Energy-Efficient Variable Stiffness Actuators

IEEE Transactions on Robotics (Impact Factor: 2.43). 11/2011; 27(5):865 - 875. DOI: 10.1109/TRO.2011.2150430
Source: IEEE Xplore


Variable stiffness actuators are a particular class of actuators that is characterized by the property that the apparent output stiffness can be changed independent of the output position. To achieve this, variable stiffness actuators consist of a number of elastic elements and a number of actuated degrees of freedom, which determine how the elastic elements are perceived at the actuator output. Changing the apparent output stiffness is useful for a broad range of applications, which explains the increasing research interest in this class of actuators. In this paper, a generic, port-based model for variable stiffness actuators is presented, with which a wide variety of designs can be modeled and analyzed. From the analysis of the model, it is possible to derive kinematic properties that variable stiffness actuator designs should satisfy in order to be energy efficient. More specifically, the kinematics should be such that the apparent output stiffness can be varied without changing the potential energy that is stored in the internal elastic elements. A concept design of an energy-efficient variable stiffness actuator is presented and implemented. Simulations of the model and experiments on the realized prototype validate the design principle.

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    • "Basic concept of the twisted string actuation system. based on the moving pivot concept and the Energy-Efficient Variable Stiffness Actuators [13] developed by the Twente University. A recent review of different variable stiffness joint implementations can be found in [14]. "
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    ABSTRACT: In this paper, an ongoing work for the implementation of a variable stiffness joint actuated by a couple of twisted string actuators in antagonistic configuration is reported. The twisted string actuation system is particularly suitable for very compact and light-weight robotic devices, like artificial limbs, exoskeletons and robotic hands, since it renders a very low apparent inertia at the load side, allowing the implementation of powerful tendon-based driving systems, using as actuators small-size DC motors characterized by high speed, low torque and very limited inertia. The basic properties of the twisted string actuation system are firstly presented, and the way how they are exploited for the implementation of a variable stiffness joint is discussed. A simple control algorithm for controlling the joint stiffness and position simultaneously is discussed, and a the feedback linearization of the device is taken into account and validated in simulation.
    2015 IEEE International Conference on Robotics and Automation (ICRA), Washington State Convention Center Seattle, Washington; 05/2015
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    • "Still following the first approach, actuators are designed in order to have variable impedance. So-called variable impedance actuators (VIA) can show a behavior where the output stiffness can vary independently from the output position (Vanderborght et al., 2009; Visser et al., 2011). "
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    • "Some of these advantages have been studied and validated in few works including safety during interaction [1], [2], and mechanical robustness and the generation of high power peaks [3], [4]. The principles of the compliant actuators range from the original series elastic actuation (SEA) concept [5] to the most recent developments on variable stiffness actuation (VSA) [1], [6], [7], [8], [9], [10], [11], [12], [13], [14], [16], [17] and variable damping implementations[15], [18]. There are also large expectations that compliant actuators with fixed or variable intrinsic elasticity can eventually improve also efficiency [19], [20], [21]. "
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    ABSTRACT: This paper introduces the design tuning of a recently introduced compliant actuation scheme which was developed to provide large energy storage capacity and demonstrate energetic efficient operation. The joint is based on an asymmetric compliant antagonistic actuation scheme where torques from two motors are transmitted to the joint through two elastic elements of different stiffness level and energy storage capacity. The paper presents the method used to tune the joint compliance and shows how this can be used to select the passive elasticity of a single degree of freedom (DOF) hopping leg for improving its energetic efficiency. The design and modeling of the hopping leg are discussed and experimental results are presented to verify the improved efficiency of the leg, particularly the power and torque reduction benefits obtained under static postures or cyclic motions.
    Int. Conf. on Humanoid Robots; 11/2014
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