Modeling and Control of Adjustable Articulated Parallel Compliant Actuation Arrangements in Articulated Robots

Abstract

Considerable advances in robotic actuation technology have been made in recent years. Particularly the use of compliance has increased, both as series elastic elements as well as in parallel to the main actuation drives. This work focuses on the model formulation and control of compliant actuation structures including multiple branches and multiarticulation, and significantly contributes by proposing an elegant modular formulation that describes the energy exchange between the compliant elements and articulated multibody robot dynamics using the concept of power flows, and a single matrix that describes the entire actuation topology. Using this formulation, a novel gradient descent based control law is derived for torque control of compliant actuation structures with adjustable pretension, with proven convexity for arbitrary actuation topologies. Extensions toward handling unidirectionality of elastic elements and joint motion compensation are also presented. A simulation study is performed on a 3-DoF leg model, where series-elastic main drives are augmented by parallel elastic tendons with adjustable pretension. Two actuation topologies are considered, one of which includes a biarticulated tendon. The data demonstrate the effectiveness of the proposed modeling and control methods. Furthermore, it is shown the biarticulated topology provides significant benefits over the monoarticulated arrangement.

On the efficient control of series-parallel compliant articulated robots

“…Necessary specifications for the PB and ESB units are tabulated in Table I. For more details about the mass, length and hardware specifications, refer to [18], [19].…”

An efficient leg with series–parallel and biarticular compliant actuation: design optimization, modeling, and control of the eLeg

“…We briefly summarise the gradient-descent-based pretension control strategy developed in Roozing (2018). Owing to the coupling created by multi-articulated tendons, control of the tendons needs to be considered for all tendons simultaneously.…”

“…1. analyzing the results of the design optimization procedure in depth, indicating the relative strengths of monoarticulated and biarticulated configurations; most notably, we show the beneficial effects of coupling introduced by the biarticular tendon; 2. presenting extensive simulations of the three actuation configurations that show the baseline comparative performance of the different actuation configurations; furthermore, they provide a basis to choose control gain of a recently developed gradient-descent-based control method (Roozing, 2018), governing the adjustment of the parallel tendons; we leverage a recently proposed modeling approach using the concept of power ports, used to model the energy flow between actuators and robot; 3. application of the gradient-descent-based control method to an updated hardware prototype, and presenting new experimental data that demonstrate further energy-efficiency improvement over previous results.…”

“…presenting extensive simulations of the three actuation configurations that show the baseline comparative performance of the different actuation configurations; furthermore, they provide a basis to choose control gain of a recently developed gradient-descent-based control method (Roozing, 2018), governing the adjustment of the parallel tendons; we leverage a recently proposed modeling approach using the concept of power ports, used to model the energy flow between actuators and robot;…”

“… 6. In Roozing (2018), we proposed an extension to compensate for q · ≠ 0 , which in general does require ∇ q τ p * . This extension, however, is not strictly necessary and not used here.…”