Control of a pneumatically actuated joint for wearable supernumerary robotic limbs application

Abstract

Presented is work on the development of the Supernumerary Robotic Limbs project, headed by Federico Parietti in the d'Arbeloff Labs under Prof. Harry Asada. Specifically, this paper focuses on the integration of lightweight, pneumatic systems for prismatic joint actuation, and the various control schemes studied. This joint serves as the leg of the robot, and extends from the hip of the wearer to contact the ground. The design consists of a two-way pneumatic cylinder inside a load bearing carbon fiber sleeve, actuated with a nominally closed 5-3 way solenoid valve, and weighs in at <1kg per actuator. The positional control scheme is closed via tracking from a linear magnetopotentiometer, while the force control scheme utilizes both the positional tracking as well as a load cell at the foot of the leg. System modeling of the actuator dynamics allowed for development of a model based proportional control method. Optimization of the proportional gain and system delay time produced a rise time of 200ms given a step input command for a 250mm stroke. The developed scheme was implemented in the full wearable system to assist a human support weight in crouched positions and standing up from a sitting position. Initial testing has shown the effectiveness of the power, compactness and compliance of pneumatic systems in a wearable robotic device.