Speed adaptation in a powered transtibial prosthesis controlled with a neuromuscular model

Biomechatronics Group, Massachusetts Institute of Technology, 75 Amherst Street, Cambridge, MA 02139, USA.
Philosophical Transactions of The Royal Society B Biological Sciences (Impact Factor: 6.31). 05/2011; 366(1570):1621-31. DOI: 10.1098/rstb.2010.0347
Source: PubMed

ABSTRACT Control schemes for powered ankle-foot prostheses would benefit greatly from a means to make them inherently adaptive to different walking speeds. Towards this goal, one may attempt to emulate the intact human ankle, as it is capable of seamless adaptation. Human locomotion is governed by the interplay among legged dynamics, morphology and neural control including spinal reflexes. It has been suggested that reflexes contribute to the changes in ankle joint dynamics that correspond to walking at different speeds. Here, we use a data-driven muscle-tendon model that produces estimates of the activation, force, length and velocity of the major muscles spanning the ankle to derive local feedback loops that may be critical in the control of those muscles during walking. This purely reflexive approach ignores sources of non-reflexive neural drive and does not necessarily reflect the biological control scheme, yet can still closely reproduce the muscle dynamics estimated from biological data. The resulting neuromuscular model was applied to control a powered ankle-foot prosthesis and tested by an amputee walking at three speeds. The controller produced speed-adaptive behaviour; net ankle work increased with walking speed, highlighting the benefits of applying neuromuscular principles in the control of adaptive prosthetic limbs.

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    • "Thanks to the use of battery-operated servomotors, powered prostheses allow positive net-energy tasks, such as step-overstep stair ambulation [1] and sit-to-stand transitions [2], while restoring more natural walking kinetics and kinematics compared to passive prostheses [3]. In stance phase, prosthesis torque can be regulated to obtain physiological body support and propulsion, [4] possibly reducing the metabolic cost of walking [5]. In swing phase, a biologically accurate movement can be generated to allow the timely placement of the foot in preparation for subsequent heel strike without requiring any additional effort from the user [6]. "
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    ABSTRACT: We present a novel swing phase controller for powered transfemoral prostheses based on minimum jerk theory. The proposed controller allows physiologically appropriate swing movement at any walking speed, regardless of the stance controller action. Preliminary validation in a transfemoral amputee subject demonstrates that the proposed controller provides physiological swing timing, without speed-or patient-specific tuning.
    36th Annual International IEEE EMBS Conference; 08/2014
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    • "Intrinsic controllers for lower-limb prostheses use finite state machines whose transitions are triggered based on onboard sensor data. Such controllers have recently been shown to generate biomimetic and speed-adaptive behavior during over-ground walking [1] [2] but are incapable of transitioning between different terrains or perform adequately during stair ambulation. This severely limits the mobility of lower extremity amputees and has a substantial impact on their quality of life and social independence [3] [4]. "
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    ABSTRACT: Although great advances have been made in the design and control of lower extremity prostheses, walking on different terrains, such as ramps or stairs, and transitioning between these terrains remains a major challenge for the field. In order to generalize biomimetic behaviour of active lower-limb prostheses top-down volitional control is required but has until recently been deemed unfeasible due to the difficulties involved in acquiring an adequate electromyographic (EMG) signal. In this study, we hypothesize that a transtibial amputee can extend the functionality of a hybrid controller, designed for level ground walking, to stair ascent and descent by volitionally modulating powered plantar-flexion of the prosthesis. We here present data illustrating that the participant is able to reproduce ankle push-off behaviour of the intrinsic controller during stair ascent as well as prevent inadvertent push-off during stair descent. Our findings suggest that EMG signal from the residual limb muscles can be used to transition between level-ground walking and stair ascent/descent within a single step and significantly improve prosthesis performance during stair-ambulation.
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    ABSTRACT: Animal movement is often complex, unsteady and variable. The critical role of muscles in animal movement has captivated scientists for over 300 years. Despite this, emerging techniques and ideas are still shaping and advancing the field. For example, sonomicrometry and ultrasound techniques have enhanced our ability to quantify muscle length changes under in vivo conditions. Robotics and musculoskeletal models have benefited from improved computational tools and have enhanced our ability to understand muscle function in relation to movement by allowing one to simulate muscle-tendon dynamics under realistic conditions. The past decade, in particular, has seen a rapid advancement in technology and shifts in paradigms related to muscle function. In addition, there has been an increased focus on muscle function in relation to the complex locomotor behaviours, rather than relatively simple (and steady) behaviours. Thus, this Theme Issue will explore integrative aspects of muscle function in relation to diverse locomotor behaviours such as swimming, jumping, hopping, running, flying, moving over obstacles and transitioning between environments. Studies of walking and running have particular relevance to clinical aspects of human movement and sport. This Theme Issue includes contributions from scientists working on diverse taxa, ranging from humans to insects. In addition to contributions addressing locomotion in various taxa, several manuscripts will focus on recent advances in neuromuscular control and modulation during complex behaviours. Finally, some of the contributions address recent advances in biomechanical modelling and powered prostheses. We hope that our comprehensive and integrative Theme Issue will form the foundation for future work in the fields of neuromuscular mechanics and locomotion.
    Philosophical Transactions of The Royal Society B Biological Sciences 05/2011; 366(1570):1463-5. DOI:10.1098/rstb.2010.0354 · 6.31 Impact Factor
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