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IN THIS ISSUE

### Research Papers

J. Dyn. Sys., Meas., Control. 2009;131(2):021001-021001-11. doi:10.1115/1.3023119.

A model for the thermal part of an ionization signal is presented that connects the ionization current to cylinder pressure and temperature in a spark ignited internal combustion engine. One strength of the model is that, after calibration, it has only two free parameters: burn angle and initial kernel temperature. By fitting the model to a measured ionization signal, it is possible to estimate both cylinder pressure and temperature, where the pressure is estimated with good accuracy. The model approach is validated on engine data. Cylinder pressure and ionization current data were collected on a Saab four-cylinder spark ignited engine for a variation in ignition timing and air-fuel ratio. The main result is that the parametrized ionization current model can be used to estimating combustion properties as pressure, temperature, and content of nitric oxides based on measured ionization currents. The current status of the model is suitable for off-line analysis of ionization currents and cylinder pressure. This ionization current model not only describes the connection between the ionization current and the combustion process, but also offers new possibilities for engine management system to control the internal combustion engine.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021002-021002-12. doi:10.1115/1.3023125.

Homogeneous charge compression ignition (HCCI) is a novel combustion strategy for IC engines that exhibits dramatic decreases in fuel consumption and exhaust emissions. Originally conceived in 1979, the HCCI methodology has been revisited several times by industry but has yet to be implemented because the process is difficult to control. To help address these control challenges, the authors here outline the first generalizable, validated, and experimentally implemented physics-based control methodology for residual-affected HCCI engines. Specifically, the paper describes the formulation and validation of a two-input, two-state control-oriented system model of the residual-affected HCCI process occurring in a single engine cylinder. The combustion timing and peak pressure are the model states, while the inducted gas composition and effective compression ratio are the model inputs. The resulting model accurately captures the system dynamics and allows the simultaneous, coordinated control of both in-cylinder pressure and combustion timing. To demonstrate this, an $H2$ optimal controller is synthesized from a linearized version of the model and used to dictate step changes in both combustion timing and peak pressure within about four to five engine cycles on an experimental test bed. The application of control also results in reductions in the standard deviation for both combustion timing and peak pressure. The approach therefore provides accurate mean tracking, as well as a reduction in cyclic dispersion. Another benefit of the simultaneous coordination of both control inputs is a reduction in the control effort required to elicit the desired response. Instead of using a peak pressure controller that must compensate for the effects of a combustion timing controller, and vice versa, the coordinated approach optimizes the use of both control inputs to regulate both outputs.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021003-021003-10. doi:10.1115/1.3072119.

Engineering design is evolving into a global activity. Globally distributed design requires efficient global distribution of models of dynamic physical systems through computer networks. These models must describe the external input-output behavior of the electrical, mechanical, fluid, and thermal dynamics of engineering systems. An efficient system model assembly method is then required to assemble these component system models into a model of a yet higher-level dynamic system. Done recursively, these higher-level system models become possible components for yet higher-level analytical models composed of external model equations in the same standardized format as that of the lowest level components. Real-time, automated exchange, and assembly of engineering dynamic models over a global network requires four characteristics. The models exchanged must have a unique standard format so that they can be exchanged and assembled by an automated process. The exchange of model information must be executed in a single-query transmission to minimize network load. The models must describe only external behavior to protect internal model details. Finally, the assembly process must be recursive so that the transfer and assembly processes do not change with the level of the model exchanged or assembled. This paper will introduce the modular modeling method (MMM), a modeling strategy that satisfies these requirements. The MMM distributes and assembles linear dynamic physical system models with a dynamic matrix representation. Using the MMM method, dynamic models of complex assemblies can be built and distributed while hiding the topology and characteristics of their dynamic subassemblies.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021004-021004-11. doi:10.1115/1.3072122.

This paper introduces a navigation system based on combined global positioning system (GPS) and laser-scanner measurements for outdoor ground vehicles. Using carrier-phase differential GPS, centimeter-level positioning is achievable when cycle ambiguities are resolved. However, GPS signals are easily attenuated or blocked, so their use is generally restricted to open-sky areas. In response, in this work we augment GPS with two-dimensional laser-scanner measurements. The latter is available when GPS is not and further enables obstacle detection. The two sensors are integrated in the range domain for optimal navigation performance. Nonlinear laser observations and time-correlated code and carrier-phase GPS signals are processed in a unified and compact measurement-differencing extended Kalman filter. The resulting algorithm performs real-time carrier-phase cycle ambiguity estimation and provides absolute vehicle positioning throughout GPS outages, without a priori knowledge of the surrounding landmark locations. Covariance analysis, Monte Carlo simulations, and experimental testing in the streets of Chicago demonstrate that the performance of the range-domain integrated system far exceeds that of a simpler position-domain implementation, in that it not only achieves meter-level precision over extended GPS-obstructed areas, but also improves the robustness of laser-based simultaneous localization and mapping.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021005-021005-9. doi:10.1115/1.3072144.

Transportation is one of the most crucial components in supply networks. In transportation lines, there exists a finite time between products leaving a point and arriving to another point in the supply network. This period of time is the delay, which accompanies all transportation lines present in the entire network. Delay is a well-known limitation, which is inevitable and pervasive in the network causing synchronization problems, fluctuating or excessive inventories, and lack of robustness of inventories against cyclic perturbations. The end results of such undesirable effects directly reflect to costs. This paper is motivated to reveal the mechanisms leading to these problems by analytically characterizing qualitative behavior of supply network dynamics modeled by continuous-time differential equations. The presence of delay forms the main challenge in the analysis and this is tackled by developing/utilizing the tools emerging from delay systems and control theory. While the backbone of the paper addresses the qualitative behavior in presence of a single delay representing delays in all transportation paths, it also reveals how to choose production rates and transportation delay without inducing any undesirable effects mentioned. Thorough cases studies with single and multiple delays are presented to demonstrate the effectiveness of the approaches proposed.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021006-021006-8. doi:10.1115/1.3023139.

In this paper we develop a new control law to steer an underactuated surface vessel along a predefined path at a constant forward speed controlled by the main thruster system. The methodology is based on the Serret–Frenet formulation to represent the ship kinematics in terms of path parameters, which allows for convenient definition of cross and along track error. Furthermore, our approach for path following overcomes the stringent initial condition constraints. This paper also addresses the path following with environmental disturbances induced by wave, wind, and ocean-current. The proposed controller is designed based on the Lyapunov direct method and backstepping technique. The closed loop path following errors is proven to be uniform ultimate bounded. Results are demonstrated by high fidelity simulation.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021007-021007-7. doi:10.1115/1.3023140.

To improve controlled performance and expand gain-scheduling control capability, we propose a switching control approach of linear fractional transformation parameter-dependent systems using multiple Lyapunov functions combined with online control techniques. At each switching instant, a gain-scheduled controller working for the next switching interval will be designed online. The switching control synthesis condition is formulated as linear matrix inequalities and can be solved efficiently, upon which the controller will be constructed. The online switching control scheme is demonstrated using an uninhabited combat aerospace vehicle problem.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021008-021008-8. doi:10.1115/1.3023141.

The output feedback stabilization problem for the class of nonlinear Lipschitz systems is considered. A discrete-time feedback controller is designed for the sampled-data case, where the output of the plant is only available at discrete points of time and where the objective is to stabilize the system continuously using a discrete-time controller. We show that exact stabilization in this case can be achieved using a direct sampled-data design approach, based on $H∞$ optimization theory, in which neither the plant model nor the controller need to be discretized a priori. The proposed design is solvable using commercially available software and is shown to have important advantages over the classical emulation approach that has been used to solve similar problems. The applicability of the proposed techniques in the robotics field is thoroughly discussed from both the modeling and design perspectives.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021009-021009-11. doi:10.1115/1.3072154.

Magnetorheological dampers are intrinsically nonlinear devices, which make the modeling and design of a suitable control algorithm an interesting and challenging task. To evaluate the potential of magnetorheological (MR) dampers in control applications and to take full advantages of its unique features, a mathematical model to accurately reproduce its dynamic behavior has to be developed and then a proper control strategy has to be taken that is implementable and can fully utilize their capabilities as a semi-active control device. The present paper focuses on both the aspects. First, the paper reports the testing of a magnetorheological damper with an universal testing machine, for a set of frequency, amplitude, and current. A modified Bouc–Wen model considering the amplitude and input current dependence of the damper parameters has been proposed. It has been shown that the damper response can be satisfactorily predicted with this model. Second, a backstepping based nonlinear current monitoring of magnetorheological dampers for semi-active control of structures under earthquakes has been developed. It provides a stable nonlinear magnetorheological damper current monitoring directly based on system feedback such that current change in magnetorheological damper is gradual. Unlike other MR damper control techniques available in literature, the main advantage of the proposed technique lies in its current input prediction directly based on system feedback and smooth update of input current. Furthermore, while developing the proposed semi-active algorithm, the dynamics of the supplied and commanded current to the damper has been considered. The efficiency of the proposed technique has been shown taking a base isolated three story building under a set of seismic excitation. Comparison with widely used clipped-optimal strategy has also been shown.

Topics: Dampers , Testing , Modeling
Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021010-021010-8. doi:10.1115/1.3023124.

In control of industrial manipulators, the position from the motor encoder has been the only sensor measurement for axis control. In this case, it is not easy to estimate the end-effector motion accurately because of the kinematic errors of links, joint flexibility of gear mechanisms, and so on. Direct measurement of the end-effector using the vision sensor is considered as a solution but its performance is often limited by the slow sampling rate and the latency. To overcome these limitations, this paper extends the basic idea of the kinematic Kalman filter (KKF) to general rigid body motion leading to the formulation of the multidimensional kinematic kalman filter (MD-KKF). By combining the measurements from the vision sensor, the accelerometers and the gyroscopes, the MD-KKF can recover the intersample values and compensate for the measurement delay of the vision sensor providing the state information of the end-effector fast and accurately. The performance of the MD-KKF is verified experimentally using a planar two-link robot. The MD-KKF will be useful for widespread applications such as the high speed visual servo and the high-performance trajectory learning for robot manipulators, as well as the control strategies which require accurate velocity information.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021011-021011-9. doi:10.1115/1.3023126.

A strategy to remove energy from finite-dimensional elastic systems is presented. The strategy is based on the cyclic application and removal of constraints that effectively remove and restore degrees of freedom of the system. In general, application of a constraint removes kinetic energy from the system, while removal of the constraint resets the system for a new cycle of constraint application. Conditions that lead to a net loss in kinetic energy per cycle and bounds on the amount of energy removed are presented. In linear systems, these bounds are related to the modes of the system in its two states, namely, with and without constraints. It is shown that energy removal is always possible, even using a random switching schedule, except in one scenario, when energy is trapped in modes that span an invariant subspace with special orthogonality properties. Applications to nonlinear systems are discussed. Examples illustrate the process of energy removal in both linear and nonlinear systems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021012-021012-8. doi:10.1115/1.3023128.

In a companion paper we have solved the basic problem of full-state stabilization of unstable “shock-like” equilibrium profiles of the viscous Burgers equation with actuation at the boundaries. In this paper we consider several advanced problems for this nonlinear partial differential equation (PDE) system. We start with the problems of trajectory generation and tracking. Our algorithm is applicable to a large class of functions of time as reference trajectories of the boundary output, though we focus in more detail on the special case of sinusoidal references. Since the Burgers equation is not globally controllable, the reference amplitudes cannot be arbitrarily large. We provide a sufficient condition that characterizes the allowable amplitudes and frequencies, under which the state trajectory is bounded and tracking is achieved. We then consider the problem of output feedback stabilization. We design a nonlinear observer for the Burgers equation that employs only boundary sensing. We employ its state estimates in an output feedback control law, which we prove to be locally stabilizing. The output feedback law is illustrated with numerical simulations of the closed-loop system.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):021013-021013-12. doi:10.1115/1.3023132.

This paper presents a sliding mode controller for a 2DOF planar pneumatic manipulator actuated by pleated pneumatic artificial muscle actuators. It is argued that it is necessary to account for the pressure dynamics of muscles and valves. A relatively detailed system model that includes pressure dynamics is established. Since the model includes actuator dynamics, feedback linearization was necessary to design a sliding mode controller. The feedback linearization and subsequent controller design are presented in detail, and the controller’s performance is evaluated, both in simulation and experimentally. Chattering was found to be quite severe, so the introduction of significant boundary layers was required.

Commentary by Dr. Valentin Fuster

### Technical Briefs

J. Dyn. Sys., Meas., Control. 2009;131(2):024501-024501-5. doi:10.1115/1.3072115.

The gain values that can be imposed in pneumatic system controllers are bounded to the restricted actuator bandwidth. That limitation, with low damping and stiffness due to the air compressibility, seriously affects accuracy and repeatability when varying payloads or supply pressures. For modeling and control intents, a correct characterization of the pneumatic actuator natural frequency is indispensable. The aim of the paper is to evaluate how heat exchange process affects the proper characteristics of pneumatic drivers and, in particular, their pneumatic stiffness. To this purpose dynamic stiffness had been studied both by imposing in the cylinder’s chambers a polytrophic transformation of the fluid with a prefixed index and by employing energy equations. Numerical results obtained by implementing the two formulations for different working conditions are reported and compared in order to point out the ranges in which they overlap, and hence both approaches produce accurate results, or the ones in which there is a difference, and then it is necessary to consider the temperature dynamics.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):024502-024502-8. doi:10.1115/1.3072146.

Fully flexible valve actuation (FFVA) system, often referred to as camless valvetrain, employs electronically controlled actuators in place of the camshaft to drive the intake or exhaust valves for internal combustion engines (ICEs). This system offers significant fuel economy benefits, emissions reduction, and better torque output performance for the ICE. It could also enable a number of advanced combustion concepts, such as homogeneous charge compression ignition. It further provides a common platform that incorporates the functions of cam phasing, two/three step cam or continuously variable lift, cylinder deactivation, port deactivation, etc. Therefore it is desirable to develop FFVA systems for future engines. In this paper, we first outline the technical barriers for developing production-viable FFVA systems. To address those challenges, a new electrohydraulic valve actuation concept with the “internal feedback” mechanism is presented. Key technical issues, such as dynamic range capability, valve motion performance, and energy consumption, are analyzed. Experimental results based on a prototype system are shown to demonstrate the capabilities and performance of the proposed system.

Topics: Engines , Valves , Feedback
Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):024503-024503-8. doi:10.1115/1.3072153.

This article addresses the optimal (minimum-time/energy) trajectory design for changing the output from one value $y̱$ to another $y¯$ within a finite time interval $[0,tf]$ called the output-transition time interval. The output should be maintained constant (at the desired value) outside the output-transition time interval. The main contribution of this article is to establish the existence of a solution to the problem when preactuation (input applied during time $t<0$) and postactuation (input applied during time $t>tf$) are allowed. The advantage of using pre- and postactuation inputs is illustrated with an experimental dual-stage actuator system.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2009;131(2):024504-024504-5. doi:10.1115/1.3023130.

A discrete-time internal model control approach for nonsmooth nonlinear systems described by a pseudo-Hammerstein model with backlash is presented. In this method, the controlled system is described by the pseudo-Hammerstein model, and the corresponding inverse model is constructed. Considering the existence of the model mismatch, the internal model control is implemented. As the model is switched among the different operating zones, the piecewise robust filters are proposed to improve the robust stability and transient performance of the control system. Finally, the simulation results based on the proposed method for a mechanical transmission system are presented.

Commentary by Dr. Valentin Fuster