Diseño y simulación de un actuador de rigidez variable

XIX Congreso Nacional de Ingeniería Mecánica (CNIM 2012), Castellón, 14-16 de noviembre de 2012Los actuadores de rigidez variable se han desarrollado como una alternativa a los actuadores convencionales en diversas aplicaciones, como son entre otras los robots de servicio y los robots caminantes. El diseño mecánico de estos actuadores debe dar solución a nuevas necesidades que no eran tenidas en consideración en los actuadores rígidos, como la reducción del daño en caso de impacto o el ajuste de la frecuencia natural del sistema. Han sido muy diversas las soluciones propuestas hasta el momento, caracterizadas por el tipo de mecanismo implementado para variar la rigidez y posición de la articulación. En este trabajo se presenta un nuevo diseño de actuador basado en transmisión por cables, en el que un primer motor controla la posición de equilibrio del eslabón y un segundo motor se encarga de variar la rigidez de la articulación. Además, se ha simulado una situación de impacto hombre-robot para estudiar su contribución en la reducción del daño en hombre y robot.This work has been supported by the CAM Project S2009/DPI-1559/ROBOCITY2030 II, developed by the research team RoboticsLab at the University Carlos III of Madrid

A continuously variable transmission system designed for human-robot interfaces

Continuously Variable Transmission (CVT) systems are being used for many applications such as automotive transmissions, robotics, aerospace. In an ideal condition, these systems have the potential to provide continuously varying power transmission within a predefined limit. This transmission is accomplished with the help of friction, belt or gear systems. CVT can find application in a human-robot interface if design criteria such as backdrivability, independent output position and impedance variation, shock absorbing and low mass and inertia can be satisfied. Even if there are various CVT designs in the literature for human-robot interfaces, the primary limitation of the two-cone drive CVT designs is that the output torque and the output position cannot be altered independently. The reason for this problem is that the friction wheel, which is designed to transmit the torque from the input cone to the output cone, gives rise to remarkable longitudinal friction force along the linear way. In order to overcome this problem, a sphere is used in this work for the CVT design as the transmission element. In addition, it is stated in the literature that common CVT drive systems do not have the capability to be used in cyclic bidirectional motion. In the presented CVT design, a second sphere is added to the system with two springs from the lower part of the cones for pre-tension in order to solve the bidirectional transmission problem. In this paper, the working principle and conceptual design details of the novel two-cone CVT drive are presented. Experimental results showed that the novel CVT has the capacity to transmit bidirectional power with some accuracy.The Scientific and Technological Research Council of Turkey (grant number 117M405

Actuador con mecanismo de rigidez variable y par umbral

Número de publicación: ES2387228 A1 (18.09.2012) También publicado como: ES2387228 B2 (05.02.2013) Número de Solicitud: Consulta de Expedientes OEPM (C.E.O.) P201200712 (29.06.2012)Actuador con mecanismo de rigidez variable y par umbral, del tipo de los utilizados en articulaciones de revolución de brazos robóticos y que pueden modificar su rigidez. El actuador incorpora un motor (1) que se encarga de controlar la posición de equilibrio del eslabón de salida (13). El mecanismo contiene un resorte (18) y una palanca (12). La rigidez del mecanismo puede ser modificada variando la posición de esta palanca (12) mediante un motor (14). Dicha rigidez determina el valor del giro entre la posición de la polea (2) solidaria al eje de salida del motor (1) y la posición del eslabón (13). Dos tensores (5) y (6) permiten modificar la precarga de dos cables (3) y (4) respectivamente, de forma que el mecanismo no entra en funcionamiento hasta que no se ha sobrepasado un cierto valor de par sobre la articulación.Universidad de Almerí

Synthesis of optimal electrical stimulation patterns for functional motion restoration: applied to spinal cord-injured patients

We investigated the synthesis of electrical stimulation patterns for functional movement restoration in human paralyzed limbs. We considered the knee joint system, co-activated by the stimulated quadriceps and hamstring muscles. This synthesis is based on optimized functional electrical stimulation (FES) patterns to minimize muscular energy consumption and movement efficiency criteria. This two-part work includes a multi-scale physiological muscle model, based on Huxley’s formulation. In the simulation, three synthesis strategies were investigated and compared in terms of muscular energy consumption and co-contraction levels. In the experimental validation, the synthesized FES patterns were carried out on the quadriceps-knee joint system of four complete spinal cord injured subjects. Surface stimulation was applied to all subjects, except for one FES-implanted subject who received neural stimulation. In each experimental validation, the model was adapted to the subject through a parameter identification procedure. Simulation results were successful and showed high co-contraction levels when reference trajectories were tracked. Experimental validation results were encouraging, as the desired and measured trajectories showed good agreement, with an 8.4 % rms error in a subject without substantial time-varying behavior. We updated the maximal isometric force in the model to account for time-varying behavior, which improved the average rms errors from 31.4 to 13.9 % for all subjects

FEEDBACK LINEARIZATION FOR DECOUPLED POSITION/STIFFNESS CONTROL OF BIDIRECTIONAL ANTAGONISTIC DRIVES

To ensure safe human-robot interaction impedance robot control has arisen as one of the key challenges in robotics. This paper elaborates control of bidirectional antagonistic drives – qbmove maker pro. Due to its mechanical structure, both position and stiffness of bidirectional antagonistic drives could be controlled independently. To that end, we applied feedback linearization. Feedback linearization based approach initially decouples systems in two linear single-input-single-output subsystems: position subsystem and stiffness subsystem. The paper elaborates preconditions for feedback linearization and its implementation. The paper presents simulation results that prove the concept but points out application issues due to the complex mechanical structure of the bidirectional antagonistic drives

Safe Human-Robot Interaction Using Variable Stiffness, Hyper-Redundancy, and Smart Robotic Skins

In service robotics, safe human-robot interaction (HRI) is still an open research topic, requiring developments both in hardware and in software as well as their integration. In UMAY1 and MEDICARE-C2projects, we addressed both mechanism design and perception aspects of a framework for safe HRI. Our first focus was to design variable stiffness joints for the robotic neck and arm to enable inherent compliance to protect a human collaborator. We demonstrate the advantages of variable stiffness actuators (VSA) in compliancy, safety, and energy efficiency with applications in exoskeleton and rehabilitation robotics. The variable-stiffness robotic neck mechanism was later scaled down and adopted in the robotic endoscope featuring hyper-redundancy. The hyper-redundant structures are more controllable, having efficient actuation and better feedback. Lastly, a smart robotic skin is introduced to explain the safety support via enhancement of tactile perception. Although it is developed for a hyper-redundant endoscopic robotic platform, the artificial skin can also be integrated in service robotics to provide multimodal tactile feedback. This chapter gives an overview of systems and their integration to attain a safer HRI. We follow a holistic approach for inherent compliancy via mechanism design (i.e., variable stiffness), precise control (i.e., hyper-redundancy), and multimodal tactile perception (i.e., smart robotic-skins)