Control system design of multhiariable non-linear space robots

Purpose - The paper's purpose is to initiate an effort that will result in a systematic approach for design of control systems for multivariable, nonlinear, and unstable space robots. Design/methodology/approach - The design approach is based on multivariable describing function (DF) models of the space robot coupled with the use of factorization technique. The design approach is to obtain the multivariable DF models followed by application of a previously developed factorization-based controller design formula. Finally, the design must be verified by a non-linear simulation to make sure that approximations made during design are valid. Findings - It is found that the DF approach may successfully be applied in order to control nonlinear, multivariable, and unstable systems such as space robots. Research limitations/implications - At present, the approach is verified to be applicable to rigid space robots. Practical implications - The major outcome of this research is that complicated controllers of a class of space robots may be replaced by simpler controllers, taking into account the amplitude dependency features of the space robot; this amplitude dependency is the most important characteristic of a non-linear system. Originality/value - This is the first paper in the area of multivariable and unstable space robot controller design that is based on the application of the DF technique. In fact this is the first work in the area of general unstable non-linear control system design that is based on a DF technique.