Showing papers on "Revolute joint published in 1994"

Simple model of human arm reachable workspace

Abstract: The paper introduces a simplified mathematical model of the human arm kinematics which is used to determine the workspace related to the reachability of the wrist. The model contains six revolute degrees of freedom, five in the shoulder complex and one in the elbow joint. It is not directly associated to the anatomical structure of the arm, but represents the spatial motion of two characteristic points, epicondylus lateralis and proc. styloideus. Use of this simplified model for the determination of reachable workspace offers several advantages versus direct measurement: (i) the workspace can be obtained in few minutes on a micro VAX II computer, (ii) patients with various injuries in various stages of recovery can be treated since only a few brief and simple measurements of the model's parameters are needed, and (iii) the calculated workspace includes complete information of the envelope, as well as inside characteristics. >

Suspension system having two degrees of rotational freedom

Abstract: A system is described which utilizes two perpendicular four-bar linkages coupled by a common plate to provide a translational-free flexible suspension having two rotational degrees of freedom about a desired point. One of the four-bar linkages is secured to a stationary "ground" structure, and the other linkage is attached to the object to be supported, such as a mirror. In one embodiment, two links of each of the two four-bar linkages are constructed from spring steel flexure elements which are rigid in all directions except about the rotational axis. The flexure elements thus comprise "revolute joints". Because the flexure elements function as spring hinges, no friction is encountered when the suspension is displaced or "pivoted".

Construction of the Equations of Motion for Multibody Dynamics Using Point and Joint Coordinates

Abstract: A systematic process for constructing the equations of motion for multibody systems containing open or closed kinematic loops is presented. We first illustrate a nonconventional method for describing the configuration of a body in space using a set of dependent point coordinates, instead of the more classical set of translational and rotational body coordinates. Based on this point-coordinate description, body mass and applied loads are distributed to the points. For multibody systems, the equations of motion are constructed as a large set of mixed differential-algebraic equations. For open-loop systems, based on a velocity transformation process, the equations of motion are converted to a minimal set of equations in terms of the joint accelerations. For multibody systems with closed kinematic loops, the equations of motion are first written as a small set of differential-algebraic equations. Then, following a second velocity transformation, these equations are converted to a minimal set of differential equations. The combination of point-and joint-coordinate formulations provides some interesting features.

Contact forces in the non-linear dynamic analysis of tracked vehicles

Abstract: It is known that when two springs are connected in series, the stiffness coefficient of an equivalent system that consists of one spring is less than the stiffness coefficients of the original springs. Experimental observations indicate that this fact can be very useful in determining the overall vibration characteristics of tracked vehicles. This simple fact is used in this investigation to develop a computer aided analysis procedure for the dynamic simulation of large-scale tracked vehicles. The track is considered as a closed kinematic chain that consists of rigid bodies connected by revolute joints. The contacts between the track links and the rollers, the sprocket, and the idler are represented by non-linear continuous force models. The stiffness and damping coefficients in these contact force models are determined by studying the viberation characteristics of the tracked vehicle. The tooth of the sprocket is defined using three surfaces. These are the left, the bottom, and the fight surfaces. Three successive transformations are used to define the contact kinematic relationships between the sprocket teeth and the pins of the track links. The equations of motions of the vehicle are formulated using the Lagrangian approach. Non-linear constraint equations that describe mechanical joints and specified motion trajectories in the system are adjoined to the differential equations of motion using the technique of Lagrange multipliers. The resulting mixed system of differential and algebraic equations is solved numerically using a direct numerical integration method. A Newton–Raphson algorithm is used to check on the violations in the kinematic constraints. The results presented in this paper are obtained using a 54 body planer tracked vehicle in which the track consists of 42 rigid links connected by revolute joints.

Mechanisms for orienting and placing articles

Abstract: A mechanism for orienting an end member utilizes paired five-bar linkages wherein two joints on each five-bar linkage may be actuated. Preferably the actuators are mounted at the base-link of the five bar linkages, such base-links being collinearly aligned. Two or three rotational and one translational degrees of freedom are available. This mechanism in its three or two degrees of rotational freedom variants has exceptional motion range, free of singularities, superior structural properties, and is easy to manufacture. This orienting mechanism can be mounted as an end member on a positioning mechanism having four main links herein three joints are actuated. The diagonally oppose joints of the positioning mechanism are respectively spherical and revolute. This positioning mechanism can operate with two actuators that are grounded and one that is elevated. In all cases sensors may be substituted for, or used in conjunction with, actuators to provide an apparatus useful, interalia, in the telerobotics and virtual reality fields.

Inverse kinematics of six-degree of freedom “general” and “special” manipulators using symbolic computation

Abstract: This paper presents an algorithm that solves the inverse kinematics problem of all six degrees of freedom manipulators, “general” or “special”. A manipulator is represented by a chain of characters that symbolizes the position of prismatic and revolute joints in the manipulator and the special geometry that may exist between its joint axes. One form of the loop closure equation is chosen and the Raghavan and Roth method is used to obtain symbolically a square matrix. The determinant of this matrix yields the characteristic polynomial of the manipulator in one of the kinematic variables. As an example of the use of this algorithm we present the solution to the inverse kinematics problem of the GMF Arc Mate welding manipulator. In spite of its geometry, this industrial manipulator has a non-trivial solution to its inverse kinematics problem.

A redesigned DCAL controller without velocity measurements: theory and experimentation

Abstract: In this paper, a link position tracking controller is formulated for an n-link, rigid, revolute robot The controller generates torque commands to the individual robot links based on adaptive estimates of the system parameters and measurements of link positions only A filtering technique, based on the link position signals, is used to remove the need for velocity measurements A complete development of the controller is presented along with a proof of semi-global 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 >

Design of anti-backlash transmissions for precision position control systems

Abstract: Position control system typical of machine tools and robots usually operate at relatively high torque and low speed. Although servo motors having these characteristics are now available, their cost, size, and weight generally exceed those of the traditional servo motor and gear reducer. Critical applications require transmissions with zero backlash and high stiffness, for which there are several solutions. This article reviews various anti-backlash techniques, discusses their subtleties and applications, develops models, and present design methodologies. Although presented in the context of geared transmissions, the ideas also apply to other machine elements and situations requiring precision and robustness. Two case studies, a robot revolute joint and a machine tool axis of rotation, help to reinforce the theory and raise practical issues.

On the numerical solution of tracked vehicle dynamic equations

Abstract: In this investigation, the solution of the nonlinear dynamic equations of the multibody tracked vehicle systems are obtained using different procedures. In the first technique, which is based on the augmented formulation that employes the absolute Cartesian coordinates and Lagrange multipliers, the generalized coordinate partitioning of the constraint Jacobian matrix is used to determine the independent coordinates and the associated independent differential equations. An iterative Newton-Raphson algorithm is used to solve the nonlinear constraint equations for the dependent variables. The numerical problems encountered when one set of independent coordinates is used during the simulation of large scale tracked vehicle systems are demonstrated and their relationship to the track dynamics is discussed. The second approach employed in this investigation is the velocity transformation technique. One of the versions of this technique is discussed in this paper and the numerical problems that arise from the use of inconsistent system of kinematic equations are reported. In the velocity transformation technique, the tracked vehicle system is assumed to consist of two kinematically decoupled subsystems; the first subsystem consists of the chassis, the rollers, the sprocket and the idler, while the second subsystem consists of the track which is represented as a closed kinematic chain that consists of rigid links connected by revolute joints. It is demonstrated that the use of one set of recursive equations leads to numerical difficulties because of the change in the track configuration. Singular configurations can be avoided by repeated changes in the recursive equations. The sensitivity of the predictor-corrector multistep numerical integration schemes to the method of formulating the state equations is demonstrated. The numerical results presented in this investigation are obtained using a planner tracked vehicle model that consists of fifty four rigid bodies.

Jacobian formulation for a novel 6-DOF parallel manipulator

Abstract: The derivation of the Jacobian matrix for a novel six degree of freedom parallel manipulator is presented in this paper. A force decomposition approach is used to compute the Jacobian. The parallel manipulator consists of a base plate, a top plate, and three connecting legs with all revolute joints. The key to the Jacobian formulation presented here is the derivation of a mapping from the applied end-effector force and torque to two force components at each spherical joint. Each leg of the manipulator can then be treated separately and the actuated joint torques can easily be computed from these spherical joint forces. >

Optimal synthesis of three-revolute manipulators

Abstract: An optimization method is proposed and discussed in order to synthesize a three-revolute open chain manipulator whose structure can have minimum size encumbrance and a workspace with prescribed constraints. The sequential quadratic programming optimization technique used has been successfully applied to the formulated problem as illustrated in some examples.

Task understanding of the crank turning

Abstract: The task understanding is examined for a popular task of the crank turning by a robot manipulator. A mathematical task model embedded uncertain factors as unknown parameters is constructed, and by analyzing the model, a robust task strategy to revolute the crank is contrived. It is shown how to design a robot controller to execute the task strategy. A controller is designed as an example and the validity of the controller is investigated by simulation. >

Kinematic analysis and synthesis of four-bar mechanisms for straight line coupler curves

Abstract: Mechanisms are means of power transmission as well as motion transformers. A fourbar mechanism consists mainly of four planar links connected with four revolute joints. The input is usually given as rotary motion of a link and output can be obtained from the motion of another link or a coupler point. Straight line motion from a four bar linkages has been used in several ways as in a dwell mechanism and as a linkage to vehicle suspension. This paper studies the straight line motion obtained from planar four-bar mechanisms and optimizes the design to produce the maximized straight line portion of the couplerpoint curve. The equations of motion for four different four-bar mechanisms will be derived and dimensional requirements for these mechanisms will be obtained in order to produce the straight line motion. A numerical procedure will be studied and computer codes that generate the coupler curves will be presented. Following the numerical results study, a synthesis procedure will be given to help a designer in selecting the optimized straight line motion based on design criteria. CONTENTS 1 . Introduction 1 2. Mechanism And Its Components 6 3. Four-BarMechanism And Its Classifications 1 0 4. Special Four-Bar Linkages For Approximate Straight Line Output 1 9 5. Position Analysis Of A Basic Four-Bar Mechanism 28 6. Equation Of Coupler Curve For A Generic Four-Bar Linkage 35 7. Four-Bar Linkages That Generate Symmetrical Coupler Curves 38 8. Analysis Of Four-Bar Linkages Generating Straight Line Coupler Curves 47 9. Numerical Generation of Coupler Point Curves 58 10. Synthesis Procedure For Designing A Four Bar Linkage 68

On the Kinematics of Nonsingular and Singular Posture Changing Manipulators

Abstract: Some non redundant robot manipulators have the unusual ability to change posture without meeting a singularity In this paper, several conditions are stated for classifying manipulators geometry As a result, a list of 3-DOF singular posture changing manipulators geometries is provided Both revolute and prismatic joints are considered in the analysis In the end of the paper, the study is enlarged to the case of 6-DOF manipulators

Path planning in the presence of obstacles based on task requirements

Abstract: We propose a novel and efficient scheme for planning a kinematically feasible path in the presence of obstacles according to task requirements. By employing geometrical analysis, we derive expressions to describe the relationship between the planned path, kinematic constraints, and obstacles in the robot workspace. The freedom available according to task requirements is then utilized to modify the infeasible portions of the planned path. We use a 6R (revolute) wrist-partitioned type of robot manipulator and a spherical obstacle as a case study to demonstrate the proposed scheme. We then extend our results to general wrist-partitioned types of robot manipulators and arbitrarily-shaped or multiple obstacles. © 1994 John Wiley & Sons, Inc.

A generalized approach to the modelling of modular machines

Abstract: This paper describes a method of graphically simulating modular machines within a computer aided design environment. This forms part of a much larger Science and Engineering Research Council (SERC) funded programme aimed at advancing modern practices when designing and building manufacturing machines. A generalized approach to the synthesis of the generic features of various kinematic motion pairs is presented and prismatic and revolute motion primitives generalized in their functional and geometric aspects. A hierarchical ring and tree data structure has been designed and implemented to comprehensively represent these motion pairs and to simulate their performance. More complex modular manufacturing machines can be represented using information from a library of up to three degree of freedom motion modules. Seven two degree of freedom motion primitives and twelve three degree of freedom motion primitives with articulation configurations have been analyzed and included in the motion primitive library. The configuration of modular machines comprised of physically separate but logically connected distributed motion primitives are described. Examples of a two-finger industrial robot gripper and a three-finger industrial robot hand are used to demonstrate the general principles.

Collision-Avoidance Robot Path Planning Using Fully Cartesian Coordinates

Abstract: An algorithm for robot path planning in the presence of obstacles is proposed. The problem is formulated in the Cartesian space. Nonlinear programming techniques are used to obtain a map of feasible robot configurations. Then a weighted graph is associated to the map, and a search algorithm is used to get a sequence of collision-free robot configurations between two previously selected points. The algorithm has been successfully applied to redundant planar robotic manipulators with revolute and prismatic joints and spatial robotic manipulators.

Measuring arrangement for position determination in manipulators

Abstract: For the determination of the end-effector position in manipulators, such as robots, it is customary to use signals from sensors directly associated with the drives. Errors due to elasticities, play and friction are not determined or determined only by additional sensors. The new measuring arrangement is intended to enable the actual position of the end effector of manipulators to be determined and also to be usable during normal operation of the manipulator. To be able to use the measuring arrangement of measuring systems for precise position measurement, its structure must correspond to that of the manipulator. For simple mounting and in order to determine the individual joint positions, the individual measuring systems are connected to the manipulator at selected points. The functional regions of the measuring systems are supported, especially in the case of revolute joints of the manipulator, by an independent drive system for the positioning of the measuring system. The measuring-system drive is equipped with a suitable activation means. The arrangement of the measuring-system elements may be used, in principle, on any manipulator and in many cases may also be integrated. Both prismatic and revolute joints in each case exclusively or also in combination may be considered.

Effect of gravity on the static behavior of manipulators

Abstract: The gravity-induced forces on revolute robot links dominate over the dynamic induced forces, particularly at low speeds. These forces, however, are generally ignored in conceptual analysis works due to the ensuing simplifications that their omission bring about. The force ellipsoid, the dynamic manipulability ellipsoid, and the generalized ellipsoid of inertia introduced by some researchers are but a few examples. For robot-arm control applications, the effect of gravity is usually isolated from the dynamic equations and then compensated for by the robot controller. This study presents a method to introduce the effect of gravity in the static analysis of robot arms. Using the concept of fields, the gravity-induced forces acting on individual links are replaced by a single force, called here the generalized weight of the arm. The generalized weight is a force that acts at the endpoint, and its magnitude and direction are functions of the configuration of the robot arm. The generalized weight field is then integrated with the force ellipsoid to result in the true force that a manipulator can apply to its environment. Since the system is conservative, the generalized weight is considered to be the gradient of a potential field called the generalized potential field. This field alone can illustrate the overall effect of gravity on the manipulator throughout its work volume.

Gaussian neural network for direct adaptive control of robotic systems

Abstract: We treat the question of direct adaptive control of multi-link robotic systems with revolute joints. It is assumed that the dynamics of the robotic systems are not known. A radial basis function (RBF) neural network is used in a feedback loop for the control. An adaptive law is derived for the joint angle trajectory tracking. Simulation results are presented to show that in the closed-loop system precise trajectory control is accomplished. Furthermore, the effect of choice of number of neurons in the RBF neural network on the performance of the controller is also examined. >

Zero-Magnitude Screws in a 3-System of Finite Displacement Screws

Abstract: Consider that a rigid body is subject to angular displacements applied, always in the same sequence, at one then the other of two fixed revolute joints. It has recently been shown, when all possible angular displacements at the joints are considered, that the totality of screws of the fmite displacements which are available to the rigid body constitute a 3-system of screws. This 3-system is not special in form; but it is unusual in not containing its own orthogonal basis screws, and in lacking an infinite number of other screws which might be expected to lie in a certain central 2-system.

Determination of the Workspace Boundary of a General n-Revolute Manipulator

Abstract: The geometrical envelope concept is used in ring and hyper-ring generation to deduce an algebraic formulation for the workspace boundary of a general n-revolute manipulator open chain. The workspace boundary can be obtained from the envelope of a torus family which is traced by the parallel circles cut in the boundary of a generating hyper-ring. In this paper, an algebraic and recursive new algorithm is proposed as a function of the link parameters and the last revolute joint angle of the chain. Cross-section contours has been obtained for an illustrative example to show some peculiarities of general workspace shape of manipulators.