Análisis numérico de una prótesis del miembro inferior bajo las condiciones de la marcha humana

El siguiente trabajo presenta el análisis numérico de la parte inferior de una prótesis transfemoral, bajo las condiciones de carga de la marcha humana. Para ello, se ha realizado la modelización de la parte situada debajo de la articulación de la rodilla, es decir, la correspondiente a la pierna y el conjunto pie-tobillo, y ha sido sometida a tres estados de carga propios del ciclo de marcha: el contacto talón, el apoyo medio y el despegue de los dedos. A fin de poder establecer una modelización coherente y un posterior análisis crítico de los resultados, se muestra una introducción teórica sobre algunos aspectos básicos de anatomía del miembro inferior, sobre el desarrollo del ciclo de la marcha humana y sus principales condiciones de carga. Posteriormente, se introduce una presentación al mundo de la protésica, indicando cúales son las partes de una prótesis transfemoral y sus principales funciones. Y finaliza, con un apartado en el que se detallan cúales son los materiales más utilizados para fabricar cada una de las piezas. Tras este marco teórico, se presenta una introducción al Método de los Elementos Finitos (MEF). Ya que éste ha sido el utilizado para la posterior modelización y obtención de resultados, mediante el software ABAQUS/CAE 6.13. Para finalizar, se aportan las conclusiones obtenidas y una serie de posibles investigaciones futuras que podrían contribuir al avance en este campo.The following work shows the numeric analysis of the inferior area of transfemoral prosthesis under the loading conditions of the gait cycle. To this end, the modeling area found beneath the knee joint; that is to say, that which refers to the leg and the foot-ankle altogether, have been placed under three states of movility cycles: the contact heel, the half support and the raising of toes. In order to be able to entablish a coheret modeling and a post-critical analysis of the results, a theoretic introduction of some basic anatomic aspects of the lower limbs on the development of the human load and its principal conditions of load is shown. After that, an introductory prosthetic science is presented, showing the major parts of a transfemoral prosthesis and their performances; and finally, in a paragraph – detailing the materials which are mostly employed to make each part. After this theoretic framework, an introduction of the Finite Element Method (FEM) is presented; since this has been employed for the modeling to achieve the results through the application of ABAQUS/CAE 6.13 software. Finally, the conclusions achieved and a series of possible research which could contribute to advancement in this field are provided.Ingeniería en Tecnologías Industriale

Design of a Fully-Passive Transfemoral Prosthesis Prototype

In this study, we present the mechanical design of a prototype of a fully-passive transfemoral prosthesis for normal walking. The conceptual working principle at the basis of the design is inspired by the power flow in human gait, with the main purpose of realizing an energy efficient device. The mechanism is based on three elements, which are responsible of the energetic coupling between the knee and ankle joints. The design parameters of the prototype are determined according to the human body and the natural gait characteristics, in order to mimic the dynamic behavior of a healthy leg. Hereby, we present the construction details of the prototype, which realizes the working principle of the conceptual mechanism

A novel hydraulic energy-storage-and-return prosthetic ankle : design, modelling and simulation

In an intact ankle, tendons crossing the joint store energy during the stance phase of walkingprior to push-off and release it during push-off, providing forward propulsion. Most prostheticfeet currently on the market – both conventional and energy storage and return (ESR) feet –fail to replicate this energy-recycling behaviour. Specifically, they cannot plantarflex beyondtheir neutral ankle angle (i.e. a 90° angle between the foot and shank) while generating theplantarflexion moment required for normal push-off. This results in a metabolic cost ofwalking for lower-limb amputees higher than for anatomically intact subjects, combined witha reduced walking speed.Various research prototypes have been developed that mimic the energy storage and returnseen in anatomically intact subjects. Many are unpowered clutch-and-spring devices thatcannot provide biomimetic control of prosthetic ankle torque. Adding a battery and electricmotor(s) may provide both the necessary push-off power and biomimetic ankle torque, butadd to the size, weight and cost of the prosthesis. Miniature hydraulics is commonly used incommercial prostheses, not for energy storage purposes, but rather for damping and terrainadaptation. There are a few examples of research prototypes that use a hydraulic accumulatorto store and return energy, but these turn out to be highly inefficient because they useproportional valves to control joint torque. Nevertheless, hydraulic actuation is ideally suitedfor miniaturisation and energy transfer between joints via pipes.Therefore, the primary aim of this PhD was to design a novel prosthetic ankle based on simpleminiature hydraulics, including an accumulator for energy storage and return, to imitate thebehaviour of an intact ankle. The design comprises a prosthetic ankle joint driving two cams,which in turn drive two miniature hydraulic rams. The “stance cam-ram system” captures theeccentric (negative) work done from foot flat until maximum dorsiflexion, by pumping oil intothe accumulator, while the “push-off system” does concentric (positive) work to power pushoff through fluid flowing from the accumulator to the ram. By using cams with specific profiles,the new hydraulic ankle mimics intact ankle torque. Energy transfer between the knee andthe ankle joints via pipes is also envisioned.A comprehensive mathematical model of the system was defined, including all significantsources of energy loss, and used to create a MATLAB simulation model to simulate theoperation of the new device over the whole gait cycle. A MATLAB design program was alsoimplemented, which uses the simulation model to specify key components of the new designto minimise energy losses while keeping the device size acceptably small.The model’s performance was assessed to provide justification for physical prototyping infuture work. Simulation results show that the new device almost perfectly replicates thetorque of an intact ankle during the working phases of the two cam-ram systems. Specifically,78% of the total eccentric work done by the prosthetic ankle over the gait cycle is returnedas concentric work, 14% is stored and carried forward for future gait cycles, and 8.21% is lost.A design sensitivity study revealed that it may be possible to reduce the energy lost to 5.83%of the total eccentric work. Finally, it has been shown that the main components of the system– cams, rams, and accumulator - could be physically realistic, matching the size and mass ofthe missing anatomy