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

ABSTRACT 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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    • "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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    • "application domains require direct interaction of the robot with the human/environment and it becomes evident that this typical ''stiff'' robotic actuation approach has limited performance related to the ability of interaction, robustness and safety, [1]. To deal with these drawbacks, completely different design and control approaches have been introduced which focus on light and compliant structures to lower the output mechanical impedance and control strategies specifically formulated to cope with unexpected interactions [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]. In detail, compliance has been identified as a key feature that these robots should incorporate. "
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    ABSTRACT: Compliance is increasingly being incorporated in the transmission of robotics actuation systems to cope with unpredictable interactions, improve the robustness of the robot and in some cases its efficiency. However, compliance also introduces some drawbacks as e.g. reduced bandwidth of the controlled system and typically underdamped vibration modes which decrease the accuracy and stability margin of the controlled system. To tackle these issues, variable physical damping has recently been incorporated in such actuation systems. This paper presents the analysis, development, control, identification and experimental evaluation of a novel actuation system which embodies transmission characteristics such as passive compliance and variable physical damping. The first part of this paper introduces an analysis on how these two physical properties affect the performance of the actuation system with the second part analysing the mechatronic design and control in detail. Furthermore, a novel damping estimation method is presented. Results are presented to validate the results obtained in the analysis section advantages gained by employing such actuation approach and to show the effectiveness of the actuation unit in replicating and estimating desired mechanical impedance values.
    Robotics and Autonomous Systems 07/2014; DOI:10.1016/j.robot.2014.06.007 · 1.26 Impact Factor
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