Showing papers on "Revolute joint published in 1989"

Global path planning using artificial potential fields

Abstract: The author describes a path planning technique for robotic manipulators and mobile robots in the presence of stationary obstacles. The planning consists of applying potential fields around configuration-space obstacles and using these fields to select a safe path for the robot to follow. The advantage of using potential fields in path planning is that they offer a relatively fast and effective way to solve for safe paths around obstacles. In the proposed method of path planning, a trial path is chosen and then modified under the influence of the potential field until an appropriate path is found. By considering the entire path, the problem of being trapped in a local minimum is greatly reduced, allowing the method to be used for global planning. The algorithm was tried with success on many different realistic planning problems. By way of illustration, the algorithm is applied to a two-dimensional revolute manipulator, a mobile robot capable of translation only, and a mobile robot capable of both translation and rotation. >

Issues in the dynamics and control of flexible robot manipulators

Abstract: Issues associated with modeling and control of robots with elastic arms are considered. An approach similar to substructure synthesis is used to model the system, where each link is first modeled independently of the others. The joint displacements are then used as constraints to synthesize the equations of motion. It is shown that the centrifugal stiffening effect is the dominating factor for the overall system behavior. Different approaches are discussed for the control design. The effects of flexibility on the response and on the closed-loop control are examined within the context of an example. N important issue of concern in the control of robots is the difference between the total mass of the manipulator and the mass of the payload. If a robot is compared with the human body, it is easily concluded that the manipulator is very inefficient. An inefficient robot implies low productivity and higher costs. A robot can be made more efficient by reducing the thickness of its arms. The resulting increased flexibility, unless considered properly, reduces pointing accuracies and affects the stability of the payload. Another source of inaccuracy is flexibility of the joints. There is considerable debate in the literature as to which source causes more inaccuracies. This paper is concerned with the modeling and control of manipulators with substantial flexibility in the arms. An approach similar to substructure synthesis is used to model the manipulator, and different control strategies are discussed. The mathematical formulation is applicable to robots with revolute or spherical joints. Several methods of modeling manipulators with elastic joints or with flexible arms exist in the literature.1"11 Each of the approaches uses a variety of assumptions. For example, Refs. 1-4 consider only the static deflections of the links; Ref. 1 treats the connecting links as massless, and Ref. 4 considers only one flexible bending mode for each link. Refer

Dynamics of an elastic multibody chain: part a—body motion equations

Abstract: In this paper—the first of a series describing the dynamics of an arbitrary multibody system—motion equations governing a set of individual bodies in a chain configuration are discussed. A chain consisting entirely of rigid bodies is considered first. Motion equations for a typical body of arbitrary shape and arbitrary mass distribution are then briefly summarized. Finally, the geometrical constraints necessary to connect the individual bodies into a chain are derived. Large translational and rotational motions are permitted at the joints connecting contiguous bodies. In other words, both prismatic and revolute joints are included, alone and in combination. As well, the interbody force constraints required to ensure that equal but opposite forces and torques exist at each joint are developed. The resulting expressions are amenable to the introduction of constraint and control forces at the chain joints. This permits the number of actively controlled degrees of freedom at any specific joint to be arbitrari...

Position Errors Due to Clearances in Journal Bearings

Abstract: The positional errors due to clearances in journal bearings intended to approximate revolute joints are analyzed. Equations are presented which relate joint geometry external loads, and errors. The paper treats the case common in serial chain manipulators where the revolute joint's nominal rotational angle is controlled, and it is desired to determine the errors that result from the clearances

An Approach To Manipulator Path Planning

Abstract: A path planning technique for fixed-base robot manipulators consists of a Mapping Phase and a Path Planning Phase. The Mapping Phase employs a closed-form relationship to map from object space to C-Space for a manipulator with revolute joints. The Path Planning Phase consists of develop ing a potential field around each object in C-Space and using the resulting field to choose an appropriate path. To accom plish this, a trial path is chosen and then modified under the influence of the potential field. Considering the entire path greatly reduces the probability of becoming trapped in a local minimum, making the method effective for global planning.

Joint trajectory generation for redundant robots

Abstract: A joint-trajectory-generation scheme for redundant robots is proposed which uses the redundancy to improve motion performance according to certain objective functions. The objective function can be either analytical or nonanalytical. For nonanalytical objective functions, a least-squares scheme is proposed to estimate the gradient vector. In addition, an approximation scheme is developed to compute the pseudoinverse of the Jacobian. Application of the scheme to a 4-link revolute planar robot manipulator is demonstrated through simulation. Several motion performance criteria are considered and their results analyzed. >

Efficient computation of manipulator inertia matrices and the direct dynamics problem

Abstract: A modeling scheme that uses the concepts of generalized and augmented links is proposed for computing joint-space inertia matrices of open-chain rigid body systems. Expressions for evaluating these matrices are derived, utilizing orthogonal Cartesian tensors and the Newton-Euler equations of motion. The resulting recursive algorithm is applicable to all rigid-link manipulators having open-chain kinematic structures with revolute and/or prismatic joints. An efficient implementation of the algorithm shows that the joint-space inertia-matrix of a six degree-of-freedom manipulator with revolute joints can be computed in approximately 420 multiplications and 339 additions. For manipulators with 0 degrees to 90 degrees twist angles, the number of computations is reduced to 271 multiplications and 250 additions. >

Horizontal revolute robot

Abstract: In a horizontal revolute robot, an upper end of a ball screw (21) of a direct-acting actuator (100) is rotatably supported by a top plate of a column (10), and the lower end thereof is coupled to a drive unit (40) disposed on a base plate of the column. A first link (220) is pivotally coupled to a coupling member (210) of a manipulator (200) fixed to a slider (30) of the actuator, and a second link (240) is pivotally coupled to the first link. The ball screw is rotated by the drive unit to move the manipulator along the ball screw in unison with the slider, and servomotors (230, 250) of the manipulator are driven to turn both the links within a horizontal plane, so that a wrist portion of the robot is positioned in a robot installation space for robot operation. Since no base is required to turnably support the actuator, the robot is small-sized, light in weight, and low-priced. Since the lower movement limit position of the manipulator is low, the range of action of the robot is wide.

The Hamilton wrist: a four-revolute-joint spherical wrist without singularities

Abstract: The authors present an inverse kinematic algorithm for a four-revolute-joint (4-R) spherical wrist that provides for a complete set of spatial orientations, is nonsingular, and is simple to implement with existing technology. The algorithm is a rate-controlled method that depends on the required Cartesian rate. In the process of presenting the algorithm, the authors have developed the fundamentals of differential motion with n-revolute-joint spherical wrists. The method is outlined and applied to a 4-R regional structure. The goal is to combine the 4-R spherical wrist with the 4-R regional structure to develop an 8-R manipulator that is free of internal singularities. >

Self-tuning control of planar two-link manipulator with non-rigid arm

Abstract: The control of the motion of a two-link manipulator with a flexible arm is studied. The first link is rigid, and the second link has a flexible part as an extension of a rigid part. The motion of the manipulator takes place on a horizontal plane. The dynamics of the manipulator are determined in Lagrange's formulation. The positions (output) of specified points on the flexible link are obtained in the Cartesian base coordinate system using strain-gage and joint-variable measurements. The inputs are applied to the actuators of the revolute and prismatic joints. For the controller design, a time-series multivariate model of the autoregressive exogeneous (ARX) type is used to describe the input-output relation. The discounted least-square method is used to estimate parameters of the time-series model. A self-tuning controller (STC) is designed so that the positions of specified points on the flexible link track the given trajectory points. The controller operates on the Cartesian coordinates, specifying the positions of the chosen discrete points on the flexible link. Simulation results as well as laboratory experiments on a Stanford/JPL arm controlled by an STC are presented to illustrate the approach. >

A Modular Computer Model for the Design of Vehicle Dynamics Control Systems1

Abstract: SUMMARY This paper describes a multiport approach to computer-aided modeling of vehicle dynamics. The modeling approach produces models that are suitable for the interactive design and evaluation of complex control strategies. The vehicle model which can be used for ride and handling analysis, is built from modular components. The components are programmed using the syntax of the computer aided control system design (CACSD) program EASYS. Seven modeling components are used to create a three-dimensional vehicle dvnamics model. The model is flexible enoug-h to simulate any suspension design with revolute joints. Each component of the model consists of a FORTRAN subroutine and a main calling module called a macro. To simplify the process of model building, the modeling components in the car model are designed to represent physical elements, such as the spring, damper, link or tire. To create a model, the components, which are represented by blocks, are interconnected through points, located on the blocks, ca...

Practical trajectory control of robot manipulators using adaptive sliding control scheme

Abstract: An adaptive sliding mode scheme is developed for the accurate tracking control of a robotic manipulator in the presence of disturbances, parameter variations, and nonlinear dynamic interactions. Coupling the online estimation of unknown manipulator and payload parameters to the sliding mode control effectively improves the tracking performance. The developed method is implemented using the Motorola 8-MHz MC68000 microprocessor on a two-link revolute joint manipulator. Experiment results show the accurate tracking capability and robust performance of the system. >

Device for actuating the valves of internal combustion engines with adjustable valve-lifting cam.

Abstract: The device disclosed has a multiple-element rotary transmission with a housing which accommodates the valve, a rotary cam connected to the housing via a revolute joint and driven by the crankshaft, an intermediate element actuated by the cam via a cam joint, and an output element which abuts on the housing and co-operates with the intermediate element via a joint and which transmits the movement to the valve. To obtain a simpler, more compact and more rigid structure, the intermediate element abuts on the housing via a cam joint, the cam of said cam joint, which is arranged on the intermediate element, has a section which forms a catch and a control section, and either the position of the cam of said cam joint, which abuts on the housing, or the position of the revolute joint of the cam can be adjusted during operation.

Vertical revolute joint robot

Abstract: A vertical revolute joint robot having an offset wrist, which is capable of rapidly calculating respective joint angles on the basis of a target position and orientation of an end effector, and hence is excellent in operation accuracy. A robot arm consists of first to third links, and the joint axis (Y0) of a first joint (1), which couples a base fixedly disposed within an operation space to the first link, extends perpendicularly to the axis of the base, whereas the joint axis (Z1) of a second joint (2), which couples the first and second links to each other, extends along the axis of the first link. The third link is mounted with a wrist offset relative to the arm, and an end effector is mounted on the offset wrist. A computer provided in the robot calculates a fist joint angle (θ1) in accordance with an arithmetic equation, which is fulfilled between corresponding ones of transformation matrices employed for coordinate transformation among zeroth to sixth coordinate systems respectively set for first to sixth joints (1)-(6) and an end effector mounting face center, the equation being represented as a function of vector components indicative of the position of the origin of the sixth coordinate system with respect to the zeroth coordinate system and determinable from target position and orientation of the end effector, link lengths determined in dependence on the robot arrangement, and offset distances (d2-d4). The computer calculates other joint angles (θ2-θ6) in accordance with similar arithmetic equations.

A complete analytical solution for the inverse instantaneous kinematics of a spherical-revolute-spherical (7R) redundant manipulator

Abstract: Using a method based upon resolving joint velocities using reciprocal screw quantities, compact analytical expressions are generated for the inverse solution of the joint rates of a seven revolute (spherical-revolute-spherical) manipulator. The method uses a sequential decomposition of screw coordinates to identify reciprocal screw quantities used in the resolution of a particular joint rate solution, and also to identify a Jacobian null-space basis used for the direct solution of optimal joint rates. The results of the screw decomposition are used to study special configurations of the manipulator, generating expressions for the inverse velocity solution for all non-singular configurations of the manipulator, and identifying singular configurations and their characteristics. Two functions are therefore served: a new general method for the solution of the inverse velocity problem is presented; and complete analytical expressions are derived for the resolution of the joint rates of a seven degree of freedom manipulator useful for telerobotic and industrial robotic application.

Experiments with a network-based geometric reasoning engine

Abstract: Fisher and Orr (1988) described a geometric reasoning engine based on a value passing constraint network. This paper reports on more recent results from this research: several experiments on detecting inconsistency between constraints, how to blind degrees of freedom in a revolute joint, some results on propagation of error in the networks, and performance on a large three dimensional reasoning problem involving three revolute joints.

Approximate Calculation of Robot Inverse Kinematics Applied to Arc Welding

Abstract: The paper presents a new approach to the inverse kinematics calculation which consists in the approximation of Cartesian orientations of the robot end effector. The approach can be well used in various practical applications, such as arc welding, and is extremely effective when applied to robot manipulators which do not have a closed-form solution to the inverse kinematics problem. Several numerical experiments are described that show the validity of the proposed approach.

PDF Subvariable Control and its Application Torobot Motion Control

Abstract: A method for determining the feedback coefficients of pseudo-derivative-feedback control is presented, along with applications of this control scheme. Simulations are performed for controlling a linear inertia system with disturbance loads and inertia variations, and for controlling a nonlinear system represented by a manipulator arm. The results show that PDF subvariable control quickly rejects disturbances and is insensitive to inertia variations. Also, the position responses do not exhibit overshoot or oscillation. Comparison with the results for proportional-plus-velocity-feedback control shows that the PDF approach is superior in response speed, robustness, and disturbance-handling ability. Experimental results from implementation of both control schemes to a revolute manipulator support this conclusion.

Bounded error interpolates for manipulators with prismatic and revolute joints

Abstract: An algorithm for interpolating workspace trajectories in the joint space of a manipulator having revolute and prismatic joints is described. This algorithm relies on bounds on the derivatives of the kinematic map of such a manipulator derived by the authors (ibid., vol.3, p.1744-9). The algorithm generates interpolates such that user-specified tolerances on position, velocity and acceleration are maintained. This is the first joint space interpolation algorithm to guarantee workspace error bounds on velocity and acceleration. The algorithm includes the prismatic case, which is also novel, and it takes into account factors beyond kinematic errors, making it a practical addition to a robotic manipulator system. >

Independent Joint Controllability of Manipulator System

Abstract: The central role in designing a manipulator with appropriate dynamic characteristics plays the inertial matrix. In general case, a weak condition on this matrix is imposed to provide independent joint controllability of the manipulator system. The condition we require is fulfilled for almost all kinds of nonredundant manipulators. The case of a planar manipulator with three revolute joints is considered as well.

Method of measuring dynamic characteristic of manipulator

Abstract: PURPOSE: To easily identify a dynamic characteristic parameter specific to a manipulator by measuring a revolute joint angle, angular velocity, angular acceleration, driving torque of the number of points by which equations equal to unknown constants in number can be obtained CONSTITUTION: For finding unknown constants existing in an equation of motion, revolute joint angles θ1 , θ2 , revolute joint angular velocity, revolute joint angular acceleration, and revolute joint driving torque of the manipulator are measured while the manipulator is operated, and simultaneous linear equations, which are equal in number to the unknown constants, are obtained When these simultaneous linear equations are solved, a dynamic characteristic parameter, which is necessary for nonlinear type compensation control of the robot manipulator and specific to the manipulator, is identified As these simultaneous linear equations are solved, labor for measurement can be reduced as much as possible, and at the same time, the dynamic characteristic parameter specific to the manipulator can be identified with fewer errors

A translation in artificial terms of the design of biological manipulators

Abstract: Powerful design methodologies obtained by exploiting modularity and analogy are used to create a spherical mechanism actuated in parallel with a larger workspace that can be used to construct a complete limb. The design synthesis is performed by translating ideas borrowed from the design of biological manipulators. The methods described make possible the construction of a complete seven-degree-of-freedom arm in terms of two spherical joints with an ordinary revolute joint in between. >

A Systematic Synthesis of the Layer Arrangements of Planar Mechanisms

Abstract: In designing planar mechanisms, individual moving links have to be arranged separately on parallel planes, which are called layers in the present paper, to avoid mutual interference during a cycle of motion, and, in addition, the mechanisms have to be constructed in the smallest space possible. In this paper about planar multilink mechanisms which are constructed with revolute pairs, a systematic synthesis of layer arrangement is discussed with consideration of the mutual interference of moving links. to determine the minimum number of layers required to construct crank mechanisms and profiles of links, relative loci of pairing points and positions of links in the mechanisms are analyzed. Moreover, conditions to avoid mutual interferences of moving links on the same layers are formulated, and a layer-arrangement system is obtained which determines the profiles and layer arrangements of links of planar multilink mechanisms.

Bounds on the derivatives of the forward kinematic map for open-kinematic-chain manipulators

Abstract: The authors develop simple, configuration-independent bounds for the Jacobian and the higher order derivatives of the forward kinematic map of a manipulator with revolute and prismatic joints. In doing so they obtain: a simple formula for the higher order derivatives of the forward kinematic map; an easily computable and meaningful metric on the group of rigid-body motions; and useful norms on the joint space of a manipulator. The bounds on the forward kinematic map are practical to implement and have proved to be very useful for trajectory interpolation, space generation, and interpolation of the robot dynamics. >

Manipulator Kinematic Model

Abstract: Kinematic modelling of manipulators plays an important role in contemporary robot control. It describes the relationship between robot end-effector position and orientation in space and manipulator joint angles. It also describes the correlation between linear and angular velocities of the end-effector and joint velocities. Since kinematic modelling is an inevitable step in modern robot control, in this chapter we will consider the main principles of manipulator kinematic model generation.

State observation of elastic joint robots

Abstract: In this paper a nonlinear observer for robots with elastic joints is presented. This observer allows to reconstruct the whole state vector on the basis of the measurement of the joint global positions only. As example a particular robot having two revolute elastic joints is considered. Simulation tests are included.