Urgent problems of UAV navigation system development and practical implementation

The demand for a reliable and accurate navigation system that can replace Global Positioning System (GPS) in GPS-denied environment has become increasingly imperative. For indoor environment where GPS is almost unavailable or unreliable, the utilization of other sensors such as inertial sensors becomes necessary. However, inertial sensors alone cannot sustain reliable long-term accuracy due to errors accumulation without external periodic corrections. Thus this paper proposes the utilization of Light Detection and Ranging (LiDAR) as an alternative system to provide periodic corrections. In this paper, a tightly-coupled integrated navigation system that integrates LiDAR, a single-axis gyroscope and wheel encoder is introduced. Straight lines detection and extraction algorithm is utilized to estimate the changes in orientation and range from LiDAR to the extracted line. LiDAR-estimated orientation change and range change to the extracted line feature between two consecutive LiDAR scans are first filtered out through a high rate extended Kalman Filter (EKF) to remove the effect of short-term noise associated with LiDAR scans. Then the smoothed orientation and range changes are fused by a low rate EKF with those predicted by gyroscope and wheel encoder. The proposed system is verified through real experiment on a wirelessly controlled Unmanned Ground Vehicle (UGV). Experimental results indicate that navigation accuracy has been improved to sub-meter and gyroscope bias is precisely estimated.

The main problem in bringing autonomy to any vehicle lies in the design of a suitable guidance law. For truly autonomous operation, the vehicle needs to have a reliable Navigation, Guidance and Control (NGC) system of which the guidance system is the key element that generates suitable trajectories to be followed. In this review paper, various guidance laws found in the literature and their relevance to autonomous underwater vehicles (AUVs) are discussed. Since existing guidance laws for underwater vehicles have emulated from tactical airborne missile systems, a number of approaches for the missile guidance systems are considered. Finally, potential guidance strategies for AUVs are proposed.

Autonomous Underwater Vehicles (AUVs) are platforms suitable for a wide variety of applications in the marine environment with economic and operational advantages. In these applications an AUV performs a given task as a mission. During the mission execution, the AUV will move around the environment following paths that allow it to fulfill the mission's objectives. To achieve this, a reliable Navigation System (NS) is required. In addition to this, the current operating concept includes the deployment of multiple AUVs on a given area, thus a communication system between vehicles is also required. In the underwater environment both navigation and communication systems deals with the particular characteristics of the medium that limits the use of conventional techniques. In this work, a complete NS for an AUV is presented. The developed NS is based on an inertial navigation scheme with velocity and position aiding. The position aiding takes advantage of the communication system onboard the vehicle, which avoids the use of additional positioning systems. The fundamentals of the applied solutions are described and experimental results and implementation details are provided. Also conclusions and future works are presented.

The use of a reliability modeling simulation tool to evaluate the reliability of a hypercube multiprocessor which is a candidate architecture for guidance, navigation, and control systems for long-duration manned spacecraft is described. The simulation tool was used to evaluate homogeneous Markovian, nonhomogeneous Markovian, and non-Markovian models of the hypercube. The study focuses on the effect of assuming Weibull decreasing component failure rates compared to the usual assumption of constant component failure rates. The effect of the use of cold spares on system reliability under the assumption of both constant and Weibull decreasing failure rates is also examined. The authors discuss simulation applied to discrete-state reliability models and the role that importance sampling can play. The results obtained from the models under the differing assumptions about failure rate behavior are presented. >

This chapter introduces a number of the issues which must be addressed during the design and development of an automatic flight control system (AFCS). It does not make a comparison of potential system architectures nor does it suggest an optimum approach because each AFCS is different, depending upon the airframe and application. However, there is a common theme associated with an AFCS development programme that can be introduced and used to familiarise the reader with some of the concepts which must be addressed during the design evolution.

This paper addresses the problems of modeling, control design, and influence analysis of the steam catapult-assisted take-off process of the carrier-based aircrafts. The mathematical models of the carrier-based aircraft, steam catapult, landing gears, and the environmental factors including deck motion and bow airflow have been established to express the aircraft dynamics in the take-off process. An engineering method based automatic flight control system has been designed, which is divided into the longitudinal channel and lateral channel. The influences of the preset control surface, ship deck motion, ship bow airflow, and automatic flight control system system are tested by a series of simulations. The simulation results show that the elevator angle preset is necessary in the stage of accelerated running on the ship deck and the deck motion is the most important factor for safe take-off, while the ship bow airflow is beneficial for climbing up of the aircraft. The automatic flight control system gives the guarantee of safety and performance in the take-off process of the carrier-based aircraft.

Accurate and reliable navigation systems will become increasingly important in future aircraft applications, in particular within unmanned aerial vehicle systems. This paper describes a particle filter approach of integrating an Inertial navigation system (INS) with a terrain-aided positioning system (TAP) to achieve such a system. The integrated system is realized applying a marginalized particle filter (MPF) where the highly nonlinear TAP is designed tightly with the INS using one and the same filter. In order to better estimate the multi-modal errors in the altitude measurements, a first order Generalized Pseudo-Bayesian (GPB1) filter is used for this purpose. This will also reduce the number of particles in the MPF and therefore also reduce the computational workload. The performance of the algorithm has been evaluated using recorded flight data from the Saab Gripen fighter aircraft. Compared to an existing INS/TAP system based on a suboptimal integration of a point mass filter representing TAP and a single extended Kalman filter estimating the INS errors, the MPF approach is similar in performance but shows better results on convergence times when recovering after loss of data.

Navigation and flight control systems often use pulse compression techniques combined with the matched filtering approach as the main signal processing scheme. Golay complementary sequences are well known signal constructions for the pulse compression technique, which are additive complementary sequences in terms of the nature of their signal processing. The similar multiplicative complementary sequences also exsist. The comparison of additive and multiplicative complementary sequences is given in the paper.

We evaluated the effectiveness of two navigation systems with optical tracking in endoscopic sinus surgery (ESS). The Signa SP/i Intraoperative navigation system (General Electric Co., Intraoperative NS) is advantageous in acquiring both real time and high-resolution images during surgery, compared to conventional image-guided navigation (Stealth Station TREON, Medtronic Inc., IGNS) that rely entirely on preoperative three-dimensional images. We studied the following in 14 patients treated with intraoperative NS and 19 treated with IGNS: 1) additional time for navigation system implementation, 2) available instrumentations in ESS, and 3) navigation system accuracy. Navigation systems required additional time to prepare ESS. The time lapse from admittance to the operating room to ESS onset was measured in patients under both systems and controls undergoing ESS without any image guidance. Preparation of the intraoperative NS required an additional 52 min and IGNS required 17 min compared to the control group. Based on operative instruments, the intraoperative NS has some limitations arising from the application of a high magnetic field. Surgical instruments must not be attracted by the magnetic field in the operating room. So those used in our study were thoroughly examined and some remanufactured using MR safe materials. All instruments in ESS could be used in surgical guidance during surgery in the IGNS. Anatomic landmarks were accurately visualized using intraoperative NS and IGNS. Intraoperative NS renews the image during surgery, so surgeons could confirm the surgical outcome during ESS. Since the average distant error in both systems was between 1 mm and 2.5 mm, we confirmed that accuracy obtained with both navigation system was suitable for ESS completion. The intraoperative NS renewed the image during navigation. In conclusion, both navigation systems are sufficient for accurate image navigation in ESS, but navigation systems must be selected based on the individual case.

The design of reliable navigation and control systems for Unmanned Aerial Vehicles (UAVs) based only on visual cues and inertial data has many unsolved challenging problems, ranging from hardware and software development to pure control-theoretical issues. This chapter addresses these issues by developing and implementing an adaptive vision-based autopilot for navigation and control of small and mini rotorcraft UAVs. The proposed autopilot includes a Visual Odometer (VO) for navigation in GPS-denied environments and a nonlinear control system for flight control and target tracking. The VO estimates the rotorcraft ego-motion by identifying and tracking visual features in the environment, using a single camera mounted on-board the vehicle. The VO has been augmented by an adaptive mechanism that fuses optic flow and inertial measurements to determine the range and to recover the 3D position and velocity of the vehicle. The adaptive VO pose estimates are then exploited by a nonlinear hierarchical controller for achieving various navigational tasks including take-off, landing, hovering, trajectory tracking, target tracking, etc. Furthermore, the asymptotic stability of the entire closed-loop system has been established using systems in cascade and adaptive control theories. Experimental flight test data over various ranges of the flight envelope illustrate that the proposed vision-based autopilot performs well and allows a mini rotorcraft UAV to achieve autonomously advanced flight behaviours by using vision.

The design of reliable navigation and control systems for Unmanned Aerial Vehicles (UAVs) based only on visual cues and inertial data has many unsolved challenging problems, ranging from hardware and software development to pure control-theoretical issues. This paper addresses these issues by developing and implementing an adaptive vision-based autopilot for navigation and control of small and mini rotorcraft UAVs. The proposed autopilot includes a Visual Odometer (VO) for navigation in GPS-denied environments and a nonlinear control system for flight control and target tracking. The VO estimates the rotorcraft ego-motion by identifying and tracking visual features in the environment, using a single camera mounted on-board the vehicle. The VO has been augmented by an adaptive mechanism that fuses optic flow and inertial measurements to determine the range and to recover the 3D position and velocity of the vehicle. The adaptive VO pose estimates are then exploited by a nonlinear hierarchical controller for achieving various navigational tasks such as take-off, landing, hovering, trajectory tracking, target tracking, etc. Furthermore, the asymptotic stability of the entire closed-loop system has been established using systems in cascade and adaptive control theories. Experimental flight test data over various ranges of the flight envelope illustrate that the proposed vision-based autopilot performs well and allows a mini rotorcraft UAV to achieve autonomously advanced flight behaviours by using vision.

Purpose: Many studies have been conducted on assessment of navigation accuracy on cadaver head using pre-installed CT fiducials. However, there are fewer studies on assessing accuracy on real patient due to its complexity in measuring Target Registration Error (TRE). In this paper we propose a new approach for quantifying navigation accuracy on the real patients. This paper summarizes the results of navigation accuracy of a novel optical image guided navigation system evaluated on over 20 patients. Method: Commercially available optical navigation system (Navient Image guided navigation system - ClaroNav Kolahi Inc., Toronto, Canada) was used on over 20 patients from 2017 to 2019. Navient employs both landmarks based and trace based registration. Since mounting CT fiducials on the real patients is invasive and impractical, we developed a new approach to measure the distance from the navigation probe to the patient’s skin as a new metric to quantify navigation accuracy. The measurement was conducted in dozens of locations including patient’s forehead, temples and base of the nose. These anatomical locations were chosen very carefully to represent navigation accuracy in coronal, sagittal and axial directions respectively. Furthermore, our method also eliminates human errors involved in the TRE measurements which is the main source of error in TRE studies. Results: The average Euclidian distance from skin on 23 patients were 1.47(mm). the standard deviation of the accuracy was 0.28(mm). Low STD demonstrates consistent accuracy during the two year course of the study. Conclusion: A new noninvasive approach for accuracy assessment of image guided navigation systems on real patient was proposed and validated using a novel optical navigation system. The low STD of navigation accuracy indicates its reliable accuracy.

In airline service the reliability of a system is more than the confirmed failures for the system; it is the total removal experience of the system. Thus, the reliability of a system lies not only in the piece part failure rates, but also in the capability to verify and isolate failures. The application of digital technology brings several significant reliability improvements to automatic flight control systems (AFCS) when compared to contemporary analog systems. These advantages are demonstrated by the experience of the digital air data computer (DADC) of the DC-10 and the digital AFCS of the JA-37 Viggen. Experience with this equipment is reviewed, and the results are interpreted in terms of projections for airline DAFCS reliability. The digital system built-in test implemented by a stored program and the central processor gives a system integrity and dispatch reliability unequaled by analog systems. This high-integrity self-test reduces removal rates by giving line personnel a trustworthy tool and more complete automatic test processes for verifying maintenance actions. Digital circuit technology is directly suitable to largescale integrated circuits (LSIC) which reduce piece part counts and improve LRU reliability. Digital circuits are less subject to drift and the attendant difficulty to detect failures. These factors, coupled with the inherent high-integrity self-test, provide the basis for a significant improvement in reliability by the use of a digital automatic flight control system.

Diver and submersible navigation using acoustic techniques in and around complex underwater structures such as drilling and production platforms is complicated by the effects of multipath acoustic propagation. The research described in this paper is concerned with the investigation of techniques to overcome such effects, thereby leading to navigation systems which yield accurate locations of divers and submersibles operating within the core of the underwater structure. Several strategies are being studied including fixed transponder systems placed at prescribed locations in the structure and systems with tracking pencil-beams. The paper describes a computer simulation of a representative underwater structure which was developed for the study of the interaction between structural members and propagating acoustic beams generated by transponders mounted on and around the structure. It evaluates the detection probability of a diver or submersible operating within the structure as a function of acoustic source coordinates and yields information on optimal placement of acoustic sources and gives additional insight into the nature of the multipath transmission effect. INTRODUCTION A requirement exists for systems which can facilitate accurate navigation and location of divers or RCVs within the vicinity of offshore structures to allow routine inspection and maintenance. 1,2 Currently available short base-line or long base-line transponder oriented navigational systems 3 cannot be directly employed as they rely entirely on line of sight communication Transponder navigation systems compute locations on the basis of time-elapse measurements which are only valid along straight line paths. Within an off-shore structure, with its multiple structural members, signals to and from omni-directional transponders will be heavily corrupted by multipath transmission effects due to multiple reflections from various members, as well as by additive acoustic noise interference which may be both random and impulsive in nature, and will lead to ambiguous computations of distance based purely on time elapse measurements. A system which can be considered as more reliable in the underwater environment of the offshore structure than an omni-directional transponder system is an Inertial Navigation System. However two factors militate against such a system being employed for diver/RCV support. The first is cost, the second is gyroscopic drift which requires frequent compensation, and is particularly critical in the Azimuth gyroscope. This paper presents details of research being conducted at Strathclyde University towards the development of an accurate and reliable acoustic navigation system which employs some novel techniques of analysis, signal processing, and simulation to overcome the disadvantages outlined above. Several different strategies for system configuration and diver location are being currently pursued. After a discussion of some of these strategies, which are based on the location of sensors, results on the optimisation of these locations for representative offshore structures will be covered, and an ensuing measure of performance probability of detection for varying numbers of sensors-will be developed. The work on optimisation of sensor location and the attendant detection probabilities is extremely important as it leads to a reliable and robust system configuration for any specified offshore structure.

The number of operations incorporating E-VTOL aircrafts is increasing each year, and the optimization of the energy consumption of such vehicles is a major problem. In this paper, a small-scale ARCHER helicopter’s energy consumption is analyzed, wherein different flight conditions, main rotor revolutions, and flight control system settings are considered. The helicopter dynamic model was developed in the FLIGHTLAB environment and was then validated based on flight test data. The model used for the calculation of energy consumption was developed using the electric and dynamic characteristics of the main rotor, electric motor, and transmission system. The main part of this work concerns the analysis of electric energy consumption during the vehicle’s flight via the use of an automatic flight control system (AFCS) that ensures repeatable flight conditions. The AFCS was designed such that it includes both path and attitude control to provide hover and cruise control modes. The helicopter’s energy consumption was analyzed during different phases of flight, when executing maneuvers, and using different main rotor angular velocities to perform - a given task. The results show that the level of energy consumption significantly depends on the helicopter’s main rotor revolutions, flight speed, and the maneuvers performed. The proposed methodology can be used in prospective energy-efficient mission planning and UAV helicopter design.