Flexible Manipulator System Research Articles

Distributed Fault Estimation for a Class of Nonlinear Multiagent Systems

This paper is devoted to the problem of distributed fault estimation for multiagent systems with nonlinear dynamic. For each agent, an augmented system can be obtained by treating the possible fault as a special system state. Utilizing the output of the neighbor agents, the nonlinear fault estimation observer can be constructed in one agent. The possible faults in both this agent and its neighbors can be estimated by the observer. By solving linear matrix inequalities, the parameter matrices of the observer can be computed. The region pole constraint is considered, which can improve the estimation performance. At last, both a numerical simulation and a network of four one-link flexible joint manipulator systems are considered to verify the proposed fault estimation approach.

A handheld flexible manipulator system for frontal sinus surgery

PurposeDraf drainage is the standard treatment procedure for frontal sinus diseases. In this procedure, rigid angled endoscopes and rigid curved instruments are used. However, laterally located pathologies in the frontal sinus cannot be reached with rigid instrumentation. In order to assist surgeons with such complicated cases, we propose a novel handheld flexible manipulator system.MethodsA cross section of 3 mm × 4.6 mm enables transnasal guiding of a flexible endoscope with 1.4 mm diameter and a standard flexible surgical instrument with up to 1.8 mm diameter into the frontal sinus with increased reachability. The developed system consists of an electrical discharge-machined flexure hinge-based nitinol manipulator arm and a purely mechanical handheld control unit. The corresponding control unit enables upward and left–right bending of the manipulator arm, translation, rolling, actuation and also quick exchange of the surgical instrument. In order to verify the fulfillment of performance requirements, tests regarding reachability and payload capacity were conducted.ResultsReachability tests showed that the manipulator arm can be inserted into the frontal sinus and reach its lateral regions following a Draf IIa procedure. The system can exert forces of at least 2 N in the vertical direction and 1 N in the lateral direction which is sufficient for manipulation of frontal sinus pathologies.ConclusionConsidering the fact that the anatomical requirements of the frontal sinus are not addressed satisfactorily in the development of prospective flexible instruments, the proposed system shows great potential in terms of therapeutic use owing to its small cross section and dexterity.

Boundary Control of a Rotating and Length-Varying Flexible Robotic Manipulator System

This article copes with vibration suppression and angular position tracking problems of a robotic manipulator system comprised of a rotating hub and a length-varying manipulator. To obtain precise dynamic response, the manipulator system is modeled in infinite-dimension with partial differential equations. S-curve acceleration/deceleration (S-CA/D) scheme is employed for speed regulation of the length-varying manipulator. Two novel observers are developed to estimate both the unknown disturbances and their time-derivatives, and two auxiliary systems are put forward to tackle input constraints. With assistance of the auxiliary systems and observers, two boundary control laws are put forward to manage vibration suppression and angular position tracking of the proposed manipulator system. Through Lyapunov’s theory, the closed-loop system is proved to be bounded. Numerical simulations have displayed the effectiveness of the observers and boundary control laws.

A two-arm flexible space manipulator system for post-grasping manipulation operations of a passive target object

Space Manipulator Systems (SMSs) are complex systems made of a platform equipped with one or more deployable robotic arms and they will be playing a major role in future autonomous on-orbit missions. The latter may as well involve manipulation operations of the target object which needs to be moved from an initial configuration to a final one suitable for the specific task under consideration. In the present study, the mission being analyzed concerns the manipulation of a passive body by means of a flexible SMS after grasping operations have been performed. The dynamics model is derived in a three-dimensional context (non-linear formulation for the rigid-body motions and linear for the elastic dynamics). The SMS involved in the investigation has two actuated seven-degree of freedom arms. Furthermore, the modeling of the grasp constraint existing between the SMS end-effectors and the target object is a critical issue which is addressed in the present paper. A combination of Jacobian Transpose and Proportional-Derivative Control is synthesized to accomplish the desired mission goals. Numerical results proving the effectiveness of the proposed strategy are presented and discussed.

Vibration control for a flexible single‐link manipulator and its application

This study focuses on vibration control design of a flexible single-link manipulator (FSLM) system and discusses its application on an experimental platform. A spatiotemporal mathematic model is presented to formulate dynamical behaviour of the FSLM system, and only a boundary controller mounted on the hub is designed to drive the link for tracking a given angular position and to reduce elastic deflection simultaneously. Under the boundary vibration control scheme, states of the system are ensured to converge exponentially to the equilibrium position. Moreover, numerical simulations demonstrate the correctness of theoretical proof for the stability analysis and the reasonability of boundary control design. Experiment validation implemented on the Quanser laboratory platform illustrates the same conclusion as well.

Boundary control and exponential stability of a flexible Timoshenko beam manipulator with measurement delays

This study mainly focuses on the boundary control problem for a novel flexible Timoshenko beam manipulator system with measurement delay terms. The actuator structure of the manipulator consisted of a translational slider and a rotational motor, which are able to provide two inputs to influence different variables in boundary conditions of the Timoshenko partial differential equations. A static feedback boundary controller is proposed to realise exponential stability of the closed-loop system based on $C_0$C 0 -semigroup and fundamental solutions. The controller is independent of the precise knowledge of parameters in the delay terms directly, so it has robustness to time delays in certain degree. Numerical simulations are provided to verify the effectiveness of the proposed control scheme.

DYNAMIC MODELING OF A SINGLE-LINK FLEXIBLE MANIPULATOR ROBOT WITH TRANSLATIONAL AND ROTATIONAL MOTIONS

The flexible manipulator is widely used in space robots, robot arm, and manufacturing industries that produce micro-scale products. This study aims to formulate the equation of motion of a flexible single-link manipulator system that moves translationally and rotationally and to develop computational codes with finite element methods in performing dynamic simulation on the vibration of the flexible manipulator system. The system of the single-link flexible manipulator (SLFM) consists of the aluminum beam as a flexible link, clamp part to hold the link, DC motor to rotate drive shaft, a trajectory to transfer link in translational motion, and servo motor to rotate link. Computational codes in time history response (THR) and Fast Fourier Transform (FFT) processing were developed to identify the dynamic behavior of the link. The finite element-method and Newmark-beta are used in simulating the SLFM. Simulation using the finite element method has displayed dynamic behavior through a graph of FFT on free vibration and THR graph on forced vibration by the excitation force due to the translational and rotational motions of the system. In the simulation of free vibration, the natural frequency of the system is 8.3 [Hz].

Boundary Output Feedback Control for a Flexible Two-Link Manipulator System With High-Gain Observers

This brief focuses on the boundary output feedback control for a flexible two-link manipulator (FTLM) system with input saturation. For the purpose of suppressing elastic vibration and regulating manipulator’s angular position, boundary output feedback controllers (BOFCs) are proposed. When the system states cannot be directly measured, a set of high-gain observers are designed to reproduce these immeasurable system states. Simultaneously, in order to solve the problem of excessive control input caused by high-gain observers, two auxiliary systems are designed to compensate for the input saturation. The stability of the FTLM system is obtained through mathematical analysis. Furthermore, the effectiveness of the designed controllers is proved by numerical simulations.

Adaptive Neural Event-Triggered Control of MIMO Pure-Feedback Systems With Asymmetric Output Constraints and Unmodeled Dynamics

In this paper, the issue of adaptive neural event-triggered control (ETC) is studied for uncertain block-structure multi-input multi-output (MIMO) constrained non-affine nonlinear systems with unmodeled dynamics. A dynamic signal produced by the auxiliary system based on the property of unmodeled dynamics is employed to solve the dynamical disturbances. The unknown continuous function obtained at each step of recursion is estimated by using radial basis function neural networks (RBFNNs). Utilizing logarithmic function as an invertible mapping, the uncertain constrained MIMO non-affine system is changed into a novel unconstrained block-structure MIMO nonaffine system. Using improved dynamic surface control (DSC) strategy, adaptive event-triggered control scheme is developed for the transformed non-affine system based on relative threshold mechanism. According to the Lyapunov method, all the signals in the closed-loop system are shown to be semi-globally uniformly ultimately bounded (SGUUB). Output constraint requirements are not triggered, and Zeno behavior is avoided. A constrained pure-feedback system and a kind of 2-DOF flexible manipulator system are used to illustrate the theoretical findings.

Hybrid Sliding Mode/H-Infinity Control Approach for Uncertain Flexible Manipulators

In this article, a hybrid control approach combining sliding mode and H-infinity is proposed for an uncertain single-link flexible manipulator. The sliding mode controller stabilizes the nonlinear manipulator system, while the H-infinity controller enhances the noise rejection capability of the system by reducing the total system nonlinearity. The proposed hybrid controller is designed with the goal of rejecting external noises, hence providing a higher system performance, compared to a pure sliding mode controller. To avoid unintentional consequences of switching between the sliding mode and H-infinity controller, a fuzzy neural network weighting method is designed providing a smooth synthesis of both controller outputs. The neuro-fuzzy method applies a weighted combination of the two controller outputs to the manipulator system. In addition, a novel fuzzy estimation method is used to characterize the unstructured nonlinear disturbances in manipulator systems. The proposed hybrid control approach along with the fuzzy estimator is capable of providing a versatile means to stabilize flexible manipulator systems while maintaining a precise reference trajectory tracking in presence of unstructured uncertainty and nonlinear dynamics, as demonstrated by simulation results.

Fractional‐order DOB‐sliding mode control for a class of noncommensurate fractional‐order systems with mismatched disturbances

This article proposes a novel fractional‐order sliding mode control based on the disturbance observer for a class of noncommensurate fractional‐order systems with mismatched disturbances. Firstly, the noncommensurate fractional‐order system is decomposed into several subsystems with commensurate order. Then the fractional‐order disturbance observers are designed independently to estimate the mismatched disturbances for each subsystems. Based on the designed disturbance observers, a uniform fractional‐order sliding mode control is proposed. The proposed method can deal with the mismatched disturbances and has better control performance. The simulations on single‐link flexible manipulator system demonstrate the effectiveness of the proposed method.

Finite element analysis on vibration of a flexible single-link manipulator moved translationally

The objectives of this study are to formulate the equation of motion of a flexible single-link manipulator system and to develop computational codes by a finite-element method in order to perform dynamics simulation on vibration of the manipulator system. The system used in this research consist of an aluminium beam as a flexible link, a clamp-part to hold the link, a DC motor and a lead screw set to move the link translationally. Computational codes on time history responses and FFT (Fast Fourier Transform) processing were developed to calculate dynamic behaviour of the link. The simulation result show the dynamic behaviour of the system on free vibration and forced vibration by excitation force due to the translational motion of the single-link manipulator system.

System identification and a model-based control strategy of motor driven system with high order flexible manipulator

Purpose This paper aims to propose a novel system identification and resonance suppression strategy for motor-driven system with high-order flexible manipulator. Design/methodology/approach In this paper, first, a unified mathematical model is proposed to describe both the flexible joints and the flexible link system. Then to suppress the resonance brought by the system flexibility, a model based high-order notch filter controller is proposed. To get the true value of the parameters of the high-order flexible manipulator system, a fuzzy-Kalman filter-based two-step system identification algorithm is proposed. Findings Compared to the traditional system identification algorithm, the proposed two-step system identification algorithm can accurately identify the unknown parameters of the high order flexible manipulator system with high dynamic response. The performance of the two-step system identification algorithm and the model-based high-order notch filter is verified via simulation and experimental results. Originality/value The proposed system identification method can identify the system parameters with both high accuracy and high dynamic response. With the proposed system identification and model-based controller, the positioning accuracy of the flexible manipulator can be greatly improved.

Partial differential equation modeling and vibration control for a nonlinear 3D rigid‐flexible manipulator system with actuator faults

SummaryIn this paper, modeling and controlling problem for a two‐link rigid‐flexible manipulator in three‐dimensional (3D) space is studied under actuator faults. For modeling, the dynamics of the 3D mechanical system is represented by nonlinear partial differential equations, which is first derived in infinite dimension form. Based on the nonlinear model, the controller is proposed, which can achieve joint angle control and vibration suppression control in the presence of actuator faults. The stability analysis of the closed‐loop system is given based on LaSalle invariance principle. Numerical simulations illustrate the effectiveness of the proposed controller. This study will promote the development of nonlinear flexible manipulator systems in 3D space.

Robust Adaptive Sliding Mode Fault Tolerant Control for Nonlinear System with Actuator Fault and External Disturbance

In this paper, an adaptive sliding mode fault tolerant control (ASMFTC) approach is proposed for a class of nonlinear systems with actuator fault, uncertainty, and external disturbance. Specifically, first, a novel observer is proposed to estimate the state, actuator fault, and external disturbance. Then, by utilising the observed information, a novel output sliding mode observer is constructed. In the control method, an adaptive law and two compensators are designed to attenuate the unknown estimation errors, actuator fault, and disturbance. Furthermore, the reaching ability of the sliding motion is analysed and the H-infinite performance is introduced to ensure the robustness of the system. Finally, a flexible single joint manipulator system and a two-cart system are used to verify the effectiveness of the proposed method.

Robustness and Disturbance Rejection of PD/H-∞ Integrated Controller for Flexible Link Manipulator System

Robustness and Disturbance Rejection of PD/H-∞ Integrated Controller for Flexible Link Manipulator System

Coupling dynamic modelling and parameter identification of a flexible manipulator system with harmonic drive

This paper formulates a coupling dynamic model for a flexible manipulator system with harmonic drive using experimental identification method. Parameters of the driven model of the harmonic joint and parameters of coupling vibration model of the flexible manipulator are identified. Accordingly, coupling dynamic models of the proposed system are obtained. Coulomb friction of the joint is identified by step current excitation and uniform rotation experiments at a low speed. Then, the transfer function model of the harmonic joint is established and identified by a pseudorandom binary sequence excitation. And predicted outputs of the obtained model are in good agreement with the experimental setup. Relationships between strain of the flexible manipulator and coupling torque are presented by theoretical derivation. Based on the theoretical model, transfer function from the angular displacement of the servo motor to the coupling torque is identified. Experimental results show this identified model match well with the proposed structure, both in the time and frequency domain. As a result, coupling dynamic modelling of the flexible manipulator system with harmonic drive is accomplished.

A Finite-Time Sliding Mode Controller Design for Flexible Joint Manipulator Systems Based on Disturbance Observer

A Finite-Time Sliding Mode Controller Design for Flexible Joint Manipulator Systems Based on Disturbance Observer

Sliding Mode Fault Tolerant Tracking Control for a Single-Link Flexible Joint Manipulator System

In this paper, the fault-tolerant tracking control problem for a class of single-link flexible joint manipulator (SFJM) system with uncertainty, fault, nonlinear function, and unmatched disturbance is investigated. An observer-based sliding mode control approach is designed. Concretely, first of all, the SFJM dynamic system with uncertainty, fault, and unmatched disturbance is established. Then, by transforming the system into two subsystems, a novel composite observer is proposed to estimate the fault and disturbance, respectively. Furthermore, a robust sliding mode controller, which contains a third-order sliding mode surface, a continuous control strategy, and a visual estimated fault signal, is constructed. In the control scheme, an adaptive law is also concluded to compensate for the estimation error. Finally, the proposed method is applied to the SFJM system and the simulation results illustrate the effectiveness of the proposed method.

Master‐Slave Composite Vibration Control of a Mobile Flexible Manipulator via Synchronization Optimization of Observation and Feedback

The elastic vibration of the flexible manipulator is the key problem to be solved before its effective application. The mobile flexible manipulator system (MFMS), under variable load conditions, is taken as the research object. Based on Lagrange’s principle and the singular perturbation theory, the two‐timescale subsystems dynamic models of the MFMS are constructed to set up the system payment function and the Hamiltonian function which correspond to the subsystems states and errors. Then, with the minimization of the system Hamiltonian function, the synchronization optimization of the designed two‐timescale optimal observer (TSOO) and the designed optimal state feedback controller is realized, under the premise of the system stability which is verified by the Lyapunov stability criterion. Furthermore, with the contradiction between the control rapidity and the accuracy of the optimal state feedback controller considered, by combining the input shaping technology, the master‐slave composite controller for the elastic vibration of the MFMS is constructed. Finally, simulation results verify the validity of the designed TSOO and the master‐slave composite controller.