Modeling and Robust Attitude Controller Design for a Small Size Helicopter

This paper addresses the design and application controller for a small-size unmanned aerial vehicle (UAV). In this work, the main objective is to study the modeling and attitude controller design for a small size helicopter. Based on a non-simplified helicopter model, a new robust attitude control law, which is combined with a nonlinear control method and a model-free method, is proposed in this paper. Both wind gust and ground effect phenomena conditions are involved in this experiment and the result on a real helicopter platform demonstrates the effectiveness of the proposed control algorithm and robustness of its resultant controller.Comment: 6 page

Experimental Investigation of Shrouded Rotor Micro Air Vehicle in Hover and in Edgewise Gusts

Due to the hover capability of rotary wing Micro Air Vehicles (MAVs), it is of interest to improve their aerodynamic performance, and hence hover endurance (or payload capability). In this research, a shrouded rotor conguration is studied and implemented, that has the potential to oer two key operational benets: enhanced system thrust for a given input power, and improved structural rigidity and crashworthiness of an MAV platform. The main challenges involved in realising such a system for a lightweight craft are: design of a lightweight and stiff shroud, and increased sensitivity to external flow disturbances that can affect flight stability. These key aspects are addressed and studied in order to assess the capability of the shrouded rotor as a platform of choice for MAV applications. A fully functional shrouded rotor vehicle (disk loading 60 N/m2) was designed and constructed with key shroud design variables derived from previous studies on micro shrouded rotors. The vehicle weighed about 280 g (244 mm rotor diameter). The shrouded rotor had a 30% increase in power loading in hover compared to an unshrouded rotor. Due to the stiff, lightweight shroud construction, a net payload benefit of 20-30 g was achieved. The different components such as the rotor, stabilizer bar, yaw control vanes and the shroud were systematically studied for system efficiency and overall aerodynamic improvements. Analysis of the data showed that the chosen shroud dimensions was close to optimum for a design payload of 250 g. Risk reduction prototypes were built to sequentially arrive at the nal conguration. In order to prevent periodic oscillations in flight, a hingeless rotor was incorporated in the shroud. The vehicle was successfully flight tested in hover with a proportional-integral-derivative feedback controller. A flybarless rotor was incorporated for efficiency and control moment improvements. Time domain system identification of the attitude dynamics of the flybar and flybarless rotor vehicle was conducted about hover. Controllability metrics were extracted based on controllability gramian treatment for the flybar and flybarless rotor. In edgewise gusts, the shrouded rotor generated up to 3 times greater pitching moment and 80% greater drag than an equivalent unshrouded rotor. In order to improve gust tolerance and control moments, rotor design optimizations were made by varying solidity, collective, operating RPM and planform. A rectangular planform rotor at a collective of 18 deg was seen to offer the highest control moments. The shrouded rotor produced 100% higher control moments due to pressure asymmetry arising from cyclic control of the rotor. It was seen that the control margin of the shrouded rotor increased as the disk loading increased, which is however deleterious in terms of hover performance. This is an important trade-off that needs to be considered. The flight performance of the vehicle in terms of edgewise gust disturbance rejection was tested in a series of bench top and free flight tests. A standard table fan and an open jet wind tunnel setup was used for bench top setup. The shrouded rotor had an edgewise gust tolerance of about 3 m/s while the unshrouded rotor could tolerate edgewise gusts greater than 5 m/s. Free flight tests on the vehicle, using VICON for position feedback control, indicated the capability of the vehicle to recover from gust impulse inputs from a pedestal fan at low gust values (up to 3 m/s)

Επιδέξιοι Ελιγμοί Ρομποτικού Ελικοπτέρου με Χρήση Οπτικής Ανατροφοδότησης

In this Dissertation we address the problem of designing a reliable aerial embedded system dedicated for autonomous unmanned helicopters. We mainly focus on navigation and motion control systems using visual feedback. In the same vein, model-free control approaches are adopted in order to succeed robust autonomous flights in dynamic environments, exploiting a wide-range of helicopters' flight envelope as well.First, we design and prototype low-cost onboard and ground systems -both hardware and software- a order to i) convert a remotely operated small-scale helicopter into an autonomous robotic platform and ii) construct a user-friendly ground station. Additionally, a non-linear mathematical model of flybarless helicopters is derived which will be used both in the navigation and control design, as well as in a realistic simulation framework.Regarding the navigation system, we propose a real-time, high-performance observer based on low-complex, robust and adaptive algorithms. Particularly, we use the complementary notion, fusing low-cost navigation sensors along with visual feedback, to extract the helicopter state vector. An adaptation scheme is also provided to allow unhindered operation of the filter to erroneous inputs introduced not only by the characteristics of low-cost sensors (i.e, biases, operation ranges, etc), but also bythe high dynamics of aggressive maneuvers.Subsequently, we design robust model-based and model-free control schemes to stabilize the helicopter in various flight conditions, even under the presence of external disturbances, such as wind gusts or ground effect phenomena, which mainly affect the landing procedure.Finally, extensive autonomous flights are conducted with the Autonomous CSL Helicopter, called "mini-Daedalus", demonstrating the efficacy of the proposed embedded system in highly demanding conditions and validating our design, navigation and control methods.Σε αυτή τη διδακτορική διατριβή επικεντρωνόμαστε στο σχεδιασμό ενός αξιόπιστου ενσωματωμένου συστήματος για αυτόνομα μη επανδρωμένα ελικόπτερα. Ειδικότερα, ασχολούμαστε με το σχεδιασμό τόσο συστημάτων πλοήγησης όσο και συστημάτων εύρωστου ελέγχου βασισμένων σε τεχνικές "αγνώστου δυναμικού μοντέλου" (model-free), με τη χρήση οπτικής ανατροφοδότησης. Με αυτόν τον τρόπο επιτυγχάνεται αυτόνομη πτήση ελικοπτέρων σε δυναμικά περιβάλλοντα αξιοποιώντας όσο το δυνατό περισσότερο τον ολοκληρωμένο φάκελο πτήσης.Αρχικά σχεδιάζουμε, τόσο για το ελικόπτερο όσο και για το κέντρο ελέγχου εδάφους, χαμηλού κόστους, πρωτότυπα ενσωματωμένα συστήματα, τόσο στο πεδίο του υλικού όσο και του λογισμικού έτσι ώστε: α) να μετατρέψουμε ένα τηλεκατευθυνόμενο μικρού μεγέθους ελικόπτερο σε πλήρως αυτόνομη ρομποτική πλατφόρμα και β) να προετοιμάσουμε ένα συνολικό σύστημα πειραματικών δοκιμών. Στην συνέχεια, εξάγουμε μια πλήρης μαθηματική μοντελοποίηση των ελικοπτέρων για να χρησιμοποιηθεί τόσο για το σχεδιασμό των συστημάτων πλοήγησης και ελέγχου όσο και για το σχεδιασμό ενός πλήρους και ρεαλιστικού περιβάλλοντος προσομοίωσης.Όσο αναφορά το σύστημα πλοήγησης του ελικοπτέρου, προτείνουμε έναν υψηλής απόδοσης εκτιμητή κατάστασης βασισμένο σε απλούς, εύρωστους και προσαρμοστικούς αλγορίθμους όπου λειτουργούν σε πραγματικό χρόνο. Ειδικότερα, ο προτεινόμενος παρατηρητής σχεδιάζεται χρησιμοποιώντας τη λογική των "συμπληρωματικών φίλτρων" (complementary filters) ώστε να συνθέσει τις μετρήσεις πολλαπλών αισθητήρων πλοήγησης και οπτικών σημάτων και να εξάγει το συνολικό διάνυσμα καταστάσεων του ελικοπτέρου (δηλ., θέσης και προσανατολισμού). Επίσης ο προτεινόμενος αλγόριθμος αποτελείται από ένα κατάλληλο σχήμα προσαρμοστικού σχεδιασμού ώστε να επιτραπεί η απρόσκοπτη λειτουργία του φίλτρου κατά την εισαγωγή λανθασμένων σημάτων εισόδου λόγω είτε της χρήσης χαμηλού κόστους αισθητήρων (π.χ., εμφάνιση φαινομένων πόλωσης, μεγαλύτερο εύρος θορύβου, περιορισμός λειτουργίας), είτε της υψηλής δυναμικής των επιδέξιων ελιγμών των ελικοπτέρων.Στη συνέχεια, το προτεινόμενο ενσωματωμένο σύστημα ολοκληρώνεται με το σχεδιασμό εύρωστων ελεγκτών βασισμένων είτε στο μοντέλο του ελικοπτέρου, είτε όχι, με σκοπό να διασφαλίσουμε την σταθεροποίηση του ελικοπτέρου σε μια επιθυμητή κατάσταση πτητικής λειτουργίας, ανεξάρτητα από την εμφάνιση εξωτερικών διαταραχών, όπως ριπές ανέμου ή την επίδραση του εδάφους (ground effect), κυρίως κατά τη διαδικασία της προσγείωσης.Τέλος, χρησιμοποιώντας ως βασική πλατφόρμα το "Αυτόνομο Ελικόπτερο CSL", διεξαγάγουμε εκτεταμένες αυτόνομες πτήσεις σε πραγματικές συνθήκες, για να αποδείξουμε την αποτελεσματικότητα του προτεινόμενου ενσωματωμένου συστήματος σε απαιτητικές συνθήκες καθώς και να επαληθεύσουμε τις προτεινόμενες μεθοδολογίες πλοήγησης και ελέγχου

Design, testing and demonstration of a small unmanned aircraft system (SUAS) and payload for measuring wind speed and particulate matter in the atmospheric boundary layer

The atmospheric boundary layer (ABL) is the layer of air directly influenced by the Earth’s surface and is the layer of the atmosphere most important to humans as this is the air we live in. Methods for measuring the properties of the ABL include three general approaches: satellite-based, ground- based and airborne. A major research challenge is that many contemporary methods provide a restricted spatial resolution or coverage of variations of ABL properties such as how wind speed varies across a landscape with complex topography. To enhance our capacity to measure the properties of the ABL, this thesis presents a new technique that involves a small unmanned aircraft system (sUAS) equipped with a customized payload for measuring wind speed and particulate matter. The research presented herein outlines two key phases in establishing the proof-of-concept of the payload and its integration on the sUAS: (1) design and testing and (2) field demonstration. The first project focuses on measuring wind speed, which has been measured with fixed wing sUASs in previous research, but not with a helicopter sUAS. The second project focuses on the measurement of particulate matter, which is a major air pollutant typically measured with ground- based sensors. Results from both proof-of-concept projects suggest that ABL research could benefit from the proposed techniques

Fault Tolerant Flight Control of Unmanned Aerial Vehicles

Safety, reliability and acceptable level of performance of dynamic control systems are the major keys in all control systems especially in safety-critical control systems. A controller should be capable of handling noises and uncertainties imposed to the controlled process. A fault-tolerant controller should be able to control a system with guaranteed stability and good or acceptable performance not only in normal operation conditions but also in the presence of partial faults or total failures that can be occurred in the components of the system. When a fault occurs in a system, it suddenly starts to behave in an unanticipated manner. Thereby, a fault-tolerant controller should be designed for being able to handle the fault and guarantee system stability and acceptable performance in the presence of faults/damages. This shows the importance and necessity of Fault-Tolerant Control (FTC) to safety-critical and even nowadays for some new and non-safety-critical systems. During recent years, Unmanned Aerial Vehicles (UAVs) have proved to play a significant role in military and civil applications. The success of UAVs in different missions guarantees the growing number of UAVs to be considerable in future. Reliability of UAVs and their components against faults and failures is one of the most important objectives for safety-critical systems including manned airplanes and UAVs. The reliability importance of UAVs is implied in the acknowledgement of the Office of the Secretary of Defense in the UAV Roadmap 2005-2030 by stating that, ”Improving UA [unmanned aircraft] reliability is the single most immediate and long-reaching need to ensure their success”. This statement gives a wide future scenery of safety, reliability and Fault-Tolerant Flight Control (FTFC) systems of UAVs. The main objective of this thesis is to investigate and compare some aspects of fault tolerant flight control techniques such as performance, robustness and capability of handling the faults and failures during the flight of UAVs. Several control techniques have been developed and tested on two main platforms at Concordia University for fault-tolerant control techniques development, implementation and flight test purposes: quadrotor and fixedwing UAVs. The FTC techniques developed are: Gain-Scheduled Proportional-Integral-Derivative (GS-PID), Control Allocation and Re-allocation (CA/RA), Model Reference Adaptive Control (MRAC), and finally the Linear Parameter Varying (LPV) control as an alternative and theoretically more comprehensive gain scheduling based control technique. The LPV technique is used to control the quadrotor helicopter for fault-free conditions. Also a GS-PID controller is used as a fault-tolerant controller and implemented on a fixedwing UAV in the presence of a stuck rudder failure case

Towards UAV-assisted monitoring of onshore geological CO2 storage site

Scientists all over the world look for solutions to reduce greenhouse gas emissions in an effort to achieve proclaimed emissions reduction targets. An intriguing candidate with the potential to make a substantial contribution to this attempt is carbon capture and storage (CCS). The key advantage of CCS is that it provides the possibility to make a significant impact on the reduction of anthropogenic carbon dioxide (CO2) emissions from power plants and carbon-rich industry processes while maintaining existing fossil fuel energy infrastructure. The technique could therefore be used as a transitional solution until fossil fuels can be eliminated from the energy generation mix, and the energy efficiency of industrial processes as well as appliances and products is further improved. Like other technologies, CCS comes with its risks and rewards. To minimize possible negative impacts on humans as well as on the environment, it is necessary to understand the risks and to address them accordingly. A range of monitoring solutions for geological CO2 storage sites is available. However, a cost-effective solution for the regular observation of atmospheric CO2 concentrations (or tracer concentrations) of large areas above onshore geological CO2 storage sites has yet to be developed. This thesis discusses the use of a helicopter unmanned aerial vehicle (UAV) to fill this gap. The robot platform and its autopilot are designed to cope with ongoing sensor developments in addition to providing safety features necessary for the beyond line-of-sight operation of the UAV. The design focuses on the use of commercial off-the-shelf components for the aerial platform in order to shorten the development time and to reduce costs. The autopilot does neither enforce a specific helicopter model nor defines a set position estimation unit to be used. Access to the control loop enables low-level extensions like obstacle avoidance to be implemented. The developed solution allows the monitoring of an area of approximately 750m2 with one set of batteries in one altitude with a spatial resolution of 2m by 2m. Experiments show that point source leaks of as low as 100kg CO2 per day can be detected and their source located. As opposed to autonomous take-offs of the helicopter UAV, autonomous landings on small dedicated helipads require an accurate localization system. A time difference of arrival (TDOA) based acoustic localization system which is based on planar microphone arrays with at least four microphones is proposed. The system can be embedded into the landing platform and provides the accuracy necessary to land the UAV on a helipad of the size of 1m by 1m. A review of existing TDOA-based approaches is given. Simulations show that the developed approach outperforms its direct competitors for the targeted task. Furthermore, experimental results with the developed UAV confirm the feasibility of the introduced method. The effects of the sensor arrangement onto the quality of the calculated position estimates are also discussed. In order to combine robotic-assisted monitoring solutions and other monitoring strategies (e.g. sensor networks and individual sensors) into a single solution, it is necessary to have a framework which allows next to the measurement data analysis also the management (path changes, robot behavior changes, monitoring of internal robot state) of possibly multiple heterogeneous mobile robotic systems. A modular user interface (UI) framework is proposed which allows robots from different vendors and with various configurations next to individual sensors and sensor networks to be managed from a single application. The software system introduces a strict separation between the robot control software and UIs. UI implementations inside the UI framework can be reused across robot platforms, which can reduce the integration time of new robots significantly. The end user benefits by being able to manage a fleet of robots from various vendors and being able to analyze all the measurement data together in a single solution

Επιδέξιοι ελιγμοί ρομποτικού ελικοπτέρου με χρήση οπτικής ανατροφοδότησης

In this Dissertation we address the problem of designing a reliable aerial embedded system dedicated for autonomous unmanned helicopters. We mainly focus on navigation and motion control systems using visual feedback. In the same vein, model-free control approaches are adopted in order to succeed robust autonomous flights in dynamic environments, exploiting a wide-range of helicopters' flight envelope as well.First, we design and prototype low-cost onboard and ground systems -both hardware and software- a order to i) convert a remotely operated small-scale helicopter into an autonomous robotic platform and ii) construct a user-friendly ground station. Additionally, a non-linear mathematical model of flybarless helicopters is derived which will be used both in the navigation and control design, as well as in a realistic simulation framework.Regarding the navigation system, we propose a real-time, high-performance observer based on low-complex, robust and adaptive algorithms. Particularly, we use the complementary notion, fusing low-cost navigation sensors along with visual feedback, to extract the helicopter state vector. An adaptation scheme is also provided to allow unhindered operation of the filter to erroneous inputs introduced not only by the characteristics of low-cost sensors (i.e, biases, operation ranges, etc), but also bythe high dynamics of aggressive maneuvers.Subsequently, we design robust model-based and model-free control schemes to stabilize the helicopter in various flight conditions, even under the presence of external disturbances, such as wind gusts or ground effect phenomena, which mainly affect the landing procedure.Finally, extensive autonomous flights are conducted with the Autonomous CSL Helicopter, called "mini-Daedalus", demonstrating the efficacy of the proposed embedded system in highly demanding conditions and validating our design, navigation and control methods.Σε αυτή τη διδακτορική διατριβή επικεντρωνόμαστε στο σχεδιασμό ενός αξιόπιστου ενσωματωμένου συστήματος για αυτόνομα μη επανδρωμένα ελικόπτερα. Ειδικότερα, ασχολούμαστε με το σχεδιασμό τόσο συστημάτων πλοήγησης όσο και συστημάτων εύρωστου ελέγχου βασισμένων σε τεχνικές "αγνώστου δυναμικού μοντέλου" (model-free), με τη χρήση οπτικής ανατροφοδότησης. Με αυτόν τον τρόπο επιτυγχάνεται αυτόνομη πτήση ελικοπτέρων σε δυναμικά περιβάλλοντα αξιοποιώντας όσο το δυνατό περισσότερο τον ολοκληρωμένο φάκελο πτήσης.Αρχικά σχεδιάζουμε, τόσο για το ελικόπτερο όσο και για το κέντρο ελέγχου εδάφους, χαμηλού κόστους, πρωτότυπα ενσωματωμένα συστήματα, τόσο στο πεδίο του υλικού όσο και του λογισμικού έτσι ώστε: α) να μετατρέψουμε ένα τηλεκατευθυνόμενο μικρού μεγέθους ελικόπτερο σε πλήρως αυτόνομη ρομποτική πλατφόρμα και β) να προετοιμάσουμε ένα συνολικό σύστημα πειραματικών δοκιμών. Στην συνέχεια, εξάγουμε μια πλήρης μαθηματική μοντελοποίηση των ελικοπτέρων για να χρησιμοποιηθεί τόσο για το σχεδιασμό των συστημάτων πλοήγησης και ελέγχου όσο και για το σχεδιασμό ενός πλήρους και ρεαλιστικού περιβάλλοντος προσομοίωσης.Όσο αναφορά το σύστημα πλοήγησης του ελικοπτέρου, προτείνουμε έναν υψηλής απόδοσης εκτιμητή κατάστασης βασισμένο σε απλούς, εύρωστους και προσαρμοστικούς αλγορίθμους όπου λειτουργούν σε πραγματικό χρόνο. Ειδικότερα, ο προτεινόμενος παρατηρητής σχεδιάζεται χρησιμοποιώντας τη λογική των "συμπληρωματικών φίλτρων" (complementary filters) ώστε να συνθέσει τις μετρήσεις πολλαπλών αισθητήρων πλοήγησης και οπτικών σημάτων και να εξάγει το συνολικό διάνυσμα καταστάσεων του ελικοπτέρου (δηλ., θέσης και προσανατολισμού). Επίσης ο προτεινόμενος αλγόριθμος αποτελείται από ένα κατάλληλο σχήμα προσαρμοστικού σχεδιασμού ώστε να επιτραπεί η απρόσκοπτη λειτουργία του φίλτρου κατά την εισαγωγή λανθασμένων σημάτων εισόδου λόγω είτε της χρήσης χαμηλού κόστους αισθητήρων (π.χ., εμφάνιση φαινομένων πόλωσης, μεγαλύτερο εύρος θορύβου, περιορισμός λειτουργίας), είτε της υψηλής δυναμικής των επιδέξιων ελιγμών των ελικοπτέρων.Στη συνέχεια, το προτεινόμενο ενσωματωμένο σύστημα ολοκληρώνεται με το σχεδιασμό εύρωστων ελεγκτών βασισμένων είτε στο μοντέλο του ελικοπτέρου, είτε όχι, με σκοπό να διασφαλίσουμε την σταθεροποίηση του ελικοπτέρου σε μια επιθυμητή κατάσταση πτητικής λειτουργίας, ανεξάρτητα από την εμφάνιση εξωτερικών διαταραχών, όπως ριπές ανέμου ή την επίδραση του εδάφους (ground effect), κυρίως κατά τη διαδικασία της προσγείωσης.Τέλος, χρησιμοποιώντας ως βασική πλατφόρμα το "Αυτόνομο Ελικόπτερο CSL", διεξαγάγουμε εκτεταμένες αυτόνομες πτήσεις σε πραγματικές συνθήκες, για να αποδείξουμε την αποτελεσματικότητα του προτεινόμενου ενσωματωμένου συστήματος σε απαιτητικές συνθήκες καθώς και να επαληθεύσουμε τις προτεινόμενες μεθοδολογίες πλοήγησης και ελέγχου