Path planning for active tensegrity structures

This paper presents a path planning method for actuated tensegrity structures with quasi-static motion. The valid configurations for such structures lay on an equilibrium manifold, which is implicitly defined by a set of kinematic and static constraints. The exploration of this manifold is difficult with standard methods due to the lack of a global parameterization. Thus, this paper proposes the use of techniques with roots in differential geometry to define an atlas, i.e., a set of coordinated local parameterizations of the equilibrium manifold. This atlas is exploited to define a rapidly-exploring random tree, which efficiently finds valid paths between configurations. However, these paths are typically long and jerky and, therefore, this paper also introduces a procedure to reduce their control effort. A variety of test cases are presented to empirically evaluate the proposed method. (C) 2015 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (author's final draft

Deep Reinforcement Learning for Tensegrity Robot Locomotion

Tensegrity robots, composed of rigid rods connected by elastic cables, have a number of unique properties that make them appealing for use as planetary exploration rovers. However, control of tensegrity robots remains a difficult problem due to their unusual structures and complex dynamics. In this work, we show how locomotion gaits can be learned automatically using a novel extension of mirror descent guided policy search (MDGPS) applied to periodic locomotion movements, and we demonstrate the effectiveness of our approach on tensegrity robot locomotion. We evaluate our method with real-world and simulated experiments on the SUPERball tensegrity robot, showing that the learned policies generalize to changes in system parameters, unreliable sensor measurements, and variation in environmental conditions, including varied terrains and a range of different gravities. Our experiments demonstrate that our method not only learns fast, power-efficient feedback policies for rolling gaits, but that these policies can succeed with only the limited onboard sensing provided by SUPERball's accelerometers. We compare the learned feedback policies to learned open-loop policies and hand-engineered controllers, and demonstrate that the learned policy enables the first continuous, reliable locomotion gait for the real SUPERball robot. Our code and other supplementary materials are available from http://rll.berkeley.edu/drl_tensegrityComment: International Conference on Robotics and Automation (ICRA), 2017. Project website link is http://rll.berkeley.edu/drl_tensegrit

Redundant Unilaterally Actuated Kinematic Chains: Modeling and Analysis

Unilaterally Actuated Robots (UAR)s are a class of robots defined by an actuation that is constrained to a single sign. Cable robots, grasping, fixturing and tensegrity systems are certain applications of UARs. In recent years, there has been increasing interest in robotic and other mechanical systems actuated or constrained by cables. In such systems, an individual constraint is applied to a body of the mechanism in the form of a pure force which can change its magnitude but cannot reverse its direction. This uni-directional actuation complicates the design of cable-driven robots and can result in limited performance. Cable Driven Parallel Robot (CDPR)s are a class of parallel mechanisms where the actuating legs are replaced by cables. CDPRs benefit from the higher payload to weight ratio and increased rigidity. There is growing interest in the cable actuation of multibody systems. There are potential applications for such mechanisms where low moving inertia is required. Cable-driven serial kinematic chain (CDSKC) are mechanisms where the rigid links form a serial kinematic chain and the cables are arranged in a parallel configuration. CDSKC benefits from the dexterity of the serial mechanisms and the actuation advantages of cable-driven manipulators. Firstly, the kinematic modeling of CDSKC is presented, with a focus on different types of cable routings. A geometric approach based on convex cones is utilized to develop novel cable actuation schemes. The cable routing scheme and architecture have a significant effect on the performance of the robot resulting in a limited workspace and high cable forces required to perform a desired task. A novel cable routing scheme is proposed to reduce the number of actuating cables. The internal routing scheme is where, in addition to being externally routed, the cable can be re-routed internally within the link. This type of routing can be considered as the most generalized form of the multi-segment pass-through routing scheme where a cable segment can be attached within the same link. Secondly, the analysis for CDSKCs require extensions from single link CDPRs to consider different routings. The conditions to satisfy wrench-closure and the workspace analysis of different multi-link unilateral manipulators are investigated. Due to redundant and constrained actuation, it is possible for a motion to be either infeasible or the desired motion can be produced by an infinite number of different actuation profiles. The motion generation of the CDSKCs with a minimal number of actuating cables is studied. The static stiffness evaluation of CDSKCs with different routing topologies and isotropic stiffness conditions were investigated. The dexterity and wrench-based metrics were evaluated throughout the mechanism's workspace. Through this thesis, the fundamental tools required in studying cable-driven serial kinematic chains have been presented. The results of this work highlight the potential of using CDSKCs in bio-inspired systems and tensegrity robots

A research on a reconfigurable hypar structure for architectural applications

Thesis (Master)--İzmir Institute of Technology, Architecture, İzmir, 2013Includes bibliographical references (leaves: 102-108)Text in English; Abstract: Turkish and Englishxii, 108 leavesKinetic design strategy is a way to obtain remarkable applications in architecture. These kinetic designs can offer more advantages compared to conventional ones. Basic knowledge of different disciplines is necessary to generate kinetic designs. In other words, interdisciplinary studies are critical. Therefore, architect's knowledge must be wide-ranging in order to increase novel design approaches and applications. The resulting rich hybrid products increase the potential of the disciplines individually. Research on kinetic structures shows that the majority of kinetic structures are deployable. However, deployable structures can only be transformed from a closed compact configuration to a predetermined expanded form. The motivation of the present dissertation is generating a novel 2 DOF 8R reconfigurable structure which can meet different hyperbolic paraboloid surfaces for architectural applications. In order to obtain this novel structure; the integration between the mechanism science and architecture is essential. The term reconfigurable will be used in the present dissertation to describe deployable structures with various configurations. The novel reconfigurable design utilizes the overconstrained Bennett linkage and the production principals of ruled surfaces. The dissertation begins with a brief summary of deployable structures to show their shortcomings and their lack of form flexibility. Afterward, curved surfaces, basic terms in mechanisms and overconstrained mechanisms were investigated. Finally, a proposed novel mechanism which is inspired from the basic design principles of Bennett linkage and the fundamentals of ruled surfaces are explained with the help of kinematic diagrams and models

Distributed Actuation and Control of a Tensegrity Based Morphing Wing

Modern aircraft wings change shape via the deflection of discrete, hinged, control surfaces, which often exhibit areas of adverse pressure gradient along the hinge line, leading to flow separation and poor wing efficiency. To reduce surface discontinuities and sharp edges, a possible solution is to replace part of the conventional wing with a smart structure with distributed actuation, allowing subtle changes in curvature. Greater wing shape adaptability also allows better matching of the aerodynamic performance to the flight regime. This article presents an active tensegrity structure concept as the basis for a morphing wing. An experimental device has been designed and built, incorporating six pneumatic actuators giving four controlled shape-changing degrees-of-freedom, and two internal load paths controlled to maintain the pre-stress in the structure. The dynamic behavior of the smart structure has been investigated via a series of simulations and experiments. Wind tunnel test results have demonstrated that the prototype morphing wing is capable of achieving accurate shape control in the presence of a variety of aerodynamic load conditions and that its aerodynamic performance matches that predicted by simulation. As a lightweight controllable structure, it is a promising candidate for future development in the challenging field of morphing wing design.</p

Distributed Actuation and Control of a Tensegrity Based Morphing Wing

Modern aircraft wings change shape via the deflection of discrete, hinged, control surfaces, which often exhibit areas of adverse pressure gradient along the hinge line, leading to flow separation and poor wing efficiency. To reduce surface discontinuities and sharp edges, a possible solution is to replace part of the conventional wing with a smart structure with distributed actuation, allowing subtle changes in curvature. Greater wing shape adaptability also allows better matching of the aerodynamic performance to the flight regime. This article presents an active tensegrity structure concept as the basis for a morphing wing. An experimental device has been designed and built, incorporating six pneumatic actuators giving four controlled shape-changing degrees-of-freedom, and two internal load paths controlled to maintain the pre-stress in the structure. The dynamic behavior of the smart structure has been investigated via a series of simulations and experiments. Wind tunnel test results have demonstrated that the prototype morphing wing is capable of achieving accurate shape control in the presence of a variety of aerodynamic load conditions and that its aerodynamic performance matches that predicted by simulation. As a lightweight controllable structure, it is a promising candidate for future development in the challenging field of morphing wing design.</p

Distributed actuation and control of a morphing tensegrity structure

Structures and actuation systems need to be closely integrated together in the future to create faster, more efficient, lightweight dynamic machines. Such actuated structures would be used for morphing aircraft wings, lightweight actuated space structures, or in robotics. This approach requires actuators to be distributed through the structure. A tensegrity structure is a very promising candidate for this future integration due to its potentially excellent stiffness and strength-to-weight ratio, and the inherent advantage of being a multi-element structure into which actuators can be embedded. This paper presents methods for analysis of the structure geometry, for closed-loop motion control, and includes experimental results for a structure actuated by lightweight pneumatic muscles. In a practical morphing tensegrity structure, it cannot be assumed that tension and compression members always meet at a point. Thus, a form-finding method has been developed to find stable geometries and determine stiffness properties for tensegrity structures with nodes of finite dimension. An antagonistic multi-axis control scheme has been developed for the shape position and motion control. In the experimental actuated tensegrity system presented the pneumatic muscles are controlled by on-off valves, for which a dead-band switching controller is designed based on a new stability criterion. The experimental system demonstrates accurate control of shape change while maintaining a desired level of internal preload in a stiff structure, showing considerable promise for future lightweight dynamic machines