Showing papers on "Robot kinematics published in 1985"

Position referencing and consistent world modeling for mobile robots

Abstract: In order to understand its environment, a mobile robot should be able to model consistently this environment, and to locate itself correctly. One major difficulty to be solved is the inaccuracies introduced by the sensors. The approach proposed in this paper to cope with this problem relies on 1) defining general principles to deal with uncertainties : the use of a multisensory system, favo ring of the data collected by the more accurate sensor in a given situation, averaging of different but consistent measurements of the same entity weighted with their associated uncertainties, and 2) a methodology enabling a mobile robot to define its own reference landmarks while exploring its environment. These ideas are presented together with an example of their application on the mobile robot HILARE.

Dynamic manipulability of robot manipulators

Abstract: The concept of dynamic manipulability measure of robot arms is proposed as a quantitative measure of their manipulating ability in positioning and orienting the end-effectors, which takes the arm dynamics into consideration. This measure is defined on the basis of the relation between the joint driving force and the acceleration of the end-effector. Some properties of the measure are established. A two-joint link mechanism is analyzed and its best posture is obtained under certain condition from the viewpoint of this measure. A numerical example is also given to illustrate the utilization of this concept for the design of robot manipulators.

A complete generalized solution to the inverse kinematics of robots

Abstract: The kinematic transformation between task space and joint configuration coordinates is nonlinear and configuration dependent. A solution to the inverse kinematics is a vector of joint configuration coordinates that corresponds to a set of task space coordinates. For a class of robots closed form solutions always exist, but constraints on joint displacements cannot be systematically incorporated in the process of obtaining a solution. An iterative solution is presented that is suitable for any class of robots having rotary or prismatic joints, with any arbitrary number of degrees of freedom, including both standard and kinematically redundant robots. The solution can be obtained subject to specified constraints and based on certain performance criteria. The solution is based on a new rapidly convergent constrained nonlinear optimization algorithm which uses a modified Newton-Raphson technique for solving a system nonlinear equations. The algorithm is illustrated using as an example a kinematically redundant robot.

Dynamic Manipulability of Robot Manipulators

Abstract: The concept of dynamic manipulability measure of robot arms is proposed as a quantitative measure of their manipulating ability in positioning and orienting the end-effectors, which takes the arm dynamics into consideration. This measure is defined on the basis of the relation between the joint driving force and the acceleration of the end-effector. Some properties of the measure are established. A two-joint link mechanism is analyzed and its best posture is obtained under certain condition from the viewpoint of this measure. A numerical example is also given to illustrate the utilization of this concept for the design of robot manipulators.

Dynamic manipulability of robot manipulators

Abstract: The concept of dynamic manipulability measure of robot arms is proposed as a quantitative measure of their manipulating ability in positioning and orienting the end-effectors, which takes the arm dynamics into consideration. This measure is defined on the basis of the relation between the joint driving force and the acceleration of the end-effector. Some properties of the measure are established. A two-joint link mechanism is analyzed and its best posture is obtained under certain condition from the viewpoint of this measure. A numerical example is also given to illustrate the utilization of this concept for the design of robot manipulators.

Redefinition of the robot motion-control problem

Abstract: The objective of this paper is a redefinition of the robot control problem, based on (1) realistic models for the industrial robot as a controlled plant, (2) end-effector trajectories consistent with manufacturing applications, and (3) the need for end-effector sensing to compensate for uncertainties inherent to most robotic manufacturing applications. Based on extensive analytical and experimental studies, robot dynamic models are presented that have been validated over the frequency range 0 to 50 Hz. These models exhibit a strong influence of drive system flexibility, producing lightly damped poles in the neighborhood of 8 Hz, 14 Hz, and 40 Hz, all unmodeled by the conventional rigid-body multiple-link robot dynamic approach. The models presented also quantify the significance of non-linearities in the drive system, in addition to those well known in the linkage itself. Simulations of robot dynamics and motion controls demonstrate that existing controls coupled with effective path planning produce dynamic path errors that are acceptable for most manufacturing applications. Major benefits are projected, with examples cited, for use of end-effector sensors for position, force, and process control.

Dynamic visual servo control of robots: An adaptive image-based approach

Abstract: Sensory systems, such as computer vision, can be used to measure relative robot end-effector positions to derive feedback signals for control of end-effector positioning. The role of vision as the feedback transducer affects closed-loop dynamics, and a visual feedback control strategy is required. Vision-based robot control research has focused on vision processing issues, while control system design has been limited to ad-hoc strategies. We formalize an analytical approach to dynamic robot visual servo control systems by first casting position-based and image-based strategies into classical feedback control structures. The image-based structure represents a new approach to visual servo control, which uses image features (e.g., image areas, and centroids) as feedback control signals, thus eliminating a complex interpretation step (i.e., interpretation of image features to derive world-space coordinates). Image-based control presents formidable engineering problems for controller design, including coupled and nonlinear dynamics, kinematics, and feedback gains, unknown parameters, and measurement noise and delays. A model reference adaptive controller (MRAC) is designed to satisfy these requirements.

Robotics for Engineers

Abstract: Robotics for engineers , Robotics for engineers , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Dynamic world modeling for an intelligent mobile robot using a rotating ultra-sonic ranging device

Abstract: A system which performs task-oriented navigation for an intelligent mobile robot is described in this paper. This navigation system is based on a dynamically maintained model of the local environment, called the "Composite Local Model." The Composite Local Model integrates information from a rotating sonar sensor, the robot's touch sensor and a pre-learned Global Model as the robot moves through its environment. Techniques are described for constructing a line segment description of the most recent sensor scan (the Sensor Model), and for integrating such descriptions to build up a model of the immediate environment (the Composite Local Model). Model integration is based on a process of reinforcing the confidence in consistent information while decaying the confidence in inconsistent information. The estimated position of the robot is corrected by the difference in position between observed sensor signals and the corresponding symbols in the Composite Local Model. This system is useful for navigation in a finite, pre-learned domain such as a house, office, or factory.

Opportunistic scheduling for robotic assembly

Abstract: Impressive strides have been made in dealing with the spatial complexity of robotic assembly tasks. Unfortunately, advances in dealing with temporal complexity have not kept pace. It is proposed that one reason for this deficiency is the unnecessary confounding of planning and scheduling. These two activities are differentiated on the basis of knowledge required/knowledge available at robot programming time. It is suggested that giving the robot the ability to reason opportunistically over knowledge of part availability at run time is a practical, efficient way to streamline assembly tasks. Initial experimental results are presented to substantiate this conclusion.

Control of two coordinated robots in motion

Abstract: When two coordinated robot touch a same object, the three form a closed kinematic chain mechanism. When the chain is in motion, the position and orientation of the two robots must satisfy a set of holonomic equality constraints for every time instant. In addition, when the joint velocities and accelerations of one robot is planned, that of the second robot are determined through two more sets of constraints. Based on the constraint conditions, the joint torques can be computed from the dynamic equations of the robots. The computed torques serves as control inputs to the two robots to generate their coordinated motions as planned.

Applications of learning method for dynamic control of robot manipulators

Abstract: Some types of learning control were developed for a class of robot manipulators to realize a desired motion. In those control schemes, the actuator input to the robot is modified by the acceleration error signal or the velocity error signal so as to make the robot motion approach the desired one by repeating operation of the robot. However, since actual measured signals of those variables are apt to be contaminated by noise, it is desirable to correct the input by an actual position signal which is more accurately measured than the acceleration or velocity signal. Motivated by this observation, a new type of learning control is proposed, in which the input is modified by the position error signal. It is theoretically shown that by using this control method the robot motion converges to the desired one with repetition of maneuvering the robot. It is also shown that this learning method can be applied to not only position control but also force control of robot manipulators. Moreover, it is experimentally shown by using such a learning method that the real robot can be trained to polish a curved surface of an object and eventually carry the task to fulfillment.

The effect of wrist force sensor stiffness on the control of robot manipulators

Abstract: This paper analyzes the effects of the mechanical stiffness of end effector force sensors on the control of robot manipulators. Modeling of the general manipulator-sensor system is presented, along with a detailed investigation of a single joint case. Analytical and experimental results indicate that the use of a mechanically compliant sensor permits a more responsive force controlled system to be realized. In addition, an active compensator for sensor deflections was developed to recover the static positional stiffness of the manipulator.

Time-optimal motions of robots in assembly tasks

Abstract: For a cylindrical, and a spherical robot, and a robot with a horizontal articulated arm with two links time-optimal unconstrained trajectories for arbitrary fixed initial and final positions are calculated. The exact equations of motion are utilized. The controls (torques and forces) are limited. The general structure of the optimal solution is discussed and explained physically for each robot. The importance of such analyses during the mechanical design of a robot is pointed out. The reduction of the duration of an optimal motion, compared to more straight-forward and natural ones, and hence the increase of the productivity of the robot in an assembly cycle can be considerable. The numerical examples include the "Automelec ACR" and the "IBM 7535 B04" robots.

Invariant manifolds and their application to robot manipulators with flexible joints

Abstract: In this paper we examine a recently developed singular perturbation formulation of the equations of motion for a robot manipulator with flexible joints, where the fast variables are the elastic forces at the joints and their time derivatives. The concept of an invariant manifold is utilized to represent the dynamics of the slow subsystem. The dynamics of the system restricted to this manifold reduce to the usual rigid body dynamics as the perturbation parameter e tends to zero. Based on a power series expansion of the exact manifold around e = 0, higher order corrections of the manifold are obtained. This leads to reduced order models of the full system which may prove more useful for control system design than either the full model or the rigid model. The case of a single link with joint flexibility is worked out in detail.

Rigid body load identification for manipulators

Abstract: A method for estimating the mass, the center of mass, and the moments of inertia of a rigid body load during general manipulator movement is presented. The algorithm is derived from the Newton-Euler equations and incorporates measurements of the force and torque from a wrist force/torque sensor and of the arm kinematics. The identification equations are linear in the desired unknown parameters, which are estimated by least squares. We have implemented this identification procedure on a PUMA 600 robot equipped with an RTI FS-B wrist force/torque sensor, and on the MIT Serial Link Direct Drive Arm equipped with a Barry Wright Company Astek wrist force/torque sensor.

Hybrid control of robot manipulators

Abstract: A robot manipulator must be able to satisfy any consistent position and force specifications in a well-defined Cartesian coordinate frame. In this paper, we present a method to achieve such a hybrid control of position and force. While the desired compliance is specified in Cartesian space, the control is accomplished in joint space, thus effectively reducing the computation load. Results show that accurate position and force control is obtained.

A method for the design of hybrid position/Force controllers for manipulators constrained by contact with the environment

Abstract: A new method for the design of hybrid position/force controllers for constrained manipulators is derived. This method can be applied to all types of constraint due to contact with the environmcnt; including constraint due to contact at the end effector, constraint due to more than one robot manipulating a workpiece, and constraint due to the bracing of a robot arm against a work surface. The manipulator and its contact with the environment are modeled in terms of lower order pairs. From this model a general equation describing the constraint on the motion of the arm is derived. The task is modeled as a set of essential position vectors and a set of essential force vectors. A hybrid position/force controller is derived to control the position and force at the joints of a manipulator such that the motion of the the robot conforms to the constraints imposed on it due to contact with the environment; and the motion at the end effector, and the force at the contact with the environment are those required for the performance of the task. The method is illustrated by a simple three degree of freedom example.

Roboust nonlinear control of robot manipulators

Abstract: In this paper we investigate the motion control of robotic manipulators using the recently developed stable factorization approach to tracking and disturbance rejection. Given a nominal model of the manipulator dynamics, the control scheme consists of an approximate feedback linearizing control followed by a linear compensator design based on the stable factorization approach to achieve optimal tracking and disturbance rejection. Using a multiloop version of the small gain theorem [17], the applicability of the linear design techniques and the stability of the closed loop system are rigorously demonstrated.

Discrete dynamic robot models

Abstract: An inherently discrete-time dynamic model is introduced for robotic manipulators. Although robot dynamics are highly coupled and nonlinear, the model is compact and suitable for control engineering applications. The model is designed to guarantee conservation of energy (and momentum, if appropriate) at each sampling instant. Initial numerical experiments with cylindrical robots confirm the feasibility and applicability of the discrete dynamic robot model.

Minimum-time path planning for robot arms and their dynamics

Abstract: Despite its close relationship to robot arm dynamics, conventional path planning does not take it into account, leading to the possible underutilization of the robot's capabilities. The authors have developed a minimum-time path-planning method in joint space taking into consideration robot arm dynamics as well as other realistic constraints. The main differences between this method and others are: (1) an absolute tolerance in the path deviation at each corner point can be specified; (2) local upper bounds on joint accelerations are derived from the arm dynamics so as to nearly fully utilize robot's capabilities; and (3) a set of local optimization problems, one at every local corner point, replaces the global minimum-time problem, thus making the minimum-time path-planning problem simpler and easier to solve. The method is applied to the path planning of the first three joints of the Unimation PUMA 600 series robot arm, using its simulator on a DEC VAX-11/780. The results show significant improvements in the total traveling time in addition to the ease and simplicity obtained from the decomposition of the global problem into a set of local optimization problems.

Efficient kinematic transformations for the PUMA 560 robot

Abstract: Efficient solutions for the kinematic positions, velocities, and accelerations for the six-degree-of-freedom PUMA 560 robot are presented. The kinematic problem is defined as the transformation from the Cartesian space to the joint space and vice versa. The solution method is based on a method that fully exploits the special geometry of the robot in the derivation of the solution. Special attention is given to the arm configuration in both directions of the transformation.

Recursive methods for world-to-joint transformation for a robot manipulator

Abstract: A method for controlling an articulated robot manipulator with an offset wrist made with only rotary joints. The method relates to transforming a given position and orientation of the robot tool or end effector in Cartesian space to the equivalent joint angles of the robot. Commands generated from the joint angles are sent to actuators connected to the rotary joints, where the desired motion of the robot tool is generated. This method of transforming a point in Cartesian space to joint angles is accomplished by providing a cross-product and dot-product recursive methods that employ the robot geometry to determine the location of the the end effector, such that the computational complexity of the techniques allows real-time computations for current state of the art microprocessors.

Robot kinematics and coordinate transformations

Abstract: This paper introduces a class of linearizing coordinate transformations for mechanical systems whose moment of inertia matrLx has a square root which is a jacobian. The transformations, when they exist, define a local isometry from joint space to euclidean space, hence, may afford further insight into the transient behavior of robot motion. It remains to be seen whether any appreciably large class of robots admit such linearizing isometries.

A spatial representation system for mobile robots

Abstract: A two dimensional spatial representation system is presented which makes efficient use of distance information for accomplishing common mobile robot tasks. Ways to use the representation for route planning, positioning, and execution monitoring are presented. The representation is very space efficient, and all the transformations to be performed on it are computationally tractable.

Coordinating the motions of robot arms in a common workspace

Abstract: A time/space planning system to coordinate the actions of two robot manipulators for transfer movements in a "sparse" environment is reported here The collision avoidance reasoning guarantees that arms will arrive safely at their destination by temporally delaying or by altering the path of one arm End effectors are constrained to follow elliptical motions The performance of the system is sufficient in normal circumstances to drive an execution module in real time with tool tip speeds about three inches per second

Recursive computations of kinematic and dynamic equations for mechanical manipulators

Abstract: Computational kinematics and dynamics of robot manipulators are dealt with A recursive method based on the vector form of Rodrigues' equation is presented for the computation of the associated coordinate transformations The method allows for forward, backward, and two-way recursions and is applied to the computations of the Jacobian matrices and dynamic equations for mechanical manipulators The computational complexities of the resulting equations are also evaluated and compared to some of the existing methods in each case It is shown that the algorithms presented have certain computational advantages over most of the existing methods