Soft Inflatable Robots for Safe Physical Human Interaction

Abstract

Robots that can operate in human environments in a safe and robust manner would be of great benefit to society, due to their immense potential for providing assistance to humans. However, robots have seen limited application outside of the industrial setting in environments such as homes and hospitals. We believe a very important factor preventing the cross over of robotic technology from the factory to the house is the issue of safety. The safety issue is usually bypassed in the industrial setting by separation of human and robot workspaces. Such a solution is clearly infeasible for robots that provide assistance to humans. This thesis aims to develop intrinsically safe robots that are suitable for providing assistance to humans. We believe intrinsic safety is important in physical human robot interaction because unintended interactions will occur between humans and robots due to: (a) sharing of workspace, (b) hardware failure (computer crashes, actuator failures), (c) limitations on perception, and (d) limitations on cognition. When such unintended interactions are very fast (collisions), they are beyond the bandwidth limits of practical controllers and only the intrinsic safety characteristics of the system govern the interaction forces that occur. The effects of such interactions with traditional robots could range from persistent discomfort to bone fracture to even serious injuries. Therefore robots that serve in the application domain of human assistance should be able to function with a high tolerance for unintended interactions. This calls for a new design paradigm where operational safety is the primary concern and task accuracy/precision though important are secondary. In this thesis, we address this new design paradigm by developing robots that have a soft inflaable structure, i.e, inflatable robots. Inflatable robots can improve intrinsic safety characteristics by being extremely lightweight and by including surface compliance (due to the compressibility of air) as well as distributed structural compliance (due to the lower Young’s modulus of the materials used) in the structure. This results in a lower effective inertia during collisions which implies a lower impact force between the inflatable robot and human. Inflatable robots can essentially be manufactured like clothes and can therefore also potentially lower the cost of robots to an extent where personal robots can be an affordable reality. In this thesis, we present a number of inflatable robot prototypes to address challenges in the area of design and control of such systems. Specific areas addressed are: structural and joint design, payload capacity, pneumatic actuation, state estimation and control. The CMU inflatable arm is used in tasks like wiping and feeding a human to successfully demonstrate the use of inflatable robots for tasks involving close physical human interaction.