This paper presents a procedure for solving a robust performance problem for SISO systems using a loop-shaping technique. We investigated first the relationship between a mixed-sensitivity H-infinity optimisation problem and classical loop shaping. It is shown how classical loop shaping can be used to minimise the H-infinity cost function. This then provides insight into a further development of loop shaping to minimise the structured singular value for robust performance. The approach is demonstrated by its application to the control of a robot arm whose moment of inertia varies considerably with angle.
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