Deformable reflective diaphragm sensors for control of soft pneumatically actuated devices

This paper presents an optical sensing method for measuring complex deformations in soft pneumatic actuators. The proposed approach involves a reflective elastic diaphragm which changes shape and position as an actuator deforms, producing measurable changes in reflected infrared (IR) light which are then used to monitor and control the kinematic and kinetic states of the actuators. In this approach, we place arrays of IR detectors near a diaphragm to capture light reflected from several angles and positions and enable the estimation of multiple coupled deformation modes simultaneously. These IR detector data, along with actuation pressure data, is used to train model that decouples complex pneumatic actuator motion into the desired actuator degrees of freedom. As an illustrative example, three soft reflective sensors are used to measure the motion of a pneumatic bending actuator having both flexion and abduction DOFs. A simple linear regression model trained on diaphragm sensor and pressure data yielded accurate and repeatable position estimates for both DOFs. Experimental evaluation of the bending actuators in a soft grasp assist device demonstrate that the reflective diaphragm sensors, when combined with actuation pressure data, allow detection of actuator tip motion and contact forces.