Defu Lin

• Managing Director at Beijing Institute of Technology

This paper presents an autonomous aerial system specifically engineered for operation in challenging marine GNSS‐denied environments, aimed at transporting small cargo from a target vessel. In these environments, characterized by weakly textured sea surfaces with few feature points, chaotic deck oscillations due to waves, and significant wind gusts...

This paper presents an autonomous aerial system specifically engineered for operation in challenging marine GNSS-denied environments, aimed at transporting small cargo from a target vessel. In these environments, characterized by weakly textured sea surfaces with few feature points, chaotic deck oscillations due to waves, and significant wind gusts...

The global positioning system (GPS) has become an indispensable navigation method for field operations with unmanned surface vehicles (USVs) in marine environments. However, GPS may not always be available outdoors because it is vulnerable to natural interference and malicious jamming attacks. Thus, an alternative navigation system is required when...

The purpose of this paper is to introduce an unmanned aerial swarm control strategy that has been developed specifically for the MBZIRC 2024 competition inspection task, which requires the UAV swarm to search within a Global Navigation Satellite System (GNSS)-denied ocean space. The proposed approach utilizes control barrier functions (CBF) to enco...

Unmanned aerial vehicles (UAVs) are required to pass through multiple important waypoints as quickly as possible in courier delivery, enemy reconnaissance and other tasks to eventually reach the target position. There are two important problems to be solved in such tasks: constraining the trajectory to pass through intermediate waypoints and optimi...

The direct/aerodynamic force compound control can enhance the maneuverability and response characteristics of missiles, and the dynamic stabilization is the precondition of normal operation for rolling missiles. Aiming at the stability problem caused by the cross-coupling effect of rolling missiles employing direct/aerodynamic force compound contro...

Differential dynamic programming (DDP) is a well-recognized method for computational guidance due to its fast convergence characteristics. However, the original DDP requires a predefined final time and cannot handle nonlinear constraints in optimization. This prohibits the application of DDP to autonomous vehicles due to the heuristic nature of set...

Strategic resources affect national development and security at all times. Actual utilization of strategic resources is crucial. In recent years, strategic resources such as coal and mineral powder usually need to be stored in closed stockyards after mining due to environmental protection, concealment, and other reasons. The existing stockpiling in...

In this paper, we propose a safe and efficient online trajectory generation method for quadrotors. This algorithm combines the sample-based motion planning method with the time-constrained trajectory optimization method. Based on the linearized state-space model of the quadrotor, we use the ellipsoid heuristic to directly sample the map and conside...

Conventional multi-sensor multi-object tracking algorithms usually fuse local positions to construct the global situation. However, low-cost cameras that have been widely-used in small-scale UAVs only provide bearing angle measurement but not target positions, which prohibits the application of conventional tracking paradigms. We propose a solution...

With its fast and accurate position and attitude estimation, the feature-based lidar-inertial odometer is widely used for UAV navigation in GNSS-denied environments. However, the existing algorithms cannot accurately extract the required feature points in the spatial grid structure, resulting in reduced positioning accuracy. To solve this problem,...

This paper presents a power-based analysis through 3D Reynolds-averaged Navier–Stokes simulations for a typical transonic transport aircraft resented by the DLR-F6 model. Two configurations were employed in CFD simulations. The original F6 model geometry was defined as the wing body configuration, and a wake-filling actuator disc was added to the F...

This article focuses on the analysis of generalized control coupling effect of spinning guided projectiles. A concept of so-called equivalent dynamics is first proposed in this article to avoid nonlinearity and facilitate understanding of control coupling for spinning guided projectiles. First, the coupling induced by an arbitrary-order dynamic is...

With the continuous expansion of the application field of UAV intelligent systems to GNSS-denied environments, the existing navigation system can hardly meet low cost, high precision, and high robustness in such conditions. Most navigation systems used in GNSS-denied environments give up the connection between the map frame and the actual world fra...

Differential dynamic programming (DDP) is a well-recognized method for trajectory optimization due to its fast convergence characteristics. However, the original DDP requires a predefined final time and cannot handle nonlinear constraints in optimization. This prohibits the application of DDP for autonomous vehicles due to the heuristic nature of s...

Unmanned aerial vehicle (UAV)’s fault-control problem was studied in this paper, and data-driven fault-tolerant control scheme was developed for acceleration tracking control of UAV in order to cope with the uncertainties induced by aerodynamic damage. A linear UAV dynamic model was given with reasonable assumptions, and the acceleration tracking c...

This paper aims to establish an approach of power bookkeeping in a numerical study. To study the process of power conversion coursed in the flow field, the methodology employs a power-based analysis to quantify power terms. This approach is examined in a simulation of jet flow and then applied to the cases of an isolated actuator disc and an isolat...

This paper describes an autonomous navigation and control system for capturing the maneuvering drones. A vision-based navigation method seeks and detects the intruding drone, then, the target trajectory is predicted by fusing onboard vision and inertial-measurement resources. The target’s relative position, velocity and acceleration are also obtain...

Collaborative unmanned systems have emerged to meet our society’s wide-ranging grand challenges, with their advantages including high performance, efficiency, flexibility, and inherent resilience. Increasing levels of group/team autonomy have also been achieved due to the embodiment of artificial intelligence (AI). However, the current networked un...

With the increase of complexity of unmanned aerial vehicles (UAV) tasks, trajectory planning algorithms, tra�jectory tracking algorithms, and coordination methods are becoming more and more important in multi-UAV collaborative task research. Based on the centralized coordination architecture, this paper studies the cooper�ative time constraint prob...

This paper proposes a three-dimensional optimal terminal velocity control guidance for multicopter intercepting maneuvering drone with equal maneuverability level. We investigate a novel multi-rate extended Kalman filter-based approach to estimate target's velocity and acceleration by fusing the measurements of onboard machine vision algorithm, ele...

Landing on a moving platform is an essential requirement to achieve high-performance autonomous flight with various vehicles, including quadrotors. We propose an efficient and reliable autonomous landing system, based on model predictive control, which can accurately land in the presence of external disturbances. To detect and track the landing mar...

This paper investigates the transient aerodynamic interference of rotors imposed on fuselage for a quadcopter through Computational Fluid Dynamics (CFD) simulations. The numerical study of transi-ent effects due to rotor rotation is enabled by sliding mesh which defines the rotation domains encompass-ing rotor blades. The results show that the inte...

In aerial image object detection, how to efficiently detect different size objects in input images of different scales and obtain a unified multi-scale representation of the object is an important issue. Existing methods rarely consider the connection between multi-scale training and multi-scale inference, and do not well optimize the constraint of...

In this paper, a highly nonlinear trajectory optimization problem for reentry vehicles is rapidly solved by the proposed modified sequential convex programming (MSCP) method. A logarithm linearization approach is proposed to decouple the dynamics of high order and nonconvex path constraints of heat rate, dynamic pressure, and normal load. Next, the...

This paper copes with the controller design problem of a micro helicopter, which is a multivariable and strongly coupled nonlinear system. The state-space model near the hovering condition of pitch and roll channels is acquired by least-square system identification method, with flight test verification. Based on the identified model, model referenc...

This paper proposes a finite-time fault-tolerant trajectory tracking control for a quadrotor system against external disturbances, parametric uncertainties and actuator faults without the need of fault diagnosis mechanism. First, a finite-time fault-tolerant control based on a multivariable integral terminal sliding mode control (TSMC) is proposed...

Considering the scenario that the obstinate and difficult-repaired sensor and actuator failure always occurs during the spacecraft rendezvous guidance phase and may cause terrible performance, this paper studies the fault-tolerant guidance method and proposes a velocity-free guidance algorithm. Above guidance law is based on a dual-layer adaptive m...

This work investigates three‐dimensional accurate guidance problem in the presence of impact angle constraint, input saturation, autopilot lag, and external disturbance, and presents a robust adaptive guidance method for maneuvering targets. More specifically, based on integral Lyapunov control algorithm, a robust guidance law, which can drive both...

This work studies accurate interception problem for salvo-attack missions and proposes a robust guidance law in the presence of impact time and angle constraints. First, the dynamic model for planar homing endgame guidance is built. Different with conventional guidance dynamic model, this work takes the derivative with respect to range, rather than...

A novel approach to address the problem of integrated guidance and control(IGC) for a missile is studied in this paper. By taking target maneuver, aerodynamic uncertainty and fin servo dynamic uncertainty as external disturbances in the adaptive backstepping design procedure, the proposed controller requires no information on target maneuver and pr...

A novel observer‐controller framework algorithm based on barrier Lyapunov function and second‐order sliding mode control is presented, which can drive the first‐ and second‐order states of the typical second‐order dynamics subject to unknowns and uncertainties simultaneously converge to zero in finite time. The obtained results are applied in the d...

Object detection in aerial images is an important task for many applications such as reconnaissance, surveillance, search, and rescue. At present, convolution neural network-based aerial image object detection algorithms mainly focus on rotation invariance and scale invariance, but ignore an important characteristic of the aerial image that the ima...

In this paper, a novel approximate finite-time convergent guidance law for missiles is presented to accurately intercept maneuvering targets when the actuators cannot perform as well as usual. First, the governing equations are proposed according to the relationship between missile and target at engagement phase, and a typical nonlinear mathematic...

A composite adaptive control (CAC) that combines the benefits of direct and indirect adaptive controls has better parameter adaptation and control response. Multilayer neural networks (NNs) can be employed to enhance a model's representation capacity, but previous composite adaptive approaches cannot easily train the model due to its nonlinearities...

In this paper, a new optimal linear-quadratic guidance law with terminal acceleration constraints is proposed for intercepting maneuvering target. Because the angle of attack is approximately proportional to the normal acceleration for aerodynamic control missile, not only miss distance, but also terminal acceleration is required to converge to zer...

This work proposes a compound control which combines backstepping control and integral sliding mode (ISM) idea. The backstepping framework is adopted to guarantee nominal performance of the closed-loop system, while the use of ISM is to eliminate the adverse effect of perturbations such that nominal performance is recovered. To avoid the chattering...

This paper documents a novel nonsingular continuous guidance which can drive the line-of-sight (LOS) angular rate to converge to zero in finite time in the presence of impact angle constraints. More specifically, based on the second-order sliding mode control (SMC) theory, a second-order observer (2-OB) is presented to estimate the unknown target m...

This paper proposes a novel vision-based autonomous landing scheme for micro aerial vehicles with perturbations by using a gimbaled camera. There are no sensors available on the moving target in the task. The relative position between the drone and moving target is obtained by the camera mounted on a two-degree-of-freedom pan-tile platform. Firstly...

An on-line guidance algorithm is presented for high L/D hypersonic reentry vehicles using plane-symmetry bank-to-turn control method. The proposed guidance algorithm can generate a feasible trajectory at each guidance cycle during the reentry flight. In the longitudinal profile, height-range (H-R) and height-velocity (H-V) joint design method is pr...

With the upsurge in use of Unmanned Aerial Vehicles (UAVs), drone detection and pose estimation by using optical sensors becomes an important research subject in cooperative flight and low-altitude security. The existing technology only obtains the position of the target UAV based on object detection methods. To achieve better adaptability and enha...

Based on sliding mode control theory and back stepping design technique, this paper proposes a robust guidance law considering autopilot dynamics for maneuvering target interception in three-dimensional environment and terminal angle constraints. The proposed guidance law is summarized as an “observer–controller” system. More specifically, to estim...

Autonomous landing in complex environments is a critical problem for unmanned aerial vehicle autonomous control, and efficiently detecting landing identification mark in real‐world scenario is still challenging. Due to the limited computational power of airborne computing equipment, current target detection algorithms cannot meet the demand efficie...

This Correspondence proposes a new guidance law based on integral sliding mode control (ISMC) technique for maneuvering target interception with impact angle constraint. A time-varying function weighted line-of-sight (LOS) error dynamics, representing the nominal guidance performance, is introduced first. The proposed guidance law is derived by uti...

In this work, a new guidance law with a meaningful performance index is designed to satisfy terminal impact angle and impact time constraints based on optimal error dynamics, which can be used for salvo attacks or cooperative missions of multi-missile. The analytical solution of the proposed guidance law is a combination of trajectory shaping guida...

This paper aims to develop a new finite‐time convergent guidance law for intercepting maneuvering targets accounting for second‐order autopilot lag. The guidance law is applied to guarantee that the line of sight (LOS) angular rate converges to zero in finite time and results in a direct interception. The effect of autopilot dynamics can be compens...

A novel systematic technique for gain-scheduled control based on fixed-structure synthesis is adopted to design the aerial vehicle autopilot. The gain-scheduled design can be transformed into the multi-model control problem with both controller architecture and gain-scheduled architecture defined a priori. Hidden coupling terms naturally arise in t...

This paper investigates the problem of robust guidance law design for multiple unmanned aerial vehicles to achieve desired formation pattern for standoff tracking of an unknown ground moving target. The proposed guidance law consists of two main parts: relative range regulation and space angle control. For the first mission, a novel control law is...

This paper investigates the problem of finite-time velocity-free autonomous rendezvous for spacecraft in the presence of external disturbances during the terminal phase. First of all, to address the problem of lack of relative velocity measurement, a robust observer is proposed to estimate the unknown relative velocity information in a finite time....

The complex battlefield environment makes it difficult to intercept maneuvering targets for guided missiles. In this paper, a finite-time convergent (FTC) guidance law based on the second-order sliding mode (SOSM) control theory is proposed to achieve the requirements of stability, accuracy and robustness. More specifically, a second-order sliding...

The problem of salvo attack of multiple missiles without time-to-go estimation has been addressed by a two-stage guidance scheme in this correspondence. In the first stage, a simple decentralized control law is designed to provide desired initial conditions (target-missile relative range and velocity lead angle) for the latter stage. As for the sec...

This paper investigates the problem of salvo attack guidance law design for multiple missiles against a stationary target considering communication delay. The proposed guidance law requires no information on time-to-go and consists of two guidance stages. More specifically, a simple decentralized midcourse guidance law is proposed to provide desire...

To study the optimal impact-angle-control guidance problem with multiple terminal constraints, a generalized optimal impact-angle-control guidance law with terminal acceleration response constraint (GOIACGL-TARC) is proposed. In the deriving, a time-to-go −nth power weighted object function is adopted to derived the GOIACGL-TARC and a general expre...

The dynamic stability of coning motion for a radar homing rolling missile is studied in this paper, and the parasitic radome loop is considered and introduced into the guidance system of the radar homing rolling missile. A mathematical model with complex summation considering the parasitic radome loop is proposed, and the sufficient and necessary c...

A new method for estimating the nonparametric time-variant frequency response function (TV-FRF) and its variance of a hybrid time-varying system is proposed. By parameterizing the hybrid time variation using Legendre polynomials and Haar multiresolution wavelets, the TV-FRF identification problem is reduced to a time-invariant FRF estimation proble...

This paper presents a novel guidance law considering the seeker dynamics for manoeuvring targets to achieve short homing time guidance using the Lyapunov method. Based on linear and nonlinear kinematics, a Lyapunov-based guidance law is synthesised to compensate for the seeker’s first-order lag. The closed-form solution of the proposed guidance sys...

The dynamic stability of a radar homing rolling missile is extremely complex due to the interaction of the parasitic radome aberration feedback loop and the cross-coupling between the pitch and yaw, which are problems that have not been presented in previous studies. This paper presents mathematical models representative of the parasitic radome abe...

This paper presents a robust impact angle guidance law for maneuvering target interception with autopilot dynamics compensation based on a systematic backstepping control technique. Since the future course of action of the target, an independent entity, cannot be predicted beforehand, an adaptive-control approach is introduced in guidance law deriv...

This paper presents a new composite robust controller for a class of uncertain nonlinear systems through backstepping method and disturbance observer (DOB) technique. By designing a generalized disturbance observer (GDOB), the mismatched/matched uncertainty is estimated and compensated at each backstepping step. By virtue of the proposed GDOB, the...

A guidance problem for impact time and angle control applicable to cooperative attack is considered based on the sliding mode control. In order to satisfy the impact angle constraint, a line-of-sight rate polynomial function is introduced with four tuning parameters. And the time-to-go derivative with respect to a downrange orientation is derived t...

Anew cooperative guidance law with impact time and impact angle constraints is presented for multiple flight vehicles to against the stationary target. The proposed guidance law has two projection components: the one that along the line-of-sight (LOS) ensures that all flight vehicles reach the target simultaneously with impact time constraints, ano...

Accurate time-to-go estimation with large heading angle error is difficult for homing guidance laws, especially for the impact time control. Considering this, a new cooperative guidance law which requires no time-to-go estimation is investigated. First, the impact time control problem is transformed to the look angle command tracking problem. The l...

This paper proposes two algorithms (ATIRMM and ALPM) for estimating the time-varying behavior of single input single output (SISO) switching piecewise linear systems. Walsh basis functions are used to capture the non-smooth fast varying dynamics. The piecewise time-varying frequency response function (TV-FRF) is approximated by the sum of a series...

Non-strapdown seeker disturbances which involve counter-electromotive force, spring restoring torque, and friction torque can corrupt the seeker tracking accuracy and degrade the missile guidance performance. In this article, the effects of guidance parameters and disturbances on the guidance stability and the miss distance are analyzed. It is show...

This article documents a new output feedback guidance scheme for autonomous spacecraft rendezvous in the presence of actuator faults. The proposed approach is essentially a compound control methodology, which consists of higher order sliding mode observer and fast nonsingular terminal sliding mode technique. More specifically, the higher order slid...

This paper presents a new robust output feedback tracking control scheme for a class of higher-order uncertain systems. Since traditional nonlinear continuous predictive control requires accurate system model as well as full system states to synthesize a controller, a composite control methodology is adopted in the proposed scheme. Specifically, th...

A new homogenous observer-based finite-time convergent guidance law is proposed to intercept maneuvering targets without line-of-sight (LOS) angular rate information. The presented formulation is obtained via a combination of homogenous theory and second-order sliding mode (SOSM) method. Different from some existing observers, the proposed algorith...

Traditional guidance laws with range-to-go information or time-to-go estimation may not be implemented in passive homing missiles since passive seekers cannot measure relative range directly. A time-varying biased proportional guidance law, which only uses line-of-sight (LOS) rate and look angle information, is proposed to satisfy both impact angle...

This paper presents a new robust output feedback guidance scheme for autonomous spacecraft rendezvous during the final phase in elliptical orbit. The proposed approach is essentially a compound control method, which consists of an input-to-state stable (ISS) concept and high-gain observer (HGO) methodology. More specifically, the HGO is used to est...

This paper presents a robust observer-based finite-time convergent guidance law to intercept maneuvering targets. To avoid the undesired chattering phenomenon existing in classical sliding mode control, the adaptive super-twisting algorithm is first introduced to design a robust guidance law to drive the line-of-sight (LOS) angular rates to a small...

A new composite guidance law for intercepting manoeuvring targets with desired terminal line-of-sight (LOS) angle constraint is proposed in this paper. The presented guidance law is derived through generalized model predictive control (GMPC) augmented by a target manoeuvre estimator. More specifically, the target manoeuvre estimator is used to esti...

This paper considers the application of nonsingular terminal sliding mode (NTSM) control and extended state observer (ESO) to the circular orbital autonomous spacecraft rendezvous problem subject to model uncertainties and external disturbances. With the aid of Lyapunov stability criteria, we first develop a continuous NTSM-based robust control law...

This paper has proposed two continuous composite finite-time convergent guidance laws to intercept maneuvering targets in the presence of autopilot lag: one is for hit-to-kill and the other is for zeroing the line-of-sight (LOS) angular rate. More specifically, the nonlinear disturbance observer (NDOB) is used to estimate the lumped uncertainty onl...

In this paper, a robust continuous guidance law with terminal angle constraint for intercepting maneuvering targets in the presence of autopilot lag is proposed and its finite-time stability is proved. First, assuming that the missile autopilot is sufficiently fast, a composite fast nonsingular terminal sliding mode guidance (CFNTSMG) law is presen...

This paper presents a new longitudinal autopilot to address the finite-time tracking problem for uncertain agile missiles. The proposed autopilot is essentially a composite control scheme, which is obtained through the finite-time control methodology and the nonlinear disturbance observer (NDOB) approach. The key idea in this scheme is that the NDO...

In this paper, a new continuous impact angle constraint guidance law in the presence of actuator fault is presented based on sliding mode control theory. The robustness and finite-time convergence of the basic guidance law is established using Lyapunov stability theory. For actuator compensation, an additional term is augmented in the original guid...

This paper documents a new guidance law for tactical missiles to intercept maneuvering targets. By incorporating linear and fractional power nonlinear terms, a faster convergent and chatter-free acceleration command is derived. With the aid of Lyapunov stability criteria, we prove that the line-of-sight angular rate can converge to a small region a...

The paper documents a new continuous adaptive fast terminal sliding mode control approach for position tracking of robotic manipulators. Combining linear sliding mode and terminal sliding mode, a fast nonsingular terminal sliding mode manifold is presented. Considering the discontinuous property of the sign function, which is often used in traditio...

This paper has proposed a new composite robust guidance law to intercept maneuvering targets without line-of-sight (LOS) angular rate information. The presented guidance law is constructed through a combination of second-order sliding mode, higher-order sliding mode (HOSM) differentiator, and finite-time convergent disturbance observer (FTDOB). Mor...

In this paper, a new continuous robust impact angle constraint guidance law with finite-time convergence is proposed for intercepting maneuvering targets with unknown acceleration bounds. The presented guidance law is based on nonsingular terminal sliding mode (NTSM), smooth second-order sliding mode and finite-time convergence disturbance observer...

This paper considers the application of compound control method to high-performance autopilot design for aerodynamically controlled agile missiles. The control objective in this paper is to track a reference angle of attack command signal in the presence of external disturbance and aerodynamic coefficient uncertainty with desired performance. The e...