Path Following Research Articles

PECLOS path-following control of underactuated AUV with multiple disturbances and input constraints

This paper presents a new position error-constrained line-of-sight (PECLOS) path-following (PF) control strategy for an underactuated AUV under multiple disturbances and input constraints. Firstly, considering that many previous studies ignored the influence of stochastic noises, which may degrade the designed controller performance or even lead to instability in practical applications, the multiple disturbances are divided into two categories based on their features, i.e., the slowly time-varying deterministic disturbances and the stochastic noises. On this basis, the time-varying deterministic disturbances are further treated as a single equivalent disturbance and a linear stochastic differential model of underactuated AUV is established by augmenting the equivalent disturbance as an extended state. Secondly, a novel PF control strategy is proposed based on an extended state based Kalman-Bucy filter (ESKBF) and auxiliary dynamic compensators. The PECLOS guidance law is established to maintain the PF errors within the specified time-varying bounds, the ESKBF technology is utilized to estimate and compensate for the equivalent disturbances under the stochastic noises, and the auxiliary dynamic compensators are adopted to overcome the input constraints. Eventually, the stability of the overall closed-loop system is verified. Simulation and comparative analysis are presented to demonstrate the enhanced performance of the presented controller.

DOPH∞-based path-following control for underactuated marine vehicles with multiple disturbances and constraints

This paper presents a new robust path-following (PF) control method for underactuated marine vehicles with multiple disturbances and constraints. To improve the control performance and reduce the conservativeness of many PF control strategies described in the previous literature, which treated the multiple disturbances of the underactuated marine vehicle as a single equivalent disturbance, the multiple disturbances are categorized into two types according to their characteristics in this paper, i.e., the slowly varying disturbance and the H2-norm bounded disturbance. Then, a composite controller combining Disturbance-Observer-based control with H∞ control, which can be abbreviated as DOPH∞-based controller, is constructed for the control model. A disturbance observer is designed for estimating and eliminating the slowly varying disturbance, and the H∞ theory is used to attenuate the H2-norm bounded disturbance. Moreover, to improve the practicability of the control method in engineering applications, the virtual yaw angular velocity constraint and the actuator constraints are considered, and the auxiliary dynamic compensators are used to compensate for them. Finally, the closed-loop stability of the whole system is guaranteed. Simulations and comparative analyses are presented to demonstrate the effectiveness and robustness of the presented strategy.

Real-Time Predictive Control of Path Following to Stabilize Autonomous Electric Vehicles Under Extreme Drive Conditions

A novel real-time predictive control strategy is proposed for path following (PF) and vehicle stability of autonomous electric vehicles under extreme drive conditions. The investigated vehicle configuration is a distributed drive electric vehicle, which allows to independently control the torques of each in-wheel motor (IWM) for superior stability, but bringing control complexities. The control-oriented model is established by the Magic Formula tire function and the single-track vehicle model. For PF and direct yaw moment control, the nonlinear model predictive control (NMPC) strategy is developed to minimize PF tracking error and stabilize vehicle, outputting front tires’ lateral force and external yaw moment. To mitigate the calculation burdens, the continuation/general minimal residual algorithm is proposed for real-time optimization in NMPC. The relaxation function method is adopted to handle the inequality constraints. To prevent vehicle instability and improve steering capacity, the lateral velocity differential of the vehicle is considered in phase plane analysis, and the novel stable bounds of lateral forces are developed and online applied in the proposed NMPC controller. Additionally, the Lyapunov-based constraint is proposed to guarantee the closed-loop stability for the PF issue, and sufficient conditions regarding recursive feasibility and closed-loop stability are provided analytically. The target lateral force is transformed as front steering angle command by the inversive tire model, and the external yaw moment and total traction torque are distributed as the torque commands of IWMs by optimization. The validations prove the effectiveness of the proposed strategy in improved steering capacity, desirable PF effects, vehicle stabilization, and real-time applicability.

Security Optimization for an AF MIMO Two-Way Relay-Assisted Cognitive Radio Nonorthogonal Multiple Access Networks With SWIPT

This paper investigates the physical layer security issue in an amplify-and-forward (AF) multi-input multi-output (MIMO) two-way relay assisted cognitive radio (CR) nonorthogonal multiple access (NOMA) network, where the simultaneous wireless information and power transfer (SWIPT) technology is employed to improve network energy efficiency. We consider the scenario that a pair of primary users and two pairs of secondary users (SUs) exchange information via a MIMO two-way relay, where the edge SU of each SU pair is untrusted and tries to wiretap the central SU’s information. For ensuring security, we aim to maximize the sum achievable secrecy rate (SASR) by jointly optimizing the power allocation at all users, power splitting factor and relay beamforming subject to the quality of service (QoS), energy harvesting and transmit power constraints. The formulated optimization problem is highly nonconvex due to coupling variables, thus it is challenging to solve. An effective path-following (PF)-based algorithm is proposed, which is proven to converge to a stationary point. Theoretical and simulation results show that the proposed PF-based algorithm has lower complexity than the state-of-art algorithm. To further reduce complexity, we proposed a zero-forcing (ZF)-based scheme. Numerical simulations show that the proposed PF-based algorithm achieves the same SASR as the state-of-art algorithm with moderate complexity, while the proposed ZF-based scheme strikes a good balance between performance and complexity.

3D path-following control of robotic penguin: an ETFLMPC approach

Path-following (PF) control is a critical technique in various underwater scenarios. This paper investigates the 3D path-following control problem of a robotic penguin propelled by median and paired fin (MPF), in which an event-triggered fuzzy linear model predictive control (ETFLMPC) method is presented. According to the discrete linear time-varying model, the LMPC controller based on line-of-sight (LOS) guidance and linear extended state observer (LESO) is further developed. Furthermore, using the appropriate back propagation neural network (BPNN) and fuzzy rules, the thrust is estimated, while the yaw moment is transformed into a controllable offset feathering angle of the pectoral fins. Then, an event-triggered condition is designed for reducing optimization frequency with strict feasibility and stability proof. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed control algorithm. Notably, this work contributes to the constrained underactuated 3D PF control issue of an MPF-propelled robotic penguin which has been rarely explored.

Associations entre les temps d’écran et les habitudes de sommeil chez des jeunes collégiens

BackgroundScreen media usage has become increasingly commonplace in daily life with children initiating themselves to screen media at an early age. Given the high prevalence of screen viewing among children worldwide, its impact on children's health has become a cause for concern. Unfortunately, little information on the independent association between sleep habits and screen time in French children is currently available. The main aim of this study was to assess possible relationships between screen time and sleep habits (quality, duration, etc.) among young middle school students in France. MethodsA total of 448 (55 % girls) 11-to-12-year-olds from 5 schools were included. Body weight and height were measured according to standard procedures and BMI percentiles were determined based on international reference values. Sleep parameters were obtained by sleep diaries and visual estimations. A sleep diary was maintained for one week to record sleeping and waking times and related information. Information on lifestyle habits (sedentary behaviours, physical activity, and dietary intake) was obtained via standardised questionnaires. ResultsParticipants were 11.5 (±0.4) years of age. From total sample, 25.5 % reported screen time ≥2hours/d during school days and 62.7 % during school-free days. High screen time was associated with significantly poorer sleep habits and these results remained valid after adjustment for several confounding factors (body mass index, sex, center and parental level of educational attainment) (P<0.05). ConclusionThis study highlights an association between longer screen time and shorter sleep duration in French middle school students aged 11 to 12 years. Preventive measures on use of and exposure to screens are called for. Further studies are necessary to confirm our findings.

Late Chronotype is Associated with Adolescent Asthma: Assessment Using the Korean-Version MCTQ.

Objectives: In the study, we explored whether sleep chronotypes are associated with asthma in adolescents. Methods: We analyzed 24,655 physician-diagnosed adolescent asthmatic patients and 253,775 non-asthmatic adolescent patients from the Korea Youth Risk Behavior Web-based Survey (KYRBWS). Socioeconomic factors, health behaviors factors, psychological factors, and sleep parameters were assessed using the Munich Chronotype Questionnaire (MCTQ). Logistic regression after adjusting for multiple confounders was used to explore the association between sleep chronotype and asthma. Results: The asthmatic adolescent group slept less (≤5 h: 24.3% vs. 23.2%) than the non-asthmatic adolescent group. Mean sleep duration (430.6 ± 95.6 vs. 433.5 ± 93.6 min), midpoint of sleep on school-free days (MSF; 255.9 ± 75.9 vs. 258.3 ± 73.6 min), midpoint of sleep on school days (MSW; 199.1 ± 49.1 vs. 200.1 ± 48.4 min), sleep duration on school days (SDW; 398.2 ± 98.1 vs. 400.2 ± 96.8 min), and sleep duration on school-free days (SDF; 511.8 ± 151.9 vs. 516.7 ± 147.2 min) were significantly lower, sleep satisfaction was significantly poorer (low sleep satisfaction: 41.3% vs. 37.5%), and late chronotype was significantly higher in the asthmatic adolescent (21.1% vs. 20.0%). After adjusting for multiple confounders, late chronotype was significantly associated with an increased frequency of adolescent asthma (OR 1.05; 95% CI 1.01–1.09) compared to intermediate chronotypes. Conclusions: Although our study shows a very modest association (OR of 1.05 in the fully adjusted model), we show that the late sleep chronotype is associated with asthma in adolescents in South Korea.

Exposure to electronic devices and sleep quality in adolescents: a matter of type, duration, and timing

ObjectivesThe objective was to describe (1) the type, (2) the amount of use, and (3) the time of usage of electronic devices, for school days and weekends, as well as its impact on adolescents' sleep quality. DesignA cross-sectional study using hierarchical regressions accounting for confounding sleep-related variables was used. SettingThe participants were from six public schools in Porto Alegre, Brazil. ParticipantsThe participants included 177 students of both sexes aged between 11 and 18 years. MeasurementsAn electronic usage diary assessed the span of time during which the electronic device was used (separated by “TV and computer monitors”, “tablets, e-readers and portable video games,” and “cell phones”) for school days and weekends. The Munich Chronotype Questionnaire was used to assess sleep duration, midpoint of sleep, and social jetlag. Sleep quality was assessed using the Pittsburgh Sleep Quality Index. ResultsGreater nighttime use and last time of use of cell phones at night are associated with worse sleep quality in univariate analyses. A hierarchical regression model shows that poor sleep quality associates with shorter sleep duration on school days and with a delayed midpoint of sleep on weekends. Electronic device use did not reach statistical significance in the regression model with confounding factors. ConclusionsAdequate sleep duration is imperative to maintain a good sleep quality on school days, independently of the use of cell phones. It is important to underpin the need for evaluation of sleep phase and chronotype in future research on the topic aiming to elucidate its relationship with electronic use on school-free days.

Robust Motion Control of an Underactuated Hovercraft

In this paper, we address the tasks of trajectory tracking (TT) and path following (PF) for a hovercraft vehicle in the presence of uncertain parameters and unknown external disturbances. Building on the backstepping technique, the proposed TT (PF) control laws are able to drive a hovercraft toward and stay within a neighborhood of a reference trajectory (path), achieving global practical stability. Moreover, the devised control strategies also guarantee that the actuations remain bounded with respect to the position error. The controller is made robust to constant external disturbances and uncertain model parameters by the introduction of dynamic estimators for the disturbance and friction coefficients. A projection operator is used to ensure the estimates remain within prescribed bounds and are sufficiently smooth to be backstepped. In order to validate the efficacy and performance of the proposed controllers, we present and analyze both simulation and experimental results.

Low‐rank path‐following algorithm for 3D similarity registration

To address the 3D point matching problem where the pose difference between two point sets is unknown, the authors propose a path following (PF)–based algorithm. This method works by reducing the objective function of robust point matching (RPM) algorithm to a function of point correspondence variable and then using PF for optimisation. By using the 3D similarity transformation which has few parameters, authors’ method needs no regularisation on transformation and, therefore, can handle the case when the pose difference between two point sets is unknown. The authors also propose a novel convex term for use in the PF algorithm which is based on the low‐rank nature of authors’ objective function and leads to a PF algorithm which converges quickly. Experimental results demonstrated better robustness of the proposed method over state‐of‐the‐art methods and authors’ method is also efficient.

Switching LOS guidance with speed allocation and vertical course control for path-following of unmanned underwater vehicles under ocean current disturbances

This paper presents an application and stability result of a modified line-of-sight (LOS) guidance law for 3-D path-following (PF) of an unmanned underactuated underwater vehicle subject to environmental disturbances. The PF problem is solved using a revised relative system model with an improved FLOW frame and a complete model of ocean current/wave disturbances. The PF approach uses course control and speed allocation, which is the problem of allocating the desired inertial total speed into desired BODY velocities including current/wave velocities. The definitions of track-errors in the general PF problem have been accurately illustrated in the inertial frame. The course control strategy, defined by incorporating the slip angles into the desired heading angles, has been extended to vertical plane with the new definition of vertical-slip. Stability results include local exponential stability (LES) of the enclosure-based LOS (ELOS) and semi-global exponential stability (SGES) of the modified LOS guidance laws. The 3-D LOS vector is tracked simultaneously in both planes using a planar speed assignment strategy in 4-DOF for a coupled 3-D tracking. Simulation results show robust PF performance of a sway-underactuated AUV in course control in the presence of significant ocean current disturbances and measurement noises. The effectiveness of simple course control and speed allocation in disturbance rejection has also been illustrated.

Path-Following Control of an AUV: A Multiobjective Model Predictive Control Approach

The path-following (PF) problem of an autonomous underwater vehicle (AUV) is studied, in which the path convergence is viewed as the main task while the speed profile is also taken into consideration as a secondary task. To accommodate the prioritized PF tasks, a novel multiobjective model predictive control (MPC) (MOMPC) framework is developed. Two methods, namely, weighted sum (WS) and lexicographic ordering, are investigated for solving the MOMPC PF problem. A logistic function is proposed for the WS method in an attempt to automatically select the appropriate weights. The Pontryagin minimum principle is subsequently applied for the WS-MOMPC implementation. The implicit relation between the two methods is shown, and the convergence of the solution with the MOMPC PF control algorithms is analyzed. Simulation studies on the Saab SeaEye Falcon AUV demonstrate the effectiveness of the proposed MOMPC PF control.

Gender influences physical activity changes during adolescence: The HELENA study

We compared differences in physical activity (PA) between pre/mid-pubertal and post-pubertal participants according to gender. The study included a total of 1842 healthy participants aged 12.5-17.4 years, who participated in the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) study. Participants wore a uniaxial accelerometer (ActiGraph© GT1M, Pensacola, FL, USA) attached to their lower back for seven consecutive days to measure PA. Pubertal status was assessed by physical examination and the population was classified as pre/mid-pubertal (Tanner stages 1-3) or post-pubertal (Tanner stages 4-5). PA was compared between these groups according to gender during the whole week, on school-free days and on school days, before and after school, and during lessons and recesses. When comparing the pre/mid-pubertal group with the post-pubertal group, girls' total PA did not differ between groups. However, a slight difference was observed in boys, among whom PA on school-free days showed a difference of 17.6% between the pre/mid-pubertal group and the post-pubertal group (679 kcounts vs 564 kcounts, respectively; P=0.0007) and 20% (162 kcount vs 135 kcounts; P=0.006) for school recess. There was no difference among girls. A reduced level of PA in the post-pubertal groups was only observed in boys during non-organized times such as on school-free days and during school recesses, with a moderate impact on total PA.

Awareness of wearing an accelerometer does not affect physical activity in youth

BackgroundThis study aimed to investigate whether awareness of being monitored by an accelerometer has an effect on physical activity in young people.MethodsEighty healthy participants aged 10–18 years were randomized between blinded and nonblinded groups. The blinded participants were informed that we were testing the reliability of a new device for body posture assessment and these participants did not receive any information about physical activity. In contrast, the nonblinded participants were informed that the device was an accelerometer that assessed physical activity levels and patterns. The participants were instructed to wear the accelerometer for 4 consecutive days (2 school days and 2 school-free days).ResultsMissing data led to the exclusion of 2 participants assigned to the blinded group. When data from the blinded group were compared with these from the nonblinded group, no differences were found in the duration of any of the following items: (i) wearing the accelerometer, (ii) total physical activity, (iii) sedentary activity, and (iv) moderate-to-vigorous activity.ConclusionsOur study shows that the awareness of wearing an accelerometer has no influence on physical activity patterns in young people. This study improves the understanding of physical activity assessment and underlines the objectivity of this method.Trial registrationNCT02844101 (retrospectively registered at July 13th 2016).

Coordinated Path-Following in the Presence of Communication Losses and Time Delays

This paper addresses the problem of steering a group of vehicles along given spatial paths while holding a desired time-varying geometrical formation pattern. The solution to this problem, henceforth referred to as the coordinated path-following (CPF) problem, unfolds in two basic steps. First, a path-following (PF) control law is designed to drive each vehicle to its assigned path, with a nominal speed profile that may be path dependent. This is done by making each vehicle approach a virtual target that moves along the path according to a conveniently defined dynamic law. In the second step, the speeds of the virtual targets (also called coordination states) are adjusted about their nominal values so as to synchronize their positions and achieve, indirectly, vehicle coordination. In the problem formulation, it is explicitly considered that each vehicle transmits its coordination state to a subset of the other vehicles only, as determined by the communications topology adopted. It is shown that the system that is obtained by putting together the PF and coordination subsystems can be naturally viewed as either the feedback or the cascade connection of the latter two. Using this fact and recent results from nonlinear systems and graph theory, conditions are derived under which the PF and the coordination errors are driven to a neighborhood of zero in the presence of communication losses and time delays. Two different situations are considered. The first captures the case where the communication graph is alternately connected and disconnected (brief connectivity losses). The second reflects an operational scenario where the union of the communication graphs over uniform intervals of time remains connected (uniformly connected in mean). To better root the paper in a nontrivial design example, a CPF algorithm is derived for multiple underactuated autonomous underwater vehicles (AUVs). Simulation results are presented and discussed.

A comparison of some global path-following methods, I.

There are two different practical ways of global path-following (PF) on potential energy surfaces (PESs) of molecular reactions: (i) the Elber–Karplus (EK) method (and its improvements), and (ii) the family of DDRP methods. The early versions of the methods under (i) are based on minimizing a functional of the entire path and applying penalty functions as constraints, and are evaluated only for molecular mechanical (MM) PESs. The first true improvement in the EK sequels is the method of Chiu et al. who—instead of using penalty functions—introduce a redistribution of the grid points to substitute the constraints employed in former versions of the EK method, and perform PF on quantum mechanical (QM) PESs. In the present paper the mathematical foundations and the performances of the above methods have been compared. The superiority of the DDRP method in accuracy and stability over the other methods has been verified and tested by a difficult mathematical function simulating the conformational change in the catechol molecule.