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This article suggests a collection of model-based and model-free output-feedback optimal solutions to a general ${H_{∞}}$ control design criterion of a continuous-time linear system. The goal is to obtain a static output-feedback controller while the design criterion is formulated with an exponential term, divergent or convergent, depending on the designer's choice. Two offline policy-iteration algorithms are presented first, which form the foundations for a family of online off-policy designs. These algorithms cover all different cases of partial or complete model knowledge and provide the designer with a collection of design alternatives. It is shown that such a design for partial model knowledge can reduce the number of unknown matrices to be solved online. In particular, if the disturbance input matrix of the model is given, off-policy learning can be done with no disturbance excitation. This alternative is useful in situations where a measurable disturbance is not available in the learning phase. The utility of these design procedures is demonstrated for the case of an optimal lane tracking controller of an automated car.

While automotive research plays a significant role nowadays, most of the experimental activity demands costly platforms and involves safety issues. Plenty of driving simulators were proposed to reduce the costs and guarantee safety. However, they still cannot reflect the physical world, resulting in subjective assessments in any aspect of the study. This paper introduces an affordable remote driving testbed based on small-scale car-like mobile platforms and a physical road. The driver in the remote driving station observes a real-time video taken from a front-facing camera installed in the car. For a realistic driving experience, we have developed a torque feedback mechanism based on the small-scale car motion to mimic the influence of the physical linkage between the front wheels and the steering wheel of a standard car. This mechanism demands knowledge of the car’s side-slip angle that is not directly measured. Here, we introduce a supervised learning-based combined regression model (RidgeCV and Bootstrap aggregating decision tree) that estimates the side-slip angle for highly non-linear behavior.

The article addresses the tracking control problem of differentially driven nonholonomic Wheeled Mobile Robots (WMRs) whose nonlinear kinematic-dynamic equations of motion subject to bounded inputs. To overcome the difficulties arising from the constraints in the system and to avoid singular states, the potential for their appearance is common in this system, we implement sigmoid functions in the feedback loop. Also, since the speed variables (linear and angular) that enter the kinematic subsystem are not independent variables and are the result of the action of bounded forces/torques on the dynamic system, we present a special way of reconstructing them. Using the flatness property of the system, the article presents a control algorithm for tracking a time-parameterized path (a geometric path with an associated timing-law). The proposed control scheme allows us to present conditions on the required trajectory that, if they are met, the input signals satisfy the given restrictions and ensures convergence to the reference trajectory.

We present a divide and conquer design approach for handling control problems with dynamically changing objectives. The approach is based on associating each objective with a virtual input and then considering a game between a set of (virtual) players, each trying to achieve an objective by controlling the associated virtual input. By guarantying a Nash equilibrium for this game, we synthesize a combined controller that establishes a stable balance between the objectives. To demonstrate the use of the approach, we describe how a controller for a non-linear system (quadrotor) can be designed to handle competing objectives that change in time. The example shows how our approach allows to model each of the objectives separately and to combine them using game theory.

This research is motivated by the problem of regenerative chatter vibration, which is a pronounced problem in machining. The problem of chatter vibration is especially critical in the internal turning process, where the material is removed from the inner part of a rotating workpiece using a slender bar. Active mechatronic solutions to the problem of regenerative chatter vibration in internal turning are mostly given by means of piezoelectric actuators embedded into the boring bar. However, due to the volume needed for accommodation of the actuators, it is difficult to apply these solutions to narrow bars. This paper presents a novel actuation approach with a potential application for active control of regenerative chatter vibration in internal turning. This approach involves a bar whose clamping has an ability to move perpendicularly to the bar axis. In addition, it involves two actuators: one of them is placed near the bar clamping, and another one is placed at the bar clamping. The presented actuation approach is compared to the related approaches in the literature. Additionally, this paper presents a method for robustness analysis of the actively controlled cutting process, which is based on the structured singular value methodology. Experiments performed on a specially designed testbed imitating the internal turning process demonstrate the potential applicability of the introduced actuation approach, as well as the utility of presented robustness analysis method.

The paper presents a control algorithm for solving the trajectory tracking problem for an Unmanned Aerial Vehicle (UAV) in flight at a fixed altitude when control signal generators are integrated in the model. The approach presented in the article allows us to implement a control law under physical constraints and to avoid singular cases in the control process. Using the concept of virtual vehicles we apply tracking controllers for a group of UAVs flying in a string-type formation. Using the proposed algorithm we establish string stability, and with the help of the concept of L 2 string stability the controller reduces the spacing error propagations between the UAVs flying in a convoy-like formation. Numerical and simulation results are demonstrated.

This paper deals with the trajectory tracking control problem in the kinematic bicycle model. To avoid possible singular states in the control system for the model under consideration we apply a sigmoid function (hyperbolic tangent) in the feedback loop. We present an error function between the real and virtual vehicles that follows the required trajectory, and introduce a control law that stabilizes asymptotically the zero error state in the error dynamics. In addition, the proposed algorithm allows us to handle the control problem in cases where actuator saturations and state constraints exist. The paper is concluded with an example that demonstrate the characteristics of the control law and its performance.

The problem of designing controllers for achieving composite goals is well studied in the literature and is considered an open problem. In this paper we propose a controller architecture that builds on approaches for designing reactive decision making systems developed in the field of computer science. Specifically, we propose an extension of the Behavioural Programming (BP) approach that is tailored to allow controller design. As the name of the paper suggests, we identify the issue of "patience" as a key feature of the new approach - in many composite control problems it is not possible to advance all goals at all time, i.e., some goals need to "patiently" wait while others are being advanced. We demonstrate how the proposed approach is capable of handling elaborated multi-objective situations that include patience in an intuitive and effective way.

In this paper, Simple Adaptive Control (SAC) is applied to a Single Degree of Freedom (SDOF) Active Magnetic Bearing (AMB) testbed. The plant on which SAC is applied is required to be Almost Strictly Positive Real (ASPR). Therefore, Parallel Feedforward Configuration (PFC) design proves to be the most important step in the algorithm implementation. Here, PFC design guidelines, based on classical SISO tools (bode plots and step response), are proposed and validated experimentally. Additionally, a slowly varying, unknown disturbance rejection method is suggested within the framework of the SAC algorithm. The proposed method is also validated experimentally, on a SDOF AMB testbed.

The article proposes low-level control schemes for a group of quadrotors with highly nonlinear uncertain models in formation flights. The paper suggests control strategies for formation flights in ...

We present a new image based visual servoing (IBVS) approach for control of micro aerial vehicles (MAVs) in indoor environments. Specifically, we show how a MAV can be stabilized and guided using only corridor lines viewed on a front facing camera and angular velocity measurements. Since the suggested controller does not include explicit attitude feedback it does not require the use of accelerometers which are susceptible to vibrations, nor complex attitude estimation algorithms. The controller also does not require direct velocity measurements which are difficult to obtain in indoor environments. The paper presents the new method, stability analysis, simulations and experiments.

Platooning has a great potential for improving highway traffic flow. Platooning research focuses on fully automated platoons. However, in the near future traffic will be mixed and will consist of automated and manually driven vehicles. This work introduces a new concept of mixed platoons, i.e., platoons consist of automated and manual vehicles. In a mixed platoon the automated vehicles are controlled as part of the mixed traffic, using global sight on traffic. This way the mixed traffic flow can be optimized using the automated vehicles. The mixed platoons control developed in this paper implements the same control components that are used for automated platoons, but modifies them to suit mixed traffic environment. That is, a new Information Flow Topology (IFT) and new Distributed Controller (DC) are developed for mixed platoons using $\mathcal{H}_{\infty}$ control methods. Subsequently, a string stability analysis for a mixed platoon is shown, demonstrates the feasibility and potential of mixed platoons.

In this article we present a simple control procedure for a quadrotor that ensures convergence to a required altitude and attitude set-points under conditions of unknown physical parameters. The quadrotor model is highly nonlinear. The altitude set-point strategy is based on a two-mode control strategy: coarse and the fine motion modes and a sort of huristic process. In the first control mode we apply piecewise control functions. In the attitude regulation the design procedure is based on the passivity-based approach and in particular the controller is independent of the system physical parameters. The considered control strategy might be useful in various aerial missions in which stable hovering is required as for example in reconnaissance and aerial photography flights. The control design complies with the system structure which restricts the thrust force to act in one direction. Simulation results demonstrate the controller performance.

The motivation behind this study is the problem of regenerative chatter vibration in internal turning. Regenerative chatter is an extremely undesired phenomenon in machining. This is since, in addition to causing surface finish degradation and cutting tool wear, regenerative chatter imposes a fundamental limitation on the material removal rate. In internal turning, due to the relatively low internal damping of the boring bar, regenerative chatter is especially undesired. Another factor, which reduces the material removal rate, as well as surface accuracy, is machining error. Machining error is very common in internal turning due to low boring bar stiffness. At the same time, machining error compensation has received little attention in the literature hitherto. This study proposes a control methodology for chatter vibration suppression with simultaneous compensation of the machining error in internal turning. The proposed methodology consists of three components. The first component is a newly developed method for the identification of the cutting force model parameters. The second component, which utilizes the cutting force model parameters identified in the previous step, is a robust stabilizing controller synthesis developed to address the key issues arising in the context of regenerative chatter control in the internal turning process. In contrast to the corresponding control methods reported in the literature, the control approach developed in this study accounts explicitly for the time-delayed term associated with the regenerative feature of chatter, as well as uncertainty in both cutting force and the flexible boring bar models. The last third component of the presented control methodology is a novel approach for machining error compensation, which is based on a feedforward term designed to eliminate the bar tip deflection. Every single component of the proposed control methodology can be utilized separately in the context of active control in internal turning. The potential applicability of the control methodology presented in this study is demonstrated experimentally, using an active slender bar demonstrator imitating the internal turning process. In particular, it is demonstrated that: (i) given the identified model of the boring bar, the proposed method for cutting parameters estimation allows to obtain reasonable estimations of the cutting coefficient and the overlap factor, (ii) the presented robust control system synthesis procedure allows to obtain controllers which increases the chatter immunity of the actively controlled cutting process, and (iii) the presented method for machining error compensation counteracts successfully the error due to flexible bar deflection caused by the DC component of the cutting force model.

This paper considers the set-point control problem of an uncertain six-degree-of-freedom precision positioning system, where only position measurements are available. As a solution, we present an iterative output feedback control algorithm whose learning mechanism is based on the concept of contraction mapping. Besides stability and convergence, the presented analysis includes practical aspects associated with the algorithm implementation. In particular, it is shown that: 1) the system response due to the iterative process converges to an arbitrarily small neighborhood of the desired equilibrium point, and 2) the steady-state response after each iteration is bounded inside the system traveling range. The presented control algorithm is demonstrated experimentally.

In this study, we present a novel concept of a multi tethered drone system. The system includes an arbitrary number of drones connected serially to an active ground station. The considered drones are of quadrotor type. Utilizing a unique pulley–gimbal mechanism, each drone can freely move along the tether, and its state is measured with respect to the ground station without the use of standard onboard inertial sensors or GPS. The proposed system can be thought of as a robotic arm where each tether section acts as a variable-length link and each drone is a joint actuator. We model the coupled behavior of the ground station and the string, taking into account an arbitrary number of drones. Then, a controller that combines tools from geometric-control and Model Predictive Control is suggested. The developed model and control approach are also applicable for other swarm applications where the position of agents is to be controlled to a string-like form. Finally, the concept is demonstrated using numerical simulations and an initial experiment, which illustrate its potential effectiveness.

This research is motivated by the problem of regenerative chatter vibration, which is an extremely harmful phenomenon in machining in general, and in internal turning in particular. In addition to limiting the production rate and accelerating the tool wear, regenerative chatter deteriorates the surface finish, which is especially undesired in the context of precision machining. This paper presents an active control design method for slender bars with delayed excitation which can be applied to the problem of active control of regenerative chatter in internal turning. The presented control method is based on the delay-dependent output feedback controller synthesis. The contribution of the presented design approach stems from incorporating into the design procedure the delayed dynamics of the regenerative chatter, the flexible bar model uncertainty, and the hardware limitations. Furthermore, the delay dynamics is taken explicitly in the synthesis of an H ∞ output feedback controller by linear matrix inequalities. The resulting controller is tested by simulations and experiments using a testbed imitating the dynamics of the internal turning process. The results demonstrate the effectiveness of the presented controller synthesis method in comparison to the commonly used approaches.

Turning machining is an important manufacturing process, widely used in industry. Dynamic interaction between the tool and the workpiece may cause regenerative chatter, which is associated with problems of poor surface finish, reduced product quality and low productivity. The demand for high accuracy motivates development of active vibration control methods that are based on realistic dynamical models of the turning process. This paper discusses the development of an active robust control law that is based on an extended regenerative chatter vibration model for orthogonal cutting. Its novelty stems from the way the workpiece elastic behavior is taken into consideration. The presented numerical results show that the vibration level can be reduced significantly, even in the presence of external disturbances, parametric uncertainty and (open loop) unstable machining conditions.

This paper presents a new yaw stability controller for a rear double-driven electric vehicle. A linear parameter varying (LPV) model of the vehicle is formulated using longitudinal speed measurement and tire cornering stiffness estimation. The LPV model is then utilized to design a gain-scheduled (H_∞) controller with guaranteed stability. Results from simulations, performed with CarSim, show that the new controller improves the vehicle performance and handling even in extreme maneuvers and that it is robust to model parameter uncertainties.

This study considers the lean angle stability problems in steering controlled tilting vehicles. Despite the fact that the considered nonlinear nonminimum phase model ignores some dynamic characteristics of the real system (we ignore wheel sleeping and wheel inertia), yet it captures important properties of the vehicle dynamics. We establish a stabilizing control strategy for the lean angle of the vehicle. To eliminate impulse behavior (due to the appearance of the derivative of the steering angle) we propose using Lyapunov stability theory a continuous feedback loop for the steering input signal that ensures exponential stability of a desired lean angle. The process of stabilizing a desired lean angle does not imply trajectory tracking, however the current approach can be extended to yield further results regarding trajectory tracking for the complicated model of a two-wheeled vehicle system like bicycles and motorcycles.

Carrying a load by a group of drones can be done in different configurations, which may also be changed during flight. There are many considerations when planning the applied configuration; most importantly, the number of drones should fit the weight of the load. Energy is a critical factor, because of its influence on the flight range. Previous configurations presented in literature include counteracting carrying forces, which deteriorate energy efficiency. To prevent this, we propose an innovative carrying configuration that is based on a string of drones. Each drone is connected to the drone below, by a cable, and the lowest drone is connected with the load. The paper deals with a point-load carried by a string of n drones. It shows the development of the group's equations of motion, and the design of a control law that allows the load to track a desired trajectory.

This paper focuses on the control design problem of a tethered drone. The suggested concept has the potential to solve some basic difficulties related to the use of small drones, such as their short flight duration, limited lifting ability and the need of precise indoor position sensing. Here, the end of the tether is connected to the drone, while the other side is wrapped on a spool driven by a DC motor, fixed on the ground. Under the assumption that the tether is kept taut at all time, a full autonomous flight can be achieved indoors, where the tether functions as a position sensor. The tether is pulled from its two sides, by the ground motor and the drone. Critical constraints, driven from this configuration, demand positive tether tension and limited flight space. Hence, a unified model is developed for the combined ground-aerial system, and a model predictive control approach is taken, to allow for optimal control under state and input constraints. Simulations results show the performance of the design for both set-point and trajectory tracking cases.

One approach to quantitative model-based fault detection and isolation (FDI) is based on analytical redundancy relations (ARRs) and fault signatures. Numerical evaluation of ARRs creates residuals, which then, provide online information of consistency between the system and its nominal model. An inconsistency is represented by a signature. Traditionally in the quantitative approach, these signatures are binary vectors, where the term 0 means a residual is consistent and 1 means inconsistent. In this paper, the measured trend of residuals is utilized for FDI by a different signature type, called sensitivity signature. In this signature, the consistency of ARRs is represented by three terms; the term + 1 indicates a residual is crossing an upper threshold, the term − 1 indicates a residual is crossing a lower threshold and 0 means otherwise. The expected sensitivity signature related to a certain fault or to a mode change is taken from partial derivative of residuals. Since consistency, in the sensitivity approach, is represented by three terms (instead of two), more distinguished signatures are generated and improved fault and mode change isolation abilities are achieved. Issues related to practical implementation of the proposed diagnosis method are extensively discussed and experimental results are presented.

In this paper, the problem of vehicle yaw control using an active limited-slip differential (ALSD) applied on the rear axle is addressed. The controller objective is to minimise yaw-rate and body slip-angle errors, with respect to target values. A novel model predictive controller is designed, using a linear parameter-varying (LPV) vehicle model, which takes into account the ALSD dynamics and its constraints. The controller is simulated using a 10DOF Matlab/Simulink simulation model and a CarSim model. These simulations exemplify the controller yaw-rate and slip-angle tracking performances, under challenging manoeuvres and road conditions. The model predictive controller performances surpass those of a reference sliding mode controller, and can narrow the loss of performances due to the ALSD's inability to transfer torque regardless of driving conditions.

Many Mössbauer spectroscopy (MS) experiments have used a rotating absorber in order to measure the second-order transverse Doppler (TD) shift, and to test the validity of the Einstein time dilation theory. From these experiments, one may also test the clock hypothesis (CH) and the time dilation caused by acceleration. In such experiments the absorption curves must be obtained, since it cannot be assumed that there is no broadening of the curve during the rotation. For technical reasons, it is very complicated to keep the balance of a fast rotating disk if there are moving parts on it. Thus, the Mössbauer source on a transducer should be outside the disk. Friedman and Nowik have already predicted that the X-ray beam finite size dramatically affects the MS absorption line and causes its broadening. We provide here explicit formulas to evaluate this broadening for a synchrotron Mössbauer source (SMS) beam. The broadening is linearly proportional to the rotation frequency and to the SMS beam width at the rotation axis. In addition, it is shown that the TD shift and the MS line broadening are affected by an additional factor assigned as thealignment shiftwhich is proportional to the frequency of rotation and to the distance between the X-ray beam center and the rotation axis. This new shift helps to align the disk's axis of rotation to the X-ray beam's center. To minimize the broadening, one must focus the X-ray on the axis of the rotating disk and/or to add a slit positioned at the center, to block the rays distant from the rotation axis of the disk. Our experiment, using the57Fe SMS, currently available at the Nuclear Resonance beamline (ID18) at the ESRF, with a rotating stainless steel foil, confirmed our predictions. With a slit installed at the rotation axis (reducing the effective beam width from 15.6 µm to 5.4 µm), one can measure a statistically meaningful absorption spectrum up to 300 Hz, while, without a slit, such spectra could be obtained up to 100 Hz only. Thus, both the broadening and the alignment shift are very significant and must be taken into consideration in any rotating absorber experiment. Here a method is offered to measure accurately the TD shift and to test the CH.

The paper presents a new approach for trajectory tracking in a quadrotor-type helicopter. The proposed closed-form control schemes apply smooth bounded hyperbolic functions of the state variables for achieving trajectory tracking in the fully nonlinear system. The current approach accounts for main sources of uncertainties. This is the first time explicit formulas are produced for solutions of the considered control problems. A comparative study with existing controller is presented.

The paper considers control issues in a multi-UAV system as both kinematics and dynamics are intertwined in the mathematical model of the aerial vehicles. To obtain an effective controller for the augmented model of the group members we apply the backstepping procedure. Special attention is given to control a group in a string-like formation and to ensure string stability for reducing the spacing error propagation between vehicles along the string. Finally, demonstrations of the performance and the efficiency of the proposed control algorithms in fulfilling various group tasks, will be presented.

This paper describes the design and control approach of a new vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAV), capable of a plane-like horizontal flight. The UAV design includes dynamical modeling, control design and implementation. The main control challenge with this UAV stems from the complicated and unpredicted behavior of the vehicle during flight state transitions. This paper suggests a safe and efficient transition approach, between horizontal and vertical flights, which is demonstrated trough simulations and experiments. Additionally, real flight tests show that the UAV is capable of both stable hovering and efficient horizontal flight.

The paper considers control problems of a group of frontsteering wheels kinematic nonholonomic vehicles with three wheels. The problems of driving the vehicles towards desired rigid and stringlike formations are considered. Special attention is given to the string stability problem and a control algorithm has been established for regulating propagation of disturbances through the vehicle string. Finally, the effectiveness of the proposed controllers for rigid formation and convoy of vehicles are demonstrated.

The paper considers some control problems of multi mobile robot systems as both kinematics and dynamics are intertwined in the mathematical model of the group members. The effects of all components (wheels and platform) and kinematic constraints will be taken into account in the equations. The problems of driving the vehicle towards a desired string-like formation and the associated stability problem will be studied. Finally, demonstrations of a group of mobile robots with the augmented model will be presented.

In this paper, information from a hybrid bond graph (HBG) model and from discrete-event systems (DESs) is integrated into a fault diagnosis method for hybrid systems. In a pure-HBG framework, mode-change detection and isolation is handled by the mode-change signature and the mode-change signature matrix. In a DES approach, discrete states and faults are traced based on observable events (e.g., control signals) and diagnosers. Based on the two approaches, a new diagnoser that is driven by both observable events and consistency indicators generated by continuous residuals is presented. The proposed method allows not only to effectively trace the system mode but also to decide whether this mode is faulty or normal. The new method is presented and implemented on a testbed. The experimental results presented in this paper demonstrate the effectiveness of the method.

In the STAMP model, based on control theory, the control relationships between various system elements enforced by the closed Control Loops (CLs) are logical and functional. A literature survey emphasized the fact that for the moment STAMP and its main tools STPA and CAST are not associated with any numerical tools. The main rationale of our work is to understand whether STAMP matches to be a quantitative model. Furthermore, in a case that we find that numerical tools can be used in STAMP, we intend to bridge the gap between the logical-functional approach in STAMP and any of the suitable quantitative approaches applied in Engineering Control Theory (ECT). As a first step, a literature comparison was performed between the basic control parameters existing explicitly at the moment in the STAMP model, and those well known in the literature of ECT. The results reveal that there are many similar terms, especially related to conceptual and general definitions. However, we have observed that there are also basic quantitative parameters from ECT which are not yet referred to in STAMP as quantitative safety evaluation parameters. Another main finding is an inherent difference in various ECT related parameters and the CLs at the various hierarchical levels. ECT was originally developed to deal with physical systems. Thus, any machine related internal control loops within the lower-physical level of a Sociotechnical System (STS) can be directly addressed with quantitative methods from ECT. However, most of the human-machine interactions in the lower levels and the human and societal controls in the higher levels are at the moment not suitable for those methods. We assume these ECT parameters may have an important role in designing and examining systems safety and hence we suggest, should be integrated into STAMP model, in purpose to be able to enhance systems safety.

The paper proposes control schemes for a multi-quadrotor system flying in formation. The underactuated quadrotor model is highly nonlinear. The control objective is two-fold: to maintain the formation structure in flight along a geometric path and to follow a timing law that dominates the rate of advancement of the group and the arrival times to an assigned site. The paper suggests control strategies for a string-like formation (where all vehicles involved are linked by a virtual thread) and for a rigid formation. The concepts of flat system and virtual formation play essential roles in the current approach. We assume that whenever needed free flow of accurate information between the group members is available. The paper is concentrated on the low level relevant control issues. The leading vehicle governs the overall group motion. However, the control scheme allows formation splitting and merging (assuming the relevant data are available by communication/sensing means) during the group motion. Simulation results conclude the study.

Hybrid systems operate in various states, which are represented by a set of modes. In each mode, the system is governed by continuous dynamics, and different modes correspond to different continuous models. For hybrid systems, model-based fault detection and isolation is a challenging task due to the fact that the system's prevailing dynamical model and its current mode (discrete state) are mutually dependent and intertwined. In this paper, a new energy-based approach is introduced for mode tracking of hybrid systems, and its associated systematic analysis is based on a hybrid bond graph. Each system's mode is characterized by a concise energy relation that allows mode identification in the new mode tracking method.

Recently, a bond-graph-based fault detection and isolation (FDI) framework has been developed with a new concept of global analytical redundancy relations (GARRs) (Low, Wang, Arogeti, and Luo, 2009, 2010; Low, Wang, Arogeti, and Zhang, 2010). This new concept allows the fault diagnosis for hybrid systems which consist of both continuous dynamics and discrete modes. A failure of a safety critical system such as the steering system of an automated guided vehicle may cause severe damage. Such failure can be avoided by an early detection and estimation of faults. In this paper, the newly developed FDI method is studied in details using an electrohydraulic steering system of an electric vehicle. The steering system and faults are modeled as a hybrid dynamic system by the hybrid bond graph (HBG) modeling technique. GARRs are then derived systematically from the HBG model with a specific causality assignment. Fault detection, isolation, and estimation are applied, experimental setup is described, and results are discussed.

This paper presents a novel multicomputer type with a unique structure. This structure allows decoupling angular motion from translational motion along one of the body axes, and by that, five of the body degrees of freedom (DoF) can be controlled independently. The proposed aerial vehicle is a hexacopter with six propellers, such that four propellers are attached to the vehicle body and the other two attached to a seesaw. The seesaw is free to rotate around a single axis that is fixed in the body frame. Compared to a standard hexacopter, this unique design improves the maneuverability of the aerial vehicle, without the price of additional actuators. As opposed to tilting-rotor aerial-vehicle, in the proposed design all actuators generate lift. The paper describes the dynamical model of the novel vehicle and suggests a nonlinear controller to track desired trajectories along five of its DoF. The performances of the design are demonstrated numerically.

This paper presents a control scheme for a linear time invariant (LTI) system with uncertainty and disturbance, which are not assumed to be matched with the control input. The presented control scheme consists of a stabilizing feedback controller and a newly developed feed forward mechanism, which counteracts the uncertainty and disturbance through the reference path. In contrast to the related control methods, such as time delay control (TDC) and uncertainty and disturbance estimation (UDE) based control, the scheme presented in this paper does not impose any structural constraints on the controlled plant. The presented control scheme was verified experimentally using a flexible mechanical testbed with a poorly damped resonance.

The paper solves the trajectory tracking control problem for an unmanned aerial vehicle (UAV) when the input generator dynamic effects are taking into considerations. Using the backstepping method we establish a controller for the considered model that ensures exponential convergence to a given reference trajectory. A two-mode control strategy is applied for increasing the domain of convergence. Then, using the concept of virtual vehicles we consider the application of the proposed controller for a group of UAVs in a rigid formation flight. Simulation results are demonstrated.

The paper presents an approach for set-point control of a quadrotor with a suspended load. In the current approach we assume that the payload is a point mass which is connected to the quadrotor by a rigid massless link. Open- and closed-loop control modes will be applied in coarse and fine phases, respectively. We are concentrating here on a control design of the planar nonlinear model of the considered system. However, the established approach and the obtained results might be a point of departure for further studies on control of the complicated underactuated system of a quadrotor that transports a suspended payload.

All experiments testing time dilation by measuring the spectral shift of a rotating Mossbauer absorber assume that vibrations do not affect the spectral shift because of their purely random nature and claim that the observed shift is due to time dilation only. Our recent experiment using the Synchrotron Mossbauer Source at ESRF revealed, however, a shift due to the non-random periodic vibration patterns caused by the rotor/bearing system. These patterns fit the predictions of the Jeffcott model for such a system with non-zero eccentricity. We have calculated this shift due to the non-random vibrations and the resulting relative shift between two states when the acceleration of the absorber is anti-parallel and parallel to the source. This relative shift exhibits the same behavior as the observed relative shift. Hence, the effect of the spectral shift due to vibrations cannot be ignored in any Mossbauer rotor experiments for testing time dilation. Recommendations for improvement of future rotor experiments testing time dilation are presented.

In this paper, a new controller for the path-following problem of a car-like autonomous vehicle is proposed. This controller is based on a new transformation that, for the case of roll with no slip, transfers the model to a chain form. However, in many practical cases, due to the strong effects of tire slip angles, a roll with no slip assumption is invalid. To cope with the presence of slip, a novel controller is proposed. The new method is based on a vehicle kinematical model, where the tire slip angles are taken into account. The control design method utilizes a peak-to-peak criterion and linear matrix inequality (LMI) tools to attenuate tire slip angle effects on the closed-loop performance.

Bond graph (BG) is an effective tool for modeling complex systems and it has been proven useful for fault detection and isolation (FDI) for continuous systems. BG provides the causal relations between system's variables which allow FDI algorithms to be developed systematically from the graph. In the same spirit, Hybrid bond graph (HBG) is a BG-based modeling approach which provides an avenue to model complex hybrid systems. However, due to mode-varying causality properties of HBG, HBG has not been efficiently-exploited for fault diagnosis. In this work, a comprehensive study on the HBG from FDI viewpoints is presented. Some properties pertaining to the HBG are gained in the study. Based on these findings, a causality assignment procedure and a model approximation technique are developed to achieve a HBG with a desirable causality assignment that leads a unified description of system's behavior. These results lay a foundation for quantitative FDI design for complex hybrid systems.

This research result consists of two parts: one is general theory on causality assignment for hybrid bond graph (HBG) and another is application of this concept to the quantitative fault diagnosis. From Low et al., 2008, a foundation for quantitative bond graph-based fault detection and isolation (FDI) design using HBG is laid. Useful causality properties pertaining to the HBG from FDI perspectives, and the concept of diagnostic hybrid bond graph (DHBG) which is advantageous for efficient and effective FDI applications are proposed. This paper is a continuation of our previous paper (Low et al., 2008). Here, the DHBG is exploited to analyze the hybrid system's fault detectability and fault isolability. Additionally, a quantitative FDI framework for effective fault diagnosis for hybrid systems is proposed. Simulation and experimental results are presented to validate some key concepts of the quantitative hybrid bond graph-based FDI framework.

A mode identification method for hybrid system diagnosis is proposed. The method is presented as a module of a quantitative health monitoring framework for hybrid systems. After fault occurrence, the fault is detected and isolated. The next step is fault parameters estimation, where the size of the fault is identified. Fault parameter estimation is based on data collected from the hybrid system while the system is faulty, and its dynamical model is partially unknown. A hybrid system's dynamics consists of continuous behavior and discrete states represented by modes. Fault parameter estimation requires knowledge of the monitored system's operating mode. The new method utilizes the partially known dynamical model to identify hybrid system modes in the presence of a single parametric fault.

This paper describes a methodology for simultaneous identification of fault parameters and mode switching events for hybrid systems. The method is developed based on the notion of Global Analytical Redundancy Relations (GARRs) from the bond graph model of the hybrid system. A unified formula with mode change time sequence and initial mode coefficients (IMC) is derived to represent the mode switching. Due to the discontinuous characteristic of the mode switching, an adaptive hybrid particle swarm optimization (AHPSO) employing the combination of real valued PSO (RPSO) and binary valued PSO (BPSO) is proposed to optimize different parts of solution simultaneously, a novel individual level adaptive method using fuzzy system is developed to dynamically adjust the algorithm parameters. GARRs are used as a fitness index of the AHPSO. Case studies of different energy domains are carried out to illustrate the efficiency of the proposed algorithm.

Bond graph (BG) is an effective tool for modeling complex systems and it has been proven to be useful for fault detection and isolation (FDI) purposes for large continuous systems. BG provides causality between system's variables which allows FDI algorithms to be developed systematically from the graph. Similarly, Hybrid bond graph (HBG) is a bond graph-based modeling approach which provides an avenue to model complex hybrid systems; however, due to the lack of understanding, HBG has not been well-utilized for fault diagnosis. This is the first of a two-part paper that investigates the feasibility of utilizing HBG for quantitative FDI applications for hybrid systems. In this first paper, we present an analysis on the causality properties of the HBG where useful properties and insights associated with FDI applications are gained. Based on these properties, a causality assignment procedure and modeling approximation techniques are developed to achieve a HBG with a causality that facilitates efficient and effective FDI design for hybrid systems.

In part I of this work, we lay a foundation for quantitative bond graph-based FDI design of hybrid systems using hybrid bond graph (HBG). We discussed the causality properties of HBG from FDI perspectives, and proposed the concept of Diagnostic Hybrid Bond graph (DHBG) which is advantageous for efficient and effective FDI applications. Part II presents a continuation of our previous paper [1]. In this part II of our work, we exploit the DHBG to analyze the system's fault monitoring ability. Additionally, we proposed a quantitative FDI framework for effective fault diagnosis for hybrid systems.