RoboANKLE: Design, Development, and Functional Evaluation of a Robotic Ankle with a Motorized Compliant Unit
Baris Baysal, Omid Arfaie, Ramazan Unal
TL;DR
RoboANKLE addresses the need for a lightweight powered transtibial prosthesis capable of natural push-off by integrating two ESAR-based energy-generation units: a Dorsi-Flexion (DF) mechanism for energy storage during mid-stance and a motor-driven Extra Energy Store (EES) for additional push-off torque. The design is supported by kinematic/kinetic analyses, CAD modeling, and experimental validation, achieving a $1.92$ kg prototype with torque and power margins over the natural ankle ($+57%$ torque, $+10%$ power) and strong alignment to natural power profiles (RMSE $12%$, correlation $97.8%$). The system employs robust instrumentation and control (ball-screw and replacer motors with PID and DOB) and leverages topology optimization and composite materials to reduce weight while maintaining strength. This work demonstrates a viable path toward energy-efficient, capable robotic ankles, with future work focusing on further weight reduction and adding a second DOF for varied terrains.
Abstract
This study presents a powered transtibial prosthesis with complete push-off assistance, RoboANKLE. The design aims to fulfill specific requirements, such as a sufficient range of motion (RoM) while providing the necessary torque for achieving natural ankle motion in daily activities. Addressing the challenges faced in designing active transtibial prostheses, such as maintaining energetic autonomy and minimizing weight, is vital for the study. With this aim, we try to imitate the human ankle by providing extensive push-off assistance to achieve a natural-like torque profile. Thus, Energy Store and Extended Release mechanism (ESER) is employed with a novel Extra Energy Storage (EES) mechanism. Kinematic and kinetic analyses are carried out to determine the design parameters and assess the design performance. Subsequently, a Computer-Aided Design (CAD) model is built and used in comprehensive dynamic and structural analyses. These analyses are used for the design performance evaluation and determine the forces and torques applied to the prosthesis, which aids in optimizing the design for minimal weight via structural analysis and topology optimization. The design of the prototype is then finalized and manufactured for experimental evaluation to validate the design and functionality. The prototype is realized with a mass of 1.92 kg and dimensions of 261x107x420 mm. The Functional evaluations of the RoboANKLE revealed that it is capable of achieving the natural maximum dorsi-flexion angle with 95% accuracy. Also, Thanks to the implemented mechanisms, the results show that RoboANKLE can generate 57% higher than the required torque for natural walking. The result of the power generation capacity of the RoboANKLE is 10% more than the natural power during the gait cycle.