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Robotics and Automation, IEEE Transactions on

Issue 5 • Date Oct 1997

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Displaying Results 1 - 15 of 15
  • Petri nets for modeling automated manufacturing systems with error recovery

    Page(s): 752 - 760
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    This paper enhances a Petri net synthesis theory with the capability to deal with reversibility, which is an important property related to the concept of error recovery in manufacturing. The theory has been proposed to synthesize a class of Petri nets for modeling shared-resource automated manufacturing systems. The class of nets has been shown to be conservative (bounded) and possess structural liveness under two sufficient conditions. The conditions can be checked structurally by an algorithm without enumerating the states. A bounded and live net means that the modeled system cannot have capacity overflows and deadlocks, two types of unwanted behaviors in manufacturing. In this paper it is further proven that under these two sufficient conditions, the class of nets possesses reversibility. Thus the liveness-checking algorithm can be used to check reversibility without modification View full abstract»

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  • A framed-quadtree approach for determining Euclidean shortest paths in a 2-D environment

    Page(s): 668 - 681
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    In this paper we investigate the problem of finding a Euclidean (L 2) shortest path between two distinct locations in a planar environment. We propose a novel cell decomposition approach which calculates an L2 distance transform through the use of a circular path-planning wave. The proposed method is based on a new data structure, called the framed-quadtree, which combines together the accuracy of high resolution grid-based path planning techniques with the efficiency of quadtree-based techniques, hence having the advantages of both. The heart of this method is a linear time algorithm for computing certain special dynamic Voronoi diagrams. The proposed method does not place any unrealistic constraints on obstacles or on the environment and represents an improvement in accuracy and efficiency over traditional path planning approaches in this area View full abstract»

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  • Nonholonomic behavior in redundant robots under kinematic control

    Page(s): 776 - 782
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    We analyze the behavior of redundant robots when the joint motion is generated by inverting task velocity commands through a kinematic control scheme. Depending on the chosen inversion scheme, the robot motion is subject to differential constraints that may or may not be integrable. Accordingly, we give a classification in terms of holonomic, partially nonholonomic, and completely nonholonomic behavior, pointing out also the relationship with the so-called cyclicity property. This general classification is illustrated by means of several examples. When the kinematic control scheme is nonholonomic, the whole configuration space of the robot is accessible by a proper choice of the task input commands. Under this assumption, we address the joint reconfiguration problem, namely the design of end-effector velocity commands that drive the robot to a desired joint configuration. To solve this problem, it is possible to borrow existing methods for motion planning of nonholonomic mechanical systems, such as the sinusoidal steering technique for chained-form systems View full abstract»

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  • Dynamic global path planning with uncertainty for mobile robots in manufacturing

    Page(s): 760 - 767
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    We propose a probabilistic approach to the problem of global path planning with uncertainty for mobile robots in a dynamic manufacturing environment. To model the changing environment, we use a topological graph weighted by scalar cost functions. The cost functions consist of two elements: a deterministic cost for the known part of the robot's environment, and an uncertainty cost for the unknown part of the environment. Statistical models are built to quantify the unknown part of the environment, forming uncertainty costs for handling unexpected events. These uncertainty costs are dynamically updated by available sensor data when the mobile robot moves around. An optimal path (suboptimal in practice) is then found from the weighted topological graph using dynamic programming View full abstract»

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  • Selective stabilization of images acquired by unmanned ground vehicles

    Page(s): 693 - 708
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    This paper studies the problem of selective stabilization of images acquired by a camera mounted on a vehicle navigating a rough terrain. Selective stabilization is defined here as the separation of rotational components into smooth and residual oscillatory rotations. We consider both kinematic and kinetic models suitable for capturing these phenomena and achieve their separation. A scheme for detecting the occurrence and disappearance of smooth rotation is devised, and appropriate dynamic laws are employed to achieve selective stabilization. As a by product of the selective stabilization algorithm, 3-D locations of close feature points are estimated in a stabilized frame of reference, thus providing more useful structural information. Experiments using synthetic images for different scenarios show encouraging results of the proposed approach View full abstract»

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  • Design of assembly systems for modular products

    Page(s): 646 - 655
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    To respond to the challenge of agile manufacturing, companies are striving to provide a large variety of products at a low cost. Product modularity allows production of different products by combining standard components. One of the characteristics of modular products is that they share the same assembly operations for a part of their structure. The special structure of modular products provides challenges and opportunities for the design of assembly systems. Given a family of modular products, designing low cost assembly systems is an important problem. In this paper, an approach for the design of assembly systems for modular products is proposed. The assembly system is decomposed into two subsystems based on the structure of modular products. The configuration problem of the assembly system is formulated and solved by a tabu search based algorithm View full abstract»

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  • A linear space of admittance control laws that guarantees force-assembly with friction

    Page(s): 656 - 667
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    Force-assembly has been defined as an assembly process for which the use of a single, properly designed, admittance control law will guarantee the proper assembly of a given pair of mating parts. In previous work in workpart-into-fixture insertion, the conditions on a manipulators accommodation control law that ensure proper insertion despite infinitesimal positional error and finite (but bounded) friction have been identified. Through the use of an optimization routine, a control law that satisfies these force-assembly conditions at or below a friction maximum value can be obtained. This single control law, however, is not unique-there exists many other control laws that will satisfy the conditions of force-assembly at the same value of friction. This paper addresses the identification and construction of a linear space of accommodation control law parameters that ensure force-assembly with friction. First, linear sufficient conditions that ensure force-assembly with friction are identified. These linear sufficient conditions are then modified to separate the N2+N dimensional space of accommodation control law parameters into N+1 different N-dimensional subspaces. A means of efficiently generating basis nominal velocity vectors and basis accommodation matrices is presented. A nominal velocity selected using any positive linear combination of the nominal velocity basis vectors and an accommodation matrix selected using any positive linear combination of the accommodation basis matrices will guarantee force-assembly (for any value of friction less than that used in generating the basis matrices). A planar example of the construction of each accommodation control law subspace is presented and illustrated in the geometry of the fixturing task View full abstract»

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  • Least inventory control of multistorage systems with non-stochastic unknown inputs

    Page(s): 633 - 645
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    We consider multiinventory production systems with control and state constraints dealing with unknown demand or supply levels. Unlike most contributions in the literature concerning this class of systems, we cope with uncertainties in an “unknown-but-bounded” fashion, in the sense that each unknown quantity may take any value in an assigned interval. For these situations, we perform a worst-case analysis. We show that a “smallest worst-case inventory level” exists, and it is associated to a steady-state control strategy. Then we consider the problem of driving the inventory levels to their smallest worst-case values. For this problem, we first give necessary and sufficient conditions, then we show that convergence occurs in a finite number of steps, and we give an upper bound for such a number View full abstract»

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  • Minimum effort inverse kinematics for redundant manipulators

    Page(s): 767 - 775
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    This paper investigates the use of an infinity norm in formulating the optimization measures for computing the inverse kinematics of redundant arms. The infinity norm of a vector is its maximum absolute value component and hence its minimization implies the determination of a minimum effort solution as opposed to the minimum-energy criterion associated with the Euclidean norm. In applications where individual magnitudes of the vector components are of concern, this norm represents the physical requirements more closely than does the Euclidean norm. We first study the minimization of the infinity-norm of the joint velocity vector itself, and discuss its physical interpretation. Next, a new method of optimizing a subtask criterion, defined using the infinity-norm, to perform additional tasks such as obstacle avoidance or joint limit avoidance is introduced. Simulations illustrating these methods and comparing the results with the Euclidean norm solutions are presented View full abstract»

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  • Robust control of robot manipulators based on dynamics decomposition

    Page(s): 783 - 789
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    This paper presents a new robust saturation-based control method for robot manipulators and related experimental results. The proposed method distinguishes between uncertainty in the inertia, Coriolis and centripetal forces, gravity and friction. A robust compensator is designed for each type of uncertainty, and each control parameter is directly related to a specific behavior of the closed-loop robot system and can be adjusted accordingly. The goal is to achieve better performance by using this fine-tuning capability of the control law. The proposed control method has been implemented on a direct-drive robot arm. Experiments were conducted to investigate the effectiveness of the proposed method, and the results are reported in this paper View full abstract»

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  • Removing singularities of resolved motion rate control of mechanisms, including self-motion

    Page(s): 741 - 751
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Resolved motion rate control is an algorithm for solving the path-tracking problem in robotic control which can fail at singular points of the kinematic function. The questions of existence and smoothness of solutions to the path tracking problem at singular points have not heretofore been addressed. In this paper we find a new second-order condition which, when satisfied, ensures the existence of a solution path with continuous, bounded joint rates. The condition is related to the curvature of the path at the singular value. We prove that a modification of the usual resolved motion rate control algorithm can successfully compute this solution path. As an application, we give a sufficient condition for the existence of self-motion for redundant manipulators at singular points. We derive a simple formula for the rate of recovery of the manipulability measure near the singularity. Several realistic examples are presented, for which we compute exact solutions to typical path tracking problems passing through singular points View full abstract»

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  • Optimal robot excitation and identification

    Page(s): 730 - 740
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    This paper discusses experimental robot identification based on a statistical framework. It presents a new approach toward the design of optimal robot excitation trajectories, and formulates the maximum-likelihood estimation of dynamic robot model parameters. The differences between the new design approach and the existing approaches lie in the parameterization of the excitation trajectory and in the optimization criterion. The excitation trajectory for each joint is a finite Fourier series. This approach guarantees periodic excitation which is advantageous because it allows: 1) time-domain data averaging; 2) estimation of the characteristics of the measurement noise, which is valuable in the case of maximum-likelihood parameter estimation. In addition, the use of finite Fourier series allows calculation of the joint velocities and acceleration in an analytic way from the measured position response, and allows specification of the bandwidth of the excitation trajectories. The optimization criterion is the uncertainty on the estimated parameters or a lower bound for it, instead of the often used condition of the parameter estimation problem. Simulations show that this criterion yields parameter estimates with smaller uncertainty bounds than trajectories optimized according to the classical criterion. Experiments on an industrial robot show that the presented trajectory design and maximum-likelihood parameter estimation approaches complement each other to make a practicable robot identification technique which yields accurate robot models View full abstract»

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  • Time-optimal motion of two omnidirectional robots carrying a ladder under a velocity constraint

    Page(s): 721 - 729
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    We consider the problem of computing a time-optimal motion for two omnidirectional robots carrying a ladder from an initial position to a final position in a plane without obstacles. At any moment during the motion, the distance between the robots remains unchanged and the speed of each robot must be either a given constant υ, or O. A trivial lower bound on time for the robots to complete the motion is the time needed for the robot farther away from its destination to move to the destination along a straight line at a constant speed of υ. This lower bound may or may not be achievable, however, since the other robot may not have sufficient time to complete the necessary rotation around the first robot (that is moving along a straight line at speed v) within the given time. We first derive, by solving an ordinary differential equation, a necessary and sufficient condition under which this lower bound is achievable. If the condition is satisfied, then a time-optimal motion of the robots is computed by solving another differential equation numerically. Next, we consider the case when this condition is not satisfied, and show that a time-optimal motion can be computed by taking the length of the trajectory of one of the robots as a functional and then applying the method of variational calculus. Several optimal paths that have been computed using the above methods are presented View full abstract»

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  • Postural stability of a human riding a unicycle and its emulation by a robot

    Page(s): 709 - 720
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    A unicycle is an inherently unstable system in three dimensions. As shown by a human riding a unicycle, the rider's complicated successive dynamic control actions are needed for the postural stability control of the unicycle, and the rider's actions for stability are quite nonlinear and jerky. By emulating the performance of a human riding unicycle, we can do tests of different classic and modern control methods used in 3-D inherently unstable systems, where a theoretical analytical methodology for the stability of this unstable system is expected to be developed. Because the longitudinal and lateral stability are coupled to each other in this system, and no actuator can be used directly for the control of unicycle's posture in 3-D (pitch, roll, and yaw angles), it is not easy for us to emulate the performance of a human riding a unicycle. In this paper, a unique unicycle robot is developed. The postural stability control of a human riding a unicycle in 3-D is realized by this robot View full abstract»

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  • Ultrasound-based robot position estimation

    Page(s): 682 - 692
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    A novel 3-D ultrasound position sensor provides low-cost, high-precision measurements of the Cartesian position of a robot wrist within a the robot's workspace. These measurements can, for instance, be used in a taskspace feedback loop to reduce the kinematic error. The basic idea is to mount ultrasound senders on the manipulator wrist and compute the 3-D Cartesian position of these sensors using 1-D range measurements between the senders and an array of ultrasound receivers at fixed, known locations. The main obstacle to precise range measurements is the presence of air turbulences and convection currents. This gives rise to noise which is spatially and temporally correlated. A stochastic model of this noise is presented and backed by experiments. It is proposed that the changing 3-D Cartesian position of the moving wrist is tracked by the sensor using a modified extended Kalman filter which incorporates the stochastic noise model and information derived from a static reference sender View full abstract»

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Aims & Scope

This Transactions ceased production in 2004. The current retitled publications areIEEE Transactions on Automation Science and Engineering and IEEE Transactions on Robotics.

Full Aims & Scope