Study of composite elastic elements for transfemoral prostheses: the MyLeg Project

In this thesis, the work on the design and realization of a semi-active foot prosthesis with variable stiffness system is presented. The final prosthesis was the result of a path started by the design of the elastic composite elements of an ESR prosthesis, a passive prosthetic device, generally prescribed to amputees with K3 and K4 of level of ambulation. The design of both the ESR prosthesis and the final variable stiffness prosthesis was carried out using a new systematic methodology of prosthesis design. This methodology has been developed and then presented in the same thesis by the author. Modelling and simulation techniques are illustrated step by step. With the variable stiffness prosthesis, the aim is to allow future users to perform more daily activities without being restricted by the conditions of the ground. It has been chosen to develop a semi-active prosthesis rather than a bionic foot for two main reasons: a bionic foot may be too expensive for most future users; and a bionic foot may be undesirable for too much weight; the much weight can be due to the motor and batteries, in addition to the structure that will certainly be much more complex than the structure of a semi-active prosthesis. To investigate the effectiveness of the variable stiffness, human subjects with amputees will be carried out

Advancements in Prosthetics and Joint Mechanisms

abstract: Robotic joints can be either powered or passive. This work will discuss the creation of a passive and a powered joint system as well as the combination system being both powered and passive along with its benefits. A novel approach of analysis and control of the combination system is presented. A passive and a powered ankle joint system is developed and fit to the field of prosthetics, specifically ankle joint replacement for able bodied gait. The general 1 DOF robotic joint designs are examined and the results from testing are discussed. Achievements in this area include the able bodied gait like behavior of passive systems for slow walking speeds. For higher walking speeds the powered ankle system is capable of adding the necessary energy to propel the user forward and remain similar to able bodied gait, effectively replacing the calf muscle. While running has not fully been achieved through past powered ankle devices the full power necessary is reached in this work for running and sprinting while achieving 4x’s power amplification through the powered ankle mechanism. A theoretical approach to robotic joints is then analyzed in order to combine the advantages of both passive and powered systems. Energy methods are shown to provide a correct behavioral analysis of any robotic joint system. Manipulation of the energy curves and mechanism coupler curves allows real time joint behavioral adjustment. Such a powered joint can be adjusted to passively achieve desired behavior for different speeds and environmental needs. The effects on joint moment and stiffness from adjusting one type of mechanism is presented.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Neuromusculoskeletal interfacing of lower limb prostheses

The method of bone-anchored attachment of limb prostheses via a percutaneous skeletal extension was developed to circumvent commonly reported problems associated with the conventional method of socket attachment. In addition to the direct structural connection, the percutaneous implant may serve as a conduit for bidirectional communication between muscles and nerves within the residual limb and the prosthesis. Implanted electrodes recording myoelectric activity within the residual limb can be used to infer the user’s movement intent and may thus be used to provide intuitive control of the prosthesis in real time. Sensory feedback from the prosthesis can be provided back to the user by neurostimulation via implanted neural electrodes, thus closing the control loop. Together the skeletal, neural, and muscular interfaces form a neuromusculoskeletal interface. This technology is currently being evaluated in a clinical trial on individuals with upper limb amputation, but it has not yet been used in the lower limb. The aim of this thesis has been to translate the concept of neuromusculoskeletal interfacing to the lower limb. An additional aim has been to reduce the limitations on high impact activities, that exist on current available systems for bone-anchored attachment of limb prostheses. To achieve these aims, a new design of the neuromusculoskeletal interface was developed where the structural capacity was increased with respect to current versions of the implant system to accommodate increased loads for highly active usage by individuals with lower limb amputation. In order to set adequate design requirements, investigations were conducted to determine the load exposure of bone-anchored implant systems during a number of loadbearing activities. Structural verification of the neuromusculoskeletal interface has been performed using numerical simulations as well as physical testing in static and dynamic conditions. The first steps towards clinical implementation of the lower limb neuromusculoskeletal interface have been taken by the development of a clinical research protocol that has been approved by the Swedish Ethical Review Authority

Design of a Lightweight Modular Powered Transfemoral Prosthesis

Rehabilitation options for transfemoral amputees are limited, and no product today can mimic the full functionality of a human limb. Powered prosthetics have potential to close this gap but contain major drawbacks which ultimately increase the energy expenditure of the user. This thesis explores the viability of new designs and methods to reduce energy expenditure. In doing so a prototype containing many of the explored concepts is also being constructed to replace the laboratory’s current powered prosthetic, AMPRO II. This goal is accomplished by reducing weight through optimizing structural components, using lightweight motors and gearing, and reducing the energy requirements through novel passive spring sub-assemblies. Adjustable and modular components also enable a wider range of use and are explored. The main objective of this thesis is to investigate these design improvements and create the next-generation prosthetic for the Human Rehabilitation Lab. This thesis explores using a combination of passive and powered components to reduce the need for heavy actuators. Methods involve coding walking simulations based on an inverse dynamics study. By simulating design concepts with elastic elements the resulting power requirements of the motors have been estimated to evaluate each concept. Motors and gearing options have also been investigated with an optimization-based approach; gearing ratio was minimized in a test comparing discrete off-the-shelf motor options to biomechanical requirements. For the structural components, the mass of each part has been minimized through an iterative approach in FEA. Elements selected for further investigation from this thesis are being constructed with a prototype. Improvements over AMPRO II include adjustable height, functionality on both legs, a flexible foot, modularity, capabilities of passive elastic elements, and a mass estimated to be 20% lighter. Components include flat motors with harmonic drives, adjustable pylons for height, a low-profile mounting frame, passive pre-loaded springs, and a rotary series elastic actuator (RSEA). Unproven concepts such as the springs and RSEA have been designed as modular and optional to reduce risk. Moving forward, the first prototype is currently being built without the optional components to test the biomechanics. Future tests will incorporate the designed elastic elements to validate simulation concepts

A Multimodal Sensory Apparatus for Robotic Prosthetic Feet Combining Optoelectronic Pressure Transducers and IMU

Timely and reliable identification of control phases is functional to the control of a powered robotic lower-limb prosthesis. This study presents a commercial energy-store-and-release foot prosthesis instrumented with a multimodal sensory system comprising optoelectronic pressure sensors (PS) and IMU. The performance was verified with eight healthy participants, comparing signals processed by two different algorithms, based on PS and IMU, respectively, for real-time detection of heel strike (HS) and toe-off (TO) events and an estimate of relevant biomechanical variables such as vertical ground reaction force (vGRF) and center of pressure along the sagittal axis (CoPy). The performance of both algorithms was benchmarked against a force platform and a marker-based stereophotogrammetric motion capture system. HS and TO were estimated with a time error lower than 0.100 s for both the algorithms, sufficient for the control of a lower-limb robotic prosthesis. Finally, the CoPy computed from the PS showed a Pearson correlation coefficient of 0.97 (0.02) with the same variable computed through the force platform

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

Sci Robot

Robotic leg prostheses promise to improve the mobility and quality of life of millions of individuals with lower-limb amputations by imitating the biomechanics of the missing biological leg. Unfortunately, existing powered prostheses are much heavier and bigger and have shorter battery life than conventional passive prostheses, severely limiting their clinical viability and utility in the daily life of amputees. Here, we present a robotic leg prosthesis that replicates the key biomechanical functions of the biological knee, ankle, and toe in the sagittal plane while matching the weight, size, and battery life of conventional microprocessor-controlled prostheses. The powered knee joint uses a unique torque-sensitive mechanism combining the benefits of elastic actuators with that of variable transmissions. A single actuator powers the ankle and toe joints through a compliant, underactuated mechanism. Because the biological toe dissipates energy while the biological ankle injects energy into the gait cycle, this underactuated system regenerates substantial mechanical energy and replicates the key biomechanical functions of the ankle/foot complex during walking. A compact prosthesis frame encloses all mechanical and electrical components for increased robustness and efficiency. Preclinical tests with three individuals with above-knee amputation show that the proposed robotic leg prosthesis allows for common ambulation activities with close to normative kinematics and kinetics. Using an optional passive mode, users can walk on level ground indefinitely without charging the battery, which has not been shown with any other powered or microprocessor-controlled prostheses. A prosthesis with these characteristics has the potential to improve real-world mobility in individuals with above-knee amputation.R01 HD098154/HD/NICHD NIH HHSUnited States/T42 OH008414/OH/NIOSH CDC HHSUnited States

The Design, Prototype, and Testing of a Robotic Prosthetic Leg

Since antiquity, health professionals have sought ways to provide and improve prosthetic devices to ease the suffering of those living with limb loss. Mid-century modern engineering techniques, in part, developed and funded by the American industrial war effort, led to numerous innovations and standardization of mass-customized products. Followed by the Digital Revolution, we are now experiencing the roboticization of prosthetic limbs. As innovations have come and gone, some essential technologies have been forgotten or ignored. Many successful products have been commercialized, but unfortunately, they are often rationed to those who need them most. Here we present a prototype device based on many prior discoveries, utilizing commercially available parts when possible. This device has the potential to reduce the overall costs of powered robotic prosthetics, making them accessible to those with knee instability or the fear of falling. Additional benefits of this device are that it is designed to improve the kinematic and kinetic symmetry of the lower extremities, including the hips. We will design, prototype, and test this robotic prosthetic leg for feasibility and safe performance. KEYWORDS: ENGINEERING, LIMB LOSS, FEAR OF FALLING, POWERED ROBOTIC PROSTHETIC LEG, PROTOTYP