Hydrodynamic bearing type rotary device and recording and reproducing apparatus including the same
View Patent ↗A hydrodynamic bearing type rotary device is configured to prevent air from being trapped inside a bearing and causing the bearing to have oil film rupture and NPPR to deteriorate. In the device, a flange having a shape substantially like a disc is provided integrally with a shaft near its lower portion. A sleeve having a bearing hole is fitted to the shaft so as to be relatively rotatable. Hydrodynamic grooves are provided on at least one of an outer periphery of the shaft and an inner periphery of the sleeve. The flange forms a thrust bearing surface with a lower end surface of the sleeve. Hydrodynamic grooves are provided on at least one of the lower surface of the sleeve and an upper surface of the flange. During rotation of the bearing, the hydrodynamic grooves circulate the lubricant. Capillary pressures at respective portions in the lubricant circulation path have different magnitudes. The principle that air tends to move toward the portion having a smaller capillary pressure is utilized to make it difficult for the air to be trapped inside the bearing and to smoothly discharge the air.
1. A hydrodynamic bearing type rotary device comprising:
a shaft having a radial hydrodynamic bearing surface provided on an outer peripheral surface thereof;
a flange provided integrally with the shaft at a lower portion of the shaft;
a sleeve having a bearing hole, the sleeve being fitted to the shaft so as to be relatively rotatable, wherein a radial gap G 1 is interposed between the sleeve and the shaft, a gap S 1 is interposed between the sleeve and the flange, and the flange forms a thrust bearing surface of the gap S 1 with a lower end surface of the sleeve;
radial hydrodynamic grooves disposed on at least one of the outer periphery of the shaft and an inner periphery of the sleeve;
thrust hydrodynamic grooves disposed on at least one of the lower end surface of the sleeve and an upper surface of the flange;
a hub integrally fixed to an outer periphery of the sleeve, wherein a radial gap having a maximum gap G 2 is provided between an outer peripheral surface of the flange and an inner surface of the hub which opposes the flange, and wherein a communication path which communicates with the flange is provided on the sleeve or the hub;
a lubricant held at least in the gaps S 1 and G 1 , and the communication path, wherein at least the gap G 1 , the gap S 1 , and the communication path form a circulation path in which the lubricant circulates,
wherein the gap G 1 has a parameter Pg 1 and the gap G 2 has a parameter Pg 2 , and each of the gaps G 1 and G 2 forms a lubricant reservoir having a tube shape, and
wherein Pg 1 >Pg 2 , and the parameters Pg 1 and Pg 2 are calculated as follows:
Fgo=π×Do ×γ×cos θ
Fgi=π×Di ×γ×cos θ
Di=Do− 2 ×rg
Fg=Fgo+Fgi
Ag =π×( Do^ 2 −Di^ 2)/4
Pg=Fg/Ag
γ: Surface tension of lubricant [N/m]
θ: Contact angle of oil [radian]
Do: Outer diameter of tube [m]
Di: Inner diameter of tube [m]
rg: Oil film thickness of tube [m].
2. The hydrodynamic bearing type rotary device according to claim 1 , wherein:
an inner peripheral surface of an upper cover opposes the outer peripheral surface of an upper portion of the shaft; and
an inner diameter of the upper cover has a length shorter than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
3. The hydrodynamic bearing type rotary device according to claim 1 , wherein:
a lower cover is fixed to the hub with a gap between the lower cover and a lower surface of the flange and
an inner diameter of the lower cover is smaller than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
4. The hydrodynamic bearing type rotary device according to claim 1 , wherein:
a first circulation path for the lubricant is provided on one end surface side of the sleeve so as to form a substantially right angle with the bearing hole;
the communication path communicates with the first circulation path and is provided substantially parallel to the bearing surface of the sleeve;
a thrust hydrodynamic bearing surface is provided on an upper end surface of the sleeve;
an opening portion having a maximum gap G 3 is provided near an intersection of the bearing hole and the first circulation path, the gap G 3 forms a lubricant reservoir;
the lubricant reservoirs formed by the gap G 2 and the gap G 3 are formed to be open to an atmosphere;
a resultant force of a pressure generated by the thrust hydrodynamic grooves and a pressure generated by the radial hydrodynamic grooves during rotation is in a direction to move the lubricant from the oil reservoir having the gap G 2 toward the inner periphery of the sleeve; and
the oil in the first circulation path is moved to the communication path by a centrifugal force.
5. A recording and reproducing apparatus comprising the hydrodynamic bearing type rotary device according to claim 1 .
6. A hydrodynamic bearing type rotary device comprising: a shaft having a radial hydrodynamic bearing surface provided on an outer peripheral surface thereof;
a flange provided integrally with the shaft at a lower portion of the shaft;
a sleeve having a bearing hole, the sleeve being fitted to the shaft so as to be relatively rotatable, wherein a radial gap G 1 is interposed between the sleeve and the shaft, a gap S 1 is interposed between the sleeve and the flange, and the flange forms a thrust bearing surface of the gap S 1 with a lower end surface of the sleeve;
radial hydrodynamic grooves disposed on at least one of the outer periphery of the shaft and an inner periphery of the sleeve;
thrust hydrodynamic grooves disposed on at least one of the lower end surface of the sleeve and an upper surface of the flange;
a different dimension portion having a maximum gap S 2 provided between the flange and the lower end surface of the sleeve in a portion other than the thrust bearing surface;
a hub integrally fixed to an outer periphery of the sleeve, wherein a radial gap having a maximum gap G 2 is provided between an outer peripheral surface of the flange and an inner surface of the hub which opposes the flange;
an upper cover provided above the sleeve with a minimum gap S 3 and a maximum gap S 4 being provided between the upper cover and an upper end surface of the sleeve, the upper cover being fixed to the hub and an inner diameter portion of the upper cover having a gap G 3 at a position opposing the outer peripheral surface of an upper portion of the shaft;
a communication path provided on the sleeve or the hub, the communication path communicating the flange with the upper cover; and
a lubricant held at least in the gaps S 1 , S 2 , G 1 and S 3 , and the communication path,
wherein the gap G 1 has a parameter Pg 1 , the gap S 2 has a parameter Ps 2 , and the gap G 2 has a parameter Pg 2 ,
wherein each of the gaps G 1 and G 2 forms a lubricant reservoir having a tube shape, and the gap S 2 forms a lubricant reservoir having a disc shape;
wherein Pg 1 >Ps 2 >Pg 2 , and the parameters Pg 1 and Pg 2 are calculated as follows:
Fgo=π×Do ×γ×cos θ
Fgi=π×Di ×γ×cos θ
Di=Do− 2 ×rg
Fg=Fgo+Fgi
Ag =π×( Do^ 2 −Di^ 2)/4
Pg=Fg/Ag
γ: Surface tension of lubricant [N/m]
θ: Contact angle of oil [radian]
Do: Outer diameter of tube [m]
Di: Inner diameter of tube [m]
rg: Oil film thickness of tube [m], and
wherein the parameter Ps 2 is calculated as follows:
Fs= 2 π×Ds ×γ×cos θ
As=π×Ds×S 1
Ps=Fs/As
Ds: Inner diameter of lubricant reservoir having maximum gap Si [m]
S: Maximum gap of lubricant reservoir between sleeve and hub [m].
7. The hydrodynamic bearing type rotary device according to claim 6 , wherein:
an inner diameter of the upper cover has a length shorter than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
8. The hydrodynamic bearing type rotary device according to claim 6 , wherein:
a lower cover is fixed to the sleeve or the hub with a gap between the lower cover and a lower surface of the flange and
an inner diameter of the lower cover is smaller than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
9. The hydrodynamic bearing type rotary device according to claim 6 , wherein:
a first circulation path for the lubricant is provided on one end surface side of the sleeve so as to form a substantially right angle with the bearing hole;
the communication path communicates with the first circulation path and is provided substantially parallel to the bearing surface of the sleeve;
a thrust hydrodynamic bearing surface is provided on the upper end surface of the sleeve;
an opening portion having the gap G 3 is provided near an intersection of the bearing hole and the first circulation path, the gap G 3 forms a lubricant reservoir;
the lubricant reservoirs formed by the gap G 2 and the gap G 3 are formed to be open to an atmosphere;
a resultant force of a pressure generated by the thrust hydrodynamic grooves and a pressure generated by the radial hydrodynamic grooves during rotation is in a direction to move the lubricant from the oil reservoir having the gap G 2 toward the inner periphery of the sleeve; and
the oil in the first circulation path is moved to the communication path by a centrifugal force.
10. A recording and reproducing apparatus comprising the hydrodynamic bearing type rotary device according to claim 6 .
11. A hydrodynamic bearing type rotary device comprising:
a shaft having a radial hydrodynamic bearing surface provided on an outer peripheral surface thereof;
a flange provided integrally with the shaft at a lower portion of the shaft;
a sleeve having a bearing hole, the sleeve being fitted to the shaft so as to be relatively rotatable, wherein a radial gap G 1 is interposed between the sleeve and the shaft;
radial hydrodynamic grooves disposed on at least one of the outer periphery of the shaft and an inner periphery of the sleeve;
thrust hydrodynamic grooves disposed on at least one of the lower end surface of the sleeve and an upper surface of the flange;
a hub integrally fixed to an outer periphery of the sleeve, wherein a gap G 2 is provided between an outer peripheral surface of the flange and an inner surface of the hub which opposes the flange;
an upper cover provided above the sleeve with a minimum gap S 3 being provided between the upper cover and an upper end surface of the sleeve, the upper cover being fixed to the hub and an inner diameter portion of the cover being provided at a position opposing the outer peripheral surface of an upper portion of the shaft so as to form a maximum radial gap G 3 ;
a different dimension portion having a gap S 4 larger than the gap S 3 , the different dimension portion being provided near an inner periphery of the gap S 3 ;
a communication path provided on the sleeve or the hub, the communication path communicating the flange with the upper cover; and
a lubricant held at least in the gaps S 1 , G 1 and S 3 , and the communication path,
wherein the gap G 1 has a parameter Pg 1 , the gap S 3 has a parameter Ps 3 , and the gap S 4 has a parameter Ps 4 ,
wherein the gap G 1 forms a lubricant reservoir having a tube shape, and each of the gaps S 3 and S 4 forms a lubricant reservoir having a disc shape,
wherein Pg 1 >Ps 3 >Ps 4 , and the parameter Pg 1 is calculated as follows:
Fgo=π×Do ×γ×cos θ
Fgi=π×Di ×γ×cos θ
Di=Do− 2 ×rg
Fg=Fgo+Fgi
Ag =π×( Do^ 2 −Di^ 2)/4
Pg=Fg/Ag
γ: Surface tension of lubricant [N/m]
θ: Contact angle of oil [radian]
Do: Outer diameter of tube [m]
Di: Inner diameter of tube [m]
rg: Oil film thickness of tube [m], and
wherein the parameters Ps 3 and Ps 4 are calculated as follows:
Fs= 2 π×Ds ×γ×cos θ
As=π×Ds×S 1
Ps=Fs/As
Ds: Inner diameter of lubricant reservoir having maximum gap Si [m]
S: Maximum gap of lubricant reservoir between sleeve and hub [m].
12. The hydrodynamic bearing type rotary device according to claim 11 , wherein:
an inner diameter of the upper cover has a length shorter than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
13. The hydrodynamic bearing type rotary device according to claim 11 , wherein:
a lower cover is fixed to the sleeve or the hub with a gap between the lower cover and a lower surface of the flange and
an inner diameter of the lower cover is smaller than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
14. The hydrodynamic bearing type rotary device according to claim 11 , wherein:
a first circulation path for the lubricant is provided on one end surface side of the sleeve so as to form a substantially right angle with the bearing hole;
the communication path communicates with the first circulation path and is provided substantially parallel to the bearing surface of the sleeve;
a thrust hydrodynamic bearing surface is provided on the upper end surface of the sleeve;
an opening portion having the maximum radial gap G 3 is provided near an intersection of the bearing hole and the first circulation hole;
an oil reservoir having the gap G 2 is provided near an intersection of the lower end surface of the sleeve and the communication path;
the opening portion having the maximum radial gap G 3 and the oil reservoir having the gap G 2 are formed to be open to an atmosphere;
a resultant force of a pressure generated by the thrust hydrodynamic grooves and a pressure generated by the radial hydrodynamic grooves during rotation is in a direction to move the lubricant from the oil reservoir having the gap G 2 toward the inner periphery of the sleeve; and
the oil in the first circulation path is moved to the communication path by a centrifugal force.
15. A recording and reproducing apparatus comprising the hydrodynamic bearing type rotary device according to claim 11 .
16. A hydrodynamic bearing type rotary device comprising:
a shaft having a radial hydrodynamic bearing surface provided on an outer peripheral surface thereof;
a flange provided integrally with the shaft at a lower portion of the shaft;
a sleeve having a bearing hole, the sleeve being fitted to the shaft so as to be relatively rotatable, wherein a radial gap G 1 is interposed between the sleeve and the shaft, a gap S 1 is interposed between the sleeve and the flange, and the flange forms a thrust bearing surface of the gap S 1 with a lower end surface of the sleeve;
radial hydrodynamic grooves disposed on at least one of the outer periphery of the shaft and an inner periphery of the sleeve;
thrust hydrodynamic grooves disposed on at least one of the lower end surface of the sleeve and an upper surface of the flange;
a hub integrally fixed to an outer periphery of the sleeve, wherein a gap G 2 is provided between an outer peripheral surface of the flange and an inner surface of the hub which opposes the flange;
an upper cover provided above the sleeve with a minimum gap S 3 being provided between the upper cover and an upper end surface of the sleeve, the upper cover being fixed to the hub and an inner diameter portion of the upper cover being provided at a position opposing the outer peripheral surface of an upper portion of the shaft so as to form a maximum radial gap G 3 ;
a communication path provided on the sleeve or the hub, the communication path communicating the flange with the upper cover; and
a lubricant held at least in the gaps S 1 , S 3 , G 1 and G 3 , and the communication path,
wherein the gap G 1 has a parameter Pg 1 , the gap S 3 has a parameter Ps 3 , and the gap G 3 has a parameter Pg 3 ,
wherein each of the gaps G 1 and G 3 forms a lubricant reservoir having a tube shape, and the gap S 3 forms a lubricant reservoir having a disc shape,
wherein Pg 1 >Ps 3 >Pg 3 , and the parameters Pg 1 and Pg 3 are calculated as follows:
Fgo=π×Do ×γ×cos θ
Fgi=π×Di ×γ×cos θ
Di=Do− 2 ×rg
Fg=Fgo+Fgi
Ag =π×( Do^ 2 −Di^ 2)/4
Pg=Fg/Ag
γ: Surface tension of lubricant [N/m]
θ: Contact angle of oil [radian]
Do: Outer diameter of tube [m]
Di: Inner diameter of tube [m]
rg: Oil film thickness of tube [m], and
wherein Ps 3 is calculated as follows:
Fs= 2 πDs ×γ×cos θ
As=π×Ds×S 1
Ps=Fs/As
Ds: Inner diameter of lubricant reservoir having maximum gap Si [m]
S: Maximum gap of lubricant reservoir between sleeve and hub [m].
17. The hydrodynamic bearing type rotary device according to claim 16 , wherein:
an inner diameter of the upper cover has a length shorter than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
18. The hydrodynamic bearing type rotary device according to claim 16 , wherein:
a lower cover is fixed to the sleeve or the hub with a gap between the lower cover and a lower surface of the flange and
an inner diameter of the lower cover is smaller than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
19. The hydrodynamic bearing type rotary device according to claim 16 , wherein:
a first circulation path for the lubricant is provided on one end surface side of the sleeve so as to form a substantially right angle with the bearing hole;
the communication path communicates with the first circulation path and is provided substantially parallel to the bearing surface of the sleeve;
a thrust hydrodynamic bearing surface is provided on the upper end surface of the sleeve;
an opening portion including the maximum radial gap G 3 is provided near an intersection of the bearing hole and the first circulation hole;
an oil reservoir having the gap G 2 is provided near an intersection of the lower end surface of the sleeve and the communication path;
the opening portion having the maximum radial gap G 3 and the oil reservoir having the gap G 2 are formed to be open to an atmosphere;
a resultant force of a pressure generated by the thrust hydrodynamic grooves and a pressure generated by the radial hydrodynamic grooves during rotation is in a direction to move the lubricant from the oil reservoir having the gap G 2 toward the inner periphery of the sleeve; and
the oil in the first circulation path is moved to the communication path by a centrifugal force.
20. A recording and reproducing apparatus comprising the hydrodynamic bearing type rotary device according to claim 16 .
21. A hydrodynamic bearing type rotary device comprising:
a shaft having a radial hydrodynamic bearing surface provided on an outer peripheral surface thereof;
a flange provided integrally with the shaft at a lower portion of the shaft;
a sleeve having a bearing hole, the sleeve being fitted to the shaft so as to be relatively rotatable, wherein a radial gap G 1 is interposed between the sleeve and the shaft, a gap S 1 is interposed between the sleeve and the flange, and the flange forms a thrust bearing surface of the gap S 1 with a lower end surface of the sleeve;
radial hydrodynamic grooves disposed on at least one of the outer periphery of the shaft and an inner periphery of the sleeve;
thrust hydrodynamic grooves disposed on at least one of the lower surface of the sleeve and an upper surface of the flange;
a hub integrally fixed to an outer periphery of the sleeve, wherein a radial gap having a maximum gap G 2 is provided between an outer peripheral surface of the flange and an inner surface of the hub which opposes the flange;
an upper cover provided above the sleeve with a minimum gap S 3 being provided between the upper cover and an upper end surface of the sleeve, the upper cover being fixed to the hub and an inner diameter portion of the upper cover being provided at a position opposing the outer peripheral surface of an upper portion of the shaft so as to form a maximum radial gap G 3 ;
a communication path provided on the sleeve or the hub, the communication path communicating the flange with the upper cover;
a lubricant held at least in the gaps S 1 and G 1 , and the communication path,
wherein at least the gap G 1 , the gap S 1 , and the communication path form a circulation path in which the lubricant circulates,
wherein the gap G 1 has a parameter Pg 1 , the gap G 2 has a parameter Pg 2 , and the gap G 3 has a parameter Pg 3 , and the communication path has a parameter Pp,
wherein each of the gaps G 1 , G 2 , and G 3 , and the communication path forms a lubricant reservoir having a tube shape,
wherein Pg 1 >Pp, Pp>Pg 2 , and Pp>Pg 3 , and the parameters Pg 1 , Pg 2 , and Pg 3 are calculated as follows:
Fgo=π×Do ×γ×cos θ
Fgi=π×Di ×γ×cos θ
Di=Do− 2 ×rg
Fg=Fgo+Fgi
Ag =π×( Do^ 2 −Di^ 2)/4
Pg=Fg/Ag
γ: Surface tension of lubricant [N/m]
θ: Contact angle of oil [radian]
Do: Outer diameter of tube [m]
Di: Inner diameter of tube [m]
rg: Oil film thickness of tube [m], and
wherein Pp is calculated as follows:
Fg= 2×( u+t )×γ g ×cos θ g
Ag=u×t
Pg=Fg/Ag
Pp= 2 ×γg ×cos θ g ×( u+t )/( u×t )
u: Length of a side of cross section [m]
t: Length of another side of cross section [m]
γg: Surface tension of oil [N/m]
θ: Contact angle of oil [rad].
22. The hydrodynamic bearing type rotary device according to claim 21 , wherein:
an inner diameter of the upper cover has a length shorter than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
23. The hydrodynamic bearing type rotary device according to claim 21 , wherein:
a lower cover is fixed to the sleeve or the hub with a gap between the lower cover and a lower surface of the flange and
an inner diameter of the lower cover is smaller than an outer diameter of the radial hydrodynamic bearing surface of the shaft.
24. The hydrodynamic bearing type rotary device according to claim 21 , wherein:
a first circulation path for the lubricant is provided on one end surface side of the sleeve so as to form a substantially right angle with the bearing hole;
the communication path communicates with the first circulation path and is provided substantially parallel to the bearing surface of the sleeve;
a thrust hydrodynamic bearing surface is provided on the upper end surface of the sleeve;
an opening portion including the maximum radial gap G 3 is provided near an intersection of the bearing hole and the first circulation hole;
an oil reservoir having the maximum gap G 2 is provided near an intersection of the lower end surface of the sleeve and the communication path;
the opening portion having the maximum radial gap G 3 and the oil reservoir having the gap G 2 are formed to be open to an atmosphere;
a resultant force of a pressure generated by the thrust hydrodynamic grooves and a pressure generated by the radial hydrodynamic grooves during rotation is in a direction to move the lubricant from the oil reservoir having the gap G 2 toward the inner periphery of the sleeve; and
the oil in the first circulation path is moved to the communication path by a centrifugal force.
25. A recording and reproducing apparatus comprising the hydrodynamic bearing type rotary device according to claim 21 .
26. A hydrodynamic bearing type rotary device comprising:
a shaft having a radial hydrodynamic bearing surface provided on an outer peripheral surface thereof;
a hub provided integrally with one end portion of the shaft;
a sleeve having a bearing hole, the sleeve being fitted to the shaft so as to be relatively rotatable, wherein a radial gap G 1 is interposed between the sleeve and the shaft, a gap S 1 is interposed between the sleeve and the hub, a radial gap having a maximum gap G 2 is provided between an outer peripheral surface of the sleeve and an inner surface of the hub which opposes the sleeve, and the hub forms a thrust bearing surface of the gap S 1 with one end surface of the sleeve;
radial hydrodynamic grooves disposed on at least one of the outer periphery of the shaft and an inner periphery of the sleeve;
thrust hydrodynamic grooves disposed on at least one of the end surface of the sleeve and an opposing surface of the hub;
a communication path provided in the sleeve, the communication path communicating with the hub;
a lubricant held at least in the gaps S 1 and G 1 , and the communication path,
wherein at least the gap G 1 , the gap S 1 , and the communication path form a circulation path in which the lubricant circulates,
wherein the gap G 1 has a parameter Pg 1 and the gap G 2 has a parameter Pg 2 ,
wherein each of the gaps G 1 and G 2 forms a lubricant reservoir having a tube shape,
wherein Pg 1 >Pg 2 , and the parameters Pg 1 and Pg 2 are calculated as follows:
Fgo=π×Do ×γ×cos θ
Fgi=π×Di ×γ×cos θ
Di=Do− 2 ×rg
Fg=Fgo+Fgi
Ag =π×( Do^ 2 −Di^ 2)/4
Pg=Fg/Ag
γ: Surface tension of lubricant [N/m]
θ: Contact angle of oil [radian]
Do: Outer diameter of tube [m]
Di: Inner diameter of tube [m]
rg: Oil film thickness of tube [m].
27. A recording and reproducing apparatus comprising the hydrodynamic bearing type rotary device according to claim 26 .
28. A hydrodynamic bearing type rotary device comprising:
a shaft having a radial hydrodynamic bearing surface provided on an outer peripheral surface thereof;
a hub provided integrally with one end of the shaft;
a sleeve having a bearing hole, the sleeve being fitted to the shaft so as to be relatively rotatable, wherein a radial gap G 1 is interposed between the sleeve and the shaft, a gap S 1 is interposed between the sleeve and the hub, a radial gap having a maximum gap G 2 is provided between an outer peripheral surface of the sleeve and an inner surface of the hub which opposes the sleeve, and the hub forms a thrust bearing surface of the gap S 1 with one end surface of the sleeve;
radial hydrodynamic grooves are provided on at least one of the outer periphery of the shaft and an inner periphery of the sleeve;
thrust hydrodynamic grooves are provided on at least one of the end surface of the sleeve and an opposing surface of the hub;
a different dimension portion having a maximum gap S 2 provided between the hub and the end surface of the sleeve in a portion other than the thrust bearing surface;
a communication path provided in the sleeve, the communication path communicating with the hub; and
a lubricant held at least in the gaps S 1 , G 1 , S 2 and G 2 , and the communication path,
wherein the gap G 1 has a parameter Pg 1 , the gap S 2 has parameter Ps 2 , and the gap G 2 has a parameter Pg 2 ,
wherein each of the gaps G 1 and G 2 forms a lubricant reservoir having a tube shape, and the gap S 2 forms a lubricant reservoir having a disc shape,
wherein Pg 1 >Ps 2 >Pg 2 , and the parameters Pg 1 and Pg 2 are calculated as follows:
Fgo=π×Do ×γ×cos θ
Fgi=π×Di ×γ×cos θ
Di=Do− 2 ×rg
Fg=Fgo+Fgi
Ag =π×( Do^ 2 −Di^ 2)/4
Pg=Fg/Ag
γ: Surface tension of lubricant [N/m]
θ: Contact angle of oil [radian]
Do: Outer diameter of tube [m]
Di: Inner diameter of tube [m]
rg: Oil film thickness of tube [m], and
wherein the parameter Ps 2 is calculated as follows:
Fs= 2 π×Ds ×γ×cos θ
As=π×Ds×S 1
Ps=Fs/As
Ds: Inner diameter of lubricant reservoir having maximum gap Si [m]
S: Maximum gap of lubricant reservoir between sleeve and hub [m].
29. A recording and reproducing apparatus comprising the hydrodynamic bearing type rotary device according to claim 28 .