface 25 fitted to the inner peripheral surface 4 a of the case 4. (See FIG. 2). Lubricating oil is interposed between the surfaces of the inner member 11 and the outer member 20 (radial bearing gap R and thrust bearing gap T) facing each other in the axial direction and the radial direction (see FIG. 5). The fluid dynamic bearing devices 10 and 10 in FIG. 1 have the same structure.

  As shown in FIG. 3, the inner member 11 is formed of a sintered metal and has an outer peripheral surface 12 and both side surfaces 13 and 13. The outer peripheral surface 12 forms a radial bearing surface 12R, and both side surfaces 13, 13 form thrust bearing surfaces 13T, 13T. The outer peripheral surface 12 has a cylindrical surface shape and is in contact with the lubricating oil filled in the radial bearing gap R (see FIG. 5). A dynamic pressure groove 12 a is formed on the outer peripheral surface 12. Specifically, as shown in FIG. 4 (b), a dynamic pressure groove 12a formed on the entire outer peripheral surface 12 and bent in a V shape, and a hill portion 12b partitioning the dynamic pressure groove 12a (shown by cross-hatching in the figure) And a herringbone shape alternately arranged in the circumferential direction. The dynamic pressure groove 12a is formed by rolling, for example. In this embodiment, since the inner member 10 is formed of a sintered metal, the plastic flow of the outer peripheral surface 12 due to the compression of the rolling process can be absorbed by the internal pores of the sintered metal. For this reason, the rise of the surface of the inner member 11 due to plastic flow is suppressed, and the dynamic pressure groove 12a and the hill portion 12b can be formed with high accuracy.

  Both side surfaces 13, 13 of the inward member 11 form a flat surface in the radial direction perpendicular to the axis A, and are in contact with the lubricating oil filled in the thrust bearing gap T (see FIG. 5). Dynamic pressure grooves 13a and 13a are formed on both side surfaces 13 and 13, respectively. Details are shown in FIGS. 4A and 4C. 4A shows the left side surface 13 and FIG. 4C shows the right side surface 13. As shown in the figure, dynamic pressure grooves 13a, 13a formed in a portion excluding a part on the inner diameter side of both side surfaces 13, 13 and bent in a V shape, and hill portions 13b, 13b (see FIG. (Shown by cross-hatching) and a herringbone shape alternately arranged in the circumferential direction. Since the inner member 11 is formed of sintered metal, the dynamic pressure grooves 13a and 13a on the side surfaces 13 and 13 can be formed with high accuracy by press working. Further, the dynamic pressure grooves 13a and 13a can be molded simultaneously with the sizing of the inner member 11.

  The inner member 11 is formed by, for example, press-fitting (light press-fitting) the inner peripheral surface 11 a into the outer peripheral surface 8 a of the rotary shaft 8, or between the inner peripheral surface 11 a and the outer peripheral surface 8 a of the rotary shaft 8. By interposing, it is fixed to the rotating shaft 8 (see FIG. 2).

  The dental handpiece 1 is operated at a high speed exceeding 300,000 revolutions per minute. Since the inner member 11 made of a sintered body that is attached to the rotary shaft 8 by tightening allowance or the like needs to withstand the acting hoop stress, the material of the metal sintered body constituting the inner member 11 is a tensile force of 100 MPa or more. It is desirable to have an allowable stress.

Moreover, the metal sintered body of the inner member 11 is made of a stainless steel material. Specifically, it is SUS304 to which 1 to 3 wt% of manganese sulfide (MnS) is added. With a general copper iron-based metal sintered body, a tensile strength of 100 MPa cannot be secured, but with a stainless steel material, the sintering temperature is as high as about 1300 ° C., so the above-described tensile strength of 100 MPa can be secured. . Moreover, since it is a stainless steel material, even if it sterilizes, corrosion of a metal sintered compact can be prevented. Moreover, the outer peripheral surface 12 that forms at least the radial bearing surface 12R of the inner member 11 has a surface open area ratio of the sintered body of 2 to 20%. When the surface opening ratio is less than 2%, the circulation of the lubricating oil is not sufficient, and when the surface opening ratio exceeds 20%, the pressure of the lubricating oil decreases. Further, the density of the sintered body is set to 6 to 8 g / mm ³ in order to maintain the lubricity and plastic workability.

  As shown in FIG. 3, the outer member 20 is formed of two members, a first outer member 20a and a second outer member 20b, and the first outer member 20a and the second outer member 20b are both The vertical cross section is formed in a substantially L shape. Specifically, the first outer member 20a includes a cylindrical portion 20a1 and a radial direction portion 20a2 formed at one end of the cylindrical portion 20a1. The second outer member 20b has a cylindrical portion 20b1 and a radial portion 20b2 formed at one end of the cylindrical portion 20b1. The first outer member 20a and the second outer member 20b are fitted between the outer peripheral surface 21 of the cylindrical portion 20a1 and the inner peripheral surface 22 of the cylindrical portion 20b1, and are fixed with an adhesive interposed therebetween. Since the end surface of the cylindrical portion 20b1 of the second outer member 20b is positioned lower than the outer surface of the radial direction portion 20a2 of the first outer member 20a, it is easy to inject adhesive.

  Both the first outer member 20a and the second outer member 20b are formed in a substantially L shape by pressing a plate material. In this embodiment, the inner peripheral surface 29 of the cylindrical portion 20a1 of the first outer member 20a forms a radial bearing surface 29R. The inner side surface 23 of the radial direction portion 20a2 of the first outer member 20a and the inner side surface 24 of the radial direction portion 20b2 of the second outer member 20b form thrust bearing surfaces 23T and 24T, respectively. Both the inner peripheral surface 29 and the inner side surfaces 23 and 24 are formed as smooth surfaces without irregularities. A small diameter inner peripheral surface 25 is formed at the inner diameter side end of the radial direction portion 20a2 of the first outer member 20a, and a small diameter inner peripheral surface 26 is formed at the inner diameter side end of the second outer member 20b. Since the fitting length between the outer peripheral surface 21 of the cylindrical portion 20a1 and the inner peripheral surface 22 of the cylindrical portion 20b1 is large, stable assembly and fixed coupling can be realized.

  As a method of setting and assembling the thrust bearing gap T of the fluid dynamic pressure bearing 10 of this embodiment, for example, the second outer member 20b is placed on a fixing jig in a posture in which the thrust bearing surface 24 faces upward. The inner member 11 is inserted so as to contact the thrust bearing surface 24T of the second outer member 20b, and the thrust bearing surface 13T of the inner member 11 contacts the thrust bearing surface 24T of the second outer member. Let Thereafter, the inner member 11 is separated upward from the second outer member 20b by a total amount of thrust bearing gaps (the thrust bearing gaps on both sides) from the moving jig. In this state, the first outer member 20a is pushed into the second outer member 20b until the thrust bearing surface 23T of the first outer member 20a contacts the thrust bearing surface 13T of the inner member 11. Then, both outer members 20a and 20b are fixed with an adhesive. By this method, the thrust bearing gap can be easily set with high accuracy.

  The small-diameter inner peripheral surface 25 at the inner diameter side end of the radial direction portion 20 a 2 of the first outer member 20 a and the small-diameter inner peripheral surface 26 at the inner diameter side end of the second outer member 20 b are the outer peripheral surface of the rotary shaft 8. It faces 8a with an appropriate gap. An oil repellent is applied to the small-diameter inner peripheral surfaces 25 and 26 in order to prevent the lubricating oil from leaking out.

  Since the dental handpiece 1 is exposed to a high-humidity atmosphere during sterilization, a corrosive material is not used, and austenitic stainless steel having excellent corrosion resistance, such as SUS304, is used. The first outer member 20a and the second outer member 20b are also made of a stainless steel material that is suitable for press work and has wear resistance. Furthermore, it is desirable to use SUS430 for the first outer member 20a fitted at least inside and having a radial bearing surface and a thrust bearing surface.

  In this embodiment, the dynamic pressure grooves 12a, 13a, 13a have a herringbone shape and are for one-way rotation. In order to identify the rotation direction, the first outer member 20a and the second outer member 20b have surfaces with different hues. Thereby, it is possible to prevent erroneous assembly. In order to form surfaces with different hues, materials of different hues are used or surface treatment is performed.

  The fluid dynamic bearing device 10 of this embodiment is formed as a dental handpiece with the same size (outer diameter, inner diameter, width) as a rolling bearing, and is highly versatile and excellent in handling.

  Lubricating oil is filled in the internal space of the fluid dynamic bearing device 10 having the above structure including the internal pores of the inner member 11 made of sintered metal. As shown in an enlarged view in FIG. 5, the lubricating oil is filled up to the entire radial bearing gap R and to the vicinity of the inner diameter end of the thrust bearing gap T. The lubricating oil is drawn to the outer diameter side (radial bearing gap R side) by the capillary force of the thrust bearing gap T. The oil level of the lubricating oil is held in the thrust bearing gap T. For easy understanding, the radial bearing gap R and the thrust bearing gap T are exaggerated.

  The lubricating oil that fills the bearing gap is not affected by the human body. Therefore, a material that satisfies the NSF H1 standard, which is the standard of the International Health Science Foundation (NSF), is used. And the lubricating oil which uses poly alpha olefin (PAO) as base oil is desirable from heat resistance and water resistance.

  In the dental handpiece 1 incorporating the fluid dynamic pressure bearing device 10 described above, as shown in FIG. 2, pressurized air is sprayed from the air supply pipe 6 provided in the head 3 to the turbine 7, and the turbine 7. Is driven, and the rotary shaft 8 rotates. When the rotating shaft 8 rotates, as shown in FIG. 5, the radial bearing gap R between the outer peripheral surface 12 of the inner member 11 of the fluid dynamic pressure bearing device 10 and the inner peripheral surface 21 of the outer member 20 and the inner surface thereof. An oil film is formed in the thrust bearing gap T between the side surfaces 13 and 13 of the side member 11 and the inner side surfaces 23 and 24 of the outer member 20. As the rotating shaft 2 rotates, the pressure of the oil film in the radial bearing gap R is increased by the dynamic pressure groove 11a, and the rotating shaft 2 and the inner member 10 are attached to the case 4 by the dynamic pressure action of the oil film. The side member 20 is supported in a non-contact manner in the radial direction and the thrust direction.

  A modification of the first embodiment of the present invention will be described with reference to FIG. In subsequent embodiments, portions having the same functions as those of the above-described first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  In this modification, the inner member 11 is made of ceramics. The inner member 11 has an outer peripheral surface 12 and both side surfaces 13 and 13. Dynamic pressure grooves 12a, 13a, 13a are formed in the radial bearing surface 12R and the thrust bearing surfaces 13T, 13T. The inner member 11 is formed by a ceramic injection molding method using ceramic powder, that is, a CIM (ceramic injection molding) molding method. After molding a molding material made by kneading ceramic powder and a binder, this molded body is put in a sintering furnace and heated to thermally decompose the binder component. For example, in this CIM molding, the radial bearing surface 12R and the thrust bearing surfaces 13T, 13T of the inner member 11 are formed with smooth surface shapes without the dynamic pressure grooves 12a, 13a, 13a. Thereafter, the dynamic pressure grooves 12a, 13a, and 13a can be finished with high precision by laser processing.

  Although the kind of ceramics which comprises the inner member 11 is not specifically limited, From a wear-resistant surface, a zirconia, an alumina, a silicon nitride, a silicon carbide, and an alumina nitride are illustrated. Among these, zirconia is preferable because it has higher mechanical strength than other ceramics and is excellent in toughness. Zirconia is desirable because it has a linear expansion coefficient substantially equal to that of metal, and even if the other member (for example, shaft member) is made of a metal member, the change in the bearing gap due to temperature change is small. Other parts are the same as those in the first embodiment, and thus the description thereof is omitted.

  Another modification of the first embodiment of the present invention will be described with reference to FIG. In this modification, the dynamic pressure grooves 23a, 24a in the thrust direction are respectively formed on the inner side surface 23 of the radial direction portion 20a2 of the first outer member 20a and the inner side surface 24 of the radial direction portion 20b2 of the second outer member 20b. Is formed. And both the side surfaces 13 and 13 of the inward member 10 are formed by the smooth surface without an unevenness | corrugation. The dynamic pressure grooves 23a and 24a in the thrust direction are formed by pressing, for example, when the first outer member 20a and the second outer member 20b are formed from a plate material by pressing. Therefore, the dynamic pressure grooves 23a and 24a can be formed with high accuracy. The shapes of the dynamic pressure grooves 23a and 24a are the same as those shown in FIGS. 4 (a) and 4 (c). Other parts are the same as those in the first embodiment.

  Next, another embodiment of the dental handpiece of the present invention will be described with reference to FIG. In this embodiment, a damper mechanism 30 is provided between the inner peripheral surface 4 a of the case 4, the inner peripheral surface 9 a of the lid member 9, and the outer member 20 of the fluid dynamic bearing device 10. A mesh spring or the like is used as the damper mechanism 30. The damper mechanism 30 can reduce the load and vibration during treatment.

  Ventilation holes 31 and 32 are provided to communicate the turbine housing space 4c of the case 4 with the outside. When the pressurized air is supplied and the turbine 4 is driven by the vent holes 31 and 32, an increase in pressure in the turbine housing space 4c is suppressed and the lubricating oil in the fluid dynamic bearing device 10 is prevented from being pushed out. Can do.

  On the cutting tool mounting side of the rotary shaft 8, a seal member 33 is provided on the inner peripheral surface of the case 4, and this seal member 33 is brought into contact with the outer peripheral surface 8 a of the rotary shaft 8. As the sealing member 33, a felt in which wax (lubricating oil) is impregnated is suitable. Thus, by providing a separate seal mechanism from the fluid dynamic bearing device 10, leakage of the lubricating oil can be further prevented.

  Furthermore, a fluid dynamic bearing device 10 according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 9 shows a state in which the fluid dynamic bearing device 10 of the present embodiment is incorporated in the same thing as the dental handpiece of FIG.

  As shown in FIG. 10, in the fluid dynamic pressure bearing device 10 of this embodiment, the side surfaces 14, 14 on both sides in the axial direction of the inner member 11 have a symmetrical shape with respect to the axial center surface of the inner member 11. ing. As shown in an enlarged view in FIG. 11, the side surface 14 includes a tapered surface 14a provided on the outer diameter side and a flat surface 14b provided on the inner diameter side. The tapered surface 14a is provided to be inclined toward the axially central portion side (that is, the side on which the side surfaces 14 and 14 approach each other) toward the outer diameter side. The flat surface 14b extends from the inner diameter end of the tapered surface 14a to the inner diameter side. The tapered surface 14a and the flat surface 14b are in contact with the lubricating oil in the thrust bearing gap T. In the present embodiment, the tapered surface 14a and the flat surface 14b are smooth surfaces without unevenness, and form the thrust bearing surfaces 14aT and 14bT, respectively.

  The inner member 11 is formed of, for example, a metal in a ring shape, and is formed of a sintered metal in the present embodiment. The outer peripheral surface 12 of the inner member 11 has a cylindrical surface shape and is in contact with the lubricating oil filled in the radial bearing gap R (see FIG. 11). The outer peripheral surface 12 of the inner member 11 forms a radial bearing surface 12R, and a dynamic pressure groove 12a is formed. As shown in FIG. 12, the dynamic pressure groove 12a of the present embodiment is formed on the entire outer peripheral surface 12, and is curved in a V shape, and a hill portion 12b (cross-hatching in the figure) that partitions the groove. And herringbone shape alternately arranged in the circumferential direction. The dynamic pressure groove 12a is formed by, for example, rolling, as in the first embodiment. In this embodiment, since the inner member 11 is formed of a sintered metal, the plastic flow of the outer peripheral surface 12 of the inner member 11 due to the compression of the rolling process can be absorbed by the internal pores of the sintered metal. For this reason, the swelling of the surface of the inner member 11 due to plastic flow is suppressed, and the dynamic pressure grooves 12a and the hill portions 12b can be formed with high accuracy.

  As shown in FIG. 10, the inner peripheral surface 11 a of the inner member 11 has chamfered portions 11 b provided at both end portions in the axial direction. The inner member 11 is formed by, for example, press-fitting (light press-fitting) the inner peripheral surface 11 a into the outer peripheral surface 8 a of the rotary shaft 8, or between the inner peripheral surface 11 a and the outer peripheral surface 8 a of the rotary shaft 8. By interposing, it is fixed to the rotating shaft 8.

  The outer member 20 has a ring shape arranged on the outer diameter side of the inner member 11, and includes a cored bar M and a resin molded portion N that is injection-molded using the cored bar M as an insert part. The core metal M is formed of, for example, a metal in a ring shape, and is formed of a sintered metal in the present embodiment. As shown in FIG. 10, the entire outer peripheral surface M <b> 1 of the core metal M and the axial end surfaces M <b> 2 and M <b> 2 and the axial end portions of the inner peripheral surface M <b> 3 are tightly held by the resin molding portion N.

  The outer member 20 has a substantially U-shape in which the axial cross section is open toward the inner diameter, and a pair of small diameter inner surfaces 21 provided on both sides of the large diameter inner peripheral surface 21 and the large diameter inner peripheral surface 29 in the axial direction. Peripheral surfaces 25 and 25, and a pair of shoulder surfaces 23 and 23 formed between both axial ends of the large-diameter inner peripheral surface 29 and the small-diameter inner peripheral surfaces 25 and 25. The large-diameter inner peripheral surface 29 is formed in a smooth cylindrical surface shape, and is configured by the inner peripheral surface M3 of the cored bar M in this embodiment. The large-diameter inner peripheral surface 29 forms a radial bearing surface 29T. The large-diameter inner peripheral surface 29 is opposed to the outer peripheral surface 12 forming the radial bearing surface 12R of the inner member 11 via the radial bearing gap R (see FIG. 11).

  The small diameter inner peripheral surfaces 25, 25 are formed in the resin molded portion N and have a smaller diameter than the large diameter inner peripheral surface 29. In the present embodiment, the small-diameter inner peripheral surfaces 25, 25 are located within the radial range of the flat surface 23 b of the side surface 23 of the inner member 11 (in the illustrated example, approximately the central portion in the radial direction of the flat surface 23 b). . An oil repellent is applied to the small-diameter inner peripheral surfaces 25, 25 in order to prevent leakage of the lubricating oil.

  The pair of shoulder surfaces 23, 23 are formed in the resin molding portion N and have a symmetrical shape with respect to the axial center surface. As shown in an enlarged view in FIG. 11, the shoulder surface 23 includes a tapered surface 23a provided on the outer diameter side and a flat surface 23b provided on the inner diameter side. The taper surface 23a is provided so as to be inclined toward the axially central portion side (that is, the side where the shoulder surfaces 23 and 23 approach each other) toward the outer diameter side. The flat surface 23b extends from the inner diameter end of the tapered surface 23a to the inner diameter side. The taper surface 23a and the flat surface 23b form thrust bearing surfaces 23aT and 23bT, respectively, and face the taper surface 23a and the flat surface 23b of the side surface 23 of the inner member 11 through the thrust bearing gap T, respectively. In the present embodiment, the tapered surface 23a and the flat surface 23b are smooth surfaces having no irregularities.

  The axial dimension of the core metal M is larger than the axial dimension of the inner member 11. Specifically, both end surfaces M2 and M2 in the axial direction of the core metal M are the flat surfaces 14b and 14b of the side surfaces 14 and 14 of the inner member 11, and the shoulder surface 23 of the outer member 20 facing the surface in the axial direction. , 23 is located on the outer side in the axial direction from the flat surface 23b (details will be described later). As a result, the portion on the inner diameter side of the cored bar M of the resin molded portion N is in a state of protruding to the axially central side from both axial end surfaces M2 and M2 of the cored bar M.

  The outer peripheral surface 27 of the outer member 20 is formed in the resin molding portion N, and as shown in FIG. 10, a cylindrical surface 27a to be attached to the case 4 and chamfers provided at both axial ends of the cylindrical surface 27a. Part 27b. The cylindrical surface 27a (attachment surface) is fixed to the case 4 side by appropriate means such as press fitting or adhesion.

  The outer member 20 is formed by resin injection molding using the core metal M and the inner member 11 as insert parts. Of the integral product of the inner member 11 and the outer member 20, molding shrinkage occurs in the resin molded portion N of the outer member 20. In general, molding shrinkage of a resin molded product occurs toward the central portion of the wall thickness. When the resin molded portion N shown in FIG. 10 is molded and contracted toward the axial center, the shoulder surface 23 of the outer member 20 may be pressed against the side surface 14 of the inner member 11. Therefore, in the present embodiment, the metal core M is disposed as an insert part on the outer member 20. The core metal M is larger in dimension in the axial direction than the inner member 11 and is provided so as to protrude from both sides in the axial direction of the inner member 11. The cored bar M prevents the resin molded part N from contracting toward the center in the axial direction. That is, the axial molding shrinkage of the shoulder surface 23 of the outer member 20 occurs with reference to the axial position of both axial end surfaces M2 of the core metal M, and the resin in the resin molding portion N in this region is directed toward the reference position. And contract from both sides in the axial direction. As a result, the shoulder surface 23 of the outer member 20 that is in close contact with the side surface 14 of the inner member 11 contracts in the direction of peeling from the inner member 11 and moves backward. Thereby, an axial gap is formed between the side surface 14 of the inner member 11 and the shoulder surface 23 of the outer member 20, and this gap functions as a thrust bearing gap T.

  At the time of injection molding, when the inner member 11 and the core metal M are positioned in the mold, the radial clearance (in the radial bearing gap R) between the outer peripheral surface 12 of the inner member 11 and the inner peripheral surface M3 of the core metal M is determined. It is necessary to set the value so that the molten resin does not enter and the inner member 11 and the outer member 20 (core metal M) can smoothly rotate relative to each other, for example, 10 to 50 μm, Preferably, it is set within a range of 20 to 40 μm. In this embodiment, since both the inner member 11 and the core metal M are formed of sintered metal having excellent moldability, the inner member 11 and the core metal M can be molded with excellent dimensional accuracy. . Therefore, the gap formed between them can be set with high accuracy, and this gap can be set within the minute range as described above.

  In this state, the molten resin is injected. As the main component resin of the molten resin, those having a large shrinkage rate (1% or more) are preferable. For example, polyacetal (POM), polyphenylene sulfide (PPS), polyamide (PA), liquid crystal polymer (LCP), or the like is used. it can. Of these, polyacetal having a particularly large shrinkage is most preferable. A material in which various fillers such as a reinforcing material and a conductive material are blended as necessary with this main component resin is used as the molten resin. By appropriately setting the type and blending amount of the filler to be blended with the molten resin, the molten resin can be made difficult to enter the radial gap between the inner member 11 and the cored bar M at the time of injection molding.

  Lubricating oil is filled in the internal space of the fluid dynamic bearing device 10 of the present embodiment configured as described above, including the inner member 11 made of sintered metal and the internal pores of the cored bar M. As shown in FIG. 11, the lubricating oil is filled up to the entire radial bearing gap R and the vicinity of the inner diameter end of the thrust bearing gap T. The lubricating oil is drawn to the outer diameter side (radial bearing gap R side) by the capillary force of the thrust bearing gap T. The oil level of the lubricating oil is held in the thrust bearing gap T, preferably between the flat surfaces 13b and 23b of the thrust bearing gap T.

  When the rotating shaft 8 rotates, the radial bearing between the outer peripheral surface 12 of the inner member 11 of the fluid dynamic pressure bearing device 10 and the large-diameter inner peripheral surface 21 (the inner peripheral surface M3 of the core metal M) of the outer member 20. An oil film is formed in the gap R. As the rotary shaft 8 rotates, the pressure of the oil film in the radial bearing gap R is increased by the dynamic pressure groove 12a, and the rotary shaft 8 and the inner member 11 are radial relative to the outer member 20 by the dynamic pressure action of this oil film. Non-contact support in the direction.

  At the same time, an oil film is formed in the thrust bearing gap T between the side surfaces 14 and 14 of the inner member 11 of the fluid dynamic bearing device 10 and the shoulder surfaces 23 and 23 of the outer member 20 facing them. Is done. As the rotating shaft 8 rotates, the pressure of the oil film in the thrust bearing gap T is increased, and the inner member 11 is supported in a non-contact manner in both thrust directions with respect to the outer member 20 by the dynamic pressure action of the oil film.

  In this embodiment, the side surface 14 of the inner member 11 facing the thrust bearing gap T and the shoulder surface 23 of the outer member 20 are formed on a smooth surface without unevenness. A dynamic pressure groove that positively generates a dynamic pressure action on the lubricating oil in the thrust bearing gap T may be formed on any one of the surfaces facing each other via the bearing gap T (not shown). If the dynamic pressure groove for thrust is a pump-out type dynamic pressure groove that pushes the lubricating oil in the thrust bearing gap T to the outer diameter side (radial bearing gap R side), the lubricating oil is drawn into the radial bearing gap R side. And oil leakage can be prevented more reliably. If a thrust dynamic pressure groove is formed in the inner member 11 made of sintered metal, the inner member 11 can be molded simultaneously with the sizing of the inner member 11. On the other hand, if the thrust dynamic pressure groove is formed in the resin molding portion N of the outer member 20, the thrust dynamic pressure groove can be molded simultaneously with the injection molding of the outer member 20.

  Moreover, in this embodiment, although the case where the dynamic pressure groove 12a was formed in the outer peripheral surface 12 of the inner member 11 was shown, it is not restricted to this, For example, while making the outer peripheral surface 12 of the inner member 11 cylindrical shape, Thus, a radial dynamic pressure generating portion may be formed on the large-diameter inner peripheral surface 21 of the outer member 20 that is opposed to the outer member 20 in the radial direction. Alternatively, by forming both the outer peripheral surface 12 of the inner member 11 and the large-diameter inner peripheral surface 21 of the outer member 20 that face each other via the radial bearing gap R into a cylindrical surface, a so-called circular bearing can be configured. Good. In this case, no radial dynamic pressure groove is formed on any surface, but a dynamic pressure action is generated when the lubricating oil in the radial bearing gap R flows as the inner member 11 rotates.

  A modification of the second embodiment of the present invention is shown in FIG. In the second embodiment, the case where the outer member 20 has the metal core M is shown. However, the present invention is not limited to this. For example, as shown in FIG. It may be configured. In this case, the outer member 20 is formed by resin injection molding using the inner member 11 as an insert part. After the injection molding, the large-diameter inner peripheral surface 21 and the end surfaces 23, 23 of the outer member 20 are peeled off from the inner member 10 due to molding shrinkage of the resin molding portion N. At this time, even if the outer member 20 is not provided with the metal core M, the outer member 20 is made of a material that is molded and contracted in the direction in which the large-diameter inner peripheral surface 21 and the end surfaces 23, 23 are peeled from the inner member 11. The resin molded part N needs to be formed. For example, if the resin molding part is formed of a resin whose main component is a liquid crystal polymer (LCP), it is possible to cause molding shrinkage as described above.

  In the above embodiment, the dynamic pressure grooves 12a, 13a, 22a, 23a, and 24a are formed in a herringbone shape, but can be formed by appropriate dynamic pressure grooves such as a spiral shape, a step shape, and an arc shape.

DESCRIPTION OF SYMBOLS 1 Dental handpiece 4 Case 7 Turbine 8 Rotating shaft 10 Fluid dynamic pressure bearing apparatus 11 Inner member 11a Inner peripheral surface 12a Dynamic pressure groove 12R Radial bearing surface 12T Thrust bearing surface 13a Dynamic pressure groove 13T Thrust bearing surface 14aT Thrust bearing surface 14bT Thrust bearing surface 20 Outer member 20a First outer member 20b Second outer member 23a Dynamic pressure groove 23T Thrust bearing surface 23aT Thrust bearing surface 23bT Thrust bearing surface 24a Dynamic pressure groove 24T Thrust bearing surface 27 Outer surface 29R Radial bearing surface 33T Thrust bearing surface 30 Damper mechanism 31 Damper mechanism 32 Communication hole 33 Seal member A Axis M Core metal N Resin molded part R Radial bearing clearance T Thrust bearing clearance

Claims (22)

  A fluid dynamic pressure bearing device for a dental handpiece, in which a cutting tool is attached and a rotating shaft driven by a turbine is rotatably supported on a case by a pair of bearing portions. The fluid dynamic pressure bearing device includes a radial bearing surface, An outer member having a thrust bearing surface formed at both ends thereof, and an inner member having a radial bearing surface and a thrust bearing surface disposed inside the outer member and facing the radial bearing surface and the thrust bearing surface, respectively. A radial bearing gap is formed between the radial bearing surfaces of the outer member and the inner member, and a thrust bearing gap is formed between the thrust bearing surfaces, and fluid is interposed in these bearing gaps. The outer member has an outer peripheral surface attached to a case, and the inner member has an inner peripheral surface attached to a rotating shaft. Family handpiece fluid dynamic pressure bearing device.   2. The fluid dynamic pressure bearing device for a dental handpiece according to claim 1, wherein the fluid interposed in the bearing gap is lubricating oil.   The fluid dynamic pressure bearing device for a dental handpiece according to claim 1 or 2, wherein a dynamic pressure groove is formed in at least one of a radial bearing surface and a thrust bearing surface of the inner member.   The fluid dynamic pressure bearing device for a dental handpiece according to claim 2, wherein a dynamic pressure groove on a radial bearing surface of the inner member is formed by rolling.   The fluid dynamic pressure bearing device for a dental handpiece according to any one of claims 1 to 4, wherein the inner member is formed of a sintered body.   The fluid dynamic bearing device for a dental handpiece according to claim 5, wherein the sintered body is a stainless steel material.   The fluid dynamic pressure bearing device for a dental handpiece according to claim 5 or 6, wherein the sintered body is a metal sintered body having a tensile allowable stress of 100 MPa or more.   The fluid dynamic bearing device for a dental handpiece according to claim 5, wherein the sintered body is ceramic.   The outer member is formed of two members, a first outer member and a second outer member, and the longitudinal cross-sectional shapes of these two members are both substantially L-shaped, and the radius of the first outer member A thrust bearing surface is formed on the inner surface of the directional portion, a radial bearing surface is formed on the inner peripheral surface of the cylindrical portion of the second outer member, and a thrust bearing surface is formed on the inner surface of the radial portion. The dental hand according to claim 1, wherein an outer peripheral surface of the cylindrical portion of the second outer member is fitted to an inner peripheral surface of the cylindrical portion of the first outer member. Fluid dynamic pressure bearing device for pieces.   2. A dynamic pressure groove is formed by press working on at least one of an inner surface of a radial portion of the first outer member and an inner surface of a radial portion of the second outer member. The fluid dynamic pressure bearing device for a dental handpiece according to any one of?   The fluid dynamic pressure bearing device for a dental handpiece according to any one of claims 1 to 10, wherein the first outer member and the second outer member are made of a stainless steel material.   The hydrodynamic bearing device for a dental handpiece according to claim 11, wherein the outer member fitted at least inside of the first outer member and the second outer member is SUS430.   The fluid dynamic pressure bearing device for a dental handpiece according to any one of claims 1 to 8, wherein the outer member is a resin injection-molded product using the inner member as an insert part.   The dental hand according to claim 13, wherein a thrust bearing gap is formed by peeling the thrust bearing surface of the outer member from the inner member by molding shrinkage in the axial direction of the resin molding portion of the outer member. Fluid dynamic pressure bearing device for pieces.   14. A core metal is provided on the outer member, and the outer member is injection-molded with resin using an inner member and a core metal disposed on the outer diameter side of the inner member as an insert part. Or the fluid dynamic pressure bearing apparatus for dental handpieces of Claim 14.   Both thrust surfaces of the inner member are formed in a tapered shape inclined in a direction approaching each other toward the outer diameter side, and a radial portion covering the thrust surface is integrally injection-molded on the outer member. The fluid dynamic bearing device for a dental handpiece according to any one of claims 13 to 15.   The fluid hydrodynamic bearing device for a dental handpiece according to any one of claims 2 to 16, wherein the lubricating oil interposed in the bearing gap satisfies the NSF H1 standard.   The fluid dynamic pressure bearing device for a dental handpiece according to any one of claims 2 to 17, wherein the lubricating oil interposed in the bearing gap is based on poly-α-olefin (PAO).   A dental handpiece incorporating the fluid dynamic bearing device according to any one of claims 1 to 18, wherein a damper mechanism is provided between the case and the outer member. . The dental handpiece according to claim 19, wherein the damper mechanism is a mesh spring.   21. The dental handpiece according to claim 19 or 20, wherein a vent hole is provided to communicate between a turbine housing space in the case of the handpiece and the outside.   The cutting tool mounting side of the rotating shaft of the handpiece is provided with a seal mechanism that is separate from the fluid dynamic pressure bearing device and contacts the rotating shaft. Dental handpiece as described.

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