3,236 research outputs found
Biomimetic-Based Output Feedback for Attitude Stabilization of Rigid Bodies: Real-Time Experimentation on a Quadrotor
International audienceThe present paper deals with the development of bounded feedback control laws mimicking the strategy adopted by flapping flyers to stabilize the attitude of systems falling within the framework of rigid bodies. Flapping flyers are able to orient their trajectory without any knowledge of their current attitude and without any attitude computation. They rely on the measurements of some sensitive organs: halteres, leg sensilla and magnetic sense, which give information about their angular velocity and the orientation of gravity and magnetic field vectors. Therefore, the proposed feedback laws are computed using direct inertial sensors measurements, that is vector observations with/without angular velocity measurements. Hence, the attitude is not explicitly required. This biomimetic approach is very simple, requires little computational power and is suitable for embedded applications on small control units. The boundedness of the control signal is taken into consideration through the design of the control laws by saturation of the actuators' input. The asymptotic stability Micromachines 2015, 6 994 of the closed loop system is proven by Lyapunov analysis. Real-time experiments are carried out on a quadrotor using MEMS inertial sensors in order to emphasize the efficiency of this biomimetic strategy by showing the convergence of the body's states in hovering mode, as well as the robustness with respect to external disturbances
Comprehensive review on controller for leader-follower robotic system
985-1007This paper presents a comprehensive review of the leader-follower robotics system. The aim of this paper is to find and elaborate on the current trends in the swarm robotic system, leader-follower, and multi-agent system. Another part of this review will focus on finding the trend of controller utilized by previous researchers in the leader-follower system. The controller that is commonly applied by the researchers is mostly adaptive and non-linear controllers. The paper also explores the subject of study or system used during the research which normally employs multi-robot, multi-agent, space flying, reconfigurable system, multi-legs system or unmanned system. Another aspect of this paper concentrates on the topology employed by the researchers when they conducted simulation or experimental studies
Robust longitudinal rate gyro bias estimation for reliable pitch attitude observation through utilization of a displaced accelerometer array
In this thesis, a novel attitude estimation device is proposed utilizing cost-effective measurement sensors. The device fuses a rate gyroscope with an accelerometer array to estimate and eliminate the rate gyro bias online yielding accurate real time aircraft attitude tracking. Attitude determination algorithms are dependent on instantaneous and accurate measurements of translational and rotational body rates for precise estimation of vehicle orientation in three-dimensional space. Measurement error of instantaneous rate sensors, gyroscopes, is introduced via inherent biases and signal noise resulting in gyro drift. Integration of the rate signal for calculation of a net displacement amplifies these minute measurement errors leading to inaccurate and unreliable attitude observation. The proposed device is a departure from typical attitude observers and bias estimators due to its reliance on accelerometers measuring the local gravitational vector in lieu of additional magnetic field sensors or GPS. The end result of this work is a longitudinal attitude estimation device able to compute a rate gyro bias in real-time producing accurate pitch angle tracking while subjected to simulated aircraft flight conditions. The effectiveness of the newly constructed attitude estimation algorithm is demonstrated by comparison of attitude and rate gyro bias estimates produced from noise corrupted and biased sensors with the actual attitude of a nonlinear aircraft model and true rate gyro bias
Fault-tolerant feature-based estimation of space debris motion and inertial properties
The exponential increase of the needs of people in the modern society and the contextual
development of the space technologies have led to a significant use of the lower Earth’s
orbits for placing artificial satellites. The current overpopulation of these orbits also
increased the interest of the major space agencies in technologies for the removal of at
least the biggest spacecraft that have reached their end-life or have failed their mission.
One of the key functionalities required in a mission for removing a non-cooperative
spacecraft is the assessment of its kinematics and inertial properties. In a few cases, this
information can be approximated by ground observations. However, a re-assessment
after the rendezvous phase is of critical importance for refining the capture strategies
preventing accidents. The CADET program (CApture and DE-orbiting Technologies),
funded by Regione Piemonte and led by Aviospace s.r.l., involved Politecnico di Torino
in the research for solutions to the above issue.
This dissertation proposes methods and algorithms for estimating the location of
the center of mass, the angular rate, and the moments of inertia of a passive object.
These methods require that the chaser spacecraft be capable of tracking several features
of the target through passive vision sensors. Because of harsh lighting conditions in
the space environment, feature-based methods should tolerate temporary failures in
detecting features. The principal works on this topic do not consider this important
aspect, making it a characteristic trait of the proposed methods. Compared to typical
v
treatments of the estimation problem, the proposed techniques do not depend solely on
state observers. However, methods for recovering missing information, like compressive
sampling techniques, are used for preprocessing input data to support the efficient usage
of state observers. Simulation results showed accuracy properties that are comparable to
those of the best-known methods already proposed in the literature.
The developed algorithms were tested in the laboratory staged by Aviospace s.r.l.,
whose name is CADETLab. The results of the experimental tests suggested the practical
applicability of such algorithms for supporting a real active removal mission
Attitude estimation and stabilization of a quadrotor aircraft
In the past few years, researchers have shown great interest in quadrotor aircraft
as a platform for UAV research due to simplicity of construction as well
as maintenance, ability to hover in small indoor locations or hazardous environments,
vertical take-off and landing capability, etc. Attitude stabilization
of a quadrotor requires accurate information about current orientation of the
vehicle. With the emergence of Micro-Electro-Mechanical System (MEMS)
sensors, a relatively cost-effective way for attitude estimation consists of using
gyroscope, accelerometer and magnetometer devices strapped down on
vehicle’s center of mass. A number of previous works deal with fusing angular
velocity with measurements of accelerometer and magnetometer to construct
an estimation of aircraft orientation
Attitude Estimation and Control of VTOL UAVs
The theoretical challenge involved in the operation of VTOL UAVs is often divided into two main problems. The first problem involves the development of an estimation scheme which can accurately recover the orientation, or angular position, of the aircraft. The second problem involves the development of algorithms which can be used to reliably control the orientation and/or the position of the vehicle. These two problems are the primary focus of this thesis.
We first consider the problem of attitude estimation. To solve this problem we use vector measurements, and in many cases, a gyroscope (to measure the angular velocity of the system) in order to develop the estimation scheme. In the case where an accelerometer is used to provide a measurement of the apparent acceleration, we consider a special class of attitude observer, known as a \emph{velocity-aided} attitude observer, which additionally use the system linear velocity to improves the estimation performance when the system is subject to high linear accelerations.
Secondly, we develop a number of algorithms which can be used to control the orientation and/or the position of the system. Two adaptive position tracking control laws are proposed which are able to compensate for exogenous disturbance forces. However, this control strategy (like other existing position control strategies) assumes that the system orientation is directly measured, where in reality only an estimate of the system orientation is available, which is obtained using some attitude estimation scheme. Therefore, we also propose an attitude stabilization control law, and two position control laws which do not assume that the system orientation is directly measured. To develop these control laws, we use vector measurements (that would normally be used by the attitude observer) directly in the control algorithms, which eliminates the requirement for an attitude observer. We also consider a special type of the vector-measurement-based position control laws which uses the accelerometer to measure the body-referenced apparent acceleration (rather than assuming only the gravity vector is measured). Therefore, this proposed control strategy may be better suited for VTOL UAVs, which are likely to be subjected to linear accelerations
Estimation of Spacecraft Attitude Motion and Vibrational Modes Using Simultaneous Dual-Latitude Ground-Based Data
Cutting-edge Space Situational Awareness (SSA) research calls for improved methods for rapidly characterizing resident space objects. In this thesis, this will take the form of speeding up convergence of spacecraft attitude estimates, and of a non-model-based approach to the detection of vibrational modes. Because attitude observability from photometric data is angle-based, dual-site simultaneous photometric observations of a resident space object are predicted to improve the convergence speed and steady-state error of spacecraft attitude state estimation from ground-based sensor data. Additionally, it is predicted that by adding polarimetric data to the measurements, the speed of convergence and steady-state error will be reduced further. This thesis models satellite motion and measurements from ground-based sensors for dual-latitude simultaneous light curve simulation, then develops a data fusion process to combine photometric, astrometric, and polarimetric data from both sites in order to more quickly estimate the attitude of an RSO. The Fractional Fourier Transform shows promise as a non-model-based approach to the detection of input vibrational frequencies from the degree of linear polarization. The main results are that dual-site observation geometry is conducive to slight improvements of attitude filter performance, and the addition of polarimetric data to the measurements yields much improved performance over both the single-site and dual-site cases
Advances in Spacecraft Systems and Orbit Determination
"Advances in Spacecraft Systems and Orbit Determinations", discusses the development of new technologies and the limitations of the present technology, used for interplanetary missions. Various experts have contributed to develop the bridge between present limitations and technology growth to overcome the limitations. Key features of this book inform us about the orbit determination techniques based on a smooth research based on astrophysics. The book also provides a detailed overview on Spacecraft Systems including reliability of low-cost AOCS, sliding mode controlling and a new view on attitude controller design based on sliding mode, with thrusters. It also provides a technological roadmap for HVAC optimization. The book also gives an excellent overview of resolving the difficulties for interplanetary missions with the comparison of present technologies and new advancements. Overall, this will be very much interesting book to explore the roadmap of technological growth in spacecraft systems
Design and application of advanced disturbance rejection control for small fixed-wing UAVs
Small Unmanned Aerial Vehicles (UAVs) have seen continual growth in both research and
commercial applications. Attractive features such as their small size, light weight and
low cost are a strong driver of this growth. However, these factors also bring about some
drawbacks. The light weight and small size means that small UAVs are far more susceptible
to performance degradation from factors such as wind gusts. Due to the generally low
cost, available sensors are somewhat limited in both quality and available measurements.
For example, it is very unlikely that angle of attack is sensed by a small UAV. These
aircraft are usually constructed by the end user, so a tangible amount of variation will
exist between different aircraft of the same type. Depending on application, additional
variation between flights from factors such as battery placement or additional sensors may
exist. This makes the application of optimal model based control methods difficult.
Research literature on the topic of small UAV control is very rich in regard to high
level control, such as path planning in wind. A common assumption in such literature
is the existence of a low level control method which is able to track demanded aircraft
attitudes to complete a task. Design of such controllers in the presence of significant wind
or modelling errors (factors collectively addressed as lumped disturbances herein) is rarely
considered.
Disturbance Observer Based Control (DOBC) is a means of improving the robustness
of a baseline feedback control scheme in the presence of lumped disturbances. The method
allows for the rejection of the influence of unmeasurable disturbances much more quickly
than traditional integral control, while also enabling recovery of nominal feedback con-
trol performance. The separation principle of DOBC allows for the design of a nominal
feedback controller, which does not need to be robust against disturbances. A DOBC
augmentation can then be applied to ensure this nominal performance is maintained even
in the presence of disturbances. This method offers highly attractive properties for control
design, and has seen a large rise in popularity in recent years.
Current literature on this subject is very often conducted purely in simulation. Ad-
ditionally, very advanced versions of DOBC control are now being researched. To make
the method attractive to small UAV operators, it would be beneficial if a simple DOBC
design could be used to realise the benefits of this method, as it would be more accessible
and applicable by many.
This thesis investigates the application of a linear state space disturbance observer to
low level flight control of a small UAV, along with developments of the method needed
to achieve good performance in flight testing. Had this work been conducted purely in
simulation, it is likely many of the difficulties encountered would not have been addressed
or discovered.
This thesis presents four main contributions. An anti-windup method has been devel-
oped which is able to alleviate the effect of control saturation on the disturbance observer
dynamics. An observer is designed which explicitly considers actuator dynamics. This
development was shown to enable faster observer estimation dynamics, yielding better
disturbance rejection performance. During initial flight testing, a significant aeroelastic
oscillation mode was discovered. This issue was studied in detail theoretically, with a pro-
posed solution developed and applied. The solution was able to fully alleviate the effect in
flight. Finally, design and development of an over-actuated DOBC method is presented.
A method for design of DOBC for over actuated systems was developed and studied. The
majority of results in this thesis are demonstrated with flight test data
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