An engineers’s assistant for balancing of flexible rotors

Abstract

Flexible rotors usually require to be balanced for multiple speeds using several balance planes. Since the sensitivity to unbalance varies with speed the selection of the locations for the balance masses are usually based on the deflected shapes of the rotor as it passes through its critical and service running speeds. When trim-balancing a machine on site the choice of locations is frequently restricted to non-enclosed parts of the rotor and a compromise must be sought to achieve satisfactory running. As part of a larger Alvey project on the use of expert systems in engineering environments, the application of expert system techniques to flexible rotor balancing has been investigated. Areas where these techniques can be beneficial include the initial assessment of the quality of vibration signals and a check whether unbalance is a likely cause of high levels, identification of critical speeds and mode shapes, and selection of the most effective balance planes from those available. A simple system has been developed to demonstrate some of these areas. In order to gain acceptance with practising balancing engineers emphasis was placed on providing information in a familiar and easily assimilated form. The nature of the task resulted in a hybrid system with procedural and rule based sections as appropriate to control acquisition of vibration data from the transducers, assess the results and make recommendations on positioning of balance weights. Due to memory size and processor speed limitations the functionality of the demonstrator was limited to simple rotor configurations but offers potential for enhancement as improved processors and software become available.