bluuebunny/crossref_metadata_2025 huggingface dataset:
An Optical System to Measure the End Effector Position for On-line Control Purposes
Authors: Heeren Theo A. G. , Veldpaus Frans E.
Published: March 2007

This article describes an optical system to measure the coordinates of a manipulator's end effector, which can move in a horizontal plane of approximately 1 × 1 m2. Two rotatable laser beams track a retroreflector pair, mounted on the end effector. The coordinates are calcu lated from the measured beam rotations. The resolution and reproducibility of the coordinate measurement is 0.05 mm. The maximum tracking speed mounts up to 5 m/s. Using components similar to those applied in CD players, the total cost of all mechanical, optical, and analog elec tronic components can be kept as low as $3000. On an IBM AT-compatible PC, it takes 1 ms to calculate the x and y coordinates from the measured signals.
Grasp Synthesis of Polygonal Objects Using a Three-Fingered Robot Hand
Authors: Park Young C. , Starr Gregory P.
Published: March 2007

Grasping an object with a multifingered robot hand requires complete constraint of its motion by contacts. Complete con straint of an object can also be described using force equilib rium. If any external force on the object can be balanced by applicable contact forces, a stable grasp has been achieved. A force closure grasp is such a grasp. This article presents a simple and efficient algorithm to find an optimum force clo sure grasp of a planar polygon using a three fingered robot hand. The optimum grasp is defined as a grasp that has the minimum value of a heuristic function. The heuristic function is formulated from the consideration of the possible uncertainties inherent in implementation. Even though a planar force clo sure grasp can be obtained using only two friction contacts, we consider only grasps where all three friction contacts explicitly participate. To find the optimum grasp, all feasible combina tions of edges and/or vertices are identified first. An edges and/or vertices combination is feasible when a stable grasp is attainable by an appropriate selection of three contacts on them. Then, using computational geometry, a single grasp is constructed on each feasible combination. Finally, the grasps obtained are compared using the heuristic quality measure. A test of our algorithm on several different polygons shows that the resulting grasp is realistic and is obtained fast enough for real-time use.
Optimal Trajectory Planning of Manipulators With Collision Detection and Avoidance
Authors: Deming Wang  , Hamam Yskandar
Published: March 2007

This article presents an optimal trajectory-planning method for robot manipulators with collision detection and avoidance. The obstacles and robot segments are represented by a set of convex polyhedra. The collision detection is performed at each discretized robot configuration by an efficient procedure devel oped with the computational geometry method, which computes a distance function of the robot segments and the obstacles. By introducing this function for specifying the collision-free con straint, the path-planning problem is formulated as an optimal control problem using the augmented Lagrangian, which may be considered as a combination of the duality, penalty and con straint relaxation methods. The problem is solved by a robust UZAWA-like algorithm, where a subgradient method is applied for the primal optimization, as the distance function is not ev erywhere differentiable. An example is given for the trajectory planning of a robot arm with three revolute joints.
Optimal Planning of a Collision-free Trajectory of Redundant Manipulators
Authors: Galicki Miroslaw
Published: March 2007

In this study, global planning of a collision-free trajectory (simultaneous planning of geometric path and its time para meterization) involving potential functions and direct kinematic and dynamic equations of the manipulator is presented. This planning is based on using the necessary conditions of min imum for an integral type criterion. General transversality conditions corresponding to the boundary ones (resulting from the task to be performed) are derived. Thus, closed systems of boundary dependences fully specifying differential equations, which arise from the necessary conditions of extreme for the above criterion, are obtained. As a result, this system renders it possible to reduce the collision-free trajectory planning problem to a two-point boundary value problem. A numerical example involving a manipulator of three-revolute kinematic pairs of the Vth class is considered.
A Video Signal Processing Technique for Vibration Measurement of a Flexible Beam
Authors: Tang Pei-Chong , Lu Shui-Shong
Published: March 2007

A video system is used as a single contactless multipoint dis placement sensor to measure the vibration displacement of a beam. In this article, several schemes are proposed to reduce the image processing time and to increase its accuracy. The vibration displacements of the entire beam are measured with a sampling rate of 60 Hz. From these measured data, the mode shapes and vibration states can be calculated. The video system is shown to have a potential for on-line control and on-line identification of flexible beam systems.
Time-varying Feedback Stabilization of Car-like Wheeled Mobile Robots
Authors: Samson Claude
Published: March 2007

Many nonholonomic mechanical systems, such as common wheeled mobile robots, are controllable but cannot be stabilized to given positions and orientations bv using smooth pure-state feedback control. However, as shown in Samson (1990), such systems may still be stabilized by using smooth time-varying feedbacks,—i.e., feedbacks that explicitly depend on the time variable. This possibility is here applied to the stabilization of a class of nonlinear systems whose equations encompass simple car models. A set of stabilizing smooth time-varying feedbacks is derived, and simulation results are given.
Eye-to-Hand Coordination for Vision-Guided Robot Control Applications
Authors: Wijesoma S.W. , Wolfe D.F.H. , Richards R.J.
Published: March 2007

A great many tasks in automated manufacturing and assem bly involve robot operations guided by vision systems. In such situations, linking of machine vision systems and robot manipu lators has relied on accurate camera-to-real world calibration processes and on highly accurate robot arms with well-known kinematics. This article describes a real-time vision-control strategy for "hand-to-eye coordination " that gives good per formance even in the presence of significant vision system miscalibrations and kinematic model parametric errors.
Object Handling Using Two Arms Without Grasping
Authors: Xiaoping Yun
Published: March 2007

Two cooperative manipulators equipped with open-palm end effectors are particularly suited to handle large objects. This can be achieved by having one palm push from one end and the other from the opposite end. This article studies modeling and coordinated control of two-arm pushing operations. The performance of such tasks requires simultaneous control of the motion trajectory of the object and the interaction force. Control of the interaction force is essential to avoid dropping or crushing objects. The motion and force control problem is complicated by the presence of unilateral constraints, as the manipulators can only push the object. The control problem is first formulated in the state space. A coordinated control method is then presented that utilizes a state feedback to de couple the motion control subsystem from the force control subsystem. The unilateral constraints are satisfied during the entire motion period by using a proposed force control plan ning algorithm. The effectiveness of the control method is verified by simulations.
Robotic Exploration of Surfaces With a Compliant Wrist Sensor
Authors: Sinha Pramath R. , Yangsheng Xu  , Bajcsy Ruzena K. , Paul Richard P.
Published: March 2007

This article presents some results of an ongoing research project to investigate the components and modules that are necessary to equip a robot with exploratory capabilities. Of particular interest is the recovery of certain material properties from a surface, given minimal a priori information, with the intent to use this information to enable a robot to stand and walk stably on a surface that is unknown and unconstrained. To this end, exploratory procedures (EPs) have been designed and implemented to recover penetrability, compliance, and surface roughness by exploring the surface using a compliant wrist sensor. A six-degree-of-freedom compliant wrist sensor that combines passive compliance and active sensing has been developed to provide the necessary flexibility for force and con tact control, as well as accurate position control. This article describes the compliant wrist and sensing mechanism design along with a hybrid control algorithm that utilizes the sensed information from the wrist to adjust the apparent stiffness of the end effector as desired.
Control of Robotic Manipulators During General Task Execution: A Discontinuous Control Approach
Authors: Mills James K. , Lokhorst David M.
Published: March 2007

In this article, a control methodology is proposed that ad dresses the problem of control of robotic manipulators during a general class of task that requires the manipulator to make a transition from (I) noncontact motion to contact motion and (2) contact motion to noncontact motion. Specifically, the problem of control of a general n-degree-of-freedom rigid-link robotic manipulator during a general class of tasks, as described ear lier, is treated. It is assumed that during the contact phase of the assumed task, frictionless point contact is made with fixed objects in the manipulator work environment, which is modeled as a linear mechanical impedance. Furthermore, it is assumed that exact knowledge of the manipulator and work environment kinematic and dynamic parameters is available.

The following closed-loop behavior is achieved with the pro posed control law: (1) the closed-loop system exhibits global asymptotic stability; (2) asymptotic trajectory tracking of gen eralized force and position inputs is achieved; and significantly, (3) on inadvertent loss of contact by the manipulator, contact is reestablished, and generalized forces and positions are again asymptotically achieved. This closed-loop behavior is achieved in the presence of collisions between the manipulator and ob jects in the manipulator work environment; such collisions may include multiple impacts as a result of bouncing on initial contact. A general mathematical framework is established to prove that the closed-loop robotic system, with a discontin uous control applied, is asymptotically stable. Experimental results performed on a two-degree-of-freedom direct-drive robot support the theoretical claims made in this work.
Periodic Motions of a Hopping Robot With Vertical and Forward Motion
Authors: M'Closkey Robert T. , Burdick Joel W.
Published: March 2007

This article analyzes the global dynamical behavior of sim plified hopping robot models that are analogous to Raibert's experimental machines. We first review a one-dimensional ver tical hopping model that captures both the vertical hopping dynamics and nonlinear control algorithm. Second, we present a more complicated two-dimensional model that includes both forward and vertical hopping dynamics and a foot placement algorithm. These systems are analyzed using a Poincare return map. In this approach, issues of stability and global dynamical behavior are reduced to the study of the fixed points of this map. For the one-dimensional model, a closed-form return map is obtained. For the two-dimensional model, we derive an exact return map based on the first integrals of motion. Because this map can only be constructed numerically, we also derive an analytical approximation to the return map based on perturba tion methods. The approximate return map is shown to closely predict the behavior of the exact map for small forward run ning velocities. In addition, the approximate return map can be used to quantitatively explore the coupling of vertical and lat eral dynamics and to determine the effect of the foot placement algorithm on dynamical behavior

The bifurcation diagrams, which capture variations in dy namical behavior with respect to the variations in system and control parameters, are also constructed. The bifurcation dia grams exhibit a period-doubling cascade. In other words, for certain system parameter values, Raibert's control algorithm can lead to an anomalous nonuniform, but stable, hopping be havior. Using the vertical model results as a guide, we interpret the interesting dynamical behavior of this system.
Dynamic Coupling Between the Joint and Elastic Coordinates in Flexible Mechanism Systems
Authors: Shabana A.A. , Hwang Y.L.
Published: March 2007

The aim of this investigation is to develop an efficient proce dure for decoupling the joint and elastic accelerations while maintaining the nonlinear inertia coupling between the rigid body motion and the elastic deformation. The inertia projec tion schemes used in most existing recursive methods for the dynamic analysis of flexible robotics and mechanism systems lead to dense coefficient matrices in the acceleration equations, and consequently there is a strong dynamic coupling between the joint and elastic coordinates. When the number of elastic degrees of freedom increases, the size of the coefficient matrix in the acceleration equations becomes large, and consequently the use of these recursive methods for solving for the joint and elastic accelerations becomes less efficient. This investigation discusses the problems associated with the inertia projection schemes used in the existing recursive methods, and it is shown that decoupling the joint and elastic accelerations using these methods requires the factorization of nonlinear matrices whose dimensions depend on the number of elastic degrees of freedom of the system. An amalgamated formulation that can be used to decouple the elastic and joint accelerations is then used to obtain a reduced system of equations whose dimension is in dependent of the number of elastic degrees of freedom of the system. This system can be solved for the joint accelerations as well as the joint reaction forces. The use of the procedure de veloped in this article is demonstrated using a four-bar flexible mechanism.
On the Kinematic Design of Spherical Three-Degree-of- Freedom Parallel Manipulators
Authors: Gosselin Clément M. , Lavoie Eric
Published: March 2007

This article studies the kinematic design of different types of spherical three-degree-of-freedom parallel manipulators. The mechanical architectures presented have been introduced elsewhere. However designs having at least one isotropic configuration are suggested here for the first time. Isotropic configurations are defined, in turn, as those configurations in which the Jacobian matrix, mapping the angular velocity vec tor of the effector into the joint velocities, is proportional to an orthogonal matrix. First, a review of the direct and inverse kinematics of spherical three-degree-of-freedom parallel ma nipulators is outlined, and a general form for the Jacobian matrix is given. Parallel manipulators with revolute or pris matic actuators are discussed. Then, the concept of kinematic conditioning is recalled and used as a performance index for the optimization of the manipulators. It is shown that this leads to designs having at least one isotropic configuration. Finally, a few examples of such designs are presented.
Kinematics and Statics of Manipulation Using the Theory of Polyhedral Convex Cones
Authors: Hirai Shinichi , Asada Haruhiko
Published: March 2007

A new approach to the kinematic and static analysis of ma nipulative tasks performed through mechanical contacts is presented. A variety of manipulation problems, including as sembly and grasps, have been treated separately in robotics research. All of the problems are treated as ways to solve a certain class of inequalities resulting from the unidirectional nature of mechanical contacts. One of the fundamental diffi culties in the analysis of manipulative tasks is the intractable nature of inequalities.

In this article, we establish an underpinning mathematical tool for dealing with a variety of manipulative tasks that are governed by unidirectional constraints. First, we introduce a coherent representation for formulating various manipulation problems. Second, we develop several procedures based on the theory of polyhedral convex cones to solve these problems in a systematic and straightforward manner. The method is then implemented on a computer and applied to a variety of manipulation problems, including grasping, fixturing, and hybrid position/force control.
Symbolic Singular Value Decomposition for a PUMA Robot and Its Application to a Robot Operation Near Singularities
Authors: KirΛanski Manja V. , Boric Mirko Dj.
Published: March 2007

Singular value decomposition has received considerable atten tion in robot control during the past several years because of the fact that it may be used in solving the problem of robot operation in singular configurations. However, its main draw back is its high computational complexity when compared with that of the Gaussian elimination or analytical inverse kinematic solution. In this article we have derived symbolic expressions for matrices of the decomposition for both a 2-DOF planar manipulator and a 6-DOF PUMA robot. This reduces the com putational burden by an order of magnitude and gives us more insight into the nature of the singularities. The symbolic ex pressions have been applied to obtain the damped least-squares solution for joint velocities. Some modifications of the damped least-squares solution are proposed, and the simulation results are included. The method can be applied to other robots when position and orientation problems can be separated.
A Simple Robust Control Scheme for Robot Manipulators With Only Joint Position Measurements
Authors: Feng Weining , Postlethwaite Ian
Published: March 2007

In this article, it is shown that the point-to-point motion con trol of rigid robot manipulators can be achieved by a simple fixed control law that requires only the measurements of the joint positions, unlike most robot motion control, in which joint velocities are invariably needed. Apart from some commonly used assumptions about the manipulator dynamic equation, the control scheme can dispense with any modeling information and yet achieve global stability. Moreover (if the joint config uration is free from singularity), the control strategy can also be used in task space control without any extra technical diffi culty, except for the on-line calculation of the Jacobian matrix. The robustness property of the control law against parasitic dynamics from the driving system is discussed.
Model Following Control of a Variable Inertia Positioner
Authors: Mukherjee S. , Mukhopadhyay S. , Sengupta S.N.
Published: March 2007

The work presented here shows the results of a simulation made on a two-degree-of-freedom plant (robot joint) driven by an ideal model. The reference input is applied only to the model, and control effort on the plant is generated by observ ing the deviations of its states from the ideal norms issued by the model. The model thus constrains the plant to follow it. The design of this system is based primarily on the construction of the model, which should have the same essential features but without the variable parameters found in the plant in question. It has been shown that satisfactory following of the model is possible with this approach, even under wide variations in the plant inertia (i.e., positive and negative rates of variation, as well as fluctuations in the load). The performance robustness of this arrangement is remarkable, and its implementation is not complex.
Dynamic Coordination of Multiple Robot Arms With Flexible Joints
Authors: Jankowski Krzysztof P. , ElMaraghy Hoda A. , ElMaraghy Waguih H.
Published: March 2007

A nonlinear decoupling and linearizing feedback control for dynamic coordination of multiple robot arms handling an ob ject constrained by the environment is considered. A general method is presented that ensures an exact feedback lineariza tion for cases of both rigid and flexible joint arms, as the joint flexibility can cause instability of robotic system control. The method takes the manipulator dynamics and object dynamics into consideration, along with material constraints imposed on the system (mixed contact conditions between arms and object and between object and the environment) and program con straints (specified internal forces, contact forces, and object motion). A method for internal force parameterization, which uses a set of kinematic constraints imposed on the motion of the robot end effectors, is proposed. Control algorithms are developed for redundant flexible joint manipulators designed to have more joints than necessary for given tasks. The appli cation of the control law produces a set of decoupled linear subsystems defined in subspaces that have different physical meaning. The implementation of this method is demonstrated for the case of a system of two planar three-link arms with the end effectors manipulating an object and with different constrained task configurations. Numerical experiments demon strate high-precision tracking capabilities of the method, prove that it can be implemented on fast contemporary computers, and show that robustness to bounded modeling errors and external disturbances can be achieved.
Comparison of Theoretical and Experimental Force/ Motion Trajectories for Dextrous Manipulation With Sliding
Authors: Kao Imin , Cutkosky Mark R.
Published: March 2007

In this article we compare theoretical and experimental tra jectories obtained for sliding an object with the fingers of a dextrous hand. The experiments were conducted using a two- fingered planar manipulator with soft fingers. Forceltorque sensors monitored the contact forces at the fingertips, and a vision system tracked the motion of the object. The predicted trajectories were obtained using a quasistatic sliding analysis and assuming Coulomb friction at the contacts. Close agree ment between the predicted and experimental results indicates that quasistatic sliding analyses can be used for motion plan ning with soft sliding fingertips, provided that the average values of the contact forces and coefficient of friction are accu rately known.
Robot Hand Grasping and Related Problems: Optimal Control and Identification
Authors: Panagiotopoulos P.D. , Al-Fahed A.M.
Published: March 2007

The optimal control problem related to the grasping of ob jects by multifingered grippers of robots is investigated. The Linear Complementarity Problem (LCP), which governs the static unilateral and frictional contact problem, is formulated, and certain propositions concerning necessary and sufficient conditions for its solution are proved. Next the optimal control problem is formulated and studied. Presented also is numeric application to illustrate the theory.
Odor Sensing for Robot Guidance
Authors: Deveza Reimundo , Thiel David , Russell Andrew , Mackay-Sim Alan
Published: March 2007

There is no generally applicable technique for finding the position of an autonomous mobile robot operating in an un structured or varying environment. This article describes a project to investigate the use of short-lived navigational mark ers consisting of olfactory chemicals to guide mobile robots and to help them search and explore efficiently. Such a method of laying a trail to mark the path of a robot provides differ ential navigational information relative to the starting point and starting direction. Many insects employ olfactory cues as navigation aids and to improve their efficiency when searching for food. Three scenarios are proposed in which navigational markers can be of assistance to a mobile robot. The design and characteristics of an adsorbed mass olfactory sensor are described. This sensor was designed to be mounted on a mo bile robot and is suitable for detecting and tracking olfactory chemicals. The performance of this sensor is described together with preliminary results of using it to track an odor trail.
A Symbolic Formulation of Dynamic Equations For a Manipulator With Rigid and Flexible Links
Authors: Lin J. , Lewis F.L.
Published: March 2007

The objective of this article is to present an efficient proce dure for computer generation of the dynamic equations for a planar robot manipulator with arbitrarily assigned rigid or flexible links using any desired flexible mode shape functions. The dynamic equations for the serial link manipulator are derived using Lagrange's formulation and elastic deflection with the assumed-mode method. Fewer approximations are made than in other approaches, resulting in greater accuracy. A method to determine the centrifugal and Coriolis matrix is presented that yields an important structural property. The approach is systematic and allows a symbolic program to be written in Mathematica using a system of several groups and a constructed database. Four examples are illustrated to verify the dynamic equations. The stability of the zero dynamics is compared for different mode shape functions.
Experiments in Control of a Flexible-Link Robotic Manipulator With Unknown Payload Dynamics: An Adaptive Approach
Authors: Alder Lawrence J. , Rock Stephen M.
Published: March 2007

This article presents technology that extends the concept of end-point control of a flexible-link robot arm to handle payloads with unknown internal dynamics. The approach is based on merging high-performance control with an innovative identification algorithm in a self-tuning regulator framework. Payload dynamics are identified in real time using recently de veloped subspace fitting techniques. Sufficient excitation issues are addressed. End-point feedback controllers are formulated using frequency-weighted linear quadratic gaussian design methods.

Experimental results demonstrating precision control of a very flexible single-link robot arm with unknown dynamic payloads are presented.
A Note on the Use of Identification Jacobians for Robot Calibration
Authors: Hanqi Zhuang
Published: March 2007

Two issues related to robot calibration are addressed in this communication. The first issue is how many position-dependent error parameters should be used in modeling a robot manipu lator. The second issue is how to select a proper identification Jacobian when only position measurements of the robot end effector are available. Conclusions are made regarding these issues after short discussions.
Efficient Collision Prediction Among Many Moving Objects
Authors: Hayward Vincent , Aubry Stéphane , Foisy André , Ghallab Yasmine
Published: March 2007

We consider the problem of flagging all collisions between a large number of dynamic objects. Because the number of possible collisions grows quadratically with the number of objects, a brute force approach is not applicable with finite computational resources.

Hence, we propose a scheduling mechanism that reduces the computational load by exploiting the coherence of the world throughout time. This mechanism has a very simple structure and easily lends itself to distributed processing. It considers all pairwise interactions between objects and maintains a structure that reflects the imminence, or urgency, of collision for each pair. Bounds on the urgency of collisions can be computed given minimal knowledge of the system dynamics. For example, we represent physical objects by their positions and by bounds on their relative speeds and accelerations. These are assumed to be available at all times. If the environment does not change too rapidly, the mechanism flags all collisions. False alarms may also be generated but can be eliminated with a specialized exact collision post-processor.

We address the question of how often to perform the col lision checks while guaranteeing that all collisions will be caught. Given the large number of possible environments and motions, no general optimal answer can be provided. Yet the soundness and efficiency of the proposed algorithm is eaper imentally verified in the case of a simple world consisting of many spheres moving simultaneously and randomly.
Modeling Gimbal Axis Misalignments and Mirror Center Offset in a Single-Beam Laser Tracking Measurement System
Authors: Hanqi Zhuang  , Roth Zvi S.
Published: March 2007

The calibration of robots and machine tools normally requires external pose measuring devices to provide precision cal ibration measurement data. Among the various coordinate measuring techniques, laser tracking systems based on in terferometry offer the potential for continuously producing noninvasive and highly accurate measurements over a large work volume. This article addresses the error modeling is sue for laser tracking coordinate measuring systems, which is crucial in the accuracy enhancement of such systems.

Relative distance measurements provided by laser interfer ometers have an extremely high resolution. However, accuracy errors of a coordinate measuring machine based on laser tracking are dominated by geometric errors in the tracking mir ror system. Major geometric error sources include gimbal axis misalignments and mirror center offset. In this article a kine matic model for the single-beam tracker is developed in which a necessary and sufficient number of kinematic parameters are used to represent these two types of error sources for ar bitrary target positions. This model, together with its error model, which is also presented in this article, can be used for design, calibration, and control of single-beam laser tracking measurement systems.
Adaptive Compliant Motion Control for Dexterous Manipulators
Authors: Colbaugh Richard , Seraji Homayoun , Glass Kristin
Published: March 2007

This article presents two adaptive schemes for compliant mo tion control of dexterous manipulators. The first scheme is developed using an adaptive impedance control approach for torque-controlled manipulators, whereas the second strategy is an adaptive admittance controller for position-controlled manipulators. The proposed controllers are very general and computationally efficient, as they do not require knowledge of the manipulator dynamic model or parameter values of the manipulator or the environment and are implemented without calculation of the inverse dynamics or inverse kinematic trans formation. It is shown that the control strategies are globally stable in the presence of bounded disturbances and that in the absence of disturbances the ultimate bound on the size of the system errors can be made arbitrarily small. The capabilities of the proposed control schemes are illustrated through both computer simulations and laboratory experiments with a dex terous Robotics Research Corporation seven-degrees-of-freedom (DOF) manipulator.
Mobile Robot Sonar for Target Localization and Classification
Authors: Kleeman Lindsay , Kuc Roman
Published: March 2007

A novel sonar array is presented that has applications in mobile robotics for localization and mapping of indoor en vironments. The ultrasonic sensor localizes and classifies multiple targets in two dimensions to ranges of up to 8m. By accounting for effects of temperature and humidity, the sys tem is accurate to within 1 mm and 0.1° in still air. Targets separated by 10 mm in range can be discriminated. The error covariance matrix for these measurements is derived to allow fusion with other sensors. Targets are statistically classified into four reflector types: planes, corners, edges, and unknown.

This article establishes that two transmitters and two re ceivers are necessary and sufficient to distinguish planes, corners, and edges. A sensor array is presented with this minimum number of transmitters and receivers. A novel de sign approach is used such that the receivers are closely spaced so as to minimize the correspondence problem of as sociating different receiver echoes from multiple targets.

A linear filter model for pulse transmission, reception, air absorption, and dispersion is used to generate a set of tem plates for the echo as a function of range and bearing angle. The optimal echo arrival time is estimated from the maximum cross-correlation of the echo with the templates. The use of templates also allows overlapping echoes and disturbances to be rejected. Noise characteristics are modeled for use in the maximum likelihood estimates of target range and bearing. Experimental results are presented to verify assumptions and characterize the sensor.
Motion and Force Control of Coordinated Robots During Constrained Motion Tasks
Authors: Hu Yan-Ru , Goldenberg Andrew A. , Zhou Chin
Published: March 2007

The motion of coordinated robots manipulating an object con strained by the contact with an environment, in the presence of uncertainty in the dynamic models, represents an important class of control problems. In this article an approach to motion and force control of such multiple coordinated robots, based on an adaptive scheme, is proposed. Three major variables are regulated simultaneously: the object motion, the contact force between the object and the environment, and the internal force. The adaptive controller estimates the unknown parameters of the coordinated robots and object in terms of certain error equations. The convergence of the motion, contact, and inter nal force errors is analyzed using Lyapunov stability theory. The proposed controller is also experimentally evaluated on two coordinated AdeptOne robots. In comparison with fixed parameter controllers, the experimental results show that the proposed controller improves the object motion, contact, and internal force tracking accuracy for a class of robotic systems with uncertain knowledge of the dynamic model.
Shortest Paths for a Car-like Robot to Manifolds in Configuration Space
Authors: Moutarlier Philippe , Mirtich Brian , Canny John
Published: March 2007

Reeds and Shepp (1990) studied the problem of finding the shortest feasible path for a car-like robot between two points in configuration space. We extend their results to find the shortest feasible path between a point and a manifold in configuration space. Our approach is based on the Lagrange method for optimizing a function while constrained to a manifold. Solving the problem analytically is much faster than numerical dis cretization techniques. In addition to providing insight into the underlying structure of Reeds and Shepp paths, this research has many applications in path planning. Planning algorithms often rely on the notion of clearance from obstacles, and for car-like mobile robots, clearance is closely related to the length of the shortest feasible path to an obstacle. In addition, one may want to bring the robot to a predefined path (such as a skeleton). Skeletonization and potential field methods are two examples of planning paradigms where our algorithm would prove useful.
Interference-Free Insertion of a Solid Body Into a Cavity: An Algorithm and a Medical Application
Authors: Joskowicz Leo , Taylor Russell H.
Published: March 2007

This article presents a novel algorithm for efficiently computing an interference-free insertion path of a body into a cavity and shows its practical use in the insertability analysis of custom orthopedic hip implants. The algorithm is designed to handle tightly fit, very complex three-dimensional bodies requiring fine, complex, coupled six-degree-of-freedom motions in a preferred direction. It provides a practical method for efficiently handling the geometric complexity of tight-fit insertions. The algorithm computes an insertion path consisting of small interference-free body motion steps. It formulates local, linearized configuration space constraints derived from the shapes and computes suc cessive motion steps by solving a series of linear optimization problems whose solution corresponds to the maximum allowed displacement in a preferred direction satisfying the constraints. It either finds a successful insertion path or a stuck conftgura tion. We demonstrate the algorithm with EXTRACT, a program for analyzing the insertability of cementless custom orthopedic hip implants. EXTRACT computes interference-free insertion paths for tightly fit implant and canal shapes described with 10,000 facets to an accuracy of 0.01 inch in 30 minutes on a workstation. It has been successfully tested on 30 real cases provided by a medical equipment manufacturer.
The Virtual Springs Method: Path Planning and Collision Avoidance for Redundant Manipulators
Authors: McLean Alistair , Cameron Stephen
Published: March 2007

Potential-field based methods for path planning have the ad vantage of speed, but also a reputation for getting stuck in local minima when used with complex systems such as re dundant manipulators. We have developed a novel method of setting up a potential-field system that replaces rigid links by stiff (virtual) springs. The method is fast, directly suitable for parallel processing, and experimentally much less prone to the danger of local minima. Although quite general, it is par ticularly suited to use with manipulators whose links are thin compared with their length.
Geometric Sensing of Known Planar Shapes
Authors: Jia Yan-Bin , Erdmann Michael
Published: March 2007

Industrial assembly involves sensing the pose (orientation and position) of a part. Efficient and reliable sensing strategies can be developed for an assembly task if the shape of the part is known in advance. In this article we investigate two problems of determining the pose of a polygonal part of known shape for the cases of a continuum and a finite number of possible poses, respectively.

The first problem, named sensing by inscription, involves determining the pose of a convex n-gon from a set of m sup porting cones. An algorithm with running time O( nm) that almost always reduces to O(n + m log n) is presented to solve for all possible poses of the polygon. We prove that the number of possible poses cannot exceed 6n, given m ≥ 2 supporting cones with distinct vertices. Simulation experiments demonstrate that two supporting cones are sufficient to determine the real pose of the n-gon in most cases. Our results imply that sensing in practice can be carried out by obtaining viewing angles of a planar part at multiple exterior sites in the plane.

On many occasions a parts feeder will have reduced the number of possible poses of a part to a small finite set. Our second problem, named sensing by point sampling, is con cerned with a more general version: finding the minimum number of sensing points required to distinguish between n polygonal shapes with a total of m edges. In practice this can be implemented by embedding a series of point light detectors in a feeder tray or by using a set of mechanical probes that touch the feeder at a finite number of predeter mined points. We show that this problem is equivalent to an NP-complete set-theoretic problem introduced as Discriminat ing Set, and present an O( n2m2) approximation algorithm to solve it with a ratio of 2 In n. Furthermore, we prove that one can use an algorithm for Discriminating Set with ratio c log n to construct an algorithm for Set Covering with ratio c log n + O(log log n). Thus the ratio 2 In n is asymptotically optimal unless NP ⊂ DTIME( npoly log n), a consequence of known results on approximating Set Covering. The complexity of subproblems of Discriminating Set is also analyzed, based on their relationship to a generalization of Independent Set called 3-Independent Set. Finally, simulation results suggest
Practical Force-Motion Models for Sliding Manipulation
Authors: Howe Robert D. , Cutkosky Mark R.
Published: March 2007

The goal of this article is to develop practical descriptions of the relationship between forces and motions in sliding manipu lation. We begin by reviewing the limit surface, a concept from the mechanics of sliding bodies that uses kinematic analysis to find the force and moment required to produce any given sliding motion. Next we provide experimental results showing that the limit surface only approximates the actual force-motion relationship. Then we look at other approximations that can be used to provide a simplified model useful in control, planning, and simulation of manipulation. These approximations include square pyramids, cones, ellipsoids, and ellipsoids with facets removed. Different approximations may be most appropriate, depending on the required computational speed and accuracy and the need to produce conservative results.
Modeling Mechanisms with Nonholonomic Joints Using the Boltzmann-Hamel Equations
Authors: Cameron Jonathan M. , Book Wayne J.
Published: March 2007

This article describes a new technique for deriving dynamic equations of motion for serial chain and tree topology mech anisms with common nonholonomic constraints. For each type of nonholonomic constraint, the Boltzmann-Hamel equations produce a concise set of dynamic equations. These equations are similar to Lagrange's equations and can be applied to mechanisms that incorporate that type of constraint. A small library of these equations can be used to efficiently analyze many different types of mechanisms.

Nonholonomic constraints are usually included in a La grangian setting by adding Lagrange multipliers and then eliminating them from the final set of equations. The ap proach described in this article automatically produces a minimum set of equations of motion that do not include La grange multipliers.
Kinematic Isotropy and the Optimum Design of Parallel Manipulators
Authors: Zanganeh Kourosh E. , Angeles Jorge
Published: March 2007

The differential kinematic equations (DKE) of parallel manip ulators usually involve two Jacobian matrices that, depending on the role they play in the kinetostatic transformation between the joint and Cartesian variables, are commonly referred to as the forward and the inverse Jacobians. In this article, we make use of the special structure of these Jacobians to define a set of conditions under which a parallel manipulator can be rendered isotropic. These conditions are general, and pro vide a systematic method for the optimum kinematic design of parallel manipulators, with or without introducing structural constraints. The application of the proposed conditions is illus trated in detail through a few examples, one of which pertains to the design of a 6-DOF isotropic parallel manipulator.
Application of a Precision-Enhancing Measure in 3D Rigid-Body Positioning Using Camera-Space Manipulation
Authors: Gonzalez-Galvan Emilio J. , Skaar Steven B. , Korde Umesh A. , Wenzong Chen
Published: March 2007

This article presents an iterative procedure for improving the precision obtainable with camera-space manipulation. It also reports on extensive experimental results using this procedure with a task of some historical note in the area of vision-guided robotics, a task that involves close-tolerance, 3D, rigid-body assembly. The procedure was devised to achieve higher pre cision by introducing to parameter estimates the accuracy of the "perspective" camera model, while retaining the numerical advantage of the orthographic model. The camera-space coor dinates of each of several visually detected cues on the grasped object are multiplied by an iteratively improved correction fac tor, so that the modified image-plane appearances of the cues more closely approach the ideal of an orthographic projection. The correction factor is normalized near the point of maneuver termination so that camera-space maneuver objectives may stay unchanged. A similar strategy may be used to determine the camera-space objectives themselves. Results of experimental and simulation studies are presented and discussed.
Obtaining Optimal Mobile-Robot Paths with Nonsmooth Anisotropic Cost Functions Using Qualitative-State Reasoning
Authors: Rowe Neil C.
Published: March 2007

Realistic path-planning problems frequently show anisotropism, dependency of traversal cost or feasibility on the traversal heading. Gravity, friction, visibility, and safety are often anisotropic for mobile robots. Anisotropism often differs qualitatively with heading, as when a vehicle has insufficient power to go uphill or must brake to avoid accelerating down hill. Modeling qualitative distinctions requires discontinuities in either the cost-per-traversal-distance function or its derivatives, preventing direct application of most results of the calculus of variations. We present a new approach to optimal anisotropic path planning that first identifies qualitative states and per missible transitions between them. If the qualitative states are chosen appropriately, our approach replaces an optimization problem with such discontinuities by a set of subproblems with out discontinuities, subproblems for which optimization is likely to be faster and less troublesome. Then the state space in the near neighborhood of any particular state can be partitioned into "behavioral regions" representing states optimally reach able by single qualitative "behaviors, " sequences of qualitative states in a finite-state diagram. Simplification of inequalities and other methods can identify the behavioral regions. Our ideas solve problems that are not easily solvable any other way, especially problems with what we define as "turn-hostile" anisotropism. We illustrate our methods on two examples, navigation on an arbitrarily curved surface with gravity and friction effects (for which we show much better performance than a previously published program 22 times longer), and flight of a simple missile.
Harmonic Functions and Collision Probabilities
Authors: Connolly Christopher I.
Published: March 2007

There is a close relationship between harmonic functions— which have recently been proposed for path planning—and hitting probabilities for random processes. The hitting proba bilities for random walks can be cast as a Dirichlet problem for harmonic functions, in much the same way as in path plan ning. This equivalence has implications both for uncertainty in motion planning and in the application of machine-learning techniques to some robot problems. In particular, Erdmann's method can directly incorporate such hitting probabilities. In addition, the value functions obtained by reinforcement learn ing algorithms can be rapidly reconstructed by relaxation or resistive networks, once the extrema for such functions are known.
Model-Based Motion and Force Control for Flexible-Joint Robot Manipulators
Authors: Massoud Atef T. , EIMaraghy Hoda A.
Published: March 2007

Two model-based control algorithms to control the motion and force of flexible-joint robot manipulators are presented. Both algorithms are based on the feedback-linearization concept, and utilize a fourth-order feedback-linearizable model of the flexible-joint manipulators. The first algorithm, dynamic hy brid controller, deals with the problem where the flexible-joint robot is constrained by a rigid environment, and aims at di rect control of the contact forces. A constraint frame is derived that enables decoupling of the system into a position subsystem and a force subsystem. A nonlinear feedback-control law is designed to first decouple and linearize the constrained flexible- joint manipulator system, then impose desired closed-loop characteristics in each subsystem independently. The second algorithm, impedance controller, aims at regulating the rela tionship between the contact force and the difference between the commanded and true positions of the end point. A desired target impedance is designed for the end point of the flexible- joint robot manipulator in the reference frame. A nonlinear feedback controller is designed to linearize the system and to impose the target impedance. The same controller is used when the robot is performing compliant and free motions. An experimental two-link, flexible-joint robot manipulator in con tact with a straight wall is used to evaluate and compare the performance of the two controllers.