Guidance laws based on a conventional sliding mode ensures only asymptotic convergence. However, convergence to the desired impact angle within a finite time is important in most practical guidance applications. These finite time convergent guidance laws suffer from singularity leading to control saturation. In this paper, guidance laws to intercept targets at a desired impact angle, from any initial heading angle, without exhibiting any singularity, are presented. The desired impact angle, which is defined in terms of a desired line-of-sight angle, is achieved in finite time by selecting the interceptor's lateral acceleration to enforce nonsingular terminal sliding mode on a switching surface designed using nonlinear engagement dynamics. Numerical simulation results are presented to validate the proposed guidance laws for different initial engagement geometries and impact angles. Although the guidance laws are designed for constant speed interceptors, its robustness against the time-varying speed of interceptors is also evaluated through extensive simulation results.

Nonsingular Terminal Sliding Mode Guidance with Impact Angle Constraints

Sense and avoid technologies with applications to unmanned aircraft systems: Review and prospects

A new and practical terminal guidance law is presented for impact angle control for two-dimensional active homing engagement scenarios. Impact angle control is required to enhance terminal effectiveness of antitank and antiship missile systems in particular. The proposed guidance law is developed to cope with missile velocity reduction due to aerodynamic drag and target maneuver. In actual applications, the proposed guidance law is combined in cascade with a target tracking filter under the certainty equivalence principle. The proposed guidance law in conjunction with the target tracking filter is shown to be effective in antiship active homing engagement scenarios by a series of Monte Carlo simulation runs.

Impact angle control for planar engagements

This paper presents a complete review of computer vision algorithms and vision-based intelligent applications, that are developed in the field of the Unmanned Aerial Vehicles (UAVs) in the latest decade. During this time, the evolution of relevant technologies for UAVs; such as component miniaturization, the increase of computational capabilities, and the evolution of computer vision techniques have allowed an important advance in the development of UAVs technologies and applications. Particularly, computer vision technologies integrated in UAVs allow to develop cutting-edge technologies to cope with aerial perception difficulties; such as visual navigation algorithms, obstacle detection and avoidance and aerial decision-making. All these expert technologies have developed a wide spectrum of application for UAVs, beyond the classic military and defense purposes. Unmanned Aerial Vehicles and Computer Vision are common topics in expert systems, so thanks to the recent advances in perception technologies, modern intelligent applications are developed to enhance autonomous UAV positioning, or automatic algorithms to avoid aerial collisions, among others. Then, the presented survey is based on artificial perception applications that represent important advances in the latest years in the expert system field related to the Unmanned Aerial Vehicles. In this paper, the most significant advances in this field are presented, able to solve fundamental technical limitations; such as visual odometry, obstacle detection, mapping and localization, et cetera. Besides, they have been analyzed based on their capabilities and potential utility. Moreover, the applications and UAVs are divided and categorized according to different criteria.

Survey of computer vision algorithms and applications for unmanned aerial vehicles

In this paper, we argue that the modularity, reusability and complexity of Unmanned Aerial Vehicle (UAV) guidance and control systems might be improved by using a Behavior Tree (BT) architecture. BTs are a particular kind of Hybrid Dynamical Systems (HDS), where the state transitions of the HDS are implicitly encoded in a tree structure, instead of explicitly stated in transition maps. In the gaming industry, BTs have gained a lot of interest, and are now replacing HDS in the control architecture of many automated in-game opponents. Below, we explore the relationship between HDS and BTs. We show that any HDS can be written as a BT and that many common UAV control constructs are quite naturally formulated as BTs. Finally, we discuss the positive implications of making the above mentioned state transitions implicit in the BTs.

/pdf/increasing-modularity-of-uav-control-systems-using-computer-19cscdx3i9.pdf

Increasing Modularity of UAV Control Systems using Computer Game Behavior Trees

P ROTECTING an aircraft from missile attack is a challenging issue. Most missile guidance algorithms [1–11] use information basically about the missile and the target but not that of the protected system. Considering only the kinematics with the aid of the collision triangle, Boyell [12] calculated a minimum range to intercept the attacking missile over a specified distance to protect a moving aircraft/torpedo and obtained a closed-form expression of the range for the missile to be successful against attacking missiles. Shneydor [13] developed conditions for the applicability of Boyell’s technique and simplified the expression for the operational range for the defense missile. However, those analyses were based on an ideal guidance assuming a perfect collision course. Rusnak [14] applied the differential game theory (DGT) to such a three-player game, a protected aircraft, an attacking missile, and a defense missile, by changing the three-player game into a two-team game by way of grouping the same cooperative players: a protected aircraft and a defensivemissile. Rusnak [14] showed that the resulting expression of the guidance lawwas represented by two line-of-sight (LOS) rate terms multiplied by variable gains derived from the differential game theory. One of the two LOS rates is the LOS rate of the aircraft with respect to the attacking missile, and the other is the LOS rate of the attacking missile with respect to the defense missile. The Rusnak method demands the recursive backward computations from the end. Perelman et al. [15] further modified Rusnak’s method to represent the two LOS rate terms in a closed form instead of using the recursive solution. Both simulation studies showed that the required acceleration could be reduced as compared with that of the conventional two-player differential game theory. Further recent work on such DGT can be found in [16]. Shima [17] proposed an optimal guidance methodology for a defense missile assuming prior knowledge of an attacking missile’s guidance law. Shaferman and Shima [18] applied a multiple model adaptive estimator algorithm with the multiple model adaptive control for such a three-player game to estimate the attacking missile’s guidance law. The proposed work here takes a basic approach to the three-player guidance law, similar to the proportional navigation (PN), in the way that it uses geometrical information of the moving object, that is, the protected aircraft’s LOS and the LOS rate. This type of guidance law can be classified as a three-point guidance [19–21]; examples are the beam rider (BR) guidance [2,19–21] and the command to LOS (CLOS) guidance [2,19–21]. The “three points” in the three-point guidance usually means amissile, a target, and a reference point from which the target LOS is drawn or the target is observed. In this study, the protected aircraft is selected as one of the three points instead of the reference point. Ratnoo and Shima [22] applied the CLOS guidance for aircraft protection. Their analysis shows that the defense missile requires less lateral acceleration (latax) than that of the attacking missile. They also proposed a guidance law for the protected aircraft that would help the defense missile against the target. However, the problem is that as the range of the target becomes larger, the resolution of the target LOS angle at a tracking pointwill be lower. This fact degrades the system performance or demands a highresolution radar to track a moving target from a distance. This Note proposes a different approach as compared with the BR or the CLOS guidance though it falls under the three-point guidance classification. The proposed approach manipulates two LOS rates associated with three vehicles and has benefits over the conventional three-point guidance law in two major aspects: 1) a simple form with one gain for two LOS rates, and 2) high sensitivity to an attacking missile’smaneuvers in the proximity of the attackingmissile, but low sensitivity to the attacking missile’s maneuvers in the proximity of the protected aircraft. This novel guidance law, called the airborneCLOS guidance (A-CLOSG) law, is derived using optimal control theory.

Modified Command to Line-of-Sight Intercept Guidance for Aircraft Defense

A guidance and control system for a trajectory-tracking unmanned aerial vehicle (UAV) is introduced. A proportional navigation guidance law is applied to a trajectory-tracking flight instead of using a traditional tracking-error correction based method. The system employs a dynamic inversion technique for the guidance force generation, which allows the UAV to maintain high maneuverability, and a simple velocity control to obtain a desired velocity. A trajectory is provided with a cubic-spline interpolation of given waypoints in order to simplify the trajectory making process. Using the cubic-spline function along to the trajectory arc, virtual target-points for the proportional navigation are easily obtained by using a flight distance instead of the trajectory arc. With the proportional navigation guidance, UAV may avoid its control saturation or divergence even in large tracking-error situations. Simulation results show that the system with the proportional navigation guidance has more robustness for trajectory-tracking than in the case of using the tracking-error correction based method.

Robust trajectory-tracking method for UAV guidance using proportional navigation

An integrated guidance and autopilot scheme for a path-following uninhabited aerial vehicle is presented in this study. A fixed-wing aircraft usually performs a bank-to-turn maneuver to change its flight direction. The novel approach presented here, however, assumes that each of the three channels of the integrated guidance and autopilot can be independently designed. This concept makes the design process simple. A virtual target moving on the prespecified path for the uninhabited aerial vehicle is introduced to facilitate the algorithm development. A first-/second-order sliding structure with a second-order sliding mode and a high-order sliding mode differentiator for the estimation of the uncertain sliding surfaces are selected to develop the uninhabited aerial vehicle’s integrated guidance and autopilot scheme. Stability analysis and error bounds due to measurement errors and model uncertainties are provided. The potential of the proposed method is demonstrated through a path-following application of a...

Separate-Channel Integrated Guidance and Autopilot for Automatic Path-Following

Integrated guidance and control (IGC) approaches exploit the synergy between guidance and control designs This study focuses on the integrated guidance and control (autopilot) design for a chasing Uninhabited Aerial Vehicle (UAV) against a target aircraft A second-order sliding structure with a second-order sliding mode (SOSM) including a high-order sliding mode (HOSM) observer for the estimation of the uncertain sliding surfaces is selected to develop an integrated guidance and autopilot scheme In order to make the design synthesis easier, intermediate control variables for partial derivatives of a sliding surface are carefully selected The resulting sliding surface structure is simple and sufficient to relate the actuator input to the sliding surface The potential of the proposed method is demonstrated through an aircraft application by comparing its simulation performance, number of tuning parameters used, and information needed for its implementation with an approach where the guidance law and the controller are designed separately

Integrated guidance and autopilot design for a chasing UAV via high-order sliding modes

This paper presents a missile intercept guidance law that can account for uncertainty and disturbance. The proposed guidance law is developed based on a novel second order sliding surface, along with an uncertainty and disturbance estimator. The proposed sliding surface is invariant for the non-impact angle constraint case as well as the impact angle constraint case. The sliding surface guarantees finite time convergence of the line-of-sight (LOS) rate and (if specified) the LOS angle error, characterized by a simple function of time-to-go. Furthermore, the proposed strategy is also effective against a maneuvering target. The line-of-sight rate convergence property can be adjusted using only one parameter that makes the design process simple. Potential of the proposed guidance laws is demonstrated with some simulations.

Hiroyuki Takano

Papers

Modified Command to Line-of-Sight Intercept Guidance for Aircraft Defense

Robust trajectory-tracking method for UAV guidance using proportional navigation

Separate-Channel Integrated Guidance and Autopilot for Automatic Path-Following

Integrated guidance and autopilot design for a chasing UAV via high-order sliding modes

Sliding mode-based intercept guidance with uncertainty and disturbance compensation