Combining energy and power based safety metrics in controller design for domestic robots

This paper presents a general passivity based interaction controller design approach that utilizes a combined energy and power based safety norms to assert safety of domestic robots. Since these robots are expected to co-habit the same environment with a human user, analysing and ensuring their safety is an important requirement. Safety analysis of domestic robots determine whether a robot achieves a desired safety level according to some quantitative safety metrics. When it comes to controller design for human friendly robots, it often involves introducing compliance and ensuring asymptotic stability using impedance control technique and passivity theories. The controller proposed in this work uses a passive design that extends the standard impedance control scheme with energy and power based safety metrics to ensure that safety requirements defined in these norms are achieved by domestic robots. The effectiveness of the proposed guideline is illustrated with simulation and experimental results

Simultaneous Position-and-Stiffness Control of Underactuated Antagonistic Tendon-Driven Continuum Robots

Continuum robots have gained widespread popularity due to their inherent compliance and flexibility, particularly their adjustable levels of stiffness for various application scenarios. Despite efforts to dynamic modeling and control synthesis over the past decade, few studies have focused on incorporating stiffness regulation in their feedback control design; however, this is one of the initial motivations to develop continuum robots. This paper aims to address the crucial challenge of controlling both the position and stiffness of a class of highly underactuated continuum robots that are actuated by antagonistic tendons. To this end, the first step involves presenting a high-dimensional rigid-link dynamical model that can analyze the open-loop stiffening of tendon-driven continuum robots. Based on this model, we propose a novel passivity-based position-and-stiffness controller adheres to the non-negative tension constraint. To demonstrate the effectiveness of our approach, we tested the theoretical results on our continuum robot, and the experimental results show the efficacy and precise performance of the proposed methodology

Disturbance Observer-based Robust Control and Its Applications: 35th Anniversary Overview

Disturbance Observer has been one of the most widely used robust control tools since it was proposed in 1983. This paper introduces the origins of Disturbance Observer and presents a survey of the major results on Disturbance Observer-based robust control in the last thirty-five years. Furthermore, it explains the analysis and synthesis techniques of Disturbance Observer-based robust control for linear and nonlinear systems by using a unified framework. In the last section, this paper presents concluding remarks on Disturbance Observer-based robust control and its engineering applications.Comment: 12 pages, 4 figure

From underactuation to quasi-full actuation: Aiming at a unifying control framework for articulated soft robots

We establish a structure preserving state and input transformation that allows a class of underactuated Euler Lagrange systems to be treated as “quasi-fully” actuated. In this equivalent quasi-fully actuated form, the system is characterized by the same Lagrangian structure as the original one. This facilitates the design of control approaches that take into account the underlying physics of the system and that shape the system dynamics to a minimum extent. Due to smoothness constraints on the new input vector that acts directly on the noncollocated coordinates, we coin the term quasi-fully actuated. The class of Euler–Lagrange systems we consider is the class of articulated soft robots with nonlinear spring characteristics that are modeled with a block diagonal inertia matrix. We illustrate how the quasi-fully actuated form enables the direct transfer of control concepts that have been derived for fully actuated manipulators. We adopt the popular energy-shaping and two passivity-based concepts. The exemplary adoptions of the PD+ and Slotine and Li controllers allow us to solve the task-space tracking problem for highly elastic joint robots with nonlinear spring characteristics. These control schemes allow compliant behavior of the robot's TCP to be specified with respect to a reference trajectory. A key aspect of the presented framework is that it enables the adoption of rigid joint controllers as well as concepts underlying the original stability analysis. We believe that our framework presents an important step toward unifying the control design for rigid and articulated soft robots

Energy shaping control of soft continuum manipulators with in-plane disturbances

Soft continuum manipulators offer levels of compliance and inherent safety that can render thema superior alternative to conventional rigid robotsfor a variety of tasks, such as medical interventions or human-robot interaction. However, the ability of soft continuum manipulators to compensate external disturbances need to be further enhanced to meet the stringent requirements of many practical applications.In this paper, we investigate the control problem forsoft continuum manipulators that consist of one inextensible segmentof constant section, which bends under the effect of the internal pressure and is subject to unknown disturbances acting in the plane of bending. A rigid-link model of the manipulatorwith a single input pressureis employed for control purposes and an energy-shaping approach isproposedto derive thecontrol law. A method for the adaptive estimation of disturbances is detailed and a disturbance compensation strategy is proposed.Finally, the effectiveness of the controlleris demonstrated with simulations and with experiments on an inextensible soft continuum manipulator that employs pneumatic actuation

From Underactuation to Quasi‐Full Actuation: A Unifying Control Framework for Rigid and Elastic Joint Robot

The quest for animal-like performance in robots has driven the integration of elastic elements in their drive trains, sparking a revolution in robot design. Elastic robots can store and release potential energy, providing distinct advantages over traditional robots, such as enhanced safety in human-robot interaction, resilience to mechanical shocks, improved energy efficiency in cyclic tasks, and dynamic motion capabilities. Exploiting their full potential, however, necessitates novel control methods. This thesis advances the field of nonlinear control for underactuated systems and utilizes the results to push the boundaries of motion and interaction performance of elastic robots. Through real-life experiments and applications, the proposed controllers demonstrate that compliant robots hold promise as groundbreaking robotic technology. To achieve these objectives, we first derive a simultaneous phase space and input transformation that enables a specific class of underactuated Lagrangian systems to be treated as if fully actuated. These systems can be represented as the interconnection of actuated and underactuated subsystems, with the kinetic energy of each subsystem depending only on its own velocity. Elastic robots are typical representatives. We refer to the transformed system as quasi-fully actuated due to weak constraints on the new inputs. Fundamental aspects of the transforming equations are 1) the same Lagrangian function characterizes both the original and transformed systems, 2) the transformed system establishes a passive mapping between inputs and outputs, and 3) the solutions of both systems are in a one-to-one correspondence, describing the same physical reality. This correspondence allows us to study and control the behavior of the quasi-fully actuated system instead of the underactuated one. Thus, this approach unifies the control design for rigid and elastic joint robots, enabling the direct application of control results inherited from the fully-actuated case while ensuring closed-loop system stability and passivity. Unlike existing methods, the quasi-full actuation concept does not rely on inner control loops or the neglect and cancellation of dynamics. Notably, as joint stiffness values approach infinity, the control equivalent of a rigid robot is recovered. Building upon the quasi-full actuation concept, we extend energy-based control schemes such as energy shaping and damping injection, Euler-Lagrange controllers, and impedance control. Moreover, we introduce Elastic Structure Preserving (ESP) control, a passivity-based control scheme designed for robots with elastic or viscoelastic joints, guided by the principle of ``do as little as possible''. The underlying hope is that reducing the system shaping, i.e., having a closed-loop dynamics match in some way the robot's intrinsic structure, will award high performance with little control effort. By minimizing the system shaping, we obtain low-gain designs, which are favorable concerning robustness and facilitate the emergence of natural motions. A comparison with state-of-the-art controllers highlights the minimalistic nature of ESP control. Additionally, we present a synthesis method, based on purely geometric arguments, for achieving time-optimal rest-to-rest motions of an elastic joint with bounded input. Finally, we showcase the remarkable performance and robustness of the proposed ESP controllers on DLR David, an anthropomorphic robot implemented with variable impedance actuators. Experimental evidence reveals that ESP designs enable safe and compliant interaction with the environment and rigid-robot-level accuracy in free motion. Additionally, we introduce a control framework that allows DLR David to perform commercially relevant tasks, such as pick and place, teleoperation, hammer drilling into a concrete block, and unloading a dishwasher. The successful execution of these tasks provides compelling evidence that compliant robots have a promising future in commercial applications

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

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