Current bipedal robots with articulated legs, even the most impressive prototypes to date, still lack the ability to execute dynamic motions such as jumping and running with comparable performance to biological systems. Recently a new biped prototype, KURMET, has been built at OSU to serve as an experimental platform for further investigation into the performance of dynamic movements in bipedal machines with biologically-realistic features. KURMET has series-elastic actuators (SEA) at all leg joints. The presence of SEAs provides the compliance that is needed in dynamic motions, yet also complicates the controller's tasks, especially when combined with articulated legs in a system that is not naturally stable.
This thesis develops a fuzzy control system for hopping with KURMET. With this controller, KURMET can stably hop at varying heights and forward/backward velocities. The control system is arranged into two levels. The low-level control executes the hop motion. It employs a hopping state machine that is specifically designed to accommodate the natural dynamics of the SEAs. The high-level control is a fuzzy controller that is called at discrete instances (every top of flight (TOF)) to regulate the key parameters in the state machine. Through proper selection of these parameters, the desired hop height and velocity can be achieved. The fuzzy rulebase is generated via an iterative training process, which is done off-line through dynamic simulation using detailed models of the articulated mechanism and the series-elastic actuation. The fuzzy rulebase is later modified by on-line adaptation.
The fuzzy rulebase has fewer than 200 rules; however, the overall fuzzy control system is able to produce robust and accurate hopping performance in KURMET. Experimental data shows that the maximum error of the torso height at TOF is controlled within 1 cm and the maximum error of the torso velocity at TOF is controlled within 5 cm/s.
This thesis also experimentally investigates the high jump potential in KURMET. With a jumping state machine that is modified from the previous hopping state machine, KURMET is able to produce a maximum nominal jump height of 75 cm. When normalized to the length of the biped's link segments (25 cm), this performance
is significant relative to human jumps.