Underactuated Soft Hip Exosuit
Based on Adaptive Oscillators
to Assist Human Locomotion 


Tricomi E, Lotti N, Missiroli F, Zhang X, Xiloyannis M, Müller T, Crea S, Papp E, Krzywinski J, Vitiello N, Masia L.

"Underactuated Soft Hip Exosuit Based on Adaptive Oscillators to Assist Human Locomotion"

IEEE Robotics and Automation Letters, vol. 7, no. 2, pp. 936-943, April 2022. PDF


Human locomotion is a mechanism refined over years of evolution: walking requires the synchronous coordination of different joints to minimize body natural dynamics and energy consumption.

When dealing with the design and control of assistive technologies for walking, main requirements should include lightness and compactness from the hardware design viewpoint, and adaptation to changes in walking pattern from the controller perspective.


In order to reduce device weight and to achieve simpler mechanical and control designs, recent trends in soft robotics have foreseen the use of fewer independent actuators than the number of controlled joints. Although several examples of underactuated soft robotic devices exist for upper-limb, very few solutions exist for lower-limb assistance.



To combine simplicity and lightweight we developed a fully embedded wearable exosuit to assist hip flexion during walking. The device is underactuated, i.e., a single actuator is used to assist bilateral hip flexion. The user is assisted through two artificial tendons wrapped in opposite directions on a double-layer pulley mounted on the motor. Motor rotation pulls one cable and releases the other according to the motion.

To provide adaptive assistance, the device incorporates a control strategy based on Adaptive Oscillators (AOs) and gait phase estimation. AOs can be described as a mathematical tool able to synchronize with a rhythmic and periodic signal to online learn its frequency, amplitude, and phase components. The control algorithm is solely driven by IMU sensors recording the hip flexion angle.



The device is able to rapidly track changes in gait pattern and to adapt to new walking speeds; as well as to provide balanced assistive torques to both legs saving muscular effort during walking. For these characteristics, the underactuated exosuit can be suitable to target different categories of individuals, from healthy subjects to mild impaired people.