Experimental comparison of nonlinear motion control methods for a variable stiffness actuator

Erler, Philipp; Beckerle, Philipp; Strah, Bruno; Rinderknecht, Stephan

doi:10.1109/biorob.2014.6913918

Cited by 10 publications

(5 citation statements)

References 18 publications

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“…For small angles, the equations for the sti actuator and the PEA can easily be linearized, and a PID controller can deliver a satisfactory control performance. For the SEA, however, the missing collocation due to the elastic coupling has to be taken into account [5], and the resulting fourth-order dynamics can no longer be controlled by a simple PID system. Because of its ability to handle these nonlinearities and collocation issues, the model-based control strategy of feedback linearization [25] provides a suitable solution for this type of problem.…”

Section: Control Algorithmmentioning

confidence: 99%

Series and Parallel Elastic Actuation: Impact of natural dynamics on power and energy consumption

Verstraten

Beckerle

Furnémont

et al. 2016

Mechanism and Machine Theory

109

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This paper provides a detailed analysis of the power and mechanical/electrical energy consumption of Series Elastic Actuators (SEAs) and Parallel Elastic Actuators (PEAs). The study is done by imposing a sinusoidal motion to a pendulum load, such that the natural dynamics automatically present itself in the power and energy consumption. This allows to link the actuators' dynamics to their loss mechanisms, revealing interesting characteristics of series and parallel elastic elements in actuator designs. Simulations demonstrate that the SEA and PEA allow to decrease both peak power and energy consumption, provided that the stiness of their elastic element is tuned properly. For the SEA, both are minimized by tuning the elastic element to the antiresonance frequency of the actuator. For the PEA, peak power is minimal at the link's resonance frequency, but the optimal stiness for minimal electrical energy consumption cannot be determined by a theoretical resonance and needs to be calculated using a complete system model. If these guidelines are followed, both types of elastic actuators can provide signicant energetic benets at high frequencies. This was conrmed by experiments, which demonstrated energy reductions of up to 78% (SEA) and 20% (PEA) compared to rigid actuators.

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Section: Control Algorithmmentioning

confidence: 99%

Series and Parallel Elastic Actuation: Impact of natural dynamics on power and energy consumption

Verstraten

Beckerle

Furnémont

et al. 2016

Mechanism and Machine Theory

109

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“…Feedback linearization is chosen to control the nonlinear dynamics of both configurations [23] and tackle the missing collocation due to the elastic coupling of the SEA [26]. For PEA and SEA, the nonlinear dynamics are compensated through applying an appropriate motor current.…”

Section: A Control Algorithmmentioning

confidence: 99%

Series and Parallel Elastic Actuation: Influence of Operating Positions on Design and Control

Beckerle

Verstraten

Mathijssen

et al. 2017

IEEE/ASME Trans. Mechatron.

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It is well-established that properly tuned elastic elements can make robotic actuators more energy-efficient, especially in cyclic tasks. Considering drive train topology, two important subcategories of elastic actuators are Series Elastic Actuation (SEA) or Parallel Elastic Actuation (PEA). There is still no definite answer to the fundamental question which topology consumes less energy in a given task. This paper approaches the problem by studying oscillatory motions of a single degree-offreedom link in a gravitational field. The imposed motion is a sinusoid with non-zero offset requiring a static torque that needs to be compensated by the actuation system. Simulations and experiments show that SEA consumes less energy up to certain offset angles. At high offsets, PEA becomes the more energyefficient alternative, provided that its no-load angle is properly tuned. Inverse dynamics simulations show how a threshold offset angle can be determined for a given task.

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“…Both actuators and the link are equipped with optical motion encoders and motor drivers with low-level current control. For appropriate tracking of the desired link trajectories and comparability between simulation and experiments, the pendulum motions are controlled using feedback linearization and a feed-forward friction compensator [25]. Stiffness control is performed using the previously presented approach by setting the position of the counter bearing according to the major frequency of the desired link motion.…”

Section: Methodsmentioning

confidence: 99%

Stiffness Control of Variable Serial Elastic Actuators: Energy Efficiency through Exploitation of Natural Dynamics

2017

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Variable elastic actuators are very promising for applications in physical human-robot interaction. Besides enabling human safety, such actuators can support energy efficiency, especially if the natural behavior of the system is exploited. In this paper, the power and energy consumption of variable stiffness actuators with serial elasticity is investigated analytically and experimentally. Besides the fundamental mechanics, the influence of friction and electrical losses is discussed. A simple but effective stiffness control method is used to exploit the corresponding knowledge of natural dynamics by tuning the system to antiresonance operation. Despite nonlinear friction effects and additional electrical dynamics, the consideration of the ideal mechanical dynamics is completely sufficient for stiffness control. Simulations and experiments show that this yields a distinct reduction in power and energy consumption, which underlines the suitability of the control strategy.

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Experimental comparison of nonlinear motion control methods for a variable stiffness actuator

Cited by 10 publications

References 18 publications

Series and Parallel Elastic Actuation: Impact of natural dynamics on power and energy consumption

Series and Parallel Elastic Actuation: Impact of natural dynamics on power and energy consumption

Series and Parallel Elastic Actuation: Influence of Operating Positions on Design and Control

Stiffness Control of Variable Serial Elastic Actuators: Energy Efficiency through Exploitation of Natural Dynamics

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