451 research outputs found

    Terrestrial Locomotion of PogoX: From Hardware Design to Energy Shaping and Step-to-step Dynamics Based Control

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    We present a novel controller design on a robotic locomotor that combines an aerial vehicle with a spring-loaded leg. The main motivation is to enable the terrestrial locomotion capability on aerial vehicles so that they can carry heavy loads: heavy enough that flying is no longer possible, e.g., when the thrust-to-weight ratio (TWR) is small. The robot is designed with a pogo-stick leg and a quadrotor, and thus it is named as PogoX. We show that with a simple and lightweight spring-loaded leg, the robot is capable of hopping with TWR <1<1. The control of hopping is realized via two components: a vertical height control via control Lyapunov function-based energy shaping, and a step-to-step (S2S) dynamics based horizontal velocity control that is inspired by the hopping of the Spring-Loaded Inverted Pendulum (SLIP). The controller is successfully realized on the physical robot, showing dynamic terrestrial locomotion of PogoX which can hop at variable heights and different horizontal velocities with robustness to ground height variations and external pushes.Comment: 7 pages, 7 figure

    Hybrid Zero Dynamics of Planar Biped Walkers

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    Planar, underactuated, biped walkers form an important domain of applications for hybrid dynamical systems. This paper presents the design of exponentially stable walking controllers for general planar bipedal systems that have one degree-of-freedom greater than the number of available actuators. The within-step control action creates an attracting invariant set—a two-dimensional zero dynamics submanifold of the full hybrid model—whose restriction dynamics admits a scalar linear time-invariant return map. Exponentially stable periodic orbits of the zero dynamics correspond to exponentially stabilizable orbits of the full model. A convenient parameterization of the hybrid zero dynamics is imposed through the choice of a class of output functions. Parameter optimization is used to tune the hybrid zero dynamics in order to achieve closed-loop, exponentially stable walking with low energy consumption, while meeting natural kinematic and dynamic constraints. The general theory developed in the paper is illustrated on a five link walker, consisting of a torso and two legs with knees

    Finite-time disturbance reconstruction and robust fractional-order controller design for hybrid port-Hamiltonian dynamics of biped robots

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    In this paper, disturbance reconstruction and robust trajectory tracking control of biped robots with hybrid dynamics in the port-Hamiltonian form is investigated. A new type of Hamiltonian function is introduced, which ensures the finite-time stability of the closed-loop system. The proposed control system consists of two loops: an inner and an outer loop. A fractional proportional-integral-derivative filter is used to achieve finite-time convergence for position tracking errors at the outer loop. A fractional-order sliding mode controller acts as a centralized controller at the inner-loop, ensuring the finite-time stability of the velocity tracking error. In this loop, the undesired effects of unknown external disturbance and parameter uncertainties are compensated using estimators. Two disturbance estimators are envisioned. The former is designed using fractional calculus. The latter is an adaptive estimator, and it is constructed using the general dynamic of biped robots. Stability analysis shows that the closed-loop system is finite-time stable in both contact-less and impact phases. Simulation studies on two types of biped robots (i.e., two-link walker and RABBIT biped robot) demonstrate the proposed controller's tracking performance and disturbance rejection capability

    Energy Shaping of Underactuated Systems via Interconnection and Damping Assignment Passivity-Based Control with Applications to Planar Biped Robots

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    The sought goal of this thesis is to show that total energy shaping is an effective and versatile tool to control underactuated mechanical systems. The performance of several approaches, rooted in the port-Hamiltonian formalism, are analyzed while tackling distinct control problems: i) equilibrium stabilization; ii) gait generation; iii) gait robustication. Firstly, a constructive solution to deal with interconnection and damping assignment passivity-based control (IDA-PBC) for underactuated two-degree-of-freedom mechanical systems is proposed. This strategy does not involve the resolution of any partial differential equation, since explicit solutions are given, while no singularities depending on generalized momenta are introduced by the controller. The methodology is applied to the stabilization of a translational oscillator with a rotational actuator system, as well as, to the gait generation for an underactuated compass-like biped robot (CBR). Then, the problem of gait generation is addressed using dissipative forces in the controller. In this sense, three distinct controllers are presented, namely simultaneous interconnection and damping assignment passivity-based control with dissipative forces, energy pumping-and-damping passivity-based control (EPD-PBC), and energy pumping-or-damping control. Finally, EPD-PBC is used to increase the robustness of the gait exhibited by the CBR over uncertainties on the initial conditions. The passivity of the system is exploited, as well as, its hybrid nature (using the hybrid zero dynamics method) to carry out the stability analysis. Besides, such an approach is applied to new gaits that are generated using IDA-PBC. Numerical case studies, comparisons, and critical discussions evaluate the performance of the proposed approaches

    Foot placement for running robots

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    Dynamic balancing of underactuated robots

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    This thesis presents the control of planar underactuated systems that have one less control input than the number of degrees of freedom. The underactuated robots are studied to achieve dynamically stable motions commonly encountered during robot locomotion. This work emphasizes the relation between the underactuated systems and biped locomotion and builds on the previous works in the literature on underactuated robot locomotion. Two planar system models are treated: an acrobatic robot and a compass biped with torso. The dynamic stability of fast periodic trajectories of these systems are regulated by designing asymptotically stable feedback controllers. The resulting internal dynamics of the systems are analyzed and shaped to achieve energy efficiency and robustness of the closed-loop system trajectories. In particular, Bézier polynomial approximations and parameter optimization methods are used to systematically construct the internal dynamics of the systems. Simulation results are presented for dynamically stable orbits of the acrobatic robot and the compass biped with torso

    Impulsive torque control of biped gait with power packets

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    Many strategies for an actuated biped gait generation have been proposed based on the passive dynamic gait. Among them, this study focuses on an impulsive excitation at the toe-off instance. The strategy offers advantages in its experimental implementation; for example, it is not required to measure and control the trajectory of the legs all the time. However, there has been no study on a realistic design of the impulsive torque itself. In this paper, we propose an impulsive actuation method based on a power packet dispatching system. Power packet is a unit of electric power transfer in a pulse shape with information tags attached in voltage waveforms. According to the tag, power packets are transferred from sources to loads. On the basis of the power packetization, the torque input is configured as a result of a power packet supply to electric motors in a realistic setup. The proposed scheme controls the supply in a digitized way, that is, by changing the number of power packets supplied in a gait step. We confirm the successful gait generation with the power packets through numerical simulations

    Control of underactuated mechanical systems via passivity-based and geometric techniques

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    Il controllo di sistemi meccanici è attualmente uno tra i più attivi settori di ricerca, a causa delle diverse applicazioni di sistemi meccanici nella vita reale. Gli ultimi decenni hanno visto un accresciuto interesse nel controllo di sistemi meccanici sottoattuati. Questi sistemi sono caratterizzati dal possedere più gradi di libertà che attuatori, vale a dire, uno o più gradi di libertà non sono attuati. Questa classe di sistemi meccanici è molto rappresentata nella vita reale. Esempi ne sono navi, veicoli spaziali, veicoli sottomarini, elicotteri, automobili, robot mobili, robot spaziali e manipolatori sottoattuati. Questa tesi si concentra su differenti generalizzazioni di alcuni risultati esistenti sul controllo di questa classe di sistemi, presenti nel lavoro di A. Tornambè, R. Ortega e J. W. Grizzle, con i quali ho collaborato nei tre anni del dottorato. Questi risultati sono stati ottenuti usando due diversi approcci: quello basato sulla passività e quello geometrico. Tre classi di problemi vengono trattate: 1. Disaccoppiamento ingresso-uscita per sistemi meccanici lineari sottoattuati; 2. Stabilizzazione asintotica di equilibri arbitrari in sistemi meccanici non lineari sottoattuati; 3. Stabilizzazione esponenziale di orbite periodiche in sistemi meccanici non lineari sottoattuati soggetti a impatti, con applicazioni alla robotica bipede.Control of mechanical systems is currently among one of the most active fields of research, due to the diverse applications of mechanical systems in real life. The last decades have shown an increasing interest in the control of underactuated mechanical systems. These systems are characterized by the fact of possessing more degrees of freedom than actuators, i.e., one or more degrees of freedom are unactuated. This class of mechanical systems are abundant in real life; examples of such systems include surface vessels, spacecraft, underwater vehicles, helicopters, road vehicles, mobile robots, space robots and underactuated manipulators. The thesis focuses on different generalizations of some of the existing results on the control of this class of systems, given in the existing work of A. Tornamb, R. Ortega and J. W. Grizzle, who I collaborated with during the last three years. They have been attained by using techniques borrowed from two different approaches: the passivity-based and the geometric ones. Three classes of problems are dealt with, namely: 1. Input-output decoupling for linear underactuated mechanical systems; 2. asymptotic stabilization of arbitrary equilibria in nonlinear mechanical systems with underactuation degree one 3. exponential stabilization of periodic orbits in nonlinear underactuated mechanical systems with impulse effects, with applications to biped robot locomotio
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