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Robotics and Automation, IEEE Transactions on

Issue 4 • Date Aug 1995

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Displaying Results 1 - 15 of 15
  • First-order stability cells of active multi-rigid-body systems

    Publication Year: 1995 , Page(s): 545 - 557
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1296 KB)  

    A stability cell is a subset of the configuration space (C-space) of a set of actively controlled rigid bodies (e.g., a manipulator) in contact with a passive body in which the contact state is guaranteed to be stable under Coulomb friction and external forces. A first-order stability cell is a subset of a stability cell with the following two properties: the state of contact uniquely determines the rate of change of the object's configuration given the rate of change of the manipulator's configuration; and the contact state cannot be altered by any infinitesimal variation in the generalized applied force. First-order stability cells can be used in planning whole-arm manipulation tasks in a manner analogous to the use of free-space cells in planning collision-free paths: a connectivity graph is constructed and searched for a path connecting the initial and goal configurations. A path through a free-space connectivity graph represents a motion plan that can be executed without fear of collisions, while a path through a stability-cell connectivity graph represents a whole-arm manipulation plan that can be executed without fear of “dropping” the object. The paper gives a conceptual and analytical development of first-order stability cells of 3D rigid-body systems as conjunctions of equations and inequalities in the C-space variables. Additionally, our derivation leads to a new quasi-static jamming condition that takes into account the planned motion and kinematic structure of the active bodies View full abstract»

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  • Automatic maintenance of robot programs

    Publication Year: 1995 , Page(s): 603 - 606
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    After writing programs for a production robot, an operator must manually teach hundreds or thousands of poses. Teaching poses is extremely time consuming and, unfortunately, periodic reteaching is necessary. The need to reteach is commonly due to: wear, repair, slight movements of workpieces, or replacement of the robot and its tools. Our experience has shown that conventional methods of adjusting pose data do not work reliably. This paper discusses an automatic reteach method. The method has been tested on a production robot in a laboratory environment. In spite of changes in the robot and environment, we want constant shaped and sized tools to arrive consistently at taught work locations within desired tolerances. This means tool pose relative to the work piece is invariant. To assure this invariance, we establish a coordinate frame on the work piece and identify the tool locations relative to this frame. We apply a calibration algorithm to the pose data to accomplish our goal. This paper demonstrates an automatic, economic implementation of kinematic calibration on an industrial manipulator. The method is retrofit to a manufacturing system and does not require real time solution of the calibrated inverse kinematic problem. As a result, the method applies to most manipulators in use today View full abstract»

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  • Formal models for control of flexible manufacturing cells: physical and system model

    Publication Year: 1995 , Page(s): 558 - 570
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1228 KB)  

    Most control implementations of flexible manufacturing cells have been developed specific to a particular facility, and no generic format or tools exist for the systematic planning and creation of control. This paper presents the first phase of research in automatic generation of control software. It focuses on the development of theoretical foundations and generic issues necessary to understand and implement control. Specific formal models are developed for the physical activities, system actions, and individual machines comprising the manufacturing cell. In a subsequent paper, the formal models presented here are used to provide the basis for creating context free control grammars which are used to automatically generate software for controlling flexible manufacturing cells View full abstract»

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  • Adaptive control of robotic manipulators including motor dynamics

    Publication Year: 1995 , Page(s): 612 - 617
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    Motor dynamics in a mechanical transmission chain of a robot are common in practice and may significantly affect the dynamic characteristics and stability of a robot. Synthesis of a robust controller for a robot, including motor dynamics, is essentially more complex than that for rigid-body manipulators. The controllers currently in existence require exact knowledge of both the robot and motor dynamics. The acceleration feedback is needed to form a complete state feedback vector for the third-order dynamic system. In this paper, an adaptive controller is proposed, which is able to deal with uncertainties in both the robot and the motor dynamics. An adaptive nonlinear observer is designed to observe the acceleration instead of measuring it by feedback. The closed-loop system is proved to be globally stable in the Lyapunov sense View full abstract»

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  • A dynamic fault tolerance framework for remote robots

    Publication Year: 1995 , Page(s): 477 - 490
    Cited by:  Papers (65)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1292 KB)  

    This paper presents a layered fault tolerance framework containing new fault detection and tolerance schemes. The framework is divided into servo, interface, and supervisor layers. The servo layer is the continuous robot system and its normal controller. The interface layer monitors the servo layer for sensor or motor failures using analytical redundancy based fault detection tests. A newly developed algorithm generates the dynamic thresholds necessary to adapt the detection tests to the modeling inaccuracies present in robotic control. Depending on the initial conditions, the interface layer can provide some sensor fault tolerance automatically without direction from the supervisor. If the interface runs out of alternatives, the discrete event supervisor searches for remaining tolerance options and initiates the appropriate action based on the current robot structure indicated by the fault tree database. The layers form a hierarchy of fault tolerance which provide different levels of detection and tolerance capabilities for structurally diverse robots View full abstract»

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  • Base-invariant symmetric dynamics of free-flying manipulators

    Publication Year: 1995 , Page(s): 585 - 597
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (968 KB)  

    The freedom of choice in designating a base-body for free-flying manipulators gives these manipulators a base-invariance symmetry that is not encountered in fixed-base manipulators. This paper analyzes the relationship between this natural symmetry and the dynamical equations for free-flying manipulators. The base-invariance symmetry is used to develop a new formulation of the manipulator dynamics in which two independent O(N) recursions proceeding in opposite directions are summed together to obtain the complete free-flying manipulator dynamics. Computation of the operational space inertia for the links in the manipulator is also discussed View full abstract»

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  • Design and development of high-performance torque-controlled joints

    Publication Year: 1995 , Page(s): 537 - 544
    Cited by:  Papers (45)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (708 KB)  

    Dynamic decoupling, motion and force control of manipulators rely on the ability of the actuation system to provide accurate joint torques. However, this ability is considerably restricted by the nonlinearities and friction inherent in the actuator-transmission systems of most industrial robots. This paper is concerned with the development of high-performance torque controlled joints and focuses on two basic issues: sensor design and torque control. The first part of the paper describes a conceptually new type of torque sensor that uses contactless inductive transducers. The new sensor provides a substantial increase in accuracy over conventional strain gauge sensors, achieves higher mechanical robustness, and presents lower sensitivity to electrical noise. The second part of the paper presents an analysis of the effect that the manipulator's transmission and structural properties have on the joint torque controller design. Two manipulators with very different mechanical characteristics are used in this analysis: the PUMA 560 manipulator and Artisan, an eleven-degree-of-freedom manipulator currently under development at Stanford. The experimental results obtained with a prototype link of Artisan are presented and compared to those previously obtained with the PUMA View full abstract»

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  • Specifying and achieving passive compliance based on manipulator structure

    Publication Year: 1995 , Page(s): 504 - 515
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1028 KB)  

    We explore the possibility of achieving passive compliance through the structure of the manipulator itself. The emphasis is on passive compliance because a minimum of passive compliance to prevent jamming will always be required even when active stiffness control is employed. Particular attention is given to the large class of robots with nonbackdrivable actuators, where the actuator must be commanded to move, and in which actuator forces or torques are not easily interpreted as end-effector forces and torques. We present a novel framework for specifying the desired end-effector compliance for several tasks in terms of stiffness matrices. We explore whether the desired stiffness matrix of a manipulator can be achieved by using the natural or designed stiffness of the manipulator limbs themselves. Several techniques for adjusting the manipulator stiffness matrix are proposed. Achieving this variable passive compliance allows the attainment of high stiffnesses for fast and accurate movements and low stiffness values for force control. Furthermore, achieving nondiagonal stiffness properties wherein there are force and motion coupling in different directions is shown to be useful to prevent jamming and contact induced vibrations View full abstract»

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  • Efficient computation of articulated-body inertias using successive axial screws

    Publication Year: 1995 , Page(s): 606 - 611
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    The articulated-body (AB) algorithm for dynamic simulation of chains of rigid bodies was developed by Featherstone (1983). The mast costly step in this algorithm is the computation of the AB inertias at each link which involves a spatial (6×6) congruence transformation. The amount of computation required is closely coupled to the kinematic modeling technique used. This paper examines this computation in detail and presents an efficient step-by-step procedure for its evaluation in a serial chain with revolute and prismatic joints using modified Denavit-Hartenberg parameters for modeling the kinematics. The result is a very efficient procedure using successive axial screws that reduces the computational requirements of the AB algorithm by about 15% from results obtained by Brandl, Johanni, and Otter (1986). The procedure developed defines a general approach and can be used to improve the efficiency of spatial congruence transformations of other types of matrices, such as spatial rigid-body inertias (used in the composite rigid-body simulation algorithm) View full abstract»

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  • Manipulating algebraic parts in the plane

    Publication Year: 1995 , Page(s): 598 - 602
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    When manipulating parts, it is important to determine the orientation of the part with respect to the gripper. This orientation may not be known precisely or may be disturbed by the act of grasping. In some cases, it is possible to use mechanical compliance to orient parts during grasping. Goldberg (1993) showed that any part with polygonal boundary can be oriented and grasped in this manner using a parallel-jaw gripper. Many of the curves currently used in engineering design are algebraic but nonlinear. Although these curves can be approximated as polygons for the purpose of visualization, such approximations can lead to false conclusions about mechanical behavior. In this paper we consider the class of parts whose planar projection has a piecewise algebraic convex hull. Our primary result is a proof that a grasp plan exists for any such part. We give a planning algorithm that produces the shortest plan and runs in time O(n2 log n+N), where n is the number of transitions in the grasp function and N is the length of the plan produced. We believe this to be the first paper to address the problem of manipulating algebraic parts when nothing is know about their initial orientation View full abstract»

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  • The kinematics of multi-fingered manipulation

    Publication Year: 1995 , Page(s): 491 - 503
    Cited by:  Papers (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1060 KB)  

    In this paper, we derive a configuration-space description of the kinematics of the fingers-plus-object system. To do this, we first formulate contact kinematics as a “virtual” kinematic chain. Then, the system can be viewed as one large closed kinematic chain composed of smaller chains, one for each finger and one for each contact point. We examine the underlying configuration space and two ways of moving through this space. The first, kinematics-based velocity control, is a generalization of some previous velocity-based approaches. The second, hyperspace jumps, is a purely configuration-space concept. We conclude with a discussion of how these concepts can be used to understand the task of twirling a baton View full abstract»

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  • On the geometry of contact formation cells for systems of polygons

    Publication Year: 1995 , Page(s): 522 - 536
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1448 KB)  

    The efficient planning of contact tasks for intelligent robotic systems requires a thorough understanding of the kinematic constraints imposed on the system by the contacts. In this paper, we derive closed-form analytic solutions for the position and orientation of a passive polygon moving in sliding and rolling contact with two or three active polygons whose positions and orientations are independently controlled. This is accomplished by applying a simple elimination procedure to solve the appropriate system of contact constraint equations. We also prove that the set of solutions to the contact constraint equations is a smooth submanifold of the system's configuration space and we study its projection onto the configuration space of the active polygons. By relating these results to the wrench matrices commonly used in grasp analysis, we discover a previously unknown and highly nonintuitive class of nongeneric contact situations. In these situations, for a specific fixed configuration of the active polygons, the passive polygon can maintain three contacts on three mutually nonparallel edges while retaining one degree of freedom of motion View full abstract»

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  • Diagonalized Lagrangian robot dynamics

    Publication Year: 1995 , Page(s): 571 - 584
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1180 KB)  

    A diagonal equation for robot dynamics is developed by combining mass matrix factorization results with classical Lagrangian mechanics. Diagonalization implies that at each fixed time instant the equation at each joint is decoupled from all of the other joint equations. The equation involves two important variables: a vector of total joint rotational rates and a corresponding vector of working joint moments. The nonlinear Coriolis term depends on the joint angles and the rates. The total joint rates are related to the relative joint-angle rates by a linear spatial operator. The total rate at a given joint k reflects the total rotational velocity about the joint, and includes the combined effects from all the links between joint k and the base. Similarly, the working moments are related to the applied moments by the spatial operator . The working moment at a given joint is that part of the applied moment which does actual mechanical work. The diagonal equations are obtained by using the mass matrix factorization in the system Lagrangian View full abstract»

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  • Alignment using an uncalibrated camera system

    Publication Year: 1995 , Page(s): 516 - 521
    Cited by:  Papers (22)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    We describe a method for the visual control of a robotic system which does not require the formulation of an explicit calibration between image coordinates and the world coordinates. By extracting control information directly from the image, we free our technique from the errors normally associated with a fixed calibration. We attach a camera system to a robot such that the camera system and the robot's gripper rotate simultaneously. As the camera system rotates about the gripper's rotational axis, the circular path traced out by a point-like feature projects to an elliptical path in image space. We gather the projected feature points over part of a rotation and fit the gathered data to an ellipse. The distance from the rotational axis to the feature point in world space is proportional to the size of the generated ellipse. As the rotational axis gets closer to the feature, the feature's projected path will form smaller and smaller ellipses. When the rotational axis is directly above the object, the trajectory degenerates from an ellipse to a single point. We demonstrate the efficacy of the algorithm on the peg-in-hole problem View full abstract»

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  • Observer based control for elastic joint robots

    Publication Year: 1995 , Page(s): 618 - 623
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    In this paper we present an approach to control elastic modes of the robot joints using only measurements of the variables on the rotor side of the transmission. First, a simple and robust observer is proposed to estimate link positions and velocities. The state estimates are used in a fast inner loop to damp oscillations in the joints. Simulations have shown good performance of the observer and the closed loop system in the presence of measurement noise and parameter uncertainties 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