Control Of Flexible Robot Arm Research Articles

Application of singular perturbation theory in modeling and control of flexible robot arm

Application of singular perturbation theory in modeling and control of flexible robot arm

A review on vision-based control of flexible manipulators

In this review, recent developments in the field of flexible robot arm control using visual servoing are reviewed. In comparison to rigid robots, the end-effector position of flexible links cannot be obtained precisely enough with respect to position control using kinematic information and joint variables. To solve the task here the use of a vision sensor (camera) system, visual servoing is proposed to realize the task of control flexible manipulators with improved quality requirements. The paper is organized as follows: the visual servoing architectures will be reviewed for rigid robots first. The advantages, disadvantages, and comparisons between different approaches of visual servoing are carried out. The using of visual servoing to control flexible robot is addressed next. Open problems such as state variables estimation as well as the combination of different sensor properties as well as some application-oriented points related to flexible robot are discussed in detail.

Development and Attitude Control of Flexible Robot Arm Using Flexible Pneumatic Cylinder with Simple Structure

A wearable actuator needs to be flexible so as not to injure the human body. The purpose of our study is to develop a flexible and lightweight actuator which can be safe enough to be attached to the human body, and to apply it to a robot arm and rehabilitation device. New types of flexible pneumatic actuator that can be used even if the actuator is deformed by external force have been developed in our previous studies. In this paper, a robot arm using the flexible pneumatic cylinder that can realize a natural flowing movement with multi-motion such as bending, expanding, and contracting is described. The analytical model of the robot arm is proposed for attitude control. In addition, an inexpensive quasi-servo valve using the on/off control valve is utilized in the master-slave control system to improve the control performance. As a result, the usability of the proposed robot arm and the effectiveness of the attitude control method using the analytical model and the quasi-servo valve are confirmed.

Control and Control Theory for Flexible Robots

As the requirements for robot performance increase, the dynamics of the manipulator become more dominated by flexibility. These flexible effects generate model uncertainty which reduces the end-point positioning accuracy of the manipulator. Residual vibration or tip deflection due to uncertain payloads may contribute to the error in tip position. This paper addresses several control strategies currently used by researchers to account for flexibility in robots and their ability to perform tasks despite the flexibility. The demands for increased robot accuracy coupled with high speed and large workspace requirements necessitate the evaluation of robot flexibility. The influence of flexibilityon modelling and controller design must be better understood to achieve these requirements. This paper presents a review of current research in the control .of flexible robots and reports on algorithms with specific experimental and theoretical results. Other researchers have conducted such surveys regarding modelling, design and control of flexible robot arms. Desoyer, Kopacek, Lugner and Troch (24) compare various modelling methods for I ightweight robots and discuss the effects of flexibi lity on possible control strategies. They examine the kinetostatic method, the vibrational mode approach and the finite element method as a means of modelling flexible systems. Troch and Kopacek (60) discuss control strategies for flexible robots, designs based on model simplification and the effects of actuator dynamics. Peng and Liou (43) survey experimental studies involving flexible mechanisms from a designer's point of view. They examine the identification of damping and mode shapes, vibration reduction and various means of measuring flexible mechanism responses. Book (11) describes the modelling of flexibility, the large motion equations used and the design of flexible arms. He also presents trajectory planning and trajectory tracking strategies for the control of flexible robot arms. . This paper begins with a short discussion of modelling the behavior of a flexible beam. The mathematical expression forthe beam deflection is given as a function of mode shapes and generalized coordinates. The difficulty in choosing appropriate mode shapes and representing the correct boundary conditions is then presented. Once an expression for t~e beam deflection is established, it can be incorporated into a recursive Lagrangian approach for modelling the dynamics of a serial chain of flexible links. The dependence of several control algorithms on model information is then investigated. The control methods surveyed involve end-point tracking, trajectory planning, modal damping and vibration suppression. Several model identification algorithms are also presented to demonstrate adaptive control for flexible systems with_variable payload.

COPING WITH TIME DELAY IN ROBOTIC SYSTEMS AND HAPTIC INTERFACES

Several works we have completed in coping with time delay problems in robotic systems and haptic interfaces are presented: ground-space teleoperation of a robot arm on a space satellite, passivity-based adaptive control of flexible robot arms and power assist devices, and partially continuous-time impedance display for haptic interface systems. For each topic, background, overview, the approach taken, and experimental results are discussed. Passivity is utilized directly or indirectly in all these works.

Robust Vibration Control of Flexible Robot Arm Taking Account of an Uncertainty in Bending and Torsional Coupling

This paper presents a design procedure of H∞ controller for bending-torsional coupled vibration of fiexible robot arm. In the case that the robot arm does not hold the inertial center of the payload, it processes uncertain bending-torsional coupled vibrations which affect in the accuracy and the stability of the controller. In this research, H>∞ robust control design scheme taking account of parameter variations as structured uncertainties and model error of uncontrolled modes as unstructured uncertainties is utilized to describe the uncertainty in coupled vibration to guarantee robustness against such uncertainty. An experimental robot arm system is built and its parameters are identified by using Seto's method. A controller is obtained by applying the present design method. Control experiments are performed and the robustness of the synthesized controller to the parameter variations and model error are confirmed. The robustness of the obtained controller against uncertainty in coupled vibration is compared with ordinary H∞ controller. The superiority of the presented controller design method is certificated.

Feedback stabilization of rotating Timoshenko beam with adaptive gain

The problem of boundary feedback stabilization of rotating Timoshenko beam, arising from control of flexible robot arms, is studied in this paper. First, under gain adaptive direct strain feedback controls, a counterexample is given to show that the corresponding closed loop system is not asymptotically stable, which is contrary to traditional conjecture. The counterexample given in this paper also exemplifies an interesting result: certain two two-order linear partial differential equations with five homogeneous boundary conditions have non-trivial solutions. Then, with an additional boundary feedback control, the related energy of the closed loop system is proved to be strongly stable, or more precisely, the configuration of the beam can be exponentially stabilized with some suitable non-linear boundary feedback controls with adaptive gain.

Rapid Control Prototyping for Flexible Arm

The paper presents an idea of controller design for complex mechatronic systems. This idea is based on virtual prototyping of controllers using model simulation. Two different types of simulation are distinguished; off-line simulation and real-time simulation. Simulated model includes design system components; mechanical, electrical, electronic, control and all these components are treated with same weight during design process. The role of controllers fast prototyping procedure is stressed. To prototype designed controllers a methodology based on real time simulation on final controller hardware is formulated. The FPGA based technology is applied for realisation of controller. The case study of control of flexible robot arm is presented.

Tracking control of flexible robot arms with a nonlinear observer

The interest in flexible robot arms has become greater in the latest years. This contribution presents a nonlinear control scheme for solving the tracking control problem of this kind of manipulators. Since typically link coordinate rates cannot be measured, a nonlinear observer is presented which provides estimates of both joint and link coordinate rates while keeping stability of the system.

Robust control of a flexible robot arm using the quadratic d-stability approach

This paper shows how the quadratic d-stability design method provides a solution to a flexible robot arm control problem. The experimental process exhibits time delay, nonminimum phase behavior and lightly damped modes. The method is based on pole placement considerations and involves the resolution of two parameter dependent Riccati equations with an extra condition. Performances achieved numerically by the designed controller are tested on the physical system.

On the exponential stability of an initial-boundary equation arising from strain feedback control of flexible robot arms with rigid offset

This paper is concerned with an initial-boundary value equation arising from direct strain feedback control of flexible robot arms with a revolute joint and rigid offset. By analyzing the spectrum and by estimating the norm of the resolvent of the system operator associated with the equation, it is verified that the equation admits a unique solution and, furthermore, the solution is exponentially stable, no matter how long is the rigid offset.

Further theoretical results on direct strain feedback control of flexible robot arms

This paper is concerned with stability analyses for some nonstandard second-order partial differential equations arising from direct strain feedback control of flexible robot arms. Exponential stability issues are addressed for three types of differential equations, one of which is in general abstract evolution equation form and the other two are in partial differential equation form. The obtained results are of especially theoretical interest because they reveal the essence of direct strain feedback control and demonstrate its power in control of flexible arms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An iterative scheme for learning gravity compensation in flexible robot arms

Mimicking the case of rigid robot arms, the set-point regulation problem for manipulators with flexible links moving under gravity can be solved by either model-based compensation or PID control. The former cannot be applied if an unknown payload is present or when model parameters are poorly estimated, while the latter requires fine and lengthy tuning of gains in order to achieve good performance on the whole workspace. Moreover, no global convergence proof has been yet given for PID control of flexible robot arms. In this paper, a simple iterative scheme is proposed for generating exact gravity compensation at the desired set-point, without the knowledge of rigid or flexible dynamic model terms. The control law starts with a PD action on the error at the joint level, updating at discrete instants an additional feedforward term. Global convergence of the scheme is proved under a mild condition on the proportional gain and a structural property on the arm stiffness, which is usually satisfied in practice. The proposed learning scheme is also extended to the direct control of the end-effector (tip) position. Experimental results are presented for a two-link robot with a flexible forearm moving on a tilted plane.

Semigroup approach to the stability of a direct strain feedback control system of elastic vibration with structure damping

In this paper, we relate a kind of second order hyperbolic system to an analytic semigroup, which is most often applied to the direct strain feedback (DSFB) control of flexible robot arms. The spectrum analysis is presented to confirm the positive function of DSFB.

An Iterative Scheme for Learning Gravity Compensation in Flexible Robot Arms

Mimicking the case of rigid robot arms, the set-point regulation problem for manipulators with flexible links moving under gravity can be solved by either model-based compensation or PID control. The former cannot be applied if an unknown payload is present or when model parameters are poorly estimated, while the latter requires fine and lengthy tuning of gains in order to achieve good performance on the whole workspace. Moreover, no global convergence proof has been yet given for PID control of flexible robot arms. In this paper, a simple iterative scheme is proposed for generating exact gravity compensation at the desired set point, without the knowledge of rigid or flexible dynamic model terms. The control law starts with a PD action on the error at the joint level, updating at discrete instants an additional feedforward term. Global convergence of the scheme is proved under a mild condition on the proportional gain and a structural property on the arm stiffness, which is usually satisfied in practice. Experimental results are presented for a two-link robot with a flexible forearm moving on a tilted plane.

Position and Force Neuro-Adaptive Control of a Flexible Robot Arm.

This paper describes the position and force neuro-adaptive control of a two-link flexible robot arm. First, the equation of motion of the flexible robot arm consisting of the first rigid link and second flexible link is shown. The end of the second flexible link is constrained by a rgid wall. Second, the position and force neuro-adaptive control system is composed of two-layer neural networks and proportional feedback control loops. Furthermore, from the experimental results and the numerically simulated ones, it is confirmed that the control error of position and force with the neuro-adaptive control is markedly smaller than the control error without the neuro-adaptive control.

Direct strain feedback control of flexible robot arms: new theoretical and experimental results

This paper addresses control problems for flexible robot arms by using direct strain feedback. The purpose is to make clear why direct strain feedback can damp out vibration of flexible arms satisfactorily. We concentrate on one-link flexible robot arms whose dynamic models can be represented by linear partial differential equations with appropriate boundary conditions which have been well examined in a number of papers. A key contribution of this paper is the introduction of the concept of (strict) A-dependent operators, which allows us to prove rigorously the closed loop stability of direct strain feedback and the existence and uniqueness of nonstandard second order abstract differential equations in Hilbert spaces. Several control experiments are performed, verifying the main theoretical points of this paper, demonstrating satisfactory control results of direct strain feedback, and leading to potential application of this simple control method for flexible robot control. >

Learning Terminal-Point Control and Its Application to the Control of Flexible Robot Arms.

The control input which moves a linear discrete-time system to goal states in finite time can be calculated in advance if the dynamics of the system are well understood. However, when the identified model is different from the actual system, residual state errors at the end of the motion are unavoidable. In this paper, a control scheme which improves the accuracy of the terminal-point control of the discrete-time system by learning is proposed, and the convergence of the learning process is discussed. Moveover, in the case that there are constraints on control inputs, a learning terminal-point control in which a weighted pseudoinverse matrix is utilized is presented. These control methods are applied to a flexible robot arm, and it is shown through experiments that they are able to realize high-speed motions and suppress residual vibrations.

Feedback linearization and linear stabilization control of flexible robots

Abstract An approach to the nonlinear control of flexible robot arms based on the differential geometric nonlinear control theory and the linear quadratic regulator (LQR) theory is considered using only the actuators at the joints. The control is separated into two parts: one derived by the differential geometric structure algorithm is a global external linearization and decoupling nonlinear feedback law for nominal trajectory tracking, and the other synthesized by combined LQR and servocompensator techniques is a robust linear time‐invariant stabilization and error correcting feedback control designed for active damping of elastic vibrations and for robustness to uncertainty in system parameters. By suitable selection of output variables, the suggested control design methodology can be used for either joint space control or task space control. For illustrations, a weightless three‐link PUMA type robot arm with a special flexible third link is tested via simulation.

Current research in robotics and automation-robotics research at USC

A number of projects are described, and the breadth of these activities is indicated. The projects concern: skill transfer from human to robot; telerobotics; knowledge-based control of robot grasping; hand-eye coordination; robot sensors; control of flexible robot arms; low-cost robots for pick-and-place operations; and simulation of material-handling components in manufacturing cells. >