bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimizing Sampling Strategies for Estimating Quality-adjusted Life Years
Authors: Ramsey Scott D. , Etzioni Ruth , Troxel Andrea , Urban Nicole
Published: March 2007

Accurate estimation of quality of life is critical to cost-effectiveness analysis. Never theless, development of sampling algorithms to maximize the accuracy and efficiency of estimated quality of life has received little consideration to date. This paper presents a method to optimize sampling strategies for estimating quality-adjusted life years. In particular, the authors address the questions of when to sample and how many ob servations to sample at each sampling time, assuming realistically that the sample variance of quality of life is not constant over time. The method is particularly useful for the design problems researchers face when time or research budget constraints limit the number of individuals that can be surveyed to estimate quality of life. The article focuses on cross-sectional sampling. The method proposed requires some knowledge of survival in the population of interest, the approximate variances in utilities at various points along the curve, and the general shape of the quality-adjusted survival curve. Such data are frequently available from disease registries, the literature, or previous studies. Key words: health-related quality of life; utility; quality-adjusted life years; variance; survival; cost-effectiveness; sampling; cross-sectional sampling. (Med Decis Making 1997;17:431-438)
The Cochrane Collaboration-Advances and Challenges in Improving Evidence-based Decision Making
Authors: Jadad Alejandro R. , Haynes R. Brian
Published: March 2007

The Cochrane Collaboration is an international organization that aims to help people make well-informed decisions about health care by preparing, maintaining, and ensur ing the accessibility of rigorous, systematic, and up-to-date reviews (and, where pos sible, meta-analyses) of the benefits and risks of health care interventions. This article describes the structure of the Cochrane Collaboration and the processes used to carry out the task of research transfer. The authors focus on recent achievements of the Collaboration, emphasize the current challenges and barriers the Collaboration is fac ing to live up to the expectations it has generated, and highlight the strategies that the organization is using to meet those challenges. Key words: research transfer; decision making; evidence-based medicine; systematic reviews; meta-analysis; education; in formatics ; Internet; communications. (Med Decis Making 1998;18:2-9)
An Analysis of Optimal Resource Allocation for Prevention of Infection with Human Immunodeficiency Virus (HIV) in Injection Drug Users and Non-Users
Authors: Richter Anke , Brandeau Margaret L. , Owens Douglas K.
Published: March 2007

Millions of dollars are spent annually to prevent infection with human immunodeficiency virus (HIV) without a thorough understanding of the most effective way to allocate these resources. The authors' objective was to determme the allocation of new resources among prevention programs targeted to a population of injection drug users (IDUs) and a population of non-injection drug users (non-IDUs) that would minimize the total number of incident cases of HIV infection over a given time horizon. They developed a dynamic model of HIV transmission in IDUs and non-IDUs and estimated the rela tionship between prevention program expenditures and reductions in HIV transmission. They evaluated three prevention programs: HIV testing with routine counseling, HIV testing with intensive counseling, and HIV testing and counseling linked to methadone maintenance programs. They modeled a low-risk IDU population (5% HIV prevalence) and a moderate-risk IDU population (10% HIV prevalence). For different available budgets, they determined the allocation of resources among the prevention programs and populations that would minimize the number of new cases of HIV infection over a five-year period, as well as the incremental value of additional prevention funds. The study framework provides a quantitative, systematic approach to funding programs to prevent HIV infection that accounts for HIV transmission dynamics, population size, and the costs and effectiveness of the interventions in reducing HIV transmission. The approach is general and can be used to evaluate a broader group of prevention pro grams and risk populations. This framework thus could enable policy makers and cli nicians to identify a portfolio of programs that provide, collectively, the most benefit for a given budget. Key words: HIV; AIDS; HIV-1; resource allocation; prevention; cost- benefit analysis. (Med Decis Making 1999;19:167-179)
Goodness-of-fit Issues in ROC Curve Estimation
Authors: Walsh Stephen J.
Published: March 2007

Zhou recently considered goodness-of-fit (GOF) testing for receiver operating char acteristic (ROC) curves estimated by applying the binormal and other bidistributional models to rating method data. He interpreted significant GOF tests as evidence that different decision thresholds were applied to diseased and nondiseased subjects and concluded that, in such circumstances, an ROC curve does not exist. In this article the author demonstrates that the GOF test accommodates many alternative hypoth eses and that a significant test result need not be equated with an interaction between disease status and decision criteria or with non-existence of an ROC curve. He de velops a new family of ROC curves based on a fully parameterized bidistributional model. The family includes the binormal ROC curve, but generalizes its structure by signifying all identifiable deviations in parameters of the latent distributions that define the model. The family provides a unified framework of alternative models to the binor mal assumption and of alternative hypotheses to the GOF test for that assumption. Key words: goodness-of-fit testing; ROC curves; rating method. (Med Decis Making 1999;19:193-201)
Incorporating the Time Dimension in Receiver Operating Characteristic Curves: A Case Study of Prostate Cancer
Authors: Etzioni Ruth , Pepe Margaret , Longton Gary , Chengcheng Hu  , Goodman Gary
Published: March 2007

Early diagnosis of disease has potential to reduce morbidity and mortality. Biomarkers may be useful for detecting disease at early stages before it becomes clinically ap parent. Prostate-specific antigen (PSA) is one such marker for prostate cancer. This article is concerned with modeling receiver operating characteristic (ROC) curves as sociated with biomarkers at various times prior to the time at which the disease is detected clinically, by two methods. The first models the biomarkers statistically using mixed-effects regression models, and uses parameter estimates from these models to estimate the time-specific ROC curves. The second directly models the ROC curves as a function of time prior to diagnosis and may be implemented using software pack ages with binary regression or generalized linear model routines. The approaches are applied to data from 71 prostate cancer cases and 71 controls who participated in a lung cancer prevention trial. Two biomarkers for prostate cancer were considered: total serum PSA and the ratio of free to total PSA. Not surprisingly, both markers performed better as the interval between PSA measurement and clinical diagnosis decreased. Although the two markers performed similarly eight years prior to diagnosis, it appears that total PSA performed better than the ratio measure at times closer to diagnosis. The area under the ROC curve was consistently greater for total PSA than for the ratio four and two years prior to diagnosis and at the time of diagnosis. Key words: time- dependent ROC curves; biomarkers; diagnosis; prostate-specific antigen. (Med Decis Making 1999; 19:242-251)
Life Expectancy Estimation with Breast Cancer: Bias of the Declining Exponential Function and an Alternative to Its Use
Authors: Holland Robert R. , Ellis Charles A. , Geller Berta M. , Plante Dennis A. , Secker-Walker Roger H.
Published: March 2007

Background. Life expectancy gain (LEG) is an outcome measure commonly estimated with a declining exponential function in a Markov model. The accuracy of such estimates has not been objectively evaluated. Purpose. To compare LEGs from declining exponential function estimates with those calculated from population data, using published screening mammography studies as examples. Method. SEER-based population data are used to compare LEG calculation with declining exponential function estimation and empinc population data in a new model, the "nested" Markov. Results. Analyses of the LEG of mammographic screening based on the declining exponential function significantly overestimate LEGs for younger women and underestimate them for older women. Because of offsetting errors, all-age analyses paradoxically appear accurate. Conclusion. Declining exponential function estimates of LEGs for chronic diseases with low mortality rates and long time horizons are liable to significant bias, especially with limited age cohorts. Key words: life expectancy; survival; mortality; DEALE; Markov model; misestimation bias; misspecification bias. (Med Decis Making 1999; 19:385-393)
A High-Resolution Imaging Touch Sensor
Authors: Hillis W. Daniel
Published: March 2007

A dexterous robot manipulator must be able to feel what it is doing. The mechanical hand of the future will be able to roll a screw between its fingers and sense, by touch, which end is which. This paper describes a step toward such a manipulator, an imaging tactile sensor with hundreds of pressure sensors in a space the size of a fingertip. The sensor was designed as part of a tendon-actuated mechan ical finger, similar in size and range of motion to a human index finger (Hillis 1981). As a demonstration, the device was programmed to distinguish among several commonly used fastening devices—nuts, bolts, flat washers, lock washers, dowel pins, cotter pins, and set screws—by touching them with the finger and analyzing the tactile image.

This paper describes how the tactile sensor array was constructed and how it works. The simple pattern- recognition techniques used in the demonstration program are also outlined. The final section notes some promising directions for future research.
Position and Velocity Transformations Between Robot End-Effector Coordinates and Joint Angles
Authors: Featherstone R.
Published: March 2007

This paper describes efficient procedures for performing transformations from the position and velocity of the end effector to the corresponding joint angles and velocities, and vice versa, for a six-degree-of-freedom robot manipulator having three revolute joint axes intersecting at the wrist. Some attention is paid to the problems that arise when the manipulator's position is near a deadpoint.
Adjustment of Robot Joint Gear Backlash Using the Robot Joint Test Excitation Technique
Authors: Dagalakis Nicholas G. , Myers Donald R.
Published: March 2007

A technique has been developed for the precise adjustment of gear backlash of the joints of an industrial robot. Bandli mited random excitation signals were injected into the drive system of the joint under test, and the output response of the joint link was monitored using an accelerometer. The coher ence function was measured and used to adjust the joint gear backlash to minimize the effect of the backlash nonlinearity on the joint drive system. Tests were performed while the joint was both loaded and unloaded and for several different steady-state positions. The test results indicate that this technique can be used for both the adjustment of the joint gears and the periodic automatic inspection of their condition.
Determining Grasp Configurations using Photometric Stereo and the PRISM Binocular Stereo System
Authors: Ikeuchi Katsushi , Nishihara H. Keith , Horn Berthold K. P. , Sobalvarro Patrick , Nagata Shigemi
Published: March 2007

This paper describes a system which locates and grasps parts from a pile. The system uses photometric stereo and binocu lar stereo as vision input tools. Photometric stereo is used to make surface orientation measurements. With this informa tion the camera field is segmented into isolated regions of a continuous smooth surface. One of these regions is then selected as the target region. The attitude of the physical ob ject associated with the target region is determined by histo graming surface orientations over that region and comparing them with stored histograms obtained from prototypical objects. Range information, not available from photometric stereo, is obtained by the PRISM binocular stereo system. A collision-free grasp configuration is computed and executed using the attitude and range data.
Dual Orthogonal Matrices in Manipulator Kinematics
Authors: McCarthy J.M.
Published: March 2007

The angular or linear displacements required at each of the joints of a robot manipulator to attain a specified position and orientation of its hand are obtained by solving the closure equations of the manipulator. These equations express the fact that the sequence of coordinate transformations between each link of the manipulator from its hand to its base must equal the transformation from the hand to the base directly. It is well known that the 4 X 4 homogeneous form of the point coordinate transformation matrix together with special coor dinate frames adapted to the structure of a manipulator yield a standard form of these coordinate transformation matrices known as the Denavit-Hartenberg matrix (Paul 1981). It is not so well known that the transformation equations of the coordinates of lines in these special coordinate frames may be used as well (Pennock and Yang 1985). Furthermore, by introducing dual numbers, the 6 X 6 matrices that arise col lapse into 3 X 3 orthogonal matrices with dual number ele ments, yielding a dual form of the Denavit-Hartenberg ma trix. Presented here is an elementary development of these results. Also discussed is a dual form of the Jacobian of a manipulator.
On the Nature of Robot Workspace
Authors: Gupta K.C.
Published: March 2007

This paper demonstrates that workspace analysis is not merely a tool of volumetric analysis. In order to emphasize its broad implications in the configuration synthesis of robot manipulators, we use the term workspace theory. After re viewing some recent research on robot workspaces, it is shown that workspace theory leads to an anthropological observation in biomanipulation, qualitative transformations of holes and voids (central or toroidal), the geometric inversion method for the prediction of the number of solution sets, the existence of solution transition boundaries within the workspace (dex terous or total), and the influence oTjoint variable limits on the workspace and the multiplicity of solution sets.
Mechanics and Planning of Manipulator Pushing Operations
Authors: Mason Matthew T.
Published: March 2007

Pushing is an essential component of many manipulator operations. This paper presents a theoretical exploration of the mechanics of pushing and demonstrates application of the theory to analysis and synthesis of robotic manipulator oper ations.
A Survey of Robot Tactile Sensing Technology
Authors: Nicholls Howard R. , Lee Mark H.
Published: March 2007

This paper reviews the current state-of-the-art in tactile sens ing technology. We examine in detail the different methods of transduction employed by tactile sensors and describe various significant designs that incorporate these methods. We then describe the different techniques used to process and analyze tactile data. Finally, we conclude with an assessment of the current state of development.
Comparison of Methods for Developing the Dynamics of Rigid- Body Systems
Authors: Ju M.S. , Mansour J.M.
Published: March 2007

Several approaches for developing the equations of motion for a three-degree-of-freedom PUMA robot were compared on the basis of computational efficiency (i.e., the number of additions, subtractions, multiplications, and divisions). Of particular interest was the investigation of the use of com puter algebra as a tool for developing the equations of motion. Three approaches were implemented algebraically: La grange's method, Kane's method, and Wittenburg's method. Each formulation was developed in absolute and relative coordinates. These six cases were compared to each other and to a recursive numerical formulation. The results showed that all of the formulations implemented algebraically re quired fewer calculations than the recursive numerical algo rithm. The algebraic formulations required fewer calculations in absolute coordinates than in relative coordinates. Each of the algebraic formulations could be simplified, using patterns from Kane's method, to yield the same number of calcula tions in a given coordinate system.
Inverse Dynamics and Kinematics of Multi- Link Elastic Robots: An Iterative Frequency Domain Approach
Authors: Bayo Eduardo , Papadopoulos Philip , Stubbe James , Serna Miguel Angel
Published: March 2007

A technique is presented and experimentally validated for solving the inverse dynamics and kinematics of multi-link flexible robots. The proposed method finds the joint torques necessary to produce a specified end-effector motion. Since the inverse dynamic problem in elastic manipulators is closely coupled to the inverse kinematic problem, the solution of the first also renders the displacements and rotations at any point of the manipulator, including the joints. Further more the formulation is complete in the sense that it includes all the nonlinear terms due to the large rotation of the links. The Timoshenko beam theory is used to model the elastic characteristics, and the resulting equations of motion are discretized using the finite element method. An iterative solu tion scheme is proposed that relies on local linearization of the problem. The solution of each linearization is carried out in the frequency domain.

The performance and capabilities of this technique are tested, first through simulation analysis, and second through experimental validation using feed-forward control. Results show the potential use of this method not only for open-loop control, but also for incorporation in feedback control strate gies.

1. This section contains a revised and corrected formulation of open-chain case. A previous method reported by the first author in: Computed Torque for the Fosition Control of Open-Chain Flexible Robots. Proc. 1988 IEEE International Conference in Robotics and Automation contained an error.
Kinematic Inversion of Robotic Manipulators in the Presence of Redundancies
Authors: Anderson Karen , Angeles Jorge
Published: March 2007

A general algorithm for the solution of the inverse kinematic problem of robotic manipulators in the presence of redundan cies is presented in this article. Redundancies are handled using a constrained nonlinear least-square minimization approach in which a positive definite performance index is minimized subject to the associated kinematic closure equa tions. The arising nonlinear problem is solved as a sequence of linear quadratic programs. The algorithm is aimed at providing an efficient and general solution that avoids the production of undesirable effects such as non-conservative joint motions. Numerical stability of the procedure is en hanced by use of the Newton-Gauss method. Examples are given using the six-axis PUMA and seven-axis CYBOTECH P-15, each performing a task for which five degrees of free dom are required to orient and position an axially-symmetric peg through a continuous path.
The Tethered Robot Problem
Authors: Sinden F.W.
Published: March 2007

Robot vehicles tethered to fixed bases move about in a com mon region. To perform its task, each vehicle must visit a prespecified set of locations. This paper discusses the problem of controlling the vehicles so that they do not tangle their tethers. The problem arises, for example, in connection with small air-bearing supported vehicles used to fetch parts for mechanical assembly. The tethers in this case are "umbilical cords" carrying compressed air, power, and signals.

The tethered robot problem can be seen as a special case of the general problem of scheduling the motions of several cooperating robots. In more conventional cases the robot's manipulator is connected to the base by a series ofjointed members whose movements in 3D space are quite compli cated. The tethered robot problem considered here is much simpler because the manipulators (vehicles) move in only two dimensions, and they are connected to their bases in the geometrically simplest way. Relatively large numbers of teth ered robots may be able to share a common space without undue complication. Such sharing can greatly increase the ef ficiency and flexibility with which an array ofprocessing equipment can be used.

The technical problem outlined above leads in particular to the following mathematical problem: identify those rectilin ear drawings ( plane embeddings) of the complete bipartite graph K m,n whose edges can be colored with n colors so that no two edges of the same color have common points (includ ing endpoints). Solutions are presented for useful special cases. The general case of this apparently new problem re mains open.
A New Computational Method for Linearized Dynamic Models for Robot Manipulators
Authors: Li Chang-Jin , Hemami A. , Sankar T.S.
Published: March 2007

In this paper, a new computational method to derive linear ized dynamic models about a nominal trajectory for robot manipulators is developed from the "straightforward" La grangian formulation. This method is very simple and sys tematic. It can be applied to compute the feedforward control law (i.e., the generalized forces and torques) about the de sired nominal trajectory, and to design the feedback con troller that reduces or eliminates any deviations from the de sired nominal trajectory. The salient advantage of using this method is the amount of computation for deriving the com plete linearized dynamic model for a manipulator is small enough to make real-time computation on a mini- or micro computer possible. The whole computation for a manipulator with six degrees of freedom requires at most about 2427 multiplications and 1798 additions. Camputationally, this is the fastest of all the existing methods.
Design and Control of a Mobile Robot with an Articulated Body
Authors: Hirose Shigeo , Morishima Akio
Published: March 2007

Mobile robots having good terrain adaptability, sufficient payload capability, and high mobility are now urgently in de mand. In this paper, design of a practical mobile robot is attempted, with an inspection task in a nuclear reactor as a concrete objective for development. The configuration of the mobile robot is first discussed. A wheel with crawler track, legs, and a snake-like articulated body are shown to be three fundamental configurations. A hybrid configuration consist ing of an articulated body and a crawler track is most ade quate for the nuclear reactor robot because of its excellent terrain adaptability, sufficient payload capability, and high mobility. Design of the joint structure of the articulated body is discussed. Basic control problems such as signal process ing for tactile sensors and control of statically indeterminant forces are also investigated. A mechanical model KR I, a robot with six articulated body segments, 16 degrees of free dom, length 1391 mm, and weight 27.8 kg, is constructed and several experiments are done to demonstrate the basic mobility of the robot and to show the validity of introducing force control.
Task-Level Adaptive Hybrid Manipulator Control
Authors: Chung Jack C. H. , Leininger Gary G.
Published: March 2007

The pole-placement self tuning control method is applied to the control of manipulators directly in the task coordinate system. This results in highly desirable task-oriented per formance characteristics. In the task coordinate, the position control axes and the force control axes are orthogonal. Therefore hybrid control can be achieved without degradation in performance of the control system. With the leaning mech anism at the task location, changing gravitational effect, dynamic friction, compliant effects, and load variations are automatically compensated for. Simulation results for both position control and hybrid control using the JPL-Stanford arm demonstrate the effectiveness of the proposed method. Real-time implementation of this algorithm for position control of a PUMA 600 industrial manipulator further sup ports the applicability of this new control method.
Vision-Aided Robotic Welding: An Approach and a Flexible Implementation
Authors: Agapakis John E. , Katz Joel M. , Friedman Joshua M. , Epstein Geoffrey N.
Published: March 2007

Conventional, nonadaptive, robot welding systems can only be used when the workpieces are highly repeatable and well fixtured. An approach for vision-aided adaptive robotic weld ing and an implementation of a flexible, sensory-controlled robotic welding system are presented in this paper. Structured lighting, in the form of a steerable cone of laser light, and machine vision are used for sensing of the weld joint location and determining the detailed three-dimensional weld joint surface geometry ahead of the welding torch. This sensory feedback is used for the off-line detection of large fixturing errors before welding starts (part finding); the real-time cor rection of robot paths to compensate for thermal distortion and loose part tolerances during single- and multipass weld ing (seam tracking); and the in-process adjustment of weld ing conditions to correct for weld joint shape variations (adaptive welding). A general approach for modeling and calibration of the novel cone-of-light structured lighting sensor is presented. Robust vision-processing schemes for the detec tion and recognition of laser stripe features in noisy images are developed and implemented using a pipelined processing architecture. Three-dimensional (3D) offsets from the taught path are computed in real time along the actual path, and a 3D surface model is developed and used to determine user- defined joint cross-sectional features and dimensions during welding. Approaches are proposed and implemented for incorporating the visually determined offsets in robot path planning and control and for controlling the welding process parameters on the basis of the monitored cross-sectional dimensions.
Kinestatic Analysis of Multifingered Hands
Authors: Romdhane Lotfi , Duffy Joseph
Published: March 2007

This paper is concerned with the handling of any object by an articulated multifingered hand. By handling we mean the secure grasp of a general object plus the manipulation of this object by the fingers without motion of the arm on which the hand is mounted. Hypothetical joints are used to express the freedom at the contact of the object with each fingertip. A pair of matrices are introduced that relate the small motions of the joints to the relative displacement of the object and the fingertips and that are derived using reciprocal screws. This analysis permits not only the determination of the necessary conditions for a secure handling of the object but also the investigation of the special configurations that may occur. In the case of a grasp with point contact with friction, a very important result is derived that leads to a considerable sim plification in the analysis of these matrices. It is further shown that there exists a particular point, called the center of the grasp, at which the direction of the force applied to the object does not influence the contact intensities. Following this it is demonstrated that the vector containing the contact intensities, generated by a unit couple applied to the object, generates an ellipsoid defined as the grasp ellipsoid. The two smaller axes of this ellipsoid show where to place the con tacts to minimize the contact forces for a given task. The results are illustrated with numeric examples in appendix C.
A Direct Application of the Decoupling Method to Euler-Lagrange Formalism
Authors: Cotsaftis M. , Vibet C.
Published: March 2007

For automatic derivation of control algorithms, the decoupling method is applied to Euler-Lagrange's formal ism. Explicit expressions to derive directly from the Lagrangian the nonlinear control laws of mechanisms and of a dynamically driven robot are given. Finally, a simple two-degree-of-freedom system driven by DC electric motors is used to illustrate the flexibility of the proposed approach over the other design methods.
A Theory of Generalized Inverses Applied to Robotics
Authors: Doty Keith L. , Melchiorri Claudio , Bonivento Claudio
Published: March 2007

Robokcs research has made extensive use of techniques based on me Moore-Penrose inverse, or generalized inverse, of matri als. Recently it has been pointed out how noninvariant results may, in general, be obtained by applying these techniques to other areas of robotics, namely hybrid control and inverse ve locity kinematics. Unfortunately, the problems are not restricted to just these particular areas in robotics but are connected with misleading definitions of the metric properties of the six- dimensional wrench and twist vector spaces used in robotics. The current definitions lead to inconsistent results (i.e., results that are not invariant with respect to changes in the reference frame andlor changes in the dimensional units used to express the problem. As a matter of fact, given a linear systemu = Ax, where the matrix A may be singular, the Moore-Penrose theory of generalized inverses may be properly and directly applied only when the vector space U of vectoru and the vector space X of vector x are inner product spaces. Arbitrary assignment of Euclidean inner products to the space U and X when the vectorsu andx have elements with different physical units can lead to inconsistent and noninvariant results. In this article the problem of inconsistent, noninvariant solutionsX s tou = Ax in robotics is briefly reviewed and a general theory for com puting consistent, gauge-invariant solutions to nonhomogeneous systems of the formu = Ax is developed. In addition, the dual relationship between rigid-body kinematics and statics is de fined formally as a particular, linear algebraic system whose solution system is also a dual system. Examples illustrate the theory.
On Computing Two-Finger Force-Closure Grasps of Curved 2D Objects
Authors: Ponce Jean , Stam Darrell , Faverjon Bernard
Published: March 2007

This article presents an algorithm for computing force-closure grasps of piecewise-smooth, curved, two-dimensional objects. We consider the case of a gripper equipped with two hard fingers and assume point contact with friction. Object bound aries are represented by collections of polynomial parametric curves, and force-closure grasps are characterized by systems of polynomial constraints in the parameters of these curves. All configuration space regions satisfying these constraints are found by a parallel numerical cell-decomposition algorithm based on curve tracing and continuation techniques. Maximal curve segments where fingers can be positioned independently are found by optimization within the grasp regions. The algo rithm has been implemented on a distributed architecture, and experiments using a PUMA robot equipped with a pneumatic two-finger gripper and a vision system are presented.
The Motion of Planar, Compliantly Connected Rigid Bodies in Contact, With Applications to Automatic Fastening
Authors: Donald Bruce R. , Pai Dinesh K.
Published: March 2007

We consider the problem of planning and predicting the mo tion of a flexible object amid obstacles in the plane. We model the flexible object as a rigid "root" body attached to compli ant members by torsional springs. The root's position may be controlled, but the compliant members move in response to forces from contact with the environment. Such a model en compasses several important and complicated mechanisms in mechanical design and automated assembly: snap-fasteners, latches, ratchet-and-pawl mechanisms, and escapements. The problem is to predict the motion of such a mechanism amid fixed obstacles. For example, our algorithm could be used to determine whether a snap-fastener design can be assembled with a certain plan.

In this article we analyze the physics of these flexible de vices and develop combinatorially precise algorithms for predicting their movement under a motion plan. Our algo rithms determine when and where the motion will terminate and also compute the time history of contacts and mating forces. In addition to providing the first known exact algorithm that addresses flexibility in motion planning, we also note that our approach to compliance permits an exact algorithm for predicting motions under rotational compliance, which was not possible in earlier work.

We discuss the following issues: the relevance of our ap proach to engineering (which we illustrate through examples we ran using our system), the computational methods em ployed, the algebraic techniques for predicting motions in contact with rotational compliance, and issues of robustness and stability of our geometric and algebraic algorithms. Our computational viewpoint lies in the interface between differen tial theories of mechanics and combinatorial collision detection algorithms. From this viewpoint, subtle mathematical difficul ties arise in predicting motions under rotational compliance, such as the forced nongenericity of the intersection problems encountered in configuration space. We discuss these problems and their solutions. Finally, we extend our work to predict the forces on the manipulated objects as a function of time and show how our algorithm can easily be extended to include uncertainty in control and initial conditions. With these extensions, we hope that our system could be used to analyze and design objects that are easy to assemble, even given control and sensing errors, and that require more force to disassemble than to mate.
Bracing to Increase the Natural Frequency of a Manipulator: Analysis and Design
Authors: Delson Nathan , West Harry
Published: March 2007

The dynamic behavior of braced manipulators is analyzed. A braced manipulator is a manipulator that has been constrained by contact with the environment at a point other than the robot end effector, tool, or gripper. The analysis is restricted to manipulators with links that are rigid but joints that may be compliant. An expression is developed for the undamped natural frequency of an unbraced manipulator for small am plitudes of vibration. The kinematics of braced manipulators is described using admissible variables (i.e., variables that define the constrained admissible motion space), and the natural fre quency analysis is extended to braced manipulators. Dynamic analysis is used to design the ideal geometry of constraint to optimize the vibration characteristics of a robotic manipulator. It is shown that the lowest braced natural frequency is always greater than or equal to unbraced lowest natural frequency and thus can improve the dynamic performance of the robot. It is shown that there is a range of directions of bracing constraints that have the greatest effect in increasing the lowest natural frequency, and of this range it is possible to choose the most practically convenient. The results of the analysis and design are illustrated by their application to a grinding robot.
Time-Optimal Trajectories for Mobile Robots With Two Independently Driven Wheels
Authors: Reister David B. , Pin François G.
Published: March 2007

This article addresses the problem of time-optimal motions for a mobile platform in a planar environment. The platform has two nonsteerable, independently driven wheels. The overall mission of the robot is expressed in terms of a sequence of via points at which the platform must be at rest in a given configuration (position and orientation). The objective is to plan time-optimal trajectories between these configurations, assuming an unobstructed environment.

Using Pontryagin's maximum principle (PMP), we formally demonstrate that all time-optimal motions of the platform for this problem occur for bang-bang controls on the wheels (at each instant, the acceleration on each wheel is at either its upper or its lower limit). The PMP, however, provides only the conditions necessary for time optimality. To find the time- optimal robot trajectories, we first parameterize the bang-bang trajectories using the switch times on the wheels (the times at which the wheel accelerations change sign). With this param eterization, we can fully search the robot trajectory space and find the switch times that will produce particular paths to a desired final configuration of the platform. We show numer ically that robot trajectories with three switch times (two on one wheel and one on the other) can reach any position, while trajectories with four switch times can reach any configuration. By numerical comparison with other trajectories involving sim ilar or greater numbers of switch times, we then identify the sets of time-optimal trajectories. These are uniquely defined using ranges of the parameters and consist of subsets of trajec tories with three switch times (for the problem when the final orientation of the robot is not specified) or four switch times (when a full final configuration is specified). We conclude with a description of the use of the method for trajectory planning for one of our robots and discuss some comparisons of sample time-optimal paths with minimum length paths.
On Computing the Friction Forces Associated With Three-Fingered Grasp
Authors: Chevallier Dominique P. , Payandeh Shahram
Published: March 2007

Computation of friction forces between fingers and object for a given external force is important in grasp planning. Based on the required friction forces, the magnitudes of the grasping forces can be adjusted to avoid slippage of the object be tween fingers. This article presents a very elegant and effective method for computing the friction forces between the fingertips of a dexterous mechanical hand and the object as a function of the external wrench which can act on the object. Fingertips are modeled such that they are able to exert normal forces and are making point contact with friction with the object. The method in this article utilizes geometric information on the grasp con figuration, screw geometry, and bi-orthogonal systems. The method is demonstrated through detailed tutorial solutions of two examples.
A Random Exploration Approach for Automatic Chamferless Insertion
Authors: Hongler Max-Olivier , Badano Fernand , Betemps Maurice , Jutard Alain
Published: March 2007

The stochastic approach strategy to realize the robotized in sertion of low-clearance, chamferless parts is studied in both the analytical and experimental contexts. The analytical ap proach is discussed in terms of stochastic differential equations that involve Gaussian white and colored noises processes to model a planar random search. Special attention is devoted to characterize the time required for the insertion, a random variable whose first moment calculation (i.e., the mean) is dealt with. In the mathematical modelization context adopted, it is remarkable that the calculated mean mating time grows slowly (i.e., logarithmically), with the precision required to perform an insertion. The. theoretical results are validated on a robo tized assembly system, also presented in this article. In this experimental system, the random movements are generated by pseudorandom binary sequences that, for the time scales con sidered, are large band processes. The experimental data are observed to sustain the logarithmic behavior obtained analyt ically. Hence, in addition to its simplicity and flexibility, the random strategy approach appears to be very efficient when high mating precision is required.
Probabilistic Analysis of Manipulation Tasks: A Conceptual Framework
Authors: Brost Randy C. , Christiansen Alan D.
Published: March 2007

This article addresses the problem of manipulation planning in the presence of uncertainty. We begin by reviewing the worst-case planning techniques introduced by Lozano-Pérez et al. (1984) and show that these methods are limited by an information gap inherent to worst-case analysis techniques. As the task uncertainty increases, these methods fail to produce useful information, even though a high-quality plan may exist. To fill this gap, we present the notion of a probabilistic back projection, which describes the likelihood that a given action will achieve the task goal from a given initial state. We provide a constructive definition of the probabilistic backprojection and related probabilistic models of manipulation task mechanics and show how these models unify and enhance several past results in manipulation planning. These models capture the fundamental nature of the task behavior but appear to be very complex. We present the results of laboratory experiments, comprising over 100,000 grasping trials, that measured the probabilistic backprojection of a grasping task under varying conditions. The resulting data support the probabilistic back projection model and illustrate a task in which probabilistic analysis is required. We sketch methods for computing these models and using them to construct multiple-step plans.
Kinematic Isotropy and Optimal Kinematic Design of Planar Manipulators and a 3-DOF Spatial Manipulator
Authors: Kirćanski Manja
Published: March 2007

Robot operation near isotropic configurations, in which the condition number of the Jacobian matrix reaches unity, is desirable from several points of view. However, determination of all such configurations, given arbitrary robot geometry, is a rather complex problem. In this article all the isotropic configurations of planar manipulators with two, three, and four degrees of freedom are determined, together with that of a 3- DOF spatial manipulator. The solutions are obtained in the form of a fourth-order polynomial for the 3-DOF robot and an eighth-order polynomial for the 4-DOF planar manipulator, resulting in a maximum of eight sets of solutions. The condition numbers are obtained as explicit analytic functions of joint coordinates and link lengths ratios. The optimal length of the links is determined by minimizing the criterion that the condition number increase most slowly with joint angles in the vicinity of isotropic configurations.
Performance Measures for Robot Manipulators: A Unified Approach
Authors: van den Doel Kees , Pai Dinesh K.
Published: March 2007

We introduce a formalism for the systematic construction of performance measures of robot manipulators in a unified framework based on differential geometry. We show how known measures arise naturally in our formalism and we construct several new ones, including a nonlinearity mea sure and a class of redundancy measures. The measures are applied to the analysis of two- and three-link planar arms for illustration.
Modeling of Flexible Manipulators Using Virtual Rigid Links and Passive Joints
Authors: Yoshikawa Tsuneo , Hosoda Koh
Published: March 2007

In this article, to derive a dynamic model of a flexible manip ulator, a modeling scheme using virtual rigid links and passive jnints is proposed. Each link is modeled individually, and by connecting models of links, a model of the whole flexible arm is obtained. Parameters of the model of each link are identified by measuring characteristics of the real flexible link. Using this modeling scheme, it is easy to make a model of a multi-link flexible arm without taking the boundary conditions into ac count, and it is easy to understand the mechanism of the model of the whole flexible arm.

First, the modeling scheme is proposed; then the equations of motion of an N-degree-of-freedom flexible manipulator using this modeling scheme are derived to simulate its dynamic behavior The results of simulation and experiment show the validity of this modeling scheme.
Dynamics of Kinematic Chains
Authors: Stokes Ann , Brockett Roger
Published: March 2007

In this article we derive the equations of motion of a kinematic chain using concepts naturally associated with the special euclidean group. A simple and coordinate-free formula for the kinetic energy of a rigid body is used to express the kinetic energy of an open chain. From this, the dynamical equations in the Lagrangian form follow easily. The structure of the equations of motion is sufficiently transparent so that one may gain insight into nontrivial problems involving analysis and design. We illustrate the applicability of this formalism by investigating the design of manipulators with configuration- independent and separable kinetic energy.
Motion Variables Leading to Efficient Equations of Motion
Authors: Mitiguy Paul C. , Kane Thomas R.
Published: March 2007

In order to formulate equations that govern the motion of a mechanical system, the analyst must choose time-dependent variables that characterize the configuration and motion of the system. Generally, the choice of variables made by the analyst has a profound effect on the efficiency of the resulting equations—"efficiency" here referring to relative simplicity, ease of manipulation for purposes of designing automatic con trol systems, and minimal consumption of computer time during numerical solution. In this article, guidelines are set forth for the selection of motion variables that lead to exceptionally effi cient dynamical differential equations for systems belonging to a large class frequently encountered in robotics.
Singularities of Nonredundant Robot Kinematics
Authors: Tchoń Krzysztof , Muszyński Robert
Published: March 2007

This article is concerned with an investigation of kinematic singularities of nonredundant robot manipulators, conducted toward describing the kinematics by simple mathematical mod els called normal forms. The adopted approach comes from the singularity theory of maps. The analysis is concentrated on kinematic singularities of codimension 1. The kinematics at singular configurations are characterized by a number called the differential degree. It is proved that, if this degree is finite, then the kinematics can be transformed to normal forms called pre-Morin or Morin forms. If the differential degree becomes infinite, the kinematics can be given either the prehyperbolic or the hyperbolic normal form. Special attention has been paid to the kinematics of the Unimation PUMA manipulator. A sin gularity analysis of the PUMA kinematics has shown that in a neighborhood of the shoulder and elbow singular configura tions, the kinematics assume a simple quadratic (Morin) form, whereas at the wrist singularity, the kinematics are represented by the hyperbolic normal form.
Analysis of a Novel 6-DOF, 3-PPSP Parallel Manipulator
Authors: Byun Y.K. , Cho H.S.
Published: March 2007

A novel kinematic structure for a parallel manipulator with 6 DOF is proposed. It consists of a platform that is connected to a fixed base by means of 3-PPSP (P—prismatic joint, S- spherical joint) subchains. Each subchain is connected to a passive prismatic joint at the one end, and a passive spherical joint at the other. The spherical joint is then attached to per pendicularly arranged prismatic actuators that are fixed to the base. Due to the efficient architecture, the closed-fonn solutions of the inverse and forward kinematics can be easily obtained. As a consequence, this new kinematic structure can be servo controlled using simple inverse kinematics, because forward kinematics allows for measuring the platform 's position and orientation in Cartesian space. Manipulator workspace determi nation is carried out through the computation of displacements in the prismatic joints. A Jacobian matrix for the proposed structure is derived so the relationship between actuator forces and output forces/moments of the mechanism can be analyzed. A series of simulations were performed to verify the results of the kinematics analyses and to evaluate the load characteristics of the system.