Design and optimization of very high torque, low ripple, low cogging PM motors for direct driving optical telescope

This paper describes the drive system design of the European Southern Observatory Very Large Telescope (ESO VLT), that will be assembled in Chile in the near future. The solution adopted directly couples the motors and the telescope structure. This assures the best dynamic performances but it calls for unusually high torque motors. For this reason a simple scaling up of traditional motor design is not suitable and instead a dedicated approach is required. The direct drives consist of segmented, dual axial air gap brushless motors directly coupled to both the altitude and azimuth telescope axis. Moreover in optical applications, a very smooth operation is necessary and therefore the torque ripple and cogging must be minimized. A motor design optimization was performed through a magnetic simulation based on finite element analysis. Very good results were obtained by redesigning the stator cores