Design considerations for a tubular linear PM servo motor

The design criteria of a tubular linear PM motor, with surface-mounted permanent magnets, are described in the paper. At first the basic equations for analysing the motor are derived, considering both slotted and slotless topologies. These equations are rearranged giving useful hints for the motor design. A finite element analysis is used to validate the results obtained from the analytical model. A good agreement is obtained comparing the magnetic field quantities as well as the mechanical forces. For servo drives the external dimensions are generally fixed, then the motor design is achieved with this constraint. The effect of the PM quality is considered, comparing motor designs with Ferrite and Nd-Fe-B magnets.