Iterative Feedforward Control for Bearing-Free Multibody Systems

Abstract

Automated machinery and robotics are commonly conventional multibody systems containing bearing components, which exhibit uncertain, discontinuous and complex tribological characteristics. These generate wear and fundamentally limit the precision of small scale motion due to the tribological effects being difficult to compensate for using model-based active control. However, they can be eliminated through the replacement of traditional bearing joints with flexure couplings, which offers a potential increase in the performance envelope. Initially a plain flexure coupling capable of large deformation is investigated, with a representative mathematical model derived based on large deformation Euler-Bernoulli theory which is validated using a bespoke experimental facility; proof of concept for the design of empirical controllers utilising experimental data is presented. Various designs of novel compound flexure couplings are conceived, comprising of multiple sections of spring steel. The presented compound flexure couplings are then characterised experimentally. A focused study of a two-compound flexure coupling-rigid body system is presented and the feasibility of generating open-loop feedfoward controllers from identified models is demonstrated in terms of accurate large displacement control. Including path correction in the presented control methodology reduces tracking errors by at least 62% and 71% in (x, y) directions, respectively, for the cases considered.