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.
