Control Aspects of a Full-body Enhancive Robotic Exoskeleton

A robotic exoskeleton is a solution that would help maintain the level of daily life and professional activities of a user when she/he gets older. Moreover, in industries such as heavy construction, assembling or warehouses, the use of enhancive exoskeletons by able-bodied will add efficiency premium due to partial automation of processes and decrease likelihood and cost of work related injuries. Another expected area of application of exoskeletons are search and rescue situations in confined spaces, where the heavy equipment cannot access. Based on the literature review, currently, a gap in the knowledge of controlling of such devices for civilian applications exists. Control requirements for the robotic exoskeletons are specified and different control laws (Master-Slave Position Control, Direct and Indirect Force Control laws) are evaluated against them. Force Control laws are shown to be superior. A motion capture study was conducted and requirements for bandwidth of upper and lower extremities, from which limits on electronics bandwidth and control algorithm sample rate are derived, was determined to be less than 10 Hz. Control electronics and torque control algorithm (required by Force Control laws) for a novel design of an enhancive exoskeleton joint are proposed and developed. The design comprises two identical hydraulic cylinders opposing each other and connected by a link. Such arrangement allows for greater range of motion of the joint, e.g. when used as a knee joint. The simulation with gait as an input trajectory shows that the developed coupled control of actuators allows for minimisation of directly measured human-machine interaction force, while maintaining synchronous extension of the piston rods of the two actuators. A model-based selection was performed to find acceptable controller settings. The control strategy requires only one load cell and one linear variable differential transducer, hence decreasing the cost of hardware. The simulated control algorithm was validated experimentally on a prototype of a single joint and robotic knee connected in parallel for emulation of gait. A full body enhancive robotic exoskeleton model, with contact to the ground, was investigated for stability during gait. Shape and design of contact surface were evaluated.