Design and Control of the Planar Bipedal Robot ERNIE

This paper presents the development of the planar bipedal robot ERNIE. ERNIE has 5 links: a torso, two femurs and two tibias without feet. ERNIE was designed and constructed to serve as a testbed for the development of novel control strategies for bipedal walking. A boom provides frontal plane stability, restricting walking motions to the sagittal plane, and ERNIE is configured to walk on a treadmill so that it can walk indefinitely in a confined space. ERNIE’s legs are modular so that morphological asymmetries and the use of feet may be explored more in future studies. Springs can be attached across the knee joints in parallel with the knee actuators to enable gaits that are more energetically efficient. ERNIE is currently controlled using the hybrid zero dynamics framework in which a function of the robot’s configuration that monotonically increases over a step is used to parameterize holonomic constraints on the robot’s motion. The constraints are designed via parameter optimization to minimize an objective function, such as the energy consumed over a step, and, at the same time, ensure gait stability. The constraints are enforced using decoupled high-gain PD control.Copyright © 2007 by ASME