Method manufacturing of fluid dynamic bearing using cutting tool that performs micro alternating drive, fluid dynamic bearing manufactured by using the method, and disk drive device using the bearing

Abstract

A method manufacturing of a fluid dynamic bearing includes: forming a substantially linear groove having a length corresponding to a circumferential direction width of the dynamic pressure groove formed on the inner circumferential surface of a shaft housing hole portion, along the circumferential direction of a surface orthogonal to a first processing direction along the central axis direction of a work, by a byte that performs a micro alternating drive in a second processing direction orthogonal to the first processing direction; and extending the dynamic pressure groove that extends in the first processing direction by continuously forming the substantially linear grooves in the first processing direction by displacing the relative positions of the work and the byte in the first processing direction.

What is claimed is: 
     
         1 . A fluid dynamic bearing comprising:
 a shaft;   a shaft housing member that rotatably houses the shaft;   a radial dynamic pressure groove arranged on an inner circumferential surface of the shaft housing member;   a lubricant that is filled in a gap between an outer circumferential surface of the shaft and the inner circumferential surface of the shaft housing member,   wherein, in the radial dynamic pressure groove, linear grooves having a length corresponding to a circumferential direction width of the radial dynamic pressure groove, the linear grooves being formed along a circumferential direction of a surface orthogonal to an axial direction on the inner circumferential surface of the shaft housing member, are continuously arranged in the axial direction, and   wherein the radial dynamic pressure groove has, on a bottom surface thereof, a projection wing formed along the circumferential direction of the shaft housing member.   
     
     
         2 . The fluid dynamic bearing according to  claim 1 , wherein the inner circumferential surface of the shaft housing member has a taper-shaped portion, the radial dynamic pressure groove is formed in the taper-shaped portion, and a depth of the radial dynamic pressure groove is constant. 
     
     
         3 . The fluid dynamic bearing according to  claim 1 , wherein the radial dynamic pressure groove is herringbone-shaped and a depth of the radial dynamic pressure groove is 3 μm to 8 μm. 
     
     
         4 . The fluid dynamic bearing according to  claim 3 , wherein a radius of curvature of a folded portion of the herringbone-shaped radial dynamic pressure groove is 0.02 mm to 0.1 mm. 
     
     
         5 . The fluid dynamic bearing according to  claim 1 , wherein the radial dynamic pressure groove is herringbone-shaped, and a depth of the radial dynamic pressure groove at a folded portion is shallower than that in another area. 
     
     
         6 . The fluid dynamic bearing according to  claim 1 , wherein an inner diameter of the inner circumferential surface of the shaft housing member is 2 mm to 4 mm. 
     
     
         7 . The fluid dynamic bearing according to  claim 1 , wherein a thickness of an area where the radial dynamic pressure groove of the shaft housing member is formed is 0.2 mm to 0.6 mm. 
     
     
         8 . The fluid dynamic bearing according to  claim 1 , wherein the shaft housing member is integrally formed of a copper material. 
     
     
         9 . The fluid dynamic bearing according to  claim 1 , wherein the shaft housing member is integrally formed of a sintered metal. 
     
     
         10 . A fluid dynamic bearing comprising:
 a shaft;   a shaft housing member that rotatably houses the shaft;   a radial dynamic pressure groove arranged on an inner circumferential surface of the shaft housing member;   a lubricant that is filled in a gap between an outer circumferential surface of the shaft and the inner circumferential surface of the shaft housing member,   wherein the inner circumferential surface of the shaft housing member has a taper-shaped portion, the radial dynamic pressure groove is formed in the taper-shaped portion, and a depth of the radial dynamic pressure groove is constant.   
     
     
         11 . The fluid dynamic bearing according to  claim 10 , wherein the radial dynamic pressure groove is herringbone-shaped and the depth of the radial dynamic pressure groove is 3 μm to 8 μm. 
     
     
         12 . The fluid dynamic bearing according to  claim 11 , wherein a radius of curvature of a folded portion of the herringbone-shaped radial dynamic pressure groove is 0.02 mm to 0.1 mM. 
     
     
         13 . The fluid dynamic bearing according to  claim 12 , wherein the radial dynamic pressure groove is herringbone-shaped, and a depth of the radial dynamic pressure groove at the folded portion is shallower than that in another area. 
     
     
         14 . The fluid dynamic bearing according to  claim 10 , wherein an inner diameter of the inner circumferential surface of the shaft housing member is 2 mm to 4 mm. 
     
     
         15 . The fluid dynamic bearing according to  claim 10 , wherein a thickness of an area where the radial dynamic pressure groove of the shaft housing member is formed is 0.2 mm to 0.6 mm. 
     
     
         16 . A fluid dynamic bearing comprising:
 a shaft;   a shaft housing member that rotatably houses the shaft;   a first radial dynamic pressure groove and a second radial dynamic pressure groove that are arranged so as to be spaced apart from each other in an axial direction on an inner circumferential surface of the shaft housing member;   a circumferential concave portion that is arranged between the first radial dynamic pressure groove and the second radial dynamic pressure groove; and   a lubricant that is filled in a gap between an outer circumferential surface of the shaft and the inner circumferential surface of the shaft housing member,   wherein the inner circumferential surface of the shaft housing member have taper-shaped portions that extend from ends of the shaft housing member toward an intermediate portion thereof, and   wherein the first radial dynamic pressure groove and the second radial dynamic pressure groove are formed in the taper-shaped portions, and depths of the radial dynamic pressure grooves are constant.   
     
     
         17 . The fluid dynamic bearing according to  claim 16 , wherein each of the first radial dynamic pressure groove and the second radial dynamic pressure groove is herringbone-shaped and the depth of the radial dynamic pressure groove is 3 μm to 8 μm. 
     
     
         18 . The fluid dynamic bearing according to  claim 16 , wherein a radius of curvature of a folded portion of each of the herringbone-shaped first radial dynamic pressure groove and the herringbone-shaped second radial dynamic pressure groove is 0.02 mm to 0.1 mm. 
     
     
         19 . The fluid dynamic bearing according to  claim 16 , wherein each of the first radial dynamic pressure groove and the second radial dynamic pressure groove is herringbone-shaped, and the depth of the dynamic pressure groove at the folded portion is shallower than that in another area. 
     
     
         20 . The fluid dynamic bearing according to  claim 16 ,
 wherein, in the first radial dynamic pressure groove and the second radial dynamic pressure groove, linear grooves having a length corresponding to a circumferential direction width of the radial dynamic pressure groove, the linear grooves being formed along a circumferential direction of a surface orthogonal to the axial direction on the inner circumferential surface of the shaft housing member, are continuously arranged in the axial direction, and   wherein the first radial dynamic pressure groove and the second radial dynamic pressure groove have, on a bottom surface thereof, a projection wing formed along the circumferential direction of the shaft housing member.