Optimization of a Servo Motor for an Industrial Robot Application 
Svante Andersson
External reviewer: Prof. Chandur Sadarangani, Dep. of Electric Power Engineering, KTH 

A permanent magnet synchronous machine has been optimized for an industrial robot application. The optimization was made with respect to material cost, considering the demands of the application. In the
optimization, drive cycle information was utilised, and the effect of the inertia of the machine was considered. 
A simple magnetic equivalent circuit was used to calculate the no load flux, and the finite element method was used for the calculation of torque ripple and induced voltage. Root mean square values for the speed and the torque profiles of the drive cycle was used for the calculation of the iron and copper losses. The optimization
yielded a smaller and less expensive machine, compared to the machine presently used in the application. The active length was reduced by 35%, the inertia of the active part of the machine was reduced by 56%, and the material cost of the active part of the machine was reduced by 38%. The new machine has a novel design of the rotor and a simple magnet geometry. FEM calculations indicate that the machine has a high torque
ripple, and it is assumed that this can be compensated for by current profiling. A prototype has been built and measurements show a very good agreement with finite element calculation results. The prototype has, due to an error in the manufacturing of the magnets, slightly inferior thermal properties to fulfil the demands of the drive cycle.