There are fundamentally two types of hard disc drive bearings which are those based on standard contact ball bearings and those based on fluid dynamic bearings.
The form, radius and surface finish of the tracks is critical to the running performance and noise characteristics of these bearings. Taylor Hobson have a range of Form Talysurf systems which are suitable for measuring the form and surface finish characteristics of hard disc drive bearings.
Fluid dynamic bearings
In fluid dynamic bearings, the bearing function is taken over by a layer of lubricant less than one tenth the thickness of a human hair. The rotor supported by the bearing essentially swims around the shaft.
The elimination of metal to metal contact in fluid dynamic bearings eliminates non-repeatable runout due to surface imperfections. This makes it possible to reduce track spacing and increase the tracks per inch on the disk.
Control of surface finish, roundness and waviness is critical to the performance of fluid dynamic bearings. However there are also typically grooves machined in the shaft and rotor of FDBs which assist in the build up of a stable lubrication layer.Through co-operation with manufacturers, Taylor Hobson has developed a special analysis tool for analysing the shape and ratio of the grooves on FDB's.