Laminated back iron structure for increased motor efficiency

摘要

A rigid disk drive spindle motor includes a bobbin carried by the motor hub which has a permanent magnet attached to the inner cylindrical surface and a laminated back iron mounted at the outer cylindrical surface. The laminated back iron may be in the form of concentric cylinders or a spiral wound strip with adjoining cylinders or convolutions secured to and electrically separated from one another by an adhesive material. In another form, the back iron may be formed as a series of washer like rings mounted on the bobbin which is a configuration similar to the laminations used in the motor stator and would permit fabrication using the same manufacturing techniques. The back iron is formed of high resistance silicon steel so that both the back iron material and the laminated structure discourage Eddy current formation. The spiral wound embodiment may also be modified by having the spiral strip periodically, axially interrupted to further reduce undesired induced currents. Use of the bobbin serves to assure the concentricity of the closely adjoining stationary and rotary parts of the spindle motor and to facilitate easier manufacture and assembly. To further confine the magnetic fields, laminated fringe ring assemblies are provided at each axial end of the back iron structure. These assemblies are formed of washer like rings of permeable material that are secured to one another and electrically separated by adhesive material.