Bidirectional Asymmetric Accordion-type Soft Robot for Respiratory Assistance

Abstract Respiratory assistance is of significant importance for achieving pulmonary rehabilitation in individuals with weakened respiratory muscles. Soft actuators has great potential in rehabilitation application, yet there is little research on soft respiratory rehabilitation robots. This paper presents a novel bidirectional asymmetric accordion-type soft robot capable of generating chest expansion and contraction actions, designed for respiratory assistance 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 human body to facilitate auxiliary expansion and contraction of the chest. A kinematic motion model is developed to couple the movements of the human arm with the actuator by analyzing their angular relationships. By modeling the airbags as compressed spheres and simplifying the contact areas, the angle can be calculated at the specified pressure and torque, thereby selecting the optimal geometric parameters of PAPA and SAPA to ensure the desired angle is achieved. Experimental validation confirmed the accuracy of the kinematic coupled motion model and output torque of PAPA. The robot's efficacy in respiratory assistance was assessed by comparing volume flow rate (VFR) and moving air volume (MAV) between ten participants with and without robot assistance. Results show the average improvement rates of exhalation VFR, inhalation VFR, and MAV of the participants are 154.4%, 147.94%, and 155.26%, which demonstrated the robot's capability to enhance respiratory function.