bluuebunny/crossref_metadata_2025 huggingface dataset:
A Flexible, Tendon-Controlled Device for Endoscopy
Authors: Sturges Robert H. , Laowattana Schitt
Published: March 2007

The high level of skill required to maneuver present-day, flexible endoscopes that are utilized in esophagoscopy and colonoscopy has prompted us to propose a new class of safer, more easily controlled devices. These devices are mechanical teleoperators with few degrees of freedom based on the famil iar bead chain with internal control cables. The study of the physics associated with the flexible control devices is carried out with respect to the design parameters of both the practical system and its envaronment. The suitable geometries for lock ing such a mechanism are presented herein. We introduce the "slide motion" scheme, which provides a smooth movement of the endoscope stem with only three continuously controlled degrees of freedom. Such movement is accomplished by imple menting a series of relative motions between an outer tube and intermittently stiff spines inside. The strength and stability of the locking mechanism, which exhibits intermittent stiffness, is also discussed.
End-Effector Motion Capabilities of Serial Manipulators
Authors: Basavaraj Udai , Duffy Joseph
Published: March 2007

This article introduces an invariant measure to quantify the motion of a rigid body attached to the end effector of a serial manipulator. The measure arises as a natural consequence of the properties of the Euclidean group. It is invariant with respect to the position and orientation of the fixed and moving coordinate systems used to parameterize the motion of the manipulator. It is independent of the type and number of joints in the chain and the dimensions used to parameterize the chain. The singularities of the manipulator are also predicted by the measure. Finally, it is shown that, when applied to redundant manipulators, the measure quantifies the importance of each joint of the manipulator.
The Effect of Friction on the Forward Dynamics Problem
Authors: Dupont Pierre E.
Published: March 2007

This article discusses the numerical solution of the forward dynamic equations of an n-degree-of-freedom manipulator with friction. Also discussed are the modeling and experimen tal identification of friction. It is shown that the inclusion of Coulomb-type friction in the dynamic equations introduces two difficulties in the forward dynamic solution. The differential equations are shown to be discontinuous in the highest-order derivative terms. In addition, the load dependency of this type of friction typically causes the equations to be implicit in the joint accelerations. For the important case of load-dependent transmission friction, the equations can be explicit. Techniques for the forward solution are described through the example of a roller screw transmission. Experimental and simulation results are used to show the importance of load-dependent friction in a particular robot.
Contact Sensing from Force Measurements
Authors: Bicchi Antonio , Salisbury J. Kenneth , Brock David L.
Published: March 2007

This article addresses contact sensing (i.e., the problem of re solving the location of a contact, the force at the interface, and the moment about the contact normals). Called "intrinsic" contact sensing for the use of internal force and torque mea surements, this method allows for practical devices that provide simple, relevant contact information in practical robotic appli cations. Such sensors have been used in conjunction with robot hands to identify objects, determine surface friction, detect slip, augment grasp stability, measure object mass, probe surfaces, and control collision and for a variety of other useful tasks. This article describes the theoretical basis for their operation and provides a framework for future device design.
Experimental Object- Level Strategic Control With Cooperating Manipulators
Authors: Schneider Stanley A. , Cannon Robert H.
Published: March 2007

This article presents the high-level control module and user interface of the Dynamic and Strategic Control of Cooperating Manipulators (DASCCOM) project at Stanford University's Aerospace Robotics Laboratory. In addition to cooperative dynamic control, DASCCOM incorporates real-time vision- based feedback, a novel strategic programming technique, and an iconic "object-only" graphical user interface. By focusing on the vertical integration problem, we are examining not only these subsystems, but also their interfaces and interactions.

The control system implements a multilevel hierarchical structure interconnected via a real-time network. At the highest level, a mouse-driven graphical user interface allows an opera tor to direct the activities of the system conceptually. Strategic command is provided by an event-driven finite state machine. This methodology provides a powerful yet flexible technique for managing concurrent system interactions. The dynamic controller implements object impedance control —an extension of Neville Hogan's impedance control concept to cooperative multiple-arm manipulation of a single object.

This article concentrates on user interfacing techniques and strategic programming capabilities. These modules allow the user to directly specify conceptual object relationships.

Experimental results are presented, showing the system lo cating and identifying a moving object, "catching" it, and performing a simple cooperative assembly. Each of these operations is executed autonomously, with only object-level task-specification direction from a remote operator.
A Theoretical and Experimental Investigation of Impact Control for Manipulators
Authors: Volpe Richard , Khosla Pradeep
Published: March 2007

This article describes a simple control strategy for stable hard- on-hard contact of a manipulator with the environment. The strategy is motivated by recognition of the equivalence of pro portional gain explicit force control and impedance control. It is shown that negative proportional force gains, or impedance mass ratios less than unity, can equivalently provide excel lent impact response without bouncing. This result is indicated by an analysis performed with an experimentally determined arm/sensor/environment model. The results are corroborated by experimental data from implementation of the control al gorithms on the CMU DD Arm II system. The results confirm that manipulator impact against a stiff environment without bouncing can be readily handled by this novel control strategy.
Trajectory Generation for Sensor-Driven and Time-Varying Tasks
Authors: Lloyd John , Hayward Vincent
Published: March 2007

In on-line robot trajectory generation, a connecting polynomial is normally used to remove discontinuities in velocity and acceleration between adjacent path segments. This article presents a new technique for performing such transitions in which adjacent path segments are "blended" together, with excess acceleration being removed using an estimate of the initial path velocities. Because this method requires no advance knowledge of the path segments, it can handle situations where the paths are changing with time (as when tracking sensor or control inputs). The method can also be used to adjust the spatial shape of the transition curve (such as to have it pass around or through the "via point"), which may be necessary to handle constraints imposed by different types of manipulator tasks. When the blended paths are nonlinear, it is possible to set a tight bound on the resulting transition acceleration. The blend technique works directly for vector trajectories and can be modified to handle 3-D rotational trajectories. A simple trajectory generation algorithm is presented as an illustration.
Computation and Implementation of Digital Time-Optimal Feedback Controllers for an Industrial X-Y Robot subjected to Path, Torque, and Velocity Constraints
Authors: Van Willigenburg L.G.
Published: March 2007

For an industrial X-Y robot, in which the links are subjected to torque and velocity constraints, the time-optimal control prob lem is solved where the robot motion is constrained to follow an arbitrary path. A numerical procedure to compute the solu tion is presented and demonstrated. The solution consists of a continuous-time state trajectory and open-loop control. Because the X-Y robot is controlled by a digital computer, a recently developed numerical procedure to compute optimal tracking digital controllers is applied to the solution to arrive at an implementable digital time-optimal feedback controller that accounts for modeling errors as well. Experimental results ob tained after implementation of the digital time-optimal feedback controllers are presented for two paths. The robot dynamics include both viscous and Coulomb friction. The extension of the solution and numerical procedures to general rigid ma nipulators, including both viscous and Coulomb friction, is straightforward.
An Investigation of Impedance Control for Robot Manipulators
Authors: McCormick W. , Schwartz H.M.
Published: March 2007

This article documents investigations into impedance control carried out on a direct drive robot manipulator. Both linear and nonlinear versions of impedance contrallers have been investigated. The two impedance controllers have been simu lated numerically and implemented on Carleton University's direct drive robot. The performance of these controllers is ex perimentally compared in terms of force trajectory following and contact stability. The article highlights the practical and experimental limitations of the proposed methods. Furthermore, the experimental results indicate that the controller design, the manipulator kinematics, and the desired task must all be considered and evaluated simultaneously.
Shape from Diameter
Authors: Rao Anil S. , Goldberg Kenneth Y.
Published: March 2007

Our objective is to automatically recognize parts in a struc tured environment (such as a factory) using inexpensive and widely available hardware. In this article we consider the pla nar problem of determining the convex shape of a polygonal part from a sequence of projections. Projecting the part onto an axis in the plane of the part produces a scalar measure, the diameter, which is a function of the angle of projection. The diameter of a part at a particular angle can be measured using an instrumented parallel-jaw gripper.

First, we present the negative result that shape cannot be uniquely recovered: for a given set of diameter measurements, there is an (uncountably) infinite set of polygonal shapes con sistent with these measurements. Because most of these shapes have parallel edges of varying lengths, we consider the related problem of identifying a representative polygon with no par allel edges. We show that, given a diameter function, deciding whether such a polygon exists is NP-complete.

These results motivate us to consider the problem of recog nizing a part from a known (finite) set of parts. Given a set of polygonal parts with a total of N faces, can we find the short est sensing plan for disambiguating the parts? Only diameters at n ≤ N stable faces can be measured. We construct an in ternal representation of these stable diameters in O(N + n 3) time and then give two planning algorithms: one constructs an optimal sensing plan in time O( n42 n), the other constructs a suboptimal sensing plan in time O( n2 log n). Neither plan requires more than n measurements.
Singularities, Stable Surfaces, and the Repeatable Behavior of Kinematically Redundant Manipulators
Authors: Roberts Rodney G. , Maciejewski Anthony A.
Published: March 2007

There has been significant interest in the periodic behavior, generally referred to as repeatability, exhibited by a kine matically redundant manipulator while performing a cyclic end-effector motion. Much of the early work in this area has been restricted to planar manipulators whose configuration is described in terms of absolute joint angles to simplify the problem. Unfortunately, this has resulted in the observation of certain phenomena that are unique to this special case and that do not describe the behavior of more complicated ma nipulators. The goal of this work is to clarify some possible misconceptions concerning the limiting behavior of a redun dant manipulator under nonconservative control strategies, with particular emphasis on pseudoinverse control. In particular, stable surfaces are shown to be extremely rare, and a weaker property, referred to as repeatable trajectories, is responsible for the repeatable behavior observed in previous work. It is also shown that the Lie bracket condition need not be satisfied for this type of repeatable behavior to occur and that such trajectories need not have zero torsion, as has been previously suggested.
Real-Time Visual Servoing Using Controlled Illumination
Authors: Urban J.P. , Motyl G. , Gallice J.
Published: March 2007

A real-time visual servoing approach is applied to robotics tasks consisting of the positioning of the end effector with respect to a priori known polyhedral objects. The vision appa ratus is constituted by a compact CCD camera rigidly coupled with two laser stripes mounted on the wrist of a robot ma nipulator. The objective is to servo the robot end effector at a constant position and orientation with respect to a known object in three-dimensional space in the field of view of the sensory system.

The approach is expressed in terms of sensor-based control (Samson et al. 1991) applied to visual servoing (Chaumette 1990; Urban 1990). In the case of camera—light stripe coupling, the elementary visual signals used for visual servoing are the points of discontinuity in the light stripes. The feasibility of the approach is demonstrated in a factory automa tion task consisting of the positioning of the end-effector tool over a vehicle battery. Both simulation and experimentation results are presented, proving the robustness and stability of the algorithm.
Planning and Control of Robotic Juggling and Catching Tasks
Authors: Buehler M. , Koditschek D.E. , Kindlmann P.J.
Published: March 2007

A new class of control algorithms—the "mirror algorithms"— gives rise to experimentally observed juggling and catching behavior in a planar robotic mechanism. The simplest of these algorithms (on which all the others are founded) is provably correct with respect to a simplified model of the robot and its environment. This article briefly reviews the physical setup and underlying mathematical theory. It discusses two significant extensions of the fundamental algorithm to juggling two objects and catching. We provide data from successful empirical verifi cations of these control strategies and briefly speculate on the larger implications for the field of robotics.
Dynamic Walking of a Vehicle With Two Telescopic Legs Controlled by Two Drives
Authors: Grishin A.A. , Formal'sky A.M. , Lensky A.V. , Zhitomirsky S.V.
Published: March 2007

This article describes a walking vehicle with two telescopic legs that was designed at the Institute of Mechanics at Moscow University. The vehicle is driven by two DC drives. Its con trol system comprises a computer, hardware servosystems, and power amplifiers. An adaptive algorithm has been developed for control of vehicle locomotion. This algorithm is based on the tracking of the commanded path. A part of the path is planned by the computer in advance using a mathematical model of the vehicle. The rest is built up during walking of the vehicle based on the information on its state. In the ex periments, the designed control algorithm was successfully implemented.
A Group Theoretic Formalization of Surface Contact
Authors: Yanxi Liu  , Popplestone Robin
Published: March 2007

The surface contacts between solids are always associated with a set of symmetries of the contacting surfaces. These symmetries form a group known as the symmetry group of the surface.

In this article we develop a group theoretic formalization for describing surface contact between solids. In particular we define (1) primitive and compound features of a solid, (2) a topological characterization of these features, and (3) the symmetry groups of primitive and compound features.

The symmetry group of a feature is a descriptor of the fea ture that is at once abstract and quantitative. We show how to use group theory concepts to describe the exact relative motion (position) of solids under surface contacts, which can be either rigid or articulated. The central result of this article is to prove the following:

1. When primitive features of a solid are mutually dis tinct, 1-congruent or 2-congruent, the symmetry group of a compound feature can be expressed in terms of the intersection of the symmetry groups of its primitive features.

2. When two solids have surface contact, their rela tive positions can be expressed as a coset of their common symmetry group, which in turn can be ex pressed in terms of the intersections of the symmetry groups of the primitive features involved in this con tact.

These results show that using group theory to formalize surface contacts is a general approach for specifying spatial relationships and forms a sound basis for the automation of robotic task planning. One advantage of this formulation is its ability to express continuous motions between two surface- contacting solids in a computational manner and to avoid combinatorics arising from multiple relationships, especially from discrete symmetries in the assembly parts and their fea tures. At the end of this article, a geometric representation for symmetry groups and an efficient group intersection algorithm using characteristic invariants are described.
A Single-Point Calibration Technique for a Six Degree-of-Freedom Articulated Arm
Authors: Edwards Charles A. , Galloway Robert L.
Published: March 2007

A technique for calibrating an articulated device used in surgery is presented. The process requires only one point in the work envelope of the device to be known. The calibration procedure discussed, a trinary search technique, improves the performance of the articulated device three- to five-fold.
Motion Planning Amid Transient Obstacles
Authors: Fujimura Kikuo
Published: March 2007

Motion planning in the presence of time-dependent obstacles is studied. Many of the prior approaches to motion planning problems assume that the obstacles always exist in the environ ment, whether they are stationary or in motion. In this article, I consider the case that the environment contains obstacles whose existing periods are dependent on time (i.e., they can appear and disappear in the environment). This formulation allows us to model a variety of time-varying situations that can arise in application domains. A concept similar to that of visibility is used to solve the problem. An algorithm is pre sented to generate a motion in such a dynamic domain, its time-minimality is proved, and computation time is analyzed.
Analysis of the Dynamics of a Six-Legged Vehicle
Authors: Qiu Xiding  , Gao Yimin  , Zhuang Jide
Published: March 2007

A six-legged vehicle with a simple leg mechanism and eight degrees of freedom is presented in this article. Dynamic simula tions are carried out. The results from the simulations indicate that it has an advantage over others.
Visualization of Dual-Arm Robot Motion Space Under Kinematic Constraints
Authors: Tarn T.J. , De P.K. , Bejczy A.K. , Li Z.
Published: March 2007

This article presents a technique for determining and visual izing the geometric motion capabilities of dual-arm robotic systems when the arms work on an object in a closed kine matic chain configuration, taking account of robot arms' base placements, object dimensions, object holding and contact constraints, and space occupancy conflicts of the two arms' links. The constrained and object orientation restricted motion space in general can be visualized as a complex 3D object with hidden unreachable holes or cavities of varying shapes. An automated visualization methodology is presented together with its graphical implementation, illustrated by an example. The methodology is an inverse computer vision technique in the sense that it creates rather than recognizes visual forms.
Comparison of the Assumed Modes and Finite Element Models for Flexible Multilink Manipulators
Authors: Theodore Rex J. , Ghosal Ashitava
Published: March 2007

The objective of this paper is to compare two discretization models—namely, the assumed modes and finite element mod els—to efficiently represent the link flexibility of robot manip ulators. We present a systematic modeling procedure based on homogeneous transformation matrices for spatial multilink flexible manipulators with both revolute and prismatic joints. The Lagrangian formulation of dynamics and computer algebra are employed to derive closed-form equations of motion. We show that fewer mathematical operations are required for in ertia matrix computation in the finite element model compared with the assumed modes formulation; however, because the number of state space equations are more, the numerical sim ulation time may be greater for finite element models. Use of the finite element model to approximate flexibility usually gives rise to overestimated stiffness matrix. We analytically show that overestimation of structure stiffness may lead to unstable closed-loop response of the original manipulator system, using a model-based control law. We illustrate the complexity owing to the time-dependent frequency equation of the assumed modes model arising in a prismatic jointed flexible link with payload and in manipulators with more than one link with revolute joints. We describe a novel method based on the differential form of the frequency equation to simulate such systems. A model-based decoupling control law is used to compare the dynamic responses of the manipulator system. The results are illustrated by numerical simulation of a flexible spatial RRP configuration robot.
Symbolic Calculation of the Base Inertial Parameters of Closed-Loop Robots
Authors: Khalil Wisama , Bennis Fouad
Published: March 2007

This article presents a symbolic solution to determine the base inertial parameters of robots containing closed loops. The method gives most of the base inertial parameters directly and in many cases even gives all the base inertial parameters. The solution is obtained using recursive relations without cal culating the energy or the dynamic model of the robot; the constraint equations of the loops need not be obtained. New results concerning the base inertial parameters of tree structure robots are also given.
Robot Grippers for Use With Fibrous Materials
Authors: Monkman G.J.
Published: March 2007

This article demonstrates a range of robot gripping techniques suitable for use with carbon and glass frber sheets. Many of the grippers discussed were originally designed for use with textile fabrics and similar sheet materials, and their suitability for the handling of carbon and glass fiber sheets, together with some commonly used filler materials, is considered. Criteria are outlined for selecting the correct gripping technique for the desired task, taking into account the many different types of material structure available.
Hand-Eye Calibration
Authors: Horaud Radu , Dornaika Fadi
Published: March 2007

Whenever a sensor is mounted on a robot hand, it is important to know the relationship between the sensor and the hand. The problem of determining this relationship is referred to as the hand-eye calibration problem. Hand-eye calibration is impor tant in at least two types of tasks: (1) map sensor centered measurements into the robot workspace frame and (2) tasks allowing the robot to precisely move the sensor. In the past some solutions were proposed, particularly in the case of the sensor being a television camera. With almost no exception, all existing solutions attempt to solve a homogeneous matrix equation of the form AX = X B. This article has the following main contributions. First we show that there are two possible formulations of the hand-eye calibration problem. One formu lation is the classic one just mentioned. A second formulation takes the form of the following homogeneous matrix equation: MY = M'YB. The advantage of the latter formulation is that the extrinsic and intrinsic parameters of the camera need not be made explicit. Indeed, this formulation directly uses the 3 x4 perspective matrices (M andM' ) associated with two positions of the camera with respect to the calibration frame. Moreover, this formulation together with the classic one covers a wider range of camera-based sensors to be calibrated with respect to the robot hand: single scan-line cameras, stereo heads, range finders, etc. Second, we develop a common mathematical framework to solve for the hand-eye calibration problem using either of the two formulations. We represent rotation by a unit quaternion and present two methods: (1) a closed-form solution for solving for rotation using unit quaternions and then solving for translation and (2) a nonlinear technique for simultane ously solving for rotation and translation. Third, we perform a stability analysis both for our two methods and for the lin ear method developed by Tsai and Lenz (1989). This analysis allows the comparison of the three methods. In light of this comparison, the nonlinear optimization method, which solves for rotation and translation simultaneously, seems to be the most robust one with respect to noise and measurement errors.
Strategies for Increasing the Tracking Region of an Eye-in-Hand System by Singularity and Joint Limit Avoidance
Authors: Nelson Bradley J. , Khosla Pradeep K.
Published: March 2007

An eye-in-hand system visually tracking objects can fail when the manipulator encounters a kinematic singularity or a joint limit. A solution to this problem is presented in which objects are visually tracked while the manipulator simultaneously avoids kinematic singularities and manipulator joint limits by moving in directions along which the tracking task space is unconstrained or redundant. A manipulability measure is introduced into the visual tracking objective function, providing an elegant and robust technique for deriving a control law that visually tracks objects while accounting for the configuration of the manipulator. Two different tracking strategies, one using a standard visual tracking strategy and the other using the newly proposed strategy, are experimentally compared on an actual hand/eye system. The experimental results demonstrate the effectiveness of the new method by showing that the tracking region of a manipulator tracking objects with planar motion can be greatly increased.
On the Closure Properties of Robotic Grasping
Authors: Bicchi Antonio
Published: March 2007

The form-closure and force-closure properties of robotic grasp ing are investigated. Loosely speaking, these properties are related to the capability of the robot to inhibit motions of the workpiece in spite of externally applied forces. In this article, form-closure is considered as a purely geometric property of a set of unilateral (contact) constraints, such as those applied on a workpiece by a mechanical fixture, while force-closure is related to the capability of the particular robotic device being considered to apply forces through contacts. The concepts of partial form- and force-closure properties are introduced and discussed, and an algorithm is proposed to obtain a synthetic geometric description of partial form-closure constraints. Al though the literature abounds with form-closure tests, proposed algorithms for testing force-closure are either approximate or computationally expensive. This article proves the equiva lence of force-closure analysis with the study of the equilibria of an ordinary differential equation, to which Lyapunov's di rect method is applied. This observation leads to an efficient algorithm for assessing the force-closure property of the grasp.
Steering Three-Input Nonholonomic Systems: The Fire Truck Example
Authors: Bushnell L.G. , Tilbury D.M. , Sastry S.S.
Published: March 2007

In this article we steer wheeled nonholonomic systems that can be represented in a so-called chained form. Sufficient condi tions for converting a multiple-input system with nonholonomic velocity constraints into a multiple-chain, single-generator chained form via state feedback and a coordinate transfor mation are presented along with sinusoidal and polynomial control algorithms to steer such systems. Our example is the three-input nonholonomic system of a fire truck, or tiller truck. In this three-axle system, the control inputs are the steering velocities of both the first and third (or tiller) axles and the forward driving velocity of the truck. Simulation results are given for parallel parking, left hand turning, right hand turn ing, and changing lanes. Comparison is made to the same vehicle without tiller steering.
Perception, Planning, and Control for Autonomous Walking With the Ambler Planetary Rover
Authors: Krotkov Eric , Simmons Reid
Published: March 2007

Producing a robotic system that can operate autonomously on other planets is a challenging task: The robot must be ex tremely self-reliant; it must be able to operate on a limited power budget; and it must be able to traverse a wide range of rugged terrain features. This article describes an integrated software system that combines perception, planning, real-time control, and task-level control to navigate autonomously the Ambler, a six-legged rover. The overall approach to walking is highly deliberative: Where actions are goal-directed, steps are planned out in detail using explicit models of the terrain and the vehicle, and moves are checked for safety prior to execution. We believe that this approach is well-suited to meet ing the challenges of reliability, efficiency, and terrainability faced by autonomous planetary rovers. The Ambler system has been extensively tested, both indoors and outdoors, and the results confirm our expectations regarding the degree of system capability and performance afforded by our approach.
Discrete-Time Model Reference Adaptive Controller Designs for Robotic Manipulators
Authors: Yang Shiaw-Pyng , Woo Peng-Yung , Wang Rongdong
Published: March 2007

On-line computer control with high speed and accuracy is needed in industrial robotics. Thus, discrete-time controller design for robotic manipulators is necessary. In this article, the two continuous-time model reference adaptive control schemes presented in Yang and Woo (1992) are put forth in discrete forms.

The stability analysis stems from Lyapunov's Direct Method (Slotine and Li 1991), which guarantees the asymptotic stability of a system. Like any discrete-time control system, the time required for the computer to perform the necessary computation may result in extended sampling time, which could degrade the stability of the system. In this article, we obtain the sufficient condition of stability for the designed discrete-time controllers. A set of right sampling time and weighting factors are chosen to show the highly accurate tracking. Through the MATLAB software (PC MATLAB MANUAL 1992) simulation, we can see that the manipulator does follow the desired trajectory with high accuracy, even when the payload is changing. It proves the effectiveness of the designed controllers.
Soft Robotic Fingertips
Authors: Shimoga K.B. , Goldenberg A.A.
Published: March 2007

Three potential problems exist in multifingered robotic hands. First, the impact forces that result during each instant of grasping a rigid object can affect the functioning of the fingertip sensors. Second, a hand with hard fingers cannot securely grasp objects that have uneven surfaces due to the poor conformability of the fingers. Third, repetitive strains are induced into the fingers throughout a manipulation task. If they are not dissipated, the manipulation becomes jerky, the func tioning of the fingertip sensors is affected, and the life of the finger's skeletal structure may become short.

In this work, six fingertips constructed from plastic, rub ber, sponge, fine powder, paste, and gel are experimentally compared for their ability to overcome the above problems. Results show that the sponge fingertip is the most suitable and the plastic fingertip the least suitable for our application. For practical reasons, however, gel is preferred over sponge. In view of these results, it is recommended that future robotic hands employ soft fingers, or at least fingers with soft tips, constructed out of carefully chosen materials.
Soft Robotic Fingertips
Authors: Shimoga K.B. , Goldenberg A.A.
Published: March 2007

Part I of this article showed that making robotic fingers from soft materials helps them cope with the following three prob lems. First, the impact forces that occur at the instant of grasping are reduced. Second, commonly used objects with uneven surfaces can be grasped comfortably due to the confor mal nature of the soft fingers. Third, the repeated strains that are induced during manipulations are dissipated. The problem to solve now is that of modeling and controlling the overall impedance of a soft finger or of a finger that has a soft tip. This is the issue addressed in this part.

This part presents the experimental determination of the pas sive impedance parameters of a soft (gel-filled) fingertip and formulates an approach to account for the soft fingertip model when controlling the overall impedance of a finger that carries the soft tip. The approach is demonstrated via four experi ments, each with a unique goal. Also showed experimentally is how the presence of passive damping helps reduce the peak impact forces that occur as a rigid object is grasped by the fingers of a robotic hand.
The Calibration Index and Taxonomy for Robot Kinematic Calibration Methods
Authors: Hollerbach John M. , Wampler Charles W.
Published: March 2007

The major approaches toward kinematic calibration are unified by considering an end-point measurement system as forming a joint and closing the kinematic loop. A calibration index is in troduced, based on the mobility equation, that considers sensed and unsensed joints and single and multiple loops and ex presses the surplus of measurements over degrees of freedom at each pose. Past work using open-loop calibration, closed-loop calibration, and screw axis measurement is classified according to this calibration index. Numerical issues are surveyed, in cluding task variable scaling, parameter variable scaling, rank determination, pose selection, and input noise handling.
Communication
Authors: Sundareswaran V. , Bouthemy P. , Chaumette F.
Published: March 2007

The visual servoing formalism provides a framework for achieving tasks in an active closed-loop fashion based on visual information. We consider a typical visual servoing ap proach that uses geometric information about image features for controlling the position and attitude of a camera and extend the applicability of this approach by using image motion infor mation. We present two different approaches to visual tasks that use motion information. The first uses the focus of expansion, which is related to the translational velocity of the camera. The second incorporates the parameters of the 2D affine motion model in control equations. Both of these approaches are il lustrated by means of a task of aligning the optical axis of the camera with the unknown direction of translational motion of the system on which it is mounted. Results of simulation experi ments and real experiments on a six degrees of freedom (DOF) robot with a camera on its end effector are presented.
On the Existence of Solutions in Modular Fixturing
Authors: Yan Zhuang  , Goldberg Ken
Published: March 2007

A fixture is a device that locates and holds parts during ma chining or assembly. A modular fixture employs reusable components on a regular lattice. Given a part, machinists combine intuition with trial and error to design an appropriate fixture. When a machinist is unable to find a design, it may be that (1) a feasible design was overlooked or (2) no feasible design exists. Complete algorithms for modular fixturing, such as those in Brost and Goldberg (1994), ensure that no fixture design is overlooked. But the question remains: are there Parts for which no modular fixture exists?

For the class of modular fixtures using three locators and a clamp, we show that there exists a class of polygonal parts that cannot be fixtured. We believe that this is the first negative re sult in the area of fixturing. We also show two positive results, namely, that a modular fixture always exists when we broaden the class of fixtures to include a T-slot and narrow the class of parts. We show that one class of fixtures strictly dominates the other. These results raise a number of open problems concern ing the existence of solutions for other classes of fixtures and parts and suggest a hierarchy of fixturing models.

1. Nguyen used the term "force-torque closure" to describe what is more commonly called form closure (Trinkle 1992).

2. Nguyen used the term independent regions of contact.
On the Synthesis of a Nominal Trajectory for Control Law of a One-Link Flexible Arm
Authors: Aoustin Y. , Formal'sky A.
Published: March 2007

In this article we propose a method for the design of a nominal trajectory for a flexible one-link manipulator. This trajectory is near time-optimal. The torque control law consists of two parts: the commanded feedforward torque and the linear an gular position and velocity feedback. Feedforward signal is proportional to nominal angular acceleration of the hub. On the first time interval, the feedforward torque approaches con tinuously to a value that is a little smaller than the maximal possible torque, then it remains constant, and then it goes to zero. On the second interval, the feedforward torque ap proaches continuously to a value that is a little greater than the minimal possible torque, then it remains constant, and then it goes to zero. On the third time interval, feedforward signal is zero. We compute the corresponding nominal (desired) angu lar acceleration, velociy, and position of the hub as functions of time. The last two functions are fed to the linear feedback system. The angular acceleration is such that, on the first time interval, the hub moves with "large" acceleration in one di rection, and the link bends on the opposite side. On the second time interval, the hub moves with deceleration, and the link bends in the direction of the motion. On the third time interval we stabilize the arm near its desired position.

In the experiments, the designed control algorithm was successfully implemented. We analyze these experiments from a theoretical point of view
Motion Planning for Carlike Robots Using a Probabilistic Learning Approach
Authors: Švestka Petr , Overmars Mark H.
Published: March 2007

In this article, a recently developed learning approach for robot motion planning is extended and applied to two types of carlike robots: normal ones, and robots that can only move for ward. In this learning approach the motion planning process is split into two phases: the learning phase and the query phase. In the learning phase, a probabilistic roadmap is incremen tally constructed in configuration space. This roadmap is an undirected graph where nodes correspond to randomly chosen configurations in free space and edges correspond to simple collision-free paths between the nodes. These simple motions are computed using a fast local method. In the query phase, this roadmap can be used to find paths between different pairs of configurations.

The approach can be applied to normal carlike robots (with nonholonomic constraints) by using suitable local methods that compute paths feasible for the robots. Application to carlike robots that can move only forward demands a more fundamen tal adaptation of the learning method; that is, the roadmaps must be stored in directed graphs instead of undirected ones.

We have implemented the planners, and we present experi mental results that demonstrate their efficiency for both robot types, even in cluttered workspaces. Also, we prove probabilis tic completeness of the planners.

1. A robot is fully controllable iff the existence of a path in the open free C space implies the existence of a feasible path.

2. By "metric," we simply mean a function of type C x C → R+ without any restrictions.

3. Formally, this requires a minor adaptation of the general outline of the learning algorithm, as presented in Section 3.1. Line 7. will be: if -connected(c, n) Λ L( c, n) ⊂ free C space then E = E U {( c, n)}.

4. This does not necessarily hold if P1 consists of just one or two circular arcs of maximal curvature. In this case, however, P1 can be found directly with the local planner.

5. We say a path Q lies within distance ∈ of a path R, iff ∀ q ∈ Q : ∃r ∈ R : |q - r| ≤ ∈ (in C space).
Nonlinear Control for a Train-like Vehicle
Authors: de Wit Carlos Canudas , NDoudi-Likoho Ange Désiré , Micaelli Alain
Published: March 2007

This article presents a feedback nonlinear control law for a train-like vehicle (TLV) that is used in nuclear power-station maintenance. The front cart is either manually or automatically guided. The rear carts are feedback controlled. The control objective is to ensure that the rear carts track the path pro duced (on-line) by the front cart. We also present a method for on-line reconstruction of this path. We present some simulation results of the feedback controller system, as well as experi mental results performed on a TLV prototype passing through singular configurations.
Invariant Hybrid Force/Position Control of a Velocity Controlled Robot with Compliant End Effector Using Modal Decoupling
Authors: De Schutter Joris , Torfs Dirk , Bruyninckx Herman , Dutré Stefan
Published: March 2007

A new method based on modal decoupling is proposed for the hybrid force/position control of a robot during constrained mo tion. The robot is equipped with an internal velocity controller, i.e., the control commands issued by the hybrid force/position controller are desired (joint) velocities. This velocity controller is supposed to be very stiff or of high bandwidth, as is the case for most commercial industrial robots. As a result, the robot dynamics are negligible compared to the contact dynam ics, which have low frequency because passive compliance is concentrated in the robot end effector. The new method incor porates results from the control of flexible robots, to damp out undesired vibrations of the end effector through active control. The contact dynamics during constrained motion are de scribed by a MIMO system: the inputs are the joint velocities; the outputs are the forces and torques measured by the wrist sensor. Using modal decoupling, this MIMO system is decom posed into its vibrational modes, i.e., a set of decoupled SISO systems. These modes are either unconstrained real vibrational modes, or constrained, and hence degenerated modes. Both are easy to control to satisfy the overall requirements of desired contact forces and vibration free motion of the manipulated object.

Attention is paid to the invariance of the approach; i.e., the resulting robot behavior is independent of the choice of reference frame and the choice of units.

The article contains experimental results of free space and partially constrained motion. Both confirm the theoretical re sults.

2. Usually, forces and torques are measured using strain gauges or dis placement transducers.

3. In practice, the effect of w g can easily be compensated for, by using a gravity model of the MO.

4. Proportional damping is an invariant concept; i.e., α and β are indepen dent of the representation of C, M and K, but few real systems exhibit this characteristic. Nevertheless, the assumption of proportional damp ing is frequently used for the ease of mathematical treatment. Indeed, Caughey (1960) showed that proportional damping is a sufficient—but not a necessary—condition for the existence of real modes.

5. Mathematically, this is easily verified using the positive definiteness of M and K, and the positive semidefiniteness of projection operator JJ †M.

6. In practice, such discontinuities are avoided by proper trajectory genera tion, but here they are deliberately introduced.
Generalized Polyhedral Object Recognition and Localization Using Crossbeam Sensing
Authors: Wallack Aaron S. , Canny John F.
Published: March 2007

Object localization is a fundamental task in industrial automa tion. In this article, we present a recognition and localization technique based upon binary beam sensors. Binary beam sen sors, which consist of modulated LED light sources and de tectors, are appropriate for manufacturing applications due to their reliability, high accuracy, robustness, inexpensiveness, and ease of calibration. By extracting sufficient information, recognition and localization can be performed as fast (~ 0.1 s) and as accurately (~ 25 microns) as high-speed manufactur ing requires. Generalized polyhedral objects are recognized and localized by being passed through a crossbeam sensor which is a set of coplanar oriented binary light-beam sensors; robot positions are recorded when the beam sensors' outputs change. Recognition and localization share two subproblems: the correspondence problem (the problem of interpreting the sensed features in terms of the model features), and the pose- estimation problem (the problem of estimating the object's pose from the sensed data and an interpretation of the sensed fea tures in terms of model features). In Wallack and Manocha (1994), we described a pose-estimation technique for crossbeam sensor data. In this article, we present two methods for solving the correspondence problem for crossbeam sensor data: a lin ear time completely on-line method, and a constant-time on-line method that utilizes preprocessing.
Designing a Parallel Manipulator for a Specific Workspace
Authors: Merlet J.-P.
Published: March 2007

We present an algorithm to determine all the possible ge ometries of Gough-type 6-DOF parallel manipulators whose workspace must include a desired workspace. This desired workspace is a set of geometric objects, limited here to points and segments, which describes the desired locations of the cen ter of the moving platform. It is assumed that the orientation of the platform is fixed for each given object. This algorithm takes into account the leg-length limits, the mechanical limits on the passive joints, and interference between links.
Development and Experimentation of a Fast 3-DOF Camera-Orienting Device
Authors: Gosselin Clément M. , St-Pierre Éric
Published: March 2007

In this article, the mechanical design and the practical im plementation of a high-performance, three-degree-of-freedom, camera-orienting device is addressed. The agile eye, as it is referred to, is based on a spherical 3-DOF parallel mechanism, which leads to high-performance dynamics. The kinematics of such a mechanism is briefly recalled, and its mechanical prop erties are described. Then, experimental results obtained with the prototype are presented and commented upon. Because of its low-moving inertia and its inherent stiffness, the mechanism is capable of velocities larger than 1,000°ls and of accelera tions larger than 20,000°/s2 .