bluuebunny/crossref_metadata_2025 huggingface dataset:
Symbolic Error Analysis and Robot Planning
Authors: Brooks Rodney A.
Published: March 2007

A program written to control a robot manipulator for industrial assembly operations must take into account possible errors in parts placement and tolerances of the parts themselves. Previous approaches to this problem have been to (1) engineer the situation so that the errors are small or (2) let the programmer analyze the errors and take explicit account of them. This paper gives the mathe matical underpinnings for building programs (plan checkers) that carry out the second approach automatically. The plan checker uses a geometric, computer-aided design (CAD) type of data base to infer the effects of actions and the propa gation of errors. It does this symbolically rather than numerically, so that computations can be reversed and desired resultant tolerances can be used to infer required initial tolerances or the necessity for sensing. The checker modifies plans to include sensing and adds constraints to the plan that ensure its success. An implemented system is de scribed, and results of its execution are presented. The plan checker could be used as part of an automatic planning system or as an aid to a human robot programmer.
Smoothed Local Symmetries and Their Implementation
Authors: Brady Michael , Asada Haruo
Published: March 2007

We introduce a novel representation of two-dimensional shape that we call smoothed local symmetries ( SLS). Smoothed local symmetries represent both the bounding contour of a shape fragment and the region that it occupies. In this paper we develop the main features of the SLS repre sentation and describe an implemented algorithm that com putes it. The performance of the algorithm is illustrated for a set of tools. We conclude by sketching a method for deter mining the articulation of a shape into subshapes.
Decoupling of a Two-Axis Robotic Manipulator Using Nonlinear State Feedback: A Case Study
Authors: Fournier S.J. , Schilling R.J.
Published: March 2007

A case study that illustrates the use of nonlinear state feed back to decouple the control of a two-axis polar-coordinate robotic manipulator is presented. One type of position cou pling and two types of velocity coupling are investigated. In each case, the application of decoupling compensation results in marked improvement in the performance of the robotic arm. The implementation difficulties associated with apply ing a nonlinear state-feedback control law to an inexpensive, indirect-drive robotic arm, using a microcomputer controller and low-resolution sensors, are examined.
On the Numerical Solution of the Inverse Kinematic Problem
Authors: Angeles Jorge
Published: March 2007

Solved in this paper is the inverse kinematic problem asso ciated with manipulators of arbitrary architecture. Its formu lation is based on invariants in the rotational part of the closure equations, which produces a formally overdetermined nonlinear algebraic system. In the translational part, a recur sive scheme similar to that of Horner's for polynomial evalu ation is introduced. This leads to a reduced number of com putations, which allows an efficient numerical solution of the problem. Velocity and acceleration kinematic inversions are also included. The procedure is illustrated with the analysis of a six-degree-of-freedom, revolute-coupled manipulator of an architecture that makes a closed-form solution difficult. This method has been successfully applied to the analysis of 7R spatial linkages as well. Appendix A lists the nomenclature and notation used in this paper.
Iterative Kinematic Inversion of General Five-Axis Robot Manipulators
Authors: Angeles Jorge
Published: March 2007

A kinematic model is derived that allows the computation of the joint coordinates and their time rates, given the Cartesian coordinates, velocities, and accelerations of five-axis manipu lators of arbitrary architecture. The model leads to a for mally overdetermined nonlinear algebraic system of six equations in five unknowns. Its least-squares approximation produces the desired joint coordinates. Joint rates are com puted as the least-squares approximation of a formally over determined linear algebraic system of six equations in five unknowns, relating the desired rates with the Cartesian ve locities. The time derivatives of the joint rates are computed similarly, but from Cartesian accelerations. The procedure is illustrated with two fully solved examples.
Workspace and Mobility of a Closed- Loop Manipulator
Authors: Bajpai Atul , Roth Bernard
Published: March 2007

This paper examines the geometry of a group of closed-loop manipulators with structures based on a planar, revolute jointed, five-bar chain. Of primary interest is the influence of the link lengths on the reachable workspace of the manipula tor. Unlike the commonly used open-loop manipulators, the entire workspace for a closed-loop manipulator will not be freely reachable, in general. The issues pertaining to the independent mobility of the driving links are discussed at length. A classification is made based on mobility criteria, and these mechanisms are further categorized into two types depending upon the influence of the link lengths on the ma nipulator's workspace. Based on this analysis, some general guidelines are laid down to assist the designer in making rational choices in selecting manipulator link lengths.
Planning of Minimum- Time Trajectories for Robot Arms
Authors: Sahar Gideon , Hollerbach John M.
Published: March 2007

The minimum-time path for a robot arm has been a long standing and unsolved problem of considerable interest. We present a general solution to this problem which involves joint-space tessellation, a dynamic time-scaling algorithm, and a graph search. The solution incorporates full dynamics of movement and actuator constraints, and can easily be extended for joint limits and workspace obstacles. It was found that optimal paths tend to be nearly straight lines in joint space. We discuss implementation difficulties due to the tessellation and to combinatorial proliferation of paths.
Simplification and Linearization of Manipulator Dynamics by the Design of Inertia Distribution
Authors: Yang D.C.H. , Tzeng S.W.
Published: March 2007

This paper presents a new approach to designing a simple manipulator with better dynamic behavior. The method is based on eliminating coefficients of nonlinear terms in the system's kinetic and potential energy equations. Accordingly, a set of design criteria regarding the link's inertia distribu tion can be established for each robot type. A robot designed to satisfy these criteria will result in much simplified dy namics. Also we find that for some configurations of three- and four-link robots, it is possible to design for completely linearized dynamic equations.
Computer-Assisted Generation of Dynamical Equations for Multibody Systems
Authors: Faessler Hanspeter
Published: March 2007

A computer-oriented method based on Kane's equations is presented that facilitates the formulation of dynamical equa tions. The method requires an analyst to formulate only the most basic ingredients of the equations in analytical form; the necessary summations and multiplications required for the final equations are left to a small computer program. Examples are shown of two short programs, which either per form the necessary numerical operations or generate equa tions in symbolic form. As for the requisite kinematical anal ysis, only velocities and angular velocities are needed, and no accelerations or kinetic energies must be formed. The method systematically avoids unnecessary operations such as the introduction and subsequent elimination of nonworking contact forces, the computation of velocity dependent terms that ultimately cancel one another, and the calculation of expressions that are determined by symmetry properties of matrices.
A General Procedure to Evaluate Robot Positioning Errors
Authors: Vaishnav Ramesh N. , Magrab Edward B.
Published: March 2007

A new, explicit, and complete formulation that describes the geometric errors due to both origin translation and misalign ments of axes in the positioning of an open-loop robot ma nipulator has been presented. The formulation does not use the usual Denavit-Hartenberg approach. The results clearly display the role of each quantity involved and allow easy physical interpretation of each error term. First, a general kinematic formulation for an ideal robot with an arbitrary number of links is developed. The geometric errors in axes locations and orientations are then shown to be skew coordi nate transformations with origin translations and are incor porated into the analysis using general tensor algebra. The final forms of forward and backward transformations contain up to 9 (N + 2) error parameters for a robot with N physical links. This theoretical formulation is applied to a specific six-degrees-of-freedom robot. It is observed that of the possi ble 72 errors in this robot, only 53 can independently contrib ute to the error at the end effector and are the only ones that can be determined by measurements made at the end effec tor. It is shown how a correlation matrix analysis can be used to isolate these 53 parameters. In addition. it is shown how, using a successive orthogonalization technique, one can eliminate from consideration error parameters (eight in the present case) that are too small to be significant but contrib ute to the ill-conditioning of the coefficient matrix. Applica tion of the procedure to computer-simulated data shows that the formulation and the numerical techniques developed here combine to form a powerful method to calibrate a robot.
The Design of Flexible Robotic Manipulators with Optimal Arm Geometries Fabricated from Composite Laminates with Optimal Material Properties
Authors: Liao D.X. , Sung C.K. , Thompson B.S.
Published: March 2007

The fabrication of lightweight robot arms in composite mate rials and the ability of robotic devices to dissipate residual vibrations at the termination of a maneuver have both been highlighted as key research problems in a recent report pub lished by the U.S. Congress, Office of Technology Assess ment. Both problems are addressed here. We develop a method for optimally configuring the geometry and the mate rial fabrication parameters of hollow box members for robo tic manipulators constructed with composite laminates. We do it by integrating a formulation for laminated beams with a recent approach for predicting the damping characteristics of laminates before incorporating this general theory into an optimization algorithm, which permits general constraint conditions to be imposed on the solution procedure.

To illustrate the proposed design methodology, we give an example of an industrial manipulator with flexible links that describes three-dimensional motion. We make a comparative study of the initial robot and optimal designs to simulate the elastodynamic behavior of the end-effectors for a prescribed maneuver. The results of the finite element simulations clearly demonstrate the superior response of the proposed optimal design.
The Kinematics of Contact and Grasp
Authors: Montana David J.
Published: March 2007

The kinematics of contact describe the motion of a point of contact over the surfaces of two contacting objects in response to a relative motion of these objects. Using concepts from differential geometry, I derive a set of equations, called the contact equations, that embody this relationship. I employ the contact equations to design the following applications to be executed by an end-effector with tactile sensing capability: ( 1) determining the curvature form of an unknown object at a point of contact; and ( 2) following the surface of an unknown object. The contact equations also serve as a basis for an investigation of the kinematics of grasp. I derive the relation ship between the relative motion of two fingers grasping an object and the motion of the points of contact over the object surface. Based on this analysis, we explore the following applications: ( 1) rolling a sphere between two arbitrarily shaped fingers ; ( 2) fine grip adjustment ( i.e., having two fingers that grasp an unknown object locally optimize their grip for maximum stability).
A Singular Perturbation Approach to Control of Lightweight Flexible Manipulators
Authors: Siciliano Bruno , Book Wayne J.
Published: March 2007

The control of lightweight flexible manipulators is the focus of this work. Theflexible manipulator dynamics is derived on the basis of a Lagrangian-assumed modes method. The full-order flexible dynamic system does not allow the deter mination of a nonlinear feedback control as for rigid manipu lators, since there are not as many control inputs as output variables. This drawback is overcome by a model order reduction, based on a singular perturbation strategy, where the fast state variables are the elastic forces and their time derivatives.

A composite control is adopted. First, a slow control is designed for the slow subsystem, which is shown to be the model of the equivalent rigid-link manipulator. Then a fast control is designed to stabilize the fast subsystem around the equilibrium trajectory set up by the slow subsystem under the effect of the slow control.

The one-link flexible-arm prototype in the Flexible Auto mation Laboratory at Georgia Institute of Technology is chosen for developing a case study. Simulation results are illustrated, and a comparison is made between the perform ance achieved with a two-time-scale controller and with a state feedback regulator.
Planning Compliant Motion Strategies
Authors: Buckley Stephen J.
Published: March 2007

This paper describes a planning program that synthesizes compliant motion strategies, in which an object in the grasp of a robot slides along obstacles, in an attempt to reach a goal region. The input to the planner is a model of the task geometry, a start region, and a goal region. To make the planning problem tractable, we reduce the task geometry to a finite state space, whose states are collections of vertices, edges, and faces from the configuration space of the robot. Strategy synthesis is complicated by uncertainty in the start ing configuration of the robot and in robot sensing and con trol. The planner synthesizes compliant motions that are guaranteed to perform state transitions despite uncertainty. Using best first search, compliant motions are synthesized until a strategy is found from the start state to a goal state. A strategy may require that the robot stop in an intermediate state, using sensors to determine the next commanded motion.
A Method for Improving the Dynamic Accuracy of a Robot Performing a Repetitive Task
Authors: Middleton Richard H. , Goodwin Graham C. , Longman Richard W.
Published: March 2007

In many applications it is desirable to improve the dynamic accuracy of robots. In this paper a simple scheme for improv ing the accuracy is presented whereby the robot improves its performance each time the task is performed. The method makes use of the discrete time internal model principle. The performance of the algorithm is confirmed by computer sim ulation studies using a full nonlinear model of a 3-degree-of- freedom robot. The studies indicate that a dramatic improve ment in dynamic accuracy is achievable with the method.
A Robot Manipulator With 16 Real Inverse Kinematic Solution Sets
Authors: Manseur Rachid , Doty Keith L.
Published: March 2007

A solution search algorithm based on a one-dimensional numerical approach to the inverse kinematic problem (pre sented in an earlier paper) led to the discovery of a six-DOF manipulator able to position and orient its end-effector in 16 distinct configurations for a given end-effector pose (position and orientation). This paper discusses the consequences of such a discovery and presents a description of the manipula tor, the end-effector pose, and the 16 kinematic solutions.
An Approach To Manipulator Path Planning
Authors: Warren C.W. , Danos J.C. , Mooring B.W.
Published: March 2007

A path planning technique for fixed-base robot manipulators consists of a Mapping Phase and a Path Planning Phase. The Mapping Phase employs a closed-form relationship to map from object space to C-Space for a manipulator with revolute joints. The Path Planning Phase consists of develop ing a potential field around each object in C-Space and using the resulting field to choose an appropriate path. To accom plish this, a trial path is chosen and then modified under the influence of the potential field. Considering the entire path greatly reduces the probability of becoming trapped in a local minimum, making the method effective for global planning.
Planning Multi-Step Error Detection and Recovery Strategies
Authors: Donald Bruce R.
Published: March 2007

Robots must plan and execute tasks in the presence of uncer tainty. Uncertainty arises from sensing errors, control errors, and the geometry of the environment. By employing a com bined strategy offorce and position control, a robot program mer can often guarantee reaching the desired final configura tion from all the likely initial configurations. Such motion strategies permit robots to carry out tasks in the presence of significant uncertainty. However, compliant motion strategies are very difficult for humans to specify. For this reason we have been working on the automatic synthesis of motion strategies for robots. In previous work (Donald 1988b; 1989), we presented a framework for computing one-step motion strategies that are guaranteed to succeed in the presence of all three kinds of uncertainty. The motion strategies comprise sensor-based gross motions, compliant motions, and simple pushing motions.

However, it is not always possible to find plans that are guaranteed to succeed. For example, if tolerancing errors render an assembly infeasible, the plan executor should stop and signal failure. In such cases the insistence on guaranteed success is too restrictive. For this reason we investigate error detection and recovery (EDR) strategies. EDR plans will succeed or fail recognizably: in these more general strategies, there is no possibility that the plan will fail without the exec utor realizing it. The EDR framework fills a gap when guar anteed plans cannot be found or do not exist; it provides a technology for constructing plans that might work, but fail in a "reasonable" way when they cannot.

We describe techniques for planning multi-step EDR strat egies in the presence of uncertainty. Multi-step strategies are considerably more difficult to generate, and we introduce three approaches for their synthesis: these are the Push-for ward Algorithm, Failure Mode Analysis, and the Weak EDR Theory. We have implemented the theory in the form of a planner, called LIMITED, in the domain ofplanar assemblies.
Tactile Sensing Mechanisms
Authors: Fearing R.S.
Published: March 2007

This paper has three main themes: design of a cylindrical tactile sensor, mechanical analysis using planar linear elas ticity models, and signal analysis for determining basic infor mation about the applied contact. An analysis of appropriate sensor depth has been used to allow accurate localization of contacts and reduced spatial aliasing. A comparison has been made between the cylindrical sensor and a simple two- dimensional stress-strain model. The effects of skin thickness and sensor depth on sensitivity are analyzed. Preliminary methods for determining contact location, total force, and tangential force with only normal deflection sensors have been implemented for a line contact.
Planning for Dexterous Manipulation with Sliding Contacts
Authors: Trinkle J.C. , Paul R.P.
Published: March 2007

Dexterous manipulation refers to the skillful execution of object reorienting and repositioning maneuvers, especially when performed within the grasp of an articulated mechani cal hand. In this paper we study the problem of gaining a secure and enveloping grasp of a two-dimensional object by exploiting sliding at the contacts between the object and the hand. This is done in two steps:first, choosing an initial grasp with which the object can be manipulated away from the support, and second, continuously altering the grasp so that envelopment is achieved. The plans generated by our technique could be executed with only position control. How ever, it would be prudent to incorporate contact force sensing to prevent damage during unexpected events.

The main contributions of this paper are the derivation of liftability regions of a planar object for use in manipulation planning; the use of the lifting phase plane in manipulation planning; and the derivation of the quasi-static forward object motion problem, which provides a basis for general three- dimensional manipulation planning with rolling and/or sliding contacts.
A Unified Methodology for Motion Planning with Uncertainty for 2D and 3D Two-Link Robot Arm Manipulators
Authors: Lumelsky Vladimir , Kang Sun
Published: March 2007

Most of the work on robot path planning revolves around two basic models: the model with complete information (often called the "Piano Mover's Problem") and the model with in complete information (called here the "South Pole Search Problem'). The approach of dynamic path planning intro duced in Lumelsky and Stepanov (1987) and Lumelsky (1987) is based on the latter model and produces nonheuristic (provable) algorithms for simple robot arm manipulators operating in an environment with unknown obstacles of arbi trary shapes. The algorithms assume local on-line input information coming from the arm sensors. Unfortunately, the existing techniques require that each kinematic configuration be considered separately, which results in different algo rithms for different kinematics. In this paper, a unified meth odology is presented for designing dynamic path planning algorithms for two- and three-dimensional two-link arm manipulators. The approach is independent of the specifics of the kinematic configuration and imposes no constraints on the shape of the arm links or obstacles in the environment. The methodology exploits some important topological char acteristics of the configuration space. However, no explicit computation of obstacles in the configuration space ever takes place, which results in fast real-time algorithms.
Kinematics of Robot Mechanisms with Closed Actuating Loops
Authors: Fanghella P. , Galletti C.
Published: March 2007

The kinematic properties of multiloop chains for robot appli cations are investigated using a structure-based approach. The basic concepts related to algebraic groups of displace ments and to Assur's groups are used in order to provide systematic foundations for analysis and synthesis procedures. Analysis techniques are described, and several examples of real applications are given.
Adaptive Friction Compensation in Robot Manipulators: Low Velocities
Authors: Canudas de Wit C. , Noël P. , Aubin A. , Brogliato B.
Published: March 2007

This article analyzes the problem of modeling and compensation of friction at velocities close to zero. A new model, linear in parameters, which captures the downward bends at low velocity is used to adoptively compensate for friction. The need for this type of model is mainly motivated by instability phenomena that can be caused by overcompensation when simple models (such as Coulomb friction models) are used as a basis for the friction compensation. This model, in combination with an adaptive computed torque method, was tested experimentally in a robot manipulator.
Closed-Loop Behavior of a Feedback-Controlled Flexible Arm: A Comparative Study
Authors: Cetinkunt Sabri , Yu Wen-Lung
Published: March 2007

The dynamics of mechanical systems with distributed flexi bility are described by infinite-dimensional mathematical models. In order to design afinite-dimensional controller, a finite-dimensional model of the system is needed. The con trol problem of a flexible beam is a typical example. The general practice in obtaining a finite-dimensional model is to use modal approximation for distributed flexibility, retain a finite number of modes, and truncate the rest. In this approx imation, the appropriate selection of the mode shape func tions and the number of modes is not clearly known. Mostly standard pinned-free and clamped-free mode shapes are used for the flexible beam model, retaining only two or three modes and truncating the rest. The actual system, on the other hand, is infinite-dimensional, and the modes describing its flexible behavior under feedback control would be neither pinned-free nor clamped-free boundary condition modes. Rather, the mode shapes themselves are a function of the feedback control.

The infinite-dimensional transcendental transfer functions for a flexible beam are formulated without any modal ap proximation. Finite-dimensional transfer functions with different shapes and numbers of modes are formulated. The closed-loop performance predictions of different models under the same colocated and noncolocated controllers, which attempt to achieve high closed-loop bandwidth, are compared. Results are surprisingly consistent in all cases; the predictions of clamped-free mode shape models are much more accurate than the predictions of the pinned-free mode shape models.
Identifying the Independent Inertial Parameter Space of Robot Manipulators
Authors: Sheu Shih-Ying , Walker Michael W.
Published: March 2007

This paper presents a new approach to the problem of finding the minimum number of inertial parameters of robot manipulator dynamic equations of motion. Based upon the energy difference equation, it is equally applica ble to serial link manipulators as well as graph structured manipulators. The method is conceptually simple, compu tationally efficient, and easy to implement. In particular, the manipulator kinematics and the joint positions and velocities are the only inputs to the algorithm. Applica tions to a serial link and a graph structured manipulator are illustrated.
Three-dimensional Finite Element Analysis of Elastic Continua for Tactile Sensing
Authors: Speeter Thomas H.
Published: March 2007

This article presents a method for determining three- dimensional stress and strain tensors within elastic layers covering or embedding tactile sensors. When an object comes in contact with the elastic surface of a sensing array, the distribution of forces on the surface is mechani cally filtered before reaching the underlying sensing ele ments. In order to predict the response of embedded sen sors and to understand the nature of the transduced variables, the relationship between surface forces and interior stress and strain tensors must be known. To deter mine this, we need to know the shape of the surface con tact area and the distribution of forces over that area, both normal and tangential. The algorithm described here discretizes the known surface force distribution into a dense array of independent point loads, approximating the surface force profile. The stress field produced by a single normal and/or a single tangential point load can be expressed analytically, given the elasticity and compressi bility of the material. Fields for each point load are calcu lated and can be summed to determine the resultant stress tensor at any point within the medium. Strains can be computed from stresses using a simple set of translation formulas.

A detailed example is illustrated, analyzing the inter action between a sphere and a planar elastic half space. From the example the relative effects of depth and dis tance from the center of contact on the response of underlying sensors is discussed. Using results from the example, methods are proposed to exploit sensors at dif ferent depths and at different orientations within the medium. An algorithm for determining the direction of surface tangential forces and a method for determining the ratio between normal and tangential forces are ana lyzed, using unidirectionally sensitive sensors at different depths in the elastic layer.
On-line Reference Trajectory Definition with Joint Torque and Velocity Constraints
Authors: Bestaoui Yasmina
Published: March 2007

The most significant control problem to be solved in robotics is the use of sensor information. This article pre sents a new method of on-line motion generation. New joint reference trajectories are calculated to be more adapted to the situation detected by the position and velocity sensors. This motion generation method uses the resolution of a minimum time optimization problem. The constraints are first expressed in terms of joint velocity and torque bounds and are then transformed into joint velocity, acceleration, and jerk limitations. This reference trajectory definition takes into account the manipulator dynamics.
Autonomous Robotic Disassembly in the Blocks World
Authors: Schmult Brian
Published: March 2007

This article describes a fully functional autonomous system with two cooperating robots that disassembles complex Duplo1 structures in a restricted environment. The system operates on a table-top world with any number of Duplo structures for which object models have been given. The structures are dis assembled down to individual parts, using basic operations of single part removal, object partitioning, and the addition of stabilizing supports to structures that would otherwise fall over. All aspects are automatically planned, including operation selection, path and grasp planning, and simultaneous cooper ative robot motion. Operations are chosen so as to not create unstable structures and to not risk breakage in areas of low structural integrity. Overall planning is done with a process mechanism that heuristically generates efficient disassembly sequences, without searching a space of all possible operations. Several examples of actual system operation, using real robots, are presented.
Singularity Avoidance and the Control of an Eight-Revolute-Joint Manipulator
Authors: Long Gregory L. , Paul Richard P.
Published: March 2007

The "optimum" 6R manipulator's singular configurations are used to develop the "best" 4R orientation and 4R regional structures for singularity avoidance. For comparison with the "best" 4R regional structure, the kinematics of a second 4R regional structure is explored. Conceptually, the control algo rithms for the 4R orientation and two 4R regional structures begin in primary mode with three actuator screws apiece. In primary mode the traditional position kinematics approach is used. However, when either the orientation or regional struc ture has difficulty following its Cartesian trajectory, control for that structure goes into secondary mode, where the redundant actuator is called on. The algorithms maintain a sixth-order screw system for an 8R manipulator with bounded actuator rates and well-behaved actuator values. The numerical com putations for an 8R manipulator are comparable to those for the "optimum" 6R manipulator and can be implemented in real time.
A New Linear Actuator for Robotics
Authors: Rodrigues M.A. , Lee M.H.
Published: March 2007

We describe the design and control of a novel contraction ac tuator that operates by generating tensions in a filament. The mechanical working principle is based on the deflection of a filament that provides both a reduction in its length (contrac tion) and amplification of the deflecting force within a specified range of operation. Two actuator prototypes are designed for analysis, fabrication, and test. Considerations regarding friction, inertia, and flexibility are discussed, and the control strategy for the prototypes' configuration is introduced. The design presented here has a wide range of engineering appli cations in many diverse areas, such as precise position control (e.g., for valves and instruments), control of all sorts of mech anisms (including robotic devices), and as an alternative drive mechanism in microelectromechanical devices.
Design and Control of an All-Direction Steering Type Mobile Robot
Authors: Koshiyama Atsushi , Yamafuji Kazuo
Published: March 2007

This article describes a new type of mobile robot that has a spherical wheel, an arched body, and motion-controlling mech anisms installed inside the wheel. The robot can travel in every direction and perform unique actions by virtue of the wheel and the motion-controlling mechanisms. We call the latter the Inside Wheel Balancing System (IWBS). Postural stability con trol, omnidirectional steering, and locomotion of the robot were achieved by means of the compound gravity center feedback control. Postural stability and traveling control on a slope and on a flat plane were also attained experimentally. The experimental results coincide well with those obtained by the simulation performed on a personal computer. The omnidirec tion traveling robot proposed here provides great possibility to the mobile robots in the manufacturing and nonmanufacturing environments.
The Definition, Determination, and Characterization of Acceleration Sets for Spatial Manipulators
Authors: Kim Y. , Desa S.
Published: March 2007

In this article, the approach developed by the authors for sys tematically studying the acceleration capability and properties of the end effector of a planar manipulator is extended to the general, serial, spatial manipulator possessing three degrees of freedom. The acceleration of the end effector at a given config uration of the manipulator is a linear function of the actuator torques and a (nonlinear) quadratic function of the joint ve locities. By decomposing the functional relationships between the inputs (actuator torques and joint velocities) and the output (acceleration of the end effector) into two fundamental map pings—a linear mapping between the actuator torques and the acceleration space of the end effector and a quadratic (nonlin ear) mapping between the joint velocities and the acceleration space of the end effector—and by deriving the properties of these two mappings, it is possible to determine the properties of all acceleration sets that are the images of the appropri ate input sets under the two fundamental mappings. A central feature of this article is the determination of the properties of the quadratic mapping, which then makes it possible to obtain analytic expressions for most acceleration properties of interest. We show that a fundamental way of studying these quadratic mappings is in terms of the mapping of (input) line congru ences into (output) line congruences. The article concludes with the application of the analytical results to the computa tion of the various acceleration properties of an actual spatial manipulator.
On the Forward Kinematics of Parallel Manipulators
Authors: Nair R. , Maddocks J.H.
Published: March 2007

In this article we present a novel procedure for the system atic analysis of the forward kinematics of a class of parallel manipulators that generalize the well-known Stewart plat form. The designs comprise a movable platform connected to a fixed base by a set of legs, the lengths of which can be con trolled. The legs are connected to the base and the platform by unactuated spherical joints. The forward kinematics prob lem is to determine all possible manipulator configurations (i.e., all possible positions and orientations of the platform) when a set of leg lengths is prescribed. The new formulation of the forward kinematics problem is general in the sense that it can, in principle, be applied to any manipulator design (i.e., to any fixed geometry of base and platform joints, with associated leg connectivities). One interesting aspect of our procedure is that it splits the forward kinematics problem into two parts, the first being a simple, design-dependent, inversion of a linear system of equations, and the second being a matrix- completion problem involving the solution of certain nonlinear, but design-independent, closure equations. The general formu lation provides some insight into which manipulator designs have simple forward kinematics. We analyze four specific ma nipulator designs from the new point of view, one of which is a design with previously unrecognized closed-form forward kinematics.
Coupling Effect of A Flexible Link and A Flexible Joint
Authors: Xi F. , Fenton R.G.
Published: March 2007

In this article the coupling effect of a flexible link and a flex ible joint is investigated. The system considered is a flexible link driven by an actuator through a flexible joint. First the dynamic equations of a flexible link-joint system are derived. Solutions of the system dynamic equations show that the fre quencies and mode shapes of the flexible link-joint system are parameterized in two ratios. One is the ratio of the moment of inertia of the link to that of the rotor of the actuator. The other is the ratio of the bending stiffness of the link to the torsion stiffness of the joint. Two important phenomena are discovered. The first is that in terms of the two ratios, there exist three regions of roots of the frequency equation—stiffening, softening, and mixed—and the coupling effect can be characterized by these three regions. The second is that the coupling effect can be reduced by appropriately choosing the combination of the two ratios. The results presented in the article are useful for design and control of flexible link-joint systems.
Static Friction Effects During Hard-on-Hard Contact Tasks and Their Implications for Manipulator Design
Authors: Alici Gürsel , Daniel Ron W.
Published: March 2007

In this article, we present the results and implications of our experimental study into the effects of static, nonlinear, fric tion during hard-on-hard contact tasks where making a stable contact is problematic. Experiments have been conducted with a PUMA 560 manipulator to address the hard-on-hard con tact stability problem and to stress the importance of damping (active-velocity feedback, and passive-nonlinear friction) for hard-on-hard applications typified by robotic drilling. Experi mental results reveal that during hard-art-hard contact, active damping is inoperative because of quantization, leaving only passive damping to stabilize the system. However, passive damping characteristics vary between joints. Most importantly, the last three joints of the manipulator, which are more af fected by contact force disturbances than others. lack sufficient passive damping, which we argue should match their respec tive joint stiffnesses to achieve contact stability. Therefore, we conclude that manipulator joints with low passive damping should have high-resolution encoders for velocity feedback. These are required to stabilize a force control system making a hard-on-hard constrained contact. The lower the joint friction, the higher the resolution required. This constitutes the main contribution of this article to manipulator design.
Tracking Manipulator Trajectories With Ordinary Singularities: A Null Space-Based Approach
Authors: Nenchev Dragomir N.
Published: March 2007

This article discusses the problem of tracking manipulator end-link trajectories passing through ordinary singularities. It is based on a method developed recently by Kieffer (1992), who suggested parameterizing the end-link trajectory with a parameter that is not time, and considering this parameter as a dependent variable. We show that this is equivalent to a kinematically redundant mechanism comprising the original nonredundant kinematic chain augmented by one more virtual link. The trajectory is actually mapped onto the joint space augmented by the parameter variable. Although the new mech anism performs only a "self-motion" tracking of the projected trajectory through regular points and ordinary singularities, the end-link of the real mechanism tracks the desired trajec tory. Our solution is based on effective null space methods that have been widely applied to kinematically redundant manipula tors. Asymptotic convergence of the tracking error to zero and stability is guaranteed through a closed-loop approach.
Sampled-Data Robot Adaptive Control With Stabilizing Compensation
Authors: Warshaw Gabriel D. , Schwartz Howard M.
Published: March 2007

This article addresses the stability and performance of dis cretized adaptive control algorithms for robotic manipulator control and the compensation of these algorithms for improved stability and tracking performance. The discretization of Slotine and Li's direct adaptive control algorithm results in a sampled- data system for which stability has not been guaranteed. By formulating the entire sampled-data system in continuous time, Lyapunov's direct method is used to determine the sta bility and to derive a nonlinear discrete-time compensating term. This compensator is added to a multirate discretization of Slotine and Li's (1987a) adaptive algorithm, to stabilize the sampled-data system. For sufficiently high gain, globally stable performance and a known bound on the norm of the fil tered error is proven. The stabilizing effect of the compensator and validity of the error bound predictions are demonstrated through simulation and implementation of 2-DOF manipulatior control.
Sense Organs of Insect Legs and the Selection of Sensors for Agile Walking Robots
Authors: Delcomyn Fred , Nelson Mark E. , Cocatre-Zilgien Jan H.
Published: March 2007

Legged robots modeled after insects have been proposed for use on rugged, dangerous, or inaccessible terrain. The agility of current hexapod robots, however, is not yet as good as that of their biological counterparts. The capability of insects for agile locomotion is likely due mainly to the rich variety of sensory information that is provided by sense organs in their legs. In this article we review the characteristics and distri bution of insect leg sense organs in terms that are relevant to researchers interested in designing agile, insect-like, walking robots, In insect locomotion, three classes of mechanosensory organs seem to play an important role in sensory feedback: detectors of leg movement, detectors of external contact, and detectors of leg stress. We review the properties of these types of sense organs and describe their functional roles in the con trol of locomotion.
A Sensor-Based Robot Transition Control Strategy
Authors: Li Y.F.
Published: March 2007

This article presents a real-time sensor-based control approach to the manipulation of the transition of a robot from free space motion to contact with an environment. Use is made of exter nal sensors, including proximity sensors and a force sensor at the end effector of the robot, to control the interaction between the robot and its environment. To achieve direct robot end-effector position control, a short-range fiber optic proximity sensor is used. A multi-phase cantrol strategy is proposed that includes an approach phase, where a force con trol scheme is used prior to contact, as well as a proximity phase where the proximity sensor-based control is employed. Implementation results carried out on an industrial robot are reported.
Adaptive Control of Robotic Manipulators Using Multiple Models and Switching
Authors: Ciliz M. Kemal , Narendra Kumpati S.
Published: March 2007

This article addresses the tracking control problem of robotic manipulators with unknown or changing dynamics. A novel adaptive control strategy is proposed to improve the overall tracking performance. The proposed method makes use of mul tiple dynamic models of the manipulator in an indirect adaptive controller architecture. The models used for the identification of the manipulator are identical, except for the initial estimates of the unknown inertial parameters of the manipulator and its load. The torque input that is applied to the joint actuators is determined at every instant by the identification model that best approximates the robot dynamics. The mathematical formula tion of the controller algorithm and the stability analysis of the overall system are presented. Simulations and experimental test results are also included to demonstrate the improvement in the tracking performance when the proposed method is used.
On the Existence and the Manipulability Recovery Rate of Self-Motion at Manipulator Singularities
Authors: Jiaqing Seng  , Chen Y.C. , O'Neil Kevin A.
Published: March 2007

This article investigates the escapability of redundant manipu lators at a singularity. Escapability means that the manipulator can reconfigure itself from a singular posture to a nonsingular posture via self-motion. Criteria for the classifications of es capable and inescapable singularities are established based on multivariable calculus theorems. For the general case, we give necessary conditions for the escapability of singular configura tions. For singular configurations with only one lost degree of freedom in the workspace, sufficient conditions for the escapa bility are provided. We then show how the arm can escape the singularity at the maximum rate if these sufficient conditions are satisfied. Our method gives the best self-motion among the set of all feasible self-motions, in the sense that the manipula bility measure of the arm increases most rapidly for the chosen self-motion. It is also shown that at a singular configuration with more than one lost degree of freedom in the workspace, the initial rate of recovery of manipulability is very slow, re gardless of the possibility of self-motion. Examples are given to demonstrate the use of these criteria.
Analytical Boundary of the Workspace for General3-DOF Mechanisms
Authors: Abdel-Malek Karim , Yeh Harn-Jou
Published: March 2007

An analytical method is presented to obtain all surfaces en veloping the workspace of a general 3-DOF mechanism. The method is applicable to kinematic chains that can be mod eled using the Denavit-Hartenberg representation for serial kinematic chains or its modification for closed-loop kinematic chains. The method developed is based upon analytical crite ria for determining singular behavior of the mechanism. By manipulating the Jacobian of the underlying mechanism, first- order singularities are computed. These singularities are then substituted into the constraint equation to parameterize singu lar surfaces representing barriers to motion. Singular surfaces are those resultihg from a singular behavior of a joint gen eralized coordinate, allowing the manipulator to lose one or more degrees of mobility. These surfaces are then intersected to determine singular curves, which represent the manipulator losing at least two degrees of mobility. Difficulties in sepa rating singular behaviors at points along singular curves are encountered. Also, difficulties in computing tangents at the intersections of singular curves are addressed. These difficul ties are resolved using an analysis of a quadratic form of the intersection of singular surfaces. An example is presented to validate the theory. Although the methods used are numerical, the main result of this work is the ability to analytically define boundary surfaces of the workspace.
An Inverse Dynamic Model of a Spherical Electrohydraulic Actuator for Use in a Dexterous Mechanical Hand
Authors: Sharma Shikha , Ogot Madara M.
Published: March 2007

The purpose of this article is to develop an inverse dynamic model of a two-degree-of-freedom electrohydraulic actuator. The actuator is to be incorporated at the base of each of three fingers of a nine-degree-of-freedom mechanical hand, currently under development. Motion in the proposed actuator is fa cilitated about intersecting pitch and yaw axes, thus creating spherical actuation. The dynamic model incorporates frictional and hydraulic losses, which are commonly overlooked sources of energy dissipation. The model is to be used in the control scheme of the mechanical hand and in the optimal synthesis procedure of the actuator. The latter application, briefly de scribed here, takes into account specified motion and torque requirements, pressure, peak-input force, and size constraints. Particular attention is paid to traditional performance indices, such as mechanical advantage.