Turtle shell-inspired exosuit with large output, model-based torque estimation, and load compensation

Pneumatic soft actuators have emerged as a promising technology in wearable robotics. However, their insufficient output force, bulky size, or lack of precise force control usually limits their wearable applications. In this paper, we present a bio-inspired exosuit for elbow assistance that mimics the morphology and functionality of a turtle shell. Mathematical models are established to characterize the force output of the actuators and predict the output torque of the exosuit. Subsequently, a model-based feedback torque control is proposed to compensate for the carrying load. Experimental validation is conducted to verify force-extension characteristics and the exosuit's output assistive torque. The experiment validates the effectiveness of the load compensation control. Electromyographic (EMG) measurements of upper limb muscles are analyzed in elbow assistance tests by human subjects. The proposed exosuit generates a maximum output torque of 82 Nm under 250 kPa air supply. The closed-loop torque control achieves constant load compensation with a root mean square error (RMSE) of 0.77 N. The EMG results indicate a 38.4% average reduction of muscle activation under a 2.5 kg weight lifting. The turtle shell-inspired exosuit design is verified in terms of large output torque, high compactness, and accurate model. The new exosuit demonstrates a promising potential for industrial and medical applications.