bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Method for the Singularity Analysis of Simple Six-link Manipulators
Authors: Lai Z.C. , Yang D.C.H.
Published: March 2007

This paper presents a new method for identifying conditions governing all singular configurations of simple six-link ma nipulators whose inverse kinematic position problems have closed-form solutions. The method is developed based on the concepts of service sphere, free service region, and dextrous wrist. For a simple six-link manipulator, we identify its singular state with finite internal degrees of freedom by using the conditions that cause the manipulator's inverse solutions to be indeterminate. Meanwhile its singular state with infini tesimal internal degrees of freedom can be identified by examining the determinant of the Jacobion of the first three links. This simple and straightforward method is illustrated by three examples.
The Representation, Recognition, and Locating of 3-D Objects
Authors: Faugeras O.D. , Hebert M.
Published: March 2007

The problem of recognizing and locating rigid objects in 3-D space is important for applications of robotics and naviga tion. We analyze the task requirements in terms of what information needs to be represented, how to represent it, what kind of paradigms can be used to process it, and how to implement the paradigms. We describe shape surfaces by curves and patches, which we represent by linear primitives, such as points, lines, and planes. Next we describe algo rithms to construct this representation from range data. We then propose the paradigm of recognizing objects while locat ing them. We analyze the basic constraint of rigidity that can be exploited, which we implement as a prediction and verifi cation scheme that makes efficient use of the representation. Results are presented for data obtained from a laser range finder, but both the shape representation and the matching algorithm are general and can be used for other types of data, such as ultrasound, stereo, and tactile.
Estimation of Inertial Parameters of Manipulator Loads and Links
Authors: Atkeson Christopher G. , An Chae H. , Hollerbach John M.
Published: March 2007

The inertial parameters of manipulator rigid-body loads and links have been automatically estimated as a result of gen eral movement. The Newton-Euler equations have been recast to relate linearly the measured joint forces or torques via acceleration-dependent coefficients to the inertial parame ters, which have then been estimated by least squares. Load estimation was implemented on a PUMA 600 robot equipped with an R TI FS-B wrist force-torque sensor and on the MIT Serial Link Direct Drive Arm equipped with a Barry Wright Company Astek wrist force-torque sensor. Good estimates were obtained for load mass and center of mass, and the forces and torques due to movement of the load could be pre dicted accurately. The load moments of inertia were more difficult to estimate. Link estimation was implemented on the MIT Serial Link Direct Drive Arm. A good match was ob tained between joint torques predicted from the estimated parameters and the joint torques estimated from motor cur rents. The match actually proved superior to predicted torques based on link inertial parameters derived by CAD modeling. Restrictions on the identifiability of link inertial parameters due to restricted sensing and movement near the base have been addressed. Implications of estimation accu racy for manipulator dynamics and control have been consid ered.
Robot Manipulator Control under Unix RCCL: A Robot Control "C" Library
Authors: Hayward Vincent , Paul Richard P.
Published: March 2007

In this paper, we present a general purpose manipulator control system. The system is run under the Unix operating system. Manipulator programs are written in the "C" lan guage and make use of primitive functions included in a library. Manipulator control is thus integrated within the lan guage in the same manner as is input-output. The system includes a world modeler and a trajectory generator that are accessed through two sets of primitive functions. The sys tem's structured world modeler is designed for an easy inte gration of sensors. The first part of the paper reviews the functional organization of the system, going through world modeling, trajectory generation, force control, and synchroni zation. The second part describes actual robot programming examples.
Contribution to Control of Redundant Robotic Manipulators in an Environment with Obstacles
Authors: Kirćanski Manja , Vukobratović Miomir
Published: March 2007

The redundancy of robot manipulators plays an important role in increasing their flexibility and versatility, especially in an environment with obstacles. In this paper, the redundancy is utilized for enabling collision-free motion for a given tra jectory of a manipulator hand. The calculation of the corre sponding trajectory in the space of joint coordinates is per formed using several performance criteria that take into account the vicinity of the obstacles. The advantages and shortcomings of the proposed algorithms are discussed. The implementation of the algorithms is real-time due to modest computational complexity.
An Anthropomorphic Robot Finger for Investigating Artificial Tactile Perception
Authors: Dario Paolo , Buttazzo Giorgio
Published: March 2007

In this paper the design, implementation, and testing of an artificial tactile sensing system incorporating an articulated robot finger are presented. It was our primary aim in this work to set up the hardware and software tools necessary for investigating basic issues in artificial tactile perception.

In the first part of the paper the criteria followed in the design of the robot finger and of its motor and sensory com ponents are outlined.

The second part of the paper deals with the problem of defining a hierarchical architecture for the control of the ex ploratory finger. In this context, particular attention is de voted to the description of a set of tactile subroutines that are intended to replicate some of the basic sensory motor se quences adopted by humans for tactile exploration. The main features of the high-level planner, which is supposed to super vise the execution of those tactile primitives, are also discussed.

Finally, experimental results that demonstrate the capabil ity of the robotic system of executing the previously defined tactile subroutines and of extracting specific object features are presented.
Nonlinear Adaptive Control of an N-Link Robot with Unknown Load
Authors: Han J.-Y. , Hemami H. , Yurkovich S.
Published: March 2007

An N-link planar robot holding an unknown load and driving its end-effector along a prespecified trajectory is studied. The effect of the unknown load is discussed, and the nonlinear dynamic equation with the unknown load is derived. A non linear model-reference adaptive control algorithm is devel oped for tracking of a trajectory that is a piecewise continuous function of time. The tracking error dynamics represent a linear stable system with persistent disturbances, and the Germaidze-Krasovskii theorem in the Lyapunov second method is applied to show the error stability. Digital com puter simulations show the effectiveness of the adaptive con trol algorithm for the unknown load with mass 2 kg, 5 kg, and 10 kg. The effect of the computation time delay on the system dynamics is also addressed.
A New Development in Camera Calibration: Calibrating a Pair of Mobile Cameras
Authors: Izaguirre Alberto , Pu Pearl , Summers John
Published: March 2007

A new method of camera calibration is proposed for active visual sensing for use in three-dimensional (3D) scene analy sis. The method permits calibration of a mobile camera as a function of the position and orientation of the camera. The algorithm for identification of the calibration matrices is divided into two steps: first, calibration for a fixed position of the camera (i.e., the transformation between the real-world coordinates and the coordinates of the corresponding points in the image plane of the camera); second, calibration as a function of the position and orientation of the camera, which uses the prior information of the calibration for a fixed posi tion.

The method can be used for any mobile camera as long as the movement of the camera support is known. For instance, if the camera is mounted on the tip of a robot or on a link, we must know the geometric transformation between this link and the base of the robot, but it is not necessary to know the placement of the camera on this link.
Experiments Toward On-Line Identification and Control of a Very Flexible One-Link Manipulator
Authors: Rovner Daniel M. , Cannon Robert H.
Published: March 2007

An adaptive control algorithm based on the self-tuning regu lator concept has been experimentally investigated for appli cation to a very flexible one-link robotic manipulator. Adap tive control is an attractive methodology for maintaining the performance of precise controllers designed for such manipu lators under conditions of varying end-effector load. The use of noncollocated sensors and actuators to give good accuracy in tip positioning also places stringent requirements on the accuracy of dynamic models used for controller design.

Identification and control design techniques suitable for on-line implementation have been demonstrated experimen tally on such a single-link flexible manipulator. The identifi cation algorithm employed is a filtered version of the recur sive least-squares algorithm. It is a development of algorithms previously used with the Stanford four-disk sys tem. Stable controllers with good step responses were de signed using the system models identified with the identifica tion algorithm. The necessity of filtering sensor data to achieve accurate identification was motivated analytically and confirmed experimentally. Accurate identification of 2 system transfer functions was achieved with a 4-s-long data record. The algorithms demonstrated could be used in an adaptive-learning setting to improve the performance of a ro botic system subject to varying loads.
Camera-Space Manipulation
Authors: Skaar Steven B. , Brockman William H. , Hanson R.
Published: March 2007

The paper involves the development of real-time estimation and control details for a new vision-based manipulator con trol method. The method permits a kind of adaptability not otherwise available in that the relationship between the cam era-space location of manipulable visual cues and the vector of manipulator joint coordinates is estimated in real time. This is done based upon a model that generalizes known manipulator kinematics to accommodate unknown relative camera position and orientation as well as uncertainty of manipulator grasp. Both large-scale trajectory planning and refined placement precision become possible despite an un known camera-manipulator juxtaposition. This feature opens the door to a range of applications of manipulation, includ ing a mobile manipulator with stationary cameras tracking and providing information for control of the manipulation event. Evidence of the ability of the estimation algorithm to perform in real time is provided with a successfully performed interception task, completed without a priori knowledge of camera or manipulator positions.
A Three-Wheeled Self-Adjusting Vehicle in a Pipe, FERRET-1
Authors: Okada Tokuji , Kanade Takeo
Published: March 2007

This paper describes three-wheeled vehicles that can move inside a pipe and adjust to the shape and size of the pipe. We propose two types of vehicles: tractive and nontractive. Both types are based on two hinged arms. The tractive vehicle has a driving wheel at a hinge and two sphere bearings at the ends of the arms. The driving wheel rotates about the axis perpendicular to the plane in which the two arms move. The wheel can freely move sideways. The sphere bearings can move in all directions like ball casters. Since the stretch force of the arm to the pipe wall is generated mechanically by pulleys and a spring, the vehicle rests in the pipe by pressing the two arms in opposite directions where the diameter is the biggest and it moves according to the action of the driving wheel. Three wheels of the nontractive vehicle are sphere bearings.

We analyze the shape geometry of the pipe to obtain sta bility conditions under which the vehicle can move, and we consider friction and gravity bringing the vehicle to rest in the pipe. We also analyze the kinematics and dynamics of lo comotion, and we simulate locomotion of the vehicle in the plane in which the biggest diameter of the pipe is measured.

The results of the simulation prove the self-adjustability of the vehicle to the shape and size of the pipe. Experimental results show that the vehicle can move and self-adjust in an inclined or twisted pipe with a deep angle.
Tabulation of the Symbolic Midframe Jacobian of a Robot Manipulator
Authors: Doty Keith L.
Published: March 2007

The symbolic midframe Jacobian for a general 6-DOF ma nipulator, a 12-DOF, 6-cylindric-jointed manipulator (6C) and a 24-DOF manipulator in which all four kinematic parameters of each link transform vary, admits to direct, manageable tabulation. For 6-link manipulators, the mid frame Jacobians 3J α and 3J α associated with rates of change in the link lengths a and twists a do not depend upon the kinematic parameters of the first link frame ( d1, θ1, a,, α1). Similarly, the Jacobians 3J d and 3Jθ associated with the rates of change in link offsets d and rotations θ do not depend on the kinematic parameters of the sixth link frame ( d6, θ6, a6, α6). A general property of a manipulator Jacobian, ex pressed in any frame, is that the column associated with the rate of change of a kinematic parameter is independent of that kinematic parameter. Furthermore, the determinant of the manipulator Jacobian is invariant with respect to its frame of representation, hence, the manipulator singularities may be calculated with relative ease in midframe. Finally, the complexity of the general form of 3J a versus 3J d and 3J α versus 3Jθ, as measured in types of symbols (+, -, ., sines, cosines, parameters) and quantity of symbols of each type, is the same.
Building, Registrating, and Fusing Noisy Visual Maps
Authors: Ayache Nicholas , Faugeras Olivier D.
Published: March 2007

This paper deals with the problem of building three-dimen sional descriptions (we call them visual maps) of the environ ment of a mobile robot using passive vision. These maps are local (i.e., attached to specific frames of reference). Since noise is present, they incorporate information about the ge ometry of the environment and about the uncertainty of the parameters defining the geometry. This geometric uncertainty is directly related to its source (i.e., sensor uncertainty). We show how visual maps corresponding to different positions of the robot can be registered to compute a better estimate of its displacement between the various viewpoint positions, as suming an otherwise static environment. We use these esti mates to fuse the different visual maps and reduce locally the uncertainty of the geometric primitives which have found correspondents in other maps. We propose to perform these three tasks (building, registrating, and fusing visual maps) within the general framework of extended Kalman filtering, which allows efficient combination of measurements in the presence of noise.
Multisensor Knowledge Systems
Authors: Henderson T. , Weitz E. , Hansen C. , Mitiche A.
Published: March 2007

We describe an approach which facilitates and makes explicit the organization of the knowledge necessary to map multi sensor system requirements onto an appropriate assembly of algorithms, processors, sensors, and actuators. We have previously introduced the multisensor kernel system and logi cal sensor specifications as a means for high-level specifi cation of multisensor systems. The main goals of such a characterization are to develop a coherent treatment of multi sensor information, to allow system reconfiguration for both fault tolerance and dynamic response to environmental con ditions, and to permit the explicit description of control.

In this paper we show how logical sensors can be incorpo rated into an object-based approach for the interpretation of 3D structure. Considering the inherent difficulties in inter preting general configurations of lines in space, and consider ing the ubiquitousness of special line configurations in manu factured environments and objects, we advocate the use of computational units tuned to the occurrence of special config urations. The organized use of these units circumvents the inherent difficulties in interpreting general configurations of lines. After a brief examination of the problem of interpreting general configurations of lines in space, a number of compu tational units are proposed which are naturally derived from angular relations. The process of propagation (which allows interpretation to spread over the image) is also advocated. Such computational units and processes, which are simple and efficient, can be conveniently organized in a rule-based framework where the occurrence of the various special config urations can be tested. The multisensor knowledge system provides such a framework.
Motor Schema — Based Mobile Robot Navigation
Authors: Arkin Ronald C.
Published: March 2007

Motor schemas serve as the basic unit of behavior specifica tion for the navigation of a mobile robot. They are multiple concurrent processes that operate in conjunction with asso ciated perceptual schemas and contribute independently to the overall concerted action of the vehicle. The motivation be hind the use of schemas for this domain is drawn from neuro- scientific, psychological, and robotic sources. A variant of the potential field method is used to produce the appropriate velocity and steering commands for the robot. Simulation re sults and actual mobile robot experiments demonstrate the feasibility of this approach.
On the Kinematics of Wheeled Mobile Robots
Authors: Alexander J.C. , Maddocks J.H.
Published: March 2007

A wheeled mobile robot is here modelled as a planar rigid body that rides on an arbitrary number of wheels. The rela tionship between the rigid body motion of the robot and the steering and drive rates of wheels is developed. In particular, conditions are obtained that guarantee that rolling without skidding or sliding can occur. Explicit differential equations are derived to describe the rigid body motions that arise in such ideal rolling trajectories. The simplest wheel configura tion that permits access of arbitrary rigid-body motions is determined. Then the question of slippage due to misalign ment of the wheels is investigated by minimization of a non- smooth convex dissipation functional that is derived from Coulomb's Law offriction. It is shown that this minimization principle is equivalent to the construction of quasi-static motions. Examples are presented to illustrate the models.
Efficient Recognition of Partially Visible Objects Using a Logarithmic Complexity Matching Technique
Authors: Gottschalk Paul G. , Turney Jerry L. , Mudge Trevor N.
Published: March 2007

An important task in computer vision is the recognition of partially visible two-dimensional objects in a gray scale image. Recent works addressing this problem have attempted to match spatially local features from the image to features generated by models of the objects. However, many algo rithms are considerably less efficient than they might be, typ ically being O(IN) or worse, where I is the number offeatures in the image and N is the number of features in the model set. This is invariably due to the feature-matching portion of the algorithm. In this paper we discuss an algorithm that significantly improves the efficiency offeature matching. In addition, we show experimentally that our recognition algo rithm is accurate and robust. Our algorithm uses the local shape of contour segments near critical points, represented in slope angle-arclength space (θ-s space), as fundamental fea ture vectors. These feature vectors are further processed by projecting them onto a subspace in θ-s space that is obtained by applying the Karhunen-Loève expansion to all such fea tures in the set of models, yielding the final feature vectors. This allows the data needed to store the features to be re duced, while retaining nearly all information important for recognition. The heart of the algorithm is a technique for performing matching between the observed image features and the precomputed model features, which reduces the runtime complexity from O(IN) to O(I log I + I log N), where I and N are as above. The matching is performed using a tree data structure, called a kD tree, which enables multidi mensional searches to be performed in O(log) time.
Technical Description of the Adaptive Suspension Vehicle
Authors: Pugh Dennis R. , Ribble Eric A. , Vohnout Vincent J. , Bihari Thomas E. , Walliser Thomas M. , Patterson Mark R. , Waldron Kenneth J.
Published: March 2007

This paper contains descriptions and specifications of the major mechanical systems of the Adaptive Suspension Vehi cle. It also contains an overview of the computer software and hardware architectures. Experimental response curves for the principal servo systems are presented.
A Six-Legged Telerobot for Nuclear Applications Development
Authors: Byrd Joseph S. , DeVries Kevin R.
Published: March 2007

A six-legged telerobot was evaluated for nuclear applications at the Savannah River Laboratory. Enhancements were added to the man-machine control interface to improve the efficiency and productivity of operations. Although this sys tem was a prototype for laboratory research and development and was not intended for operation in a nuclear environment, the work demonstrated the feasibility of sophisticated walk ing robots in nuclear service. The Savannah River system has served as a valuable prototype forerunner to a production model telerobot that is now under development by Odetics Incorporatedfor the Electric Power Research Institute.
Three Uses for Springs in Legged Locomotion
Authors: Alexander R. McN.
Published: March 2007

Running animals and robots can save energy and reduce unwanted heat production by bouncing along on springs, using the principle of the pogo stick. (The principal springs in animals are tendons.) They can make further energy savings by using return springs to halt the legs at the end of each foward or backward swing and start them swinging the other way. The forces at impact of feet with the ground can be moderated by compliant foot pads, which can improve road holding by preventing "chatter" (vibrations in which the foot repeatedly leaves and returns to the ground before settling). Animals use springs in all three ways but there seems to be a need for more use of springs in legged robots, especially in robots designed to run fast.
Biped Gymnastics
Authors: Hodgins Jessica K. , Raibert Marc H.
Published: March 2007

In this paper we examine the nature of a gymnastic maneu ver, the forward flip, and describe how a planar biped run ning machine executes it. To perform a flip the machine runs forward, thrusts with both legs to jump while pitching the body forward, shortens the legs to tuck once airborne, untucks in time to land on the feet, and then continues running. The control system produces these actions and the resulting flip by issuing a prespecified pattern of actuator commands to the actuators in conjunction with a set of control algorithms used for normal running. When all components of the system are working properly, the machine executes nine out of 10 flips successfully.
Approaches for Recognition and Interpretation of Workpiece Surface Features Using Structured Lighting
Authors: Agapakis John E.
Published: March 2007

Vision sensing of the exact location and orientation of a workpiece and determination of its detailed surface geometry are often necessary for robot guidance, inspection, quality evaluation, or process control in manufacturing applications of robots, as well as for sensing and operator feedback in telerobotic tasks. In the work reported in this paper, con trolled illumination in the form of projected planes of laser light is used in order to determine such three-dimensional (3D) workpiece geometry. A data-driven approach for the rec ognition of general stripe contour features is proposed and implemented. A computationally efficient scheme for 3D surface modeling using a local ruled surface approximation is also developed for the determination of cross-sectional features and dimensions. The interpretation of the visually detected workpiece surface geometry and features typically requires specialized engineering knowledge and expertise. The feasibility of encoding such knowledge in the form of production rules is demonstrated through the development of a prototype defect interpretation system for weld inspection.
A Robust, Correspondenceless, Translation- Determining Algorithm
Authors: Basu Anup , Aloimonos John
Published: March 2007

A method is presentedfor the recovery of the three-dimen sional translation of a rigtdly translating object. The novelty of the method consists of the fact that four cameras are used in order to avoid the solution of the correspondence problem. The method is immune to low levels of noise and has good behavior when the noise increases. The noise immunity is so high that even though the algorithm is intended only for translating objects, its accuracy is very high even if the object is also rotating (with a small rotation) around an axis pass ing through its center of mass. We provide a theoretical analysis of the robustness of our algorithm and present ex perimental results from the application of the theory to syn thetic and real images.
A Bayesian Approach to Optimal Sensor Placement
Authors: Cameron Alec , Durrant-Whyte Hugh
Published: March 2007

By "intelligently" locating a sensor with respect to its envi ronment, it is possible to minimize the number of sensing operations required to perform many tasks. This is particu larly important for sensing media, such as tactile sensors and sonar, that provide only "sparse" data. In this paper, a sys tem is described that uses the principles of statistical decision theory to determine the optimal sensing locations for per forming recognition and localization operations. The system uses a Bayesian approach to utilize any prior object informa tion (including object models or previously acquired sensory data) in choosing the sensing locations.
A Physically Based Navigation Strategy for Sonar-Guided Vehicles
Authors: Kuc Roman , Viard Victor Brian
Published: March 2007

A novel navigation strategy is described that employs a time- of-flight sonar system to guide an autonomous vehicle through an unstructured environment composed of specular surfaces. Collisions are avoided by employing a scanning procedure that exploits the physics of sound propagation to detect objects. Physical models for the transducer beam and the reflection process are described. These models provide understanding about sonar ranging and are applied to deter mine the necessary scanning procedure for obstacle detection. In our environment, two types of echoes are observed: those reflected from surfaces and those diffracted from edges. Acoustic pulses reflected from oblique surfaces are not usually detected, and diffraction echoes are small and decrease with distance, making them difficult to detect. A scanning proce dure is developed to detect both types of obstacles. This pro cedure is employed to develop a navigation strategy that indicates the perceived obstacle-free region that guarantees that no collision will occur. The approach is illustrated with results produced by a vehicular robot equipped with a Polaroid sensor.
Special Configurations of Multi-finger Multi- freedom Grippers — A Kinematic Study
Authors: Hunt K.H. , Samuel A.E. , McAree P.R.
Published: March 2007

Screw theory is used to establish the general kinematic prin ciples offully-in-series and fully-in-parallel devices. Through screw theory, we show that a workpiece grasped by a fully-in- series manipulator can only lose freedom while a workpiece grasped by a fully-in-parallel manipulator can only gain freedom. Multi-finger multi-freedom grippers or robot hands use a mixture of in-parallel and serial actuation, and so a workpiece grasped by such a device can both gain and lose freedom. These linkages belong to a class called composite serial/in-parallel manipulators. Using the well-established concepts of screw systems and reciprocity, we identify the general criteria that govern the gain and loss of workpiece freedoms. We illustrate how these gains and losses of work piece freedom arise, by considering the Stanford/JPL hand.
Manipulator Motion Planning in the Presence of Obstacles and Dynamic Constraints
Authors: Singh S.K. , Leu M.C.
Published: March 2007

Motion planning algorithms are traditionally restricted to finding spatial or "physical" paths only, while manipulator dynamics is ignored. The attendant low-level problem of timing and velocity along the path is left to the trajectory planner. In this study, these two aspects have been combined. The overall problem has been cast as an optimal control problem. The obstacle avoidance conditions have been for mulated as state-variable inequality constraints. These con straints are shown to be continuously differentiable in our formulation. The continuous-time problem is converted to a discrete-time problem to permit the use of nonlinear pro gramming algorithms for the heavily constrained problem. Computational issues such as discretization effects and al gorithmic efficiency have been addressed. Simulations are performed for the proposed method.
Uncertainty and Compliance of Robot Manipulators with Applications to Task Feasibility
Authors: Pai Dinesh K. , Leu M.C.
Published: March 2007

The uncertainty and compliance of a robot manipulator used to perform a task are considered. A formula is derived for the efficient computation of a tight bound on the uncertainty of the end effector, given the uncertainty in the kinematic pa rameters of the robot. It is shown that the total uncertainty is the Minkowski difference of the manipulator uncertainty and the task position uncertainty. Simulations are performed in which the results are used to determine configurations of a robot for which the total uncertainty is within a specified tolerance.

The suitability of the compliance of a manipulator for performing a planar peg-in-hole type assembly task is also studied. Manipulators are modeled as having rigid links and compliant joints, following experimental results. It is shown that given any symmetric positive semidefinite compliance, a robot manipulator of the above type can be constructed that will realize this compliance at some point in its work space. A new condition on the stiffness is proposed for preventing jamming. If the peg is supported by the end effector of a robot, we can determine configurations of the robot at which jam ming can be avoided. Simulations are performed to compute the no-jam configurations of a manipulator.

The results developed here have direct application to sev eral areas of robotics: determining whether a robotic task is feasible in the presence of uncertainty and joint compliance, choosing work space locations for a robotic task, and the design and selection of robot manipulators.

1. This is called two- point contact in Whitney (1982).

2. That is, errors resulting from both the end-effector and task position uncertainties.

3. The symbol ( ) T denotes the transpose.

4. The half-size of a box is half the length of the box in a specified coordinate direction.

5. Also called the set-sum.

6. The effective compliance refers to the compliance at the peg tip resulting from the compliance of the robot or some other support.
Ability of a Robot to Travel Through its Free Work Space in an Environment with Obstacles
Authors: Wenger Philippe , Chedmail Patrick
Published: March 2007

This article presents a new geometric analysis of the free work space of a robot among obstacles. The free work space (FW) is defined as the set of positions and orientations that the robot's end effector can reach, according to the joint limits and the various obstacles lying in the environment. The aim is to give global descriptions of the robot's ability to move in the operational space (which coincides with Carte sian space when only position coordinates are specified).

The main contribution of this work is the characterization of the effects of obstacles on the work space geometry, as well as on its topology. The ability of a robot to move freely in its work space (called the "moveability") is difficult to describe and needs stringent formalizations. The concept of move ability is introduced through various properties and their cor responding necessary and sufficient conditions. Using a Con structive Solid Geometry (CSG) Computer-Aided Design (CAD) description of robots and obstacles and an octree model of the FW, these properties permit characterization of selected moveability areas in the FW, where, for instance, any n points can be linked together or where any continuous trajectory can be achieved without changing configuration. This new global description is of great interest for the user of CAD systems when designing robotic cells.
Analysis of a Simplified Hopping Robot
Authors: Koditschek Daniel E. , Bühler Martin
Published: March 2007

This article offers some analytical results concerning sim plified models of Raibert's hopper. We represent the task of achieving a recurring hopping height for an actuated "ball" robot as a stability problem in a nonlinear discrete dynamical control system. We model the properties of Raibert's control scheme in a simplified fashion and argue that his strategy leads to closed-loop dynamics governed by a well-known class of functions, the unimodal maps. The rich mathematical literature on this subject greatly advances our ability to determine the presence of an essentially globally attracting fixed point-the formal ren dering of what we intuitively mean by a "correct" strat egy. The motivation for this work is the hope that it will facilitate the development of general design principles for "dynamically dexterous" robots.
Efficient Dynamic Simulation of a Quadruped Using a Decoupled Tree-Structure Approach
Authors: Freeman P.S. , Orin D.E.
Published: March 2007

Efficient simulation of a dynamically stable, fast-moving quadruped vehicle has been undertaken at The Ohio State University. Individual leg-link inertial properties, espe cially important at high speeds, are incorporated into the simulation. Also incorporated are the ground contact con siderations of compliance, friction, and impulsive impact forces. Basic efficiency is gained by decoupling of the closed-chain system into a tree-structured, open chain through introduction of spring/damper systems at the ground. The ensuing tree-structure dynamics are solved by developing and applying an extended form of the effi cient O(N) open-chain algorithm of Brandl et al. (1986). Additional speedup in the computations is gained through application of multirate integration and parallelization. One second of real-time simulation on a single Intel iPSC/ 2 Hypercube node takes 66.7 s. Use of multirate integra tion improves four-node parallel performance, giving a total speedup factor of more than 3.
Real-Time Configuration Space Transforms for Obstacle Avoidance
Authors: Newman Wyatt S. , Branicky Michael S.
Published: March 2007

A method is presented for computation of obstacle bound aries in configuration space, with particular emphasis on time efficiency. Properties of configuration space transfor mations are presented in general, and these properties are invoked in algorithms that result in highly efficient com putations. The approach depends on the definition of a set of primitives, which are themselves efficiently trans formed and may be combined logically to construct more complex transformations. The concepts are illustrated with both computed and empirically obtained configura tion space obstacles in two and three dimensions. Perfor mance data for real-time transformations are reported.
A Long-Range Adaptive Controller for Robot Manipulators
Authors: Coito F.J. , Lemos J.M.
Published: March 2007

The control of mechanical manipulators is an important application area for adaptive control. However, standard self-tuning controllers turn out to be nonrobust with respect to unmodeled dynamics. Attempting to overcome this limitation, long-range adaptive controllers are receiv ing an increasing interest. In this work an adaptive con trol structure based on a variant of the MUSMAR algo rithm is developed and tested on the control of a model for a two-link planar mechanical manipulator. Problems concerning the controller implementation are discussed.
Task Space Dynamic Analysis of Multiarm System Configurations
Authors: Chiacchio P. , Chiaverini S. , Sciavicco L. , Siciliano B.
Published: March 2007

The aim of this article is to provide a systematic method to perform dynamic analysis in the task space for a sys tem composed of multiple arms holding a rigid object. The dynamic manipulability ellipsoid is introduced to obtain quantitative indices of the system's capability, in each configuration, of performing object accelerations along given task space directions. The ellipsoid is derived on the basis of the mapping of object accelerations onto joint driving torques via the proper kineto-static and dynamic equations of the system. The maximum joint torque limits are taken into account, and the effects of gravitational loads onto the ellipsoid are evidenced. Anal ysis of multiarm system configurations is carried out in a number of case studies.
Identification and Analysis of Robot Manipulator Singularities
Authors: Tourassis Vassilios D. , Ang Marcelo H.
Published: March 2007

The existence of singular positions inside the robot workspace is an inherent problem for task planning and robot control. At manipulator configurations near singular positions, very large joint motions are required to produce relatively small end-effector displacements. In the limit, when a singularity is encountered, the required joint motions become unbounded and the manipulator loses at least one degree of freedom. Identify ing the singularities in the robot workspace is not always an analytically tractable problem, except for manipulators with op portune placement of the joint axes. Typically, it is easier and more informative to evaluate the robot "arm" and "wrist" sin gularities, which reflect the limitations of the lower-order robot subsystems responsible for positioning and orienting, respec tively, the end effector in space. The objective of this article is to define analytically the interplay between the individual "arm" and "wrist" singularities and the global manipulator singularities. Specifically, a general formula that defines ma nipulator singularities in terms of the subsystem singularities is developed. The analysis leads to a novel, efficient method for identifying the singularities of six-axis manipulators. This is then illustrated through an example.
Dynamic Map Building for an Autonomous Mobile Robot
Authors: Leonard John J. , Durrant-Whyte Hugh F. , Cox Ingemar J.
Published: March 2007

This article presents an algorithm for autonomous map building and maintenance for a mobile robot. We believe that mobile robot navigation can be treated as a problem of tracking ge ometric features that occur naturally in the environment. We represent each feature in the map by a location estimate (the feature state vector) and two distinct measures of uncertainty: a covariance matrix to represent uncertainty in feature loca tion, and a credibility measure to represent our belief in the validity of the feature. During each position update cycle, pre dicted measurements are generated for each geometric feature in the map and compared with actual sensor observations. Suc cessful matches cause a feature's credibility to be increased. Unpredicted observations are used to initialize new geometric features, while unobserved predictions result in a geometric feature's credibility being decreased. We describe experimental results obtained with the algorithm that demonstrate successful map building using real sonar data.
Hybrid Position/Force Control: A Correct Formulation
Authors: Fisher William D. , Mujtaba M. Shahid
Published: March 2007

This article will show conclusively that "kinematic instability" is not inherent to the hybrid position/force control scheme of robot manipulators but is a result of an incomplete and inap propriate formulation. The inverse of the manipulator Jacobian matrix is identified as causing the kinematic instability of the hybrid position/force control scheme. Linear algebra is used to explain clearly the implications of mapping between vec tor spaces and to reveal why the inverse of the manipulator Jacobian matrix should not be used in hybrid position/force control. A generalized architecture for hybrid position/force control is presented that can influence both joint positions and torques. This generalized formulation also includes the control of redundant manipulators. Some sufficient conditions for kine matic stability are proposed to determine when a system may become unstable without requiring a complete system analysis. A stable hybrid position/force control scheme is given and is demonstrated using an example that was previously shown to be unstable.
Vertical and Horizontal Motion Control of a One-Legged Hopping Machine
Authors: Lapshin V.V.
Published: March 2007

The problem of control of the body center of mass of a hopping machine with a telescopic, springy, weightable leg is analyti cally investigated.
Analysis of Swept Volume via Lie Groups and Differential Equations
Authors: Blackmore Denis , Leu M.C.
Published: March 2007

The development of useful mathematical techniques for an alyzing swept volumes, together with efficient means of im plementing these methods to produce serviceable models, has important applications to numerically controlled (NC) machin ing, robotics, and motion planning, as well as other areas of automation. In this article a novel approach to swept volumes is delineated—one that fully exploits the intrinsic geometric and group theoretical structure of Euclidean motions in or der to formulate the problem in the context of Lie groups and differential equations.

Precise definitions of sweep and swept volume are given that lead naturally to an associated ordinary differential equation. This sweep differential equation is then shown to be related to the Lie group structure of Euclidean motions and to generate trajectories that completely determine the geometry of swept volumes.

It is demonstrated that the notion of a sweep differential equation leads to criteria that provide useful insights concern ing the geometric and topologic features of swept volumes. Several new results characterizing swept volumes are obtained. For example, a number of simple properties that guarantee that the swept volume is a Cartesian product of elementary mani folds are identified. The criteria obtained may be readily tested with the aid of a computer.
Kinematic Isotropy and the Conditioning Index of Serial Robotic Manipulators
Authors: Angeles Jorge , López-Cajún Carlos S.
Published: March 2007

The conditioning index of a serial robotic manipulator is de fined in this article in terms of the reciprocal of its minimum condition number. The condition number of a manipulator is defined, in turn, as that of its Jacobian matrix. Moreover, in defining the Jacobian condition number, a quadratic norm of the Jacobian matrix is needed. However, this norm, or for that matter any other norm, brings about dimensional inho mogeneities. It is shown here that by properly defining the said norm based on a weighting positive definite matrix, the dimensional inhomogeneity is resolved. Manipulators with a conditioning index of 100% are termed isotropic, a six-axis isotropic manipulator being introduced. This manipulator has all its angles between neighboring revolute axes at 90° and all its distances between neighboring axes identical; more over, these distances are identical to the offsets of those axes. The kinematic conditioning of wrist-partitioned manipulators is given due attention, and illustrated with some examples of industrial robots of this type.
Restricted Jacobian Matrices of Redundant Manipulators in Constrained Motion Tasks
Authors: Nenchev Dragomir N.
Published: March 2007

Kinematically redundant manipulators are considered, with a prespecified end-effector task and multiple additional tasks. The number of additional tasks is assumed to be equal to or less than the degree of redundancy. This assumption justifies an equal-priority (or duality) concept for the end-effector task and additional tasks. Based on this concept, expressions for two restricted Jacobian matrices are derived: the restricted manipulator Jacobian and the restricted additional-task Jaco bian. It is shown that generalized inverses of these matrices can be utilized to derive two alternative solutions of instanta neous inverse kinematics that satisfy both tasks simultaneously. The first solution, which is based on the null space of the manipulator Jacobian, has been widely applied in various redundancy-resolution techniques; it is shown that when used in manipulator self-motion tasks, this solution yields cyclic- path motion in joint space. The second solution utilizes the null space of the additional-task Jacobian; it is dual to the first one. Hence, in the particular case of end-effector motion with additional-task maintenance, this solution yields cyclic-path motion as well.

It is further shown that at algorithmic singularities, both restricted Jacobian matrices lose rank simultaneously. Algo rithmic singularities, together with the well-known manipulator singularities, and newly defined additional-task singularities are shown to play an important role in kinematic analysis. The duality concept calls for the definition of a new type of dexterity measure: the additional-task performance measure. The restricted Jacobian matrices are shown to also provide a convenient tool for deriving "restricted" dexterity measures that are directly related to the various types of singularities. Typical end-effector/additional-task combinations have been tested through computer simulation, illustrating the application of the restricted Jacobian matrices to configuration analy sis and path-planning problems of redundant manipulators in constrained-motion tasks.
Toward a Robot Architecture Integrating Cooperation between Mobile Robots: Application to Indoor Environment
Authors: Noreils Fabrice R.
Published: March 2007

This article describes an architecture for cooperative and au tonomous mobile robots. The architecture is composed of three levels: functional, control, and planner levels. The functional and control levels manage robot resources, while the planner level carries out complex operations such as planning and cooperation.

The cooperation is composed of two phases: (1) collabora tion, in which a task is decomposed into subtasks and subtasks are allocated through a set of robots; and (2) coordination, in which robots actually coordinate their activities to fulfill the initial task using the notion of coordinated protocols. Moreover, a language has been developed to program the coordination.

This architecture exhibits important benefits such as (1) mod ularity (the robot can work autonomously or within a team), (2) robustness (although some modules on the robot fail, it is still able to perform useful tasks), and (3) programmability. Two actual examples using two indoor mobile robots are described to demonstrate the interest of this approach.