Control Of Flexible Joint Robots Research Articles

Operational Space Prescribed Tracking Performance and Compliance in Flexible Joint Robots

In this work, an admittance control scheme is proposed utilizing a highly robust prescribed performance position tracking controller for flexible joint robots which is designed at the operational space. The proposed control scheme achieves the desired impedance to the external contact force as well as superior position tracking in free motion without any robot model knowledge, as opposed to the torque based impedance controllers. Comparative simulation results on a three degrees-of-freedom (3DOF) flexible joint manipulator, illustrate the efficiency of the approach.

Consensus control of flexible-joint robots

Synchronisation of networks composed by fully actuated robot manipulators has received a lot of attention from the control theory community. Unfortunately, the case of under-actuated robots has not been deeply studied. The aim of this paper is to extend previous results reported by the authors addressing the particular (but of practical interest) case of networks composed by flexible-joint robots. The main feature of the contribution is to consider a change of coordinates, first introduced in Nuno, Ortega, Basanes and Hill, to solve the consensus problem assuming the existence of unknown delays in the communication channels. The extension is twofold, namely: the presentation of a control scheme that, in contrast to the one considered in Avila-Becerril and Espinosa-Perez, does not require knowledge of the initial conditions and the proof that the controller can also be implemented in Cartesian coordinates. The usefulness of the contribution is illustrated through numerical simulations.

Modelling and adaptive tracking control for flexible joint robots with random noises

This paper investigates modelling and adaptive tracking control problems for flexible joint robots subjected to random disturbances. A stochastic flexible joint robot model is given by introducing random noises reasonably. Under some weaker assumptions, a new controller is constructed by exploiting adaptive dynamic surface control technique. It is proved that the mean square of the tracking error can be made arbitrarily small by choosing appropriate design parameters. A mechanics model is provided in the simulation to show the effectiveness of the presented theory.

Improved Takagi–Sugeno fuzzy model-based control of flexible joint robot via Hybrid-Taguchi genetic algorithm

In this paper Takagi–Sugeno (T–S) fuzzy approach is used for control of a flexible joint robot (FJR). The control method in this paper is based on parallel distributed compensation approach (PDC). In this method, a state feedback controller is designed using a fuzzy model that consists of a set of linear fuzzy local models. These fuzzy local models are combined to get an overall fuzzy inference mechanism. In order to improve the efficiency of the system and to set the parameters of the controller the Hybrid-Taguchi genetic algorithm (HTGA) is used. The use of orthogonal arrays (OA) speeds up the convergence of the algorithm and the contribution of signal to noise (S/N) ratio will result in a more appropriate response. The stability of the controller is analyzed and finally it is implemented on the plant. The experimental results confirm the efficiency of the proposed intelligent method in controlling FJRs. Therefore, it can be considered as a proper method in controlling systems that are based on flexible robot arms.

Fuzzy Passivity Control of Flexible Joint Robot

This paper researches a fuzzy control method for passive flexible joint robot. Stability control method applying T-S fuzzy model is employed for single-link flexible joint robot. T-S fuzzy model is used to approximate the flexible joint robot firstly, and then fuzzy controller is developed based on the principle of parallel distributed compensation. The fuzzy controller is also applied to the passive properties of model error. The stability conditions are proposed by Lyapunov function and linear matrix inequalities are also applied to solve the controller parameters. Simulation results show that the proposed method of application value.

Fuzzy Passivity Non-Fragile Control of Flexible Joint Robot

The paper proposes a fuzzy passivity non-fragile control approach for flexible joint robot. The T-S fuzzy model is applied to approximate the flexible joint robot at first, and then the fuzzy controller is developed based on parallel distributed compensation principle. The passivity non-fragile performance of controller is also employed to limit the influence of model error. The conditions for the stability of the flexible joint robot control system are proposed by using Lyapunov function, and linear matrix inequality is applied to resolve the controller parameter. The simulation experiment results show the effectiveness of the proposed method.

Modelling and control of flexible joint robot based on Takagi–Sugeno fuzzy approach and its stability analysis via sum of squares

This article proposes a Takagi–Sugeno (T-S) fuzzy model of single-link rotary flexible joint robot. The proposed control method is based on parallel distributed control. The parameters of T-S controller are improved by distributed population genetic algorithm (GA) with chaos GA. Using Hermite–Biehler theorem in distributed population, GA is made to have a fast convergence. Dividing search space into several sub-spaces causes a better response, and chaos disturbance helps the whole algorithm to reach a best answer. The stability of the controller is analysed via the sum of squares programming, and finally, it is implemented on the plant.

Robust dynamic surface control of flexible joint robots using recurrent neural networks

A robust neuro-adaptive controller for uncertain flexible joint robots is presented. This control scheme integrates H-infinity disturbance attenuation design and recurrent neural network adaptive control technique into the dynamic surface control framework. Two recurrent neural networks are used to adaptively learn the uncertain functions in a flexible joint robot. Then, the effects of approximation error and filter error on the tracking performance are attenuated to a prescribed level by the embedded H-infinity controller, so that the desired H-infinity tracking performance can be achieved. Finally, simulation results verify the effectiveness of the proposed control scheme.

Prescribed performance tracking for flexible joint robots with unknown dynamics and variable elasticity

In this paper, we consider the design of tracking controllers for flexible joint robots with unknown and possibly variable elasticity, achieving pre-set performance attributes on the link position error. The developed full state feedback controller, is realized without incorporating knowledge relative to the actual system nonlinearities. Furthermore, no approximators are employed to acquire such information. Comparative simulation results on a 2-d.o.f. flexible joint manipulator, illustrate the efficiency of the approach.

Stability Control of Flexible Joint Robot Based T-S Fuzzy Model Using Fuzzy Lyapunov Function

Abstract In this paper, a stability control approach of flexible joint robot (FJR) based T-S fuzzy model using fuzzy Lyapunov function is proposed. First, the Takagi and Sugeno (T-S) fuzzy model is employed to approximate the flexible joint robot, then a fuzzy controller is developed based on parallel distributed compensation principle (PDC). The non-quadratic stability conditions for the flexible joint robot control system are proposed by using fuzzy Lyapunov function combined with linear matrix inequality (LMI). Finally, the simulation example is given to illustrate the effectiveness of the proposed method.

Modeling and observation of hysteresis lost motion in elastic robot joints

Abstract In this paper the modeling and observation of elastic robot joints with hysteresis is addressed. An adequate model of the joint torque transmission which could capture the hysteresis lost motion is of outstanding interest for design and control of flexible joint robots. A method of describing the significant joint nonlinearities such as dynamic friction and state-dependent stiffness with hysteresis is proposed. The joint dynamics is considered as an interplay between the propulsion and reactive torque. Direct and inverse hysteresis models of state-variant joint stiffness are introduced and identified from experiments. The proposed joint torque observer can serve as a “virtual” sensor of hysteresis lost motion without measuring the joint output.

H<sub>∞</sub> Control of Flexible Joint Robot via T-S Fuzzy Model

In this paper, a H∞ control approach based on T-S fuzzy model for flexible joint robot is proposed. First, the Takagi and Sugeno (T-S) fuzzy model is applied to approximate the flexible joint robot. Then, a fuzzy controller is developed based on parallel distributed compensation principle (PDC), and H∞ performance is employed to restrain the influence of modeling error caused by variety of stiffness. The stability conditions for the flexible joint robot control system are proposed by Lyapunov function. Finally, the simulation results are given to show the effectiveness of the proposed method.

Design for Flexible Joint Controller Based on a New Compensation Control Strategy

For the uncertain disturbance,friction and parameter variation,modeling errors and other issues in flexible joint robot control system,conventional PID control can not take into account both the requirements of stability and control accuracy.To solve this problem,a novel robust joint controller based on a new compensation control strategy is designed.In the controller design,the friction is divided into two parts,linear and nonlinear,and the disturbance into certain and uncertain. The part associated with the robot self structure,deterministic disturbance and the linear part of the friction can be controlled effectively by the feedforward compensation part.Feedback compensation part of the proposed controller can compensate nonlinear part of friction,system parameter variation,external uncertain disturbance,modeling error and so on.Its stability is completely proved by Lyapunov stability theory.Finally,the results on the platform of HIT 4-DOF flexible manipulator show that the controller has good position tracking performance and robustness.

Position Control of Flexible Joint Robots by Adapting Methods for Rigid Robots

AbstractIn this paper, it is demonstrated that many position control laws developed for rigid joint robots can also be used for flexible joint robots after some modifications. The main assumptions are smoothness of the control law and the availability of a Lyapunov function. The adaptation is based on a simple control principle: With the help of a position control method known from rigid joint robots, desired values for the motor positions are determined. If the motor positions and their desired values are identical, the link positions converge to their desired trajectories. Afterwards, the system inputs are specified such that the motor positions converge to their desired values. The method can also be applied under system uncertainties.

Global Output Tracking Control of Flexible Joint Robots via Factorization of the Manipulator Mass Matrix

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper investigates the problem of global output feedback tracking control of flexible joint robots. Despite the fact that only link position and actuator position are available from measurements, the proposed controller ensures that the link position globally tracks the desired trajectory while keeping all the remaining signals bounded. The controller development uses a partial state-feedback linearization technique combined with the integrator backstepping control design method whereas a filter and an observer are utilized to remove the requirement of link and actuator velocity measurements. Partial state-feedback linearization of robot dynamics is performed by factoring the manipulator mass matrix into a quadratic form involving an integrable root matrix. The applicability of the proposed general design methodology is illustrated by an example of flexible joint planar robots. Numerical results for a two-link flexible joint planar robot are also provided. </para>

On the Passivity-Based Impedance Control of Flexible Joint Robots

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, a novel type of impedance controllers for flexible joint robots is proposed. As a target impedance, a desired stiffness and damping are considered without inertia shaping. For this problem, two controllers of different complexity are proposed. Both have a cascaded structure with an inner torque feedback loop and an outer impedance controller. For the torque feedback, a physical interpretation as a scaling of the motor inertia is given, which allows to incorporate the torque feedback into a passivity-based analysis. The outer impedance control law is then designed differently for the two controllers. In the first approach, the stiffness and damping terms and the gravity compensation term are designed separately. This outer control loop uses only the motor position and velocity, but no noncollocated feedback of the joint torques or link side positions. In combination with the physical interpretation of torque feedback, this allows us to give a proof of the asymptotic stability of the closed-loop system based on the passivity properties of the system. The second control law is a refinement of this approach, in which the gravity compensation and the stiffness implementation are designed in a combined way. Thereby, a desired static stiffness relationship is obtained exactly. Additionally, some extensions of the controller to viscoelastic joints and to Cartesian impedance control are given. Finally, some experiments with the German Aerospace Center (DLR) lightweight robots verify the developed controllers and show the efficiency of the proposed control approach. </para>

A Unified Passivity-based Control Framework for Position, Torque and Impedance Control of Flexible Joint Robots

This paper describes a general passivity-based framework for the control of flexible joint robots. Recent results on torque, position, as well as impedance control of flexible joint robots are summarized, and the relations between the individual contributions are highlighted. It is shown that an inner torque feedback loop can be incorporated into a passivity-based analysis by interpreting torque feedback in terms of shaping of the motor inertia. This result, which implicitly was already included in earlier work on torque and position control, can also be used for the design of impedance controllers. For impedance control, furthermore, potential energy shaping is of special interest. It is shown how, based only on the motor angles, a potential function can be designed which simultaneously incorporates gravity compensation and a desired Cartesian stiffness relation for the link angles. All the presented controllers were experimentally evaluated on DLR lightweight robots and their performance and robustness shown with respect to uncertain model parameters. Experimental results with position controllers as well as an impact experiment are presented briefly, and an overview of several applications is given in which the controllers have been applied.

A SURVEY ON THE CONTROL OF FLEXIBLE JOINT ROBOTS

ABSTRACTThe robotics literature of the last two decades contains many important advances in the control of flexible joint robots. This is a survey of these advances and an assessment for future developments, concentrated mostly on the control issues of flexible joint robots.

Passivity based cartesian impedance control for flexible joint manipulators

The paper presents a Cartesian impedance controller for flexible joint robots based on the feedback of the complete state of the system, namely the motor position, the joint torque and their derivatives. The controller uses the torque feedback to shape the kinetic energy and the feedback of the motor position to shape the potential energy. By using a collocated feedback for shaping the potential energy, the passivity of the system can be ensured, while exactly satisfying all steady state requirements formulated in terms of the link side positions (such as desired stiffness and desired equilibrium position). The closed loop system can be seen as a feedback interconnection of passive systems and is proven to be asymptotically stable. Experimental results validate the proposed controller.

Synchronizing Tracking Control for Flexible Joint Robots via Estimated State Feedback

In this paper, we propose a synchronization controller for flexible joint robots, which are interconnected in a master-slave scheme. The synchronization controller is based on feedback linearization and only requires measurements of the master and slave link positions, since the velocities and accelerations are estimated by means of model-based nonlinear observers. It is shown, using Lyapunov function based stability analysis, that the proposed synchronization controller yields local uniformly ultimately boundedness of the closed loop errors. A tuning gain procedure is presented. The results are supported by simulations in a one degree of freedom master-slave system.