Convergence of a rotary-leg and humanoid model: Stability effects of leg retraction, muscle torque and multi-segment legs

Xiaoxiao Lu, Purdue University

Abstract

To obtain a complete walking model with dynamical and structural accuracy, three fundamental changes are made to the original clock-torqued spring-loaded-inverted-pendulum model (CT-SLIP). First, rotating leg is replaced by a oscillate leg to mimic the leg movement pattern in human and other animals; second, muscles are applied to the oscillate leg model as power input; third, multi-segments leg are restored for the oscillate single segment leg model. We first set out to determine how the whole-body dynamics of legged locomotion are affected by whether legs are oscillated or simply rotated around the hip position. We compared the stability of CT-SLIP with leg rotation versus leg retraction and find that there exists no clear general trends regarding the superior stability of one method over the other. For small perturbations the two methods are shown to yield identical stability of whole-body motion. For large perturbations, while particular cases show differences, on the whole it is not clear which method proves more stable in general. We then modified the motor torque function in original model with muscle torques. Unlike the Rhex robot from which CT-SLIP is derived, most animals use skeleton muscle to power their locomotion. We want to determine if this difference on torque function would effect the system dynamics. We found that the muscle damping which is not included in original CT-SLIP would slow down the walking speed of system. Increasing larger damping coefficient would eventually cause the system to fail. Finally we replaced the single segment spring leg in CT-SLIP with a two segments stiff leg. Most legged animal has knee and/or ankle joints in addition to the hip joint, we set out to determine whether the extra joint would change the dynamics of the system. Simulation result shows stable gaits for the multi-segment leg model, while their forward speed are much lower than that of the CT-SLIP.

Degree

M.S.E.

Advisors

Seipel, Purdue University.

Subject Area

Biomechanics

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