Friction Disturbance Research Articles

A comprehensive study on frictional dependence and predictive accuracy of viscoelastic model for optical glass using compression creep test

AbstractCompression creep tests (CCTs) have been widely used in phenomenological characterization of viscoelastic materials such as glasses. However, disturbed by specimen‐tool interface friction, the real stress‐strain data regarding the pure viscoelastic deformation are frequently misestimated in conventional CCTs, causing decreased accuracies of the derived viscoelastic parameters. This study proposes a comprehensive CCT‐based approach to develop a viscoelastic model with weakened frictional disturbance and enhanced predictive accuracy. An integrated calculation procedure is first built to mathematically characterize the frictional and viscoelastic behaviors of glass during compression. Uniaxial CCTs of a typical borosilicate glass (L‐BAL42) are then performed at varied frictional conditions. The quantified coefficients of interface friction indicate that a minor frictional disturbance is achieved when Nickel foils are used as interfacial layers, whereby a more realistic viscoelastic constitutive relation of the glass is derived. The obtained frictional and viscoelastic constants are further incorporated into computational modeling of the CCT and precision molding processes. The demonstrated consistencies between the simulated and measured results (creep displacement and molding force) suggest that, by technically slashing the interface friction and theoretically correcting the friction‐involved stress in CCTs, the frictional disturbance to experimental stress‐strain data can be effectively weakened, and a viscoelastic model of enhanced predictive accuracy can be thus developed.

Pre-compensation of servo tracking errors through data-based reference trajectory modification

This paper presents a new dynamic error compensation approach with novel data-based closed-loop tuning scheme to enhance tracking accuracy of machine tool feed-drives. Both servo dynamics and friction disturbance induced positioning errors are pre-compensated by modifying the reference trajectory. Velocity and acceleration profiles of reference trajectory are modulated to achieve perfect tracking. Reference position profile is modified based on the pre-sliding friction regime to eliminate quadrant glitches. Optimal error compensation is achieved by a digital trajectory pre-filter whose parameters are tuned automatically by making on-the-fly iterative adjustments. Effectiveness of proposed compensation approach is validated experimentally in multi-axis feed-drive systems.

Adaptive robust neural control of a two-manipulator system holding a rigid object with inaccurate base frame parameters

The problem of self-tuning control with a two-manipulator system holding a rigid object in the presence of inaccurate translational base frame parameters is addressed. An adaptive robust neural controller is proposed to cope with inaccurate translational base frame parameters, internal force, modeling uncertainties, joint friction, and external disturbances. A radial basis function neural network is adopted for all kinds of dynamical estimation, including undesired internal force. To validate the effectiveness of the proposed approach, together with simulation studies and analysis, the position tracking errors are shown to asymptotically converge to zero, and the internal force can be maintained in a steady range. Using an adaptive engine, this approach permits accurate online calibration of the relative translational base frame parameters of the involved manipulators. Specialized robust compensation is established for global stability. Using a Lyapunov approach, the controller is proved robust in the face of inaccurate base frame parameters and the aforementioned uncertainties.

Sliding mode controller design for trajectory tracking of a non-holonomic mobile robot with disturbance

This paper develops sliding mode controller for the trajectory tracking of a non-holonomic differentially driven wheeled mobile robot (DDWMR) with measurement noise, frictional disturbances and model uncertainties. The proposed controller is designed with the help of an existing Proportional-Integral (PI) sliding surface for trajectory tracking followed by a new Proportional-Integral-Derivative (PID) sliding surface for velocity tracking. The PI and PID sliding surfaces are based on the kinematic model and dynamic model of the robot, respectively. An adjustable gain switching controller is incorporated for minimizing the effect of disturbances and uncertainties. The closed loop stability of the system is proved using Lyapunov stability criteria. The proposed controller is validated with the help of numerical examples and real-time experiments on DDWMR.

Robust position-based impedance control of lightweight single-link flexible robots interacting with the unknown environment via a fractional-order sliding mode controller

SUMMARYThis paper presents a fractional-order sliding mode control scheme equipped with a disturbance observer for robust impedance control of a single-link flexible robot arm when it comes into contact with an unknown environment. In this research, the impedance control problem is studied for both unconstrained and constrained maneuvers. The proposed control strategy is robust with respect to the changes of the environment parameters (such as stiffness and damping coefficient), the unknown Coulomb friction disturbances, payload, and viscous friction variations. The proposed control scheme is also valid for both unconstrained and constrained motions. Our novel approach automatically switches from the free to the constrained motion mode using a simple algorithm of contact detection. In this regard, an impedance control scheme is proposed with the inner loop position control. This means that in the free motion, the applied force to the environment is zero and the reference trajectory for the inner loop position control is the desired trajectory. However, in the constrained motion the reference trajectory for the inner loop is determined by the desired impedance dynamics. Stability of the closed loop control system is proved by Lyapunov theory. Several numerical simulations are carried out to indicate the capability and the effectiveness of the proposed control scheme.

Sliding mode control of the automobile electro-coating conveying mechanism with a nonlinear disturbance observer

The trajectory-tracking performance of the automobile electro-coating conveying mechanism is severely interrupted by highly nonlinear crossing couplings, unmodeled dynamics, parameter variation, friction, and unknown external disturbance. In this article, a sliding mode control with a nonlinear disturbance observer is proposed for high-accuracy motion control of the conveying mechanism. The nonlinear disturbance observer is designed to estimate not only the internal/external disturbance but also the model uncertainties. Based on the output of the nonlinear disturbance observer, a sliding mode control approach is designed for the hybrid series–parallel mechanism. Then, the stability of the closed-loop system is proved by means of a Lyapunov analysis. Finally, simulations with typical desired trajectory are presented to demonstrate the high performance of the proposed composite control scheme.

Indirect adaptive robust mixed H2/H∞ general type-2 fuzzy control of uncertain nonlinear systems

General type-2 fuzzy logic offers an added ability to manage uncertainties, but it also carries a high computational burden and added mathematical complexity. Further development of this paradigm is hence considerably challenged in terms of both time-constrained industrial implementations and mathematical guarantees of performance. In this paper, we propose a stable indirect adaptive robust mixed H2/H∞ control approach to an α-plane representation of a general type-2 fuzzy framework. The resulting structure is shown to be both computationally efficient and amenable to theoretical analysis. Specifically, this hybrid paradigm is mathematically derived to minimize energy consumption, keep all signals bounded during the transient states, guide the tracking error to zero, and keep the effect of uncertainties such as the external disturbances below a desired level. To validate these theoretical results, two sets of simulations on an inverted pendulum and a robotic manipulator with time-varying payloads and friction disturbances are performed. To illustrate real-time computational efficacy, the proposed algorithm is then experimentally implemented on a 3-PSP parallel robot in our laboratory. Comparative analysis indicates that the proposed method achieves smaller tracking error, less consumed control energy, and better robustness against uncertainties when compared with its type-1 fuzzy, interval type-2 fuzzy counterparts. This is while computational time for each control cycle increases only slightly when compared with its interval type-2 counterpart.

Continuous Friction Feedforward Sliding Mode Controller for a TriMule Hybrid Robot

This paper presents a continuous friction feedforward sliding mode controller (CFSMC) for a TriMule hybrid robot to improve its trajectory-tracking performance. The dynamic model depicts that the TriMule robot is a multivariable system with nonlinearity and strong coupling, which poses significant challenges in controller design. Hence, a novel CFSMC that consists of a friction feedforward control loop and a continuous sliding mode feedback control loop is specially developed. The feedforward control item calculated with a speed related function is used to handle discontinuous friction disturbance and achieve good transient performance. The feedback control item designed with a continuous sliding mode algorithm is applied to cope with other nonlinear dynamics and assure zero steady-state error. The robustness of the proposed hybrid control scheme is validated in the sense of Lyapunov. Comparative experimental studies with the double closed-loop controller, the sliding mode controller, and the continuous sliding mode controller are conducted, confirming that the CFSMC with the superior control accuracy is an effective and practical robust control scheme for the TriMule hybrid robot. Taking advantages of the CFSMC, a high-precision circular motion is achieved by the TriMule hybrid robot.

A High-Precision Control Scheme Based on Active Disturbance Rejection Control for a Three-Axis Inertially Stabilized Platform for Aerial Remote Sensing Applications

This paper presents a high-precision control scheme based on active disturbance rejection control (ADRC) to improve the stabilization accuracy of an inertially stabilized platform (ISP) for aerial remote sensing applications. The ADRC controller is designed to suppress the effects of the disturbance on the stabilization accuracy that consists of a tracking differentiator, a nonlinear state error feedback, and an extended state observer. By the ADRC controller, the effects of both the internal uncertain dynamics and the external multisource disturbances on the system output are compensated as a total disturbance in real time. The disturbance rejection ability of the ADRC is analyzed by simulations. To verify the method, the experiments are conducted. The results show that compared with the conventional PID controller, the ADRC has excellent capability in disturbance rejection, by which the effect of main friction disturbance on the control system can be weakened seriously and the stabilization accuracy of the ISP is improved significantly.

A novel dynamic contour error estimation and control in high-speed CNC

High-speed CNC machining requires high-precision servo response and dynamic performance of feed drives with better control parameters matched in coupled axis. In this paper, an electromechanical coupling system of multi-axis CNC machine tool feed drive model is established for servo parameter optimization and high-precision contour error improvement. The influences of the joint stiffness and the friction disturbance in servo dynamic have been considered. The disturbance parameter and joint stiffness have been identified by unbiased least squares scheme. The electromechanical coupling model is used to study the contour error estimation and compensation technology in high-speed machining. The multi-axis contour error is estimated by using Ferguson curve to approximate the curve between the interpolation points. The calculation is fast and accurate enough for contour error pre-compensation. Experiments prove that five-axis contour error can be effectively reduced by dynamics pre-compensation in high-speed CNC with better processing quality and stability improvement.

Study on nonlinear friction compensation control in the electro-hydraulic servo loading system of triaxial apparatus

Nonlinear friction and uncertain disturbance are two of the most important factors affecting the tracking performance and the robustness in the electro-hydraulic servo loading system of triaxial apparatus. In this paper, an iterative learning control (ILC) based sliding mode control (SMC) has been proposed to solve such a problem. A P-type learning function is used to compensate the model of nonlinear friction. The state-space model of the triaxial apparatus is established and the corresponding controller is designed. The controller employs an ILC based SMC of input-output feedback linearisation (IOFL) method to determine the control rule and accomplish the compensation for the nonlinear friction. A Lyapunov method is applied to analyse the condition of convergence in the finite time and the impact acting on the system caused by the control parameters. The simulation results indicate that the tracking performance and the robustness of the system have been remarkably improved.

Adaptive integral backstepping sliding mode control for opto-electronic tracking system based on modified LuGre friction model

ABSTRACTIn order to improve the control accuracy and stability of opto-electronic tracking system fixed on reef or airport under friction and external disturbance conditions, adaptive integral backstepping sliding mode control approach with friction compensation is developed to achieve accurate and stable tracking for fast moving target. The nonlinear observer and slide mode controller based on modified LuGre model with friction compensation can effectively reduce the influence of nonlinear friction and disturbance of this servo system. The stability of the closed-loop system is guaranteed by Lyapunov theory. The steady-state error of the system is eliminated by integral action. The adaptive integral backstepping sliding mode controller and its performance are validated by a nonlinear modified LuGre dynamic model of the opto-electronic tracking system in simulation and practical experiments. The experiment results demonstrate that the proposed controller can effectively realise the accuracy and stability control of opto-electronic tracking system.

Pressure-tracking control of a novel electro-hydraulic braking system considering friction compensation

This work presents an integrated pressure-tracking controller for a novel electro-hydraulic brake (EHB) system considering friction and hydraulic disturbances. To this end, a mathematical model of an EHB system, consisting of actuator and hydraulic sub-systems, is derived for describing the fundamental dynamics of the system and designing the controller. Due to sensor inaccuracy and measurement noise, a Kalman filter is constructed to estimate push rod stroke for generating desired master cylinder pressure. To improve pressure-tracking accuracy, a linear friction model is generated by linearizing the nonlinear Tustin friction model, and the unmodeled friction disturbances are assumed unknown but bounded. A sliding mode controller is designed for compensating friction disturbances, and the stability of the controller is investigated using the Lyapunov method. The performance of the proposed integrated controller is evaluated with a hardware-in-the-loop (HIL) test platform equipped with the EHB prototype. The test results demonstrate that the EHB system with the proposed integrated controller not only achieves good pressure-tracking performance, but also maintains robustness to friction disturbances.

A compound scheme on parameters identification and adaptive compensation of nonlinear friction disturbance for the aerial inertially stabilized platform

A compound scheme is proposed to compensate the effect of nonlinear friction disturbance on the control precision of a three-axis inertially stabilized platform (ISP) for aerial remote sensing applications. The scheme consists of friction parameters identification and adaptive compensation. A LuGre model-based ISP friction model is first developed. Then, a comprehensive experimental scheme is proposed to obtain the static friction parameters. Further, the dynamic parameters are identified by experiments and dynamic optimization. On the basis of identified parameters and Lyapunov stability theory, a backstepping integral adaptive compensator is designed to compensate the nonlinear friction disturbance. Simulations and experiments are carried out to validate the scheme. The results show that the compound scheme can accurately obtain the friction parameters and improve the control precision and stability of ISP.

The effects of ice cover on flow characteristics in a subarctic meandering river

AbstractThe effects of ice cover on flow characteristics in meandering rivers are still not completely understood. Here, we quantify the effects of ice cover on flow velocity, the vertical and spatial flow distribution, and helical flow structure. Comparison with open‐channel low flow conditions is performed. An acoustic doppler current profiler (ADCP) is used to measure flow from up to three meander bends, depending on the year, in a small sandy meandering subarctic river (Pulmanki River) during two consecutive ice‐covered winters (2014 and 2015).Under ice, flow velocities and discharges were predominantly slower than during the preceding autumn open‐channel conditions. Velocity distribution was almost opposite to theoretical expectations. Under ice, velocities reduced when entering deeper water downstream of the apex in each meander bend. When entering the next bend, velocities increased again together with the shallower depths. The surface velocities were predominantly greater than bottom/riverbed velocities during open‐channel flow. The situation was the opposite in ice‐covered conditions, and the maximum velocities occurred in the middle layers of the water columns. High‐velocity core (HVC) locations varied under ice between consecutive cross‐sections. Whereas in ice‐free conditions the HVC was located next to the inner bank at the upstream cross‐sections, the HVC moved towards the outer bank around the apex and again followed the thalweg in the downstream cross‐sections. Two stacked counter‐rotating helical flow cells occurred under ice around the apex of symmetric and asymmetric bends: next to the outer bank, top‐ and bottom‐layer flows were towards the opposite direction to the middle layer flow. In the following winter, no clear counter‐rotating helical flow cells occurred due to the shallower depths and frictional disturbance by the ice cover. Most probably the flow depth was a limiting factor for the ice‐covered helical flow circulation, similarly, the shallow depths hinder secondary flow in open‐channel conditions. Copyright © 2016 John Wiley & Sons, Ltd.

Finite-Time Sliding Mode Control for Trajectory Tracking of WMRs with Wheel-Soil Friction Disturbance Adaptability

ABSTRACTThis paper presents a trajectory tracking approach based on terminal sliding mode control (TSMC) technique for wheeled mobile robot where the wheel-soil friction can be measured and the estimated errors will converge to their stable values within finite-time, by which the control system is able to be designed in accordance with the prescribed performance. Three kinds of friction effects and their acting mechanisms, at the first place, are argued by exploring the disturbance-like friction behaviors, and then two updated laws, i.e., taking uncertain friction as an entire term or as a parametric form for varied effects, are proposed. In addition, the adoption of TSMC enables the tracking error estimation being faster and more reliable, and the stability and reliability of closed-loop control system are guaranteed by means of Lyapunov stability theorem. Subsequently, the numerical simulation validates the feasibility and effectiveness of the proposed controllers by which the terrain adaptability, movement precision, and maneuvering capability will be improved significantly.

Input-state feedback linearization control of a single-link flexible robot arm moving under gravity and joint friction

In this paper we address the trajectory tracking problem of the end-effector of a single link flexible arm in which the gravity forces and the joint friction forces are taken into account. As an overall approach, a double loop cascade control is used to deal with the joint friction: in its inner loop a two-degree-of-freedom controller is responsible for the joint position in the presence of Coulomb friction disturbances, while in its outer loop an input-state feedback linearization-based controller is implemented to suppress the vibrations and track an end-effector trajectory. To highlight the benefits of the proposed controller in presence of joint friction, the controller was compared with other approaches based on feedback linearization reported in the literature, which considered only a single loop. The results of this comparison showed that our approach provides superior performance in terms of settling time, maximum overshoot and residual vibrations.The design of the controller presented relies on a non-linear single-lumped mass dynamic model that describes the dynamics of a single link arm with only one significant vibrational mode. The hypothesis of a single lumped mass model could be considered inaccurate given the distributed nature of the link mass, especially in situations in which the link mass is comparable to the payload mass held by the robot. However, for the parameters of our physical platform two studies are presented to demonstrate that the single lumped mass model is a proper description of the system even in situations in which the link mass is up twice bigger than the payload mass. The results of the paper are demonstrated with co-simulations with Matlab/Simulink and MSC ADAMS, and experimental validation.

Guiding mechanism design and precision pressure control in composites filament winding system

During the composite winding process, pressure fluctuation will affect the density and homogeneity of the products and will make the interfacial strength disaccord with the fiber volume fraction. In order to improve the guiding precision and stability of the winding pressure, the bearing guide is replaced by the rolling guide in designing the pressure guiding mechanism, and parametric model of the guiding mechanism is established based on dynamics experiment of the joint surfaces. By analyzing the modal and harmonic response, the corresponding measures for improvement are proposed. Experimental results show that the designed guiding mechanism based on the rolling guide has high precision and perfect stability. Additionally, roundness error and installation error of the mandrel can cause the winding pressure to fluctuate and the gas compressibility, nonlinear flow, dead zone, cylinder friction, measurement noise and other nonlinear disturbances have significant impact on the pneumatic pressure control system. Considering the above circumstance, an adaptive fuzzy proportional–integral–derivative (PID) controller based on the grey prediction is proposed. By predicting the output pressure, trend of the pressure signal can be reflected accurately, which provides a reliable basis for the decision-making of the fuzzy PID controller. Simultaneously, two separate fuzzy inference systems are employed to adjust the step length of the predictive control and the scale factor of the step self-tuning algorithm. Simulation and experimental results show that the fuzzy PID controller based on grey prediction has shorter settling time, smaller overshoot and error, stronger robustness and interference immunity. The designed guiding mechanism and control algorithm have effectively improved the precision and stability of the pressure control system for the composite materials winding formation.

Nanometric positioning accuracy in the presence of presliding and sliding friction: Modelling, identification and compensation

ABSTRACTPresliding and sliding frictional effects, limiting the performances of ultrahigh precision mechatronics devices, are studied in this work. The state-of-the-art related to frictional behavior in both motion regimes is, hence, considered, and the generalized Maxwell-slip (GMS) friction model is adopted to characterize frictional disturbances present in a micromanipulation device. All the parameters of the model are identified via experimental set-ups and included in the overall MATLAB/SIMULINK model. With the aim of compensating frictional effects, the modelled response of the system is thus compared to experimental results when using proportional-integral-derivative (PID) control, feed-forward model-based compensation and a self-tuning adaptive regulator. The adaptive regulator proves to be the most efficient and is, hence, used in the final repetitive point-to-point positioning tests allowing to achieve nanometric precision and accuracy.

Adaptive Tracking Control of the Minimum-Energy Trajectory for a Mechatronic Motor-Table System

In this paper, a mechatronic motor-table system is realized to plan the minimum input electrical energy trajectory based on the Hamiltonian function. In this system, unknown parameters are identified by particle swarm optimization, and an adaptive tracking controller is designed to track the minimum input electrical energy trajectory to overcome the nonlinear friction and external disturbance. Moreover, trapezoidal trajectory and regulator control are compared with the minimum input electrical energy trajectory by an adaptive tracking controller. Finally, it can be concluded that the minimum input electrical energy trajectory based on the adaptive tracking controller can obtain the minimum input electrical energy and robustness performance for the mechatronic motor-table system. Numerical simulations and experimental results demonstrate the adaptive tracking control strategy successfully in the minimum-energy trajectory.