The WAM arm : modelling, control and its application in a HMI based on gaze tracking

In this thesis we describe the design and implementation of a Human Machine Interface (HMI) based on gaze tracking proposed to control robot prostheses. Robot manipulators hold a strong similarity with arm prosthetics, we used a 7 degrees of freedom (DOF) whole arm manipulator to test our HMI in the execution of reaching and grasping tasks. We showed that the interface worked under different control strategies using several velocity profiles. The system was tested by ten subjects with encouraging results. We analysed the performance of the 7-DOF robot manipulator in order to determine the suitability of its application in the development of this project. The original setup of the manipulator worked under joint Proportional and Derivative (PD) control but considering the results of the initial analysis of the system we proposed two alternative control strategies aimed to improve the performance of the manipulator: a feedforward friction compensation technique and joint Proportional Integral and Derivative control (PID). We created a dynamic model of the 7-DOF manipulator in Simmechanics in order to have a better understanding of the system. The friction phenomena of the manipulator was identified, represented through a fitted model and included in the system’s model with the aim of incrementing its accuracy with respect to the real system. The characteristics of the model made it suitable to test and to design control strategies for motion and friction compensation in MATLAB/Simulink. The model of the system was validated using data from the real robot arm and it was used later to tune the PID controllers of the joints of the 7-DOF manipulator using Iterative Feedback Tuning (IFT). Both experimental data and model simulations were used for the tuning procedure considering two different approaches. The data obtained from the friction identification process was used to implement a module for feedforward friction compensation over the pre-configured joint PD control of the manipulator. The responses of the system when using joint PID control and joint PD control with gravity and friction compensation were compared in the execution of motion tasks.