A line scanning device for laser based High Definition Television applications is being developed at IOF. High speed scanning is achieved by a rotating polygonal mirror supported from two hemispherical aerodynamic bearings. For an operation of around 80 000 rotations per minute (rpm), balancing of the rotor to a high precision is necessary. We derive the balancing requirements from elementary considerations and describe in detail how balancing is performed. The method of balancing and the measurement equipment are presented. From the experimental results it is seen, that sufficient balancing for operation at target speed can be obtained within the Rigid Rotor Approximation. However, stability is not satisfactory without additional efforts. Therefore, an `elastic' balancing concept is presented, where mirror related unbalances are compensated on the part itself. Preliminary results within this approach show that stability of the system is improved. This opens up the possibility to significantly increase long term stability and confirms the basic design concept.
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