Active versus passive transformations in robotics

Most current texts on robotics use the passive approach, where the rigid body has a coordinate frame embedded in it, and then its position and orientation is given by the coordinate transformation from the world frame to a frame moving with the body. If there are several bodies carrying several different frames, it can be hard to account for all the different frames. On the other hand, active approach has only a single fixed coordinate frame. The position and orientation of a rigid body is specified by the transformation, which moves the body from its home position to its current position. It is therefore more convenient for students and teachers to use the active view which has only a single frame compared to passive which has multiple frames. ©2006 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

On the Manifold: Representing Geometry in C++ for State Estimation

Manipulating geometric objects is central to state estimation problems in robotics. Typical algorithms must optimize over non-Euclidean states, such as rigid transformations on the SE(3) manifold, and handle measurements expressed in multiple coordinate frames. Researchers typically rely on C++ libraries for geometric tasks. Commonly used libraries range from linear algebra software such as Eigen to robotics-targeted optimization frameworks such as GTSAM, which provides manifold operations and automatic differentiation of arbitrary expressions. This thesis examines how geometric operations in existing software can be improved, both in runtime performance and in the expression of geometric semantics, to support rapid and error-free development of robotics algorithms. This thesis presents wave_geometry, a C++ manifold geometry library providing representations of objects in affine, Euclidean, and projective spaces, and the Lie groups SO(3) and SE(3). It encompasses the main contributions of this work: an expression template-based automatic differentiation system and compile-time checking of coordinate frame semantics. The library can evaluate Jacobians of geometric expressions in forward and reverse mode with little runtime overhead compared to hand-coded derivatives, and exceeds the performance of existing libraries. While high performance is achieved by taking advantage of compile-time knowledge, the library also provides dynamic expressions which can be composed at runtime. Coordinate frame conversions are a common source of mistakes in calculations. However, the validity of operations can automatically be checked by tracking the coordinate frames associated with each object. A system of rules for propagating coordinate frame semantics though geometric operations, including manifold operations, is developed. A template-based method for checking coordinate frame semantics at compile time, with no runtime overhead, is presented. Finally, this thesis demonstrates an application to state estimation, presenting a framework for formulating nonlinear least squares optimization problems as factor graphs. The framework combines wave_geometry expressions with the widely used Ceres Solver software, and shows the utility of automatically differentiated geometric expressions

Reliable and safe autonomy for ground vehicles in unstructured environments

This thesis is concerned with the algorithms and systems that are required to enable safe autonomous operation of an unmanned ground vehicle (UGV) in an unstructured and unknown environment; one in which there is no speci c infrastructure to assist the vehicle autonomy and complete a priori information is not available. Under these conditions it is necessary for an autonomous system to perceive the surrounding environment, in order to perform safe and reliable control actions with respect to the context of the vehicle, its task and the world. Speci cally, exteroceptive sensors measure physical properties of the world. This information is interpreted to extract a higher level perception, then mapped to provide a consistent spatial context. This map of perceived information forms an integral part of the autonomous UGV (AUGV) control system architecture, therefore any perception or mapping errors reduce the reliability and safety of the system. Currently, commercially viable autonomous systems achieve the requisite level of reliability and safety by using strong structure within their operational environment. This permits the use of powerful assumptions about the world, which greatly simplify the perception requirements. For example, in an urban context, things that look approximately like roads are roads. In an indoor environment, vertical structure must be avoided and everything else is traversable. By contrast, when this structure is not available, little can be assumed and the burden on perception is very large. In these cases, reliability and safety must currently be provided by a tightly integrated human supervisor. The major contribution of this thesis is to provide a holistic approach to identify and mitigate the primary sources of error in typical AUGV sensor feedback systems (comprising perception and mapping), to promote reliability and safety. This includes an analysis of the geometric and temporal errors that occur in the coordinate transformations that are required for mapping and methods to minimise these errors in real systems. Interpretive errors are also studied and methods to mitigate them are presented. These methods combine information theoretic measures with multiple sensor modalities, to improve perceptive classi cation and provide sensor redundancy. The work in this thesis is implemented and tested on a real AUGV system, but the methods do not rely on any particular aspects of this vehicle. They are all generally and widely applicable. This thesis provides a rm base at a low level, from which continued research in autonomous reliability and safety at ever higher levels can be performed

Development of a Chain Climbing Robot and an Automated Ultrasound Inspection System for Mooring Chain Integrity Assessment

Mooring chains used to stabilise offshore floating platforms are often subjected to harsh environmental conditions on a daily basis, i.e. high tidal waves, storms etc. Chain breakage can lead to vessel drift and serious damage such as riser rupture, production shutdown and hydrocarbon release. Therefore, integrity assessment of chain links is vital, and regular inspection is mandatory for offshore structures. Currently, structural health monitoring of chain links is conducted using either remotely operated vehicles (ROVs), which are associated with high costs, or by manual means, which increases the risk to human operators. The development of climbing robots for mooring chain applications is still in its infancy due to the operational complexity and geometrical features of the chain. This thesis presents a Cartesian legged magnetic adhesion tracked-wheel crawler robot developed for mooring chain inspection. The crawler robot presented in this study is suitable for mooring chain climbing in air and the technique can be adapted for underwater use. The proposed robot addresses straight mooring chain climbing and a misaligned scenario that is commonly evident in in-situ conditions. The robot can be used as a platform to convey equipment, i.e. tools for non-destructive testing/evaluation applications. The application of ultrasound for in-service mooring chain inspection is still in the early stages due to lack of accessibility, in-field operational complexity and the geometrical features of mooring systems. With the advancement of robotic/automated systems (i.e. chain-climbing robotic mechanisms), interest in in-situ ultrasound inspection has increased. Currently, ultrasound inspection is confined to the weld area of the chain links. However, according to recent studies on fatigue and residual stresses, ultrasound inspection of the chain crown should be further investigated. A new automated application for ultrasonic phased-array full-matrix capture is discussed in this thesis for investigation of the chain crown. The concept of the chain-climbing robot and the inspection technique are validated with laboratory-based climbing experiments and presented in this thesis

Automatische Konfiguration der Bewegungssteuerung von Industrierobotern

Robotersteuerungen erfordern sehr lange Entwicklungszeiten und hohe Entwicklungskosten. Die Software wird sehr aufwändig von Hand entwickelt und implementiert. Die automatische, schnelle und zuverlässige Konfiguration der Bewegungssteuerung von beliebigen Robotertypen ist neuartig. Hierfür wurde in dieser Arbeit ein System zur automatisierten Konfiguration komponentenbasierter Software auf Basis einer Beschreibung der mechanischen Struktur und Eigenschaften von Industrierobotern entwickelt