RESUMEN
In the recent past, the development of lower-limb prostheses has taken a new turn with the emergence of active systems. However, their intrinsic wearable nature induces strict requirements regarding weight and encumbrance. In order to reduce the load - and thus the bulkiness - of their active part, several prototypes leverage the concept of compliant actuation, consisting in including an elastic element in parallel and/or in series with the actuator. In this paper, we explore the usability of polymer compliant ropes placed in parallel with the actuator of an ankle prosthesis. Ropes are intrinsically light and compact, and thus offer several advantages as compared to more traditional coil or leaf springs. Polymer materials were selected for their high energy density and yield strength. We conducted a set of experimental tests with several ropes, pretension levels, and periodic loading profiles. Results show that polymer-based ropes have a high potential for ankle assistance devices, since they can store the required energy in a low volume. However, further research should be conducted to improve their efficiency, since we estimated that only about 50% of the stored energy can be released, with few variations as a function of the rope preconditioning and loading profile.
Asunto(s)
Tobillo , Prótesis Articulares , Humanos , Fenómenos Biomecánicos , Articulación del Tobillo , TendonesRESUMEN
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.
Asunto(s)
Tobillo , Miembros Artificiales , Marcha , Diseño de Prótesis , Robótica , Caminata , Amputados , Articulación del Tobillo , Fenómenos Biomecánicos , HumanosRESUMEN
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 transfered to the ankle.