Large Tracking Errors Research Articles

Modeling and Friction Effect of Shipborne Tracking Antenna Servo System

In order to improve the friction nonlinear perturbation effect on shipboard antenna tracking, first to a certain type of ship azimuth servo system as an example, considering the establishment of a mathematical model with friction, and the model is carried out using PID control method. The results show that with friction disturbance considered, there are tracking exist "flat top" phenomenon and large tracking error, and when the speed is low, there is the "crawl" phenomenon.Keywords: ship servo system, friction disturbance, disturbance compensation

Multiloop Pilot Model for Boundary-Triggered Pilot-Induced Oscillation Investigations

This paper presents the development of a multiloop pilot model for use in boundary-triggered pilot-induced oscillation investigations. In doing so, the point-tracking and boundary-avoidance elements of the pilot control strategy are assumed to act simultaneously for a point-tracking-dominant task during a boundary-avoidance tracking event. The theoretical analysis indicates that the essence of the boundary-avoidance tracking phenomenon consists of an additional requirement for the pilot to provide lead equalization as the boundary is approached as the task transitions from a full-attention point-tracking task to both a point-tracking and boundary-avoidance task. This process leads to a narrower open-loop system bandwidth and a larger tracking error, or the triggering of a pilot-induced oscillation. It is also found that the severity of the boundary-avoidance influence can be reduced by including the effects of vestibular and proprioceptive cues into the model. The boundary-avoidance tracking pilot model exhibits pilot–vehicle responses that are consistent with those observed in a piloted-simulation study and can therefore be considered to be representative of pilot activity. Consideration of the results in the round indicates that the boundary-triggered pilot-induced oscillation can be categorized as Category III pilot-induced oscillation within the existing recognized taxonomy.

Friction modeling, identification, and compensation based on friction hysteresis and Dahl resonance

This paper studies effects of friction on control systems and utilizes the observed frictional behavior to develop a parameter identification method for a friction model using frequency domain measurements. Friction exists in a wide range of drive systems due to physical contacts in bearing elements, transmissions, or motion guides. Friction in a control system can deteriorate performance by causing limit cycles or stick–slip, as well as larger tracking errors. Friction compensation can help to reduce following errors, but requires physical understanding and a reliable model of friction in both the gross- and the pre-sliding regimes. In this paper, we adopt the Generalized Maxwell-Slip (GMS) model and develop a frequency-domain method to identify the model parameters based on the frictional resonances, which occur due to the elastic behavior of friction at small amplitudes. With the experimentally identified parameters, the friction model is utilized to compensate the friction effects in a motion control system. The resulting system performance of a compensated and uncompensated control system is then compared in both the frequency and time domains to demonstrate the Dahl resonance identification method for a GMS model.

Model Based Adaptive Piecewise Linear Controller for Complicated Control Systems

A model based adaptive piecewise linear control scheme for industry processes with specifications on peak overshoots and rise times is proposed. It is a gain stabilized control technique. Large gain is used for large tracking error to get fast response. Small gain is used between large and small tracking error for good performance. Large gain is used again for small tracking error to cope with large disturbance. Parameters of the three-segment piecewise linear controller are found by an automatic regulating time series which is function of output characteristics of the plant and reference model. The time series will be converged to steady values after the time response of the considered system matching that of the reference model. The proposed control scheme is applied to four numerical examples which have been compensated by PID controllers. Parameters of PID controllers are found by optimization method. It gives an almost command independent response and gives significant improvements for response time and performance.

Adaptive Piecewise Linear Controller for Servo Mechanical Control Systems

In this paper, an adaptive piecewise linear control scheme is proposed for improving the performance and response time of servo mechanical control systems. It is a gain stabilized control technique. No large phase lead compensations or pole zero cancellations are needed for performance improvement. Large gain is used for large tracking error to get fast response. Small gain is used between large and small tracking error for good performance. Large gain is used again for small tracking error to cope with disturbance. It gives an almost command independent response. It can speed up the rise time while keeping robustness unchanged. The proposed control scheme is applied to a servo system with large time lag and a complicated electro-hydraulic velocity/position servo system. Time responses show that the proposed method gives significant improvements for response time and performance.

Observations and Forecasts from the Landfall of Tropical Cyclones John, Lane, and Paul (2006) over Northwestern Mexico

Abstract This study focuses on track and intensity changes of three tropical cyclones that, during the season of 2006, developed in the eastern North Pacific basin and made landfall over northwestern Mexico. Observational datasets, including satellite and radar imagery and a rain gauge network, are used to document regional-scale structures. Additionally, gridded fields are applied to determine the large-scale environment. John made landfall as a category-2 hurricane on the Saffir–Simpson scale and moved along the Baja California Peninsula during more than 40 h, resulting in total rainfall of up to 506 mm. The largest accumulations were located over mountains and set new records with respect to daily rates from the 1969–2005 period. Later in the season, Lane and Paul made landfall over the mainland and brought moderate rainfall over the coastal plains. Lane became a category-3 hurricane and was the third strongest hurricane to make landfall since 1969. In contrast, Paul followed a recurving track to reach the coastline as a weakening tropical depression. Strong wind shear, associated with a midlatitude trough, is found to be related to the intensity change. Examination of the official forecasts reveals that first inland positions were predicted several days before the actual landfall events. An assessment of the forecasts issued 1–3 days prior to landfall shows large track errors associated with some of the above tropical cyclones and this resulted in a westward bias. It is suggested that the track errors are due to an inadequate representation of the large-scale environment that steered the tropical cyclones.

On adaptive sliding mode control without switching gain overestimation

SUMMARYThis paper presents some further results on adaptive sliding mode control (ASMC) for a class of nonlinear systems with bounded uncertain parameters. Given a large initial tracking error, current ASMC design generally produces an unnecessarily large switching gain, consequently leading to a serious chattering problem or a large‐amplitude control jump for the continuous counterpart. To solve such an overadaptation problem, the switching gain adaptation mechanism is first analyzed in this paper, and the adaptation induced by the initial tracking error is suggested to be removed. Then, by exploiting the global sliding mode feature of time‐varying sliding mode control and integral sliding mode control, we present two effective methodologies for ASMC design. The proposed ASMC algorithms ensure that there is no overestimation of the switching gain and the system response is not slowed down when a small switching gain is generated. The validity of the proposed methods is verified by both theoretical analysis and simulation results. Copyright © 2012 John Wiley & Sons, Ltd.

A Bioinspired Neurodynamics-Based Approach to Tracking Control of Mobile Robots

Tracking control is a fundamentally important issue for robot and motor systems, where smooth velocity commands are desirable for safe and effective operation. In this paper, a novel biologically inspired tracking control approach to real-time navigation of a nonholonomic mobile robot is proposed by integrating a backstepping technique and a neurodynamics model. The tracking control algorithm is derived from the error dynamics analysis of the mobile robot and the stability analysis of the closed-loop control system. The stability of the robot control system and the convergence of tracking errors to zeros are guaranteed by a Lyapunov stability theory. Unlike some existing tracking control methods for mobile robots whose control velocities suffer from velocity jumps, the proposed neurodynamics-based approach is capable of generating smooth continuous robot control signals with zero initial velocities. In addition, it can deal with situations with a very large tracking error. The effectiveness and efficiency of the proposed neurodynamics-based tracking control of mobile robots are demonstrated by experimental and comparison studies.

Approximation-based adaptive control for a class of mobile robots with unknown skidding and slipping

An adaptive tracking control approach using function approximation technique is proposed for trajectory tracking of Type (2,0) wheeled mobile robots with unknown skidding and slipping in polar coordinates and at the dynamic level. The nonlinear disturbance observer (NDO) is used to estimate a nonlinear disturbance term including unknown skidding and slipping. The adaptive control system is designed via the function approximation technique using neural networks employed to compensate the NDO error. It is proved that all signals of the controlled closed-loop system are uniformly bounded and the point tracking errors converge to an adjustable neighborhood of the origin regardless of large initial tracking errors and unknown skidding and slipping. Simulation results are presented to validate the good tracking performance and robustness of the proposed control system against unknown skidding and slipping.

Feedforward signal prediction for accurate motion systems using digital filters

A positioning system that needs to accurately track a reference can benefit greatly from using feedforward. When using a force actuator, the feedforward needs to generate a force proportional to the reference acceleration, which can be measured by means of an accelerometer or can be created by double differentiation of the reference position.The positioning system’s response to the feedforward usually shows some delay, caused by calculation time of the digital control computer, the digital-to-analog converter that drives the actuator’s amplifier, and digital differentiation of the reference position. At higher frequencies, even a small delay causes a large tracking error. Prediction of the feedforward signal by one or two samples can reduce this error.This paper describes three methods to predict a feedforward signal over a time span of a few samples. Polynomial extrapolation of past data does not require knowledge of the signal’s properties. Sinusoidal extrapolation produces an exact prediction at a set of chosen design frequencies. Both filter types can be implemented as FIR filters. A particular form of frequency sampling filters, having digital zeros which are not each other’s conjugates, can also be used for prediction purposes. The complex filter output allows reconstruction of input signal properties and its prediction. The filters are compared with regard to their suitability for predicting feedforward signals.

Fuzzy Adaptive Tracking Control of Wheeled Mobile Robots With State-Dependent Kinematic and Dynamic Disturbances

Unlike most works based on pure nonholonomic constraint, this paper proposes a fuzzy adaptive tracking control method for wheeled mobile robots, where unknown slippage occurs and violates the nonholononomic constraint in the form of state-dependent kinematic and dynamic disturbances. These disturbances degrade tracking performance significantly and, therefore, should be compensated. To this end, the kinematics with state-dependent disturbances are rigorously derived based on the general form of slippage in the mobile robots, and fuzzy adaptive observers together with parameter adaptation laws are designed to estimate the state-dependent disturbances in both kinematics and dynamics. Because of the modular structure of the proposed method, it can be easily combined with the previous controllers based on the model with the pure nonholonomic constraint, such that the combination of the fuzzy adaptive observers with the previously proposed backstepping-like feedback linearization controller can guarantee the trajectory tracking errors to be globally ultimately bounded, even when the nonholonomic constraint is violated, and their ultimate bounds can be adjusted appropriately for various types of trajectories in the presence of large initial tracking errors and disturbances. Both the stability analysis and simulation results are provided to validate the proposed controller.

Output feedback based adaptive robust fault-tolerant control for a class of uncertain nonlinear systems

An adaptive robust approach for actuator fault-tolerant control of a class of uncertain nonlinear systems is proposed. The two chief ways in which the system performance can de- grade following an actuator-fault are undesirable transients and unacceptably large steady-state tracking errors. Adaptive control based schemes can achieve good final tracking accuracy in spite of change in system parameters following an actuator fault, and robust control based designs can achieve guaranteed transient response. However, neither adaptive control nor robust control based fault-tolerant designs can address both the issues associ- ated with actuator faults. In the present work, an adaptive robust fault-tolerant control scheme is claimed to solve both the problems, as it seamlessly integrates adaptive and robust control design techniques. Comparative simulation studies are performed using a nonlinear hypersonic aircraft model to show the effectiveness of the proposed scheme over a robust adaptive control based fault- tolerant scheme.

Multi-Hierarchical Model Predictive Control Based on K-Means Clustering Algorithms

Multi-model predictive control has become an effective method for nonlinear system. But the traditional multi-model has large tracking error compared with desired output when it is used to solve the operating condition with large scale transition. To solve this problem, this paper presents a new structure of multi-model called multi-hierarchical model. The new structure consists of many layers that each layer is constituted of different number of multiple models. In each layer, multi-model is obtained by partial least squares method after k-means clustering algorithm divides the global working spaces into desired parts. Because of this special structure, the models chose from different layers can deal with the operating condition changed with large scale. At the end of this paper, experiments are carried on the pH neutralization process which is a MIMO nonlinear system and the simulation results demonstrate that the multi-hierarchical model is superior to single-hierarchical model with smaller model tracking error faster convergence speed and better stability.

Lateral Control for UAVs using Sliding Mode Technique

AbstractThis paper presents sliding mode based lateral control for UAVs using a nonlinear sliding approach. The control is shown to perform well in different flight conditions including straight and turning flight and can recover gracefully from large track errors. Saturation constraints on the control input are met through the nonlinear sliding surface, while maintaining high performance for small track errors. Stability of the nonlinear sliding surface is proved using an appropriate Lyapunov function. The main contribution of this work is to develop a robust lateral control scheme that uses readily available sensor information and keeps the track error as small as possible without violating control constraints. In the proposed scheme the only information used in the control law is the lateral track error and the heading error angle. No information is required about the desired path/mission, which therefore can be changed online during run-time. This scheme is implemented on a high fidelity nonlinear 6-degrees-of-freedom (6-dof) simulation and different scenarios are simulated with large and small track errors in windy and calm conditions. Simulation results illustrate the robustness of the proposed scheme for straight and turning flight, in the presence of disturbances, both for large and small track errors. Furthermore it is shown that the saturation limits of the control input are not exceeded in all cases.

Adaptive tracking control for a class of wheeled mobile robots with unknown skidding and slipping

This study presents an adaptive tracking control approach for trajectory tracking of wheeled mobile robots with torque saturation in the presence of unknown skidding and slipping. The robot kinematics and dynamics are induced from the perturbed non-holonomic constraints. The adaptive control system using the kinematics transformed in polar coordinates is developed to compensate unknown skidding and slipping at the dynamic level of mobile robots with the input saturation. All signals of the controlled closed-loop system are uniformly bounded and the point tracking errors converge to an adjustable neighbourhood of the origin regardless of large initial tracking errors, input saturation and unknown skidding and slipping. Simulation results are provided to demonstrate the performance and stability of the proposed control scheme.

Adaptive trajectory control and friction compensation of a flexible-link robot

An adaptive trajectory-tracking controller is developed for a single flexible-link manipulator with presence of friction in the joint and parametric uncertainties. The distributed-parameter dynamic modeling approach is used to design the controller. To eliminate large steady-state tracking error, an adaptive friction compensation technique is proposed based on general static friction model. Reduction of effects of data corruption by noise is obtained using a filtering technique. The global asymptotic stability is guaranteed using the Lyapunov stability theorem. The position tracking performance and link vibration attenuation is verified through experimental results. It also shows that the steady-state joint error is significantly eliminated and the noise effect in the control signal is efficiently reduced.

Real-Time Tracking Error Estimation for Augmented Reality for Registration with Linecode Markers

Augmented reality tasks require a high-reliability tracking method. Large tracking error causes many problems during AR applications. Tracking error estimation should be integrated with them to improve the reliability of tracking methods. Although some tracking error estimation methods have been developed, they are not feasible to be integrated because of computational speed and accuracy. For this study, a tracking error estimation algorithm with screen error estimation based on the characteristic of linecode marker was applied. It can rapidly estimate tracking error. An evaluation experiment was conducted to compare the estimated tracking error and the actual measured tracking error. Results show that the algorithm is reliable and sufficiently fast to be used for real-time tracking error warning or tracking accuracy improvement methods.

Exchange-Traded Fund: Nature, Developments, and Implications

1. The AMEX provides market liquidity and continuous trading at or near current market prices for index shares. Continuous trading provides more flexibility in rebalancing portfolios. Prices are determined by supply and demand. Index shares may be traded in small lots and the trading strategies available to common stock are also available for index shares. 2. Most index shares transactions are executed on the AMEX, especially less than block size trades. Bid-ask spreads are not unreasonable, and brokerage commissions and fees can be reduced by online and/or discount brokers. But, index share trading costs favor buy-and-hold strategies. 3. Large investors may also directly purchase and redeem index shares packaged as minimum block-size creation/redemption units. Creation/redemption units are purchased/redeemed in exchange for stock portfolios that match specific benchmark indexes. But, there are purchase and redemption fees. 4. Investor exchanges of redemption units for in-kind baskets of stock are tax-free exchanges. ETFs do not sell stocks with potential capital gains to meet redemptions and there are no performance drags from holdings of cash assets. Investors may also unbundle portfolio shares received and sell them for any tax losses.5. AMEX trading and tax-free direct exchanges with continuous portfolio transparency facilitate arbitrage that maintains index share prices at or very near NAVs of underlying portfolios. Arbitrageurs buy index shares selling at discount to NAVs on the AMEX, directly exchange redemption units for underlying stock portfolios, and sell unbundled stocks on the AMEX for more than paid for index share redemption units. 6. ETFs are very tax efficient due to direct tax-free exchanges, portfolio transparency, index portfolios, and control over specific composition of underlying stock portfolios. Index portfolios are not actively managed, which minimizes turnover and realized capital gains. Shares of stock with largest unrealized capital gains are exchanged for redemption units to minimize realized capital gains. Shares with smallest unrealized capital gains are sold to meet changes in composition of benchmark indexes and to minimize realized capital gains. 7. Domestic ETFs are inherently less costly to manage than traditional domestic mutual funds. They have lower expense ratios than actively managed domestic mutual funds and also most index funds with the same benchmark indexes.8. ETFs and mutual funds provide instant diversification with broadly based portfolios or homemade portfolios with allocations of narrowly focused ETFs, such as foreign/domestic, specific country, investment style and/or industry sectors.9. ETFs provide access to benchmark indexes and global sectors not (yet) available from mutual funds. 10. Investors may practice cash management by temporarily sweeping cash inflows into index shares. ETFs Disadvantages1. Index share trading costs are higher than pure no-load mutual funds with zero shareholder transaction costs. This difference is increased by market timing and dollar cost averaging strategies that trade frequently, even given online and/or discount brokerage commissions and small bid-ask spreads. 2. Investor purchase and redemption of creation and redemption units are subject to fees, which are higher than for pure no-load mutual funds.3. ETF brokers generally provide less in the way of diversity and quality of shareholder services than mutual funds. 4. ETF index shares risk selling at discounts (also premiums) to NAVs of underlying stock portfolios, but arbitrage normally keeps them small. But, index shares can trade at significant discounts/premiums for extended periods, especially in small, less liquid international markets. HOLDRs have proven to have large discounts to NAV. 5. No sponsor of both EFTs and index mutual funds has yet matched the annual returns of the Vanguard 500 Index Fund. 6. ETFs often have large tracking errors in matching the performance of international small market benchmark indexes. These indexes do not provide required portfolio diversification and markets have low liquidity and high trading costs. Tracking error derives from use of statistical methods to approximate benchmark performance. These ETFs also have higher expense ratios and higher portfolio turnover and trading costs than comparable mutual funds. 7. Performance and liquidity of ETF shares have yet to be severely tested in major market declines. 8. The settlement period for index share trades is three days, but it is overnight for mutual fund redemptions.

Full constellation phase detector for carrier recovery in high-order QAM systems

A full constellation phase detector that improves carrier acquisition performance in high-order quadrature amplitude modulation (QAM) is proposed. The weighting function of the phase detector is mathematically derived, and simulated phase detector characteristics are presented for 256QAM. The results of an experimental evaluation are also reported, which show that the carrier recovery loop based on the proposed phase detector has a large frequency acquisition range and low phase tracking error in high-order QAM.

Stratification Approach for 3-D Euclidean Reconstruction of Nonrigid Objects From Uncalibrated Image Sequences

This paper addresses the problem of 3-D reconstruction of nonrigid objects from uncalibrated image sequences. Under the assumption of affine camera and that the nonrigid object is composed of a rigid part and a deformation part, we propose a stratification approach to recover the structure of nonrigid objects by first reconstructing the structure in affine space and then upgrading it to the Euclidean space. The novelty and main features of the method lies in several aspects. First, we propose a deformation weight constraint to the problem and prove the invariability between the recovered structure and shape bases under this constraint. The constraint was not observed by previous studies. Second, we propose a constrained power factorization algorithm to recover the deformation structure in affine space. The algorithm overcomes some limitations of a previous singular-value-decomposition-based method. It can even work with missing data in the tracking matrix. Third, we propose to separate the rigid features from the deformation ones in 3-D affine space, which makes the detection more accurate and robust. The stratification matrix is estimated from the rigid features, which may relax the influence of large tracking errors in the deformation part. Extensive experiments on synthetic data and real sequences validate the proposed method and show improvements over existing solutions.