Showing papers on "Parallel manipulator published in 1987"

Stability analysis of an adaptive controller for robotic manipulators

Abstract: The stability analysis of an adaptive control scheme for robotic manipulators, originally introduced by Horowitz and Tomizuka (1980), is presented in this paper. In the previous stability proof it was assumed that the manipulator parameter variation is negligible compared with the speed of adaptation. It is shown that this key assumption can be removed by introducing two modifications in the adaptive control scheme: 1. Reparametrizing the nonlinear terms in dynamic equations as linear functions of unknown but constant terms. 2. Defining the Coriolis compensation term in the control law as a bilinear function of the manipulator and model reference joint velocities, instead of a quadratic function of the manipulator joint velocities. The modified adaptive control scheme is shown to be globally asymptotically stable.

A linear dynamic model for flexible robotic manipulators

Abstract: The design of lightweight links for robotic manipulators results in flexible links. Accurate control of lightweight manipulators during the large changes in configuration common to robotic tasks requires dynamic models that describe both the rigid-body motions, as well as the flexural vibrations. This paper describes a linear state-space model for a single-link flexible manipulator and compares simulation of the model to measurements made on a 4-ft-long direct-drive arm.

Experiments Toward On-Line Identification and Control of a Very Flexible One-Link Manipulator

Abstract: An adaptive control algorithm based on the self-tuning regu lator concept has been experimentally investigated for appli cation to a very flexible one-link robotic manipulator. Adap tive control is an attractive methodology for maintaining the performance of precise controllers designed for such manipu lators under conditions of varying end-effector load. The use of noncollocated sensors and actuators to give good accuracy in tip positioning also places stringent requirements on the accuracy of dynamic models used for controller design.Identification and control design techniques suitable for on-line implementation have been demonstrated experimen tally on such a single-link flexible manipulator. The identifi cation algorithm employed is a filtered version of the recur sive least-squares algorithm. It is a development of algorithms previously used with the Stanford four-disk sys tem. Stable controllers with good step responses were de signed using the system models identified with the identifica tion algo...

Development of a novel intelligent robotic manipulator

Abstract: This paper describes the design features of a new robotic manipulator incorporating a novel spherical motor capable of three degrees of motion in a single joint for purposes of dexterous actuation, a loadable device at the end of the wrist actuator as the end effector with tactile and proximity sensing capabilities, and appropriate conventional and intelligent planning and control algorithms to support the execution of a series of complex tasks in an uncertain or hostile environment. The spherical wrist actuator is developed through analytic studies and the design of position and torque control instrumentation. The end effector is a micromanipulator based on the principle of in-parallel mechanisms. Heuristics, manifested in fuzzy logic, are employed to incorporate artificial intelligence for decision making and control in the robotic manipulator. The intent is to provide an overview of the significant design and algorithmic features of the manipulator deferring a detailed treatment of the proposed approaches to forthcoming publications.

A dynamic solution to the inverse kinematic problem for redundant manipulators

Abstract: Redundancy represents one key towards design and synthesis of more versatile manipulators. Obstacle avoidance and limited joint range constitute two kinds of constraints which can be potentially met by a kinematically redundant manipulator. The natural scenario is the inverse kinematic problem which is certainly a crucial point for robotic manipulator analysis and control. Based on a recently proposed dynamic solution technique, the inverse kinematic problem for redundant manipulators is solved in this paper. The kinematics of the manipulator is appropriately augmented in order to include the above mentioned constraints; the result is an efficient, fast dynamic algorithm which only makes use of the direct kinematics of the manipulator. Extensive simulation results illustrate the tracking performance for a given trajectory in the Cartesian space, while guaranteeing a collision-free trajectory and/or not violating a mechanical jointiimit.

Feedback Control of a Flexible Manipulator with a Parallel Drive Mechanism

Abstract: A flexible manipulator having a parallel drive mechanism is treated. Only the forearm of the manipulator is assumed to be flexible, because it is slender and carries a heavy end-ef fector. The elastic vibration of the arm, which is due to its flexibility, and the position of the driving motors should be controlled simultaneously. On the basis of the mathematical model developed in our previous paper, we construct an optimal feedback control system by using the outputs of sev eral sensors. A set of experiments for the point-to-point position control was carried out with a microcomputer, which controls the whole servo system and plays the role of dynamic compensator. Several satisfactory experimental results are shown.

Varible compliance manipulator

Abstract: A variable compliance manipulator comprising a five linkage structure in which one stationary segment and at least four moving segments are connected with one another through joints each having one degree of freedom, and actuators disposed on two or three of the joints and having a variable-stiffness property, wherein the stiffness of motion of the manipulator in working can be adjusted by detecting and delivering the change in angle of the moving segments to a servo system for controlling the actuators.

Quasi-minimal computation of the dynamic model of a robot manipulator utilizing the newton-euler formalism and the notion of augmented body

Abstract: Real-time dynamic control of robot manipulators requires on-line computation of the dynamic model that expresses the generalized forces to be applied to their joints, as a function of their generalized coordinates, velocities and accelerations. To do this, this paper presents a method of computation of this model that uses a quasiminimal number of elementary arithmetical operations and that can be applied systematically to robot manipulators with a simple kinematic chain structure and revolute and/or prismatic joints. To reach this quasi-minimal number, use if primarily made of the following : * a computation that is intrinsic rather than extrinsic, analytical rather than numerical and iterative rather than developed ; * the Newton-Euler formalism rather than the Lagrangian one and * the notion of augmented body, generalized to this type of structure. An example demonstrates that the computation of the dynamic model of an industrial robot manipulator with six revolute joints (the most complicated case in practice) can be effected with less than 300 arithmetical operations (adds and multiplies).

C-surface applied to the design of an hybrid force-position robot controller

Abstract: C-surfaces are defined in the parameter's space by the border between the subspace where the robot's positions are constrained by the surrounding and the subspace where there is no contact. Thus force control must be performed along the C-surface normal and position control along the tangent hyperplane of the C-surface. We have shown that the C-surface normal can be calculated by the use of force measurements. This yield to the design of an hybrid force-position controller where the direction to be force controlled is automatically determined. Experimental results are presented and compared to simulation for the surface following problem. Assembly tasks and the turning of a crank have been executed in simulation by using this hybrid controller. Experiments with a parallel manipulator are currently under development.

Computation of the direct and inverse geometric models of the Delta 4 parallel robot

Abstract: Description des modeles geometriques direct et inverse representatifs des mouvements du robot delta 4 d'un institut technologique de Lausanne. Ce robot comprend une plaque triangulaire articulee, a ses sommets, par rotules, a 3 bielles articulees par rotules a 3 manivelles dont les axes forment un triangle equilateral

Generalized joint model for robot manipulator kinematic calibration and compensation

Abstract: A generalized model that goes beyond the usual assumption of “ideal” joint behavior is proposed. The “real” joint has five ancillary degrees of freedom besides the dominant motion. The resulting manipulator transformation with its greater degree of sophistication is expected to help in calibration and compensation of the various kinematic contributions to robot inaccuracy. The procedure to compute this generalized manipulator transformation is presented. The generalized model also results in manipulator differential relationships and these are discussed.

Efficient parallel algorithms for robot forward dynamics computation

Abstract: Computing the robot forward dynamics is important for real-time computer simulation of robot arm motion. Two efficient parallel algorithms for computing the forward dynamics for robot arm simulation were developed to be implemented on an SIMD computer with n processors, where n is the number of degrees-of-freedom of the manipulator. The first parallel algorithm, based on the Composite Rigid-Body method, generates the inertia matrix using the parallel Newton-Euler algorithm, the parallel linear recurrence algorithm, and the row-sweep algorithm, and then inverts the inertia matrix to obtain the joint acceleration vector desired at time t. The second parallel algorithm, based on the conjugate gradient method, computes the joint accelerations with a time complexity of O(n) for multiplication operation and O(nlogn) for addition operation. The proposed parallel computation results are compared with the existing methods.

On the Dynamics and Control of Robotic Manipulators with an Automatic Balancing Mechanism

Abstract: Non-linear characteristics and uncertainty in manipulator dynamics caused by payload effects are major hurdles in controller design. To overcome such hurdles the authors have introduced an automatic balancing concept which has been proved to reduce the non-linear complexity in manipulator dynamics as well as to remove gravity loading. This paper examines the characteristic features of balanced manipulator dynamics in more detail and presents an efficient control algorithm suitable for the dynamics. Since the dynamics of a balanced manipulator are characterized by partially configuration-independent inertial properties, the present algorithm adopts two different control concepts ‘the computed torque control’ for the joint having coupled, configuration-dependent inertia and ‘an optimal constant feedback control’ for the joints having configuration-independent inertia. To evaluate the proposed control algorithm, simulation studies were made over a wide range of manipulator speeds and payloads. Based upon the...

A robotic manipulator arrangement

Abstract: A robotic manipulator arrangement comprises a first robotic manipulator (12) which is driven along a linear track (15) above a work table (16) and has at least one other degree of freedom. The arrangement also has a second manipulator (30) which can grip a workpiece and can rotate about two mutually orthogonal axes (X, Y) lying in a plane parallel to the worktable (16).

An alternative method for minimization of the driving forces in redundant manipulators

Abstract: A discretized equation allows the acceleration terms to be changed to velocity terms in the definition of joint driving forces in robotic manipulators. An eleven degrees of freedom, three dimensional robotic manipulator is used in a numerical example to test the developed algorithm. Numerical and algorithmic stabilities are also discussed.

Robot manipulator kinematic compensation using a generalized jacobian formulation

Abstract: The kinematic error compensation of robot manipulators is at present being attempted by improving the precision of the nominal robot kinematic parameters This paper addresses the problem of kinematic compensation using a new mathematical joint model proposed to account for shortcomings in existing methods The corrected manipulator transformation is formulated in terms of “generalized Jacobians”: relating differential errors at the joints to the differential change in the manipulator transformation The details of application are discussed for a particular industrial manipulator

An analytical and experimental investigation of flexible manipulator performance

Abstract: A critical modeling of a flexible manipulator will involve a thorough understanding of the issues specific to flexible manipulator performance and an experimental investigation of a physical system. A comprehensive dynamic model of a flexible manipulator has been presented in this paper together with a preliminary experimental investigation that examines the performance of this comprehensive model. The analytical model recognizes in particular, the coupling characteristics of the deformations in a flexible manipulator configuration and realizes an efficient and dedicated finite element scheme to model general spatial manipulator configurations with revolute and prismatic pairs. The experimental results indicate a favorable level of performance for the application of the special finite element for a practical manipulator.

A Robot Simulation System

Abstract: A robot simulation system realized by us on IBM-PC is described.This system dis-plays in 3-D the manipulator and its working environment,and simulates the kinema-tics of.Stanford Manipulator under interactive mode,The system is shown efficient bothin display and in simulation.

Formulation of the kinematic model of a general (6 DOF) robot manipulator using a screw operator

Abstract: In general, the manipulator's end-effector can be located in a desired position and orientation in its work-space through angular and/or linear displacements of its joints. These joint coordinates can be obtained by solving the loop-closure equation of the manipulator's kinematic model. The most common method for obtaining this equation is based on the point coordinates 4×4 homogeneous transformation matrix. This method uses a special set of frames which are adapted to the manipulator's configuration. Within the last few years there has been some interest in the use of screw operators (line transformations) to model the kinematic configuration of manipulators and to form the loop-closure equation. In this article, a kinematic model of a general (6 DOF) manipulator is obtained through the application of a screw operator (dual-unit quaternion) to represent the screw displacements of the line coordinates of the manipulator link and joint axes. The loop-closure equation of the closed kinematic chain is obtained by introducing a hypothetical link/joint at the manipulator's end-effector location. The resultant non-linear loop-closure equation is then solved for the joint coordinates using a numerical technique. The method is illustrated with an example.

Master-slave manipulator with redundancy joint and method and device for controlling said manipulator

Abstract: PURPOSE: To smoothly control a slave arm with redundant joints by providing a long cycle computing part for executing operation for determining the joints of the slave arm with six joints or more from six joints of a master arm, regardless of a control cycle required by an automatic control system for the joints. CONSTITUTION: An arithmetic means 3 computes to distribute the target joint value of a slave manipulator with six joints or more related to the position of each joint of a master manipulator with six joints, to each joint of the slave manipulator. The arithmetic means 3 has a long cycle computing part 6 for computing and updating a matrix used to convert the target value based on the master manipulator, into the angular velocity of each joint of the slave manipulator in a low speed cycle, and a short cycle computing part 15 for computing to convert the target value based on the master manipulator into the angular velocity of each joint of the slave manipulator in a high speed cycle using the matrix computed in the low speed cycle and updated. Each joint of the slave manipulator is driven on the basis of the computed result of the arithmetic means 3.

Interference Detection among Manipulator Links and Obstacles for Planning Collision-free Movement of A Manipulator

Abstract: マニピュレータの障害物回避動作を決定するためには, マニピュレータ・リンクと障害物との干渉チェックをする必要がある.これまでは, 主にいろいろな制約を設けてチェックを容易にしてきたが, 本稿はなるべく一般的で, かつ計算の単純な干渉チェック法を提案する.マニピュレータ・リンク及び障害物は, 凸多面体またはその組合せで表現し, それらの面と頂点の位置関係のみを用いて, 干渉するための必要十分条件を比較的単純な関数を用いて表す.さらにこの関数は, Denavit等の表記法を用いれば, 容易に関節変数ベクトルの関数となり, 干渉チェックが関節空間でできるため, マニピュレータの障害物回避動作計画に適用できる.

Simplification of robot dynamic model based on system performance

Abstract: The dynamic performance of a robot manipulator is directly dependent on the efficiency of the controller and the dynamic model of the robot. This paper addresses the fundamental issue of how much manipulator dynamics information should be included in the manipulator dynamic model for control such that the manipulator will achieve the desired system performance under a proportional-plus-derivatlve control scheme. An efficient minimax simplification scheme has been developed which automatically generates simplified closed-form manipulator motion equations in symbolic form while maintaining the desired manipulator system performance under a proportional-plus-derivative controller. The scheme involves the identification and selection of basis functions that represent the dynamic coefficients in the dynamic model. These basis functions consist of a linear combination of the product terms of sinusoidal and polynomial functions of the generalized coordinates and form a Chebyshev set on the workspace of the manipulator. A multi-layered decision scheme is developed for selecting significant basis terms in each layer for each dynamic coefficient. The linear combination of these significant basis terms is then utilized to construct each simplified dynamic coefficient based on the minimax approximation technique. A verification of the proposed scheme on a Stanford robot arm is included for discussion.

The Optimum Kinematic Design of a Spherical Three-Degree-of-Freedom Parallel Manipulator

Abstract: Optimisation de la cinematique d'un manipulateur utilisant un mecanisme parallele spherique a trois degres de liberte

Dynamics and control of a spacecraft based manipulator

Abstract: A mathematical model of a spacecraft based manipulator system is defined, Recursive algorithms are derived to numerically determine the dynamic motion of the combined spacecraft manipulator system An algorithm is defined for the control of the manipulator end effector motion in inertial space This same algorithm serves to determine the reaction torque and force on the spacecraft due to the manipulator presence For an attitude controlled spacecraft, modifications are made in the manipulator control law to assure system stability and reduce computational effort Results of these control methods are presented for the case of a six degree of freedom manipulator mounted on a Hermes type spacecraft

A centralized/decentralized approach to the robust control of a robotic manipulator

Abstract: This paper is concerned about solving the robust servomechanism problem for a rigid robotic manipulator for the case of set point reference inputs that tend to constant values. It is shown that by using a combination of centralized and decentralized control, this problem can be solved and global asymptotic stability of the closed loop system can be achieved, under a wide class of variations of the manipulator's load and dynamics. The implementation of the controller obtained only requires that an approximation of some of the manipulator's parameters be available. An example of a two link rigid robotic manipulator is included to illustrate the type of results obtained.