Resumen de Una nueva filosofía de diseño basada en sinergias para exotrajes de asistencia a la marcha actuados por cable
The growing tendency of worldwide societies, but particularly in the West, to aging leads to a growing number of individuals that might require any kind of walking assistance. Life expectancy in Spain, for instance, has doubled in barely four generations. As such, there exist numerous solutions, among which exoskeletons must be highlighted as wearable devices with rigid elements that assist, generally driven by motors, human gait in any way. As an alternative to these devices, a new variant, much lighter and cheaper for the user has been proposed: wearable exoskeletons, or exosuits. They, made only of textile elements aside from the actuation system, offer a more comfortable and economic solution to those who can walk, but need an assistive device or, alternatively, wish to increase their motion capabilities: the lack of rigid elements forces the subject to sustain themselves, yet at the same time does not restrict or impede their natural gait in any way. A common variety of exosuits consists of an actuation system, including the motors and the power transmission system, generally included in a backpack and transmitting force via cables anchored to the joints in the so-called anchor points, in most cases textile elements located at the joints that will be actuated. A motor might be required for each target joint and leg: if all hip, knee, and ankle are to be actuated, six motors will be required, which will be the main contributors to the overall system weight and price. This work arises from the need of reducing such weight and price, as well as increasing the wearability of walking-assistance exosuits. The document focuses on the development of a new design approach for exosuits that allows a heavy reduction in the number of actuators required to provide the desired assistance and, thus, offers a much more affordable solution, at the reach of many more potential users. The thesis is, thus, supported by two main cornerstones. On one side, the development of an inverse-dynamics model capable of predicting the forces and torques to be produced by the system to assist human gait, establishing a base for the system design and for its control. On the other side, stands the detailed description of the novel design approach that provides the desired improvements, serving as a guide for future exosuit designs for the lower limb. The latter is where lies the main contribution of this work, which will try to improve current technology with regards to cost and weight: the mechanical design based on synergies. Statistical analysis of human gait demonstrates a rather evident fact: as opposed to other movements, such as grasping an object or holding it, walking has a cyclic nature and presents clear similarities between several of its parameters. A kinematic study performed on the joint flexion-extension angles for hip, knee, and ankle, among others, yields a notable degree of similarity between them. The same happens in the cable forces during gait required to provide a certain fraction of the total joint torque, or in the cable extensions themselves. These similarities make it possible to approach, by statistical means, a dimensionality reduction problem while keeping a high degree of correspondence with the original variables. In other words, the number of required actuation curves, thus the number of required motors, can be significantly reduced, as much as the problem's dimensions. Therefore, a design allowing the actuation of six simultaneous degrees of freedom (up to three joints per leg) has been proposed with only one motor. All of it leads to the main contribution of the work to the current walking-assistance exosuits design: the detailed, rigorous, and mathematical description of a novel method of design targeting the significant reduction in the weight and price of these devices, while also improving their wearability and making them more accessible.
