58 research outputs found

    An Overview on Principles for Energy Efficient Robot Locomotion

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    Despite enhancements in the development of robotic systems, the energy economy of today's robots lags far behind that of biological systems. This is in particular critical for untethered legged robot locomotion. To elucidate the current stage of energy efficiency in legged robotic systems, this paper provides an overview on recent advancements in development of such platforms. The covered different perspectives include actuation, leg structure, control and locomotion principles. We review various robotic actuators exploiting compliance in series and in parallel with the drive-train to permit energy recycling during locomotion. We discuss the importance of limb segmentation under efficiency aspects and with respect to design, dynamics analysis and control of legged robots. This paper also reviews a number of control approaches allowing for energy efficient locomotion of robots by exploiting the natural dynamics of the system, and by utilizing optimal control approaches targeting locomotion expenditure. To this end, a set of locomotion principles elaborating on models for energetics, dynamics, and of the systems is studied

    Design and Control of Compliant Actuation Topologies for Energy-Efficient Articulated Robots

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    Considerable advances have been made in the field of robotic actuation in recent years. At the heart of this has been increased use of compliance. Arguably the most common approach is that of Series-Elastic Actuation (SEA), and SEAs have evolved to become the core component of many articulated robots. Another approach is integration of compliance in parallel to the main actuation, referred to as Parallel- Elastic Actuation (PEA). A wide variety of such systems has been proposed. While both approaches have demonstrated significant potential benefits, a number of key challenges remain with regards to the design and control of such actuators. This thesis addresses some of the challenges that exist in design and control of compliant actuation systems. First, it investigates the design, dynamics, and control of SEAs as the core components of next-generation robots. We consider the influence of selected physical stiffness on torque controllability and backdrivability, and propose an optimality criterion for impedance rendering. Furthermore, we consider disturbance observers for robust torque control. Simulation studies and experimental data validate the analyses. Secondly, this work investigates augmentation of articulated robots with adjustable parallel compliance and multi-articulated actuation for increased energy efficiency. Particularly, design optimisation of parallel compliance topologies with adjustable pretension is proposed, including multi-articulated arrangements. Novel control strategies are developed for such systems. To validate the proposed concepts, novel hardware is designed, simulation studies are performed, and experimental data of two platforms are provided, that show the benefits over state-of-the-art SEA-only based actuatio

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

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    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 multi-articulation, and significantly contributes by proposing an elegant modular formulation that describes the energy exchange between the compliant elements and articulated multi-body 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 towards 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 modelling and control methods. Furthermore, it is shown the biarticulated topology provides significant benefits over the monoarticulated arrangement

    Natural Motion for Energy Saving in Robotic and Mechatronic Systems

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    Energy saving in robotic and mechatronic systems is becoming an evermore important topic in both industry and academia. One strategy to reduce the energy consumption, especially for cyclic tasks, is exploiting natural motion. We define natural motion as the system response caused by the conversion of potential elastic energy into kinetic energy. This motion can be both a forced response assisted by a motor or a free response. The application of the natural motion concepts allows for energy saving in tasks characterized by repetitive or cyclic motion. This review paper proposes a classification of several approaches to natural motion, starting from the compliant elements and the actuators needed for its implementation. Then several approaches to natural motion are discussed based on the trajectory followed by the system, providing useful information to the researchers dealing with natural motion

    Inherently Elastic Actuation for Soft Robotics

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    The Development of an Antagonistic SMA Actuation Technology for the Active Cancellation of Human Tremor.

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    Human Tremor is an unintentional bodily motion that affects muscle control among both healthy individuals and those with movement disorders, occasionally to severe detriment. While assistive devices avoid the risk of side effects from pharmacological or surgical treatments, most devices are impractical for daily use due to limitations inherent in conventional actuators. The goal of this research is to address these limitations by developing an antagonistic Shape Memory Alloy (SMA) actuation technology, enabling a new class of active tremor cancellation devices. This is accomplished through the construction of a model and body of empirical support that provides the necessary design insight and predictive power for an antagonistic actuator that ensures stable amplitude and high frequency motion with low power draw. Actuation frequency and power draw were improved while balancing their competing effects through the development of: 1) a method that accurately measures the convective coefficient of SMA to enhance actuator design, 2) a growth process for carbon nanotube cooling fins to enhance cooling in a fixed medium, and 3) an understanding of the antagonistic architecture to produce increased frequency in a controllable manner. To enable applications requiring predictability for positioning and complex control, a thermodynamic model for antagonistic SMA was derived to account for inertial, slack, boiling, friction, and convective effects. Using the model, a series of simulation studies provided design insight on the effect of operating environment, driving signal, and environmental conditions so that the generic actuation system can be utilized in a wide variety of applications beyond tremor cancellation. If high forces are required in such applications, stability issues can arise, which were addressed in experimental shakedown research that broadens the high-stress SMA design space. The technology enabled by this dissertation was demonstrated in a working Active Cancellation of Tremor (ACT) prototype that produced 71% RMS cancellation of human tremor. The cancellation results show significant improvement over the current state of the art by providing intuitive, lightweight, compact hand-held tremor cancellation that is a promising solution to numerous assistive applications in medical, military, and manufacturing sectors.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/76010/1/apathak_1.pd
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