Passive Control of Fluid Powered Human Power Amplifiers

A unified control framework is proposed for the control of fluid powered human power amplifiers. Human power amplifiers are mechanical tools that humans operate directly and the human force is amplified hydraulically or pneumatically. The tool and the environment forces would therefore appear to the human as having been scaled down. Ideally, the assistive force is transparent to the human such that the tool should feel haptically like any other passive mechanical tool to the human. To ensure safety and coupling stability, it is helpful that the controlled human power amplifier interacts with the human opeartor and other environments passively. In the proposed unified control framework, the hydraulic or pneumatic actuator is controlled to interact virtually with a fictitious inertia. The control problem then becomes one of coordinating the velocities between virtual inertia and the actuator. Both processes of augmentation with virtual inertia, and coordination can be done passively; the latter via the energy preserving passive decomposition approach into locked and shaped systems. The overall control system can be shown to possess the needed passivity property. The control schemes for both the hydraulic and pneumatic cases have been experimentally implemented.