Virtual Constraints and Hybrid Zero Dynamics for Realizing Underactuated Bipedal Locomotion

Underactuation is ubiquitous in human locomotion and should be ubiquitous in bipedal robotic locomotion as well. This chapter presents a coherent theory for the design of feedback controllers that achieve stable walking gaits in underactuated bipedal robots. Two fundamental tools are introduced, virtual constraints and hybrid zero dynamics. Virtual constraints are relations on the state variables of a mechanical model that are imposed through a time-invariant feedback controller. One of their roles is to synchronize the robot's joints to an internal gait phasing variable. A second role is to induce a low dimensional system, the zero dynamics, that captures the underactuated aspects of a robot's model, without any approximations. To enhance intuition, the relation between physical constraints and virtual constraints is first established. From here, the hybrid zero dynamics of an underactuated bipedal model is developed, and its fundamental role in the design of asymptotically stable walking motions is established. The chapter includes numerous references to robots on which the highlighted techniques have been implemented.Comment: 17 pages, 4 figures, bookchapte

Review and Unification of Methods for Computing Derivatives of Multidisciplinary Systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97061/1/AIAA2012-1589.pd

ADOL-F Automatic Differentiation of Fortran Codes

The package ADOL--F described here is a Fortran 90 interface to the ADOL--C library and facilitates the evaluation of first and higher derivatives of vector functions that are defined by computer programs written in Fortran 90/77. The numerical values of derivative vectors are obtained free of truncation errors at a small multiple of the run time and randomly accessed memory of the given function evaluation program. Derivative matrices are obtained by columns or rows. For solution curves defined by ordinary differential equations, special routines are provided that evaluate the Taylor coefficient vectors and their Jacobians with respect to the current state vector. The derivative calculations involve a possibly substantial (but always predictable) amount of data that are accessed strictly sequentially and are therefore automatically paged out to external files. 1 Introduction Automatic differentiation [4, 9] is a non-approximative method just like symbolic differentiation and allows f..

Theoretical study of electromagnetic and optical properties of periodic conductive networks based on Voronoi diagrams

This paper is a preliminary report on a theoretical study of transparent shielding materials with potentially very high shielding efficiency based on quasi-periodic conductive networks. Optical transmittance as a function of beam incident angle and mesh geometry is modelled in the geometrical approximation by exact ray-tracing and compared to the analytical solution for ideal hexagonal meshes. An empirical model for rapid calculation of shielding efficiency vs frequency and mesh geometrical parameters is suggested based on numerical simulation results. (C) 2019 Elsevier Ltd. All rights reserved

Human Mitoribosome Biogenesis and Its Emerging Links to Disease

Mammalian mitochondrial ribosomes (mitoribosomes) synthesize a small subset of proteins, which are essential components of the oxidative phosphorylation machinery. Therefore, their function is of fundamental importance to cellular metabolism. The assembly of mitoribosomes is a complex process that progresses through numerous maturation and protein-binding events coordinated by the actions of several assembly factors. Dysregulation of mitoribosome production is increasingly recognized as a contributor to metabolic and neurodegenerative diseases. In recent years, mutations in multiple components of the mitoribosome assembly machinery have been associated with a range of human pathologies, highlighting their importance to cell function and health. Here, we provide a review of our current understanding of mitoribosome biogenesis, highlighting the key factors involved in this process and the growing number of mutations in genes encoding mitoribosomal RNAs, proteins, and assembly factors that lead to human disease