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IN THIS ISSUE

### Research Papers

J. Dyn. Sys., Meas., Control. 2018;140(9):091001-091001-11. doi:10.1115/1.4039485.

A high-performance controller and strategy can significantly ameliorate the dynamic and transient capability of doubly fed induction generator (DFIG) based wind turbine. As regards, the wind speed has essentially defined the generated power by DFIG, thus, both the active and the reactive power must be followed out according to the entrance wind in the nominal and disturbance conditions. Toward this objective, noninteger order fuzzy proportional integral derivative (NIOFPID) controller based direct power control (DPC) strategy is proposed in this paper to minimize the deviation of both active and reactive power with the aim of accurate and speedy tracking of these powers. In the same vein, the aforementioned problem must be formulized in the form of the multi-objective optimization problem. Multi-objective particle swarm optimization (MOPSO) is here taken into account to intermingle with the simultaneous coordination of NIOFPIDs. The performance of held forth controller has been further evaluated under the affected power system caused by short circuit and flicker events. Eventually, the simulation results under transient and steady-state conditions demonstrate the dynamic and transient performance of NIOFPID-based DPC.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091002-091002-8. doi:10.1115/1.4039414.

Magnetorheological (MR) fluids, well established as components of a variety of suspension systems, may offer opportunities to improve the performance of fabric ballistic protection systems, which typically do not incorporate significant energy dissipation mechanisms. A series of ballistic impact experiments has been conducted to investigate the potential of MR fluid damped fabric suspension systems to improve upon current fabric barrier designs. The results indicate that for the simple fabric suspension systems tested, MR fluid damping does not improve upon the very high weight specific ballistic performance of state of the art aramid fibers.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091003-091003-11. doi:10.1115/1.4039365.

This paper investigates a nonlinear control design for trajectory tracking and rate of penetration (ROP) control of the vertical downhole drilling process. The drilling system dynamics are first built incorporating the coupled axial and torsional dynamics together with a velocity-independent drill bit–rock interaction model. Given the underactuated, nonlinear, and nonsmooth feature of the drilling dynamics, we propose a control design that can prevent significant downhole vibrations, enable accurate tracking, and achieve desired rate of penetration. It can also ensure robustness against modeling uncertainties and external disturbances. The controller is designed using a sequence of hyperplanes given in a cascade structure. The tracking control is achieved in two phases, where in the first phase the drilling system states converge to a high-speed drilling regime free of stick–slip behavior, and in the second phase, the error dynamics can asymptotically converge. Finally, we provide simulation results considering different case studies to evaluate the efficacy and the robustness of the proposed control approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091004-091004-8. doi:10.1115/1.4039468.

This paper deals with the design of sliding mode controller (SMC) with proportional plus integral sliding surface for regulation and tracking of uncertain process control systems. However, design method requires linear state model of the system. Tuning parameter of SMC has been determined using linear quadratic regulator (LQR) approach. This results in optimum sliding surface for selected performance index. Matched uncertainty is considered to obtain the stability condition in terms of its upper bound. A conventional state observer has been used to estimate the states. The estimated states are then fed to controller for determining control signal. The simulation study and experimentation on real-life level system have been carried out to validate performance and applicability of the proposed controller.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091005-091005-11. doi:10.1115/1.4039277.

Owing to the hierarchical architecture of the derived model of the omni-direction autonomous ground vehicle (OD-AGV), the virtual desired trajectory (VDT) is first designed by the first switching surface, which is set as the linear dynamic pose error of the OD-AGV. In sequence, the trajectory tracking control (TTC) is designed by the second switching surface, which is the linear dynamic tracking error of the VDT. To deal with nonlinear time-varying uncertainties including system disturbance and different ground conditions, enhanced fuzzy second-order variable structure control (EF2VSC) is designed into both VDT and TTC. Finally, the experiments for tracking the circular trajectories with different curvatures, traveling velocities, and poses of the OD-AGV are presented to validate the effectiveness and robustness of the proposed hierarchical enhancement using fuzzy second-order variable structure control (HEF2VSC).

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091006-091006-15. doi:10.1115/1.4039483.

New efforts have been made to build up prototypes of subcutaneous closed-loop systems for controlling blood glucose (BG) levels in type I diabetes mellitus (TIDM) patients with the development of clinically accurate continuous glucose monitors, automated micro-insulin dispenser (MID), and control algorithms. There is an urgency to develop new control algorithm to determine the desired dose of insulin for maintaining normal BG levels. As a solution to the above issue, a novel backstepping sliding mode Gaussian controller (BSMGC) is proposed whose gains vary dynamically with respect to the error signal. A feedback control law is formulated by a hybrid approach based on BSMGC. A ninth-order linearized state-space model of a nonlinear TIDM patient with the MID is formulated for the design of the BSMGC. This controller is evaluated, and the results are compared with other recently published control techniques. The output responses clearly reveal the better performance of the proposed method to control the BG level within the range of normoglycaemia in terms of accuracy, robustness and handling uncertainties.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091007-091007-14. doi:10.1115/1.4039488.

In this paper, we present a discontinuous cytotoxic T cells (CTLs) response for HTLV-1. Moreover, a delay parameter for the activation of CTLs is considered. In fact, a system of differential equation with discontinuous right-hand side with delay is defined for HTLV-1. For analyzing the dynamical behavior of the system, graphical Hopf bifurcation is used. In general, Hopf bifurcation theory will help to obtain the periodic solutions of a system as parameter varies. Therefore, by applying the frequency domain approach and analyzing the associated characteristic equation, the existence of Hopf bifurcation by using delay immune response as a bifurcation parameter is determined. The stability of Hopf bifurcation periodic solutions is obtained by the Nyquist criterion and the graphical Hopf bifurcation theorem. At the end, numerical simulations demonstrated our results for the system of HTLV-1.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091008-091008-10. doi:10.1115/1.4039484.

In this work, we have discussed the fuzzy solutions for fuzzy controllable problem, fuzzy feedback problem, and fuzzy global controllable (GC) problems. We use the method of successive approximations under the generalized Lipschitz condition for the local existence and furthermore, we have described the contraction principle under suitable conditions for global existence and uniqueness of fuzzy solutions. We have too the GC results for fuzzy systems. Some examples and computer simulation illustrating our approach are also given for these controllable problems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091009-091009-15. doi:10.1115/1.4039482.

Gravity is usually neglected in the dynamic modeling and analysis of the transmission system, especially in some relatively lightweight equipment. The weight of wind turbine gearbox is up to tens of tons or even hundreds of tons, and the effects of gravity have not been explored and quantified. In order to obtain accurate vibration response predictions to understand the coupled dynamic characteristics of the wind turbine gear transmission system, a comprehensive, fully coupled, dynamic model is established by the node finite element method with gravity considered. Both time-domain and frequency-domain dynamic responses are calculated using the precise integration method with various excitations being taken into account. The results indicate that gravity has a significant impact on the vibration equilibrium position of central floating components, but the changing trends are different. Gravity does not change the composition of the excitation frequency, but will have a certain impact on the distribution ratio of the frequency components. And the high frequency vibrations are hardly affected by gravity. In addition, the load sharing coefficient is greater when gravity is taken into account, both of internal gearing and of external gearing system. When the planet gears have a certain position error in accordance with certain rules, the load sharing performance of the system will be better.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091010-091010-12. doi:10.1115/1.4039486.

Hybrid electric vehicles (HEV) offer improved fuel efficiency compared to their conventional counterparts at the expense of adding complexity and at times, reduced total power. As a result, HEV generally lack the dynamic performance that customers enjoy. To address this issue, the paper presents a HEV with electric all-wheel drive (eAWD) capabilities via the use of a torque vectoring electric rear axle drive (TVeRAD) unit to power the rear axle. The addition of TVeRAD to a front wheel drive HEV improves the total power output. To further improve the handling characteristics of the vehicle, the TVeRAD unit allows for wheel torque vectoring (TV) at the rear axle. A bond graph model of the proposed drivetrain model is developed and used in cosimulation with carsim. The paper proposes a control system, which utilizes slip ratio optimization to allocate control to each tire. The optimization algorithm is used to obtain optimal slip ratio targets to at each tire such that the targets avoid tire saturation. The Youla parameterization technique is used to develop robust tracking controllers for each axle. The proposed control system is ultimately tested on the drivetrain model with a high fidelity carsim vehicle model for validation. Simulation results show that the control system is able to maximize vehicle longitudinal performance while avoiding tire saturation on a low μ surface. More importantly, the control system is able to track the desired yaw moment request on a high-speed double-lane change (DLC) maneuver through the use of the TVeRAD to improve the handling characteristic of the vehicle.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091011-091011-8. doi:10.1115/1.4039666.

The consensus problem for multiple Euler–Lagrange systems has been extensively studied under various assumptions on the connectivity of the communication graph. In practice, it is desirable to enable the control law the capability of maintaining the connectivity of the communication graph, thus achieving consensus without assuming the connectivity of the communication graph. We call such a problem as consensus with connectivity preservation. In this paper, we will study this problem for multiple uncertain Euler–Lagrange systems. By combining the adaptive control technique and potential function technique, we will show that such a problem is solvable under a set of standard assumptions. By employing different potential functions, our approach will also lead to the solution of such problems as rendezvous and flocking.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091012-091012-11. doi:10.1115/1.4039669.

We present a novel approach to achieve decentralized distribution of forces in a multirobot system. In this approach, each robot in the group relies on the behavior of a cooperative virtual teammate that is defined independent of the population and formation of the real team. Consequently, such formulation eliminates the need for interagent communications or leader–follower architectures. In particular, effectiveness of the method is studied in a collective manipulation problem where the objective is to control the position and orientation of a body in time. To experimentally validate the performance of the proposed method, a new swarm agent, $Δρ$ (Delta-Rho), is introduced. A multirobot system, consisting of five $Δρ$ agents, is then utilized as the experimental setup. The obtained results are also compared with a norm-optimal centralized controller by quantitative metrics. Experimental results prove the performance of the algorithm in different tested scenarios and demonstrate a scalable, versatile, and robust system-level behavior.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091013-091013-10. doi:10.1115/1.4039664.

Previously, the authors have proposed the concept of piston trajectory-based homogeneous charge compression ignition (HCCI) combustion control enabled by a free piston engine (FPE) and shown its benefits on both engine thermal efficiency and emissions by implementing various piston trajectories. In order to realize the HCCI trajectory-based combustion control in practical applications, a control-oriented model with sufficient chemical kinetics information has to be developed. In this paper, such a model is proposed and its performance, in terms of computational speed and model fidelity, is compared to three existing models: a simplified model using a one-step global reaction, a reduced-order model using Jones–Lindstedt mechanism, and a complex physics-based model including detailed chemical reaction mechanisms. A unique phase separation method is proposed to significantly reduce the computational time and guarantee the prediction accuracy simultaneously. In addition, the paper also shows that the high fidelity of the proposed model is sustained at multiple working conditions, including different air-fuel ratios (AFR), various compression ratios (CR), and distinct piston motion patterns between the two end positions. Finally, an example is presented showing how the control-oriented model enables real-time optimization of the HCCI combustion phasing by varying the trajectories. The simulation results show that the combustion phasing can be adjusted quickly as desired, which further demonstrates the effectiveness of the piston trajectory-based combustion control.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091014-091014-12. doi:10.1115/1.4039670.

The line-of-sight (LOS) kinematics and dynamics of a mirror-stabilized platform are derived using the virtual mass stabilization method. Accounting for the coupled and nonlinear kinematics and dynamics, the uncertainty of external disturbances, and the actuator input saturation in the mirror-stabilized platform, a modified adaptive robust control (ARC) scheme is proposed based on the command filtered method and the extended state observer (ESO). The command-filtered approach is used to ensure the stability and tracking performance of the adaptive control system under the input saturation. In the proposed scheme, the ESO is designed to observe the modeling error and unknown external disturbances. The stability of the control system is proved using the Lyapunov method. Simulation results and experimental results proved that the proposed control scheme can effectively reduce the occurrence of input saturation, attenuate the effect of unknown disturbances, and improve the position tracking accuracy.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091015-091015-14. doi:10.1115/1.4039665.

Proper design of feedback controllers is crucial for ensuring high performance of active magnetic bearing (AMB) supported rotor dynamic systems. Annular seals in those systems can contribute significant forces, which, in many cases, are hard to model in advance due to complex geometries of the seal and multiphase fluids. Hence, it can be challenging to design AMB controllers that will guarantee robust performance for these kinds of systems. This paper demonstrates the design, simulation, and experimental results of model-based controllers for AMB systems, subjected to dynamic seal forces. The controllers are found using $H∞$ and μ synthesis and are based on a global rotor dynamic model in which the seal coefficients are identified in situ. The controllers are implemented in a rotor-dynamic test facility with two radial AMBs and one annular seal with an adjustable inlet pressure. The seal is a smooth annular type, with large clearance (worn seal) and with high preswirl, which generates significant cross-coupled forces. The $H∞$ controller is designed to compensate for the seal forces and the μ controller is furthermore designed to be robust against a range of pressures across the seal. In this study, the rotor is nonrotating. Experimental and simulation results show that significant performance can be achieved using the model-based controllers compared to a reference decentralized proportional-integral-derivative (PID) controller and robustness against large variations of pressure across the seal can be improved by the use of robust synthesized controllers.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091016-091016-9. doi:10.1115/1.4039286.

Appearance-based localization is a robot self-navigation technique that integrates visual appearance and kinematic information. To analyze the visual appearance, we need to build a regression model based on extracted visual features from raw images as predictors to estimate the robot's location in two-dimensional (2D) coordinates. Given the training data, our first problem is to find the optimal subset of the features that maximize the localization performance. To achieve appearance-based localization of a mobile robot, we propose an integrated localization model that consists of two main components: the group least absolute shrinkage and selection operator (LASSO) regression and sequential Bayesian filtering. We project the output of the LASSO regression onto the kinematics of the mobile robot via sequential Bayesian filtering. In particular, we examine two candidates for the Bayesian estimator: the extended Kalman filter (EKF) and particle filter (PF). Our method is implemented in both indoor mobile robot and outdoor vehicle equipped with an omnidirectional camera. The results validate the effectiveness of our proposed approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091017-091017-10. doi:10.1115/1.4039572.

In this paper, an efficiency map is created for a double-acting, single-rod hydraulic-actuator using a critically centered four-way spool valve and a load-sensing pump. The purpose of this research is to provide an understanding of the performance of a valve-controlled hydraulic actuator under all operating conditions. This paper considers a four-quadrant set of operating conditions, where each quadrant represents a different combination of actuator retraction or extension and overrunning or resistive loading. This four-quadrant efficiency map is the first presentation of its kind in the literature, and clearly demonstrates the performance characteristics and limitations for this hydraulic system. For its most common operation of an actuator extending under a resistive load, the map shows that this system can operate at over 82% efficiency and can move large loads. The map also shows physical limitations for the system, such as maximum pressure limits, maximum displacement limits, and valve limits. The efficiency map is plotted in nondimensional form, which presents the most general understanding of system performance and also allows dimensional values to be reconstructed for a similar system of any size.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(9):091018-091018-5. doi:10.1115/1.4039487.

The problem addressed in this paper is the online differentiation of a signal/function that possesses a continuous but not necessarily differentiable derivative. In the realm of (integer) high-order sliding modes, a continuous differentiator provides the exact estimation of the derivative $f˙(t)$, of f(t), by assuming the boundedness of its second-order derivative, $f¨(t)$, but it has been pointed out that if $f˙(t)$ is casted as a Hölder function, then $f˙(t)$ is continuous but not necessarily differentiable, and as a consequence, the existence of $f¨(t)$ is not guaranteed, but even in such a case, the derivative of f(t) can be exactly estimated by means of a continuous fractional sliding mode-based differentiator. Then, the properties of fractional sliding modes, as exact differentiators, are studied. The novelty of the proposed differentiator is twofold: (i) it is continuous, and (ii) it provides the finite-time exact estimation of $f˙(t)$, even if $f¨(t)$ does not exist. A numerical study is discussed to show the reliability of the proposed scheme.

Topics: Signals
Commentary by Dr. Valentin Fuster

### Technical Brief

J. Dyn. Sys., Meas., Control. 2018;140(9):094501-094501-6. doi:10.1115/1.4039367.

A negative input shaped command is presented for flexible systems to reduce the residual oscillation under unequal acceleration and braking delays of actuators that are common issues in industrial applications. Against this nonlinearity, a compensated unit magnitude zero vibration (UMZV) shaper is analytically developed with a phasor vector diagram and a ramp-step function to approximate the dynamic response of the unequal acceleration and braking delays of actuators. A closed-form solution is presented with a benchmark system without sacrificing the generality and simplicity for industrial applications. The robustness and control performance of the exact solution are numerically evaluated and compared with those of an existing negative input shaper in terms of the switch-on time, command interference, and effects of the shaper parameters. The proposed negative input shaped commands are experimentally validated with a mini-bridge crane.

Commentary by Dr. Valentin Fuster