Bidirectional Asymmetric Accordion-Type Soft Robot for Respiratory Assistance

Respiratory assistance is of significant importance for achieving pulmonary rehabilitation in individuals with weakened respiratory muscles. Soft actuators have great potential in rehabilitation application; yet, there is little research on soft respiratory rehabilitation robots. This article presents a novel bidirectional asymmetric accordion-type soft robot capable of generating chest expansion and contraction actions, designed for respiratory assistance training in patients with respiratory muscle weakness. The robot consists of two bidirectional asymmetric accordion-type pneumatic actuators (APA), each composed of a primary accordion-type pneumatic actuator (PAPA) and a subordinate accordion-type pneumatic actuator (SAPA), capable of providing torque to the human body to facilitate auxiliary expansion and contraction of the patient’s chest. A kinematic model is developed to couple the angular movements of the human arm with the actuator by analyzing their angular relationships. By modeling the airbags of actuators as compressed spheres and simplifying the contact areas, the effective angle can be calculated at the specified pressure and output torque, thereby selecting the optimal geometric parameters of PAPA and SAPA to ensure that the desired angle is achieved for lifting the arm. Experimental validation confirmed the accuracy of the proposed kinematic coupled model and output torque of PAPA. The robot’s efficacy in respiratory training was assessed by comparing volume flowrate (VFR) and moving air volume (MAV) between ten healthy participants with and without robot assistance. The experimental results show that the average improvement rates of exhalation VFR, inhalation VFR, and MAV of the 10 participants are 154%, 148%, and 155%, which demonstrated the robot’s capability to enhance respiratory function.