Identification and Control of a Soft-Robotic Bladder Towards Impedance-Style Haptic Terrain Display

Abstract: This paper evaluates the capabilities of a soft robotic pneumatic actuator derived from the terrain display haptic device, "The Smart Shoe." The bladder design of the Smart Shoe is upgraded to include a pressure supply and greater output flow capabilities. A bench top setup is created to rigorously test this new type of actuator. The bandwidth and stiffness capability of this new actuator are evaluated relative to forces and displacements encountered during human gait. Four force vs. displacement profiles relevant to haptic terrain display are proposed and tested using sliding-mode tracking control. It was found that the actuator could sustain a stiffness similar to a soft-soled shoe on concrete, as well as other terrain (sand, dirt, etc.), while the bandwidth of 7.3 Hz fell short of the goal bandwidth of 10 Hz. Compressions of the bladder done at 20 mm/s, which is similar to the speed of human gait, showed promising results in tracking a desired force trajectory. The results in this paper show this actuator is capable of displaying haptic terrain trajectories, providing a basis for futurep wearable haptic terrain display devices.