Variable Stiffness Actuators:A Port-Based Power-Flow Analysis

Variable stiffness actuators realize a novel class of actuators, which are capable of changing the apparent output stiffness independently of the output position. This is mechanically achieved by the internal introduction of a number of elastic elements and a number of actuated degrees of freedom (DOFs), which determine how the elastic elements are sensed at the output. During the nominal behavior of these actuators, the power flow from the internal actuated DOFs can be such that energy is undesirably stored in the elastic elements because of the specific kinematic structure of the actuator. In this study, we focus on the analysis of the power flow in variable stiffness actuators. More specifically, the analysis is restricted to the kinematic structure of the actuators, in order to show the influence of the topological structure on the power flow, rather than on the realization choices. We define a measure that indicates the ratio between the total amount of power that is injected by the internal actuated DOFs and the power that is captured by the internal elastic elements which, therefore, cannot be used to do work on the load. In order to define the power-flow ratio, we exploit a generic port-based model of variable stiffness actuators, which highlights the kinematic properties of the design and the power flows in the actuator structure

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

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

Efficient computation of inverse dynamics and feedback linearization for VSA-based robots

We develop a recursive numerical algorithm to compute the inverse dynamics of robot manipulators with an arbitrary number of joints, driven by variable stiffness actuation (VSA) of the antagonistic type. The algorithm is based on Newton-Euler dynamic equations, generalized up to the fourth differential order to account for the compliant transmissions, combined with the decentralized nonlinear dynamics of the variable stiffness actuators at each joint. A variant of the algorithm can be used also for implementing a feedback linearization control law for the accurate tracking of desired link and stiffness trajectories. As in its simpler versions, the algorithm does not require dynamicmodeling in symbolic form, does not use numerical approximations, grows linearly in complexity with the number of joints, and is suitable for online feedforward and real-time feedback control. A Matlab/C code is made available

Control motion approach of a lower limb orthosis to reduce energy consumption

By analysing the dynamic principles of the human gait, an economic gait‐control analysis is performed, and passive elements are included to increase the energy efficiency in the motion control of active orthoses. Traditional orthoses use position patterns from the clinical gait analyses (CGAs) of healthy people, which are then de‐normalized and adjusted to each user. These orthoses maintain a very rigid gait, and their energy cosT is very high, reducing the autonomy of the user. First, to take advantage of the inherent dynamics of the legs, a state machine pattern with different gains in eachstate is applied to reduce the actuator energy consumption. Next, different passive elements, such as springs and brakes in the joints, are analysed to further reduce energy consumption. After an off‐line parameter optimization and a heuristic improvement with genetic algorithms, a reduction in energy consumption of 16.8% is obtained by applying a state machine control pattern, and a reduction of 18.9% is obtained by using passive elements. Finally, by combining both strategies, a more natural gait is obtained, and energy consumption is reduced by 24.6%compared with a pure CGA pattern