Tracking Subsystem Research Articles

Robust Time-Varying Tracking Control of Sandwich Nonlinear Systems with Sandwiched Saturation Nonlinearity

This paper addresses the output-tracking control problem for a class of nonlinear sandwich systems with external disturbances and model uncertainties. Sandwich systems are a special class of nonlinear systems in the cascade structure, which are made up of several distinct subsystems while the non-smooth nonlinear functions are sandwiched among their separate subsystems. This paper concentrates on the sandwich systems consisting of two arbitrary-order nonlinear cascaded subsystems, while the saturation nonlinearity is sandwiched between them. The robust control law is designed such that the output of the sandwich system tracks the desired time-varying reference signal despite the saturation occurrence. Due to the characteristics of the saturation function and also the existence of the external disturbances and model uncertainties, the considered problem is facing some serious challenges. To deal with these difficulties, the design procedure is divided into two phases. In the first phase, the second subsystem and the sandwiched saturation nonlinearity are considered. In this phase, by utilizing the backstepping approach, the desired input signal of the saturation function is designed. In the second phase, the control input of the first subsystem is designed based on the sliding mode technique in a way that the output of the first subsystem tracks the desired signal which is obtained in the first phase. Finally, to verify the effectiveness of the proposed method, it is applied to a practical sandwich system.

Tracking Attacks on Virtual Reality Systems

Virtual reality (VR) is a rapidly advancing technology with diverse applications. VR systems offer an immersive, life-like virtual experience by rendering interactive views on a head-mounted display. VR systems are vulnerable to various types of attacks, which could have dire consequences as they are designed to replace our perception of the physical world. However, there have been few studies on the security and integrity issues of the VR systems. We focus on the popular HTC Vive VR system and propose novel attack methods on blocking and manipulating its tracking subsystem. It is shown that simple attacks can jam or even manipulate the entire position and pose tracking process. Possible countermeasures are suggested to make VR systems safer and more secure.

Coordinated circumnavigation by multiple agents under directed topology

ABSTRACT This paper focuses on the coordinated circumnavigation problem for multiple agents with directed communication topology. All agents are required to be evenly spaced around a moving target, and orbit around it with prescribed radii and circular velocity. We divide the coordinated circumnavigation system into a cascaded system consisting of a standoff tracking subsystem and a spacing distribution subsystem. A tracking controller and an additional controller for the two subsystems are developed, respectively. The global uniform stability of the coordinated circumnavigation system is analysed using the cascaded control theory. The presented controllers render each individual agent circumnavigating the target with the desired requirements. More importantly, we show that the derived tracking controller is a general extension of existing controllers for single agent circumnavigation problem. Another feature of the proposed controllers is that the directed topology considered only needs to have a directed spanning tree. Furthermore, the proposed controllers take the velocity constraints into consideration, that is more rational for practical applications. Numerical simulations are provided to verify the effectiveness of the proposed methods.

Circular formation flight control for unmanned aerial vehicles with directed network and external disturbance

This paper proposes a new distributed formation flight protocol for unmanned aerial vehicles ( UAVs ) to perform coordinated circular tracking around a set of circles on a target sphere. Different from the previous results limited in bidirectional networks and disturbance-free motions, this paper handles the circular formation flight control problem with both directed network and spatiotemporal disturbance with the knowledge of its upper bound. Distinguishing from the design of a common Lyapunov function for bidirectional cases, we separately design the control for the circular tracking subsystem and the formation keeping subsystem with the circular tracking error as input. Then the whole control system is regarded as a cascade connection of these two subsystems, which is proved to be stable by input-to-state stability ( ISS ) theory. For the purpose of encountering the external disturbance, the backstepping technology is introduced to design the control inputs of each UAV pointing to North and Down along the special sphere ( say, the circular tracking control algorithm ) with the help of the switching function. Meanwhile, the distributed linear consensus protocol integrated with anther switching anti-interference item is developed to construct the control input of each UAV pointing to east along the special sphere ( say, the formation keeping control law ) for formation keeping. The validity of the proposed control law is proved both in the rigorous theory and through numerical simulations.

Stabilization of a stock‐loan valuation PDE process using differential flatness theory

AbstractThe article proposes flatness‐based control for stabilization of a stock‐loan valuation process that is described by a partial differential equation. By applying semi‐discretization and the finite differences method, the state‐space model of the stock loan has been obtained. It has been proven that the individual rows of this state‐space model are nonlinear ODEs which can be viewed as differentially flat subsystems. For the local subsystems, into which the stock‐loan PDE is decomposed, it becomes possible to apply boundary feedback control. The controller design proceeds by showing that the state‐space model of the stock loan PDE stands for a differentially flat system. Next, for each subsystem which is related to a nonlinear ODE, a virtual control input is computed, that can invert the subsystem's dynamics and can eliminate the subsystem's tracking error. From the last row of the state‐space description, the control input (boundary condition) that is actually applied to the stock loan PDE system is found. This control input contains recursively all virtual control inputs which were computed for the individual ODE subsystems associated with the previous rows of the state‐space description. Thus, by tracing the rows of the state‐space model backwards, at each iteration of the control algorithm, one can finally obtain the control input that should be applied to the stock loan PDE system so as to assure that all its state variables will converge to the desirable setpoints.By showing the feasibility of such a control method it is also proven that through selected modification of the PDE boundary conditions the value of the stock loan can be made to converge and stabilize at specific reference values.

ELOS-based path following control for underactuated surface vehicles with actuator dynamics

This paper presents an improved extended state observer-based line-of-sight (ELOS) guidance law for robust path following of underactuated surface vehicles without linear velocity measurement. First, two extended state observers are resorted to separately estimate the surge and sway linear velocities, such that the unmeasured side-slip angle can be indirectly calculated and accurately compensated in the line-of-sight guidance law. Especially, in this improved ELOS design no assumptions on constant or small side-slip angle are made. Second, a more high-order sliding mode surface is defined for the input of third-order heading tracking subsystem due to actuator dynamics. Subsequently, an adaptive fuzzy sliding mode control (AFSMC)-based tracking law is designed to robustly track the heading guidance angle without a prior on the vehicle’s complex hydrodynamics parameters. Finally, comparative simulation results are provided to show the performance of the designed path following controller, composed of ELOS and AFSMC for underactuated surface vehicles with actuator dynamics.

A Study of the Effectiveness of Message Content, Length, and Rate Control for Improving Map Accuracy in Automated Driving Systems

By providing information about the objects that are non-line of sight and/or beyond the detection range of the local sensors, inter-vehicle communication compensates for the limitations of vehicle tracking subsystem in automated driving systems that relies on on-board sensing devices. Tracking capability in such systems can further be improved by making optimal use of the communication channel through sharing of locally created map data instead of transmitting only beacon messages. Message length adaptation, together with transmit rate control can address the scalability issue inherent in the vehicular network. The content of the exchanged information is another important aspect that has significant impact on the map accuracy in cooperative driving systems. In this paper, we study different congestion and content control schemes for a communication architecture aimed at map sharing, and evaluate their performance in terms of a situational awareness metric, namely position tracking error. This paper determines that message content should be concentrated on mapped objects that are located farther away from the sender, but near the edge of local sensor range. This paper also finds that optimized combination of message length and transmit rate ensures the optimal channel utilization for cooperative vehicular communication, which in turn improves the situational awareness of the whole system.

Towards an immersive and safer driving experience using computer vision integrated with encoded vibro-tactile feedback

This paper claims to set up an immersive, responsive vehicle driving system and mechanism for an assisted driving technology. The purpose is to expand the sensory horizon of humans while driving and is motivated by absence of any such system in real world. The system can control and direct an assembly of electronic devices in real time, through usage of an image acquisition subsystem, an object-recognition and tracking algorithm and a haptic modelling subsystem working in-tandem with the user. The object tracking subsystem operates in real time to determine the current position of a vehicle in front by using a camera and continuously updates it in a live video feed, while also identifying and tracking the moving or stationary vehicle. The haptic system, which is integrated with the tracking system, has been programmed to warn the driver of the potential threats that moving/stationary vehicles may generate. All the subsystems are updated and synchronised with each other in real-time to produce a seamless and smooth transition between frames, facilitating a precise and immersive driving experience for anyone. The high accuracy and robustness of the proposed system makes it a versatile component, which can be integrated in variety of applications for enhancing a person's reality perception.

Line-of-sight guidance law for path following of amphibious hovercrafts with big and time-varying sideslip compensation

We present a novel nonlinear adaptive path following controller that compensates for drift forces though time-varying sideslip for amphibious hovercrafts. The sideslip arises and changes with time during path following when the hovercraft is subject to drift forces caused by ocean disturbances or control forces. The time-varying sideslip of hovercraft is estimated online and independent of the tracking error by a bounded-gain-forgetting (BGF) adaptive estimator. Then, a line-of-sight (LOS) guidance law based on BGF is designed to follow the desired path accurately in the presence of ocean disturbances, in which the parameter estimation and the tracking errors are both proven to be bounded. Furthermore, the closed-loop cascade BGF-LOS guidance system, which is composed of tracking subsystem and sideslip parameter estimation subsystem, is proven to be input-to-state stable (ISS) according to the stability theory of cascaded system. The proposed guidance law is intended for maneuvering of an amphibious hovercraft in the horizontal-plane to follow a predefined parametrized curve without time constraints. The theoretical results are supported by two cases studies of an amphibious hovercraft.

Mobile robot location algorithm based on image processing technology

To improve the reconfigurable micro mobile robot cluster system based on precision detection, a positioning and tracking system based on computer digital image processing technology was developed. The system consisted of three subsystems: image acquisition and preprocessing subsystem, rapid positioning subsystem based on robot marker recognition, and tracking subsystem based on position estimation. First, after studying the related algorithms in the subsystem, the threshold selection method of adaptive gray weight conversion was proposed for image preprocessing. Then, a fast positioning method based on marker recognition for miniature mobile robots was proposed. The selection of micro-robot markers and the basis for judging the selection of moments were given. A triangular projection positioning method was implemented, and related experimental results were given. Finally, the windowing scanning algorithm was optimized. According to the speed and direction of the robot, a tracking algorithm for position estimation was proposed. Through the simulation experiment, the effect of system positioning tracking and the system reference time in 0.270 s were given. The results showed that the system had high real-time performance.

Channel Modeling and Parameter Optimization for Hovering UAV-Based Free-Space Optical Links

Recently, the use of multi-rotor (MR) unmanned aerial vehicles (UAVs) has emerged as a promising solution for establishing flexible free-space optical communication links. We address, in this paper, the accurate channel modeling to assess the benefits of MR UAV-based deployment for such links. In particular, in the absence of active tracking subsystems, we derive statistical models for ground-to-UAV, UAV-to-UAV, and UAV-to-ground links over both Gamma–Gamma and log-normal atmospheric turbulence models. Unlike previous works on this topic, our proposed model considers the joint effect of atmospheric turbulence along with position and angle-of-arrival fluctuations. The high accuracy of the proposed analytical models is verified by comparing numerically solved and Monte Carlo simulation results in terms of link outage probability. We further discuss the impact of different transmitter/receiver parameters and their optimization in view of maximizing the link availability.

Statistical analysis and performance evaluation of optical array receivers for deep-space optical communications under random tracking errors

Telescope array receiver is a viable architecture for Earth-based reception in a deep-space optical communication system. In this paper, effects of random tracking errors on the performance of optical array receivers for an inter-planetary deep-space optical communications link between Earth and Mars is investigated. The paper has two major parts. In the first part, statistical analysis and mathematical modeling of the impact of tracking errors on general direct-detection optical communication receivers is presented. The analytical results show that tracking errors could severely degrade the performance of optical receivers; hence, these need to be compensated, especially in a deep-space link. In the second part, design and analysis of a closed-loop tracking subsystem for telescope array receivers operating in a deep-space link is presented. An end-to-end simulation platform for communication between Earth and Mars is implemented that incorporates direct-detection array receivers and the proposed tracking subsystems to alleviate the effects of random tracking errors. Extreme channel conditions, i.e., maximum distance, strong background noise and turbulence conditions are modeled to evaluate the performance bounds. Simulations results depict that in worst-case channel conditions, the proposed architecture mitigates the impact of tracking errors to be within reasonable limits. Comparison of achievable data rates show that in the presence of random tracking errors, replacement of a large telescope (10m diameter) with an array of relatively smaller-sized telescopes (i.e., 100, 1m telescopes) results in acceptable performance loss (i.e., <13%). Hence, performance degradation due to tracking errors does not pose a major limitation in employing array architecture in deep-space communication. The presented analysis further strengthens the viability of array architecture compared to a monolithic, large telescope for deep-space communications.

Approximate decoupling and output tracking for MIMO nonlinear systems with mismatched uncertainties via ADRC approach

In this paper, we consider output tracking for a class of MIMO nonlinear systems which are composed of coupled subsystems with vast mismatched uncertainties. First, all uncertainties influencing the performance of controlled outputs, which include internal unmodelled dynamics, external disturbances, and uncertain nonlinear interactions between subsystems, are refined into the total disturbance in the control channels of subsystems. The total disturbance is shown to be sufficiently reflected in the measured output of each subsystem so that it can be estimated in real time by an extended state observer (ESO) in terms of the measured outputs. Second, we decouple approximately the MIMO systems by cancelling the total disturbance based on ESO estimation so that each subsystem becomes approximately independent linear time invariant one without uncertainty and interaction with other subsystems. Finally, we design an ESO based output feedback for each subsystem separately to ensure that the closed-loop state is bounded, and the closed-loop output of each subsystem tracks practically a given reference signal. This is completely in comply with the spirit of active disturbance rejection control (ADRC). Some numerical simulations are presented to demonstrate the effectiveness of the proposed output feedback control scheme.

Robust adaptive boundary control of semilinear PDE systems using a dyadic controller

SummaryIn this paper, we describe a dyadic adaptive control framework for output tracking in a class of semilinear systems of partial differential equations with boundary actuation and unknown distributed nonlinearities. The dyadic adaptive control framework uses the linear terms in the system to split the plant into 2 virtual subsystems, one of which contains the nonlinearities, whereas the other contains the control input. Full‐plant‐state feedback is used to estimate the unmeasured individual states of the 2 subsystems as well as the nonlinearities. The control signal is designed to ensure that the controlled subsystem tracks a suitably modified reference signal. We prove the well posedness of the closed‐loop system rigorously and derive conditions for closed‐loop stability and robustness using finite‐gain stability theory.

Digital rate MEMS vibratory gyroscope modeling, tuning and simulation results

This paper is dealing with modeling, tuning and simulation of standing wave control and information processing algorithm for rate MEMS ring-type vibratory gyroscope. Standing wave control algorithm is presented in the form allowing transition from rate to rate integrating and to differential modes of MEMS gyro operation by simple switching command. It enables to implement triple mode MEMS gyro. Block diagrams of the standing wave control algorithm and resonance frequency tracking subsystem are presented. Drive and compensation signal phases tuning are described. Detailed explanations to the main operations which are used in information processing algorithm are given. Also, simulation results in case of measurement of a constant and variable angle rates are presented.

Initial result of the Chinese Deep Space Stations’ coordinates from Chinese domestic VLBI experiments

China’s Lunar Exploration Program (CLEP) prompted the design and construction of the globally distributed Chinese Deep Space Network (CDSN). This network consists of Jiamusi and Kashi stations in China, and Zapala station in Argentina. However, the positions of Jiamusi and Kashi are not accurate enough for future Chinese deep space missions, and geodetic Very Long Baseline Interferometry (VLBI) is the most effective way to determine their positions. Since the CDSN stations are equipped with narrow-band receivers, they cannot participate in current international VLBI sessions in which wide-band frequencies are utilized. Thus a cooperative geodetic program of the CDSN and Chinese VLBI Network (CVN, the VLBI tracking subsystem of the CLEP) was initiated to determine their positions, in which specially designed frequencies can be utilized, and some CVN stations can act as position reference stations owing to their precise positions from long-term international VLBI observations. Primary results have been obtained from the CDSN–CVN combined domestic VLBI experiments from September 28, 2014, through December 10, 2015. The positions of Jiamusi and Kashi are determined to be better than 10-mm precision in the X, Y, and Z directions, which are improved by a factor of approximately 20 over their a priori values.

Noise adaptive fading Kalman filter for free-space laser communication beacon tracking.

We proposed a prediction algorithm for laser communication pointing, acquisition, and tracking (PAT) subsystems in order to further improve PAT accuracy and reduce the effect of processing delay. In terms of this prediction algorithm, a fading Kalman filter is employed, with the observation noise obtained by the gray value distribution of the laser images. Moreover, to better fit the dynamics of a laser target, the two-stage dynamic model has been chosen as the state transition model for Kalman filtering. In addition, the two-stage dynamic model has been modified by accommodating its form to a change of time lag, thereby compensating the effect of time delay. A series of horizontal path (17 km) experiments under different atmospheric conditions were conducted in the fields. According to the experimental results, the algorithm we proposed could effectively reduce the tracking error and improve pointing accuracy.

Finite-time robust H ∞ control for high-speed underwater vehicles subject to parametric uncertainties and disturbances

Traditional underwater vehicles are limited in speed due to dramatic friction drag on the hull. Supercavitating vehicles exploit supercavitation as a means to reduce drag and increase their underwater speed. Compared with fully wetted vehicles, the nonlinearities in modeling of cavitator, fin, and in particular, nonlinear planing force make the control design of supercavitating vehicles more challenging. By combining cascaded design and backstepping approach, this paper reformulates the supercavitating vehicle model into a novel cascade model with two error tracking subsystems. Based on linear matrix inequalities (LMIs) and by introducing the sector conditions of the nonlinear characteristics of planing force, a new finite-time robust \(H_{\infty }\) control scheme is proposed for the error tracking subsystems which ensures that the closed-loop system is finite-time bounded and the effect of the disturbance input on the controlled output is reduced to a prescribed level. A sufficient condition is presented for the solvability of the design problem, which is further reduced to a feasibility problem of a set of LMIs. Simulations have been conducted for both initial and tracking responses to evaluate the performance and robustness of the proposed \(H_{\infty }\) controller for all admissible uncertainties and the disturbance inputs.

Application of binary descriptors to multiple face tracking in video surveillance systems

Subject of Research. The paper deals with the problem of multiple face tracking in a video stream. The primary application of the implemented tracking system is the automatic video surveillance. The particular operating conditions of surveillance cameras are taken into account in order to increase the efficiency of the system in comparison to existing general-purpose analogs. Method. The developed system is comprised of two subsystems: detector and tracker. The tracking subsystem does not depend on the detector, and thus various face detection methods can be used. Furthermore, only a small portion of frames is processed by the detector in this structure, substantially improving the operation rate. The tracking algorithm is based on BRIEF binary descriptors that are computed very efficiently on modern processor architectures. Main Results. The system is implemented in C++ and the experiments on the processing rate and quality evaluation are carried out. MOTA and MOTP metrics are used for tracking quality measurement. The experiments demonstrated the four-fold processing rate gain in comparison to the baseline implementation that processes every video frame with the detector. The tracking quality is on the adequate level when compared to the baseline. Practical Relevance. The developed system can be used with various face detectors (including slow ones) to create a fully functional high-speed multiple face tracking solution. The algorithm is easy to implement and optimize, so it may be applied not only in full-scale video surveillance systems, but also in embedded solutions integrated directly into cameras.

ATLAS Transition Radiation Tracker (TRT): Straw tubes for tracking and particle identification at the Large Hadron Collider

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three inner detector tracking subsystems and consists of ∼300,000 thin-walled drift tubes (“straw tubes”) that are 4mm in diameter. The TRT system provides ∼30 space points with ∼130micron resolution for charged tracks with |η|<2 and pT>0.5GeV/c. The TRT also provides electron identification capability by detecting transition radiation (TR) X-ray photons in an Xe-based working gas mixture.Compared to Run 1, the LHC beams now provide a higher centre of mass energy (13TeV), more bunches with a reduced spacing (25ns), and more particles in each bunch leading to very challenging, higher occupancies in the TRT. Significant modifications of the TRT detector have been made for LHC Run 2 mainly to improve response to the expected much higher rate of hits and to mitigate leaks of the Xe-based active gas mixture. The higher rates required changes to the data acquisition system and introduction of validity gate to reject out-of-time hits. Many gas leaks were repaired and the gas system was modified to use a cheaper Ar-based gas mixture in some channels. A likelihood method was introduced to optimise the TRT electron identification.