1,720,964 research outputs found
Embedded Model Control for UAVs: theoretical aspects, simulations and experimental results
No full textUnmanned Aerial Vehicles (UAVs) and, more specifically, n-copters have come to
prominence in the last decade. Indeed, unmanned vehicles may have several applications
in society, spanning from complex operations, also in potentially hazardous
environments for humans to more entertaining purposes. Furthermore, UAVs have
drawn great attention in the automatic control research community. This is mainly
due to two reasons. First of all, designing a control for this non-linear and underactuated
system can represent a stimulating challenge for control researchers. Secondly,
n-copters, being typically mechanically simple and fast-prototyping devices, are
widely considered as a good technology for testing a wide range of control algorithms
and designs, also employing a wide range of sensors. In fact, the possibility
of having several low cost sensors on-board enables the implementation of many
navigation solutions as well as sensor calibration algorithms.
In this work, the control unit design for a quadrotor was addressed. In particular,
the study regards the Borea quadrotor which is part of an internal project (Borea) of
the former Space and Precision Automatics research, now Systems and Data Science
group, at Politecnico di Torino. The Borea project aims to test Guidance, Navigation
and Control (GNC) algorithms designed within the framework of the Embedded
Model Control (EMC) methodology. In particular, one of the main project objectives
regards the testing of planetary landing algorithms because of the similitude in the
command authority between n-copters and spacecrafts during the landing phase. In
fact, both n-copters and spacecrafts can provides a thrust vector which is constant in
direction whereas its intensity can be regulated.
The EMC framework matches the GNC architecture perfectly. More important,
EMC is a methodology based on an internal model which includes the uncertainties,
in the form of disturbances, that have to be rejected. Indeed, the main design effort
is focused on the internal model design, which is the core of the whole control unit. The Borea UAV has been endowed with a control system in order to control
its position, velocity, and attitude. These results has been achieved by means of a
well structured design process which started from the plant modelling and arrived
to the flight test. Indeed, the process has involved intensive numerical simulation
and control refinements as well as multi-staged tests and model validations. During
the design process some neglected dynamics has turned out to be very important
for the control design and their identification was revealed mandatory. On the other
hand, the control problem was separated into two independent controllers in order
to have a more simple controller which makes the quadrotor able to fly allowing to
test all the subsystems, improve the simulator fidelity and support the design and
validation of the second controller. Each controller has required specifics flight tests
aimed to validates particular functionalities and control performance. Testing has
included the design and building of a single axis test-bench in order to perform the
very first control tuning in a safety way. The objective of the first controller was the
attitude stabilization of the quadrotor in order to perform a hovering flight initially
and the attitude tracking later. The design of the attitude controller has required
the identification of the actuator dynamics as well as the sensors calibration. The
attitude control unit has been implemented in all its parts and successfully tested in
real flight.
As mentioned before, the next step has been focused on controlling the quadrotor
position within a limited flight area. In particular, this study investigates the use
of the feedback linearization approach as a novel way to design the internal model
for EMC. The feedback linearization allows us to collect all the non-linearities
at the command level. EMC, by means of a disturbance dynamics model, makes
possible to estimate and then reject the non-linear terms through the control law. The
control solution has been validated by means of intensive numerical simulations and
real-flight tests. As a final result, the control units developed in this work enhance
the EMC applicability to non-linear systems, such as quadrotor UAVs, and evidence
the EMC disturbance rejection capabilities
Control Architecture and Simulation of the Borea Quadrotor
Full text linkThe paper presents modelling, control design and simulated results preliminary to test the Borea quadrotor. Guidance, navigation and control strategy are implemented following the Embedded Model Control (EMC) schem
Satellite-to-satellite attitude control of a long-distance spacecraft formation for the Next Generation Gravity Mission
Full text linkThe paperpresentsthedesignandsomesimulatedresultsoftheattitudecontrolofasatelliteformation
under studybytheEuropeanSpaceAgencyfortheNextGenerationGravityMission.Theformation
consists oftwospacecraftswhich fly morethan200kmapartatanaltitudefromtheEarth'sgroundof
between 300and400km.Theattitudecontrolmustkeeptheopticalaxesofthetwospacecraftaligned
with amicroradianaccuracy(pointingcontrol).Thisismadepossiblebyspecific opticalsensors
accompanyingtheinter-satellitelaserinterferometer,whichisthemainpayloadofthemission.These
sensors alloweachspacecrafttoactuateautonomousalignmentafterasuitableacquisitionprocedure.
Pointing controlisconstrainedbytheangulardrag-freecontrol,whichisimposedbymissionscience
(Earth gravimetryatalowEarthorbit),andmustzerotheangularaccelerationvectorbelow0.01 μrad/s2
in thesciencefrequencyband.Thisismadepossiblebyultrafine accelerometersfromtheGOCE-class,
whose measurementsmustbecoordinatedwithattitudesensorstoachievedrag-freeandpointing
requirements.EmbeddedModelControlshowshowcoordinationcanbeimplementedaroundthe
embedded modelsofthespacecraftattitudeandoftheformationframequaternion.Evidenceand
discussion aboutsomecriticalrequirementsarealsoincludedtogetherwithextensivesimulatedresults
of twodifferentformationtypes
Embedded Model Control: design separation under uncertainty
No full textThe key signal of the Embedded Model Control (EMC) is the model error, measured minus model output, which is used by Internal Model Control and in a more efficient way by Active Disturbance Rejection Control (ADRC). EMC extends ADRC along four lines explained in the paper: a more generic disturbance dynamics, design of the noise layout (where uncertainty enters the model), dynamic uncertainty estimation, a design degree of freedom similar to Youla parameterization. The latter freedom is shown to favor separation between control and estimation under uncertainty, a principle hidden in ADRC. As a result, control law can be practically designed model-based, only limited by command saturation. The main theorems are developed in some detail starting from two model classes (design and embedded model), that are essential to define uncertainty. The paper extends part of previous results from SISO to MIMO systems, but some theorems and the free feedback dynamics are original. Theory is accompanied by a study cas
Saturation managing for the propulsion system and optimal dispatching proposal for multi-rotor UAV
No full textThis paper states a methodology in order to manage the saturation of the propulsion system providing flexibility to the vehicle control unit. To reach this objective a n-copter propeller system is described and a general dispatching law without constrains is found. Furthermore, an optimal propeller problem is proposed and a possible solution using a recursive least squares method is presente
Active Disturbance Rejection Control and Embedded Model Control: a case study comparison
No full textThe paper aims to compare Active Disturbance Rejection Control (ADRC) and Embedded Model Control (EMC). Both control algorithms are designed and implemented around an internal model which includes a disturbance dynamics, capable of encoding external disturbances and model discrepancies. Both schemes appear to be an extension of the internal model control (IMC). The disturbance dynamics is driven by the so-called uncertainty input signals (briefly noise) that are real-time estimated by an observer feedback (uncertainty estimator) driven by the model error: plant output minus model output. The main advantage of ADRC and EMC is that the estimated disturbance contains the past uncertainty that now enters both the internal model and the control law as a signal, and allows the rest of the control law (state feedback) to be designed model-based, not depending on the uncertainty. The main difference between ADRC and EMC is that the former assumes that model errors can be treated like input disturbances, whereas EMC shows that high-frequency neglected dynamics cannot be treated as such. The former standpoint does not place any limitation to the control bandwidth (BW), unlike the latter one which is compelled to find out an optimal BW in the presence of uncertainty. The different design has been enhanced by treating the same case study with two different internal models. The simpler model adopted by EMC is affected by the neglected dynamics. The different models do not impede performance comparison with the aid of suitable scale factor
The feedback linearisation method for Embedded Model Control: The Borea project case-study
No full textFeedback linearisation has been proved to be a powerful tool for making non-linear system dynamics fully or partially linear. This study investigates the use of the feedback linearisation approach as a novel way to design the internal model for Embedded Model Control, when applied to non-linear systems. This idea is applied to the control of an Unmanned Aerial Vehicle: the Borea project quadrotor. Embedded Model Control methodology implies the design of an internal model (Embedded Model) coded into the control unit and running in parallel with the plant. The difference between the internal model output and the plant output is used to estimate the unknown disturbances. These unknown disturbances include all the non-linearities that can be rejected by means of the control law. Using a numerical simulator, we demonstrate the feasibility of this methodology for accurate design of the internal model, starting from the non-linear system. This indicates that a feedback linearisation approach allows the extension of embedded model control techniques to non-linear systems control. What is more, the EMC is successfully applied to the control of the Borea quadrotor
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