Modeling and Control of a novel Variable Stiffness three DoF Wrist

This paper presents a novel design for a Variable Stiffness 3 DoF actuated wrist to improve task adaptability and safety during interactions with people and objects. The proposed design employs a hybrid serial-parallel configuration to achieve a 3 DoF wrist joint which can actively and continuously vary its overall stiffness thanks to the redundant elastic actuation system, using only four motors. Its stiffness control principle is similar to human muscular impedance regulation, with the shape of the stiffness ellipsoid mostly depending on posture, while the elastic cocontraction modulates its overall size. The employed mechanical configuration achieves a compact and lightweight device that, thanks to its anthropomorphous characteristics, could be suitable for prostheses and humanoid robots. After introducing the design concept of the device, this work provides methods to estimate the posture of the wrist by using joint angle measurements and to modulate its stiffness. Thereafter, this paper describes the first physical implementation of the presented design, detailing the mechanical prototype and electronic hardware, the control architecture, and the associated firmware. The reported experimental results show the potential of the proposed device while highlighting some limitations. To conclude, we show the motion and stiffness behavior of the device with some qualitative experiments.Comment: 13 pages + appendix (2 pages), 19 figures, submitted to IJR

Force Estimation for Teleoperating Industrial Robots

As the energy on the particle accelerators or heavy ion accelerators such as CERN or GSI, fusion reactors such as JET or ITER, or other scientific experiments is increased, it is becoming increasingly necessary to use remote handling techniques in order to interact with the remote and radioactive environment

Design and Analysis of Novel Actuation Mechanism with Controllable Stiffness

Actuators intended for human–machine interaction systems are usually designed to be mechanically compliant. Conventional actuators are not suitable for this purpose due to typically high stiffness. Advanced powered prosthetic and orthotic devices can vary their stiffness during a motion cycle and are power-efficient. This paper proposes a novel actuator design that modulates stiffness by means of a flexible beam. A motorized drive system varies the active length of the cantilever beam, thus achieving stiffness modulation. New large deflection formulation for cantilever beams with rolling contact constraints is used to determine the moment produced by the actuator. To validate the proposed solution method, an experiment was performed to measure large static deformations of a cantilever beam with the same boundary conditions as in the actuator design. The experiments indicate excellent agreement between measured and calculated contact forces between beam and roller, from which the actuator moment is determined

Architectural study of the design and operation of advanced force feedback manual controllers

A teleoperator system consists of a manual controller, control hardware/software, and a remote manipulator. It was employed in either hazardous or unstructured, and/or remote environments. In teleoperation, the main-in-the-loop is the central concept that brings human intelligence to the teleoperator system. When teleoperation involves contact with an uncertain environment, providing the feeling of telepresence to the human operator is one of desired characteristics of the teleoperator system. Unfortunately, most available manual controllers in bilateral or force-reflecting teleoperator systems can be characterized by their bulky size, high costs, or lack of smoothness and transparency, and elementary architectures. To investigate other alternatives, a force-reflecting, 3 degree of freedom (dof) spherical manual controller is designed, analyzed, and implemented as a test bed demonstration in this research effort. To achieve an improved level of design to meet criteria such as compactness, portability, and a somewhat enhanced force-reflecting capability, the demonstration manual controller employs high gear-ratio reducers. To reduce the effects of the inertia and friction on the system, various force control strategies are applied and their performance investigated. The spherical manual controller uses a parallel geometry to minimize inertial and gravitational effects on its primary task of transparent information transfer. As an alternative to the spherical 3-dof manual controller, a new conceptual (or parallel) spherical 3-dof module is introduced with a full kinematic analysis. Also, the resulting kinematic properties are compared to those of other typical spherical 3-dof systems. The conceptual design of a parallel 6-dof manual controller and its kinematic analysis is presented. This 6-dof manual controller is similar to the Stewart Platform with the actuators located on the base to minimize the dynamic effects. Finally, a combination of the new 3-dof and 6-dof concepts is presented as a feasible test-bed for enhanced performance in a 9-dof system

Payload analysis and control of manipulators for human interactive environments

Esta tesis doctoral presenta los resultados de simulaciones numéricas y algunos análisis experimentales de tres aspectos principales: el modelamiento dinámico de manipuladores de múltiples grados de libertad (GdL) (n 2 GdL), el cálculo de la capacidad dinámica de carga asociada al manejo de dicha carga, y el análisis y diseño de controladores no lineales incluyendo el Control Adaptativo por Desfalsificación (CAD). Se desarrollaron análisis de dos (2) casos de estudio: el SCORBOT ER V PLUS fabricado por Intelitech Corp. de 5 grados de libertad y el manipulador redundante de 7 grados de libertad conocido como el Whole Arm Manipulator (WAM) fabricado por Barrett Technology Inc. y que cuenta con características de seguridad intrínseca, manipulación inversa y docilidad, y es aplicable en la interacción humano-robot (IHR). Inicialmente, se calculó y validó el modelado dinámico de los casos de estudio. Los modelos dinámicos inverso y directo del SCORBOT ER V PLUS fueron validados numéricamente. Luego, una validación experimental para el WAM presenta una comparación entre los datos numéricos y experimentales, identificando la necesidad de un mejor modelo de la fricción seca. Después, se propuso y evaluó una metodología para el cálculo de la capacidad dinámica de carga en el espacio de trabajo completo de manipuladores para diferentes tipos de controladores. Luego, para el análisis del Control Adaptativo por Desfalsificación con factor de olvido para manipuladores de múltiples grados de libertad, se realizó una comparación con un controlador adaptativo tradicional basado en el modelo y se aplicó al modelo del manipulador SCORBOR ER V PLUS. Finalmente, la técnica de Control por Desfalsificación fue exitosamente aplicada al modelo del WAM. En conclusión, este trabajo puede contribuir al uso de técnicas de control no lineal avanzado y manejo de carga para manipuladores redundantes con manipulación inversa, aplicables en ambientes de interacción con humanosAbstract : This doctoral thesis presents the results of numerical simulations and some experimental analysis of three main topics: the dynamical modeling of multiple degree of freedom (MDoF) manipulators (n 2 DoF), dynamic load carrying capacity computation (DLCC) for the payload handling issue and nonlinear control analysis and design including Unfalsified Adaptive Control (UAC). We performed analysis of two (2) cases of study: the 5 DoF SCORBOT ER V PLUS manufactured by Intelitech Corp. and the 7 DoF redundant Whole Arm Manipulator (WAM) manufactured by Barrett Technology Inc. with intrinsic safety, backdrivable and compliant characteristics and suitable for human-robot interaction (HRI). Initially, we computed and validated the dynamical model of the cases of study. The inverse and direct dynamical models of the SCORBOT ER V PLUS were numerically validated. Then, an experimental validation of inverse dynamical model of the WAM presents a comparison between numerical and experimental data, identifying the need for better friction models. After that, we proposed and evaluated a methodology for DLCC computation in the entire workspace of manipulators for different types of controllers. Then, for the analysis of the data-driven UAC with fading memory for multiple DoF manipulators, we performed a comparison with a traditional modelbased Adaptive Controller and applied to the SCORBOT ER V PLUS manipulator. Finally, the Unfalsified Control technique was successfully applied to the WAM model for a similar simulation setup. In conclusion, this work may contribute to the use of advanced nonlinear control and payload handling techniques for redundant backdrivable multiple DoF manipulators, suitable for human interactive environmentsDoctorad

Whole-Hand Robotic Manipulation with Rolling, Sliding, and Caging

Traditional manipulation planning and modeling relies on strong assumptions about contact. Specifically, it is common to assume that contacts are fixed and do not slide. This assumption ensures that objects are stably grasped during every step of the manipulation, to avoid ejection. However, this assumption limits achievable manipulation to the feasible motion of the closed-loop kinematic chains formed by the object and fingers. To improve manipulation capability, it has been shown that relaxing contact constraints and allowing sliding can enhance dexterity. But in order to safely manipulate with shifting contacts, other safeguards must be used to protect against ejection. “Caging manipulation,” in which the object is geometrically trapped by the fingers, can be employed to guarantee that an object never leaves the hand, regardless of constantly changing contact conditions. Mechanical compliance and underactuated joint coupling, or carefully chosen design parameters, can be used to passively create a caging grasp – protecting against accidental ejection – while simultaneously manipulating with all parts of the hand. And with passive ejection avoidance, hand control schemes can be made very simple, while still accomplishing manipulation. In place of complex control, better design can be used to improve manipulation capability—by making smart choices about parameters such as phalanx length, joint stiffness, joint coupling schemes, finger frictional properties, and actuator mode of operation. I will present an approach for modeling fully actuated and underactuated whole-hand-manipulation with shifting contacts, show results demonstrating the relationship between design parameters and manipulation metrics, and show how this can produce highly dexterous manipulators

Human-friendly robotic manipulators: safety and performance issues in controller design

Recent advances in robotics have spurred its adoption into new application areas such as medical, rescue, transportation, logistics, personal care and entertainment. In the personal care domain, robots are expected to operate in human-present environments and provide non-critical assistance. Successful and flourishing deployment of such robots present different opportunities as well as challenges. Under a national research project, Bobbie, this dissertation analyzes challenges associated with these robots and proposes solutions for identified problems. The thesis begins by highlighting the important safety concern and presenting a comprehensive overview of safety issues in a typical domestic robot system. By using functional safety concept, the overall safety of the complex robotic system was analyzed through subsystem level safety issues. Safety regions in the world model of the perception subsystem, dependable understanding of the unstructured environment via fusion of sensory subsystems, lightweight and compliant design of mechanical components, passivity based control system and quantitative metrics used to assert safety are some important points discussed in the safety review. The main research focus of this work is on controller design of robotic manipulators against two conflicting requirements: motion performance and safety. Human-friendly manipulators used on domestic robots exhibit a lightweight design and demand a stable operation with a compliant behavior injected via a passivity based impedance controller. Effective motion based manipulation using such a controller requires a highly stiff behavior while important safety requirements are achieved with compliant behaviors. On the basis of this intuitive observation, this research identifies suitable metrics to identify the appropriate impedance for a given performance and safety requirement. This thesis also introduces a domestic robot design that adopts a modular design approach to minimize complexity, cost and development time. On the basis of functional modularity concept where each module has a unique functional contribution in the system, the robot “Bobbie-UT‿ is built as an interconnection of interchangeable mobile platform, torso, robotic arm and humanoid head components. Implementation of necessary functional and safety requirements, design of interfaces and development of suitable software architecture are also discussed with the design

An Overview on Principles for Energy Efficient Robot Locomotion

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