Modeling and control of an anthropomorphic robotic hand

Mención Europea en el título de doctorThis thesis presents methods and tools for enabling the successful use of robotic hands. For highly dexterous and/or anthropomorphic robotic hands, these methods have to share some common goals, such as overcoming the potential complexity of the mechanical design and the ability of performing accurate tasks with low and efficient computational cost. A prerequisite for dexterity is to increase the workspace of the robotic hand. For this purpose, the robotic hand must be considered as a single multibody system. Solving the inverse kinematics problem of the whole robotic hand is an arduous task due to the high number of degrees of freedom involved and the possible mechanical limitations, singularities and other possible constraints. The redundancy has proven to be of a great usefulness for dealing with potential constraints. To be able to exploit the redundancy for dealing with constraints, the adopted method for solving the inverse kinematics must be robust and extendable. Obviously, addressing such complex problem, the method will certainly be computationally heavy. Thus, one of the aims of this thesis is to resolve the inverse kinematics problem of the whole robotic hand under constraints, taking into account the computational cost. To this end, this thesis extends and reduces the most recent Selectively Damped Least Squares method which is based on the computation of all singular values, to deal with constraints with a minimum computational cost. New estimation algorithm of singular values and their corresponding singular vectors is proposed to reduce the computational cost. The reduced extended selectively damped least squares method is simulated and experimentally evaluated using an anthropomorphic robotic hand as a test bed. On the other hand, dexterity depends not only on the accuracy of the position control, but also on the exerted forces. The tendon driven modern robotic hands, like the one used in this work, are strongly nonlinear dynamic systems, where motions and forces are transmitted remotely to the finger joints. The problem of modeling and control of position and force simultaneously at low level control is then considered. A new hybrid control structure based on the succession of two sliding mode controllers is proposed. The force is controlled by its own controller which does not need a contact model. The performance of the proposed controller is evaluated by performing the force control directly using the force sensor information of the fingertip, and indirectly using the torque control of the actuator. Finally, we expect that the applications of the methods presented in this thesis can be extended to cover different issues and research fields and in particular they can be used in a variety of algorithm that require the estimation of singular values.This work was partially supported by the European project HANDLE, FP7-231640, and by the Spanish ministry MICINN through FPI scholarship within the project DPI-2005-04302.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Anis Sahbani.- Secretario: Fares Jawad Moh D Abu-Dakka.- Vocal: Claudio Ross

A memetic approach to the inverse kinematics problem for robotic applications

The inverse kinematics problem of an articulated robot system refers to computing the joint configuration that places the end-effector at a given position and orientation. To overcome the numerical instability of the Jacobian-based algorithms around singular joint configurations, the inverse kinematics is formulated as a constrained minimization problem in the configuration space of the robot. In previous works this problem has been solved for redundant and non-redundant robots using evolutionary-based algorithms. However, despite the flexibility and accuracy of the direct search approach of evolutionary algorithms, these algorithms are not suitable for most robot applications given their low convergence speed rate and the high computational cost of their population-based approach. In this thesis, we propose a memetic variant of the Differential Evolution (DE) algorithm to increase its convergence speed on the kinematics inversion problem of articulated robot systems. With the aim to yield an efficient trade-off between exploration and exploitation of the search space, the memetic approach combines the global search scheme of the standard DE with an independent local search mechanisms, called discarding. The proposed scheme is tested on a simulation environment for different benchmark serial robot manipulators and anthropomorphic robot hands. Results show that the memetic differential evolution is able to find solutions with high accuracy in less generations than the original DE. -----------------------------------------------------------La cinemática inversa de los robots manipuladores se refiere al problema de calcular las coordenadas articulares del robot a partir de coordenadas conocidas de posición y orientación de su extremo libre. Para evitar la inestabilidad numérica de los métodos basados en la inversa de la matriz Jacobiana en la vecindad de configuraciones singulares, el problema de cinemática inversa es definido en el espacio de configuraciones del robot manipulador como un problema de optimización con restricciones. Este problema de optimización ha sido previamente resuelto con métodos evolutivos para robots manipuladores, redundantes y no redundantes, obteniéndose buenos resultados; sin embargo, estos métodos exhiben una baja velocidad de convergencia no adecuada para aplicaciones robóticas. Para incrementar la velocidad de convergencia de estos algoritmos, se propone un método memético de evolución differencial. El enfoque de búsqueda directa propuesto combina el esquema estándar de evolución diferencial con un mecanismo independiente de refinamiento local, llamado discarding o descarte. El desempeño del método propuesto es evaluado en un entorno de simulación para diferentes robot manipuladores y manos robóticas antropomórficas. Los resultados obtenidos muestran una importante mejora en precisión y velocidad de convergencia en comparación del método DE original.Programa en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Pedro M. Urbano de Almeida Lima; Vocal: Cecilia Elisabet García Cena; Secretario: Mohamed Abderrahim Fichouch