Methods of Hydraulic Compensation for Magnetically Biased Fluid Dynamic Bearing Motor

Abstract

A fluid dynamic bearing motor including a stationary sleeve, a rotating shaft axially disposed through the sleeve, a journal gap between the shaft and the sleeve, the gap defined by first and second interfacial surfaces of the shaft and sleeve, at least one set of fluid dynamic grooves formed on the first interfacial surface of the journal gap, and at least one step defined on the second interfacial surface of the journal gap.

1 . A method of operating a motor having a fluid dynamic bearing formed between a fixed sleeve and a rotatable shaft disposed in the sleeve, and the bearing having a fluid with a variable viscosity disposed therein, the method comprising:
 generating a thrusting force for lifting the rotatable shaft from fluid pressure created, at least in part, by interaction between a surface of one of the shaft and sleeve and pumping grooves disposed on the other of the shaft and the sleeve, whereby the thrusting force produces an amount of lift determined at least in part by the fluid viscosity; and   dynamically adjusting the thrusting force to regulate the amount of lift by varying a size of a gap formed between the surface and the pumping grooves.   
     
     
         2 . The method of  claim 1 , wherein the size of the gap is varied by relative axial movement of the shaft and the sleeve, wherein the surface includes one or more steps proud from a remainder of the surface, such that as the pumping grooves become more aligned with the steps, the gap decreases, causing the fluid pressure to increase, and produce more thrusting force. 
     
     
         3 . The method of  claim 2 , wherein the pumping grooves are disposed on an outer diameter of the shaft, and the surface comprises an inner diameter of the sleeve. 
     
     
         4 . The method of  claim 2 , wherein the pumping grooves are disposed on an inner diameter of the sleeve, and the surface comprises an outer diameter of the shaft. 
     
     
         5 . The method of  claim 1 , wherein the pumping grooves are asymmetric to establish pumping pressure toward an end of the shaft. 
     
     
         6 . The method of  claim 1 , wherein generating the thrusting force for lifting the rotatable shaft further comprises a thrusting force generated by pumping grooves on at least one of a counterplate and a facing surface of the shaft. 
     
     
         7 . A motor having a fluid dynamic bearing formed in a gap disposed between a fixed sleeve and a rotatable shaft disposed in the sleeve, lubricating fluid disposed in the gap, the motor formed by a method comprising:
 providing a base under the shaft;   defining one or more steps proud from a surface of one of the fixed sleeve and the rotatable shaft; and   defining pumping grooves on a surface of the other of the fixed sleeve and the rotatable shaft, the pumping grooves positioned relative to the one or more steps to establish, at least in part, during operation, an asymmetric fluid pressure profile that supports the shaft for rotation over the base, and responds to effects from fluid viscosity changes that affect the asymmetric fluid pressure profile by an relative axial movement between the grooves and the one or more steps, thereby countering the effects from fluid viscosity changes to the asymmetric fluid pressure profile.   
     
     
         8 . The method of  claim 7 , wherein the pumping grooves are asymmetric to establish pumping pressure toward an end of the shaft. 
     
     
         9 . The method of  claim 7 , wherein defining the one or more steps comprises adding material to the surface of one of the fixed sleeve and the rotatable shaft by at least one of the following methods: plating, coating, and sputtering. 
     
     
         10 . The method of  claim 9 , wherein the material is added by sputtering a Diamond Like Coating upon the surface of one of the fixed sleeve and the rotatable shaft. 
     
     
         11 . The method of  claim 7 , wherein defining the one or more steps comprises removing material from the surface of one of the fixed sleeve and the rotatable shaft by at least one of the following methods: turning, grinding, electrochemical machining, and electrical discharge machining. 
     
     
         12 . The method of  claim 7 , wherein the pumping grooves are defined on an inner diameter of the sleeve, and the surface opposite the pumping grooves comprises an outer diameter of the shaft. 
     
     
         13 . The method of  claim 7 , wherein the pumping grooves are defined on an outer diameter of the shaft, and the surface opposite the pumping grooves comprises an inner diameter of the sleeve. 
     
     
         14 . The method of  claim 7 , wherein the pumping grooves are asymmetric to establish pumping pressure toward an end of the shaft proximate the base. 
     
     
         15 . The method of  claim 7  further comprising defining pumping grooves on at least one of the base under the shaft and a surface of the shaft opposite the base to aid in establishing the pressure profile that supports the shaft for rotation over the base. 
     
     
         16 . A method for countering effects from fluctuating fluid viscosity of fluid disposed in a gap of a fluid dynamic bearing comprising:
 moving a first surface axially relative to a second surface during operation at least in part by the effects from fluctuating fluid viscosity;   generating hydraulic force by interaction between at least one set of fluid dynamic grooves on the first surface and at least one step extending from the second surface; and   countering the axial movement of the first surface relative to the second surface by, at least in part, the hydraulic force changing to compensate for the effects from fluctuating fluid viscosity that would otherwise cause increased axial movement of the first surface relative to the second surface.   
     
     
         17 . The method of  claim 16 , wherein the fluid dynamic grooves are defined on an inner diameter of a sleeve, and the second surface comprises an outer diameter of the shaft. 
     
     
         18 . The method of  claim 16 , wherein the fluid dynamic grooves are defined on an outer diameter of a shaft, and the second surface comprises an inner diameter of the sleeve. 
     
     
         19 . The method of  claim 16 , wherein the pumping grooves are asymmetric to establish pumping pressure toward an end of the shaft adjacent the base. 
     
     
         20 . The method of  claim 16 , wherein the moving comprises operating a motor, in which the fluid dynamic bearing is a part, the operating resulting in changing fluid viscosity