Sensory systems in micro-processor controlled prosthetic leg: a review

Micro-processor controlled prosthetic legs (MPCPL) offer better functionality than conventional prosthetic legs as they use actuators to replace missing joint function. This potentially reduces the user's metabolic energy consumption and normal walking gait can be mimicked as closely as possible. However, MPCPL require a good control system to perform efficiently, and one of the essential components is the system of sensors. The sensory system must satisfy two important criteria; the practicality in donning and doffing the prosthesis, i.e. the process of putting on and taking off the prosthesis by the amputee user, and the quality in the information provided. In this paper, a comprehensive review was conducted on studies related to the state of the art of sensory system adopted in MPCPL. The publications were searched using four electronics databases within the last 13 years. A total of 31 papers were reviewed. The articles were classified into three main categories: prosthetic-device oriented, user's-biological-input oriented and neuro-mechanical fusion sensory system. Types of sensors used and their application to the prosthetic system were analyzed. This review indicates that the sensors technology reported in the literature still does not fulfil the criteria of an efficient sensory system. Hence, a sensory system that eases the don and doff process of the prosthesis, yet informative in terms of providing enough useful data to effectively control the prosthesis, is needed for a successful MPCPL

Robôs quadrúpedes: geração de trajectórias em tempo real usando sistemas dinâmicos não-lineares

A geração de trajectórias de robôs em tempo real é uma tarefa muito complexa, não existindo ainda um algoritmo que a permita resolver de forma eficaz. De facto, há controladores eficientes para trajectórias previamente definidas, todavia, a adaptação a variações imprevisíveis, como sendo terrenos irregulares ou obstáculos, constitui ainda um problema em aberto na geração de trajectórias em tempo real de robôs. Neste trabalho apresentam-se modelos de geradores centrais de padrões de locomoção (CPGs), inspirados na biologia, que geram os ritmos locomotores num robô quadrúpede. Os CPGs são modelados matematicamente por sistemas acoplados de células (ou neurónios), sendo a dinâmica de cada célula dada por um sistema de equações diferenciais ordinárias não lineares. Assume-se que as trajectórias dos robôs são constituídas por esta parte rítmica e por uma parte discreta. A parte discreta pode ser embebida na parte rítmica, (a.1) como um offset ou (a.2) adicionada às expressões rítmicas, ou (b) pode ser calculada independentemente e adicionada exactamente antes do envio dos sinais para as articulações do robô. A parte discreta permite inserir no passo locomotor uma perturbação, que poderá estar associada à locomoção em terrenos irregulares ou à existência de obstáculos na trajectória do robô. Para se proceder á análise do sistema com parte discreta, será variado o parâmetro g. O parâmetro g, presente nas equações da parte discreta, representa o offset do sinal após a inclusão da parte discreta. Revê-se a teoria de bifurcação e simetria que permite a classificação das soluções periódicas produzidas pelos modelos de CPGs com passos locomotores quadrúpedes. Nas simulações numéricas, usam-se as equações de Morris-Lecar e o oscilador de Hopf como modelos da dinâmica interna de cada célula para a parte rítmica. A parte discreta é modelada por um sistema inspirado no modelo VITE. Medem-se a amplitude e a frequência de dois passos locomotores para variação do parâmetro g, no intervalo [-5;5]. Consideram-se duas formas distintas de incluir a parte discreta na parte rítmica: (a) como um (a.1) offset ou (a.2) somada nas expressões que modelam a parte rítmica, e (b) somada ao sinal da parte rítmica antes de ser enviado às articulações do robô. No caso (a.1), considerando o oscilador de Hopf como dinâmica interna das células, verifica-se que a amplitude e frequência se mantêm constantes para -5<g<5. No (a.2), usando novamente o oscilador de Hopf, a amplitude e a frequência têm o mesmo comportamento, crescendo e diminuindo nos intervalos de g [-0.5,0.34] e [0.4,1.83], sendo nos restantes valores de g nulas. Isto traduz-se em variações na extensão do movimento e na velocidade do robô, proporcionais à amplitude e à frequência, respectivamente. Ainda com o oscilador Hopf, no caso (b), a frequência mantêm-se constante enquanto a amplitude diminui para g<0.2 e aumenta para g>0.2. A extensão do movimento varia de forma directamente proporcional à amplitude. No caso das equações de Morris-Lecar, quando a componente discreta é embebida (a.2), a amplitude e a frequência aumentam e depois diminuem para - 0.17<g<0.037. Quando se somam as duas componentes, mais uma vez a frequência mantém-se constante enquanto a amplitude diminui para g0.5 Pode concluir-se que: (1) a melhor forma de inserção da parte discreta que menos perturbação insere no robô é a inserção como offset; (2) a inserção da parte discreta parece ser independente do sistema de equações diferenciais ordinárias que modelam a dinâmica interna de cada célula. Como trabalho futuro, é importante prosseguir o estudo das diferentes formas de inserção da parte discreta na parte rítmica do movimento, para que se possa gerar uma locomoção quadrúpede, robusta, flexível, com objectivos, em terrenos irregulares, modelada por correcções discretas aos padrões rítmicos.Online generation of trajectories is a hard and complex task in robotics, still lacking a proficient solution. In fact, there are efficient controllers to previously defined trajectories; nevertheless, adaptation to unpredictable variables, such as irregular terrains, is a major problem for online controllers. In this work, it is introduced a bio-inspired controller that generates locomotion patterns of a quadruped robot. It allows for gait switching, maintaining robots’ stability. Non-linear systems of ordinary differential equations are used to generate the locomotion rhythms. These are called Central Pattern Generators (CPGs). Trajectories consist of both rhythmic and discrete parts. The rhythmic part is modelled by the Hopf oscillator or by Morris-Lecar equations. The discrete part is modelled by the VITE system. The discreet part allows entering in quadruped locomotion disturbances, which may be associated to irregular terrain or the existence of obstacles in trajectory of the robot. To proceed to system analysis with discreet part, parameter g will be varied. The parameter g, present in the equations of the discrete part, represents the offset of the signal after inclusion of discrete part. We review the bifurcation theory and symmetry techniques that allow us to classify the periodic solutions of the CPG models with locomotion quadruped rhythms. We simulate numerically the CPG models and compute the amplitude and the frequency of the periodic solutions, identified with two quadruped gaits, for varying g in interval [-5;5]. The discrete part is inserted into the rhythmic part as (a.1) an offset, (a.2) as part of the equations that generate the rhythmic part, (b) is summed. Using Hopf oscillator to model cell’s dynamics, in case (a.1), we obtain that the frequency and amplitude of the periodic solution identified with the two gaits is held constant for -5<g<5. In case (a.2), using Hopf oscillator, we find that the amplitude and the frequency both increase and decrease for g ∈ [-0.5,0.34] and g ∈ [0.4,1.83], and are zero for other values of g. This translates in varying range of motion and velocity, proportional to the amplitude and frequency respectively. In the case (b), the frequency is constant and the amplitude decreases for g0.2. The range of motion varies proportional to the amplitude. Using Morris-Lecar equations to model cells’ internal dynamics, in case (a.2), the amplitude and the frequency increase and then decrease in for 0.17<g<0.037. In the case (b), the frequency remains constant and the amplitude decreases for g0.5. We may conclude that: (1) the best way to insert the discrete part to cause less disturbance in the robot movement is the insertion as an offset; (2) the integration of discrete part seems to be independent of the systems of ordinary differential equations that model the internal dynamics of each cell. As future work, it is important to pursue the study of different forms of insertion of discrete part in the rhythm part of the movement, so you can generate a robust, flexible and an objective quadruped locomotion, in irregular terrain modelled by discrete corrections to rhythmic patterns

Development of Adaptive Modular Active Leg (AMAL) Using Bipedal Robotics Technology

The objective of the work presented here is to develop a low cost active above knee prosthetic device exploiting bipedal robotics technology which will work utilizing the available biological motor control circuit properly integrated with a Central Pattern Generator (CPG) based control scheme. The approach is completely different from the existing Active Prosthetic devices, designed primarily as standalone systems utilizing multiple sensors and embedded rigid control schemes. In this research, first we designed a fuzzy logic based methodology for offering suitable gait pattern for an amputee, followed by formulating a suitable algorithm for designing a CPG, based on Rayleigh’s oscillator. An indigenous probe, Humanoid Gait Oscillator Detector (HGOD) has been designed for capturing gait patterns from various individuals of different height, weight and age. These data are used to design a Fuzzy inference system which generates most suitable gait pattern for an amputee. The output of the Fuzzy inference system is used for designing a CPG best suitable for the amputee. We then developed a CPG based control scheme for calculating the damping profile in real time for maneuvering a prosthetic device called AMAL (Adaptive Modular Active Leg). Also a number of simulation results are presented which show the stable behavior of knee and hip angles and determine the stable limit cycles of the network. </p

Modélisation et compensation des déficiences linéaires et non linéaires dans les transmissions électromécaniques des robots humanoïdes

Walking robots need precise control for legs articulations because it influence their equilibrium. It is necessary to compensate vibrational effects caused by imperfections in their articulations, like elasticities, mechanical backlashes, frictions and structural deformations and those appearing during shocks with the ground or when forces become significant. Our approach consists in correcting the inputs of the robot control system in a robust way according to variations of functional conditions and robot parameters. To reach this objective, we use adaptive and learning control methods, nonlinear oscillators.The research problematic, objectives, and state of the art are presented in the chapter 1. As it’s necessary to know exact torques of a robot, we present in the chapter 2 an approach of polyarticulated multi-masses systems modeling that takes into account its control system, mechanical transmissions and nonlinearities of transmissions. Experimental validations are carried on the biped robot ROBIAN. The chapter 3 explains the instrumentation of the non-direct articulation accelerations measurement method based on distributed accelerometer measurements on the body of the robot. The chapter 4 concerns experimental validation of compensation and control methods for ROBIAN for different kinds of flexion/extension movements.Les robots marcheurs demandent un contrôle articulaire des jambes précis car cela influence leur équilibre. Il est important de compenser les effets vibratoires provoqués par les imperfections dans leurs articulations comme les élasticités, les jeux mécaniques, les frottements, les déformations structurelles et celles qui apparaissent lors des chocs contre le sol ou lorsque les efforts deviennent importants.Notre démarche consiste à ajouter une correction dans les boucles d’asservissement articulaires du robot qui améliore la robustesse par rapport aux changements des conditions du fonctionnement et aux paramètres du robot. Pour atteindre cet objectif, nous comparons différentes méthodes dont celles de contrôle par adaptation et par apprentissage, à base d’oscillateurs non linéaires.Dans le chapitre 1, la problématique et les objectifs de la recherche, l’état de l’art sont présentés. Dans le but de connaitre les couples articulaires exacts d’un robot, le chapitre 2 présente la modélisation des systèmes polyarticulés multimasses avec système d’asservissement, les transmissions prenant en compte les non linéarités articulaires. La validation expérimentale est donnée pour le robot bipède ROBIAN. Le chapitre 3 explique le système d’instrumentation de mesure indirecte à base d’accéléromètres permettant de calculer des accélérations articulaires à partir des mesures réparties sur le corps d’un robot marcheur. Le chapitre 4 concerne la validation expérimentale des méthodes de compensation et de contrôle sur ROBIAN