Design of a Passive Ankle Prosthesis with Energy Return That Increases with Increasing Walking Velocity

Patients who undergo a transtibial (below the knee) amputation are often met with a difficult decision: selection of a prosthesis. Limitations of currently available prostheses motivate work on a new solution, the EaSY Walk, a passive device that mimics two key aspects of the natural ankle: non-linear rotational stiffness through implementation of a stiffening flexure mechanism and rotational work output that varies as a function of walking velocity to propel the user forward. To achieve the latter, a strategy to convert the maximum available translational energy acquired from deflection along the leg into rotational energy about the ankle joint through coupling of these two degrees of freedom is used. This strategy utilizes maxima/minima of known ankle profiles to control timing of critical device functions as well as the quantity of energy input from leg deflection. In doing so, both consistent operation of the device and maximal energy output at a given walking velocity are theoretically obtained. Optimizing for both aforementioned ankle criteria, 25.1% of the work of the average natural ankle was achieved for 15 mm of leg deflection, less deflection than is exhibited by many shock absorbing pylon prostheses. After fabricating and testing the optimized design using a repeatable robot trajectory, the device was found to convert 26.6% of input translational work as rotational work, accounting for 63.1% of modeled rotational work. Through human subject testing, the device was found to function inconsistently due to the large impact loadings associated with human gait. In order to achieve proper functionality with human gait, design modifications to the energy storage and release devices are recommended

Simulation of an interlocking hydraulic direct-drive system for a biped walking robot

Biped robots with serial links driven by an electric motor experience problems because the motor and transmission are installed in each joint, causing the legs to become very heavy. Previous solutions involved robots using servo valves, a type of highly responsive proportional valve. However, high supply pressure is necessary to realize high responsiveness and the resulting energy losses are large. To address this problem, we proposed a hydraulic direct-drive system in which the pump controls the cylinder meter-in flow, while a proportional valve controls the meter-out flow. Furthermore, our hydraulic interlocking drive system connects two hydraulic direct-drive systems for biped humanoid robots and concentrates the pump output on one side cylinder. The meter-in flow rate of the other side cylinder is controlled by the meter-out flow rate of the cylinder on which the pump is concentrated. A comparison of the walking simulation performance with that of the conventional independent system shows that our proposed system reduces the motor output power by 24.3%. These results prove the feasibility of constructing a two-legged robot without having to incorporate highly responsive servo valves

Understanding and Improving Locomotion: The Simultaneous Optimization of Motion and Morphology in Legged Robots

There exist many open design questions in the field of legged robotics. Should leg extension and retraction occur with a knee or a prismatic joint? Will adding a compliant ankle lead to improved energetics compared to a point foot? Should quadrupeds have a flexible or a rigid spine? Should elastic elements in the actuation be placed in parallel or in series with the motors? Though these questions may seem basic, they are fundamentally difficult to approach. A robot with either discrete choice will likely need very different components and use very different motion to perform at its best. To make a fair comparison between two design variations, roboticists need to ask, is the best version of a robot with a discrete morphological variation better than the best version of a robot with the other variation? In this dissertation, I propose to answer these type of questions using an optimization based approach. Using numerical algorithms, I let a computer determine the best possible motion and best set of parameters for each design variation in order to be able to compare the best instance of each variation against each other. I developed and implemented that methodology to explore three primary robotic design questions. In the first, I asked if parallel or series elastic actuation is the more energetically economical choice for a legged robot. Looking at a variety of force and energy based cost functions, I mapped the optimal motion cost landscape as a function of configurable parameters in the hoppers. In the best case, the series configuration was more economical for an energy based cost function, and the parallel configuration was better for a force based cost function. I then took this work a step further and included the configurable parameters directly within the optimization on a model with gear friction. I found, for the most realistic cost function, the electrical work, that series was the better choice when the majority of the transmission was handled by a low-friction rotary-to-linear transmission. In the second design question, I extended this analysis to a two-dimensional monoped moving at a forward velocity with either parallel or series elastic actuation at the hip and leg. In general it was best to have a parallel elastic actuator at the hip, and a series elastic actuator at the leg. In the third design question, I asked if there is an energetic benefit to having an articulated spinal joint instead of a rigid spinal joint in a quadrupedal legged robot. I found that the answer was gait dependent. For symmetrical gaits, such as walking and trotting, the rigid and articulated spine models have similar energetic economy. For asymmetrical gaits, such as bounding and galloping, the articulated spine led to significant energy savings at high speeds. The combination of the above studies readily presents a methodology for simultaneously optimizing for motion and morphology in legged robots. Aside from giving insight into these specific design questions, the technique can also be extended to a variety of other design questions. The explorations in turn inform future hardware development by roboticists and help explain why animals in nature move in the ways that they do.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144074/1/yevyes_1.pd

Knee joint biomechanics after anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) is an important stabilizer of the knee joint. After ACL rupture, the knee joint has difficulty maintaining its stability; thus the patient often has to receive an ACL-reconstructive surgery to regain the knee joint functions. Unfortunately, traditional transtibial surgical techniques could not fully restore the normal knee joint kinematics during daily activities. Moreover, a higher rate of osteoarthritis was found from the ACL-reconstructed knees compared to the knees without a history of ACL-injuries. The reason for the increased risk of knee osteoarthritis is still unclear, and the pathologies due to abnormal knee joint kinematics remain controversial. The dissertation was to delineate the knee joint motion and loading after ACL-reconstruction. Thirty patients who received ACL-reconstructive surgeries using the traditional transtibial technique and 14 using the recently developed anteromedial portal technique were recruited from the same center (OrthoCarolina). Twenty healthy subjects without history of knee injuries were recruited as the control group. Human motion data and ground reaction force data were collected during level walking and downstairs pivoting using an optical motion capture system. Three-dimensional (3D) knee joint motions were determined from redundant markers using an optimization approach. The 3D knee joint moments and forces were calculated from motion data, ground reaction data by using an inverse dynamics model of the lower extremity. A finite element model was created, and the distributions of stress/strain within articular cartilage under physiological loading were estimated. The results from two groups of patients using different reconstruction techniques were compared. In the transtibial group, excessive internal tibial rotation (2° on average during stance phase), varus rotation and anterior femur translation (swing phase) were observed in the ACL-reconstructed knees when compared to the control group during level walking. The 3D knee joint motion following ACL-reconstruction was found to be influenced by the leg dominance. The motion and load in the uninjured contralateral knee were also affected. During downstairs pivoting, the normal varus rotation and adduction moment were not fully restored by the transtibial technique. Overall, the anteromedial portal technique improved the postsurgical knee joint kinematics by reducing the offsets in the internal tibial rotation, varus rotation and anterior femur translation during level walking. It also improved the adduction moment during downstairs pivoting. At the same time, the anteromedial portal technique may cause a flexion/extension deficit during the stance phase of walking. Results of finite element analysis demonstrated higher pressures within the medial femoral cartilage during the stance phase of walking; it also demonstrated that there is an increased knee joint laxity after ACL-reconstruction. The anteromedial portal technique was overall better than the traditional transtibial technique in respect to postsurgical knee joint compressive loading and contact pressure. The study provides evidence of the possibility by using anatomical single-bundle ACL-reconstruction technique to fight the knee joint osteoarthritis after ligament injury

Redesign of the Restrainer band for a Horse Leg Protective Device Based on a Static Analysis

A horse leg orthosis employing a restrainer band is designed to prevent metacarpo-phalangeal joint (MCPJ) hyperextension of horse forelimb. Current band design by Manta Design Inc. produces inconsistent tensions and inadequately protects the forelimb. The goal was to improve the restrainer band design using a static analysis at MCPJ. Band length, cross-sectional area and stiffness effects were studied to meet the tension specifications from the static analysis. The improved restrainer band achieves an 8.4% MCPJ moment reduction at maximum extension

Study of design issues in a prototype lower-limb prosthesis - proof-of-concept in a 3D printed model

Dissertação de Mestrado Integrado em Engenharia Biomédica Ramo de Biomateriais, Reabilitação e BiomecânicaThe amputation of one or both lower limbs, which can be brought on by trauma, diabetes, or other vascular diseases, is an increasingly common occurrence, especially due to the increase in the number of cases of diabetes in the developed world. In Portugal alone 1300 amputations each year are attributed to diabetes. These amputations severely impact the mobility, self-esteem, and quality of life of the patients, a situation that can be alleviated via the installation of a lower limb prosthesis. Sadly, these prostheses are not yet capable of completely emulating a sound limb in an affordable fashion. In this dissertation, state-of-the-art research was carried out regarding the mechanics of human gait, both healthy and prosthetic. An investigation regarding the state-of-the-art research was also carried out regarding lower-limb prostheses, their evolution, mechanics, and prospects, as well as additive manufacturing techniques, and how they can be crucial to the development of affordable prostheses. Special attention was provided to the study of the leading edge of prostheses research, namely active prostheses, capable of generating and introducing energy into the human gait, rather than simply acting as passive devices. This dissertation follows up on previous work carried out in the BioWalk Project of Universidade do Minho’s BiRDLab: “Prosthetic Devices and Rehabilitation Solutions for the Lower Limbs Amputees”. This work consisted of the development of an active lower-limb prosthesis prototype, with the goal of providing an affordable, but functional, prosthesis for future testing with patients. However, the resulting prototype was laden with issues, such as excessive weight and an underpowered motor. As such, this work set out to identify these issues, design, implement and test modifications to the prosthesis to produce a satisfying prototype. Given the limited resources and facilities available, it was decided to work on a smaller model prosthesis installed in a bipedal robot, the DARwIn-OP, using it as proof-of-concept for modifications to be implemented in the BiRDLab prosthesis. Modifications were successfully implemented, chiefly among them a planetary gear-based reductor and a novel attachment mechanism built using additive manufacturing techniques. It is possible to conclude that there is a great potential in the implementation of additive manufacturing techniques in the development of affordable prosthesis.A amputação de um ou ambos os membros inferiores, que pode ser causada por trauma, diabetes, ou outras doenças vasculares, é um evento cada vez mais frequente, especialmente devido ao aumento do número de casos de diabetes no mundo desenvolvido. Em Portugal, 1300 amputações são atribuídas aos diabetes todos os anos. Estas amputações influenciam negativamente a mobilidade, autoestima e qualidade de vida dos pacientes, mas estes efeitos podem ser minimizados através da instalação de uma prótese de membro inferior. Infelizmente, estas próteses ainda não são capazes de emular completamente um membro saudável de forma económica. Nesta dissertação, um estado da arte do caminhar humano foi realizado, tendo em atenção o funcionamento deste, quer em sujeitos saudáveis ou amputados. Um estado da arte também foi realizado relativamente às próteses de membros inferiores, a sua evolução, funcionamento, e perspetivas futuras, e também relativamente a técnicas de fabrico aditivas e a forma como estas podem ser aplicadas em próteses acessíveis. Tomou-se atenção especial ao estudo das próteses ativas, capazes de gerar e introduzir energia no caminhar, ao invés das próteses passivas tradicionais. Esta dissertação baseia-se em trabalho prévio ao abrigo do projeto BioWalk do laboratório BiRDLab da Universidade do Minho: “Dispositivos prostéticos e soluções de reabilitação para amputados dos membros inferiores”. Este trabalho consistiu no desenvolvimento de um protótipo de prótese de membro inferior ativa, com o objetivo de criar uma prótese de baixo custo para testes em pacientes. No entanto, o protótipo produzido possuí vários problemas, tais como peso excessivo e um motor subdimensionado. Assim sendo, este trabalho propôs-se a identificar estes problemas e a desenhar, implementar, e testar modificações. Tendo em conta os limitados recursos disponíveis, decidiu-se trabalhar numa prótese modelo mais pequena, instalada num robô bipedal, o DARwIN-OP, e a usá-la para testar modificações a implementar na prótese do BiRDLab. As modificações foram implementadas com sucesso, especialmente um redutor de engrenagens planetárias e um novo método de conectar a prótese, usando técnicas de fabrico aditivas

Non-Linear Trajectory Control of Tensegrity Prosthetic (ProTense) Leg

There has been a continuous rise in the number of amputees over the past decades and estimates put the number of amputees in the US alone at over 3 million by 2050. With the rising amputee population, the development of better prosthesis is needed to return quality of life to millions. The field of prosthetic development is active, with improved prosthesis entering the market owing to the advent of new materials and control strategies. The improvement in sensor technology and understanding of the bio-mechanics of the limbs have further bolstered the confidence of engineers to provide prosthetic legs with added power and degrees of freedom allowing the amputees to run faster, trek steeper and scale new heights. Tensegrity, a word coined by Buckminster Fuller in the 1960s, is an amalgam of the words tension and integrity. A tensegrity structure is a prestressable network of bars and strings with specific boundary conditions and external forces applied at the nodes. Tensegrity structures were introduced as an art form by Kenneth Snelson. Civil engineers paid little attention to the Tensegrity due to absence of a full dynamical model to define it which people like Skelton provided. More recently, the concept of tensegrity became popular with roboticists and control theorists for making complex robots manipulated by strings as actuators. The shape control capability of tensegrity structures without change in stiffness and the capability to provide minimal mass solutions to many engineering problems can be exploited for various applications. In the last 25 years tensegrity has come to be associated with various inquiries into the nature of living structure by Professors like Donald E. Ingber, who has claimed tensegrity to be the best explanation of the working of a cytoskeleton of the cell in his journal, ‘The Architecture of life’. This work describes an initial effort aimed at applying the huge potential of tensegrity structures into the field of leg prosthetics. The objective is to provide a stable and comfortable prosthetic leg for above/below knee amputees with both strong and weak residual leg for motion in the sagittal plane while they walk on level ground

Bioinspired template-based control of legged locomotion

cient and robust locomotion is a crucial condition for the more extensive use of legged robots in real world applications. In that respect, robots can learn from animals, if the principles underlying locomotion in biological legged systems can be transferred to their artificial counterparts. However, legged locomotion in biological systems is a complex and not fully understood problem. A great progress to simplify understanding locomotion dynamics and control was made by introducing simple models, coined ``templates'', able to represent the overall dynamics of animal (including human) gaits. One of the most recognized models is the spring-loaded inverted pendulum (SLIP) which consists of a point mass atop a massless spring. This model provides a good description of human gaits, such as walking, hopping and running. Despite its high level of abstraction, it supported and inspired the development of successful legged robots and was used as explicit targets for control, over the years. Inspired from template models explaining biological locomotory systems and Raibert's pioneering legged robots, locomotion can be realized by basic subfunctions: (i) stance leg function, (ii) leg swinging and (iii) balancing. Combinations of these three subfunctions can generate different gaits with diverse properties. Using the template models, we investigate how locomotor subfunctions contribute to stabilize different gaits (hopping, running and walking) in different conditions (e.g., speeds). We show that such basic analysis on human locomotion using conceptual models can result in developing new methods in design and control of legged systems like humanoid robots and assistive devices (exoskeletons, orthoses and prostheses). This thesis comprises research in different disciplines: biomechanics, robotics and control. These disciplines are required to do human experiments and data analysis, modeling of locomotory systems, and implementation on robots and an exoskeleton. We benefited from facilities and experiments performed in the Lauflabor locomotion laboratory. Modeling includes two categories: conceptual (template-based, e.g. SLIP) models and detailed models (with segmented legs, masses/inertias). Using the BioBiped series of robots (and the detailed BioBiped MBS models; MBS stands for Multi-Body-System), we have implemented newly-developed design and control methods related to the concept of locomotor subfunctions on either MBS models or on the robot directly. In addition, with involvement in BALANCE project (\url{http://balance-fp7.eu/}), we implemented balance-related control approaches on an exoskeleton to demonstrate their performance in human walking. The outcomes of this research includes developing new conceptual models of legged locomotion, analysis of human locomotion based on the newly developed models following the locomotor subfunction trilogy, developing methods to benefit from the models in design and control of robots and exoskeletons. The main contribution of this work is providing a novel approach for modular control of legged locomotion. With this approach we can identify the relation between different locomotor subfunctions e.g., between balance and stance (using stance force for tuning balance control) or balance and swing (two joint hip muscles can support the swing leg control relating it to the upper body posture) and implement the concept of modular control based on locomotor subfunctions with a limited exchange of sensory information on several hardware platforms (legged robots, exoskeleton)