bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics Simulation and Controller Interfacing for Legged Robots
Authors: Reichler Jesse A. , Delcomyn Fred 
Published: July 2003

Dynamics simulation can play a critical role in the engineering of robotic control code, and there exist a variety of strategies both for building physical models and for interacting with these models. This paper presents an approach to dynamics simulation and controller interfacing for legged robots, and contrasts it to existing approaches. We describe dynamics algorithms and contact-resolution strategies for multibody articulated mobile robots based on the decoupled tree-structure approach, and present a novel scripting language that provides a unified framework for control-code interfacing, userinterface design, and data analysis. Special emphasis is placed on facilitating the rapid integration of control algorithms written in a standard object-oriented language (C++), the production of modular, distributed, reusable controllers, and the use of parameterized signal-transmission properties such as delay, sampling rate, and noise.
Robust Geometric Computing in Motion
Authors: Halperin Dan 
Published: July 2003

Transforming a geometric algorithm into an effective computer program is a difficult task. This transformation is particularly made hard by the basic assumptions of most theoretical geometric algorithms concerning complexity measures and (more crucially) the handling of robustness issues, namely issues related to arithmetic precision and degenerate input. The paper starts with a discussion of the gap between the theory and practice of geometric algorithms, together with a brief review of existing solutions to some of the problems that this dichotomy brings about. We then turn to an overview of the CGAL project and library. The CGAL project is a joint effort by a number of research groups in Europe and Israel to produce a robust software library of geometric algorithms and data structures. The library is now available for use with significant functionality. We describe the main goals and results of the project. The central part of the paper is devoted to arrangements (i.e., space subdivisions induced by geometric objects) and motion planning. We concentrate on the maps and arrangements part of the CGAL library. Then we describe two packages developed on top of CGAL for constructing robust geometric primitives for motion algorithms.
An Autonomous Crop Treatment Robot: Part I. A Kalman Filter Model for Localization and Crop/Weed Classification
Authors: Southall B. , Hague T. , Marchant J.A. , Buxton B.F. 
Published: July 2003

This work is concerned with a machine vision system for an autonomous vehicle designed to treat horticultural crops. The vehicle navigates by following rows of crop (individual cauliflower plants) that are planted in a reasonably regular array typical of commercial practice. We adopt an extended Kalman filter approach where the observation model consists of a grid which is matched to the crop planting pattern in the perspective view through the vehicle camera. Plant features are extracted by thresholding near infrared images of the scene evolving before the camera. A clustering method collects the features into groups representing single plants. An important aspect of the approach is that it provides both localization information and crop/weed discrimination within a single framework, since we can assume that features not matching the planting pattern are weeds. Off-line tests with two image sequences are carried out to compare the tracking with assessment by three different humans. These show that the extended Kalman filter is a viable method for tracking and that the model parameters derived from the filter are consistent with human assessment. We conclude that the performance will be good enough for accurate in-field navigation.
An Autonomous Crop Treatment Robot: Part II. Real Time Implementation
Authors: Hague T. , Southall B. , Tillett N.D. 
Published: July 2003

Implementation of an autonomous vehicle for precision treatment of crop plants is described. The navigation system integrates the vision system described in Part I with inertial and odometric sensing. A modular approach is adopted, where the crop grid observation model is re-formulated as a non-linear compression filter, which combines a set of observations of crop plants into a single pseudo-observation of the position of the crop planting grid relative to the vehicle position. The compression filter encapsulates all internal detail of the vision system (camera calibration, crop layout, etc.). The output from this vision module can be used as an observation in the conventional way by the vehicle's navigation Kalman filter. Plant features classified into crop and weed by the vision module are registered into a treatment map. The need to treat targets from a moving platform requires time delays in the processing of observations to be considered. A method of compensation is introduced which allows time delayed vision observations to be used; the effectiveness of the technique is illustrated by an example with an artificially extended time delay. In field trials of the vehicle have been performed, and the accuracy of both vehicle navigation and crop treatment are reported. We conclude that the navigation accuracy falls within the 20 mm root mean square error region thought appropriate for precise horticultural operations, and that spray application is sufficiently accurate for the treatment of individual crop plants.
Postural Stability of Biped Robots and the Foot-Rotation Indicator (FRI) Point
Authors: Goswami Ambarish 
Published: July 2003

The focus of this paper is the problem of foot rotation in biped robots during the single-support phase. Foot rotation is an indication of postural instability, which should be carefully treated in a dynamically stable walk and avoided altogether in a statically stable walk. We introduce the foot-rotation indicator (FRI) point, which is a point on the foot/ground-contact surface where the net ground-reaction force would have to act to keep the foot stationary. To ensure no foot rotation, the FRI point must remain within the convex hull of the foot-support area. In contrast with the ground projection of the center of mass (GCoM), which is a static criterion, the FRI point incorporates robot dynamics. As opposed to the center of pressure (CoP)—better known as the zero-moment point (ZMP) in the robotics literature—which may not leave the support area, the FRI point may leave the area. In fact, the position of the FRI point outside the footprint indicates the direction of the impending rotation and the magnitude of rotational moment acting on the foot. Owing to these important properties, the FRI point helps not only to monitor the state of postural stability of a biped robot during the entire gait cycle, but indicates the severity of instability of the gait as well. In response to a recent need, the paper also resolves the misconceptions surrounding the CoP/ZMP equivalence.
Using Partial Sensor Information to Orient Parts
Authors: Akella Srinivas , Mason Matthew T. 
Published: July 2003

Parts orienting, the process of bringing parts in initially unknown orientations to a goal orientation, is an important aspect of automated assembly. The most common industrial orienting systems are vibratory bowl feeders, which use the shape and mass properties of parts to orient them. Bowl feeders rely on a sequence of mechanical operations and typically do not use sensors. In this paper, we describe the use of partial information sensors along with a sequence of pushing operations to eliminate uncertainty in the orientations of parts. We characterize the shorter execution lengths of sensor-based plans and show that sensor-based plans are more powerful than sensorless plans in that they can bring a larger class of parts to distinct orientations. We characterize the relation among part shape, orientability, and recognizability to identify conditions under which a single plan can orient and recognize multiple part shapes. Although part shape determines the results of the actions and the sensed information, we establish that differences in part shape do not always lead to differences in part behavior. We show that for any convex polygon, there exists an infinite set of nonsimilar convex polygons that behave identically under linear normal pushes. Furthermore, there exists an infinite set of nonsimilar convex polygons whose behavior cannot be distinguished even with diameter sensing after each push. We have implemented several planners and demonstrated generated plans in experiments.
Visual Servoing of Robot Manipulators Part I: Projective Kinematics
Authors: Ruf Andreas , Horaud Radu 
Published: July 2003

Visual servoing of robot manipulators is a key technique where the appearance of an object in the image plane is used to control the velocity of the end-effector such that the desired position is reached in the scene. The vast majority of visual servoing methods proposed so far uses calibrated robots in conjunction with calibrated cameras. It has been shown that the behavior of visual control loops does not degrade too much in the presence of calibration errors. Nevertheless, camera and robot calibration are complex and time-consuming processes requiring special-purpose mechanical devices, such as theodolites and calibration jigs. In this paper, we suggest formulating a visual servoing control loop in a nonmetric space, which in our case amounts to the projective space in which a triangulation of the scene using an uncalibrated stereo rig is expressed. The major consequence of controlling the robot in nonmetric space rather than in Euclidean space is that both the robot’s direct kinematic map and the robot’s Jacobian matrix must be defined in this space as well. The elementary joint-space motions that can be performed by a robot manipulator are pure rotations and pure translations. Traditionally, these motions are represented as Euclidean transformations. Since these motions are observed with an uncalibrated stereo rig, it will be convenient to represent them as projective transformations (homographies) rather than Euclidean transformations. Indeed, it will be shown that rotations and translations can be parameterized as special cases of homographies, which will be called projective rotations and projective translations. The algebraic properties of this nonmetric representation of elementary motions will be thoroughly investigated allowing us to characterize the direct kinematic map and the Jacobian matrix of a manipulator. Therefore, we introduce the concepts of projective kinematics and a projective Jacobian matrix. Unlike the classical robot Jacobian matrix of a manipulator that relates the robot joint-velocities to the kinematic screw associated with the end-effector, we establish a direct relationship between joint-velocities and image-plane velocities. The latter are velocities associated with image points arising from the 3-D to 2-D projection of end-effector points. Finally, we provide a practical method to estimate the projec tive kinematic model and we describe some preliminary simulated experiments that use this nonmetric model to perform stereo-based servoing. Nevertheless, in-depth analysis of projective control will be the topic of a forthcoming paper.
Analytical Study of Clamped Steel Fiber Reinforced Aluminum Metal Matrix Composite Including Elasto-Plastic Behavior
Authors: Aslan Züleyha , Okutan Buket , Karakuzu Ramazan 
Published: July 2003

The elasto-plastic behaviour of steel fiber reinforced aluminum metal matrix composite with five different orientations has been investigated, including the effect of single force. A composite beam with a rectangular cross section is fixed at one end and is bent by a transverse force P applied to the free end. To determine analytically, residual stresses and the expansion of plastic zone for different orientation angles a software program is developed and this program makes it possible to establish elastic region, plastic region, the distributions of the residual stress component, the distance between the free end and yield points for 0°, 30°, 45°, 60° and 90° orientation angles. To verify the analytical solutions, the sophisticated finite element code such as ANSYS 5.6 was used to perform numerical analyses. The results from this analytical approach show that the composites with different orientation angles start yielding at the same distances from the free end at the upper and lower surfaces of the beam. In other words, the plastic region spread at the upper and lower surfaces together. It is also shown that the distance between plastic region and free end of the beam decreases due to increasing orientation angle.
The Modified Quadric Surfaces Criterion for Composite Materials
Authors: Yeh Hsien-Liang , Yeh Hsien-Yang 
Published: July 2003

A modification of the generalized quadric surfaces criterion for composite materials is presented in this paper. The unique features of the generalized quadric surfaces criterion are maintained. Thus, it is shown that the entire closed failure envelope of the modified quadric surfaces criterion is composed of piecewise quadric surfaces. And no biaxial tests are required for the determination of the coefficients about the stress interaction terms (i.e., σ iσ j). Consider the fact that for isotropic and orthotropic materials loaded in principal material directions, there is no coupling between the in-plane and shear responses. To further simplify the use of failure criterion in engineering design, it is reasonable to assume the coefficients of in-plane and shear coupling terms to be zero in the modified quadric surfaces failure criterion. The validity of the modified quadric surfaces criterion is examined with experimental results from off-axis uniaxial strength tests of unidirectional fiber composites, and angle-ply composite laminates. Comparisons were made with other well-known anisotropic failure theories and the generalized quadric surfaces criterion as well.
A Comparative Study of Finite Element Models for the Bonded Repair of Composite Structures
Authors: Odi Randolph A. , Friend Clifford M. 
Published: July 2003

In this paper, the issues surrounding the repair of composite structures have been reviewed. This review has highlighted the need for the development of analytical techniques for the design of repair schemes. The finite element method is shown to be an appropriate candidate for such a task. Modelling approaches for adhesively bonded joints are well documented in the literature. Although bonded joints and repair joints share similar features, designing repairs and bonded joints are two different tasks. The open literature on modelling approaches specifically for repair joints is not abundant. Furthermore, there is no evidence of any studies undertaken with the specific aim of looking at the fundamental aspects of applying the finite element method to the analysis of bonded repairs to composite structures. This paper highlights the philosophy behind these modelling approaches that have been used or suggested in the past. These approaches have been compared in order to gain a better understanding of the current state of affairs and how they relate to each other.
Devolatilization of Polymers by Diffusion and Foaming
Authors: Gestring Ingo , Mewes Dieter 
Published: July 2003

Devolatilization is a key step in polymer processing. Low-molecular-weight components are removed from a polymeric system. The transport of these components takes place by diffusion to the polymer-vapor interface. This interface can be formed by free surfaces of single-phase polymer melts or by bubbles. In this study the transport with and without bubble nucleation is investigated independently from each other in a specially designed apparatus. The mass transport in thin films and in rotating pools with surface renewal is measured. High surface renewal rates and thick films enhance the mass transfer for single phase flow. For two phase flow and devolatilization the conditions for bubble nucleation and foam formation are investigated. The bubble nucleation is observed in the rotating pool in the area of high shear velocity.
Elongational Effects of Die Flows: Pressure Distribution and Shape Prediction
Authors: Sun J. , Waucquez C. , Rubin Y. 
Published: July 2003

There are many industrial applications in which shear and extensional behaviors of the material both play a role. This is true, for example, for flows in converging channels or flows in abrupt contractions typical of cable coating, fiber spinning or indeed flows in many plastics and rubber extrusion dies. Viscoelastic flow simulation has made it possible to predict these effects, at least qualitatively. Numerical simulations using a 3-mode PTT model reported here show a good quantitative agreement with experimentally measured pressure drops over a range of flow rates for both a short and a long conical capillary die. While this approach is physically meaningful, convergence at high Weissenberg number remains a challenge for the scientific community. This fact can sometimes justify the call for simpler, qualitative engineering approximations. By adding in the flow equations the dependence of the viscosity function on the third invariant of the rate of deformation tensor, it becomes possible to consider some effects of extensional viscosity in axisymmetric and 3D flows. We observe an increase in the pressure drop and the onset of recirculation patterns. We present numerical simulations of flow in a converging cone capillary and compare the results with available experimental data. We include simulation results for 3D die swell which show the influence of this extensional effect.
Ultrasonic Monitoring of Nozzle and Cavity during Injection Moulding
Authors: Brown E. C. , Dawson A. J. , Coates P. D. 
Published: July 2003

Ultrasonic techniques are recognised as powerful sources of process information. Transducers are applied directly, are non-invasive, yet interrogate the entire melt cross-section, while data are available real-time. During injection moulding, two zones are considered: nozzle and cavity. In the nozzle, ultrasonic velocity measurement provides temperature and pressure information. Mean temperatures not observed by other techniques are detected. Previous extrusion based experience is used to address issues of high temperature transducer operation. In the cavity, changes in reflection coefficient and ultrasonic velocity provide information on mould filling and part cooling. Various mould geometries are monitored using a number of ultrasonic transducers.
The Kinetics of Shear-Induced Crystallization in Poly(Ethylene Terephthalate)
Authors: Ahn Seung Hyoun , Cho Chin Bong , Lee Kee Yoon 
Published: July 2003

The kinetics of shear-induced crystallization in PET was studied. The shear-treated samples were obtained from Controlled Shear Rate apparatus (CSR, Figure 1) and the capillary viscometer. In the samples were observed the differences of crystallization behavior by DSC. The kinetic model suggested by Hoffman-Lauritzen, Nakamura was used to analyze experimental results. The crystallization behavior of shear-treated samples depended on temperature and shear stress. On the lower shear rate region, the rate of crystallization depended on shear stress and the growth rate induced by fluid flow reached the critical point in the region of a certain high shear rate. The empirical data were simulated by the suggested model.
Incompressible Model of Solids Conveying in a Single-Screw Extruder
Authors: Zhang Shibo , Sernas Valentinas 
Published: July 2003

Experiments in corn meal extrusion [Zhang, S. and Sernas, V. (1998). Proc. 1998 ASME Int ME. Congress and Exposition, Anaheim, CA, HTD-Vol. 361-1. pp. 309-315] have shown that the flow of solids in the screw channel of a single-screw extruder has a helical pattern. This observation implies that there is a cross-channel velocity component in the solids conveying zone of the extruder. Existing solids conveying models [Broyer, E. and Tadmor, Z. (1972). Polym. Eng. Sci., 12(1): 12-24; Campbell, G.A. and Dontula, N. (1995). International Polymer Process X. Hanser Publishing. pp. 30-35; Darnell, W.H. and Mol, E.A. (1956). Soc. Plast. Eng. J., 12(4), 20-29; Hyun, K.S. and Spalding, M.A. (1997). ANTEC ’97 Proc. 163: 211-218] treat the solids moving in the channel as a plug flow without a cross-channel velocity component. The two-dimensional powder conveying model proposed in this paper contains both a down-channel component and a cross-channel component. The stress generating mechanism is much more complicated in a powder flow than in a fluid flow. The incompressible model incorporates a constitutive equation for the powder flow with slip boundary conditions. The energy equation with appropriate boundary conditions is also included in the model. The numerically solved model shows that the predicted down-channel pressure development, velocity and temperature distributions are all reasonable.
In Vitro Interactions of Biomedical Polyurethanes with Macrophages and Bacterial Cells
Authors: Visai Livia , Rindi Simonetta , Speziale Pietro , Petrini Paola , Farè Silvia , Tanzi M. Cristina 
Published: July 2003

Three commercial medical-grade polyurethanes (PUs), a poly-ether-urethane (Pellethane), and two poly-carbonate-urethanes, the one aromatic (Bionate) and the other aliphatic (Chronoflex), were tested for macrophages and bacterial cells adhesion, in the presence or absence of adhesive plasma proteins. All the experiments were carried out on PUs films obtained by solvent casting. The wettability of these films was analysed by measuring static contact angles against water. The ability of the selected PUs to adsorb human fibronectin (Fn) and fibrinogen (Fbg) was checked by ELISA with biotin-labelled proteins. All PUs were able to adsorb Fn and Fbg(Fn > Fbg). Fn adsorption was in the order: Pellethane > Chronoflex > Bionate, the highest Fbg adsorption being detected onto Bionate (Bionate > Chronoflex > Pellethane). The human macrophagic line J111, and the two main bacterial strains responsible for infection in humans (Staphylococcus aureus Newman and Staphylococcus epidermidis 14852) were incubated in turn with the three PUs, uncoated or coated with plasma proteins. No macrophage or bacterial adhesion was observed onto uncoated PUs. PUs coated with plasma, Fn or Fbgpromoted bacterial adhesion (S. aureus > S. epidermidis), whereas macrophage adhered more onto PUs coated with Fn or plasma. The coating with Fbg did not promote cell adhesion. Pellethane showed the highest macrophage activation (i.e. spreading), followed, in the order, by Bionate and Chronoflex.