10 research outputs found
Bio-inspired design and validation of the Efficient Lockable Spring Ankle (ELSA) prosthesis
Over the last decade, active lower-limb prostheses demonstrated their ability to restore a physiological gait for transfemoral amputees by supplying the required positive energy balance during daily life locomotion activities. However, the added-value of such devices is significantly impacted by their limited energetic autonomy, excessive weight and cost, thus preventing their full appropriation by the users. There is thus a strong incentive to produce active yet affordable, lightweight and energy efficient devices. To address these issues, we developed the ELSA (Efficient Lockable Spring Ankle) prosthesis embedding both a lockable parallel spring and a series elastic actuator, tailored to the walking dynamics of a sound ankle. The first contribution of this paper concerns the developement of a bio-inspired, lightweight and stiffness-adjustable parallel spring, comprising an energy efficient ratchet and pawl mechanism with servo actuation. The second contribution is the addition of a complementary rope-driven series elastic actuator to generate the active push-off. The system produces a sound ankle torque pattern during flat ground walking. Up to 50% of the peak torque is generated passively at a negligible energetic cost (0.1 J/stride). By design, the total system is lightweight (1.2kg) and low cost
Multi-purpose Electromagnetic Energy Harvesting System
This thesis proposes a multi-purpose electromagnetic energy harvesting system that harnesses mechanical energy from diverse types of mechanical motion sources and converts it into low power electrical energy. The harvested electrical energy is either used to supply power to low-power electronic devices or stored in an internal storage battery for later use. The proposed energy harvester can be i) mounted on a human’s knee, elbow, or hip, ii) hand-cranked, as well as iii) installed on any enclosure with fixed and movable parts (e.g., doors and/or windows). When mounted on a knee or hip, the device is actuated only during the so-called negative energy cycle of the motion and does not disturb the motion in the forward direction.
The key building blocks of the proposed multi-purpose electromagnetic energy harvesting system is a new brushless AC electromagnetic generator, an adaptive motion translation mechanism and a smart power management system. The brushless AC generator consists of a new structure with a detachable rotor arrangement comprising mainly Neodymium rare-earth magnets mounted on an adjustable height rotor shaft and a stator made up of top and bottom flanges and a single continuous coil arrangement on a non-magnetic spool worn on a center magnetic stator core. The stator and rotor arrangement is carefully designed to allow for variable air gap so that the initial amount of torque required to move the rotor is adjustable and the amount of the generated output voltage can be controlled.
Finite-element modeling magnetics (FEMM) simulation tool was used for the optimization of the new brushless generator, selecting the different generator materials, and determining the placement of the key components to achieve an efficient and truly adjustable system to the variation of frequencies and torque conditions. Furthermore, a gearbox was used as a mechanical up conversion mechanism to multiply the relatively low human motion to up to 5000 RPM at a walk pace of about one step per second. For this purpose, a three-stage spur gear system was designed using a roller-clutch at the front end to only allow motion during the negative cycle. The gearbox, when assembled together with the generator, works together with the adjustable height rotor to create the desired effect – adaptive, multi-purpose energy harvesting system.
The power management design was optimized to maximum energy harvesting at rated RPM. When an external load is detected, the harvested power is routed to the external load, else, the power is routed to the internal storage battery for later use.
The completed system generates between 2.5 watts and 7.5 watts of electrical power at an overall system efficiency of up to 84%
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Biomechanical adaptations involved in ramp descent: Impact of microprocessor-controlled ankle-foot prothesis. Kinetic and kinematic responses to using microprocessor-controlled ankle-foot prosthesis in unilateral trans-tibial amputees during ramp descent
Ramp descent is a demanding task for trans-tibial amputees, due to the difficulty in controlling body weight progression over the prosthetic foot. A deeper understanding of the impact of foot function on ramp descent biomechanics is required to make recommendations for rehabilitation programs and prosthetic developments for lower-limb amputees. The thesis aim was to determine the biomechanical adaptations made by active unilateral trans-tibial amputees (TT) using a microprocessor-controlled ankle-foot prosthesis in active (MC-AF) compared to non-active mode (nonMC-AF) or elastically articulated ankle-foot device. A secondary aim was to determine the biomechanical adaptation made by able-bodied individuals when ankle motion was restricted using a custom made ankle-foot-orthosis and provide further insight into the importance of ankle dynamics when walking on ramps. Kinetic and kinematic data were recorded from nine TT’s and twenty able-bodied individuals. Able-bodied participants, ankle restriction, led to an increase in involved limb loading response knee flexion that is accompanied by the increased knee power generation during the single-limb-support phase that correlates to TTs results. TT’s use of an MC-AF reduced the ‘plantar-flexion’ resistance following foot contact allowing foot-flat to be attained more quickly. Followed by the increased ‘dorsi-flexion’ resistance which reduced the shank/pylon rotation velocity over the support foot, leading to an increase in negative work done by the prosthesis. These findings highlight the importance of having controlled ankle motion in ramp descent. Use of an MC-AF can provide TTs controlled motion for descending ramps and hence provide biomechanical benefits over using more conventional types of ankle-foot devices.Engineering and Physical Science Research Council (EPSRC) via Doctoral Training Account (DTA) (EP/P504821/1)
Chas. A. Blatchford and Sons Ltd., Basingstoke, UK provided the prosthetic hardware, prosthetist support, and facilitated the attendance of the TT participants for this stud
Wearable exoskeletons to support ambulation in people with neuromuscular diseases, design rules and control
Neuromuscular diseases are degenerative and, thus far, incurable disorders that lead to large muscle wasting. They result in constant deterioration of activities of daily living and in particular of ambulation. Some common types include Duchenne muscular dystrophy, Charcot-Marie-Tooth disease, polymyositis and amyotrophic lateral sclerosis. While these diseases individually have a low rate of occurrence and are mostly unknown to most people, collectively they affect a significant part of the population. About 1 person in 2000 suffer from neuromuscular diseases, which means an approximate total of 370â000 people over the European continent. Recent technology breakthroughs have made possible the realization of advanced powered orthotics, which are commonly called exoskeletons. The most advanced devices have successfully been able to support patients in walking despite a debilitating condition such as complete spinal cord injury. Such technology could be ideal for people with mid-stage neuromuscular diseases as it provides more mobility and independence.
This work investigates the definitions and requirements that would need to be fulfilled for any proposed orthotic device to assist people living with neuromuscular diseases. To define the needs of patients with neuromuscular disease, a large literature review is conducted on gait compensation patterns. The research also includes the data collection of experimental gait measurements from fourteen people with heterogeneous neuromuscular diseases. Conclusions show that orthotics for people with neuromuscular diseases require tunable assistance at each joint and a collaborative control strategy in order to let the user control motion. Eventually, most people may not be able to use crutches.
A full lower limb exoskeleton, AUTONOMYO, is designed, realized and evaluated. A particular attention is put on the optimization of the actuator and transmission units. In order to reduce the effects of inertia and weight of those units, a design is explored with actuation remotely located from the joints. The transmission is realized by custom cable wire and pulley systems, combined with standard planetary gears. The dynamics of different coupling between the hip and the knee flexion/extension joints are explored, and their benefits and tradeoffs analyzed.
A novel control strategy based on a finite-state active impedance model is designed and implemented on the AUTONOMYO device. The controller consists of three states of different active impedances mimicking a visco-elastic behavior. The switching condition between states is uniquely based on the hip flexion velocity to detect the user intent. The performance of the strategy regarding the detection of intention and the modulation of the assistance is evaluated on a test bench and in real conditions with healthy pilots and with a person with limb girdle muscular dystrophy. The preliminary results are promising since all pilots (including the one with muscular dystrophy) are able to initiate and terminate assisted walking on demand. They are all able both to walk with a good stride rate and to reach moderate velocities. Healthy pilots are able to ambulate alone with the exoskeleton, while the pilot with muscular dystrophy requires human assistance for the management of balance
Design of an energy efficient transfemoral prosthesis using lockable parallel springs and electrical energy transfer
Over the last decade, active lower-limb prostheses demonstrated their ability to restore a normal gait for transfemoral amputees by supplying the required positive energy balance [1]. However, the added-value of such devices is significantly impacted by their limited energetic autonomy preventing their full appropriation by the patients. There is thus a strong incentive to reduce the overall power consumption of active prostheses. Addressing this need requires to revisit the electromechanical design. For both the ankle and the knee, the present paper demonstrates that both the use of a lockable parallel spring and the transfer of electrical energy between joints can significantly improve the energetic performance for overground walking. A simulation model of such a prosthesis was implemented in order to quantify the energy gain being achievable when augmenting a classical series elastic actuator (SEA) with different parallel spring topologies. Simulations predict that adding a lockable parallel spring (LPS) to the SEA reduces the ankle motor consumption by 24% and allows the knee (naturally dissipative) to produce 38% more electrical energy. Moreover, the total energy consumption of the device is reduced to 22J/stride when the harvested electrical energy from the knee is stored and transferred to the ankle