Showing papers by "Andrew A. Goldenberg published in 1989"

Force and position control of manipulators during constrained motion tasks

Abstract: Regulation d'effort et de position d'un manipulateur durant l'execution de mouvements avec contraintes

Force and position control of manipulators during constrained motion tasks

Abstract: Trajectory control of a manipulator constrained by the contact of the end-effector with the environment represents an important class of control problems. A method is proposed whereby both contact force exerted by the manipulator, and the position of the end-effector while in contact with the surface are controlled. The controller parameters are derived based on a linearized dynamic model of the manipulator during constrained motion. Hence the method is valid only in a neighborhood about the point of linearization. Additionally, a perfect kinematic model of the contact surface is assumed. The proposed method utilizes the fundamental structure of the dynamic formulation of the manipulator's constrained motion. With this formulation, the trajectory control problem is naturally expressed in terms of the state vector variables of the model of the constrained dynamic system. A detailed numerical example illustrates the proposed method. >

An adaptive approach to motion and force control of multiple coordinated robot arms

Abstract: An approach to motion and force control of multiple coordinated robot arms based on an adaptive scheme is developed. The adaptation law uses Popov hyperstability theory to estimate online the uncertain parameters of multiple robot arms and payload. The approach can be used to control the motion of an object held by the arms, the contact forces between the object and the environment, and the internal forces that do not contribute to the motion and the contact forces. Three subsystem error equations are generated, i.e. a position error subsystem, a contact force error subsystem, and an internal force error subsystem. The unknown parameters of the multiple coordinated robot arms and the object are estimated in terms of the three error subsystem equations. It is shown that the proposed adaptive control scheme improves the position and internal and contact force tracking accuracy of a class of systems with an uncertain knowledge of the dynamic model. >

An approach to force and position control of robot manipulators

Abstract: An approach is proposed to simultaneously control the contact forces exerted on a constraint surface and the position of the end-effector, both in the presence of frictional forces on the constraint surface. The approach, using a novel formulation of the dynamics model, is based on a linear state feedback. A feedforward and PI (proportional-integral) feedback control strategy is proposed along with a design procedure. Using the proposed control method the trajectory following problem is solved and the closed-loop system is shown to be asymptotically stable. Numerical examples of a two-link robot moving along a constraint surface are presented for illustration. >

An Approach to Adaptive Control of Robot Manipulators Using the Computed Torque Technique

Abstract: Manipulator’s control system based on computed torque techniques incorporates a model of the manipulator dynamics. The nominal torque, computed using this mathematical model, does not reflect the effects of unknown loadings and uncertainty in modelling the parameters. An approach is presented which compensates for unknown loading and parameter uncertainty. This compensation is based on the “recursive” identification of a new dynamics operator which maps a vector of generalized coordinates into the vector of generalized forces (joint torques). The identification is based on a least-square approximation. Using the identified operator, which provides the compensated nominal torque, the system is controlled in closed-loop to generate regulation of the error in joint coordinates. The regulation is obtained using a common discrete optimization feedback law which is based on a recursive identification of the first order approximation of the dynamics model. The approach is illustrated with simulation results.

Robust Control of Position and Force for a Robot Manipulator in Non-Contact and Contact Tasks

Abstract: The problem of designing a robust controller for position and force control of a robot manipulator in both non-contact and contact tasks is considered. Using classical dynamics concepts, and under certain assumptions, a mathematical model for non-contact and contact tasks is developed. A controller based on proportional-integral (PI) and feedforward control is proposed for this model. A sufficient condition, which ensures that the closed-loop system is asymptotically stable, and the proposed controller are both presented. Theoretical analysis and numerical simulations have shown that the proposed controller is robust with respect to perturbations in system parameters and joint friction force. It is shown in this paper, that there is no need to change the controller configuration when the robot comes into contact with the environment from free motion.

Real-time control of robots: Strategies for hardware and software development

Abstract: A review of various strategies for hardware and software development of real-time controllers for commercial robots is presented. These developments, all depending on state-of-the-art hardware and software, are designed to correspond to specific research objectives. The Robotics and Automation Laboratory (RAL) TUNIS multiptocessor system, used to control a PUMA without VAL, is presented. The proposed scheme is suitable for implementing the computed torque technique, the feedback linearization technique, and various modern control methods applied to both joint and task space variables.

Analysis and design of a modular electro-optical tactile sensor

Abstract: The development of an experimental tactile sensor utilizing optical fibers is analyzed. In the first stage of this research, a single-point experimental force sensor was designed and manufactured. In the single-point sensor, light from an emitting fiber is reflected from the surface of a cantilever beam into a receiving fiber, and the intensity of the light reflected is continuously measured as the beam deflects due to applied force. The experimental sensor is designed such that it allows variation in design parameters to determine the best set of parameter values for optimal performance of the sensor. In the second stage of the research the optimal design parameters obtained from the single-point sensor experiments were used to design and manufacture a four-point prototype tactile sensor. This prototype sensor makes use of electrical amplification and digital conversion which can enable the force signals to provide tactile information to the controller of a multifingered hand. >

A new approach to force and position control of robot manipulators

Abstract: Trajectory control of a robot manipulator when motion is constrained by the environment represents an important class of control problems. We consider the problem of controlling the position and force of a robot manipulator during contact tasks. Based on a dynamics model developed earlier, both position and contact force are modeled as the state variables of the system. These variables are simultaneously controlled using a nonlinear feedback compensator. Using Lyapnouv's theory, a sufficient condition, which guarantees that the closed loop system remains "practically stable", is presented. The simulation of a two-link planar robot manipulator following a semi-circle surface is given to illustrate the result.

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.

Position and force control approach to automatic deburring by a robot manipulator

Abstract: Some aspects of automatic deburring by a robot are considered. The strategy proposed is based on constrained motion control, in which both force and position of the robot are simultaneously controlled. However, in practice, a robot may be in free unconstrained motion before it comes in contact with the environment. In order to control the deburring operation without switching controllers for the unconstrained and constrained motions respectively, an additional controller is proposed, and a control strategy is used so that these three controllers for the robot are automatically switched. This ensures that the robot is stable during the whole process of deburring. A numerical example of a deburring process with a two degrees-of-freedom robot is presented for illustration. >

Modelling the interaction between robot and environment

Abstract: The contact between robot and environment generates forces of interaction which need to be controlled. In addition, the motion of the robot interacting with the environment must also be controlled. The unification of these two objectives is usually titled ‘force and position control’. In the recent past this issue has been extensively addressed in the research, and several basic approaches to force control have emerged. The synthesis of controllers for force and position control has also been addressed. The paper reviews some of the relevant work in this area in particular the techniques used to generate models of the interaction between robot and environment. The paper also addresses conceptually the implementation of impedance control and presents an application of this technique as well as of the descriptor system to control of interaction forces in a dexterous multifingered hand.