Articulated wooden blades for a horizontal-axis wind turbine. Design, construction and testing.

A pair of blades were constructed following a Tapered Chord, Zero Twist pattern after Anderson. The construction uses the Wood Epoxy Saturation Technique, with a solid Beech main spar and leading edge joined together with laminated veneers of beech forming a D-section; the trailing edge is formed from millimetre ply skins, foam filled to resist compressive loads. This construction leads to an extremely light, flexible blade, with the centres of gravity and torsion well forward, giving good stability. Each blade has three built-in strain gauges, alowing flapwise bending to be measured. Stiffness, and natural frequencies, were measured, to input to a numerical computer model to calculate blade deformation during operation, and to determine stability boundaries of the blade. Preliminary aerodynamic performance measurements are presented and close agreement is found with theory.

Active roll control of an experimental articulated vehicle

A new experimental articulated vehicle with computer-controlled suspensions is used to investigate the benefits of active roll control for heavy vehicles. The mechanical hardware, the instrumentation, and the distributed control architecture are detailed. A simple roll-plane model is developed and validated against experimental data, and used to design a controller based on lateral acceleration feedback. The controller is implemented and tested on the experimental vehicle. By tilting both the tractor drive axle and the trailer inwards, substantial reductions in normalized lateral load transfer are obtained, both in steady state and transient conditions. Power requirements are also considered. © IMechE 2005.

Specifying a hydraulic regenerative braking system for an articulated urban delivery vehicle

Previous research has shown that hydraulic systems offer potentially the lightest and smallest regenerative braking technology for heavy goods vehicles. This paper takes the most practical embodiment of a hydraulic system for an articulated urban delivery vehicle and investigates the best specification for the various components, based on a simulated stop-start cycle. The potential energy saving is quantified. © 2011 IEEE.

Path-following steering control for articulated vehicles

Passive steering systems have been used for some years to control the steering of trailer axles on articulated vehicles. These normally use a 'command steer' control strategy, which is designed to work well in steady-state circles at low speeds, but which generates inappropriate steer angles during transient low-speed maneuvers and at high speeds. In this paper, 'active' steering control strategies are developed for articulated heavy goods vehicles. These aim to achieve accurate path following for tractor and trailer, for all paths and all normal vehicle speeds, in the presence of external disturbances. Controllers are designed to implement the path-following strategies at low and high speeds, whilst taking into account the complexities and practicalities of articulated vehicles. At low speeds, the articulation and steer angles on articulated heavy goods vehicles are large and small-angle approximations are not appropriate. Hence, nonlinear controllers based on kinematics are required. But at high-speeds, the dynamic stability of control system is compromised if the kinematics-based controllers remain active. This is because a key state of the system, the side-slip characteristics of the trailer, exhibits a sign-change with increasing speeds. The low and high speed controllers are blended together using a speed-dependent gain, in the intermediate speed range. Simulations are conducted to compare the performance of the new steering controllers with conventional vehicles (with unsteered drive and trailer axles) and with vehicles with command steer controllers on their trailer axles. The simulations show that active steering has the potential to improve significantly the directional performance of articulated vehicles for a wide range of conditions, throughout the speed range. © VC 2013 by ASME.

The Grasping Problem: Toward Task-Level Programming for an Articulated Hand

This report presents a system for generating a stable, feasible, and reachable grasp of a polyhedral object. A set of contact points on the object is found that can result in a stable grasp; a feasible grasp is found in which the robot contacts the object at those contact points; and a path is constructed from the initial configuration of the robot to the stable, feasible final grasp configuration. The algorithm described in the report is designed for the Salisbury hand mounted on a Puma 560 arm, but a similar approach could be used to develop grasping systems for other robots.

Specialized Mappings Architecture with Applications to Vision-based Estimation of Articulated Body Pose

A fundamental task of vision systems is to infer the state of the world given some form of visual observations. From a computational perspective, this often involves facing an ill-posed problem; e.g., information is lost via projection of the 3D world into a 2D image. Solution of an ill-posed problem requires additional information, usually provided as a model of the underlying process. It is important that the model be both computationally feasible as well as theoretically well-founded. In this thesis, a probabilistic, nonlinear supervised computational learning model is proposed: the Specialized Mappings Architecture (SMA). The SMA framework is demonstrated in a computer vision system that can estimate the articulated pose parameters of a human body or human hands, given images obtained via one or more uncalibrated cameras. The SMA consists of several specialized forward mapping functions that are estimated automatically from training data, and a possibly known feedback function. Each specialized function maps certain domains of the input space (e.g., image features) onto the output space (e.g., articulated body parameters). A probabilistic model for the architecture is first formalized. Solutions to key algorithmic problems are then derived: simultaneous learning of the specialized domains along with the mapping functions, as well as performing inference given inputs and a feedback function. The SMA employs a variant of the Expectation-Maximization algorithm and approximate inference. The approach allows the use of alternative conditional independence assumptions for learning and inference, which are derived from a forward model and a feedback model. Experimental validation of the proposed approach is conducted in the task of estimating articulated body pose from image silhouettes. Accuracy and stability of the SMA framework is tested using artificial data sets, as well as synthetic and real video sequences of human bodies and hands.

Articulated Pose Estimation in a Learned Smooth Space of Feasible Solutions

A learning based framework is proposed for estimating human body pose from a single image. Given a differentiable function that maps from pose space to image feature space, the goal is to invert the process: estimate the pose given only image features. The inversion is an ill-posed problem as the inverse mapping is a one to many process. Hence multiple solutions exist, and it is desirable to restrict the solution space to a smaller subset of feasible solutions. For example, not all human body poses are feasible due to anthropometric constraints. Since the space of feasible solutions may not admit a closed form description, the proposed framework seeks to exploit machine learning techniques to learn an approximation that is smoothly parameterized over such a space. One such technique is Gaussian Process Latent Variable Modelling. Scaled conjugate gradient is then used find the best matching pose in the space of feasible solutions when given an input image. The formulation allows easy incorporation of various constraints, e.g. temporal consistency and anthropometric constraints. The performance of the proposed approach is evaluated in the task of upper-body pose estimation from silhouettes and compared with the Specialized Mapping Architecture. The estimation accuracy of the Specialized Mapping Architecture is at least one standard deviation worse than the proposed approach in the experiments with synthetic data. In experiments with real video of humans performing gestures, the proposed approach produces qualitatively better estimation results.

Comparison of crash dynamics of articulated and non-articulated trains

This paper presents a comparison of impact dynamic performance between articulated trains and non-articulated trains. This is carried out by investigation of the characteristics of the two trains types and analysis of their effects on impact dynamics. The analysis shows that the differences in bogie support positions on the carbody and coupling devices lead to differences in several structural and compositional characteristics. These characteristics result in different impact responses for the two types of train and are directly related to their impact stablity. Articulated trains have stiff connection and integral performance in collisions but with less capability for absorbing impact energy between carriages, whereas non-articulated trains show loose connection and scattered performance in collisions but with more options for energy absorber installation between carriages.

The Irish fossil Polyplacophora

Three species of fossil polyplacophoran molluscs are known from Ireland. Two species were originally described in the nineteenth century: Helminthochiton griffithi Salter in M‘Coy, 1846 and Pterochiton thomondiensis (Baily, 1859), and an articulated specimen representing a third indeterminate species, described here for the first time. Previous work on the evolutionary context of these species has relied on published illustrations and descriptions without examination of the type material. as chitons are considered rare in the fossil record, these specimens represent an interesting and important aspect of Irish palaeobiology.

A chiton without a foot

The palaeoloricate ‘polyplacophorans’ are an extinct paraphyletic group of basal chiton-like organisms known primarily from their fossilized valves. Their phylo- genetic placement remains contentious, but they are likely to include both stem-group Polyplacophora and stem- group Aplacophora. Candidates for the latter position include ‘Helminthochiton’ thraivensis from the Ordovician of Scotland, which we redescribe here through a combined optical and micro-CT (XMT) restudy of the type material. The 11 specimens in the type series are all articulated, presenting partial or complete valve series as well as moul- dic preservation of the girdle armature; they demonstrate a vermiform body plan. The valves are typically palaeolori- cate in aspect, but differ in detail from all existing palaeol- oricate genera; we hence erect Phthipodochiton gen. nov. to contain the species. The most notable feature of the fossils is the spicular girdle; this is impersistently preserved, but demonstrably wraps entirely around the ventral surface of the animal, implying that a ‘true’ (i.e. polyplacophoran like) foot was absent, although we do not exclude the pos- sibility of a narrow solenogastre-like median pedal groove having been present. Phthipodochiton thraivensis presents an apparent mosaic of aplacophoran and polyplacophoran features and as such will inform our understanding of the relationship between these groups of extant molluscs. An inference may also be drawn that at least some other pal- aeoloricates possessed an ‘armoured aplacophoran’ body plan, in contrast to the ‘limpet-like’ body plan of extant Polyplacophora.

Dealing with non-linearity in shape modelling of articulated objects

We address the problem of non-linearity in 2D Shape modelling of a particular articulated object: the human body. This issue is partially resolved by applying a different Point Distribution Model (PDM) depending on the viewpoint. The remaining non-linearity is solved by using Gaussian Mixture Models (GMM). A dynamic-based clustering is proposed and carried out in the Pose Eigenspace. A fundamental question when clustering is to determine the optimal number of clusters. From our point of view, the main aspect to be evaluated is the mean gaussianity. This partitioning is then used to fit a GMM to each one of the view-based PDM, derived from a database of Silhouettes and Skeletons. Dynamic correspondences are then obtained between gaussian models of the 4 mixtures. Finally, we compare this approach with other two methods we previously developed to cope with non-linearity: Nearest Neighbor (NN) Classifier and Independent Component Analysis (ICA).