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Title: Energy Efficient Bipedal Locomotion
Author: Hasaneini, Seyed Javad
Advisor: Macnab, Chris
Bertram, John
Leung, Henry
Keywords: Computer Science;Robotics
Issue Date: 30-Jan-2014
Abstract: In this research, dynamic optimization of a minimally constrained bipedal model (free to exhibit almost any arbitrary gait) is used to find the characteristics of energy efficient gaits. I find that using a work-based cost yields gait optimization that automatically predicts many features of human locomotion. This includes the optimality of walking and running at their respective speeds. The results show the determinant energetic factors are: (i) the cost of stance-leg work to make up for energy loss during downward-to-upward redirection of body motion at each step; and (ii) the cost to move the swing leg forward and prepare it for support transfer. To minimize the net energetic cost, the calculations discover various strategies. For energy-effective walking the critical control actions are identified as: (i) a burst extension force along the support leg just before heel-strike; (ii) a burst hip torque at the start of leg-swing to accelerate the swing leg motion; and (iii) a decelerating burst torque at the end of swing to reduce foot velocity at landing, leading to less energy loss at support transfer between the legs. The burst hip torques at the beginning and end of the swing phase are also used in energy-efficient running. However, exploiting an extension force before heel-strike is not possible in running as there is no support leg during flight. Instead, energy-loss at heel-strike can be minimized by landing on a near-vertical leg. Swing-leg retraction in walking is also investigated in depth. The approach focuses on simple closed-form analytic solutions. The three principal control actions identified in my gait optimizations are replaced by impulsive forces and torques. With this simplified model it was shown analytically that: (i) it is energetically favorable to delay the retracting hip torque until the end of the pre-emptive push-off; (ii) swing-leg retraction torque reduces the push-off force; and also (iii) increases the maximum possible walking speed; and (iv) the energetic advantage of active swing-leg retraction depends on the step length, average walking speed, ratio of actuator efficiencies for positive and negative work, and percentage of active work done during heel-strike.
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