Event Detail

Event Type: 
Applied Mathematics and Computation Seminar
Friday, May 2, 2008 - 05:00
Gilkey 113

Speaker Info

OSU Mechanical Engineering

Reduced order models have been utilized to accurately model the steady locomotion dynamics of a variety of running animals and have been used as a target for control of higher dimensional robotic implementations. Tuned appropriately, these models exhibit passively stable periodic gaits when utilizing a fixed leg touch-down angle protocol to determine foot placement. However, incorporating a similar leg touch-down protocol into a spatial spring loaded inverted pendulum model yields only unstable gaits, suggesting that changes in the leg touch-down angle in response to perturbations are important for stability. Additionally, while each template models the leg dynamics by an energy-conserving spring, insects and animals have structures that dissipate, store and produce energy during a stance phase. Recent investigations into the spring-like properties of limbs, as well as animal response to drop-step perturbations, suggest that animals use their legs to manage energy storage and dissipation, and that this management is important for gait stability. In this presentation, we modify the planar reduced order locomotion models to include changes in leg touch-down angle and energy. We introduce leg touch-down angle variations through a simple feedback control law based upon the previous leg touch-down and lift-off angles. Energy variations in the sagittal plane model are incorporated via a clock-driven leg actuation protocol that varies the force-free leg length during the stance phase, yet maintains qualitatively correct force and velocity profiles. In contrast to the partially asymptotically stable gaits identified in previous analyses, we find that incorporating energy and leg angle variations in this manner enables the system to recover from perturbations similar to those that might be encountered during locomotion over rough terrain.