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Research Papers

J. Dyn. Sys., Meas., Control. 2017;139(5):051001-051001-12. doi:10.1115/1.4035168.

Input constraints are active in robot trajectory planning when a mobile robot traverses mobility challenges such as steep hills that limit the acceleration of the robot due to the torque constraints of the motor or engine or in manipulator lifting tasks when the load is sufficiently heavy that the torque constraints of the robot's motor prevent it from statically supporting the load in regions of the robot's workspace. This paper presents a general methodology for solving these planning tasks using a minimum-time cost function and applies it to the problem of a multiple degrees-of-freedom (DOF) manipulator lifting a heavy load. Planning for these types of problems requires use of the robot's dynamic model. Here, we plan using sampling-based model predictive optimization (SBMPO), which is only practical if the planning can be done quickly. Hence, substantial attention is given to efficient computations by: (1) using the dynamic model without integrating it, (2) using optimal control theory to develop an “optimistic A* estimate of cost-to-goal,” which is in this case a rigorous lower bound on the minimum time from a current state to a goal state, and (3) using prior experience to speed up the computation of a new trajectory. The methodology is experimentally verified for heavy lifting using a two-link manipulator.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051002-051002-12. doi:10.1115/1.4035174.

A first principle based-control oriented gasoline engine model is proposed that is based on the mathematical model of the actual piston and crankshaft mechanism. Unlike conventional mean value engine models (MVEMs), which involve approximating the torque production mechanism with a volumetric pump, the proposed model obviates this rather over-simplistic assumption. The alleviation of this assumption leads to the additional features in the model such as crankshaft speed fluctuations and tension in bodies forming the mechanism. The torque production dynamics are derived through Lagrangian mechanics. The derived equations are reduced to a suitable form that can be easily used in the control-oriented model. As a result, the abstraction level is greatly reduced between the engine system and the mathematical model. The proposed model is validated successfully against a commercially available 1.3 L gasoline engine. Being a transparent and more capable model, the proposed model can offer better insight into the engine dynamics, improved control design and diagnosis solutions, and that too, in a unified framework.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051003-051003-8. doi:10.1115/1.4035297.

In this paper, we develop a model to determine the temperature distribution in moving webs due to heating by radiation panels and convection from the web surface. Heating of the transported material is common in many web processes, such as printing, coating, and lamination. Radiation panels provide a simple and noncontact means for web heating. To develop a governing equation for moving web temperature, we treat the web as a moving medium under a heating source which is the radiation panel. We consider both radiation and convection and changes in the convection coefficient in the air film between the web surface and the heating source. Using the temperature governing equation, one can predict the web temperature in the moving web that is transported with different speeds under the heating panels. The model development and analysis are dimensionless; therefore, it can be applied to a variety of web materials and heating panel locations. The model development is motivated by the roll-to-roll (R2R) atomic/molecular layer deposition (ALD/MLD) application, and an experimental platform designed to conduct ALD/MLD is employed to validate the model for different scenarios. Comparative results from experiments and model simulations for varying speeds and different operating conditions are provided to validate the model.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051004-051004-9. doi:10.1115/1.4035169.

A novel open-loop control method is presented for mobile robots based on an asymptotic inverse dynamic solution and trajectory planning. The method is based on quantification of sliding by a small nondimensional parameter. Asymptotic expansion of the equations yields the dominant nonslip solution along with a first-order correction for sliding. A trajectory planning is then introduced based on transitional circles between the robot initial states and target reference trajectory. The transitional trajectory ensures smooth convergence of the robot states to the target reference trajectory, which is essential for open-loop control. Experimental results with a differential drive mobile robot demonstrate the significant improvement of the controller performance when the first-order correction is included.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051005-051005-15. doi:10.1115/1.4035235.

Electricity generation from moving currents without using dams (i.e., in-stream hydrokinetic electricity) has the potential to introduce multiple GW of renewable power to U.S. grids. This study evaluates a control system designed to regulate the generator rotor rate (rpm) to improve power production from in-stream hydrokinetic turbines. The control algorithm is evaluated using numerical models of both a rigidly mounted tidal turbine (TT) and a moored ocean current turbine (OCT) coupled to an induction electric machine model. The moored simulation utilizes an innovative approach for coupling a multiple degrees-of-freedom (DOF) nonlinear hydrodynamic/mechanical turbine model with a nonlinear electromechanical generator model. Based on the turbine torque-speed characteristic, as well as the asynchronous machine features, a proportional–integral (PI) controller is used to generate a correction term for the frequency of the three-phase sinusoidal voltages that are supplied to the asynchronous generator. The speed control of the induction generator through the supply frequency is accomplished by a simplified voltage source inverter (VSI). The simplified VSI consists of control voltage sources (CVSs), while the comparison with a real VSI using diodes and transistors, which are controlled by pulse width modulation (PWM) technique, is also presented. Simulations are used to evaluate the developed algorithms showing that rpm fluctuations are around 0.02 for a tidal turbine operating in a wave field with a 6 m significant wave height and around 0.005 for a moored ocean current turbine operating in a wave field with a 2 m significant wave height.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051006-051006-17. doi:10.1115/1.4035236.

This paper presents a simplified decoupler-based multivariable controller with a gain scheduling strategy in order to deal with strong nonlinearities and cross-coupled characteristics for exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT) systems in diesel engines. A feedback controller is designed with the gain scheduling strategy, which updates control gains according to engine operating conditions. The gain scheduling strategy is implemented by using a proposed scheduling variable derived from indirect measurements of the EGR mass flow, such as the pressure ratio of the intake, exhaust manifolds, and the exhaust air-to-fuel ratio. The scheduling variable is utilized to estimate static gains of the EGR and VGT systems; it has a large dispersion in various engine operating conditions. Based on the estimated static gains of the plant, the Skogestad internal model control (SIMC) method determines appropriate control gains. The dynamic decoupler is designed to deal with the cross-coupled effects of the EGR and VGT systems by applying a simplified decoupler design method. The simplified decoupler is beneficial for compensating for the dynamics difference between two control loops of the EGR and VGT systems, for example, slow VGT dynamics and fast EGR dynamics. The proposed control algorithm is evaluated through engine experiments. Step test results of set points reveal that root-mean-square (RMS) error of the gain-scheduled feedback controller is reduced by 47% as compared to those of the fixed gain controller. Furthermore, the designed simplified decoupler decreased the tracking error under transients by 14–66% in various engine operating conditions.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051007-051007-13. doi:10.1115/1.4035349.

In comparison control performance with more complex and nonlinear control methods, the classical linear controller is poor because of the nonlinear uncertainty action that the continuously variable transmission (CVT) system is operated by the synchronous reluctance motor (SynRM). Owing to good learning skill online, a blend amended recurrent Gegenbauer-functional-expansions neural network (NN) control system was developed to return to the nonlinear uncertainties behavior. The blend amended recurrent Gegenbauer-functional-expansions NN control system can fulfill overseer control, amended recurrent Gegenbauer-functional-expansions NN control with an adaptive dharma, and recompensed control with a reckoned dharma. In addition, according to the Lyapunov stability theorem, the adaptive dharma in the amended recurrent Gegenbauer-functional-expansions NN and the reckoned dharma of the recompensed controller are established. Furthermore, an altered artificial bee colony optimization (ABCO) yields two varied learning rates for two parameters to find two optimal values, which helped improve convergence. Finally, the experimental results with various comparisons are demonstrated to confirm that the proposed control system can result in better control performance.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051008-051008-11. doi:10.1115/1.4035296.

A computational solution to the inverse sinusoidal input describing function (SIDF) for a broad class of static nonlinearities is presented. The proposed numerical solution uses the SIDF gain and phase distortions to identify the nonlinearity. This solution, unlike existing methods in the literature, does not require a priori knowledge of the nonlinearity structure in the estimation process and is applicable to both single- and double-valued nonlinearities. The output from the algorithm is a nonparametric model of the nonlinearity from which a parametric model can be recovered by least-square estimation (LSE) method. Three examples are presented to validate the proposed algorithm.

Topics: Algorithms , Signals
Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051009-051009-11. doi:10.1115/1.4035295.

This research study performs an observability analysis of the relative localization problem related to multirobotic systems. The study considers different constraints related to the availability of relative position measurements and platform velocity measurements. Constraints related to these measurement sources arise due to several reasons such as, sensing limitations especially in aerial platforms, field of view limitations of sensors, and communication bandwidth limitations that may affect the available measurement rate. Although numerous observability studies are reported for localization of multirobot systems, most of these studies do not investigate the problem under constraints related to platform velocity sensing capabilities, and moreover, these do not investigate the global uniqueness of its results. This paper analyzes observability of the relative localization problem in detail for multiple practical scenarios having limited measurement sources and then extends the study with a global uniqueness analysis of the results. The paper establishes theoretical limitations and design recommendations relevant to relative localization frameworks, which are validated through numerical and experimental evaluations using a multirobot system equipped with relative positioning sensors.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051010-051010-6. doi:10.1115/1.4035240.

In this paper, a new systematic approach for stability analysis and controller design of nonlinear solar photovoltaic (PV) power system is proposed. Based on a nonquadratic Lyapunov function (NQLF), a model-based dynamic nonparallel-distributed compensation (non-PDC) controller and descriptor representation, the problem of the output tracking is formulated in terms of linear matrix inequalities (LMIs). Furthermore, some slack LMI variables are introduced in the problem formulation which lead to more relaxed conditions. Finally, to illustrate the merits of the proposed approach, it is applied to a PV power system in which the reference voltage is calculated from the maximum power point tracking (MPPT) method.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051011-051011-12. doi:10.1115/1.4035238.

This paper deals with the attitude stabilizing control problem for a rigid spacecraft in the presence of model uncertainties, external disturbances, and actuator faults when delay effects and control input constraints are taken into consideration. First, a backstepping method is introduced in the control design for compensating unknown delays in inputs. Then, a disturbance observer is investigated for estimating model uncertainties, external disturbances, and actuator fault effects. The backstepping controller is augmented with the reconstructed information provided by the disturbance observer to make the closed-loop system insensitive to disturbances and faults. Next, the proposed observer–controller structure is redesigned to deal with control constraints. Rigorous proofs show that the developed control under simple sufficient conditions can render the system globally input-to-state stable (ISS). Numerical simulations are presented to illustrate the effectiveness of the proposed controllers.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051012-051012-7. doi:10.1115/1.4035455.

The control of overhead transmission lines vibrations is achieved by Stockbridge dampers. However, the effectiveness of the damper is significantly dependent on its location on the conductor. This paper studies the arrangement of Stockbridge dampers on power lines vibrations using both analytical and experimental approaches. An explicit expression of the loop length is presented for the first time. This expression is used to determine the optimal damper location based on a rational approach. The effectiveness of the proposed approach is validated numerically and experimentally. The results show very good agreement and indicate that Stockbridge dampers are more effective for asymmetrical damping arrangement with the bigger counterweight oriented toward the tower.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(5):051013-051013-10. doi:10.1115/1.4035398.

This paper studies the inverse kinematics (IKs) of a space robot with a controlled-floating base. Different from the traditional space robot which has a free-floating base, the momentum conservation is no longer satisfied so that the degrees-of-freedom (DOFs) and redundancy of the robot obviously increase, and motion limits exist for both base and manipulator. To deal with such a problem, a gradient projection of weighted Jacobian matrix (GPWJM) method is proposed. The Jacobian matrix is derived considering the additional DOFs of the base, and the trajectory tracking by the end-effector is chosen as the main task. A clamping weighted least norm scheme is introduced into the derived Jacobian matrix to avoid the motion limits, and the singular-robustness is enhanced by the damping least-squares. The convergence and accuracy analysis indicates the calculation of damping factor; while the verification of motion limits avoidance indicates the inequality constraint of clamping velocity. Finally, the effectiveness of the proposed GPWJM method is investigated by the numerical simulation in which a planar 3DOF manipulator on a 3DOF base is taken as a demo.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Dyn. Sys., Meas., Control. 2017;139(5):054501-054501-7. doi:10.1115/1.4035234.

A method is presented for tip-over stability analysis of a wheeled mobile manipulator. A wheeled mobile manipulator may tip over resulting from its operation. In this study, first a Newton–Euler formulation is applied to formulate the manipulator’s reaction forces and moments exerted onto the mobile platform. Tip-over criterion is derived to judge the system stability. Three load and motion analyses are carried on. The first static load deals with links and payload to show the effect of the horizontal position of the system’s center of gravity (CG). The second and third are the inertial forces resulting from joint speeds and accelerations, respectively. Case study is path planning with tip-over criterion result which can make the system stable along the path. The simulation results demonstrate the effectiveness of the proposed method.

Commentary by Dr. Valentin Fuster

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