Decoupled control of flexure-jointed hexapods using estimated joint-space mass-inertia matrix

By exploiting properties of the joint-space mass-inertia matrix of flexure-jointed hexapods (or Stewart platforms), a new decoupling method is proposed. The new decoupling method, through a static input-output mapping, transforms the highly coupled six-input six-output dynamics into six independent single-input single-output (SISO) channels. Controls for these SISO channels are far simpler than their multiple-input multiple-output (MIMO) counterparts. Prior decoupling control methods imposed severe constraints on the allowable geometry and payload. The new method loosens and removes these constraints, thus greatly expanding the applications. Based on the new decoupling method, identification algorithms using the constrained least squares (CLS) and the symmetric positive definite estimation (SPDE) methods are introduced to estimate the joint-space mass-inertia matrix using payload accelerations and base forces. These identification algorithms can be used for precision payload calibration, thus improving performance and removing the labor required to design the control for different payloads. The new decoupling method, together with the identification algorithms, is experimentally compared with earlier techniques. These experimental results indicate that the new approach is practical and improves performance.