bluuebunny/crossref_metadata_2025 huggingface dataset:
A Preliminary Step for Path Tracking of Coordinated Robot Arms Based on Kinematics
Authors: Hemami A. , Cheng R.M.H.
Published: March 2007

This work concerns the kinematics of two collaborating robot arms handling an object. Such a task is much more difficult, both kinematically and dynamically, than when only one robot arm is involved, in view of the fact that (1) the two end ef fectors must always remain in their respective workspace and (2) the mutual forces from the two arms must contribute to giv ing the object held the required motion. One case in material handling with two arms is when the orientation of the object is not of importance in transition. In this sense, if a task becomes impossible to continue because of the inaccessibility of the required position and orientation by the end effector, it might be possible to overcome the difficulty by performing the nec essary orientation adjustments at each instant during motion. As a preliminary step toward this goal, this problem is stud ied for one robot arm and is presented with some illustration examples.
The Design of Isotropic Manipulator Architectures in the Presence of Redundancies
Authors: Angeles Jorge
Published: March 2007

The design of redundant isotropic architectures for robotic nia nipulators is the subject of this article. A manipulator is said to have a redundant isotropic architecture if (1) its number of controlled axes is greater than the dimension of its task space. and (2) it is possible for the manipulator to attain configura tions at which all the singular values of its Jacobian matrix are identical and nonzero. The concept of isotropy, which has already been applied to the design of nonredundant manip ulators, is applied to the design of redundant ones. General geometric conditions on the manipulator parameters and on its configuration variables under which isotropy is attained are derived.
Existence and Uniqueness for Shape From Shading Around Critical Points: Theory and an Algorithm
Authors: Saxberg Bror V. H.
Published: March 2007

To approach the difficult question of existence and unique ness of solutions for the shape-from-shading problem, we have examined the image irradiance equation using notation and concepts from dynamic systems theory. The method of charac teristic strips used by Horn (1975) defines a dynamic system on a four-dimensional space. Using modern methods for analyzing the behavior of dynamic systems, general uniqueness results and a new shape-from-shading algorithm emerge based on the image dynamic system. Solution surfaces for the shape-from- shading problem are invariant manifolds of the flow generated by the image dynamic system. The stable and unstable man ifolds associated with certain critical points in the image determine locally unique solution surfaces. A theorem about unstable manifolds (the Lambda Lemma) suggests a class of computational methods for finding stable and unstable mani folds around these critical points. A simple example of such a method is described and found to be robust in the presence of image noise and errors in assumptions about the light source.
A 3D World Model Builder with a Mobile Robot
Authors: Zhengyou Zhang  , Faugeras Olivier
Published: March 2007

This article describes a system to incrementally build a world model with a mobile robot in an unknown environment. The model is, for the moment, segment based. A trinocular stereo system is used to build a local map about the environment. A global map is obtained by integrating a sequence of stereo frames taken when the robot navigates in the environment. The emphasis of this article is on the representation of the uncer tainty of 3D segments from stereo and on the integration of segments from multiple views. The proposed representation is simple and very convenient to characterize the uncertainty of segment. A Kalman filter is used to merge matched line seg ments. An important characteristic of our integration strategy is that a segment observed by the stereo system corresponds only to one part of the segment in space, so the union of the different observations gives a better estimate on the segment in space. We have succeeded in integrating 35 stereo frames taken in our robot room.
Robust Force Control of a Robot Manipulator
Authors: Dawson D.M. , Lewis F.L. , Dorsey J.F.
Published: March 2007

In this article, we develop a robust position/force controller based on the impedance approach without requiring exact knowledge of the robot dynamics. The controller is constructed so that a desired positional trajectory can be followed along the surface of the environment while the forces exerted on the environmental surface are regulated according to a target impedance. A global uniform ultimate boundedness result is ob tained for the position tracking error and the force regulation error (i.e., the error between the actual manipulator impedance and the desired target impedance). The controller only requires measurement of the end-effector force, joint velocity, and joint position.
Recursive Formulation of Operational Space Control
Authors: Kreutz-Delgado K. , Jain A. , Rodriguez G.
Published: March 2007

A recently developed spatial operator algebra approach to modeling and analysis of multibody robotic systems is used to develop O(n) recursive algorithms that compute the op erational space mass matrix and the operational space coriolis/centrifugal and gravity terms of an n-link serial manipulator. These algorithms enable an O(n) recursive im plementation of operational space control.
Magnetic Levitation Servo for Flexible Assembly Automation
Authors: Tsuda Masahiro , Higuchi Toshiro , Fujiwara Shigeki
Published: March 2007

Active magnetic levitation with servo control has the inherent potential to be a friction-free, backlash-free, lubrication-free, and precision multi-degree-of-freedom (DOF) actuator with the capability of multi-axis force sensing. However, magnetic levitation has been conventionally used only for contactless suspension such as magnetic bearings and magnetically levi tated vehicles. This article develops an application of magnetic levitation for actuation and force sensing and calls such a sys tem magnetic levitation servo to distinguish from conventional suspension-only systems.

On the other hand, flexible assembly automation is a techni cal and engineering challenge to be accomplished promptly. For this purpose, the authors have developed a Magneti cally end-effector-levitating Instrument for a Skilled-Task- undertaking Expert Robot (MEISTER) by applying magnetic levitation servo.

The MEISTER is located between a wrist and an end effec tor in a manipulator to levitate and control the end effector by magnetic forces without any mechanical contact. This friction- free and backlash-free mechanism enables precision control of multi-DOFs and permits the MEISTER to have three versatilely functional properties: (1) programmable compliance: the com pliance and viscous damping of supporting an end effector are magnetically changeable by software; (2) precision multi-DOF actuation: the position and attitude of an end effector can be accurately controlled without friction or backlash by chang ing magnetic forces; and (3) multi-axis force sensing: external forces and moments acting on an end effector can be computed by the MEISTER without any additional sensory equipments from the force equivalent equation. By using these functional properties, the MEISTER can correct a minute misalignment between a couple of mating parts to automate precision inser tion.

To investigate the fundamental performance of the MEISTER in experiments, a prototype of a 5-DOF controllable MEISTER is developed. The experiments have shown the following re sults :

1. The MEISTER can be used as an advanced/active Remote Center Compliance (RCC) device.

2. The prototype can quickly position the 5-DOF of a mat ing part with 1-μm resolution.

3. It can measure a five-axis resultant force acting on a part with a resolution of about 0.04N and 0.001 N m.

4. It can successfully perform the RCC assembly method, the ideal RCC method, and the float method in precision insertion operations with the clearance ratio of 0.0004 (where a workpiece has a 20-mm diameter and the clear ance is 8 μm.)
A New Computational Structure For Real-Time Dynamics
Authors: Izaguirre Alberto , Hashimoto Minoru , Paul Richard P. , Hayward Vincent
Published: March 2007

We present an efficient structure for the computation of robot dynamics in real time. The fundamental characteristic of this structure is the division of the computation into a high-priority synchronous task and low-priority background tasks, possibly sharing the resources of a conventional computing unit based on commercial microprocessors. The background tasks compute the inertial and gravitational coefficients as well as the forces due to the velocities of the joints. In each control sample pe riod, the high-priority synchronous task computes the product of the inertial coefficients by the accelerations of the joints and performs the summation of the torques due to the velocities and gravitational forces. Kircanski et al. (1986) have shown that the bandwidth of the variation of joint angles and of their velocities is an order of magnitude less than the variation of the joint accelerations. This result agrees with the experiments that we have carried out using a PUMA 260 robot.

Two main strategies contribute to reduce the computational burden associated with the evaluation of the dynamic equa tions. The first involves the use of efficient algorithms for the evaluation of the equations. The second is aimed at reducing the number of dynamic parameters by identifying beforehand the linear dependencies among these parameters, as well as carrying out a significance analysis of the parameters' contri bution to the final joint torques.

We selected an iterative procedure for the computation of the inertial and gravitational coefficients (Featherstone 1984; Renaud 1985; Izaguirre and Paul 1986), and a recursive iter ation for the computation of the velocity torques (Khalil et al. 1986). In our experiments with a PUMA 260, we obtained a set of 52 linearly independent parameters from an initial set of 78 parameters. Identification of the parameters revealed only 23 parameters to be significant.

These reductions permit the calculation of the inertias and gravitational coefficients, for the PUMA 260 without load, with 98 multiplications and 70 additions and calculation of the ve lacity torques with 140 multiplications and 110 additions. In the case of an arbitrary load at the end effector, calculation of the inertias and gravitational coefficients requires 190 multi plications and 150 additions and that of the velocity torques, 200 multiplications and 170 additions. Velocity torques, inertial coefficients, and gravitational coefficients can be computed in the background in 20 ms using an Intel 8087 microprocessor. The synchronous task requires only six multiplications and six additions per joint.

The actual code used to evaluate this dynamic model is entirely computer generated from experimental data, requiring no other manual intervention than performing a campaign of measurements.
Exciting Trajectories for the Identification of Base Inertial Parameters of Robots
Authors: Gautier M. , Khalil W.
Published: March 2007

A common way to identify the inertial parameters of robots is to use a linear model in relation to the parameters and standard least-squares (LS) techniques. This article presents a method to generate exciting identification trajectories in order to minimize the effect of noise and error modeling on the LS solution. Using nonlinear optimization techniques, the condition number of a matrix W obtained from the energy model is minimized, and the scaling of its terms is carried out. An example of a three-degree-of-freedom robot is presented.
Path Planning Using a Tangent Graph for Mobile Robots Among Polygonal and Curved Obstacles
Authors: Liu Yun-Hui , Arimoto Suguru
Published: March 2007

This article proposes a tangent graph for path planning of mobile robots among obstacles with a general boundary. The tangent graph is defined on the basis of the locally shortest path. It has the same data structure as the visibility graph, but its nodes represent common tangent points on obstacle boundaries, and its edges correspond to collision-free common tangents between the boundaries and convex boundary seg ments between the tangent points. The tangent graph requires O( K2) memory, where K denotes the total number of convex segments of the obstacle boundaries. The tangent graph in cludes all locally shortest paths and is capable of coping with path planning not only among polygonal obstacles but also among curved obstacles.
Imperfect Form Tolerancing on Manifold Objects: A Metric Approach
Authors: Boyer M. , Stewart N.F.
Published: March 2007

In an earlier article we proposed a modeling space for objects defined in terms of tolerances, based on Requicha's ideas on variational classes. To do this, we introduced a certain number of requirements, including the requirements that objects within tolerance should be tamely homeomorphic to the nominal solid and that variational classes should be regular, in the relative topology defined by a certain metric dw and the set of objects tamely homeomorphic to the nominal solid. The practical con sequence of d w-regularity is to exclude variational classes that require all or part of the boundary of an admissible set to be in a fixed or exact position. The subscript in dw is intended to suggest weakness, as the metric in effect introduces a weak condition to be satisfied by the boundary of acceptable r-sets. These ideas led us to the definition of the R-classes, which we claim provides the appropriate definition for a permissible variational class in the context of object tolerancing. In par ticular, we proved that the position, size, and form tolerances ( S, Mp), ( S, Ms), and ( S, M f) are R-classes, at least in the simple case when S is an n-dimensional ball. Generalized ver sions of the regularized Boolean operations, operating not on r-sets but on R -classes, were also introduced; the R-classes are closed under these generalized versions of the regularized Boolean operations.

In this article we will extend these results to quite a wide class of position tolerances and present three possibilities for the introduction of a "slow variation constraint. " The latter will be done by means of new metrics d s, which im pose "strong" conditions on the boundary of acceptable sets. Stricter requirements, which ensure slow variation, will be im posed by adding the condition that variational classes be open with respect to these stronger metrics.

Finally, it will be shown how the usual "perfect form" approach to tolerancing may be viewed as a special case of the variational class approach by using an appropriately strong slow variation constraint.
Optimal Synthesis of Robot Manipulators Based on Global Dynamic Parameters
Authors: Singh J.R. , Rastegar J.
Published: March 2007

The local nature of inertial, nonlinear, and coupling character istics of manipulators is an impediment to their optimal design. In this article, a method to represent and measure the global and posture-independent measures of inertia, coupling, and nonlinear forces is presented. A new concept, referred to as the global inertia ellipsoid, which represents the global iner tial characteristics of a manipulator, is introduced. The global inertia ellipsoid is obtained by considering a weighted distri bution of the end-effector position over the workspace of the manipulator. Based on this concept, four global parameters, representing the global nonlinear, coupling, and inertial char acteristics of the manipulator, are obtained. The number of global parameters does not change with the degrees of freedom or the complexity of the manipulator structure. A probabilistic or deterministic description of payload range can be included while designing the manipulator. Criteria for the optimal de sign of manipulators are presented in the form of an objective function of the global parameters. The method is illustrated by the design of a 2R manipulator, a 2R manipulator with given payload range, and a 3R manipulator. The extension of the concept of the global inertia ellipsoid to task placement and task planning is discussed.
A Fully Decentralized Multi-Sensor System For Tracking and Surveillance
Authors: Rao B.S.Y. , Durrant-Whyte H.F. , Sheen J.A.
Published: March 2007

In many tracking and surveillance systems, multisensor config urations are used to provide a greater breadth of measurement information and also to increase the capability of the system to survive individual sensor failure. Most architectures currently used in such systems rely on having either a central processor where global data fusion takes place or a central communi cations medium through which all messages between sensors must pass. Such centralized architectures give rise to problems with communication and computational bottlenecks and are susceptible to total system failure should the central facility fail.

In this article we describe a multisensor surveillance system that achieves a high degree of survivability by employing a decentralized sensing architecture (Durrant-Whyte, Rao, and Hu 1990). Using CCD cameras and optical barriers the system is able to track (in real time) people and robots as they move around a factory room. The decentralized sensing architecture takes the form of a network of Transputer-based sensor nodes, each with its own processing facility, that together do not re quire any central processor, any central communication facility, or any common clock. In this architecture, computation is per formed locally, and communication occurs between any two nodes as and when required.

The starting point for the surveillance system is an algo rithm that allows complete decentralization of the multisensor Kalman filter equations among a number of sensing nodes. We develop the algorithm to ensure that internodal commu nication is minimized and can take place without any prior synchronization between nodes. By designing a suitable track management scheme, we are able to extend the system to cope with multitarget tracking. Finally, the specific sensors used in the implementation are interfaced to the algorithm, and the results of the working system are given.
A Reduced-Order Regressor and Its Application to Adaptive Robotic Control
Authors: Stepanenko Yury , Jing Yuan
Published: March 2007

Manipulator regressors are n x l matrix functions in the dynamic expressions τ = Y(q, q, q)ζr or (1/ D + σ)τ = W(q, q)ζr, which linearize the robot dynamics with respect to a properly defined inertia parameter vector ζr ∈ Rl. Many modern adaptive controllers require on-line computation of a regressor to estimate the unknown inertia parameters and ensure robustness of the closed-loop system.

Although the computation ofY(q, q, q) has been studied by Atkeson et al. (1985), Khosla and Kanade (1985), and Khosla (1989), the computation ofW(q, q) for a general n-link robot has not been reported in the literature. This article presents an algorithm to compute W(q, q) for a general n-link robotic manipulator The variables used to construct the regressor matrix are directly available from the outward iteration of a Newton-Euler algorithm; some additional arithmetic operations and first-order, low-pass filtering are needed. The identification of unknown inertia parameters is also discussed.
Combined Analytical- Pseudoinverse Inverse Kinematic Solution for Simple Redundant Manipulators and Singularity Avoidance
Authors: Kiréanski Manja V. , Petrovié Tatjana M.
Published: March 2007

One of the problems in real-time control of redundant manip ulators is considerably increased computational complexity compared with nonredundant robots. This is due to the rela tively high dimensions of the Jacobian matrix (6 x n, n ≥ 7) and the fact that its pseudoinverse is to be computed. On the other side, analytical solutions for nonredundant robots offer minimal numerical complexity (if such exist). The main idea in this article is to reduce computational complexity by com bining the analytical and the pseudoinverse solution. Namely, some of the joint angles that do not actively participate in the redundancy are evaluated analytically, while the group of joint angles that are actually redundant are solved using the pseu doinverse of the Jacobian matrix. In this way the dimensions of Jacobian are considerably reduced yielding several times less computational complexity. Further reduction of computational time is achieved by applying the gradient projection method (Dubey et al. 1991) to the actually redundant subrobot. In this article the solution is derived for a 7-DOF manipulator, and the possibility of application to other robots is discussed. At the end, simple performance criteria for avoiding wrist singularity that take into account the knowledge of robot geometry are proposed.
Coordinated Dynamic Hybrid Position/Force Control for Multiple Robot Manipulators Handling One Constrained Object
Authors: Yoshikawa Tsuneo , Zheng Xin-Zhi
Published: March 2007

In coordinated manipulation of a single object using multiple robot arms or a multifingered robot hand, simultaneous control of the object motion and of the internal force exerted by arms or fingers on the object is required. Furthermore, in the case where the motion of the object is constrained in some direc tions because of contact with its environment, control of the constraint force also becomes necessary. In this article, we pro pose a coordinated dynamic hybrid control method for multiple robotic mechanisms. The method takes the manipulator dynam ics and object dynamics into consideration and controls the motion of an object under constraint as well as the constraint force and the internal force. The motion control of an object in free space can be treated as a special case within the same formulation. A unified description for accommodating various grasp types is used. Several experimental results that show the validity of the proposed approach are presented. The results of this article will be useful for fine manipulation tasks using multiple robotic mechanisms, where the individual specifications of the object motion, the interaction force between the object and its environment, and the grasping force of the object are given.
Bounds on the Friction-Dominated Motion of a Pushed Object
Authors: Alexander J.C. , Maddocks J.H.
Published: March 2007

We consider the friction-dominated, or quasistatic, motion of a rigid body being pushed over a horizontal plane in situations where the precise frictional interaction cannot be determined. Consequently, the complete set of motions corresponding to all possible friction distributions must be found. We demonstrate that if the contact region between the body and the support ing plane has one or two components, the set of all possible motions coincides with the set of motions arising for friction distributions restricted to two-point contact in the boundary of the contact region. These two-point problems are solved analytically. In previous formulations of the problem, general friction support had only been reduced to the case of tripods, which does not have an analytic solution. Various examples are presented, and an effective numerical scheme based on a dissipation function is implemented.
Identification of Position-Independent Robot Parameter Errors Using Special Jacobian Matrices
Authors: Mirman C.R. , Gupta K.C.
Published: March 2007

Common production manipulators are designed to be controlled through the use of a closed-form kinematic solution algorithm. This closed-form solution uses manufacturer-specified nomi nal parameter values to model the given manipulator. These position-independent parameters, link lengths, twists, and off sets are geometrical and do not change as the manipulator is driven. However, manufacturing tolerances or usage may cause the actual parameters to deviate from the nominal robot para meters. In some cases, this deviation may be large and thus may cause the closed-form inversion to yield inaccurate joint value results.

To assure proper end-effector positioning, it is important to identify these position-independent error values. The identifi cation algorithm to be presented uses the Denavit-Hartenberg (D-H) parameter notation to model any given M-jointed manip ulator. For the given model, a set of special Jacobian matrices are formulated with respect to the four D-H parameters (J θ, Js, Jα, and Ja). This set of four special Jacobian matrices is used to determine a set of D-H error parameter values, which will allow one to estimate the actual D-H parameter values.

The iterative regression algorithm for parameter identifi cation uses the end-effector information at several arbitrary manipulator positions, as well as nominal parameter and joint variable information to compute the parameter error values. The use of the special Jacobian matrices allows for easy de termination of mathematical singularity conditions. In addition, statistical methods are employed to provide numerical uni formity between examples and aid in the evaluation process. Through several examples, it will be shown that the use of this parameter identification algorithm produces accurate results. This article will discuss the possibilities of deterministic as well as probabilistic parameter errors. Through the use of this parameter identification algorithm, one is able to identify the D-H parameter error values that will otherwise cause a loss in end-effector accuracy.
Coordination of Motion in a Spacecraft/ Manipulator System
Authors: Egeland Olav , Sagli Jan Richard
Published: March 2007

A control scheme for the coordination of motion in a space craft/manipulator system is presented. It is shown how end- effector motion can be decoupled from satellite motion, satellite rotation, or total system momentum by selecting suitable gen eralized speeds for the satellite. The schemes are based on recursive calculation of kinematics and dynamics, and 12 degrees of freedom can be controlled without excessive com putational effort. Feedback linearization and decoupling of end-effector motion and total system momentum are discussed in detail. The satellite controller can then be developed in dependently of the manipulator controller, and reaction jets and momentum wheels are used only to reposition the satel lite. The end effector can be controlled accurately with a high bandwidth, while a slow, gross positioning can be used for the satellite. The resulting controller is very efficient in terms of fuel. The spacecraft/manipulator system is regarded as a re dundant manipulator of the macro-micro type with 12 degrees of freedom, and a redundancy resolution scheme based on the augmented task space approach is used to generate the position and orientation reference for the spacecraft. The proposed con troller was simulated with a 12-degrees-of-freedom model that was generated with a recursive formulation of the Jacobians. The results are presented in this article.
An Atlas of Remote Actuated Bevel Gear Wrist Mechanisms of up to Nine Links
Authors: Pio Belfiore Nicola
Published: March 2007

An atlas of topological and functional representations of bevel gear-type basic robotic wrists of up to nine links with all the actuators connected to the frame link is presented. Each wrist mechanism is depicted by means of a canonical diagram that can be adopted as a schematic model for the final constructive embodiment. The corresponding graphic representation is also shown, together with a reference number that classifies the structure through the concepts of nonfractionated degree of freedom and equivalent-open-loop chain.
Configuration of Autonomous Walkers for Extreme Terrain
Authors: Bares John E. , Whittaker William L.
Published: March 2007

Robots that can competently, efficiently, and autonomously operate in extreme terrain do not exist. Although walking locomotion offers unique advantages, existing walking mech anisms are not suited to the comprehensive requirements of extreme terrain autonomy. This work synthesizes and ana lyzes candidate walker configurations, implements and tests a walker of unprecedented capability and design, and devel ops insights regarding walker configuration and the class of orthogonal-legged walking robots. Three orthogonal-legged walker configurations are described and compared in a variety of terrain situations. Two of the configurations-circulating and weaving-are unique, as they place recovering feet ahead of supporting feet and are specifically notable for their long stride. The third uses a traditional follow-the-leader gait. The Ambler is a fully operable autonomous walking robot built in part to further investigate the benefits of the orthogonal leg and circulating gait configuration. The orthogonal leg appears to be well suited to autonomous walking in extreme terrain. A circulating walker's advantages—as demonstrated by the Am bler-notwithstanding, a follow-the-leader orthogonal-legged walker appears to have superior overall mobility and stability (the crucial capabilities in extreme terrain).
Kinematic Dexterity of Robotic Mechanisms
Authors: Park Frank C. , Brockett Roger W.
Published: March 2007

In this article we develop a mathematical theory for optimizing the kinematic dexterity of robotic mechanisms and obtain a collection of analytical tools for robot design. The performance criteria we consider are workspace volume and dexterity; by the latter we mean the ability to move and apply forces in arbitrary directions as easily as possible. Clearly, dexterity and workspace volume are intrinsic to a mechanism, so that any mathematical formulation of these properties must necessarily be independent of the particular coordinate representation of the kinematics.

By regarding the forward kinematics of a mechanism as defining a mapping between Riemannian manifolds, we apply the coordinate-free language of differential geometry to define natural measures of kinematic dexterity and workspace volume. This approach takes into account the geometric and topolog ical structures of the joint and workspaces. We show that the functional associated with harmonic mapping theory provides a natural measure of the kinematic dexterity of a mechan ism. Optimal designs among the basic classes of mechanisms are determined as extrema of this measure. We also examine the qualitative connections between kinematic dexterity and workspace volume.
Control of Mechanical Systems With Rolling Constraints
Authors: Sarkar Nilanjan , Xiaoping Yun  , Kumar Vijay
Published: March 2007

There are many examples of mechanical systems that require rolling contacts between two or more rigid bodies. Rolling contacts engender nonholonomic constraints in an otherwise holonomic system. In this article, we develop a unified ap proach to the control of mechanical systems subject to both holonomic and nonholonomic constraints. We first present a state space realization of a constrained system. We then dis cuss the input-output linearization and zero dynamics of the system. This approach is applied to the dynamic control of mo bile robots. Two types of control algorithms for mobile robots are investigated: trajectory tracking and path following. In each case, a smooth nonlinear feedback is obtained to achieve asymptotic input-output stability and Lagrange stability of the overall system. Simulation results are presented to demonstrate the effectiveness of the control algorithms and to compare the performance of trajectory-tracking and path-following algo rithms.
On the Extremal Fundamental Frequencies of One-Link Flexible Manipulators
Authors: Wang Fei-Yue
Published: March 2007

The problem of maximizing the fundamental vibration frequency of a flexible manipulator through the optimum design of its link is addressed. A larger fundamental vibration frequency is desired because it will enable the manipulator to move faster without causing serious oscillation of its end point. Using the variational method, we show that this design problem can be formulated as a nonlinear eigenvalue problem and thus solved by a set of successive iteration schemes. Sensitivity analysis for the optimum design is also performed to obtain useful in formation for machining allowance specifications. The results of this investigation should be very useful in the design of lightweight and high-performance robotic arms. For example, numeric calculations indicated that an increase ranging from 194.92% to 600.25% in the fundamental vibration frequency can be achieved by the optimum tapering of a flexible manip ulator with a link of geometrically similar cross sections. This may lead to a significant improvement in productivity, as the manipulator can rotate three to seven times faster.
Position Control Experiments Using Vision
Authors: Chen W.Z. , Korde U.A. , Skaar S.B.
Published: March 2007

This article presents results of experiments carried out to test the vision-based method of camera-space manipulation using a fully three-dimensional rigid-body mating task. In this work, the performance of the method under various operating conditions is studied experimentally using a large six-axis manipulator. Further, an analytical study is carried out to understand the influence of relative orientation of cameras and their number on the terminal positioning precision expected with the method.
Passive Joint Control of Dynamic Coupling in Mobile Robots
Authors: Wiens G.J. , Jang W.-M.
Published: March 2007

The results of an investigation on the effects of the dynamic interactions between the vehicle and robot arm motions of a mobile robot system are presented. The objective of this work is to determine whether a mobile robot's dynamic coupling effects can be controlled passively. In this article, various spring- damper combinations (passive control systems) are added to a mobile robot system and evaluated in terms of their effec tiveness in controlling the dynamic coupling. The evaluation procedure utilizes a numerical technique (Runge Kutta-Vemer fifth- and sixth-order method) in conjunction with an algorithm based on the differences between the mobile and nonmobile robot systems' models. The algorithm provides a measure of dynamic coupling and stability. The results are presented in a condensed form via application of Simpson's rule on the cor responding deviations between desired and actual trajectories. In conclusion, the use of passive control systems in conjunc tion with relatively simple controllers (available for existing nonmobile robots and vehicle systems) is expected to provide improved system performance.
Dynamic Analysis of a Manipulator in a Fluid Environment
Authors: Lévesque Benoît , Richard Marc J.
Published: March 2007

The computation of the generalized forces produced by a fluid acting on the links of manipulators is considered here. The evaluation of these forces is necessary for the controller of an underwater manipulator (partially or totally immersed). This article presents an approximate method for the computation of buoyancy in local coordinates. The drag forces are computed by numerical integration of the local drag force. Numerical integration is necessary here to achieve a good precision. A new local reference frame is also added on each link to allow an easy description of the geometry of the links. When those computations are included in the dynamic model, a compromise must be made between computation time and precision, because this inclusion may result in doubling or tripling the number of operations to be performed in comparison with a standard dynamic algorithm.
Energy-Based Stability Measures for Reliable Locomotion of Statically Stable Walkers: Theory and Application
Authors: Nagy P.V. , Desa S. , Whittaker W.L.
Published: March 2007

To plan safe, reliable walker motions, it is important to assess the stability of a walker. In this article, two basic modes of walker stability are defined and developed: stance stability and walker stability. For slowly moving, statically stable walkers, it is convenient to use the magnitude of the amount of the work required to destabilize a walker as a measure of the stability of that walker. Furthermore, as shown in this article, the com pliance of the walker and/or terrain can significantly affect the work necessary to destabilize the walker. Consideration of compliance and the two modes of walker stability leads to the definition and development of four energy-based stability mea sures : the rigid stance stability measure, the compliant stance stability measure, the rigid walker stability measure, and the compliant walker stability measure. (The rigid stance stability measure is identical to the energy stability margin reported in Messuri and Klein [1985].) Several examples are used to demonstrate the application and use of these stability measures in type selection, gait planning, and control of the walker. The outcome of the present work is a more complete approach to using stability measures to ensure reliable walker gait planning and control.
Application of Change Detection to Dynamic Contact Sensing
Authors: Eberman Brian , Salisbury J. Kenneth
Published: March 2007

The forces of contact during manipulation convey substan tial information about the state of the manipulation. Textures, slip, impacts, grasping, and other contact conditions produce force and position signatures that can be used for identifying the state of contact. This article addresses the fundamental problems of interpreting the force signals without any addi tional context on the state of manipulation. Techniques based on forms of the generalized sequential likelihood ratio test are used to segment individual strain signals into statistically equivalent pieces. The results of the segmentation are designed to be used in a higher level procedure that will interpret the results within a manipulation context. We report on our ex perimental development of the segmentation algorithm and on its results for detecting and labeling impacts, slip, changes in texture, and condition. The sequential likelihood ratio test is reviewed, and some of its special cases and optimal properties are discussed. Finally, we conclude by discussing extensions to the techniques and lessons for sensor design.
Robust Control of Robot Manipulators Based on Joint Torque Sensor Information
Authors: Imura Jun-ichi , Yokokohji Yasuyoshi , Yoshikawa Tsuneo , Sugie Toshiharu
Published: March 2007

This article is concerned with robust control of robot manip ulators in the case where joint torque sensors are available. First, we derive a dynamic equation of the manipulator with joint torque sensors that explicitly expresses a nonlinear mul tivariable structure. This dynamic equation makes it possible to construct the control systems of the manipulators with joint torque sensors based on a similar method used in the conven tional case without the sensors. Second. based on this dynamic equation, we propose a robust trajectory control scheme that achieves the specified tracking accuracy in the presence of modeling error, including the modeling error of actuator sys tems. The proposed method fully exploits joint torque sensor information to compensate the uncertainty of link and load parameters. Furthermore, an illustrative simulation result is given to show the effectiveness of the proposed control method.
Avoidance of Obstacles With Unknown Trajectories: Locally Optimal Paths and Periodic Sensor Readings
Authors: de Lamadrid James Gil
Published: March 2007

We consider the problem of moving a mobile robot through a two-dimensional workspace containing obstacles moving on unknown trajectories. The workspace and obstacles are convex polygons, and the robot is a point. We propose to use sensor information to predict the trajectories of the obstacles and in terleave path planning and execution. Sensors are read only at equally spaced intervals of time. We discuss how small this in terval must be to guarantee that the robot will be able to avoid collisions. We also define a locally minimum velocity path as an optimal robot trajectory, given only local information about obstacle trajectories. We prove that our algorithm can ap proximate the locally minimum velocity path to any required accuracy.
Inertial Properties in Robotic Manipulation: An Object-Level Framework
Authors: Khatib Oussama
Published: March 2007

Consideration of dynamics is critical in the analysis, design, and control of robot systems. This article presents an extensive study of the dynamic properties of several important classes of robotic structures and proposes a number of general dynamic strategies for their coordination and control. This work is a synthesis of both previous and new results developed within the task-oriented operational space formulation. Here we in troduce a unifying framework for the analysis and control of robotic systems, beginning with an analysis of inertial prop erties based on two models that independently describe the mass and inertial characteristics associated with linear and angular motions. To visualize these properties, we propose a new geometric representation, termed the belted ellipsoid, that displays the magnitudes of the mass/inertial properties directly rather than their square roots. Our study of serial macro/mini structures is based on two models of redundant mechanisms. The first is a description of the task-level dy namics that results from projecting the system dynamics into operational space. The second is a unique dynamically con sistent relationship between end-effector forces and joint torques. It divides control torques at the joint level into two dynamically decoupled vectors: torques that correspond to forces at the end effector, and torques that affect only internal motions. The analysis of inertial properties of macro-/mini- manipulator systems reveals another important characteristic: that of reduced effective inertia. We show that the effective mass/inertia of a macro-/mini-manipulator is bounded above by the mass/inertia of the mini-manipulator alone. Because mini structures have a limited range of motion, we also pro pose a dextrous dynamic coordination strategy to allow full use of the high mechanical bandwidth of the mini-structures in extended-motion operations. Finally, a study of the dy namics of parallel, multiarm structures reveals an important additive property. The effective mass and inertia of a multi arm system at some operational point are shown to be given by the sum of the effective masses and inertias associated with the object and each arm. Using this property, the mul tiarm system can be treated as a single augmented object and controlled by the total operational forces applied by the arms. Both the augmented object construct and the dynam ically consistent force/torque relationship are extended for the analysis and control of multiarm systems involving redun dancy.
Visualization of Force-Closure Grasps for Objects Through Contact Force Decomposition
Authors: Chen Yu-Che , Walker Ian D. , Cheatham John B.
Published: March 2007

This article presents an analysis of the mechanics for grasps of solid objects. The main feature in the approach followed in this article is the decomposition of the contact finger forces. At each grasp point, a contact force is resolved into components along the normal and tangential directions. This concept of force decomposition results in a new formulation relating the contact forces and the geometry of contact points. Mathemati cally, under the assumption of a frictional point contact model, this formulation motivates the need of forming degenerate (es sentially planar) and general solid object grasps with three and four contact points, respectively. Simple rules for testing the feasibility of a set of contact points are developed based on the closed-form expression for the internal contact forces, which is expressed in terms of the geometrical quantities of the con tact points and their relative orientations. The functions of the normal and tangential contact force components for manipu lating an object are easily visualized as squeezing and twisting through this new formulation.
Application of Parallel Processing to Robotic Computational Tasks
Authors: Nabhan Tarek M. , Zomaya Albert Y.
Published: March 2007

Robotic tasks (e.g., kinematics and dynamics) are computation ally expensive. The majority of these tasks must be computed in real-time to meet the high sampling rate modes of oper ations. Recently parallel processing has been used to speed up these computations. In this work, we propose a graph- based algorithm to map computational tasks onto multiple instruction-multiple data (MIMD) type of architectures. The algorithm automatically generates the task graph of a given task. Then an annealing procedure is used to allocate the gen erated subtasks to different processors, taking into account the network topology and the communication constraints. Moreover, the proposed technique is simple, flexible, and computationally viable. The efficiency of the algorithm is demonstrated by a case study with good results.
Pulling by Pushing, Slip With Infinite Friction, and Perfectly Rough Surfaces
Authors: Lynch Kevin M. , Mason Matthew T.
Published: March 2007

When one rigid object (the pusher) pushes another (the slider) across a horizontal support plane, Coulomb's law of friction admits some surprising phenomena. First, it is possible to move the slider by moving the pusher away from the slider: pulling. Second, even with an infinite coefficient of friction, it is possible to obtain slip between the two objects as the pusher moves into the slider. This contradicts the common conception that infinite friction always prevents slip. The per fectly rough contact of classical mechanics is not realized by an infinite coefficient of friction. This article shows examples of the phenomena with both quasistatic and dynamic analy ses.
Time-Optimal Paths for High-Speed Maneuvering
Authors: Reister David B. , Lenhart Suzanne M.
Published: March 2007

Recent theoretical results have completely solved the problem of determining the minimal length path for a vehicle moving from an initial configuration to a final configuration. Time- optimal paths for a constant-speed vehicle are a subset of the minimum length paths. The time-optimal paths consist of sequences of arcs of circles and straight lines. The Pontrya gin Maximum Principle introduces concepts (dual variables, bang-bang solutions, singular solutions, and transversality conditions) that provide important insight into the nature of the time-optimal paths. We have created a module that finds the time-optimal path from an initial canfrguration to a final configuration. We have demonstrated that the paths can be followed by a large (820-kg) mobile robot.
A General Algorithm for Dynamic Control of Multilink Robots
Authors: Overgaard Lars , Petersen Henrik G. , Perram John W.
Published: March 2007

One of the major tasks in the development of sophisticated methods for robot control is finding algorithms that are appli cable to a wide range of different robots. Another major task is to find algorithms that can be used for on-line control. Several attempts have been made to solve one or the other of these problems. This article presents a general method for solving both. It can be applied to any redundant or nonredundant robot with rigid subunits connected by revolute joints in a tree-like structure. The number of joints can be chosen arbitrarily large without singularity problems, in contrast to traditional inverse kinematics models. A system based on the presented method needs no modifications when changing from one specifrc robot to another structurally or kinematically completely different robot, only input parameters describing the robot are different. The method is founded on a very general algorithm for finding the Lagrangian equations of motion for a robot subject to a given set of artificial forces. The generality and power of the method are demonstrated by two examples. In the first example the method is used to simulate a 25-degrees-of-freedom (DOF) snake-like robot moving through a maze. In the second example the method is used to control an actual application: an 8-DOF industrial robot system welding a ship section.