bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformation Mathematics of a Mobile Robot Work Center
Authors: Sturdivant Vernon R.
Published: March 2007

A mobile robot work center has been constructed for the Navy by Southwest Research Institute for the purpose of re moving rivets from airplane wings during overhaul and re pair. This system is referred to as a deriveter. Two features of the robotic deriveter system required the derivation of new mathematical relationships. The first feature is the computa tion of the transformation relating the robot and wing refer ence frames to each other based on measurements made by the robot, which is mounted on a movable vehicle. Four methods for finding this transformation are presented and the applicability of each to the deriveter is discussed. The second feature is that of positioning the end-effector, tool cen terline so that it is perpendicular to the wing surface, with the tool center point at a given offset from the wing based on measurements made by the robot end effector.
Historical Perspective and State of the Art in Robot Force Control
Authors: Whitney Daniel E.
Published: March 2007

This paper combines histarical lineage, assessment of the state of the art, and discussion of unsolved problems in robot force control. The difference between continuous and logic branching strategies is described. The development of various impedance strategies and hybrid methods is traced and com pared. The problem of stability is discussed, and remedies are related to higher strategy issues.
Determining a Depth Map Using a Dual Photometric Stereo
Authors: Ikeuchi Katsushi
Published: March 2007

This paper describes a method for determining a depth map from a pair of surface-orientation maps obtained by a dual photometric stereo. A photometric stereo system determines surface orientations by taking three images from the same position under different lighting conditions, based on the shading information. A photometric stereo system can deter mine surface orientations very rapidly, but cannot determine absolute depth values. This paper proposes a dual photomet ric stereo system to obtain absolute depth values.

A dual photometric stereo generates a pair of surface-ori entation maps. Then, the surface-orientation maps can be segmented into isolated regions with respect to surface orien tations, using a geodesic dome for grouping surface orienta tions. The resulting left and right regions are compared to pair corresponding regions. The following three kinds of constraints will be used to search for corresponding regions efficiently: a surface-orientation constraint, an area con straint, and an epipolar constraint. Region matching is done iteratively, starting from a coarse segmented result and pro ceeding to a fine segmented result, using a parent-children constraint. The horizontal difference in the position of the center of mass of a region pair determines the absolute depth value for the physical surface patch imaged onto that pair. This system takes only a few minutes on a Lisp machine to determine an absolute depth map in complicated scenes and could be used as an input device for a bin-picking system.
Coupling Effects of Kinematics and Flexibility in Manipulators
Authors: Naganathan G. , Soni A.H.
Published: March 2007

This paper presents a finite, element-based, nonlinear model of flexibility effects in manipulators. The model allows for the coupling effects due to elastic deformations of the manip ulator links and the kinematics at the manipulator joints. The governing equations of motion are derived including the effects of rotatory inertia, shear deformation. and the effects of gross nonlinear motion of each of the links. Using Timo shenko beam theory, a simple and efficient finite element is proposed for the manipulator links. The complete dynamic model is further integrated with a simplistic representation of actuator-servo effects. The model is described in detail for the case of a planar manipulator with revolute joints. The same model can also be extended to spatial manipulators with prismatic pairs.
Design and Modeling of a Computer- Controlled Planar Manipulator
Authors: Nye Theodore W. , LeBlanc David J. , Cipra Raymond J.
Published: March 2007

This paper describes the design of a computer-controlled planar manipulator and the modeling necessary to derive the dynamic equations of motion. The planar manipulator was built as an experimental research device for work in kine matics, dynamics, controls, design, and sensor development. The device consists of three joints and three links with a gripper and operates in a horizontal plane on air bearings. The planar manipulator was instrumented for position, veloc ity, and torque feedback from each joint and is controlled either manually, using a teach pendant, or directly from a computer. A modularity feature was also designed into the robot to allow for interchanging any electromechanical com ponents and to enable structural substitutions for investiga tions into flexibility and vibrations. The completed robot successfully exceeded performance specifications and design criteria.

The next phase of the research focused on the development and evaluation of a computer model designed to simulate the open-loop dynamic behavior of the three-link, three-jointed, high-speed planar manipulator. Describing equations were developed for both the servo actuator and arm dynamics at each joint. Significant terms included were coulomb, viscous, and hysteresis damping; and centripetal, Coriolis, and cou pling inertial effects induced by relative motions of the arm structure. The model used the voltage into the power ampli fiers for each servo drive as the system input, and the joint angular position, velocity, and acceleration as the system output. Results from various inputs including a step-input function, a sinusoidal-input function, and a ramp-input func tion were found to compare closely with experimental data measured from the actual planar manipulator built during the course of the research.
Consistent Integration and Propagation of Disparate Sensor Observations
Authors: Durrant-Whyte Hugh F.
Published: March 2007

To operate efficiently in an unknown or uncertain environ ment, robots must take observations from many different sensors to provide information with which to build a robust world model. We describe a methodfor integrating partial, uncertain, geometric sensor observations into a robust, con sistent estimate of the state of the environment. The integra tion process uses a Bayes procedure for comparing disparate observations of geometric features, rejecting spurious mea surements, and providing partial updates of object locations to a world model. This integration mechanism can combine any number of observations from sensors that provide mea surements of different geometric features. The invariant topology of relations between uncertain geometric features is used to develop a method for propagating observations through the world model. This propagation mechanism forces a consistent interpretation of the environment to be main tained and makes maximum use of sensor information. The method described has been applied in a distributed sensing system, consisting of an active stereo camera platform and a robot-mounted force-tactile gripper. The results demonstrate the usefulness of the proposed techniques.
On the Adaptive Control of Robot Manipulators
Authors: Slotine Jean-Jacques E. , Weiping Li
Published: March 2007

A new adaptive robot control algorithm is derived, which consists of a PD feedback part and a full dynamics feedfor ward compensation part, with the unknown manipulator and payload parameters being estimated online. The algorithm is computationally simple, because of an effective exploitation of the structure of manipulator dynamics. In particular, it requires neither feedback of joint accelerations nor inversion of the estimated inertia matrix. The algorithm can also be applied directly in Cartesian space.
Constrained Relations between Two Coordinated Industrial Robots for Motion Control
Authors: Luh J.Y.S. , Zheng Y.F.
Published: March 2007

Tasks for two coordinated industrial robots always bring the robots in contact with the same object. Physically the three form a closed kinematic chain mechanism. When the chain is in motion, the positions and orientations of the two robots must satisfy a set of holonomic equality canstraints for every time instant. To eliminate motion errors between them, we assign one of them to carry the major part of the task. Its motion is planned accordingly. The motion of the second robot is to follow that of the first robot, as specified by the re lations of the joint velocities derived from the constraint conditions. Thus if any modification of the motion is needed in real time, only the motion of the first robot is modified. The modification for the second robot is done implicitly through the constraint conditions. Specifically, when the joint displacements, velocities, and accelerations of the first robot are known for the planned or modified motion, the corre sponding variables for the second robot and the forces/torques can be determined through the constrained relations.
Dynamic Simulation of Legged Machines Using a Compliant Joint Model
Authors: Shih Liang , Frank Andrew A. , Ravani Bahram
Published: March 2007

A computerized simulation of the dynamics of multilegged walking machines is presented. The simulation includes the effects of leg mass and compliance, joint compliance and friction, as well as the effects of leg contact with the ground. An approach is presented in which the Newton-Euler formu lation is used to develop the dynamic equations of each link. Kinematic constraints are not imposed explicitly. Instead, a compliant joint model is used to relate the dynamic reaction forces between neighboring links. The approach can handle multiloop devices with a combination of closed and open kinematic chains. Simulation results for the Ohio State Uni versity Hexapod walking machine are presented and shown to be in close agreement with previously published experi mental data.
A Perturbation Approach to Robot Calibration
Authors: Kirchner H.O.K. , Gurumoorthy B. , Prinz F.B.
Published: March 2007

The forward and reverse solutions of a manipulator with six joints are expanded up to second order in the 24 joint param eters. Assuming that the 24 errors of the 24 joint parameters are independent of the setting of the six controllable joint parameters, if suffices to triangulate the six coordinates (three translational, three rotational) of the end-effector and sub tract the ideal position computed from the forward solution of the ideal error-free robot. This provides 24 equations for 24 unknowns. Calibration compensation consists of correcting the six controllable joint parameters by six controllable ad justments so that the effect of the 24 errors is compensated for.
Constructing Force- Closure Grasps
Authors: Nguyen Van-Duc
Published: March 2007

This paper presents fast and simple algorithms for directly constructing force-closure grasps based on the shape of the grasped object. The synthesis of force-closure grasps finds in dependent regions of contact for the fingertips, such that the motion of the grasped object is totally constrained. A force- closure grasp implies equilibrium grasps exist. In the reverse direction, we show that most nonmarginal equilibrium grasps are force-closure grasps.
An Investigation of Frictionless Enveloping Grasping in the Plane
Authors: Trinkle Jeffrey C. , Abel Jacob M. , Paul Richard P.
Published: March 2007

Grasping by a two-dimensional hand composed of a palm and two hinged fingers is studied. The mathematics of fric tionless grasping is presented and used in the development of a planner/simulator. The simulator computes the motion of the object using an active constraint set method and assuming exact knowledge of the physical properties of the polygonal object, hand, and support. Grasping is divided into three phases. During the first phase, the initial grasping configura tion is found. In the second phase, the object is manipulated away from the support, bringing it into contact with the palm. In the last phase, the grip is adjusted to minimize the contact forces acting on the object.
A Three-Dimensional Assembly Task Quantification with Application to Machine Dexterity
Authors: Sturges R.H.
Published: March 2007

Quantification of assembly tasks is a key element in finding the net dexterity of a task/effector system. Three-dimensional task models of a general kind have been constructed for nonrotational and nonsymmetrical peg-and-hole problems. The square-peg-and-hole model developed extends the two- dimensional wedging and jamming diagrams into their three-dimensional counterparts. Contact constraint equations and contact modalities have been expressed in terms of line algebra. New transformations of line coordinates have been introduced to facilitate the production of constraint equations. A taxonomy of contacts has been developed based on con straint equations, which recognizes conditions under which special cases occur, such as line-plane and plane-plane con tacts.
Combining Sonar and Infrared Sensors for Mobile Robot Navigation
Authors: Flynn A.M.
Published: March 2007

Multiple sensors can be used on a mobile robot so that it can perceive its environment with better accuracy than if either sensor were used alone. Sonar and infrared sensors are used here in a complementary fashion, where the advantages of one compensate for the disadvantages of the other. The robot then combines the information from the two sensors to build a more accurate map. Another representation, a modified version of the curvature primal sketch, is extracted from this perceived workspace and is used as the input to two path planning programs: one based on configuration space and one based on a generalized cone formulation of free space.
Integrating Vision and Touch for Object Recognition Tasks
Authors: Allen Peter K.
Published: March 2007

A robotic system for object recognition is described that uses passive stereo vision and active exploratory tactile sensing. The complementary nature of these sensing modalities allows the system to discover the underlying 3-D structure of the objects to be recognized. This structure is embodied in rich, hierarchical, viewpoint-independent 3-D models of the objects which include curved surfaces, concavities and holes. The vision processing provides sparse 3-D data about regions of interest that are then actively explored by the tactile sensor mounted on the end of a six-degree-of-freedom manipulator. A robust, hierarchical procedure has been developed to inte grate the visual and tactile data into accurate 3-D surface and feature primitives. This integration of vision and touch provides geometric measures of the surfaces and features that are used in a matching phase to find model objects that are consistent with the sensory data. Methods for verification of the hypothesis are presented, including the sensing of visually occluded areas with the tactile sensor. A number of experi ments have been performed using real sensors and real, noisy data to demonstrate the utility of these methods and the ability of such a system to recognize objects that would be difficult for a system using vision alone.
Object Localization with Multiple Sensors
Authors: Shekhar Shashank , Khatib Oussama , Shimojo Makoto
Published: March 2007

We present a method to obtain the position and orientation of an object through measurement from multiple sensors. Raw sensor measurements are subject to limitations of sensor precision and accuracy. Although for most measurements the estimate of position parameters is a linear function of the measurements, the estimate of orientation parameters is a nonlinear function of the measurements. Thus, error in orien tation estimate depends on the distance over which the raw measurements are made. For example, the estimate of the orientation of a line is better, the farther apart two points on the line are. The problem of finding the orientation parame ters is formulated in two steps. The first step computes vec tors from sensor measurements of points. A concept of best features is developed to select an optimal set of all possible vectors. The second step relates the orientation parameters to the vectors from the first step as a linear system. The best estimate is obtained by solving a weighted linear system of the optimal set of vectors in a least squares sense. The opti mal selection of best features improves the estimate substan tially. This method has been implemented for localizing an object in a manipulator end-effector instrumented with cen troid and matrix tactile sensors.
Optimal Combination and Constraints for Geometrical Sensor Data
Authors: Porrill John
Published: March 2007

A formalism is described for the statistical combination of geometrical information from multiple sensors. This is illus trated by its applications to stereo vision, including the com bination of multiple stereo views to increase the accuracy of a wire frame model and the consistent imposition of geometri cal constraints on such a model.
A Foundation for the "Flexible-Trajectory" Approach to Numeric Path Planning
Authors: Buckley C.E.
Published: March 2007

This paper describes the development of a new type of non- collision constraint function for use in numeric path planning. It is valid even when computed for configurations in collision. This allows for greater freedom in hypothesizing trajectories to be relaxed intact into admissibility. The motivation lead ing to its development is discussed, along with its theory and properties. By way of example, its application in a naive path planning algorithm is described, which leads to surprising results when compared with a contemporary subdivision method.
A Direct Minimization Approach for Obtaining the Distance between Convex Polyhedra
Authors: Bobrow James E.
Published: March 2007

Computational methods used for the automatic generation of robot paths must be fully developed if truly automated manu facturing systems are to become a reality. An important requirement for determining feasible robot paths is the ability to compute the distance between the various elements of the robot and the workspace fixtures, jigs, and machinery. In this research, it is assumed that the robot and workspace solid geometry are represented as a collection of convex polyhe drons, and an efficient numerical algorithm for determining the minimum distance between two such polyhedrons is presented. In addition to determining the minimum distance between solids, the algorithm can also be used to efficiently ascertain whether a collision has occurred.

The numerical technique presented uses a sequence of constrained minimizations to obtain the closest three-dimen sional points on any two solid objects. Computational effi ciency is achieved with the algorithm presented because only the collection of planes (points and normals) which define the solids are used for the analysis. The bounding lines and vertices do not need to be explicitly calculated during the minimization procedure. The algorithm uses a direct ap proach for minimizing the nonlinear distance function which generates a sequence of search directions along the surfaces of the objects to obtain the global minimum. An extensive set of numerical tests are used to demonstrate the performance of the algorithm.
The Role of Dynamic Models in Cartesian Force Control of Manipulators
Authors: An Chae H. , Hollerbach John M.
Published: March 2007

Dynamic models are as important in Cartesian force control as they are in position control. A variety of Cartesian force control schemes are examined, comprising some that do incorporate a dynamic model into the control loop (resolved acceleration force control, operational space method, and impedance control) and some that do not (hybrid control and stiffness control). Stability analyses and experimental imple mentations are presented that demonstrate not only that using a dynamic model leads to more accurate control, but also that not using a model can in certain cases make force control unstable. Experiments on the MIT Serial Link Direct Drive Arm show that resolved acceleration force control is stable and accurate in producing force steps and sinusoidal force responses and in complying to sinusoidal position dis turbances.
Trajectory Planning for a Mobile Robot
Authors: Steer Barry
Published: March 2007

Robotics, when successfully carried out, is concerned with artifacts that optimize their own behavior in the light of information using sensors and actuators. The information includes both that which is stored and that which is immedi ately available from the sensors.

In this paper the problem addressed is how the speed and the steer angle of a path curvature limited robot-vehicle, one that has to move in order to turn, may be altered in order to achieve desirable changes in its position and orientation. A kinematic description of both a tricycle and "turtle" vehicle architecture is developed. A comparison is made between the two architectures. The effect of modulating the steer angle of a path curvature limited vehicle, a tricycle, with a gaussian envelope is illustrated for various amplitudes of the gaussian and speed of the robot-vehicle. The effect of the time concat enation of the steer angle with two or more gaussian enve lopes shows that a range of activities relevant to the functional needs of a robot-vehicle are possible. A number of other "modulating" functions are identified, and it is suggested that these deserve further investigation.
Singular Configurations of Parallel Manipulators and Grassmann Geometry
Authors: Merlet Jean-Pierre
Published: March 2007

Parallel manipulators have a specific mechanical architecture where all the links are connected both at the base and at the gripper of the robot. By changing the lengths of these links we are able to control the position1 of the gripper. In general, for a given set of links lengths there is only one position for the gripper. However, it may be suspected that in some cases more than one solution may be found for the position of the gripper: the robot is in a singular configuration. To determine these singular configurations the classical method is to find the roots of the determinant of the jacobian matrix. In our case the jacobian matrix is complex, and it seems not to be possible to find these roots. We propose here a new method based on Grassmann line geometry. The set of lines, P3, constitutes a linear variety of rank 6. We show that a singular configuration is obtained when the variety spanned by the lines associated to the robot links has a rank less than 6. An important feature of the varieties of this geometry is that they can be described by simple geometric rules. Thus to find the singular configurations of parallel manipulators we have to find the configuration in which the robot matches these rules. Such an analysis is performed on a special parallel manip ulator. We show that we find all the well-known singular configurations, and also some new ones.
Reuleaux Pairs and Surfaces That Cannot Be Gripped
Authors: Selig J.M. , Rooney J.
Published: March 2007

It is well known that there exist surfaces whose motion cannot be completely constrained by non-frictional contact forces. We give a new proof of the classification of these surfaces based on group theory. Having derived a simple character ization of these "surfaces that cannot be gripped, " we show that they are equivalent to the Reuleaux lower pairs. The proof emphasizes the symmetry of the surfaces rather than their analytic form. We also show that the screw system of such a surface is isomorphic to the Lie algebra of the surface's symmetry group.
On Finding Exciting Trajectories for Identification Experiments Involving Systems with Nonlinear Dynamics
Authors: Armstrong Brian
Published: March 2007

When designing an identification experiment for a system described by nonlinear functions such as those of manipulator dynamics, it is necessary to consider whether the excitation is sufficient to provide an accurate estimate of the parameters in the presence of experimental noise. It is shown that the convergence rate and noise immunity of a parameter identifi cation experiment depend directly on the condition number of the input correlation matrix, a measure of excitation. The sensitivity of an identification experiment to unmodeled dynamics is also studied; a dimensionless measure of this sensitivity—bias susceptibility—is proposed and related to excitation. The issue of how exciting a trajectory may be is addressed, and a method is presented to maximize the exci tation. Two identification experiments reported in the litera ture are studied; analysis of these experiments shows that intuitively selected trajectories may provide poor excitation, and considerable improvement results from employing the optimization to maximize excitation. A typical improvement is the reduction of parameter convergence time from 15 min to 33 s. This work illustrates the difficulty of maintaining persistent excitation during the experimental identification of complex models.
Some Paradigms for the Automated Design of Parts Feeders
Authors: Natarajan B.K.
Published: March 2007

This paper concerns the automated design of parts feeders- a dual to the motion planning problem. Three particular paradigms for feeders are presented and their computational abstractions analyzed. The focus is on the computational issues involved and not on the physics of the problem.
Kinematics of an n-Degree- of-Freedom Multi-Link Robotic System
Authors: Choudhury Alamgir , Genin Joseph
Published: March 2007

A kinematic model is developed for n-degree-of-freedom multi-link manipulator systems. An essential step in the de velopment is the formulation of modified Eulerian angles, to allow maximum flexibility in positioning each link. Using the modified Eulerian angle method the kinematics of a system can be solved by multiplying fewer transformation matrices than is required by existing methods, thus reducing the complexity of computation. By allowing for a maximum number of kinematic variables (three for position and three for orientation) for each link, the analysis can be pursued in a general form without preimposed constraints on the system. The resulting formulation can be used as a basis for off-line analysis and design of a multi-link system. The inverse kine matics problem is solved by minimizing an objectivefunction that quantifies the joint displacements. A 16-degree-of- freedom redundant system is presented as an illustrative problem. Our algorithm provides highly accurate numerical solutions. Also, using our method a PUMA 560 robot arm is analyzed, and theformulation is compared with that ob tained by the Denavit-Hartenberg method.
The Geometry of Grasping
Authors: Markenscoff Xanthippi , Luqun Ni  , Papadimitriou Christos H.
Published: March 2007

A form closure (or complete restraint) of a solid object is a finite set of wrenches (force-moment combinations) applied on the object, with the property that any other wrench acting on the object can be balanced by a positive combination of the original ones. Intuitively, form closure is a way of defining the notion of a "firm grip" of the object (when friction is not taken into account). It has been pointed out by Reuleaux (1875) and Somoff ( 1897), and more recently by Lakshmin arayana (1978), that the form closure of a two-dimensional object requires at least four wrenches, and that form closure of a three-dimensional object requires at least seven wrenches. It was also conjectured that these numbers can be achieved by wrenches realizable as forces normal to the surface of the object (such wrenches are called fingers). In this paper we prove this conjecture. In particular we show that form closure of any two-dimensional bounded object with piecewise smooth boundary (except a circle) can be achieved by four fingers. For three dimensions, we prove that form closure of any bounded object with piecewise smooth boundary can be achieved with 12 fingers if and only if the object does not have a rotational symmetry (in which case, of course, form closure is not achievable, since no moment along the axis of symmetry can be opposed). We also show that, under very general conditions, form closure of three-dimensional objects without rotational symmetries can be achieved with seven fingers. Finally, we show that when Coulomb friction is taken into account, under the most relaxed assumptions three fingers are necessary and sufficient in two dimensions, and four fingers in three dimensions.
2D Path Planning: A Configuration Space Heuristic Approach
Authors: Ilari Joan , Torras Carme
Published: March 2007

In this paper we describe a heuristic technique for solving the 2D find-path problem for a rigid mobile body amidst a set of fixed obstacles of arbitrary shapes. The proposed approach tackles path planning as an informed search process in dis crete configuration space. Three heuristics are proposed to guide this search process, all of them relying on a global path computed from the R-MAT model of free-space (a retraction of MA T defined specifically for path planning). One of the heuristics guides the evolution of the two Cartesian degrees of freedom of the mobile body along the search, while the remaining two guide the evolution of its rotational degree of freedom. The benefits derived from the use of the proposed heuristics are twofold: on the one hand, a speed-up of the search process as compared to noninformed search algo rithms is attained, and on the other hand, the features of the resulting solution path can be somewhat controlled. Other advantages and shortcomings of the proposed path planning approach are discussed, with the practical interest of the overall process being justified by the experimental results ob tained.
Force Control in Locomotion of Legged Vehicles over Rigid and Soft Surfaces
Authors: Gorinevsky D.M. , Shneider A. Yu.
Published: March 2007

The control system of the hexapod walking vehicle, designed at the Institute for Mechanics at Moscow State University and at the Institute for Problems of Information Transmis sion at the USSR Academy of Sciences, is extended to effect the control of foot-contact forces and locomotion in soft soil. The previously developed positional control system enables the computation of commanded motion of the vehicle legs and positional feedback to track this commanded motion. Force feedback is added to the control system, in addition to computation of commanded forces and leg position correc tions for leg sinkage during soft soil locomotion.

Such an elaborate control system has made it possible to solve the problems of controlling the distribution of vertical foot force components in locomotion over a rigid surface and of foot-force vectors in locomotion between planes forming a dihedral angle. A number of algorithms are proposed to control vertical force components (loads on legs) and leg sink age in locomotion in elastic and consolidating soils. In the latter case, which corresponds to most natural soils, the bear ing properties of the surface are considered a priori unknown. The results of the experimental implementation of the algorithms are presented.
Buoyancy- and Gravity-Powered Underwater Robots
Authors: Baz A. , Gumusel L.
Published: March 2007

This paper presents a new concept for driving underwater robots that is based on the interaction between the natural forces of buoyancy and gravity present in the underwater environment.

Mathematical models are developed to simulate the static and dynamic characteristics of a single-link arm as in fltcenced by its design parameters and operating conditions. A computer-controlled prototype of the arm is designed, built, and tested to demonstrate the feasibility of the concept. The effect of varying the control gains, sample interval, and con trol law on the dynamic performance of the arm is presented for different payloads.

The obtained results suggest the potential of this type of robot in handling objects underwater with minimal external energy.
A Tactile Sensing System for Robotic Manipulation
Authors: Speeter Thomas H.
Published: March 2007

A tactile sensing system (TSS) for articulated robotic hands is described. The system is composed of flexible touch sensing arrays, access electronics, and algorithms for data sampling and processing. The TSS is meant to exist in a multiprocess ing control environment and is designed to keep low-level procedures such as sensor addressing and data access off of the control system's shared bus. Up to 16 arrays of 256 taxels each can be accessed in parallel with achieved sampling rates of more than 60 Hz. The resolution of the sensors can be dynamically modified by a simple switching technique. This allows very fast sampling rates at low resolution while retain ing the ability to sample with high precision at lower rates. Variance of the resolution changes only the number of taxels and the size of their receptive fields but does not affect the coverage of the array.

As part of the discussion about TSS, a generic class of resistive touch sensors is described. These sensors are inex pensive, flexible, and easy to build. Methods for efficient sampling, variable resolution, and shear force detection are introduced, and implementation issues for use with the Utah/ MIT Dextrous Hand are discussed.
An Implementation of a Parallel Algorithm for Real-Time Model- Based Control on a Network of Microprocessors
Authors: Hashimoto Koichi , Ohashi Kenjo , Kimura Hidenori
Published: March 2007

Model-based trajectory control is a class of advanced manip ulator control strategies that are based on the kinematic and dynamic models of manipulators. Many schemes of model- based control have been proposed; however, most of them are limited within the stage of simulation study and very few have been installed on actual manipulators. The main reason is that the computations required for inverse dynamics are far beyond the ability of the present commercially available microprocessors. In order to achieve real-time high sample- rate control, we have proposed a parallel processing scheme for inverse dynamic computations that is called the resolved Newton-Euler algorithm. It resolves the process for computing the desired torques into subprocesses that have almost com plete concurrency. Because these subprocesses communicate with each other in a regular and local way, they can be di rectly mapped on a distributed processing network system.

In this paper, we present a real-time parallel computation architecture for implementing the resolved Newton-Euler algorithm composed of a host personal computer and a net work of microprocessors and transputers. All programs are written in a high-level language, occam. This computation scheme is applied to the trajectory control of the PUMA 560 manipulator. Our controller achieves the sampling period of 0.66 ms.
An Efficient Snell's Law Method for Optimal-Path Planning across Multiple Two-Dimensional, Irregular, Homogeneous-Cost Regions
Authors: Rowe Neil C. , Richbourg R.F.
Published: March 2007

We are exploring a new approach to high-level optimal-path planning when homogeneous irregularly shaped regions of a plane have different traversal costs per unit distance. It is based on the simple idea that optimal paths must be straight in homogeneous regions, and so those regions need not be subdivided for path planning. Our approach uses optics anal ogies, ray tracing, and Snell's Law and reduces the problem to an efficient graph search with a variety of pruning criteria. The time and space of our algorithm is O(V 2) in an intui tively average case, where V is the number of region vertices. In experiments in which space is held constant, an imple mentation of our algorithm was not only dramatically faster but also gave better cost solution paths than a representative implementation of the chief competing technique, grid-based wavefront propagation. This appears to be because of the quite different and considerably smaller search space required for our more intelligent algorithm.
Roads, Rivers, and Obstacles: Optimal Two-Dimensional Path Planning around Linear Features for a Mobile Agent
Authors: Rowe Neil C.
Published: March 2007

We present an efficient algorithm for finding least-cost paths for an agent of negligible size across an important special case of two-dimensional terrain, terrain consisting of (1) a single isotropic homogeneous-cost-per-distance background region, (2) "roads" or narrow transportation corridors of low cost per distance, (3) "rivers" or narrow features of high crossing cost, and (4) untraversable "obstacles. " This work extends that of Mitchell (1987) by including rivers and new pruning heuristics for roads; our algorithm remains O(n2 log n) in time complexity. We also show results of a first com puter implementation for this class of algorithms and analyze average-case performance and error sensitivity. This work applies primarily to high-level path planning for robots but also can help plan military maneuvers and guide construction of roads and pipelines.
Qualitative Understanding of Scene Dynamics for Mobile Robots
Authors: Burger Wilhelm , Bhanu Bir
Published: March 2007

In this paper, we present a new approach to analyzing motion sequences as they are observed from a mobile robot operating in a dynamic environment. In particular, we address the problems of (a) estimating the robot's egomotion, (b) recon structing the 3D scene structure, and (c) evaluating the mo tion of individual objects from a sequence of monocular images. Our approach consists of a two-stage process starting from given sets of displacement vectors between distinct image features in successive frames. First, the robot's egomo tion is computed in terms of rotations and the direction of translation. To cope with the problems of noise, we have extended the concept of the Focus of Expansion (FOE) by computing a Fuzzy FOE, which defines an image region rather than a single point. In the second stage, a 3D scene model is constructed by analyzing the movements and posi tions of image features relative to each other and relative to the Fuzzy FOE. Using a mainly qualitative strategy of rea soning and modeling, multiple scene interpretations are pursued simultaneously. This second stage allows the deter mination of moving objects in the scene. Results of this ap proach applied to a real image sequence are presented.
Using Tactile Data for Real-Time Feedback
Authors: Berger Alan D. , Khosla Pradeep K.
Published: March 2007

Object recognition through the use of input from multiple sensors is an important aspect of an autonomous manipula tion system. In tactile object recognition, it is necessary to determine the location and orientation of object edges and surfaces. We propose a controller that utilizes a tactile sensor in the feedback loop of a manipulator to track edges in real time. In our control system, the data from the tactile sensor is processed in two stages to determine the location of edges. The first stage involves adaptive thresholding of tactile images. This thresholded image is used to detect edges. In the second stage, we use a combination of weighted least squares and the Modified Adaptive Hough Transform to choose the edge to be tracked from the multiple edges present in the tactile image. The parameters of these edges are then used to generate a set-point signal to drive the manipulator. In our implementation, we use a Hybrid controller that uses both position and force set points. The edge tracker, pre sented in this article, has been implemented on the CMU DD Arm II system. While the signal processing and the control computation require 30 ms, the tactile images are transferred from the sensor to the computer every 240 ms. Consequently, the acquisition of tactile images limits the sampling rate to 4.2 Hz. In this article, we describe both the theory and exper imental implementation of tactile edge detection and an edge tracking controller.
Geometric Reasoning in a Parallel Network
Authors: Fisher Robert B. , Orr Mark J. L.
Published: March 2007

The general principles of geometric reasoning for computer vision are discussed and some previous attempts at imple menting reasoners reviewed. A new implementation is pro posed that involves interval arithmetic to cope with uncer tainties and has a network structure that promotes efficiency from parallelism and accuracy from feedback. Typical con straints from a 3D model/3D image vision system are dis cussed and used to evaluate the network performance.
Performance in Adaptive Manipulator Control
Authors: Niemeyer Günter , Slotine Jean-Jacques E.
Published: March 2007

Effective adaptive controller designs potentially combine high speed and high precision in robot manipulation and further more can considerably simplify high-level programming by providing consistent performance in the face of large varia tions in loads or tasks. A simple, globally tracking-conver gent, direct adaptive manipulator controller has previously been developed and experimentally demonstrated. In this article, we further explore the performance issues linked to a computationally effective implementation. Specifically, we develop a recursive implementation applicable to both open and closed kinematic chains, as well as rules for obtaining minimal parametrizations. We also discuss implementations of the algorithm directly in Cartesian space, the exploitation of kinematic redundancies, and applications to adaptive compliant motion control. These developments are illustrated experimentally on a four-degrees-of-freedom articulated robot arm and suggest a wide range of application well beyond adaptation to grasped loads.
Finding the Position and Orientation of a Sensor on a Robot Manipulator Using Quaternions
Authors: Chou Jack C. K. , Kamel M.
Published: March 2007

The problem of finding the relative position and orientation between the reference frames of a link-mounted sensor and the link has been formulated as a kinematic equation of the form H l H x = H x H c in terms of homogeneous transformation matrices by Shiu and Ahmad (1987). In this article, normal ized quaternions (Euler parameters) are used to transform the kinematic equation into two simple and structured linear systems with rank-deficient coefficient matrices. Closed-form solutions to these systems are derived using the generalized inverse method with singular-value decomposition analysis. To obtain a unique solution, two distinct robot movements are required. This leads to an overdetermined system of equations. A criterion for selecting the independent set of equations is developed. A set of closed-form formulae for the solution of these equations are derived. The selection crite rion and the solution formulae can be easily incorporated in application programs that require the calculation of the rela tive position and orientation of the sensor.
The Structural Synthesis of Tendon-Driven Manipulators Having a Pseudotriangular Structure Matrix
Authors: Lee Jyh-Jone , Tsai Lung-Wen
Published: March 2007

Tendons have been widely used for power transmission in the field of anthropomorphic manipulating systems. This article deals with the identification and enumeration of the kine matic structure of tendon-driven robotic mechanisms. The structural isomorphism of tendon-driven manipulators is defined, and the structural characteristics of such mechanical systems are described. Applying these structural characteris tics, a methodology for the enumeration of tendon-driven robotic mechanisms is developed. Mechanism structures with up to six degrees of freedom are enumerated.
Probability Distribution of Repeatability of Industrial Robots
Authors: Ramsli Einar
Published: March 2007

The accuracy with which an industrial robot brings the load to a position and holds it there is perhaps the most important characteristic of an industrial robot. Many researchers have consequently been interested in this field during recent years.

A common method for characterizing an industrial robot's ability to return to a position is to use the terms "accuracy" and "repeatability, " where accuracy characterizes the degree to which the actual measured value corresponds to a com manded value and repeatability the closeness of agreement between repeated measured values, under the same condi tions, to the same commanded value (ISO definitions). The normal approximation is regularly used when calculating the repeatability.

A test on this assumption for six different industrial robots is reported in this article. Two approaches for this test are used: one looks at the shape of the frequency function for the repeatability figures measured, and the second uses a chi square test on the six data sets. The different tests show that there are small chances that the deviation of an industrial robot will follow a normal distribution. It seems to be a trend that the deviation has longer tails than the normal distribution.

Simulation is used to elaborate on the consequences of the invalid assumption of normality in the definition of repeat ability. The conclusion is that it is reasonable to use the normal approximation when there is no strong evidence that the deviation distribution is negatively skewed.
Quasistatic Manipulation with Compliance and Sliding
Authors: Kao Imin , Cutkosky Mark R.
Published: March 2007

We propose a method for modeling dextrous manipulation with sliding fingers. The approach combines compliance and friction limit surfaces. The method is useful for describing how a grasp will behave in the presence of external forces (e.g., when and how the fingertips will slide) and for planning how to control the fingers so that the grasped object will follow a desired trajectory. The sliding trajectories are characterized by a transient and steady-state solution. The underlying theory is first dis cussed and illustrated with several single-finger examples. Experimental results are also presented. The analysis is then extended to grasps with multiple sliding and nonslid ing fingers. The multifinger analysis is illustrated with an example of manipulating a card with two soft-contact fingers.
Geometry and Prediction of Drift-Free Trajectories for Redundant Machines Under Pseudoinverse Control
Authors: Bay John S.
Published: March 2007

In this article, classical differential geometric techniques are used for two purposes: (1) to describe in geometric terms the trajectories to which redundant robots under pseudoinverse control will drift and (2) to formulate from this geometric description a practical and quick method for predicting these limit trajectories, thereby suggesting sets of initial conditions under which no drift will occur. Through this analysis, several useful results were obtained. First, it is demonstrated for a 3R example that the drifting trajectories are geodesics in the constrained joint space, and that as a result of this, all drift-free tra jectories are space curves of zero torsion. Second, it is found that each self-motion manifold in the joint space crosses the limiting (drift-free) trajectories at points where they themselves have zero torsion. Because self-motion manifolds are often more easily computed than exhaustive kinematic simulation of manipulator drift, these results provide a fast, new technique for locating and character izing drift-free trajectories based only on geometry of these self-motion manifolds. This work extends the results of previous work in pseudoinverse control to the point that the drift problem may be circumvented without resort to either exhaustive simulation or symbolic computation of Lie brackets of vector fields.