Showing papers on "Revolute joint published in 1997"

Hemispherical, high bandwidth mechanical interface for computer systems

Abstract: A mechanical interface for providing high bandwidth and low noise mechanical input and output for computer systems. A gimbal mechanism includes multiple members that are pivotably coupled to each other to provide two revolute degrees of freedom to a user manipulatable about a pivot point located remotely from the members at about an intersection of the axes of rotation of the members. A linear axis member, coupled to the user object, is coupled to at least one of the members, extends through the remote pivot point and is movable in the two rotary degrees of freedom and a third linear degree of freedom. Transducers associated with the provided degrees of freedom include sensors and actuators and provide an electromechanical interface between the object and a computer. Capstan band drive mechanisms transmit forces between the transducers and the object and include a capstan and flat bands, where the flat bands transmit motion and force between the capstan and interface members. Applications include simulations of medical procedures, e.g. epidural anesthesia, where the user object is a needle or other medical instrument, or other types of simulations or games.

Complete, minimal and model-continuous kinematic models for robot calibration

Abstract: New general kinematic models for robot calibration are presented in this paper These models have the distinct advantage of satisfying the model-parameter identification requirements of completeness, minimality and model continuity for all combinations and configurations of revolute and prismatic joints A set of 17 model parametrizations are developed, including simple criteria for deciding which parametrizations are to be used in modelling a robot The parametrizations presented also result in an accurate representation of the physical robot and thus allow realistic integration of elastic deformation models Model continuity within each parametrization's application range is shown by means of differential geometry Also shown is how these models are be extracted from a non-complex “vector-chain” description of a robot

Shear force feedback control of a single-link flexible robot with a revolute joint

Abstract: In this paper we present a shear force feedback control method for a single-link flexible robot arm with a revolute joint for which it has been shown that direct bending strain feedback can suppress its vibration. Our primary concern is the stability analysis of the closed-loop equation which has not appeared in the literature. We show the existence of a unique solution and the exponential stability of this solution by doing spectral analysis and estimating the norm of the resolvent operator associated with this equation. Some experiments are also conducted to verify these theoretical developments.

Forearm-supported exoskeleton hand-tracking device

Abstract: A man-machine interface device is provided which employs rigid links interconnected by measured revolute joints to provide the position of a hand relative to a reference location, such as a desk, keyboard or chair By proper selection of kinematic structure, and by placing one of the joints near the elbow and extending one of the links along the line of the forearm, translation of the joint-link structure is minimized, hence the undesirable perception of friction and inertia are also minimized When Hall-Effect sensors are used as the revolute joint goniometers, the permanent magnets of neighboring joints are placed in the same link so the effects of magnetic field interference can be calibrated out A hand-sensing joint-link device as described herein can produce data which is more noise free, at a higher sample rate, with less latency and more robust that competing electromagnetic, optical and ultrasonic sensing technologies, without adding much encumbrance The output from the hand-sensing device may be used to produce a graphical "virtual hand" on a computer monitor which mimics the movement of the measured physical hand The hand-sensing joint-link device may also be used with a finger-sensing joint-link device to provide data on the movements of the fingers and hand When a right and left finger- and hand-sensing joint-link devices are used, the wearer can use both hands to manipulate virtual objects on a computer monitor

Genetic design of 3D modular manipulators

Abstract: This paper proposes a method for task based design of modular robotic systems using genetic algorithms (GA). We introduce a 3D kinematic description for modular serial manipulators and a two-level GA to optimize their topology from task specifications. Revolute and prismatic joints are considered and the number of DOF is let to the GA to determine (allowing redundant manipulators). The upper-level GA is dedicated to the topology evolution and uses the lower-level GA to search for inverse kinematics problem solutions. The topology is evolved for adaptation to a global task constituted by several required end effector configurations (subtasks). The implemented GA optimizes several performance criteria under constraints. To illustrate the method capacities, an example is presented for a redundant manipulator in a cluttered workspace.

Kinematics and dynamics of a six-degree-of-freedom parallel manipulator with revolute legs

Abstract: This paper presents the kinematics and dynamics of a six-degree-of-freedom platform-type parallel manipulator with six revolute legs, i.e. each leg consists of two links that are connected by a revolute joint. Moreover, each leg is connected, in turn, to the base and moving platforms by means of universal and spherical joints, respectively. We first introduce a kinematic model for the manipulator under study. Then, this model is used to derive the kinematics relations of the manipulator at the displacement, velocity and acceleration levels. Based on the proposed model, we develop the dynamics equations of the manipulator using the method of the natural orthogonal complement. The implementation of the model is illustrated by computer simulation and numerical results are presented for a sample trajectory in the Cartesian space.

Kinematic analysis and singularity representation of spatial five‐degree‐of‐freedom parallel mechanisms

Abstract: This article addresses the kinematic modeling and the determination of the singularity loci of spatial five-degree-of-freedom parallel mechanisms with prismatic or revolute actuators. The architecture of the spatial five-degree-of-freedom parallel mechanisms is first introduced. Then, algorithms are derived for the solution of the inverse kinematic problem for the two types of mechanisms considered here. Two different methods are presented for the derivation of the velocity equations and the corresponding Jacobian matrices are derived. The numerical determination of the workspace boundaries is then briefly discussed. Finally, the determination of the singularity loci is performed, using the velocity equations, and examples are given to illustrate the results. It is shown that the vector formulation of the velocity equations leads to more efficient algorithms for the determination of the singularity loci. Spatial five-degree-of-freedom parallel mechanisms can be used in several robotic applications as well as in flight simulators. The kinematic analysis and the determination of the singularity loci are very important design issues. © 1997 John Wiley & Sons, Inc.

A redesigned DCAL controller without velocity measurements: theory and demonstration

Abstract: A link position tracking controller is formulated for an n-link, rigid, revolute, serially-connected robot. The controller generates torque commands to the individual robot links based on adaptive estimates of the system parameters and measurements of only link positions. A filtering technique, based on the link position signal, is used to alleviate the need for velocity measurements. A complete development of the controller is presented along with a proof of semiglobal asymptotic link position-velocity tracking performance. Experimental validation of the proposed controller on the Integrated Motion Inc. (IMI) two-link direct drive robot is also presented. Several extensions to the basic controller are described that consider the use of fixed parameter estimates.

Dynamic modelling of a class of tendon driven manipulators

Abstract: This paper deals with the n-DOF serial manipulators which have n rotary actuators located on the base link, each driving a revolute joint via a pair of opposed tendons. With a Lagrangian approach, the dynamic equations of such class of manipulators are derived. In particular it is investigated how the torques and angular displacement of the actuators are related to those of the joints. In addition to rigid link dynamics and DC electrical motor dynamics, the present work takes also into account the viscous-elastic properties of the tendons, the inertia of the pulleys guiding the tendons and the fact that the tendon transmission driving a joint is routed over all the precedent joints. The proposed analysis is especially the design of high performance tendon driven manipulators.

Modeling of flexible-link manipulators with prismatic joints

Abstract: The axially translating flexible link in flexible manipulators with a prismatic joint can be modeled using the Euler-Bernoulli beam equation together with the convective terms. In general, the method of separation of variables cannot be applied to solve this partial differential equation. In this paper, we present a nondimensional form of the Euler-Bernoulli beam equation using the concept of group velocity and present conditions under which separation of variables and assumed modes method can be used. The use of clamped-mass boundary conditions lead to a time-dependent frequency equation for the translating flexible beam. We present a novel method to solve this time-dependent frequency equation by using a differential form of the frequency equation. We then present a systematic modeling procedure for spatial multi-link flexible manipulators having both revolute and prismatic joints. The assumed mode/Lagrangian formulation of dynamics is employed to derive closed form equations of motion. We show, using a model-based control law, that the closed-loop dynamic response of modal variables become unstable during retraction of a flexible link, compared to the stable dynamic response during extension of the link. Numerical simulation results are presented for a flexible spatial RRP configuration robot arm. We show that the numerical results compare favorably with those obtained by using a finite element-based model.

Experimental Characterization of Hysteresis in a Revolute Joint for Precision Deployable Structures

Abstract: Recent studies of the micro-dynamic behavior of a deployable telescope metering truss have identified instabilities in the equilibrium shape of the truss in response to low-energy dynamic loading. Analyses indicate that these micro-dynamic instabilities arise from stick-slip friction within the truss joints (e.g., hinges and latches). The present study characterizes the low-magnitude quasi-static load-cycle response of the precision revolute joints incorporated in the deployable telescope metering truss, and specifically, the hysteretic response of these joints caused by stick-slip friction within the joint. Detailed descriptions are presented of the test setup and data reduction algorithms, including discussions of data-error sources and data-filtering techniques. Test results are presented from thirteen specimens, and the effects of joint preload and manufacturing tolerances are investigated. Using a simplified model of stick-slip friction, a relationship is made between joint load-cycle behavior and micro-dynamic dimensional instabilities in the deployable telescope metering truss.

Achieving impedance objectives in robot teleoperation

Abstract: This work describes the experimental application of impedance control to a seven joint revolute manipulator built for neutral buoyancy operation. Compensator design methodologies previously applied to a single joint are extended to the full manipulator and tested in 1 g tasks. The controller was configured to mimic three useful modes at the end-effector: accommodation control, spring-dashpot control, and inertial mode. Simulated parameter errors were negligible even for outer force loop rates as low as 40 Hz. Hard contact tasks typically required damping augmentation of 5-10 times the freespace values to maintain stable contact. Preliminary experiments indicate that this controller can be a useful tool in fulfilling future objectives in space telerobotic operations.

Redundancy utilization for obstacle avoidance of planar robot manipulators

Abstract: Two obstacle avoidance criteria are developed, utilizing the kinematic redundancy of serial redundant manipulators having revolute joints and tracking pre-determined end effector paths. The first criterion is based on the instantaneous distances between certain selected points along the manipulator, called configuration control points (CCP), and the vertices of the obstacles. The optimized joint configurations are obtained by maximizing these distances. Thus, the links of the manipulator are configured away from the obstacles. The second criterion uses a different approach, and is based on Voronoi boundaries representing the equidistant paths between two obstacles. The optimized joint configurations are obtained by minimizing the distances between the CCP and control points selected on the Voronoi boundaries. The validities of the criteria are demonstrated through computer simulations.

Near-optimal motion planning for nonholonomic systems with state/input constraints via quasi-Newton method

Abstract: An optimal motion planning scheme using quasi-Newton method is proposed for nonholonomic systems. A cost functional is used to incorporate the final state errors, control energy, and constraints on states and controls. The motion planning is to determine control inputs to minimize the cost functional and is formulated as a nonlinear optimal control problem. By using the control parametrization, one can transform an infinite-dimensional optimal control problem to a finite-dimensional one and use quasi-Newton method to solve for a feasible trajectory which satisfies nonholonomic constraints and state/input constraints. The proposed scheme was applied to a free-floating robot for numerical simulation. A three-link planar floating robot was designed and built to verify the proposed scheme. The robot consists of two one-link arms connected to a main base via revolute joints. From the experimental results, the proposed optimal motion planning scheme controls the robot from initial state to final state along the planned path within /spl plusmn/0.1 rad final position error.

Design of a minimum surface-effect three degree-of-freedom micromanipulator

Abstract: This paper describes the fundamental physical motivations for small-scale minimum surface-effect design, and presents a three degree-of-freedom micromanipulator design that incorporates a minimum surface-effect approach. The primary focus of the design is the split-tube flexure, a unique small-scale revolute joint that exhibits a considerably larger range of motion and significantly better multi-axis revolute joint characteristics than a conventional flexure. The development of this joint enables the implementation of a small-scale spatially-loaded revolute joint-based manipulator with well-behaved kinematic characteristics and without the backlash and stick-slip behavior that would otherwise prevent precision control.

Cooperative control of two-manipulator systems handling flexible objects

Abstract: There is growing interest in robotic manipulation of flexible materials due to its potential applications in industries. This thesis addresses the problem of controlling a two-manipulator system handling flexible objects. A particular case of handling a flexible beam is first concerned, where the vibration dynamics of the beam is approximated by m assumed modes. Three approaches focusing on the position control and trajectory tracking are presented. The first approach shows that a PD position feedback plus an I-type force feedback is able to stabilize the beam to a desired position and orientation while suppressing its vibration, and simultaneously control the internal forces between the beam and manipulators. The second approach is to develop a hybrid impedance control scheme that combines impedance control and an I-type force feedback into one scheme by designing a proper response of the interaction including external and internal forces. Compared to the PD feedback, the impedance control is robost to external disturbances and displays a higher rate of convergence. The proposed controllers use no feedback of the flexible coordinates but the measurable information. The asymptotic stability of the system is investigated by LaSalle theorem. To achieve position and force tracking, a tracking scheme is developed in the third approach by utilizing the saturation functions to compensate the flexible effect so that no information about the vibration is used. Under this controller, the errors of position and force as well as the vibrations are under an upper bound determined by control parameters. It must be noted that the proofs in the three approaches are not limited to any specific number m of vibration modes. The simulation results illustrate the validities of the three approaches. We further consider the case of handling a general flexible object handled by two manipulators with six revolute joints. It is shown that under a PD position feedback, the position/orientation of the object is able to approach the desired one and at the same time the vibration of each contact is suppressed. The investigation is based on such a boundary condition that one contact is fixed and the other one free so that the flexible object is decomposed into two components representing the rigid body and the deformation by using the finite element method.

A Uniform Bound for the Jacobian of the Gravitational Force Vector for a Class of Robot Manipulators

Abstract: In this paper, we study the boundedness of the Jacobian of the gravitational force vector of serial link robot manipulators with respect to the generalized coordinate vector. The uniform bound of this matrix plays an important role in the stability analysis and design of many control systems. In order to insure the existence of a uniform bound, it is typically assumed that manipulators under consideration have only revolute joints. We therefore propose a larger class of manipulators, referred to as class BD manipulators, for which a uniform bound exists. This bound can easily be computed using basic link parameters including the link masses, the Denavit-Hartenberg link parameters, and the link center of mass locations.

A generalised approach for the modelling of articulated open chain planar linkages

Abstract: In this paper a model to cover all possible topologies of robot manipulators composed of prismatic and revolute joints is presented. For simplicity, only planar systems are considered, hence to provide plane positioning, systems handled are of three degrees of freedom. The physical model assumes three moving rigid links in articulation with one revolute and one prismatic joint between each link pair, forming a six degrees of freedom open chain linkage. Among each joint pair, one is real and the other fictitious. The real joint is arbitrarily actuated by an externally applied force or torque while the fictitious one is acted upon by an appropriately controlled force or torque as to keep that joint velocity zero, keeping fixed at its initial position. The physical model is accompanied by a mathematical model obtained by Lagrange formulation. This approach is called ‘The method of Fictititous Degrees of Freedom’.

Robotic TCF and rigid-body calibration methods

Abstract: For off-line programming to work, systematic methods must be developed to account for non-ideal performance of the parts and devices in the manufacturing cell. Although much of the literature focuses on robot inaccuracy, this paper considers practical methods for the tool control frame (TCF) calibration and rigid-body compensation required to close the inverse kinematics loop for target driven tasks.In contrast to contemporary estimation methods, a closed-form, easily automated, solution is introduced for calibrating the position and orientation (pose) of orthogonal end-effectors when the distal robot joint is revolute. This paper also considers methods for measuring and compensating the small rigid-body perturbations that result from non-repeatable part delivery systems or from geometric distortion. These methods are designed to eliminate r*theta* error from the rigid-body prediction and can be conducted in real-time. Without accurate TCF calibration and rigid-body compensation, even the most accurate robot will fail to complete an off-line programmed task if the task tolerances are stringent.

A solution to the end-effector position optimisation problem in robotics using neural networks

Abstract: The paper presents an original application of the Hopfield-type neural network to a robotics optimisation problem. The robot considered features an arm composed of three revolute joints, the last of which is the end-effector. The robot is planar as the movement of the end-effector is limited to one plane. The mechanical characteristics of the actuators in the joints, the accuracy of the angle position sensors, and dimensional errors in the mechanical elements which make up the end-effector all contribute towards an end-effector positioning error along an assigned trajectory. The computational complexity of the algorithmic solution to the minimisation of this error is at times incompatible with certain particularly critical industrial applications. To reduce the calculation time, the author presents a neural approach based on a Hopfield-type model. A detailed definition of the neural approach is given, its capacity for solving the problem is demonstrated, and the computational complexity is analysed. This analysis shows the drastic computational reduction provided by the neural approach as compared with an algorithmic solution to the problem of end-effector position optimisation.

Control of a Rover-Mounted Manipulator

Abstract: In this paper, we present a control algorithm for a mechanical system built from a six revolute joint robot manipulator mounted on a nonholonomic mobile platform. We describe a global control of this mechanical system which calculates the joint values for both the robot manipulator and the mobile platform. We want the end-effector location (position+orientation) to evolve between starting and final required locations and to follow a required trajectory. First, we present simulated results to illustrate the efficiency of the control algorithm. Then, the controls are implanted and checked on the real mechanical system.

Singularity robustness: methods for joint-space and task-space control

Abstract: Presents methods for the robust handling of the kinematic singularities inherent in all revolute joint manipulators. For joint-space control, the method of damped-least-squares at both the velocity and acceleration levels is revisited and new stability results are presented; for task-space control a new task-space trajectory filter is presented. Simulation results are given for the PUMA 762 robot and the RRC K-1207 redundant arm, and demonstrate that the proposed methods handle singularities successfully.

Dynamics and Control of Elastic Joint Manipulators

Abstract: The investigations presented in this paper are based on our previous studies where the modeling and control problems of rigid body manipulators were treated through the so-called vector-parametrization of the SO(3) group. The nice property of this parametrization, which also displays a Lie group structure, is that it drastically simplifies some considerations and reduces the computational burden in solving direct kinematic problems, inverse kinematic problems and dynamic modeling by more than 30 hitherto. This statement, which is valid for models built through vector-parameter, becomes stronger in pure vector-parameter considerations. It is proved additionally that the computational effectiveness of the vector-parameter approach increases with the increasing number of the revolute degrees of freedom. Here we show that this can be used successfully in the problems of elastic joint manipulators where, besides the real n links,n fictious links are included and an additional n revolute degrees of freedom are involved. The present paper also considers the role of group representations of the rotation motions in the modeling and control of manipulators with elastic joints. Dynamic models ‘through’ vector-parameter and in ‘pure’ vector-parameter form are developed and the inverse dynamic problem is discussed. It is shown that the nonlinear equations of motion are globally linearizable by smooth invertible coordinate transformation and nonlinear state feedback.