Abstract
We address the optimal control problem of robotic systems with variable stiffness actuation (VSA) including switching dynamics and discontinuous state transitions. Our focus in this paper is to consider dynamic tasks that have multiple phases of movement, contacts and impacts with the environment with a requirement of exploiting passive dynamics of the system. By modelling such tasks as a hybrid dynamical system with time-based switching, we develop a systematic methodology to simultaneously optimize control commands, time-varying stiffness profiles and temporal aspect of the movement such as switching instances and total movement duration to exploit the benefits of VSA. Numerical evaluations on a brachiating robot driven with VSA and a hopping robot equipped with variable stiffness springs demonstrate the effectiveness of the proposed approach. Furthermore, hardware experiments on a two-link brachiating robot with VSA highlight the applicability of the proposed framework in a challenging task of brachiation.
Highlights
Towards the aim of achieving highly dynamic and flexible movements in close interaction with the environment, a number of variable stiffness actuators (VSAs) have been recently developed (Van Ham et al 2007; Catalano et al 2010; Hurst et al 2010; Eiberger et al 2010; Jafari et al 2010) (see (Van Ham et al 2009) for reviews)
In order to demonstrate the effectiveness of the proposed approach, we present numerical evaluations of robot brachiation and hopping driven by VSA
We have presented a systematic methodology for movement optimization with multiple phases and switching dynamics in robotic systems with VSA with the focus on exploiting intrinsic dynamics of the system
Summary
Towards the aim of achieving highly dynamic and flexible movements in close interaction with the environment, a number of variable stiffness actuators (VSAs) have been recently developed (Van Ham et al 2007; Catalano et al 2010; Hurst et al 2010; Eiberger et al 2010; Jafari et al 2010) (see (Van Ham et al 2009) for reviews). In contrast to conventional stiff actuators, VSAs are expected to have desirable properties such as intrinsic compliance, energy storage capability with potential applications in human-robot interaction and improvements of task performance in dynamic tasks. Taking an optimal control approach, recent studies have investigated the benefits of VSA such as energy storage in explosive movements from a viewpoint of performance improvement (Braun et al 2012, 2013; Garabini et al 2011; Haddadin et al 2011).
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