Abstract
An unbalance in high speed rotating machines leads to unwanted noise and vibration and thus to increased wear in bearings and higher friction losses. Therefore, it is desired to reduce the unbalance of the rotor to a well-defined amount, at which the radial forces and moments do not peril the intended life-time of the whole system. Taking an air-driven small-scale turbine as an exemplary application, a balancing device for small high speed rotors has been designed and characterized. The device is designed to allow rotational speeds up to 65 000 rpm. Based on dynamic force measurement using piezo-electric PZT stacks and digital lock-in-amplifiers, unbalance can be measured down to less than 1 mg?mm. In an iterative process, manual correction of the unbalance using a hand-operated rotary tool is verified and, if necessary, repeated. A key experiment shows, that an initial unbalance of 300 mg?mm can be reduced by a factor of more than 100, using the balancing device outlined above.
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