bluuebunny/crossref_metadata_2025 huggingface dataset:
Singularity-Robust Trajectory Generation
Authors: Lloyd John E. , Hayward Vincent
Published: July 2003

A singularity-robust trajectory generator is presented that, given a prescribed manipulator path and corresponding kinematic solution, computes a feasible trajectory in the presence of kinematic singularities. The resulting trajectory is close to minimum time, subject to individual bounds on joint velocities and accelerations, and follows the path with precision. The algorithm has complexity O(M log M), where M is the number of robot joints, and works using “coordinate pivoting,” in which the path timing near singularities is controlled using the fastest changing joint coordinate. This allows the handling of singular situations, including linear self-motions (e.g., wrist singularities), where the speed along the path is zero but some joint velocities are nonzero. To compute the trajectory, knot points are inserted along the path, dividing it into intervals, with the knot density increasing near singularities. An appropriate path velocity is then computed at each knot point, and the resulting knot velocity sequence is integrated to yield the path timing. Examples involving the PUMA manipulator are shown.
Global Planning for Dexterous Reorientation of Rigid Objects: Finger Tracking with Rolling and Sliding
Authors: Cherif Moëz , Gupta Kamal K.
Published: July 2003

We address global motion planning for quasi-static reorientation of convex objects (polyhedral and smooth objects) with a four-fingertip grasp. We make use of a simple humanlike manipulation strategy in which a single finger is moved at each instant while the other three are maintained fixed (with regard to the palm)—an extended version of the original finger-tracking scheme of Rus. This new version es sentially incorporates frictional rolling and sliding at the fingertips and deals with the related contact kinematics and quasi-static mo tion/force prediction issues. Our contribution is twofold. First, we describe an analysis showing that this extended scheme is suitable for reducing the space of the object motions, thereby making motion planning easier and operating on a search space of low dimension. Our second contribution is a planner that exploits such a search space reduction and applies the extended finger tracking at the core of a multilevel hierarchical framework to search for global reorien tation trajectories. The planner has been implemented and used for achieving several nontrivial frictional reorientation tasks that show the capabilities and the promise of our approach.
Closed-Form Forward-Position Solution for a 6-Dof 3-PPSP Parallel Mechanism and Its Implementation
Authors: Kim Whee Kuk , Byun Yong Kyu , Cho Hyung Suck
Published: July 2003

Closed-form forward/reverse position solutions for a 6-degree-of-freedom (DoF) parallel mechanism that has some type of nonsymmetric geometry are derived in this study. Particularly, the derived forward-position analysis is applicable to the mechanisms in which three passive joints are constrained to move parallel to the moving plate. Its kinematic and dynamic characteristics are investigated via isotropic index of the Jacobian matrix and isotropic index of the output effective inertia matrix, respectively. From this investigation, it is found that the mechanism has fairly uniform kinematic/dynamic characteristics throughout its workspace. To examine the effectiveness of the proposed 3-PPSP-type mechanism, a prototype is designed, implemented, and tested experimentally under various operating conditions. A simple PID controller is applied to the system, and its joint positions are servo-controlled. The controlled system showed a good trajectory performance. Noting that a more advanced controller requiring a forward- and/or reverse-position solution can be applied to the system in real time, it can be contended that the manipulator is a candidate for the high-precision manipulator.
Classification of Textured Surfaces for Robot Navigation Using Continuous Transmission Frequency-Modulated Sonar Signatures
Authors: Politis Z. , Smith P. J. Probert
Published: July 2003

Whereas in the past ultrasonic sensors have been largely used only to estimate the proximity of objects and the location and identification of primitive targets in a robot workspace, the development of biomimetic sonar has opened up new possibilities for their application. Broadband sonar echoes have sufficient resolution so that characteristics on reflection, especially geometry and texture, can be distinguished with only a few measurements. In this paper, we describe how a model of texture can be used to distinguish between a number of different surfaces using only a single measurement of each, showing results on a number of surfaces that might be considered typical pathways for a mobile robot, both those with periodicity in pattern and those with statistically homogeneous features. In particular, we consider textures corresponding to hard smooth floors, carpets and asphalts, and surfaces with a repeating pattern made up of tiles. Each random rough surface is modeled using an extension of the Kirchhoff approximation method describing the scattering of the acoustic wave on the surface while the periodic surfaces are modeled assuming distinctive reflections from the tile borders. The continuous transmission frequency-modulated sonar signature corresponding to each class is derived and compared with the experimental measurement. A set of features is extracted that exploits the differences between the surface models, and a hierarchical classification scheme is proposed for recognition.
A New Zero-Dimension Robot Wrist: Design and Accessibility Analysis
Authors: Yang Daniel C. H. , Rauchfuss Jason W.
Published: July 2003

This paper presents the design of a robot wrist with zero hand length and unlimited mutually orthogonal joints. This design is an improvement over existing ones. When equipped with this type of wrist, a robot’s entire reachable workspace becomes the dexterous workspace. Because some wrist joint limitations may need to be imposed under practical consideration, to better assess this new wrist design, kinematics on robot point accessibility is derived. An algorithm and a software package are developed that enable the plotting of the point accessibility throughout the robot’s entire workspace. Examples for demonstration are also included.
Planning Paths for Elastic Objects under Manipulation Constraints
Authors: Lamiraux Florent , Kavraki Lydia E.
Published: July 2003

This paper addresses the problem of planning paths for an elastic object from an initial to a final configuration in a static environment. It is assumed that the object is manipulated by two actuators and that it does not touch the obstacles in its environment at any time. The object may need to deform to achieve a collision-free path from the initial to the final configuration. Any required deformations are automatically computed by the planner according to the principles of elasticity theory from mechanics. The problem considered in this paper differs significantly from that of planning for a rigid or an articulated object. In the first part of the paper, the authors point out these differences and highlight the reasons that make planning for elastic objects an extremely difficult task. The authors then present a randomized algorithm for computing collision-free paths for elastic objects under the above-mentioned restrictions of manipulation. The paper includes a number of experimental results. The work is motivated by the need to consider the physical properties of objects while planning and has applications in industrial problems, in maintainability studies, in virtual reality environments, and in medical surgical settings.
Immobilization-Based Control of Spider-Like Robots in Tunnel Environments
Authors: Shapiro Amir , Rimon Elon , Shoval Shraga
Published: July 2003

This paper presents an immobilization-based control method for spider-like robots that move quasi-statically in tunnel environments. The control method is based on a recent immobilization theory of bodies in contact. This theory ensures that when a spider-like mechanism is bracing against the environment at an immobile posture, the naturally occurring compliance at the contacts stabilizes the mechanism as a single body. Based on this result, we present two versions of a position control law for general k-limbed robots. We show that if the controller’s stiffness (i.e., proportional gain) is above a lower limit determined by the robot and environment parameters, stability of the closed-loop spider system is guaranteed. Next, we present dynamic simulations of a spider robot moving in a tunnel under the influence of the immobilization-based control law. The simulations show excellent convergence properties of the control algorithm. A four-legged spider prototype has been built, and we conclude with a description of initial experiments with this prototype.
Impulsive Motion Planning for Positioning and Orienting a Polygonal Part
Authors: Han Inhwan , Park Sang-Uk
Published: July 2003

In this paper, the authors analyze the dynamic behavior of a rigid polygonal part struck on a horizontal surface under the action of friction and present how to propel the part to a desired configuration through the impulsive operation. In the dynamic analysis of the impulsive operation, the part motion is typically analyzed in two phases, impact motion and sliding motion. These are usually analyzed in reverse order of occurrence. The authors characterize the impact and sliding dynamics with friction for polygonal parts and develop an approach to compute the inverse dynamic solution for motion planning of the impulsive operation. Finally, the authors verify the effectiveness of the simulation results and the developed motion plans through comparison with experimental results using a high-speed video camera.
Road Detection and Vehicle Tracking by Vision for Adaptive Cruise Control
Authors: Aufrère R. , Marmoiton F. , Chapuis R. , Collange F. , Dérutin J. P.
Published: July 2003

This article deals first with a process designed to detect the circulation lane of a vehicle by onboard monocular vision. This detection process is based on a recursive updating of a statistical model of the lane obtained by a training phase. Once the lane has been located, a reconstruction algorithm computes the vehicle location on its lane and the three-dimensional shape of the road. Thereafter, the authors seek to detect and track vehicles situated in front of their vehicle and equipped with specific visual markers in order to achieve an accurate determination of their location and speed. By combining these various data, the most dangerous obstacle can be identified. Each of these three processes is described in detail, and significant examples are provided.
Failure Tolerance through Active Braking: A Kinematic Approach
Authors: English James D. , Maciejewski Anthony A.
Published: July 2003

For a manipulator operating in a hazardous or remote environment, an important concern is its capability after a component failure, since retrieval or repair is not always possible. Methods have been presented in the literature for optimizing capabilities after specific types of failures. However, techniques for achieving failure tolerance when conversion between failure types is possible has not been fully explored. This paper presents an approach to improving postfailure performance by converting between locked-joint failures and free-swinging failures through active braking. When a manipulator is moved slowly, gravitational forces can be used to control the failed joint in free-swinging mode, allowing the problem to be cast as a kinematic one. The validity of the kinematic formulation and its implementation and global consequences are explored.
Cusp-Free, Time-Invariant, 3D Feedback Control Law for a Nonholonomic Floating Robot
Authors: Aicardi Michele , Cannata Giorgio , Casalino Giuseppe , Indiveri Giovanni
Published: July 2003

In this paper, the feedback control of a nonholonomic 3D vehicle is considered; namely, the problem of steering an underactuated rigid body to a target position along a desired direction is addressed. A simple time-invariant strategy is determined on the basis of standard vector kinematics and a Lyapunov-like stability analysis. The resulting control law guarantees almost global exponential convergence of the configuration error to zero with paths that do not exhibit any cusps, thus satisfying a major requirement for the application of such results on real systems that are not allowed or desired to move in both the forward and backward directions.
A Probabilistic On-Line Mapping Algorithm for Teams of Mobile Robots
Authors: Thrun Sebastian
Published: July 2003

An efficient probabilistic algorithm for the concurrent mapping and localization problem that arises in mobile robotics is presented. The algorithm addresses the problem in which a team of robots builds a map on-line while simultaneously accommodating errors in the robots’ odometry. At the core of the algorithm is a technique that combines fast maximum likelihood map growing with a Monte Carlo localizer that uses particle representations. The combination of both yields an on-line algorithm that can cope with large odometric errors typically found when mapping environments with cycles. The algorithm can be implemented in a distributed manner on multiple robot platforms, enabling a team of robots to cooperatively generate a single map of their environment. Finally, an extension is described for acquiring three-dimensional maps, which capture the structure and visual appearance of indoor environments in three dimensions.
Robot Control Using Disparate Multiple Sensors
Authors: Malis Ezio , Morel Guillaume , Chaumette François
Published: July 2003

A simple and efficient control algorithm that combines several sensors in order to realize the positioning task of a robot end effector is presented in this paper. The multiple-sensor control was designed as a part of the task function approach. A particular choice of the task function allows the researcher to simplify the design of the control law and the stability analysis. This global controller is based on the weighted sum of individual task functions. The approach was applied to the control with vision and force sensors. In spite of its simplicity, this approach provides satisfactory experimental results. Improvements in the positioning of cumbersome objects were obtained using cameras observing different parts of a scene. Moreover, peg-in-hole insertion experiments involving large initial errors were performed using a seven-axis robot manipulator without any computation of the peg trajectory by combining vision and force sensors.
Randomized Kinodynamic Planning
Authors: LaValle Steven M. , Kuffner James J.
Published: July 2003

This paper presents the first randomized approach to kinodynamic planning (also known as trajectory planning or trajectory design). The task is to determine control inputs to drive a robot from an ini ial configuration and velocity to a goal configuration and velocity while obeying physically based dynamical models and avoiding obstacles in the robot’s environment. The authors consider generic systems that express the nonlinear dynamics of a robot in terms of the robot’s high-dimensional configuration space. Kinodynamic planning is treated as a motion-planning problem in a higher dimensional state space that has both first-order differential constraints and obstacle-based global constraints. The state space serves the same role as the configuration space for basic path planning; however, standard randomized path-planning techniques do not directly apply to planning trajectories in the state space. The authors have developed a randomized planning approach that is particularly tailored to trajectory planning problems in high-dimensional state spaces. The basis for this approach is the construction of rapidly exploring random trees, which offer benefits that are similar to those obtained by successful randomized holonomic planning methods but apply to a much broader class of problems. Theoretical analysis of the algorithm is given. Experimental results are presented for an implementation that computes trajectories for hovercrafts and satellites in cluttered environments, resulting in state spaces of up to 12 dimensions.
Forward Kinematics of a General Fully Parallel Manipulator with Auxiliary Sensors
Authors: Chiu Yu-Jen , Perng Ming-Hwei
Published: July 2003

This paper presents a solution scheme for forward kinematics of a general fully parallel manipulator that guarantees a unique solution with only three redundant sensors. The redundant sensors were designedtominimizeengineeringdifficultiesintherealization, whereas an optimal sensor location was proposed to achieve a numerical efficiency and accuracy significantly better than existing solutions. As a result, the present approach is insensitive to misalignment of sensor location and measurement errors. Due to these merits, the present approach can handle joint misalignment due to machining error and assembly when it is applied to the task of self-calibration, which requires extreme precision. It is also suitable for applications in which real-time computation is needed.
Analysis of Control Architectures for Teleoperation Systems with Impedance/Admittance Master and Slave Manipulators
Authors: Hashtrudi-Zaad Keyvan , Salcudean Septimiu E.
Published: July 2003

A large number of bilateral teleoperation control architectures in the literature have been designed based on assumed impedance models of the master and slave manipulators. However, hydraulic or heavily geared and many other manipulators cannot be properly described by impedance models. In this paper, a common four-channel bilateral control architecture designed for the above impedance models is extended to teleoperation systems with master and slave manipulators of either the admittance or impedance type. Furthermore, control parameters that provide perfect transparency under ideal conditions are found for each type of teleoperation system. Because in practice such parameters may not lead to systems that are robust to time delays and model uncertainties, an analysis of the stability and performance robustness of this very general architecture and two-channel architectures is also presented. The analysis uses the passivity-based Llewellyn two-port network absolute stability criterion, as well as bounds on the minimum and range of values of the impedance transmitted to the operator. The results of these evaluations provide design guidelines on choosing a particular control architecture and its parameters given different master and slave manipulator structures.
An Orientation-Based Pruning Tool to Speed Up Contact Determination between Translating Polyhedral Models
Authors: Jiménez P. , Torras C.
Published: July 2003

Contact determination in terms of edge-face intersection tests permits handling nonconvex polyhedra directly, without decomposing them into convex entities, which saves the decomposition time and avoids having to deal with fictitious features but requires checking all possible pairings. However, by considering only translations and departing from a noninterfering situation, the number of pairings to be checked decreases drastically. The set of critical pairings can be determined efficiently using the spherical face orientation graph (SFOG), a representation developed by the authors. An algorithm to exploit the SFOG in convex settings provides controlled evidence of the pruning potential of this approach: the number of critical pairings grows linearly with the complexity of the polyhedra, instead of quadratically as the total number of pairings does. Experiments with a similar algorithm on nonconvex settings confirm the expected potential of the approach: for workpieces with many concavities moving in close proximity, the contact determination procedure presented in this paper performs one order of magnitude faster than RAPID, at the expense of a much higher preprocessing time.
Quantitative Evaluation of Matching Methods and Validity Measures for Stereo Vision
Authors: Banks Jasmine , Corke Peter
Published: July 2003

The authors present a qualitative and quantitative comparison of various similarity measures that form the kernel of common area-based stereo-matching systems. The authors compare classical difference and correlation measures as well as nonparametric measures based on the rank and census transforms for a number of outdoor images. For robotic applications, important considerations include robustness to image defects such as intensity variation and noise, the number of false matches, and computational complexity. In the absence of ground truth data, the authors compare the matching techniques based on the percentage of matches that pass the left-right consistency test. The authors also evaluate the discriminatory power of several match validity measures that are reported in the literature for eliminating false matches and for estimating match confidence. For guidance applications, it is essential to have an estimate of confidence in the three-dimensional points generated by stereo vision. Finally, a new validity measure, the rank constraint, is introduced that is capable of resolving ambiguous matches for rank transform–based matching.
Distributed Manipulation Using Discrete Actuator Arrays
Authors: Luntz Jonathan E. , Messner William , Choset Howie
Published: July 2003

Distributed manipulation systems induce motions on objects through the application of many external forces. An actuator array performs distributed manipulation using a planar array of many small stationary elements (which are called cells) that cooperate to manipulate larger objects. Typically, highly dense actuator arrays are modeled as spatially continuous, programmable forcefields, althoughinmany implementations a relatively small number of actuators supports an object and continuous assumptions break down. This paper serves two purposes: to present a methodology for modeling and analyzing the dynamics of manipulation on a highly discrete actuator array and to present a methodology for designing manipulation strategies on discrete actuator arrays. This is done in the context of a particular macro-scale actuator array comprising a fixed planar array of motorized wheels. Modeling of the dynamics takes into account several models of the interaction between the actuators and the object, the distribution of the weight of the object among the supports, and the discrete nature of the system. Under certain modeling assumptions, the manipulation dynamics of an object are extremely simple for a given set of supporting cells. An inversion of these piecewise-continuous dynamics generates a fully continuous open-loop manipulation strategy, effectively smoothing out the discontinuities. The authors show that although the resulting manipulation field may stably position and orient any object in the continuous field case, discreteness causes many objects to experience unstable rotational equilibria. Thus, poor orientation precision is a limitation of open-loop manipulation using discrete actuator arrays and motivates the use of feedback. The authors also derive closed-loop manipulation strategies through an inversion of the discrete dynamics that reduce the many-input, three-output distributed control problem to a standard three-input, three-output control problem that operates under distributed control. In effect, the array of actuators is reduced to a single virtual actuator capable of applying a desired net force and moment on an object. It is proven that even in the presence of dynamic coupling and nonlinearities introduced due to discreteness, these closed-loop strategies are asymptotically stable. Multimedia extensions include a complete simulator and videos of the experimental prototype.
Automatic Generation of High-Level Contact State Space
Authors: Xiao Jing , Ji Xuerong
Published: July 2003

A divide-and-merge approach is introduced for automatic generation of high-level, discrete contact state space, represented as contact state graphs, between two contacting polyhedral solids from their geometric models. Based on the fact that a contact state graph is the union of the subgraphs called a goal-contact relaxation (GCR) graph, the approach consists of algorithms (1) to generate a complete GCR graph automatically given the most constrained contact state in the GCR graph and (2) to merge GCR graphs automatically. The algorithms arplemented for cases in which the most constrained contact state in a GCR graph consists of up to three principal contacts. The ability to capture and represent contact state information effectively and efficiently is essential for robotic operations involving compliant motions, for simulation of contact motions, and for haptic interactions.
A Three-Dimensional Passive-Dynamic Walking Robot with Two Legs and Knees
Authors: Collins Steven H. , Wisse Martijn , Ruina Andy
Published: July 2003

The authors have built the first three-dimensional, kneed, two-legged, passive-dynamic walking machine. Since the work of Tad McGeer in the late 1980s, the concept of passive dynamics has added insight into animal locomotion and the design of anthropomorphic robots. Various analyses and machines that demonstrate efficient human-like walking have been developed using this strategy. Human-like passive machines, however, have only operated in two dimensions (i.e., within the fore-aft or sagittal plane). Three-dimensional passive walking devices, mostly toys, have not had human-like motions but instead a stiff legged waddle. In the present three-dimensional device, the authors preserve features of McGeer’s two-dimensional models, including mechanical simplicity, human-like knee flexure, and passive gravitational power from descending a shallow slope. They then add specially curved feet, a compliant heel, and mechanically constrained arms to achieve a harmonious and stable gait. The device stands 85 cm tall. It weighs 4.8 kg, walks at about 0.51 m/s down a 3.1-degree slope, and consumes 1.3 W. This robot further implicates passive dynamics in human walking and may help point the way toward simple and efficient robots with human-like motions.
RHex: A Simple and Highly Mobile Hexapod Robot
Authors: Saranli Uluc , Buehler Martin , Koditschek Daniel E.
Published: July 2003

In this paper, the authors describe the design and control of RHex, a power autonomous, untethered, compliant-legged hexapod robot. RHex has only six actuators—one motor located at each hip— achieving mechanical simplicity that promotes reliable and robust operation in real-world tasks. Empirically stable and highly maneuverable locomotion arises from a very simple clock-driven, open-loop tripod gait. The legs rotate full circle, thereby preventing the common problem of toe stubbing in the protraction (swing) phase. An extensive suite of experimental results documents the robot’s significant “intrinsic mobility”—the traversal of rugged, broken, and obstacle-ridden ground without any terrain sensing or actively controlled adaptation. RHex achieves fast and robust forward locomotion traveling at speeds up to one body length per second and traversing height variations well exceeding its body clearance.
Gauge-Based Tip Position Control of a New Three-Degree-of-Freedom Flexible Robot
Authors: Feliu V. , García A. , Somolinos J. A.
Published: July 2003

Flexible robots have given rise to numerous investigations, and their use is easily justified in two main cases: (1) when the weight of the robot has to be minimized and (2) when collisions of the robot with the environment are foreseen, as a flexible lightweight robot delivers less impact energy. Much work has been done by different authors on the position control of flexible robots using feedback of the tip position or tip acceleration. However, the use of these sensing devices is problematic in practical applications of flexible arms: three-dimensional tip position sensing is expensive, and occlusions appear at some arm configurations. Accelerometers cannot be used when contact of the tip with the environment is expected because these sensors cannot stand the high negative accelerations produced at the impact (unless very low speed motions are performed). This paper studies the possibility of carrying out the tip position control of a three-degree-of-freedom flexible arm using sensing devices placed far away from the tip (where contact is expected) in such way that they can easily stand the impact, which will be needed in the development of a position/force control for flexible robots. A control scheme based on motor position sensing plus some strain gauges placed on the arm structure is proposed. Stability of this control scheme is proven and is experimentally verified on a flexible manipulator prototype that was developed in the authors’ laboratory.
Real-Time Trajectory Generation for Redundant Manipulators with Path Constraints
Authors: Galicki Miroslaw
Published: July 2003

This paper addresses the problem of tracking a prescribed geometric path by the end effector of a kinematically redundant manipulator at the control loop level. The constraints imposed on the robot actuator controls are taken into account. The Lyapunov stability theory and/or the calculus of variations is used to derive the control scheme. Through the use of an exterior penalty function approach, an additional objective to be fulfilled by the robot, thatis, collisionavoidance of the manipulator links with obstacles, is ensured. The extensive computer simulation results illustrate the trajectory performance of the proposed control scheme for a geometric end effector path given in both an obstacle-free work space and a work space including obstacles.
Algorithms for Computing Numerical Optimal Feedback Motion Strategies
Authors: Lavalle Steven M. , Konkimalla Prashanth
Published: July 2003

The authors address the problem of computing a navigation function that serves as a feedback motion strategy for problems that involve generic differential constraints, nonconvex collision constraints, and the optimization of a specified criterion. The determination of analytical solutions to such problems is well beyond the state of the art; therefore, the authors focus on obtaining numerical solutions that are based on discretization of the state space (although they do not force trajectories to visit discretized points). This work improves classical optimal control techniques for problems of interest to the authors. By introducing a simplicial complex representation, the authors propose a novel interpolation scheme that reduces a key bottleneck in the techniques from O(2n) running time to O(n lg n), in which n is the state space dimension. By exploiting local structure in the differential constraints, the authors present a progressive series of three improved algorithms that use dynamic programming constraints to compute an optimal navigation function. Each makes an assumption that is more restrictive than the previous one, and exploits that assumption to yield greater efficiency. These improvements yield a practical increase in the applicability of dynamic programming computations by one or two dimensions over classical techniques. Theoretical convergence to the optimal solution is established for these proposed algorithms. The algorithms are implemented and evaluated on a variety of problems. Several computed results are presented.
AIBO: Toward the Era of Digital Creatures
Authors: Fujita Masahiro
Published: July 2003

The 21st century will become an era of autonomous robots that help and support people. Thus, they will be considered as partners of human beings. In this paper, the author introduces AIBO, the first product model of Robot Entertainment Systems. The main application of this robot is a pet-style robot, which must maintain a lifelike appearance. The author suggests how to maximize the complexity of responses and movements to solve the problem of substantially increasing the lifelike appearance of autonomous robots. The technologies used in AIBO are also described. Although AIBO is not intended for service or hazardous work, the development of AIBO is a major step toward a new era of autonomous robots in the new century.
Aggressive Maneuvering of Small Autonomous Helicopters: A Human-Centered Approach
Authors: Gavrilets V. , Frazzoli E. , Mettler B. , Piedmonte M. , Feron E.
Published: July 2003

Unmanned small autonomous helicopters can perform aggressive maneuvers that will be useful for operations in challenging conditions. This paper presents an analysis of the pilot’s execution of aggressive maneuvers from flight test data, collected on an instrumented small-scale acrobatic helicopter. A full-envelope nonlinear dynamic model of the helicopter was developed and validated for aggressive maneuvering. This model was used as part of the hardware-in-the-loop simulation environment to demonstrate intuitive control strategies that were determined from the analysis of flight data. This insight will be helpful in determining closed-loop strategies for autonomous aggressive maneuvering on MIT’s platform.
Manipulating Parts with an Array of Pins: A Method and a Machine
Authors: Blind Sebastien J. , McCullough Christopher C. , Akella Srinivas , Ponce Jean
Published: July 2003

This article investigates the manipulation of polygonal parts using a simple device consisting of a grid of retractable pins mounted on a vertical plate. This “Pachinko machine” is intended as a reconfigurable parts feeder for flexible assembly. A part dropped on this device may come to rest on the actuated pins, bounce out, or fall through. The authors propose a novel algorithm for part reorientation. Its input consists of the shape of a part, its initial position and orientation, and a goal configuration, and its output is a sequence of pin actuations that will bring the part to the goal configuration. The proposed approach does not attempt to predict the part motion between the equilibria associated with the active pins in the output sequence; instead, it constructs the capture region of each equilibrium (i.e., the maximal subset of the part’s configuration space such that any motion starting within it is guaranteed to end at the equilibrium). Assuming frictionless contacts and dissipative dynamics, reorienting a part reduces to finding a path from initial to goal states in a directed graph whose nodes are the equilibria and whose arcs link pairs of nodes such that the first equilibrium lies in the capture region of the second one. The proposed approach has been implemented on a prototype of the Pachinko machine, and initial experiments are presented.
Uncertainty Singularity Analysis of Parallel Manipulators Based on the Instability Analysis of Structures
Authors: Kong Xianwen , Gosselin Clément M.
Published: July 2003

When all the inputs of a parallel manipulator (PM) are locked, the manipulator is usually turned into a structure. When an uncertainty singularity occurs for a PM, the latter structure is unstable or, in other words, it may undergo infinitesimal or finite motion. Hence, the investigation of the uncertainty singularities of a PM can be reduced to the instability analysis of its corresponding structure. PMs with a 3-XS structure cover a broad class of PMs. A 3-XS structure is composed of two platforms connected by three XS serial chains in parallel. Here, X and S denote a generalized joint with one degree of freedom (DOF) and a spherical joint, respectively. An X joint can take the form of any kinematic joint with one DOF, such as a revolute joint or a prismatic joint, or the form of any closed kinematic chain with one DOF, such as a parallelogram. In this paper, the instability condition of the 3-XS structure is derived by simply differentiating its constraint equations. The geometric interpretation of the instability condition is revealed using a method based on linear algebra. The uncertainty singularity analysis of the 6-3 Gough-Stewart PM is performed to illustrate the application and efficiency of the proposed approach. Several specific cases of the 6-3 Gough-Stewart PM with singularity surfaces of reduced degree are proposed. The geometric interpretation of the singularity conditions is also given for some of the specific cases.
Visual Servoing Based on Image Motion
Authors: Crétual Armel , Chaumette François
Published: July 2003

The general aim of visual servoing is to control the motion of a robot so that visual features acquired by a camera become superimposed with a desired visual pattern. Visual servoing based on geometrical features such as image point coordinates is now well established. Nevertheless, this approach has the drawback that it usually needs visual marks on the observed object to retrieve geometric features. The idea developed in this paper is to use motion in the image as the input of the control scheme since it can be estimated without any a priori knowledge of the observed scene. Thus, more realistic scenes or objects can be considered. Two different methods are presented. In the first method, geometric features are retrieved by integration of motion, which allows the use of classical control laws. This method is applied toa6degree-of-freedom positioning task. The authors show that, in such a case, an affine model of 2-D motion is insufficient to ensure convergence and that a quadratic model is needed. In the second method, the principle is to try to obtain a desired 2-D motion field in the image sequence. In usual image-based visual servoing, variations of visual features are linearly linked to the camera velocity. In this case, the corresponding relation is more complex, and the authors describe how it is possible to use this relation. This approach is illustrated with two tasks: positioning a camera parallel to a plane and following trajectory.
Trap Design for Vibratory Bowl Feeders
Authors: Berretty Robert-Paul , Goldberg Ken , Overmars Mark H. , van der Stappen A. Frank
Published: July 2003

The vibratory bowl feeder is the oldest and still most common approach to the automated feeding (orienting) of industrial parts. In this paper, the authors consider a class of vibratory bowl filters that can be described by removing polygonal sections from the track; this class of filters is referred to as traps. For an n-sided polygonal part and an m-sided polygonal trap, an O(n2m log n) algorithm is given to decide whether the part in a specific orientation will safely move across the trap or will fall through the trap and thus be filtered out. For an n-sided convex polygonal part and m-sided convex polygonal trap, this bound is improved to O((n+m) log n). Furthermore, the authors show how to design various trap shapes, ranging from simple traps to general polygons, which will filter out all but one of the different stable orientations of a given part. Although the runtimes of the design algorithms are exponential in the number of trap parameters, many industrial part feeders use few-parameter traps (balconies, canyons, slots); in these cases, the running times of the algorithms range from linear to low-degree polynomial.
Self-Calibration of Camera-Equipped Robot Manipulators
Authors: Meng Yan , Zhuang Hanqi
Published: July 2003

A new approach to self-calibrate a camera-equipped robot manipulator is proposed in this paper. Self-calibration here means that the camera-robot system is capable of determining its geometric parameters without any external measurements and/or ground truth calibration data. With the proposed approach, one is able to identify all the rotational parameters and, up to a scale factor, all the translational parameters of a robotic system without any ground truth data. It is known from the computer vision literature that the extrinsic and intrinsic parameters of the camera can be obtained up to a scale factor by using the corresponding points of objects in a natural environment from an image sequence without knowing the positions of these object points. It is also well known that if the camera is treated as the tool of the robot, one is able to compute the corresponding robot pose directly from the camera-extrinsic parameters. An important question is how to determine the scale factors, which vary from one robot pose to another. It is discovered in this paper that if the robot pose measurement configurations follow a specially planned optimal trajectory, a unique scale factor can be used for all the poses measured along the trajectory. Thus, one is able to identify all the independent parameters of the robot with the poses measured in this manner with an inherently undetermined scale factor. One question remains: how do we obtain this unknown scale factor? Actually, the problem can be solved in a separate process. By two views of, say, a yardstick with the known length, the scale factor can be computed. If more than one measurement of the scale or measurements of multiple scales are provided from different viewing angles, the scale factor can be estimated with better accuracy in a least squares sense. Extensive simulation and experiment studies on a PUMA 560 robot reveal the convenience and effectiveness of the proposed approach.
Feature Detection for Haptic Exploration with Robotic Fingers
Authors: Okamura Allison M. , Cutkosky Mark R.
Published: July 2003

The authors consider the detection of small surface features, such as cracks, bumps, and ridges, on the surface of an object during haptic exploration and dexterous manipulation. Surface feature definition and detection are essential for intelligent haptic exploration and modeling of unknown objects. First, the authors review the representation of object surface geometry and present definitions of features based on local surface curvature. These definitions depend on both the geometry of the robot fingertips and the object being explored. It is also shown that the trajectory traced by a round fingertip rolling or sliding over the object surface has some intrinsic properties that facilitate feature detection. Several algorithms for feature detection based on feature definitions are described and compared, and simulated and experimental results are presented for feature detection using a hemispherical fingertip equipped with a tactile sensor.
Self-Excited Walking of a Biped Mechanism
Authors: Ono Kyosuke , Takahashi Ryutaro , Shimada Toru
Published: July 2003

The authors studied the self-excited walking of a four-link biped mechanism that possesses an actuated hip joint and passive knee joints with stoppers. They showed that the self-excitation control enables the three-degree-of-freedom planar biped model to walk on level ground by numerical simulation. From the parameter study, it was found that stable walking locomotion is possible over a wide range of feedback gain and link parameter values and that the walking period is almost independent of the feedback gain. Various characteristics of the self-excited walking of a biped mechanism were examined in relation to leg length, and length and mass ratios of the shank. Next, a biped mechanism was manufactured similar to the analytical model. After parameter modification, the authors demonstrated that the biped robot can perform natural dynamic walking on a plane with a 0.8 degree inclination. The simulated results also agree with the experimental walking locomotion.
Design of a Hollow Hexaform Torque Sensor for Robot Joints
Authors: Aghili Farhad , Buehler Martin , Hollerbach John M.
Published: July 2003

This work describes the design of a new one-axis torque sensor. It achieves the conflicting requirements of high stiffness for all six force and torque components, high sensitivity for the one driving torque of interest, and yet very low sensitivity for the other five force/torque components. These properties, combined with its donut shape and small size, make this sensor an ideal choice for direct-drive robotic applications. Experimental data validate the basic design ideas underlying the sensor’s geometry, the finite element model used in its optimization, and the advertised performance.
Artificial Muscles: Actuators for Biorobotic Systems
Authors: Klute Glenn K. , Czerniecki Joseph M. , Hannaford Blake
Published: July 2003

Biorobotic research seeks to develop new robotic technologies modeled after the performance of human and animal neuromuscular systems. The development of one component of a biorobotic system, an artificial muscle and tendon, is reported here. The device is based on known static and dynamic properties of biological muscle and tendon that were extracted from the literature and used to mathematically describe their force, length, and velocity relationships. A flexible pneumatic actuator is proposed as the contractile element of the artificial muscle and experimental results are presented that show the force-length properties of the actuator are muscle-like, but the force-velocity properties are not. The addition of a hydraulic damper is put forward to improve the actuator's velocity-dependent properties. Further, an artificial tendon is set forth whose function is to serve as connective tissue between the artificial muscle and a skeletal structure. A complete model of the artificial muscle-tendon system is then presented which predicts the expected force-length-velocity performance of the artificial system. Experimental results of the constructed device indicate muscle-like performance in general: higher activation pressures yielded higher output forces, faster concentric contractions resulted in lower force outputs, faster eccentric contractions produced higher force outputs, and output forces were higher at longer muscle lengths than shorter lengths.
Morse Decompositions for Coverage Tasks
Authors: Acar Ercan U. , Choset Howie , Rizzi Alfred A. , Atkar Prasad N. , Hull Douglas
Published: July 2003

Exact cellular decompositions represent a robot's free space by dividing it into regions with simple structure such that the sum of the regions fills the free space. These decompositions have been widely used for path planning between two points, but can be used for mapping and coverage of free spaces. In this paper, we define exact cellular decompositions where critical points of Morse functions indicate the location of cell boundaries. Morse functions are those whose critical points are non-degenerate. Between critical points, the structure of a space is effectively the same, so simple control strategies to achieve tasks, such as coverage, are feasible within each cell. This allows us to introduce a general framework for coverage tasks because varying the Morse function has the effect of changing the pattern by which a robot covers its free space. In this paper, we give examples of different Morse functions and comment on their corresponding tasks. In a companion paper, we describe the sensor-based algorithm that constructs the decomposition.
Sensor-based Coverage of Unknown Environments: Incremental Construction of Morse Decompositions
Authors: Acar Ercan U. , Choset Howie
Published: July 2003

The goal of coverage path planning is to determine a path that passes a detector over all points in an environment. This work prescribes a provably complete coverage path planner for robots in unknown spaces. We achieve coverage using Morse decompositions which are exact cellular decompositions whose cells are defined in terms of critical points of Morse functions. Generically, two critical points define a cell. We encode the topology of the Morse decomposition using a graph that has nodes corresponding to the critical points and edges representing the cells defined by pairs of critical points. The robot simultaneously covers the space while incrementally constructing this graph. To achieve this, the robot must sense all the critical points. Therefore, we first introduce a critical point sensing method that uses range sensors. Then we present a provably complete algorithm which guarantees that the robot will encounter all the critical points, thereby constructing the full graph, i.e., achieving complete coverage. We also validate our approach by performing experiments on a mobile robot equipped with a sonar ring.