Flexible Link Robot Arm Research Articles

Precise tip-positioning control of a single-link flexible arm using a fractional-order sliding mode controller

This article presents an efficient scheme based on fractional order sliding mode control approach for precision tip position control of a single link flexible robot arm. The proposed control strategy is robust against the system parameters variations such as payload and viscous friction variations in the presence of the sinusoidal disturbance and the unknown Coulomb friction disturbances. The aim of controller design is reduction of the deviation caused by the link flexibility and then the precision tip positioning control of the single-link flexible arm. In this regard, sliding mode control strategy is performed in two stages. In the first stage, the difference between the motor angle (load angle) and the tip angle of the flexible link is reduced by applying the proposed fractional order sliding mode controller and then, in the second step, the precision tracking of the tip position of the link is done by adding another sliding mode control scheme. The feasibility and effectiveness of the proposed control scheme is demonstrated via numerical simulation results.

A robust high-speed position control scheme based on computed torque method for 2 DOF flexible link robot arms

Our group has proposed a high-speed tip position control scheme (Sawada and Itamiya, 2012b) which can be applied to both a flexible link robot arm and a rigid link robot arm. It can be regarded as a natural extension of the computed torque method for a rigid link robot arm. This method can achieve a high-speed position control for 2 DOF flexible link robot arm when the exact model of the controlled object is known. However, this method does not have robustness to modelling errors. In this paper, we propose an adaptive identification method in order to decrease the modelling error from the control system in which a nominal control law is used. Then, we use the closed loop adaptive identification, considering the movable range of the robot arm. As a result, the high-speed position control can be achieved by using parameter estimates. Its validity of the proposed scheme is shown by a stability analysis and is also illustrated by the experimental results on the frequency response of the link angle and that of the deflection angle.

A Position Control of 2 DOF Flexible Link Robot Arms Based on Computed Torque Method

Our group has proposed a tip position control method [13] which can be applied to both a flexible link robot arm and a rigid link robot arm. It can be regarded as a natural extension of the computed torque method for a rigid link robot arm. It is a nonlinear state feedback control based on an inverse dynamic model (states consist of link angles, deflection angles and those velocities). Also, it is quite different from a PD control and a sliding mode control. However, the discussion of stability and realization of the control system was inadequate in [13]. In this paper, we propose a robust design method which achieves the ultimate boundedness of control error system. Its effectiveness is illustrated by a brief analysis and numerical simulation results.

H Infinity Robust Motion and Vibration Control of Three Dimensional Two Link Flexible Robot Arm Taking Account of Variation of Orientation

This paper presents a design procedure of robust H∞ controller for bending-torsional vibration of three dimensional two link flexible robot arm. As the posture of the arm and the payload varies according to tasks, it possesses uncertain vibration modes. The controller must be designed to be robust to such posture fluctuation. In this research, H∞ robust control design with structured uncertainties is utilized to describe the model error in bending-torsional vibration. An experimental system is set up, and two physical models are identified by utilizing Seto's modeling method. A H∞ controller is designed by using these models and an integrator to realize servo control for positioning. Control simulations and experiments are performed. According to these results, the presented modeling and controller design method is certified to be effective.

10215 2リンク柔軟ロボットアームの運動と振動の制御((IV),OS15 知能ロボット)

The purpose of this study is to control simultaneously, motion and vibration of flexible 2-link robot arms. For this purpose, we had used modeling method called an 'extended reduced-order physical model (extended model)' to make a model of one-link flexible robot arm. The model of the flexible 2-link robot arms is made of a combination of the model of each link that is regarded as one link flexible robot arm. To connect each link, the constraint addition method is used. This is creating method of an equation of motion in multi-body systems. It is verified that the results of the simulation are effective for control of flexible 2-link robot arms.

RECURSIVE IDENTIFICATION OF PHYSICAL PARAMETERS IN A FLEXIBLE ROBOT ARM

ABSTRACTRecursive identification of a physically parameterized model of a single link flexible robot arm is considered. The parameters are estimated using a recursive prediction error method applied to a linear continuous time model structure and discrete time data. The algorithm is applied to real data from an industrial robot, and three important parameters are identified using only measurements of the motor angle. The experiments show that the particular parameter that is estimated will have big influence on the algorithm behavior.

Hierarchical fuzzy logic controller for a flexible link robot arm performing constrained motion tasks

An examination is performed on the dynamics and control issues for a robotic manipulator with link structural flexibility modelled during the execution of a task that requires the robot tip to contact fixed rigid objects. A multi-time-scale fuzzy logic controller is applied to this system. The large-scale system is decomposed into a finite number of reduced-order subsystems using the singular perturbation approach. A hierarchical ordering of fuzzy rules is used to reduce the size of the inference engine. Real-time implementation of fuzzy controllers can help reduce the burden of large-sized rule sets by fusing sensory data before input and the system's output to the inference engine. Using this approach the control of the force and position of the robot end point is possible while the end-effector moves on the constraint surface.

107 2 リンク柔軟ロボットアームのモデリングと制御

The purpose of this study is to make a model of two-link flexible robot arms. We had used a modeling method called an 'extended reduced-order physical model (extended model)' to make a model of one-link flexible robot arm. The model of the two-link flexible robot arms is made of a combination of the model of each link that is regarded as one link flexible robot arm. To connect each link, the constraint addition method is used. This is creating method of an equation of motion in multi-body systems. The model of the two-link flexible robot arms agrees qualitatively with the experimental results. The LQI control theory is applied to the control of motion and vibration. It is verified that the results of the simulation are effective for control of two-link flexible robot arms.

Two-time scale fuzzy logic controller of flexible link robot arm

A flexible link arm is a distributed parameter system of infinite order, but due to onboard computer limitations, sensor inaccuracy, and system noise, it must be approximated by a lower-order model and controlled by a finite-order controller. The main object of this paper is concentrated on the hierarchical fuzzy logic by the singular perturbation approach for flexible-link robot arm control. A composite control design is adopted. Therefore, a two-time scale fuzzy logic controller will be applied for such system. In this paper, the fast-subsystem controller will be damp out the vibration of the flexible structure by two hierarchical fuzzy logic controllers. Moreover, the other slow-subsystem fuzzy controller dominates the trajectory tracking. We guarantee the stability of the internal dynamics by adding a boundary-layer correction based on singular perturbations. In addition, various case studies are given in illustration to verify the control algorithm. It appears that the fuzzy control method is quite useful as regards reliability and robustness.

Fuzzy logic control for flexible link robot arm by singular perturbation approach

This work addresses flexible-link robot arm control using fuzzy logic, and a singular perturbation approach. A singular perturbation approach is introduced to derive the slow and fast subsystems and thus reduce the effect of spillover. Consequently, a two-time scale fuzzy logic controller will be applied for such systems. The fast-subsystem controller damps out the vibration of the flexible structure by the optimal control method. Thus, the slow-subsystem fuzzy controller dominates the tracking of the trajectory. The stability of the internal dynamics was guaranteed by adding a boundary-layer correction based on singular perturbations. The first investigation of hybrid LQ-fuzzy controller yielded a favorable output response for the flexible link robot arm than does the traditional outer-loop PD control with the boundary layer stabilizer. The fuzzy control method is reliable and robust.

Vibration control for a flexible-link robot arm with deflection feedback

The use of flexible links in a robot inevitably causes the elastic deflection and vibration of the endpoint of the robot during high-speed operations. The deflection and vibration will tend to degrade the positioning performance of the robot. In this paper, an optical sensing system consisting of a laser diode and a position sensitive detector is introduced for the real-time measurement of the dynamic deflection. Utilising a non-linear, coupled and measurement-based dynamic system model, a Lyapunov-type controller based on the deflection feedback is then proposed to damp out the tip oscillations and regulate the endpoint of the flexible robot. Experimental tests are conducted for a flexible one-link robot arm with a payload mass at the tip. The results demonstrate the effectiveness of the proposed measuring and control schemes.

Fuzzy controller for flexible-link robot arm by reduced-order techniques

The design and analysis of a large-scale control system should be based on the best available knowledge instead of the simplest available model when treating uncertainties in the system. Therefore, a large-scale system is better treated by knowledge-based methods such as fuzzy logic, neural networks, expert systems, etc. This paper concentrates on fuzzy logic using the singular perturbation approach for flexible-link robot arm control. To reduce the spillover effect, we will introduce a singular perturbation approach to derive the slow and fast subsystems. A composite control design is adopted. Therefore, a two-time scale fuzzy logic controller will be applied to the system. The fast-subsystem controller will damp out the vibration of the flexible structure by an optimal control method. Hence, the slow-subsystem fuzzy controller dominates the trajectory tracking. We guarantee the stability of the internal dynamics by adding a boundary-layer correction based on singular perturbations. Various case studies are given to verify the control algorithm. It appears that the fuzzy control method is quite useful in terms of reliability and robustness.

Experimental Investigation of Vibration Suppression Control for 2 Link Flexible Robot Arm by Sliding Mode Control.

A reduced order output feedback control algorithm based on a low order modeling methodology for suppressing the vibration and obtaining the high speed, high precision positioning of flexible robot arm is proposed and discussed. The proposed low order modeling methodology gives no modal truncation error and makes it possible to vary the mode shapes of the link according to the change of the boundary conditions due to the feedback gains and the payload at the tip of the arm. Furthermore, this methodology can take into account not only the flexibility of links but also the flexibility of joints. The reduced order output feedback control algorithm is designed by the combination of sliding mode controller and suboptimal output feedback controller so as to achieve both the damping of the system vibration and the stabilization at the same time. The results of numerical simulation and of experiment for a two-link robot arm model are compared. And they prove that the proposed modeling methodology is able to describe the dynamic behaviors of the arm, and the controller designed applying the suboptimal output feedback sliding mode control is able to control the arm quite well.

Vibration Suppression Control of 2 Link Flexible Robot Arm by Sliding Mode Control.

A low order modeling methodology and a reduced order output feedback control algorithm for suppressing the vibration and obtaining the high speed, high precision positioning of flexible robot are presented and discussed. The low order modeling methodology gives no modal truncation error and make it possible to vary the mode shapes of the link according to the change of the boundary conditions due to the feedback gains and the payload at the tip of the arm. The reduced order output feedback sliding mode control algorithm is designed by the combination of sliding mode controller and suboptimal output feedback controller so as to achieve both the damping of the system vigration and the stabilization at the same time. According to the presented method, the vibration suppression control of the two-link robot arm is realized by only 6 sensors, that is, this robot arm model is reduced to 6 output and 2 control input noncollocated system in spite of 34 state variables system.

Adaptive nonlinear boundary control of a flexible link robot arm

We consider the problem of designing a boundary controller for a flexible link robot arm with a payload mass at the link's free-end. Specifically, we utilize a nonlinear, hybrid dynamic system model (the model is hybrid in the sense that it comprises a distributed parameter, dynamic field equation coupled to discrete, dynamic boundary equations) to design a model-based control law which asymptotically stabilizes the link displacement while driving the actuator hub's position to a desired setpoint. We then illustrate how the control law can be redesigned as an adaptive controller which achieves the same control objective while compensating for parametric uncertainty including unknown payload mass. The control strategy is composed of a boundary control torque applied to the actuator hub and a boundary control force at the link's free-end. Experimental results are presented to illustrate the performance of the proposed control laws.

Mathematical modeling and fuzzy control of a flexible-link robot arm

In this paper, the Timoshenko theory is applied to investigate a new mathematical model for the “shoulder-elbow-like” single flexible-link robot arm with dampings. Detailed analysis and derivation are given to support the mathematical modeling of this particular flexible mechanism. A new design of a fuzzy-logic-based ( PI + D) 2 control scheme is developed for both vibration suppression and set-point tracking. Computer simulation results for the modeling are performed to observe the significant vibration modes, and simulation results for the control scheme demonstrate that the controllers perform very well for the tracking based on this flexible-link model. A newly developed method for stability analysis using the “two-straight-lines” criterion is also presented.

A neural network controller for flexible-link robots

The object of this paper is to achieve tracking control of a partially known flexible-link robot arm. We show how to stabilize the internal dynamics by selecting a physically meaningful modified performance output for tracking. The controller is composed of a singular-perturbation-based fast control and an outer-loop slow control. The slow subsystem is controlled by a neural network (NN) for feedback linearization, plus a PD outer-loop for tracking, and a robustifying term to assure the closed-loop stability. No off-line training or learning is needed for the NN. Tracking and stability are proven using Lyapunov techniques that yield a novel modified NN weight tuning algorithm. >

Experiments in Control of a Flexible-Link Robotic Manipulator With Unknown Payload Dynamics: An Adaptive Approach

This article presents technology that extends the concept of end-point control of a flexible-link robot arm to handle payloads with unknown internal dynamics. The approach is based on merging high-performance control with an innovative identification algorithm in a self-tuning regulator framework. Payload dynamics are identified in real time using recently de veloped subspace fitting techniques. Sufficient excitation issues are addressed. End-point feedback controllers are formulated using frequency-weighted linear quadratic gaussian design methods. Experimental results demonstrating precision control of a very flexible single-link robot arm with unknown dynamic payloads are presented.

A hybrid frequency?time domain adaptive fuzzy control scheme for flexible link manipulators

This paper addresses the implementation of an adaptive fuzzy controller for flexible link robot arms. The design technique is a hybrid scheme involving both frequency and time domain techniques. The eigenvalues of the open loop plant can be estimated through application of a frequency domain based identification algorithm. The region of the eigenvalue space, within which the system operates, is partitioned into fuzzy cells. Membership function are assigned to the fuzzy sets of the eigenvalue universe of discourse. The degree of uncertainty on the estimated eigenvalues is encountered through these membership functions. The knowledge data base consists of feedback gains required to place the closed loop poles at predefined locations. A rule based controller infers the control input variable weighting each with the value of the membership functions at the identified eigenvalue. The afore-mentioned controller is compared through simulation with conventional techniques, namely pole placement and gain scheduling.

On Trajectory Planning for Flexible Robots

A computational technique, based on radial basis functions, for deriving trajectories for a single link flexible robot arm, is presented in this paper. Using an approximation based on radial basis functions and point collocation method, the trajectory planning problem is transformed into a linear least-squares problem. This technique is easy to implement and is computationally efficient. Furthermore, the trajectories obtained do not produce any residual vibration at the end of the move. A computer simulation based on a finite-element model indicates the effectiveness of the proposed technique.