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IN THIS ISSUE

### Research Papers

J. Dyn. Sys., Meas., Control. 2017;139(6):061001-061001-9. doi:10.1115/1.4035359.

A direct integration method (DIM) for time-delayed control (TDC) is proposed in this research. For a second-order dynamic system with time-delayed controllers, a Volterra integral equation of the second kind is used instead of a state derivative equation. With the proposed DIM where matrix exponentials are avoided, semi-analytical representation of the Floquet transition matrix for stability analysis can be derived, the stability region on the parametric space comprising control variables can also be plotted. Within this stability region, optimal control variables are subsequently obtained using a multilevel conjugate gradient optimization method. Further simulation examples demonstrated the superiority of the proposed DIM in terms of computational efficiency and accuracy, as well as the effectiveness of the optimization-based controller design approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061002-061002-8. doi:10.1115/1.4035404.

The objective of this paper is to develop a robust decentralized observer-based feedback model reference tracking control approach for a class of nonlinear disturbed interconnected systems. The proposed H control and observation design method is formulated within an optimization problem involving linear matrix inequalities (LMIs), efficiently solved by a one-step LMI procedure, to compute the decentralized observation and control gain matrices of each subsystem, and to attenuate the external disturbances affecting the subsystems by minimizing a H performance criterion. A numerical simulation is highlighted on a power system with three-interconnected machines to demonstrate the effectiveness of the developed control approach despite the interconnections between different generators, nonlinearities in the system, and external disturbances.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061003-061003-10. doi:10.1115/1.4035451.

This paper presents a model-based blind system identification approach to estimation of central aortic blood pressure (BP) waveform from noninvasive diametric circulatory signals. First, we developed a mathematical model to reproduce the relationship between central aortic BP waveform and a class of noninvasive circulatory signals at diametric locations by combining models to represent wave propagation in the artery, arterial pressure–volume relationship, and mechanics of the measurement instrument. Second, we formulated the problem of estimating central aortic BP waveform from noninvasive diametric circulatory signals into a blind system identification problem. Third, we performed identifiability analysis to show that the mathematical model could be identified and its parameters determined up to an unknown scale. Finally, we illustrated the feasibility of the approach by applying it to estimate central aortic BP waveform from two diametric pulse volume recording (PVR) signals. Experimental results from ten human subjects showed that the proposed approach could estimate central aortic BP waveform accurately: the average root-mean-squared error (RMSE) associated with the central aortic BP waveform was 4.1 mm Hg (amounting to 4.5% of the underlying mean BP) while the average errors associated with central aortic systolic pressure (SP) and pulse pressure (PP) were 2.4 mm Hg and 2.0 mm Hg (amounting to 2.5% and 2.1% of the underlying mean BP). The proposed approach may contribute to the improved monitoring of cardiovascular (CV) health by enabling estimation of central aortic BP waveform from conveniently measurable diametric circulatory signals.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061004-061004-8. doi:10.1115/1.4035348.

Electrohydrostatic actuators (EHAs), as a class of pump-controlled hydraulic actuators, are known for energy efficiency and easy maintainability. Thus, they can be widely used in the situations where actuating pressure/force control of hydraulic actuators is essential. Examples are automotive active suspension, deep-drawing press, molding machine, and vibration isolation. However, a leaky piston seal in an EHA system can be especially problematic as it is not visually detectable, but causes internal leakage flowing across actuator chambers impairing the performance. This paper employs quantitative feedback theory (QFT) to design a robust fixed-gain linear actuating pressure controller that is tolerant to actuator internal leakage. Since QFT captures uncertainties by templates, representing frequency responses of the plant on Nichols chart, the first step, to design a QFT controller, is to establish plant templates. In doing so, a set of offline parametric system identifications are implemented, and the family of identified models, providing frequency responses, are used to design the QFT fault-tolerant controller. The controller also satisfies the prescribed design tolerances on tracking, stability and sensitivity (disturbance rejection at plant output) under different conditions, including various levels of actuator internal leakage, environmental stiffnesses, and load masses. The ability of the controller to maintain actuating pressure within the acceptable response envelope is demonstrated in experiments. The experimental results show that the system specifications are satisfied despite internal leakage up to 12 L/min.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061005-061005-13. doi:10.1115/1.4035403.

New generation of torque converter automatic transmissions (ATs) include a large number of gears for improved fuel economy and performance. Control requirements for such a transmission become more demanding, which calls for the development of new shift control optimization tools. A pseudospectral collocation method is used in the paper to optimize AT clutch and engine control trajectories for comfortable and efficient shifts. Since the optimization method requires a smooth formulation of plant model, the emphasized clutch model nonlinearity around the zero slip speed has been found to be a major difficulty to be resolved through proper modeling of the optimization problem. Therefore, different approaches of describing the friction behavior are considered and assessed, starting from simple static models, through dynamics models, toward torque-source approaches subject to the clutch passivity constraint. Apart from the conventional optimization approach based on minimizing the cost function (including the vehicle jerk and clutch energy loss terms), the so-called feasibility approach based on restricting the cost through an inequality constraint is considered, as well. The proposed optimization method has been verified on a characteristic example of 10-speed AT for both single- and double-transition shifts (DTSs). It has been found out that the clutch passivity constraint-based approach results in numerically most efficient optimizations for a wide range of shift tasks and scenarios.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061006-061006-9. doi:10.1115/1.4035239.

The problem of parameter estimation of permanent-magnet synchronous machines (PMSMs) can be formulated as a nonlinear optimization problem. To obtain accurate machine parameters, it is necessary to develop easily applicable but efficient optimization algorithms to solve the parameter estimation models. This paper proposes a novel dynamic differential evolution with adaptive mutation operator (AMDDE) algorithm for the multiparameter simultaneous estimation of a nonsalient pole PMSM. The dynamic updating of population enables AMDDE to responds to any improved changes of the population immediately and thus generates better optimization solutions compared with the static mechanism used in original differential evolution. Two mutation strategies, namely DE/rand/1 and DE/best/1, are adaptively employed to balance the global exploration and local exploitation. The effectiveness of the proposed AMDDE is demonstrated on the multiparameter estimation for a nonsalient pole PMSM. Experimental results indicate that the proposed method significantly outperforms the existing peer algorithms in efficiency, accuracy, and robustness. Furthermore, the new algorithm can be potentially realized in digital microcontroller due to its simple structure and lower memory requirement. The proposed algorithm can also be applied to other parameter estimation and optimization problems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061007-061007-8. doi:10.1115/1.4035454.

The focus of this paper is on the development of time-delay filters to accomplish tracking of periodic signals with zero phase errors. The class of problems addressed include systems whose dynamics are characterized by lightly damped modes. A general approach for the zero-phase tracking of periodic inputs is presented followed by an illustration of single harmonic tracking of underdamped second-order systems with relative degree two. A general formulation of the approach is then posed for higher-order systems and systems including zeros. The paper concludes with the illustration of enforcing constraints to desensitize the time-delay filter to uncertainties in the location of the poles of the system and forcing frequencies. A numerical practical design case based on a medical X-ray system is used to illustrate the potential of the proposed technique.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061008-061008-7. doi:10.1115/1.4035614.

This paper presents a distributed formation control for multirobot dynamic systems with external disturbances and system uncertainties. First from the Lagrangian analysis, the dynamic model of a wheeled mobile robot can be derived. Then, the robust distributed formation controller is proposed based on sliding-mode control, consensus algorithm, and graph theory. In this study, the robust stability of the closed-loop system is guaranteed by the Lyapunov stability theorem. From the simulation results, the proposed approach provides better formation responses compared to consensus algorithm.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061009-061009-10. doi:10.1115/1.4035610.

This paper considers homing guidance for a vehicle with a single omnidirectional receiver traveling to a stationary, omnidirectional transmitting beacon by using spatially quantized signal strength measurements. Two homing strategies are presented, and simulations are performed for cases with signal noise and vehicle turn rate limits. The first strategy is the Oyler strategy, which adapts a sliding mode controller and observer from the previous work. The second strategy is based on constant heading changes (CHCs) each time a range increment is detected, and this strategy is shown to be sufficient for homing. This study also discusses a signal filter designed to improve the homing controllers' performance. Performance metrics are developed for strategy evaluation and parameter optimization. The performance of each guidance strategy is shown through simulations for a variety of conditions. The Oyler strategy guides the vehicle to the beacon more efficiently than the constant heading change strategy, but it comes with a slight penalty in success rate.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061010-061010-8. doi:10.1115/1.4035457.

This paper considers the problem of finite-time disturbance observer (FTDO) design and the problem of FTDO based finite-time control for systems subject to nonvanishing disturbances. First of all, based on the homogeneous systems theory and saturation technique, a continuous FTDO design approach is proposed. Then, by using the proposed FTDO design approach, a FTDO is constructed to estimate the disturbances that exist in a rigid spacecraft system. Furthermore, based on a baseline finite-time control law and a feedforward compensation term produced by the FTDO, a composite controller is constructed for the rigid spacecraft system. It is shown that the proposed composite controller will render the rigid spacecraft track the desired attitude trajectory in a finite-time. Simulation results are included to demonstrate the effectiveness of the proposed control approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061011-061011-9. doi:10.1115/1.4035456.

The problem of reversing vehicles with two trailers could be solved with a semi-autonomous assistance system for automatically steering the vehicle. In the literature found, no controllers have been implemented on a full-size vehicle with two trailers. In this paper, two simple path-tracking controllers are presented for automating the reversing of a “B-double” vehicle, consisting of a tractor and two trailers. One of the controllers is a heuristic “preview point” controller; the other uses a state feedback approach. The controllers steer the wheels on the front axle so as to stabilize the vehicle in reverse and control the path of the rearmost axle to follow a prescribed path. A tuning strategy is outlined where both controllers are tuned using the linear quadratic regulator and have the same closed-loop poles. The two controllers are implemented on a full-size B-double test vehicle. Experimental results are discussed, and the controller performances are evaluated against criteria. With the state feedback controller, the test vehicle was able to track target paths, consisting of a roundabout and a lane change, to within 50 mm.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061012-061012-9. doi:10.1115/1.4035453.

In this work, a time-optimal trajectory generation approach is developed for the multiple way-point navigation of the quadrotor based on the nonuniform rational B-spline (NURBS) curve and linear programming. To facilitate this development, the dynamic model of the quadrotor is formulated first. Then, the geometric trajectory regarding multiple way-point navigation is constructed based on the NURBS curve. With the constructed geometric trajectory, a time-optimal interpolation problem is imposed considering the velocity, acceleration, and jerk constraints. This optimization problem is solved in two steps. In the first step, a preliminary result is obtained by solving a linear programming problem without jerk constraints. Then by introducing properly relaxed jerk constraints, a second linear programming problem is formulated based on the preliminarily obtained result, and the time-optimal problem can be fully solved in this way. Subsequently, a nonlinear trajectory tracking controller is developed to track the generated trajectory. The feasibilities of the proposed trajectory generation approach as well as the tracking controller are verified through both simulations and real-time experiments. With enhanced computational efficiency, the proposed approach can generate trajectory for an indoor environment with the smooth acceleration profile and moderate velocity $V≈1$ m/s in real-time, while guaranteeing velocity, acceleration, and jerk constraints: $Vmax=1 m/s, Amax=2 m/s2$, and $Jmax=5 m/s3$. In such a case, the trajectory tracking controller can closely track the reference trajectory with cross-tracking error less than 0.05 m.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061013-061013-9. doi:10.1115/1.4035458.

This paper compares and evaluates the performance of two major feature selection and fault identification methods utilized for the condition monitoring (CM) of centrifugal equipment, namely fast Fourier transform (FFT)-based segmentation, feature selection, and fault identification (FS2FI) algorithm and neural network (NN). Multilayer perceptron (MLP) is the most commonly used NN model for fault pattern recognition. Feature selection and trending play an important role in pattern recognition and hence affect the performance of CM systems. The technical and developmental challenges of both methods were investigated experimentally on a Paxton industrial centrifugal air blower system with a rotational speed of 15,650 RPMs. Five different machine conditions were experimentally emulated in the laboratory. A low training-to-testing ratio of 50% was utilized to evaluate the performance of both methods. In order to maximize fault identification accuracy and minimize computing time and cost, a near-optimal NN configuration was identified. The results showed that both techniques operated with a fault identification accuracy of 100%. However, the FS2FI algorithm showed a number of advantages over NN. These advantages include the ease of implementation and a reduction of cost and time in development and computing, as it processed the data from the first trial in less than 6.2% of the time taken by the NN.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):061014-061014-13. doi:10.1115/1.4035460.

In this paper, we develop an energy-focused model of an industrial roller hearth heat treating furnace. The model represents radiation heat transfer with nonparticipating gas and convective heat transfer. The model computes the exit temperature profile of the treated steel parts and the energy consumption and efficiency of the furnace. We propose a dual iterative numerical scheme to solve the conservation equations and validate its efficacy by simulating the dynamics of the furnace during startup, as well as for steady-state operation. A case study investigates energy consumption within the furnace under temperature control. We first consider a heuristic control strategy using simple linear controllers. A response surface approach is then used to find the optimal set points that minimize energy consumption while ensuring desired part temperature properties are met when processing is complete. With optimized set points, 4.8% less energy per part is required versus the heuristic set points.

Commentary by Dr. Valentin Fuster

### Technical Brief

J. Dyn. Sys., Meas., Control. 2017;139(6):064501-064501-10. doi:10.1115/1.4035237.

In this paper, the finite-time regulation problem of robot manipulators under saturated actuator inputs with position measurements only is addressed. A simple saturated finite-time proportional-derivative (PD) plus gravity compensation (PD+) controller is presented, in which the joint velocity is estimated by constructing a simple nonlinear filter. Global finite-time stability is shown by using Lyapunov stability theory and geometric homogeneity technique. The benefits of this design are that the proposed control can be easily implemented and ensures global finite-time stability with bounded control by selecting control gains a priori. Simulations and experimental results illustrate the expected performance of the proposed approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2017;139(6):064502-064502-6. doi:10.1115/1.4035298.

Pressure-compensated pumps are routinely used for supplying fluid power for hydraulic control systems. These pumps traditionally exhibit significant overshoot and oscillation before reaching a steady-state pressure condition, thus requiring the use of downstream safety valves to prevent over pressurization. In addition to over pressurizing the hydraulic control system, the response of the traditional pressure-compensated pump often induces excessive noise and creates instability for other components within the system. In this paper, a nontraditional pressure-compensated hydraulic pump is studied based upon the paradigm that has been offered by diesel-engine technology. This technology uses an inlet-metered pump to provide pressurized fuel for the high-pressure, fuel-injector rail. The analysis of this paper shows that a system of this type may be used to produce a first-order pressure response with no overshoot and oscillation, and that the characteristic time constant and settling time may be designed by specifying parameters that are identified in this research. The problem of cavitation damage is also discussed based upon preliminary testing done at the University of Missouri, and it is suggested that by using hardened machine parts cavitation damage may be prevented in these machines. In conclusion, this paper shows that continued development of the inlet-metered pump may be warranted for those applications where pressure overshoot and oscillation cannot be tolerated due to safety, noise, or other dynamical considerations.

Commentary by Dr. Valentin Fuster