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Research Papers

J. Dyn. Sys., Meas., Control. 2014;136(4):041001-041001-9. doi:10.1115/1.4026533.

It has been known that redundant constrains in a mechanism can improve the rigidity and stiffness of the mechanism. Some Parallel Kinematic Machines (PKMs) have adopted redundant constraints to enhance their performance and stability. However, limited studies have been conducted on the dynamics of over-constrained mechanisms. While a dynamic model is not essential to machine control, a clear understanding of the dynamic behavior of the system can be useful in identifying the weakest components, optimizing the overall structure, and improving the quality of control. In this paper, the dynamic characteristics of an over-constrained PKM are investigated for the first time. The Newton–Euler formulation is extended to develop the dynamic model of the machine. It is shown that the compliance of deformations of the redundant constraints needs to be taken into account to build a complete and solvable dynamic model since the number of equations derived from the force and moment equilibrium of the PKM components is insufficient to determine all unknown variables. The proposed approach is generic in sense that it can be applied to model dynamic behaviors of other over-constrained machines with a combination of the Newton–Euler formulation and compliance conditions. Its effectiveness has been verified by the dynamic model established for Exechon PKM. The developed dynamic model has its potential to be integrated with control systems to improve accuracy and dynamic performance of real-time control.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041002-041002-10. doi:10.1115/1.4026534.

Reduction of cold start hydrocarbon (HC) emissions requires a proper compromise between low engine-out HC emission and fast light-off of the three way catalytic converter (TWC). In this paper, a hybrid switching system is designed and optimized for reducing HC emissions of a mid-sized passenger car during the cold start phase of FTP-75 (Federal Test Procedure). This hybrid system has the benefit of increasing TWC temperature during the early stages of the driving cycle by switching between different operational modes. The switching times are optimized to reduce the cumulative tailpipe HC of an experimentally validated automotive emission model. The designed hybrid system is tested in real-time on a real engine control unit (ECU) in a model-in-the-loop structure. The results indicate the new hybrid controller reduces the HC emissions over 6.5% compared to nonswitching cold start controller designs.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041003-041003-11. doi:10.1115/1.4026412.

The next generation of aircraft will face more challenging demands in both electrical and thermal loads. The larger thermal loads reduce the propulsion system efficiency by demanding bleed air from the main engine compressor or imposing a shaft load on the high or low pressure shaft. The approach adopted to power the thermal management system influences the overall fuel burn of the aircraft for a given mission. To assess these demands and to explore conceptual designs for the electrical and thermal management system, a dynamic vehicle level tip-to-tail (T2T) model has been developed. The T2T model captures and quantifies the energy exchanges throughout the aircraft. The following subsystems of the aircraft are simulated in the T2T model: air vehicle system, propulsion system, adaptive power thermal management system, fuel thermal management system, electrical system, and actuator system. This paper presents trade studies evaluating the impact of various approaches in power take-off from the main engine and approaches in control strategy. The trade studies identify different control strategies resulting in significant fuel savings for a given mission profile.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041004-041004-8. doi:10.1115/1.4026468.

The aim of this study is to assess the possibility to apply a new control approach dedicated to turbomachinery. The controller is fuzzy based using inputs expressed in polar coordinates. The advantage is that it manages two significant physical quantities, namely tangential and radial velocities that are related to steady state and transient behaviors, respectively. A synchronous filter is associated to the controller in order to enhance the ratio command force/bearing dynamic capacity. The approach was previously applied experimentally with success for the control of an academic test rig. It is adapted here for the control of an industrial compressor whose flexible rotor is supported by active magnetic bearings (AMB). At this stage, only numerical investigations are performed. The controller has to satisfy the standards and the end users requirements. In addition, it should be easy to implement. The behavior of the machine studied is assessed for several configurations of unbalances. A test that corresponds to usual industrial excitations (subsynchronous excitations at nominal speed) is also carried out. Results obtained are satisfactory and give insight into the potential of the approach. In addition, and as the fuzzy controller parameters are independent from the rotor design, the approach is a first step for the standardization of magnetic bearing controller synthesis.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041005-041005-10. doi:10.1115/1.4026473.

Nearly all dynamic systems have input excitations that are either unmeasurable or unknown due to practical constraints such as feasibility or cost. Estimation of these excitations can be useful both in control applications as well as system modeling applications. The objective of this work is to expand upon an observer based approach to estimate unmeasurable or unknown inputs to a dynamic system using linear systems theory in an efficient manner that is suitable for real-time implementation. In this work, we explicitly explore two fundamental questions. How should the structure, dimensionality, and parameterization of an internal model or waveform generator model be selected for a given dynamic system? How do we determine, based on the structure of the dynamic system, whether estimation of exogenous and endogenous inputs is possible? A series of numerical simulations is performed, providing insight into these issues.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041006-041006-5. doi:10.1115/1.4026516.

This paper proposes a method to identify non-Gaussian random noise in an unknown system through the use of a modified system identification (ID) technique in the stochastic domain, which is based on a recently developed Gaussian system ID. The non-Gaussian random process is approximated via an equivalent Gaussian approach. A modified Fokker–Planck–Kolmogorov equation based on a non-Gaussian analysis technique is adopted to utilize an effective Gaussian random process that represents an implied non-Gaussian random process. When a system under non-Gaussian random noise reveals stationary moment output, the system parameters can be extracted via symbolic computation. Monte Carlo stochastic simulations are conducted to reveal some approximate results, which are close to the actual values of the system parameters.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041007-041007-10. doi:10.1115/1.4026324.

Prediction by simulation of the minimum-time lap of a flat and level racing circuit by a high-performance motorcycle is treated. A novel method is described. Constituents of the method comprise: (i) a high-fidelity mathematical model of the vehicle; (ii) a rider model with control of throttle/brake position, steering torque, and upper-body lean torque. The rider model uses linear quadratic optimal preview control with adaptation to variations in running conditions by gain scheduling; (iii) a circuit model; and (iv) a learning process through which the rider arrives at the best speed target. The constituents are discussed in turn. Then, systematic reduction of lap times for each of two circuits is demonstrated. Aspects of the performance of the motorcycle in very fast laps of the circuits are shown, providing evidence of the effectiveness of the method established.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041008-041008-13. doi:10.1115/1.4026532.

Models of the gas exchange process in modern diesel engines typically use manufacturer-provided maps to describe mass flows through, and efficiencies of, the turbine and compressor based on pressure ratios across the turbine and compressor, as well as the turbocharger shaft speed, and in the case of variable-geometry turbochargers, the nozzle position. These look-up maps require multiple interpolations to produce the necessary information for turbocharger performance, and are undesirable when modeling for estimation and control. There have been several previous efforts to reduce dependence on maps with general success, yet many of these approaches remain complex and are not easily integrated into engine control systems. The focus of this paper is the reduction of turbomachinery maps to analytical functions that are amenable to estimator and control design, and have been validated against manufacturer-provided turbomachinery data.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041009-041009-9. doi:10.1115/1.4026602.

The container crane represents the link between the containership and the port. It dictates the general conditions for the efficiency of container handling from the ship to the land and vice versa. While containers are handled by the crane, load swing reduces the rate of container turnover. In order to reduce load swing control systems are employed. Closed-loop control systems contain devices to track the position of the load with respect to the trolley's position. Accurate tracking of the load's motion during operation requires additionally installed sensors. Alternatively, the principle of state estimation can be employed. The observation of the motion of the container is carried out by a system model in parallel to the real system, taking into account the available rope force sensor information. Both, nonlinear system model and nonlinear sensor model are taken into consideration. An unscented Kalman filter is designed to estimate the states of the motion of the load. The observer is validated at the container crane test stand in order to provide accurate states for load swing control. Results are presented and discussed.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041010-041010-12. doi:10.1115/1.4026511.

Analysis of closed-loop systems involving hysteresis is important to both the understanding of these systems and the synthesis of control schemes. However, such analysis is challenging due to the nonsmooth nature of hysteresis nonlinearities. In this paper, singular perturbation techniques are employed to derive an analytical approximation to the tracking error for a system consisting of fast linear dynamics preceded by a piecewise linear hysteresis nonlinearity, which is motivated by applications such as piezo-actuated nanopositioning. The control architecture considered combines hysteresis inversion and proportional-integral feedback, with and without a constant feedforward control. The analysis incorporates the effect of uncertainty in the hysteresis model, and offers insight into how the tracking performance depends on the system parameters and the references, thereby offering guidance in the controller design. Simulation and experimental results on a piezo-actuated nanopositioning system are presented to support the analysis. In particular, the control scheme incorporating the feedforward element consistently outperforms the classical PI controller in tracking a variety of references.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041011-041011-8. doi:10.1115/1.4026467.

In this paper, a robust fuzzy observer-based tracking controller for continuous-time nonlinear systems presented by Takagi–Sugeno (TS) models with unmeasurable premise variables, is synthesized. Using the H norm and Lyapunov approach, the control design for TS fuzzy systems with both unmeasurable premises and system states is developed to guarantee tracking performance of closed loop systems. Sufficient relaxed conditions for synthesis of the fuzzy observer and the fuzzy control are driven in terms of linear matrix inequalities (LMIs) constraints. The proposed method allows simplifying the design procedure and gives the observer and controller gains in only one step. Numerical simulation on a two tank system is provided to illustrate the tracking control design procedure and to confirm the efficiency of the proposed method.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041012-041012-8. doi:10.1115/1.4026652.

This paper develops reduced order, linear models of lithium ion batteries that can be used for model-based power train simulation, design, estimation, and controlling in hybrid and electric vehicles (HEV). First, a reduced order model is derived from the fundamental governing electrochemical charge and Li+ conservation equations that are linearized at the operating state of charge and low current density. The equations are solved using analytical and numerical techniques to produce the transcendental impedance or transfer function from input current to output voltage. This model is then reduced to a low order state space model using a system identification technique based on least squares optimization. Given the prescribed current, the model predicts voltage and other variables such as electrolyte and electrode surface concentration distributions. The second model is developed by neglecting electrolyte diffusion and modeling each electrode with a single active material particle. The transcendental particle transfer functions are discretized using a Padé Approximation. The explicit form of the single particle model impedance can be realized by an equivalent circuit with resistances and capacitances related to the cell parameters. Both models are then tuned to match experimental electrochemical impedance spectroscopy (EIS) and pulse current-voltage data.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041013-041013-7. doi:10.1115/1.4026654.

One of the main issues with vanadium redox flow batteries (VRFBs) is that vanadium ions travel across the membrane during operation which leads to a concentration imbalance and capacity loss after long-term cycling. Precise state-of-charge (SOC) monitoring allows the operator to effectively schedule electrolyte rebalancing and devise a control strategy to keep the battery running under optimal conditions. However, current SOC monitoring methods are too expensive and impractical to implement on commercial VRFB systems. Furthermore, physical models alone are neither reliable nor accurate enough to predict long-term capacity loss due to crossover. In this paper, we present an application of using an extended Kalman filter (EKF) to estimate the total vanadium concentration in each half-cell by combining three voltage measurements and a state prediction model without crossover effects. Simulation results show that the EKF can accurately predict capacity loss for different crossover patterns over a few hundred cycles.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041014-041014-9. doi:10.1115/1.4026659.

In this paper, a new framework for evolution of multi-agent systems (MAS) based on principles of continuum mechanics is developed. Agents are treated as mass particles of a continuum whose evolution (both translation and deformation) is modeled as a homeomorphism from a reference to the current configuration. Such a mapping assures that no two mass particles of the continuum occupy the same location at any given time, thus guaranteeing that inter-agent collision is avoided during motion. We show that a special class of mappings whose Jacobian is only time varying and not spatially varying has some desirable properties that are advantageous in studying swarms. Two specific scenarios are studied where the evolution of a swarm from one configuration to another occurs with no inter-agent collisions while avoiding obstacles, under (i) zero inter-agent communication and (ii) local inter-agent communication. In the first case, a desired map is computed by each agent all knowing the positions of a few leader agents in a reference and the desired configurations. In the second case, paths of n + 1 leader agents evolving in an n-D space are known only to the leaders, while positions of follower agents evolve through updates that are based on positions of n + 1 adjacent agent through local communication with them. The latter is based on a set of weights of communication of follower agents that are predicated on certain distance ratios assigned on the basis of the initial formation of the MAS. Properties of homogeneous maps are exploited to characterize the necessary communication protocol.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041015-041015-10. doi:10.1115/1.4026660.

A control-oriented two-zone charge mixing model is developed to simplify, but to describe mixing of fresh charge and residual gas during the intake stroke. Engine valve timing has a strong influence on the realization of stable homogeneous charge compression ignition (HCCI), since it affects turbulent flow that promotes mixing of fresh charge and residual gas. Controlled auto-ignition of a HCCI engine is achieved by good mixing of fresh charge and residual gas. Therefore, it is useful to develop a mixing model that can be executed in real-time to help extend the operational range of HCCI. For model derivation, the cylinder volume is artificially divided into two zones with a fictitious divider between them. First, the mixed zone consists of fresh charge induced by opening intake valves and some residual gas transferred from the unmixed zone. They are assumed to have been mixed homogeneously so that cold fresh charge gains thermal energy from hot residual gas. Second, the unmixed zone contains the rest of hot residual gas. Mass transfer between them which is forced by a fluid jet is directed from the unmixed zone to the mixed one. Based on the definitions of two zones and interaction between them, a two-zone charge mixing model is derived. To investigate phasing effects of valve timing on charge mixing, comparative simulation was carried out with different valve timings. For experimental validation and calibration of the proposed model, optical engine tests were performed with an infrared (IR) camera, together with GT-power simulation. From good agreement between the model temperature and the estimated temperature from IR images, the model turns out to be useful to describe mixing of fresh charge and residual gas.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041016-041016-5. doi:10.1115/1.4026515.

This paper proposes a novel fault diagnosis approach for the satellite attitude control system with flywheel faults. The key contributions include fault estimation by sparse approximation algorithm and diagnosis of multiple faults. In this paper, a Taylor series expansion is used to derive a fault estimation representation. Based on the sparse property of the faults, fault estimation is formulated as a sparse approximation problem and solved using the orthogonal matching pursuit (OMP) algorithm. Simulation results demonstrate the effectiveness of the proposed method.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041017-041017-9. doi:10.1115/1.4026831.

Flexible link systems are increasingly becoming popular for advantages like superior performance in micro/nanopositioning, less weight, compact design, lower power requirements, and so on. The dynamics of distributed and lumped parameter flexible link systems, especially those in vertical planes are difficult to capture with ordinary differential equations (ODEs) and pose a challenge to control. A representative case, an inverted flexible pendulum with tip mass on a cart system, is considered in this paper. A dynamic model for this system from a control perspective is developed using an Euler Lagrange formulation. The major difference between the proposed method and several previous attempts is the use of length constraint, large deformations, and tip mass considered together. The proposed dynamic equations are demonstrated to display an odd number of multiple equilibria based on nondimensional quantity dependent on tip mass. Furthermore, the equilibrium solutions thus obtained are shown to compare fairly with static solutions obtained using elastica theory. The system is demonstrated to exhibit chaotic behavior similar to that previously observed for vibrating elastic beam without tip mass. Finally, the dynamic model is validated with experimental data for a couple of cases of beam excitation.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041018-041018-8. doi:10.1115/1.4026658.

In this paper, we present a class of nonlinear control scheme for swinging up and stabilization of an underactuated two-link robot called as Pendubot. The main objective of this paper is to present a switched control that swing up and stabilize for almost all combination of initial states given on the four equilibrium points of the double underactuated pendulum. The proposed methodology is based on two control strategies to swing up and stabilize the Pendubot system. The first one is based on Lagrangian dynamics, energy analysis, and stability theory, while the second one is based on linear quadratic regulator. Moreover, here we present a stability analysis of the switched control algorithm. In order to verify the proposed control strategy, experimental results were performed.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041019-041019-11. doi:10.1115/1.4026836.

The paper investigates the optimality of the handbrake cornering, a strategy widespread among rally drivers. Nonlinear optimal control techniques are used to mimic real driver behavior. A proper yet simple cost function is devised to induce the virtual optimal driver to control the car at its physical limits while using the handbrake technique. The optimal solution is validated against experimental data by a professional rally driver performing the handbrake technique on a loose off-road surface. The effects of road surface, inertial properties, center of mass position, and friction coefficient are analyzed to highlight that the optimality of the maneuver does not depend on the particular vehicle data set used. It turns out that the handbrake maneuvering corresponds to the minimum time and minimum (lateral) space strategy on a tight hairpin corner. The results contribute to the understanding of one of the so-called aggressive driving techniques.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041020-041020-7. doi:10.1115/1.4026872.

This paper addresses the problem of absolute stability of Lurie system with interval time-varying delay. The delay range is divided into two equal segments and an appropriate Lyapunov–Krasovskii functional (LKF) is defined. A tighter bounding technique for the derivative of LKF is developed. This bounding technique in combination with the Wirtinger inequality is used to develop the absolute stability criterion in terms of linear matrix inequalities (LMIs). The stability analysis is also extended to the Lurie system with norm-bounded parametric uncertainties. The effectiveness of the proposed approach has been illustrated through a numerical example and Chua's oscillator.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041021-041021-13. doi:10.1115/1.4026832.

We present a new method to compute output gain-scheduled controllers for nonlinear systems. We use structured H-control to precompute an optimal controller parametrization as a reference. We then propose three practical methods to implement a control law which has only an acceptable loss of performance with regard to the optimal reference law. Our method is demonstrated in longitudinal flight control, where the dynamics of the aircraft depend on the operational conditions velocity and altitude. We design a structured controller consisting of a PI-block to control vertical acceleration, and another I-block to control the pitch rate.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041022-041022-7. doi:10.1115/1.4026833.

This paper deals with the problem of robust sampled-data control for an automotive seat-suspension system subject to control input saturation. By using the nature of the sector nonlinearity, a sampled-data based control input saturation in the control design is studied. A passenger dynamic behavior is considered in the modeling of seat-suspension system, which makes the model more precisely and brings about uncertainties as well in the developed model. Robust output feedback control strategy is adopted since some state variables, such as, body acceleration and body deflection, are unavailable. The desired controller can be achieved by solving the corresponding linear matrix inequalities (LMIs). Finally, a design example has been given to demonstrate the effectiveness and advantages of the proposed controller design approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041023-041023-10. doi:10.1115/1.4026834.

This paper describes the design and control of a robotic elbow system, which is actuated with a novel sleeve muscle actuator. The sleeve muscle is a significant step forward from the traditional pneumatic muscle, and provides a substantially improved performance through a fundamental structural change. Specifically, the sleeve muscle incorporates a cylindrical insert to the center of the pneumatic muscle, which eliminates the central portion of the internal volume. As a result of this change, the sleeve muscle provides multiple advantages over the traditional pneumatic muscle, including the increased force capacity over the entire range of motion, reduced energy consumption, and expedited dynamic response. Furthermore, utilizing the load-bearing tube as the insert, the sleeve muscle enables an innovative “actuation-load bearing” structure, which generates a highly compact robotic system to mimic the structure and functionality of biological limbs. The robotic elbow design in this paper serves an example that shows the design and control process of a robotic joint in this integrated structure. This robotic elbow provides a range of motion of 110 deg, approximately 80% of that for a human elbow, and an average torque capacity that exceeds the peak torque of the human elbow. The servo control capability is provided with a model-based sliding-mode control approach, which is able to provide good control performance in the presence of disturbances and model uncertainties. This controller is implemented on the robotic elbow prototype, and the effectiveness was demonstrated with step response and sinusoidal tracking experiments.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041024-041024-12. doi:10.1115/1.4026874.

The development and validation of a novel current-based induction motor (IM) condition monitoring (CM) system is described. The system utilizes only current and voltage signals and conducts fault detection using a combination of model-based and model-free (motor current signature analysis) fault detection methods. The residuals (or fault indicator values) generated by these methods are analyzed by a fuzzy logic diagnosis algorithm that provides a diagnosis with regard to the health of the induction motor. Specifically, this includes an indication of the health of the major induction motor subsystems, namely the stator windings, the rotor cage, the rolling element bearings, and the air-gap (eccentricity). The paper presents the overall system concept, the induction motor models, development of parameter estimation techniques, fault detection methods, and the fuzzy logic diagnosis algorithm and includes results from 110 different test cases involving four 7.5 kW four pole squirrel cage motors. The results show good performance for the four chosen faults and demonstrate the potential of the system to be used as an industrial condition monitoring tool.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041025-041025-16. doi:10.1115/1.4026835.

This research investigates a novel data-driven approach to condition monitoring of electromechanical actuators (EMAs) consisting of feature extraction and fault classification. The approach is able to accommodate time-varying loads and speeds since EMAs typically operate under nonsteady conditions. The feature extraction process exposes fault frequencies in signal data that are synchronous with motor position through a series of signal processing techniques. A resulting reduced dimension feature is then used to determine the condition with a trained Bayesian classifier. The approach is based on signal analysis in the frequency domain of inherent EMA signals and accelerometers. For this work, two common failure modes, bearing and ball screw faults, are seeded on a MOOG MaxForce EMA. The EMA is then loaded using active and passive load cells with measurements collected via a dSPACE data acquisition and control system. Typical position commands and loads are utilized to simulate “real-world” inputs and disturbances and laboratory results show that actuator condition can be determined over a range of inputs. Although the process is developed for EMAs, it can be used generically on other rotating machine applications as a Health and Usage Management System (HUMS) tool.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041026-041026-12. doi:10.1115/1.4026956.

A novel fault detection and identification (FDI) scheme based on sliding mode observer (SMO) residual generator and state machine residual evaluator is presented in this paper. The FDI scheme is applied to actuator and sensor faults in a vehicle chassis steering system described by a nonlinear bicycle model with three degrees of freedom. Primary residual is generated by an expanded SMO designed for linear time varying (LTV) systems. To cope with the multiple faults isolation problem, the state machine records and utilizes the previous fault information to determine the current fault state. Simulation results show that multiple fault detection and isolation can be successfully achieved by the proposed SMO and state-machine-based FDI scheme.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041027-041027-10. doi:10.1115/1.4026957.

A class of problems in air traffic management (ATM) asks for a scheduling algorithm that supplies the air traffic services authority not only with a schedule of arrivals and departures but also with speed advisories. Since advisories must be finite, a scheduling algorithm must ultimately produce a finite data set, hence must either start with a purely discrete model or involve a discretization of a continuous one. The former choice, often preferred for intuitive clarity, naturally leads to mixed-integer programs (MIPs), hindering proofs of correctness and computational cost bounds (crucial for real-time operations). In this paper, a hybrid control system is used to model air traffic scheduling, capturing both the discrete and continuous aspects. This framework is applied to a class of problems, called the fully routed nominal problem. We prove a number of geometric results on feasible schedules and use these results to formulate an algorithm that attempts to compute a collective speed advisory, effectively piecewise linear with finitely many vertices, and has computational cost polynomial in the number of aircraft. This work is a first step toward optimization and models refined with more realistic detail.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):041028-041028-8. doi:10.1115/1.4026965.

Gliding robotic fish, a new type of underwater robot, combines both strengths of underwater gliders and robotic fish, featuring long operation duration and high maneuverability. In this paper, we present both analytical and experimental results on a novel gliding motion, tail-enabled three-dimensional (3D) spiraling, which is well suited for sampling a water column. A dynamic model of a gliding robotic fish with a deflected tail is first established. The equations for the relative equilibria corresponding to steady-state spiraling are derived and then solved recursively using Newton's method. The region of convergence for Newton's method is examined numerically. We then establish the local asymptotic stability of the computed equilibria through Jacobian analysis and further numerically explore the basins of attraction. Experiments have been conducted on a fish-shaped miniature underwater glider with a deflected tail, where a gliding-induced 3D spiraling maneuver is confirmed. Furthermore, consistent with model predictions, experimental results have shown that the achievable turning radius of the spiraling can be as small as less than 0.4 m, demonstrating the high maneuverability.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Dyn. Sys., Meas., Control. 2014;136(4):044501-044501-3. doi:10.1115/1.4026664.

To effectively control a complex mechanical structure for precise performance, a model-based type of controller is usually desired. In cases of controlling parallel robots, however, the iterative computation due to the complexity of the dynamic models can result in difficulties in controller implementations and system stability analysis. To avoid this problem, simplified dynamic models can be obtained through approximation, nevertheless, performance accuracy will suffer due to simplification. This paper suggests applying the effective Design For Control (DFC) approach to handle this problem. The underlying idea of the DFC approach is that, no matter how complex a system is, as long as its mechanical structure can be judiciously designed such that it results in a simple dynamic model, a simple control algorithm may be good enough for a satisfactory control performance. Through out the discussion in the paper, the integrated design and control of a two DOF parallel robot is studied as an illustration example. Experimental validation has demonstrated the effectiveness of the DFC approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):044502-044502-4. doi:10.1115/1.4006079.

This paper focuses on the problem of nonfragile guaranteed cost control for a class of T-S discrete-time fuzzy bilinear systems (DFBS) with time-delay in both states and inputs. Based on the parallel distributed compensation approach, the sufficient conditions are derived such that the closed-loop system is asymptotically stable and the closed-loop performance is no more than a certain upper bound in the presence of the additive controller gain perturbations.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):044503-044503-10. doi:10.1115/1.4026873.

Pneumatic muscle actuators offer a higher force-to-weight ratio compared to traditional cylinder actuators, and introduce stick-slip-free operation that offers an interesting option for positioning systems. Despite several advantages, pneumatic muscle actuators are commonly avoided in industrial applications, mainly due to rather different working principles. Due to the highly nonlinear characteristics of the muscle actuator and pneumatic system, a reliable control strategy is required. Although muscle actuators are widely studied, the literature lacks detailed studies where the performance for servo systems is compared with traditional pneumatic cylinders. In this paper, a pneumatic servo actuation system is compared with a traditional cylinder actuator. As the overall system dynamics are highly nonlinear and not well defined, a sliding mode control (SMC) strategy is chosen for the control action. In order to improve the tracking performance, an SMC strategy with an integral action (SMCI) is also implemented. The control algorithms are experimentally applied on the pneumatic muscle and the cylinder actuator, for the purposes of position tracking. The robustness of the systems are verified and compared by varying the applied loads.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):044504-044504-5. doi:10.1115/1.4026875.

This paper investigates a kind of consensus problem in multi-agent systems, revises an existing control input for consensus by dynamic quantizers, and also gives a visible distributed event-triggered rule to update the parameters for dynamic quantizers. In other words, distributed event-triggered dynamic quantizers are firstly proposed and employed when designing a consensus strategy for multi-agent systems by this paper. Meanwhile, the overall steps of the control strategy are included. The numerical results come to agreement with the theoretical analysis, and shows that the proposed strategy can get faster convergence speed in comparison with an existing one.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):044505-044505-8. doi:10.1115/1.4026876.

In this article, the problem of eigenstructure in descriptor matrix second-order linear systems using combined velocity and acceleration feedbacks is considered. This is promising for better applicability in many practical applications where the velocity and acceleration signals are easier to obtain than the proportional and velocity ones. First, the necessary and sufficient conditions which ensure solvability are derived. Then the parametric expressions of gain controller and eigenvector matrix are formulated. The proposed approach can offer all the degrees of freedom and has great potential in practical applications. The solution is general and can be applied when mass matrices that can be either singular or nonsingular. In this framework, infinite eigenvalues for descriptor systems are relocated by finite ones.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2014;136(4):044506-044506-5. doi:10.1115/1.4026837.

In this study, an Autoregressive with eXogenous input (ARX) model and an Autoregressive Moving Average with eXogenous input (ARMAX) model are developed to predict the overhead temperature of a distillation column. The model parameters are estimated using the recursive algorithms. In order to select an optimal model for the process, different performance measures, such as Aikeke's Information Criterion (AIC), Root Mean Square Error (RMSE), and Nash–Sutcliffe Efficiency (NSE), are calculated.

Commentary by Dr. Valentin Fuster

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