Optimization of robotic arms made of a fibre composite material for a maximun fundamental frequency

The paper deals with the design of a composite arm, to be employed in the architecture of industrial, measuring robots. Based on the real working conditions, the arm is reduced to a cantilever beam, shaped as a thin walled tube, supporting a mass at the free end. An optimization study is carried out, aiming to determine the laminate properties capable of providing the maximum fundamental frequency (FF) in bending. The optimization relies on an approximate solution, obtained by modifying the Rayleigh energy method to account for the shear effect. It results in a closed-form formula, explicitly correlating FF with composite elastic properties. Two classes of laminates, namely (± θ)sand ( 0 ± 45n)s, are examined in order to assess their ability to fulfil the requirement of a maximum FF value. Moreover, the advantages and drawbacks of composites compared to metals are highlighted for the application under concern. Finally, the validity of the proposed solution is demonstrated by comparison with the results of a finite element analysis.