J. Dyn. Sys., Meas., Control. 2003;125(3):281-286. doi:10.1115/1.1590681.

This paper proposes the parallel observer system (POS), a multirate estimation technique for discrete time systems, to compensate for systems whose output measurements are only periodically available and under the presence of matched and unmatched uncertainties/disturbances. A stability proof and error bounds are provided, given maximum bounds of the uncertainties/disturbances. A simulation of the POS is provided to show proof of concept.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):287-293. doi:10.1115/1.1590682.

This paper presents a new strategy for state estimation. The strategy may be applied to linear systems and is referred to as the variable structure filter. The filter is considered for discrete-time systems subject to random disturbances and measurement noise. It requires a parametric model and can be formulated to accommodate modeling uncertainties. A proof of stability for the filter is provided. For stability, this concept requires a specification of an upper bound for uncertainties, disturbances, and measurement noise. The application of this filter to a third-order linear system is demonstrated.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):294-302. doi:10.1115/1.1590683.

Many modern engineering systems use multiple sensors for monitoring, diagnosis and control. Some of these sensors contain not only time domain and frequency domain information, but also valuable spatial domain information to which little attention has been paid. This paper presents a new method for capturing the spatial characteristics of the sensor signals. The basic idea is to model the spatial information of the signals using a Bézier surface. For example, given m one-dimensional force signals: X1(t),X2(t),[[ellipsis]],Xm(t), at each time instance t, a Bézier surface can be constructed, which describes the distribution of the force. Furthermore, lining up the surfaces at different time t1,t2,[[ellipsis]],tn, will show how the force changes as a function of time. Since the graph looks like a snake skeleton, the new method is called the snake skeleton graph. The paper first describes how the snake skeleton graph is constructed using a demonstration example: a foot walking on a plate. Then it presents an application for fault diagnosis in sheet metal stamping operation. Future research topics are also discussed.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):303-309. doi:10.1115/1.1590684.

This paper proposes the adaptive parallel observer system (APOS), a multirate estimation technique for discrete time systems, to compensate for output measurements that are available only periodically and for systems whose frequency content is beyond that of the Nyquist frequency. The APOS provides the controller with stable state and system parameter estimates, which allow for the extraction of the system damping ratio and resonant frequency despite the presence of aliasing. A stability proof and error bounds are provided. The APOS is applied to the actuator dynamics of an IBM Head/Disk Assembly (HDA) System, and the APOS parameter estimates are used to extract values of the system damping ratio and aliased resonant frequency via a trained neural network.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):310-319. doi:10.1115/1.1590685.

Impedance control facilitates the execution of tasks that involve contact with the environment. However, task performance depends on the accuracy at which the desired impedance is attained. This paper focuses on feedback methods for implementing impedance control and reveals the underlying conflict between impedance accuracy and robustness to uncertainties. Furthermore, we propose a novel yet practical method that facilitates robustness while maintaining accurate impedance tracking. Eigenvalue analysis and simulation results are presented to demonstrate the accuracy/robustness dilemma and the relative merits of the different methods.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):320-329. doi:10.1115/1.1592188.

In this paper, a new method of analyzing for the performance loss caused by faults in the systems is presented, and applied to the design of a fault tolerant longitudinal controller for a transit bus. Based on the amount of performance loss measured by a quadratic function, fault impact assessment is developed for both single and multiple faults. More specifically, ellipsoidal approximation of the tracking error bounds via dynamic surface control (DSC) is obtained via convex optimization technique for the nonlinear closed-loop system. Relying on the fault impact to the closed loop system and its isolatability on a fault detection and diagnosis system, the fault classification is proposed to provide a switching logic in the framework of a switched hierarchical structure. Finally, simulation results of the fault tolerant controller and corresponding fault classification are shown for multiple multiplicative faults.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):330-338. doi:10.1115/1.1592189.

The design of seat suspensions having linear stiffness and damping characteristics involves a tradeoff between three performance measures. These measures are: (1) suspension range of motion, (2) improved average vibration isolation (weighted average across a wide exposure spectrum), and (3) improved isolation at the frequency of peak transmissibility. To overcome the limitations associated with this tradeoff, nonlinear mechanical properties are used here in the design of a seat suspension. From the infinite number of possible nonlinear mechanical characteristics, several possibilities that showed promise in previous studies were selected. The selected nonlinear force-deflection relationship (stiffness) of the seat is described by a combination of cubic and linear terms. The selected damping behavior of the seat is described by a combination of a linear term and a position-dependent term. A lumped parameter model (linear-human/nonlinear-seat) of the human/seat-suspension coupled system and a robust direct search routine are used to obtain pseudo-optimal values of the seat design parameters (mass, stiffness, and damping) via simulation in the time domain. Results indicate that the optimal nonlinear seat suspension is significantly better than the optimal linear seat suspension in overall vibration isolation characteristics.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):339-353. doi:10.1115/1.1592190.

This paper describes the design, analysis, and implementation of a vehicle control system using control state information obtained from a carrier phase (CP) differential global positioning system (DGPS) aided inertial navigation system (INS). Experimental data from CP DGPS/INS control experiments onboard a PATH1 vehicle is included. This testing was completed with a magnetometer sensing system onboard and running to provide a ground truth reference for comparison with the CP DGPS/INS. Navigation accuracy has previously been demonstrated at the cm level with the full navigation state updated at 150 Hz. In this article, lateral position control performance is demonstrated during challenging high-speed maneuvers with trajectory tracking accuracy at the decimeter level. During these initial experiments, the control state updated at 30 Hz. Increased trajectory following accuracy is possible, but there is an inherent tradeoff between the tracking accuracy and the ride comfort. This level of performance demonstrates that CP DGPS/INS technology has the potential to serve as one component of the reliable multisensor centimeter-level position reference system that is necessary for vehicle position control applications, including automated highway systems (AHS).

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):354-360. doi:10.1115/1.1592191.

This paper presents the development of an active control strategy for railway vehicles with independently rotating wheels. The proposed control scheme is intuitively formulated with a simple control structure and adaptive to vehicle speed. It does not require basic guidance measurements (e.g., wheel-rail deflection and angle of attack) that are expensive and impractical to implement. Speed sensors are used to measure the relative rotational speed of the two wheels on a same axle and sensors are also used to measure the relative yaw velocity of the wheelset and the body it is connected. Both curving performance and passenger ride comfort of the actively controlled vehicle are compared with that of a typical passive vehicle and an optimal control scheme.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):361-371. doi:10.1115/1.1590678.

This paper investigates the role of active dancers in attenuation of web tension disturbances in a web process line. A general structure of the active dancer is considered; governing equations for web spans upstream and downstream to the dancer roller are developed. A structural limitation that facilitates efficient design of the active dancer system for web tension disturbance attenuation is derived and discussed based on the developed model. An open-architecture experimental web platform is developed for conducting real-time control experiments using the active dancer system. The active dancer system model is experimentally identified using the standard system identification techniques available in literature. Three types of control designs were investigated for the active dancer system: a proportional-integral-derivative controller, an internal model based controller, and a linear quadratic optimal controller. Data collected from a series of experiments using the three control designs validate the usefulness of the active dancers in attenuating web tension disturbances in a web process line. A representative sample of the experimental data is presented and discussed.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):372-381. doi:10.1115/1.1590679.

The problem of active balancing of speed-varying rotors, whose dynamics are changing or hard to be known beforehand, is frequently encountered in many applications. This paper presents a new adaptive method for balancing speed-varying rotors with multi-plane active balancing devices. The new method utilizes the positive realness of the transfer function of the active balancing system. This paper first shows the positive realness of the active balancing system and combines it with a direct adaptive control design method. A set of simulations was conducted to show the validity of the developed control law. The simulation studies show that the new method works as expected and has potential impact on future active balancing control systems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):382-395. doi:10.1115/1.1592192.

This paper presents a model of sound propagation in a duct, for the purpose of active noise control. A physical model generally different from those explored in much of the literature is derived, with non-constant acoustic load impedance at the one end, and a coupled disturbance loudspeaker model at the other end. Experimental results are presented which validate the derived transfer function.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):396-404. doi:10.1115/1.1592193.

In this paper, the theoretical flow ripple of an external gear pump is studied for pumps of similar size using different numbers of teeth on the driving and driven gears. In this work, the flow ripple equation is derived based upon the flow of incompressible fluid across the changing boundaries of a control volume. From this method, it is shown that the instantaneous length of action within the gear mesh determines the instantaneous flow ripple. A numerical and a closed-form approximation are presented for the instantaneous length of action and it is shown that the difference between these two solutions is negligible. Fast Fourier transform analysis is employed for identifying the harmonic frequencies and amplitudes of the flow pulse and these results are compared for 16 different pump designs. In summary, the results of this study show that the driving gear dictates the flow ripple characteristics of the pump while the driven gear dictates the pump size. As a result, it may be advantageous to design an external gear pump with a large number of teeth on the driving gear and a fewer number of teeth on the driven gear. This design configuration will tend to reduce both the physical pump size (without reducing the volumetric displacement of the pump) and the amplitude of the flow pulsation, while increasing the natural harmonic frequencies of the machine.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):405-412. doi:10.1115/1.1592812.

In digital valves, stepper motors are often used as the electro-to-mechanical interface. To sustain both high speed of response and good quantitative accuracy, a special algorithm has been designed to control the stepper motor to produce a continuous rotary displacement. Since in this algorithm the current to each coil is cyclic as the rotor tooth advances, several cycles can be used to achieve the desired angular displacement of the motor. This process can result in a reduction or “scaling down” of magnetic nonlinearities such as hysteresis and saturation. This cyclic algorithm has been defined as “stage control” because the algorithm need only be developed for one stage and then repeated when applied to subsequent stages. Critical to the development and understanding of the algorithm is an accurate model of the electromagnetic saturation and hysteresis which exist between the input current and output torque. In this paper, a special mathematical formulation is developed to simulate magnetic saturation and hysteresis which can be applied to a more generic situation. The mathematical formulation derived is one in which hysteresis and saturation parameters are established; an error rate of both saturation and hysteresis is defined from this. Since the error rates are easily determined experimentally or through manufacturers’ specifications, the parameters can be found from these mathematical formulations. The parameters can then be used to predict the hysteresis and saturation characteristics. Special experiments are designed to obtain the input-output characteristics of a stepper motor/valve system under single and multistage control. The model follows the experimental results reasonably well and can be used with confidence to model any system with hysteresis and saturation. The model also predicts very well the effects of using stage control in reducing hysteresis and saturation in a practical valve.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):413-423. doi:10.1115/1.1592194.

The development of a fault tolerant control (FTC) strategy to compensate for the degrading effects of fluid leakage across a faulty actuator piston seal in an electrohydraulic positioning system is presented. Due to relatively large variations in the dynamics of the plant, accomplishing the FTC task with a single controller requires a compensator of relatively high gain. Hence, the problem is first reformulated by discretizing the desired range of fault tolerance into a number of distinct levels. Next, a set of low gain local controllers is synthesized via quantitative feedback theory, such that the resulting closed-loop systems all conform to a priori defined performance specifications. Each controller is designed to compensate for a specific level of leakage. A simple switching algorithm is then employed to determine the appropriate control action by scaling each controller’s output based upon an estimate of the leakage level. Experimental results illustrate the ability of the designed FTC scheme to compensate for the degrading effect of the leakage fault.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):424-428. doi:10.1115/1.1589028.

Feedback control has been pursued to address the rotating stall problem in axial flow compressors in order to extend the stable operating range and to improve engine performance. These controllers guarantee the stability of the bifurcated operating solution near the stall point. In this paper, an analytic approach is developed to characterize the robustness of some stabilizing controllers for rotating stall in axial-flow compressors. The numerical examples show that the size of the admissible uncertainty set changes for stabilizing controllers with different feedback gains. It is also proved that a nonlinear stabilizing control is not necessarily superior to a linear one.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):429-438. doi:10.1115/1.1589029.

The paper considers design of a predictive Linear Time Varying model-based controller with nonlinear feedforward for regulation of transient processes caused by setpoint step changes in a nonlinear plant. An optimal feedforward control sequence is computed based on an empirical Finite Impulse Response model of the process. Though the control techniques developed in this paper are meant to have more general industrial applicability, a specific automotive engine control application—control of Variable Cam Timing automotive engine—is pursued. An advantage of the proposed controller design in this problem is that no first principle models are required. Instead, nonlinear parametric approximations of a neural network type are being used to describe and identify static nonlinear mappings encountered in the problem. A number of simplifying assumptions and approximations are made to make practical implementation of the proposed scheme possible. Validity of the designed controller is verified by simulation. The proposed “model-free” design can potentially increase flexibility and save labor in development and deployment of such controllers for industrial systems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):439-447. doi:10.1115/1.1589030.

The solution of linear quadratic predictive optimal control problems for systems represented in state-equation form, but using a polynomial systems approach, is considered. A multistep cost-function is used that includes future set-point information. A novel method is introduced for computing the vector of future controls and for solving a simpler optimization problem for the current control.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):448-450. doi:10.1115/1.1589031.

Analytical details are developed for a robust adaptive control strategy that combines switching control and on-line adaptive learning, for a class of nonlinear systems. The condition for stable learning is derived, guidelines for design parameter selection are provided, and the tradeoff between performance and chattering control effort is examined. The results of the study are summarized in the form of a constructive procedure for controller design for the class of systems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):451-454. doi:10.1115/1.1589032.

We present a fault detection method called the gray-box. The term “gray-box” refers to the approach wherein a deterministic model of system, i.e., “white box,” is used to filter the data and generate a residual, while a stochastic model, i.e., “black-box” is used to describe the residual. The residual is described by a three-tier stochastic model. An auto-regressive process, and a time-delay feed-forward neural network describe the linear and nonlinear components of the residual, respectively. The last component, the noise, is characterized by its moments. Faults are detected by monitoring the parameters of the auto-regressive model, the weights of the neural network, and the moments of noise. This method is demonstrated on a simulated system of a gas turbine with time delay feedback actuator.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):455-461. doi:10.1115/1.1589033.

This paper proposes a control solution for a vehicular driveline with an internal combustion engine, a continuously variable transmission and an additional flywheel unit. This unit plays a part only in transient situations. It compensates for the engine inertia, enabling optimal fuel economy in stationary situations without losing driveability during transients. For control design, a simple, nonlinear model is developed and used for feedback linearization. The proposed controller is evaluated by simulations, using an advanced simulation model. The compensation of the engine inertia by the additional flywheel is demonstrated by vehicle experiments.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):462-467. doi:10.1115/1.1589034.

A low-complexity virtual sensor for the pressure peak position of the crank angle in a spark-ignited car motor is proposed. The algorithm estimates the pressure peak position from the ion current, measured from the spark plug. The complexity of the algorithm is an order of magnitude smaller than any other proposed schemes. Still, performance is not sacrificed. Closed-loop control is demonstrated on a SAAB 9000 driven on the highway.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):468-474. doi:10.1115/1.1589035.

Free-piston diesel engines are characterized by freely moving pistons without any crankshaft or camshaft connected to the pistons. This allows a compact and efficient engine design, but requires automatic control of the piston motion. This paper present a dynamic mathematical model of a free-piston diesel engine, and a control oriented dynamic analysis leading to a piston motion control structure. Experimental results using a full scale test cylinder are included and show feasibility of the suggested control approach.

Commentary by Dr. Valentin Fuster


J. Dyn. Sys., Meas., Control. 2003;125(3):475-480. doi:10.1115/1.1590686.

Ball, Helton, and Walker (BHW) derived the nonlinear dissipative controller formulas with the assumption implying that no stable mode uncontrollable from the exogenous input. The assumption is more restrictive than that considered in DGKF. In this paper, we address the numerical difficulty encountered by BHW’s controller formulas when the assumption is not satisfied. Next, we propose a modified nonlinear dissipative controller and successfully remove the numerical difficulty. We also show that the linear version of the proposed controller formulas is identical to the DGKF H controller. An example is given to demonstrate constructing the proposed controller and simulating the closed-loop pulse responses.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2003;125(3):480-482. doi:10.1115/1.1591811.

This paper applies the concept of variable speeds to vibration control of elastic cam-follower systems. A multi-design-point approach, based on optimal control theory, is developed for selecting suitable input speed functions of the cam that can reduce both primary and residual vibrations of the output in elastic cam-follower systems despite parameter variations. A design example is given to verify the feasibility of the approach.

J. Dyn. Sys., Meas., Control. 2003;125(3):482-485. doi:10.1115/1.1591804.

State estimation of linear systems under the influence of both unknown deterministic inputs as well as Gaussian noise is considered. A Kalman like filter is developed which does not require the estimation of the unknown inputs as is customarily practiced. Therefore, the developed filter has reduced computational requirements. Comparative simulation results, under the influence of various types of unknown disturbance inputs, show the merits of the developed filter with respect to a conventional Kalman filter using disturbance estimation. It is found that the developed filter enjoys several practical advantages in terms of accuracy and fast tracking of the system states.

J. Dyn. Sys., Meas., Control. 2003;125(3):485-489. doi:10.1115/1.1591805.

This brief paper synthesizes an output feedback L2-gain Control law for linear parameter varying (LPV) systems. The control law is embedded with an observer that does not require on-line measurements of the scheduling parameter variation rate. Results of simulation experiments are presented to evaluate the control law on a simulation experiments on a two-degree-of-freedom mass-spring-damper system.

J. Dyn. Sys., Meas., Control. 2003;125(3):489-491. doi:10.1115/1.1591806.

In this paper, a receding-horizon control, using systematic projection on a Chebyshev’s polynomial basis, is proposed for the stabilization of a rigid spacecraft operating with only two actuators. The proposed scheme privileges the speed of the algorithm. Simulations on SPOT4 spacecraft with a robustness test are provided.

J. Dyn. Sys., Meas., Control. 2003;125(3):491-494. doi:10.1115/1.1591807.

Recently reported finite-dimensional nonlinear thruster models employing empirically determined lift–drag curves have been shown to accurately model both the transient and steady state response of marine thrusters. These reports have employed the standard off-line paradigm for model parameter identification: First, real-time sensor data (force, torque, fluid velocity) is logged in laboratory experiments. Second, the experimental data is analyzed with a least-square regression technique to complete a best fit for the model parameters. This paper reports an on-line technique for adaptive identification of model parameters for marine thrusters. The stability of the proposed technique is shown analytically. The performance of the on-line adaptive identification technique, evaluated with respect to an experimentally validated plant model, is shown to compare favorably to its off-line counterpart, but does not require the thrust and torque instrumentation required by conventional off-line least-squares parameter identification techniques.

J. Dyn. Sys., Meas., Control. 2003;125(3):494-497. doi:10.1115/1.1591808.

The technique of input shaping has been successfully applied to the problem of maneuvering flexible structures without excessive residual vibration. Because a shaper is designed such that vibration is eliminated at the end of the shaped input, a short shaper length means that vibration is eliminated sooner. As different shaper design methods yield different shapers, it is advantageous to know how the shaper lengths of these different methods compare. In this paper we draw comparisons between time-domain input shaping methods and frequency-domain input shaping methods after outlining conditions when non-negative amplitude shapers exist when using frequency-domain methods.

J. Dyn. Sys., Meas., Control. 2003;125(3):497-504. doi:10.1115/1.1591809.

A backhoe is a tractor-like vehicle that has a hydraulically actuated bucket loader at the front and a hydraulically actuated backhoe shovel at the rear. The operator sits inside a canopy or cab that is mounted to the tractor chassis, and operates the hydraulic controls. The cab is typically isolated somewhat from the chassis using cab mounts. There are instances when the bucket is raised or lowered or wrapped that an instability of the entire machine is excited. In this mode, a frequency oscillation of the vehicle occurs and the operator is unable to keep his hands on the controls. This instability is investigated here and demonstrated through simulation. The instability described here is due to an interaction between the mechanical dynamics and hydraulic dynamics of the machine. All instabilities require an energy source, and, in this case, the energy comes from the fuel. It turns out that the hydro-mechanical interaction has positive feedback components and produces an instability. In order to expose the fundamental cause of the instability, a model is needed that allows the interaction of mechanical and hydraulic components. Bond graphs are a logical choice for development of the model. Bond graphs are a concise pictorial representation of the interactive dynamics of all types of energetic systems. They allow the model to be developed in pieces and then put together into an overall computational model. This procedure is demonstrated for the system here. The end result is a reasonably low order model that exposes the fundamental cause of the instability in backhoes. It also allows assessment of cures for the problem, some requiring redesign of components, and some requiring an automatic stabilization control system.

J. Dyn. Sys., Meas., Control. 2003;125(3):504-508. doi:10.1115/1.1591810.

This paper presents a control design methodology that provides a prescribed degree of stability robustness for plants characterized by discontinuous (i.e., switching) dynamics. The proposed control methodology transforms a discontinuous switching model into a linear continuous equivalent model, so that loop-shaping methods may be utilized to provide a prescribed degree of stability robustness. The approach is specifically targeted at pneumatically actuated servo systems that are controlled by solenoid valves and do not incorporate pressure sensors. Experimental demonstration of the approach validates model equivalence and demonstrates good tracking performance.

J. Dyn. Sys., Meas., Control. 2003;125(3):509-514. doi:10.1115/1.1590680.

A hydraulic circuit design composed of a pressure-regulating device in conjunction with a spring-loaded flow compensator is shown to be an effective mechanism to improve the pressure control functionality, specifically by minimizing the excursions of pressures experimented in the system and by minimizing the time required by the supply pump to restore pressure. The design stores fluid energy and restores it to a system where fast switching devices control fluid consumption. The effectiveness of the mechanism resides in controlling the back pressure on the pressure regulator and compensator to just below the system pressure. The flow compensator can reduce pressure recovery times by over 60% and minimize pressure drops by 20%. The compensator effectively allows for better pump size optimization and smaller required volumes for added power savings and better packaging.

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