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IN THIS ISSUE

### Research Papers

J. Dyn. Sys., Meas., Control. 2011;133(2):021001-021001-8. doi:10.1115/1.4003090.

The input shaping technique has proven to be highly effective in reducing or eliminating residual vibration of flexible structures. The exact elimination of the residual vibration via input shaping depends on the amplitudes and instants of utilized impulses. However, systems always have parametric uncertainties, which can lead to performance degradation. Furthermore, input shaping method does not deal with vibration excited by external disturbances and time-delays. In this paper, a closed-loop input shaping control scheme is developed for uncertain flexible structure and uncertain time-delay flexible structure systems. The algorithm is based on the sliding mode control and $H∞/μ$ techniques. This scheme guarantees closed-loop system stability, and yields good performance and robustness in the presence of parametric uncertainties, time-delays and external disturbances as well. Also, it is shown that increasing the robustness to parametric uncertainties and time-delays does not lengthen the duration of the impulse sequence. Numerical examples are presented to verify the theoretical analysis.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021002-021002-11. doi:10.1115/1.4003091.

In the last few years, driver assistance systems are increasingly being investigated in the automotive field to provide a higher degree of safety and comfort. Lane position determination plays a critical role toward the development of autonomous and computer-aided driving. This paper presents an accurate and robust method for detecting road markings with applications to autonomous vehicles and driver support. Much like other lane detection systems, ours is based on computer vision and Hough transform. The proposed approach, however, is unique in that it uses fuzzy reasoning to combine adaptively geometrical and intensity information of the scene in order to handle varying driving and environmental conditions. Since our system uses fuzzy logic operations for lane detection and tracking, we call it “FLane.” This paper also presents a method for building the initial lane model in real time, during vehicle motion, and without any a priori information. Details of the main components of the FLane system are presented along with experimental results obtained in the field under different lighting and road conditions.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021003-021003-5. doi:10.1115/1.4003092.

Terrain topology is the principal source of vertical excitation into the vehicle system and must be accurately represented in order to correctly predict the vehicle response. It is desirable to evaluate vehicle models over a wide range of terrain, but it is computationally impractical to simulate long distances of every terrain type. A method to characterize terrain topology is developed in this work so that terrain can be grouped into meaningful sets with similar physical characteristics. Specifically, measured terrain profiles are considered realizations of an underlying stochastic process; an autoregressive model provides the mathematical framework to describe this process. The autocorrelation of the spatial derivative of the terrain profile is examined to determine the form of the model. The required order for the model is determined from the partial autocorrelation of the spatial derivative of the terrain profile. The stability of the model is evaluated and enforced by transforming the autoregressive difference equation into an infinite impulse response filter representation. Finally, the method is applied to a set of U.S. highway profile data and an optimal model order is determined for this application.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021004-021004-8. doi:10.1115/1.4003213.

We consider hostile conflicts between two multi-agent swarms. First, we investigate the complex nature of a single pursuer attempting to intercept a single evader (1P-1E), and establish some rudimentary rules of engagement. The stability repercussions of these rules are investigated using a Lyapunov-based stability analysis. Second, we extend the modeling and stability analysis to interactions between multi-agent swarms of pursuers and evaders. The present document considers only swarms with equal membership strengths for simplicity. This effort is based on a set of suggested momenta deployed on individual agents. The control of group pursuit is divided into two phases: the approach phase during which the two swarms act like individuals in the 1P-1E interaction, and the assigned pursuit phase, where each pursuer follows an assigned evader. A simple, single-step dissipative control strategy, which results in undesirable control chatter, is considered first. A distributed control logic is then introduced, in order to ameliorate the chatter problems. In this new logic, the dissipative control action is spread out over a time window. A wide range of case studies is tested in order to quantify the parametric effects of the new strategy.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021005-021005-10. doi:10.1115/1.4002952.

This paper proposes to use optimal dynamic quantizers for feedback control in mechatronics systems when the actuator signals are constrained to discrete-valued signals. Here, the dynamic quantizer is a device that transforms the continuous-valued signals into the discrete-valued ones depending on the past signal data, as well as the current data. First, a closed form optimal quantizer is presented in a general linear fraction transformation representation setting. The optimal quantizer minimizes the deviation of the output produced by the quantized signals from the corresponding output yielded by the continuous-valued signals before quantization. Then, its experimental evaluation is performed by using a crane positioning system with a discrete-valued input to demonstrate the effectiveness of the proposed quantizers.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021006-021006-8. doi:10.1115/1.4003208.

This paper describes the design and control of a new chemomuscle actuation system for robotic systems, especially the mobile systems inspired by biological principles. Developed based on the pneumatic artificial muscle, a chemomuscle actuation system features a high power density, as well as similar characteristics to the biological muscles. Furthermore, by introducing monopropellant (a special type of liquid fuel) as the energy storage media, the chemomuscle system leverages the high energy density of liquid fuel and provides a compact form of high-pressure gas supply with a simple structure. The introduction of monopropellant addresses the limitation of pneumatic supply on mobile devices and thus is expected to facilitate the future application of artificial muscle on biorobotic systems. In this paper, the design of a chemomuscle actuation system is presented, as well as a robust controller design that provides effective control for this highly nonlinear system. To demonstrate the proposed chemomuscle actuation system, an experimental prototype is constructed, on which the proposed control algorithm provides good tracking performance.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021007-021007-10. doi:10.1115/1.4003261.

This paper presents two different control strategies for paper position control in printing devices. The first strategy is based on standard feedback linearization plus dynamic extension (dynamic feedback linearization). Even though this controller is very simple to design, we show that it is not able to handle actuator multiplicative uncertainties, and therefore, it fails when it is implemented on the experimental setup. The second strategy we present uses similar concepts, but it is more robust since feedback linearization is used only to linearize the kinematics of the system and internal loops are used to locally control the actuator’s positions and velocities. In this paper, not only do we formally prove the robustness of the second control strategy but we also show its successful implementation.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021008-021008-9. doi:10.1115/1.4003097.

This paper considers the design of input shaping filters used in motion control of vibratory systems. The filters preshape a command or actuation signal in order to negate the effect of vibratory modes. A class of finite impulse response filter satisfying a set of orthogonality conditions that ensure zero residual vibration is introduced. Filter solutions having minimum quadratic gain, both with and without the inclusion of non-negativity (peak gain) constraints, are presented. Unlike impulse-based shapers, the filters have impulse responses with no singularities and therefore automatically remove discontinuities from an input signal. Minimum duration impulse response solutions are also presented. These contain singularities but may also have smooth components. Discrete-time designs can be obtained numerically from system modal parameters, accounting for all modes simultaneously so that convolving single-mode solutions, which leads to suboptimality of the final design, is not required. Selected designs are demonstrated experimentally on a flexible link planar manipulator.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021009-021009-8. doi:10.1115/1.4003098.

Modern terrain measurement systems use an inertial navigation system (INS) to measure and remove vehicle movement from laser measurements of the terrain surface. Instrumental and environmental biases inherent in the INS produce noise and drift errors in these measurements. The evolution and implications of terrain surface measurement techniques and existing methods for correcting INS drift are reviewed as a framework for a new compensation method for INS drift in terrain surface measurements. Each measurement is considered a combination of the true surface and the error surface, defined on a Hilbert vector space, in which the error is decomposed into drift (global error) and noise (local error). The global and local subspaces are constructed such that the drift is modeled as a random walk process and the noise is a zero-mean process. This theoretical development is coupled with careful experimental design to identify the drift component of error and discriminate it from true terrain surface features, thereby correcting the INS drift. It is shown through an example that this new compensation method dramatically reduces the variation in the measured surfaces to within the resolution of the measurement system itself.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021010-021010-14. doi:10.1115/1.4003209.

We propose a framework for synthesizing real-time trajectories for a wide class of coordinating multi-agent systems. The class of problems considered is characterized by the ability to decompose a given formation objective into an equivalent set of lower dimensional problems. These include the so called radar deception problem and the formation control problems that fall under formation keeping and/or formation reconfiguration tasks. The decomposition makes the approach scalable, computationally economical, and decentralized. Most importantly, the designed trajectories are dynamically feasible, meaning that they maintain the formation while satisfying the nonholonomic and saturation type velocity and acceleration constraints of each individual agent. The main contributions of this paper are (i) explicit consideration of second order dynamics for agents, (ii) explicit consideration of nonholonomic and saturation type velocity and acceleration constraints, (iii) unification of a wide class of formation control problems, and (iv) development of a real-time, distributed, scalable, computationally economical motion planning algorithm.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021011-021011-7. doi:10.1115/1.4003245.

This paper studies the problem of robustly stochastic stability and stabilization for a class of uncertain Markov jump linear systems with time delay. A new stochastic Lyapunov–Krasovskii functional (LKF) is constructed for the stability analysis and stabilization, in which the delay is uniformly divided into multiple segments. Based on this LKF and using an improved Jensen's integral inequality, the improved delay-dependent stochastic stability criteria are first derived in terms of linear matrix inequalities (LMIs). Then, an LMI approach to the design of stabilizing controllers via delayed state feedback is developed. The previous stability criteria are extended to give the delay-dependent stabilization conditions in terms of LMIs. Furthermore, an LMI optimization algorithm is proposed to find the maximum allowable delay of the system. Finally, numerical examples show that the proposed results are effective and much less conservative than some existing results.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):021012-021012-10. doi:10.1115/1.4003263.

This paper applies integrated system modeling and control design process to a continuously variable valve timing (VVT) actuator system that has different control input and cam position feedback sample rates. Due to high cam shaft torque disturbance and high actuator open-loop gain, it is also difficult to maintain the cam phase at the desired constant level with an open-loop controller for system identification. As a result, multirate closed-loop system identification becomes necessary. For this study, a multirate closed-loop system identification method, pseudo-random binary signal $q$-Markov Cover, was used for obtaining linearized system models of the nonlinear physical system at different engine operational conditions; and output covariance constraint (OCC) controller, an $H2$ controller, was designed based upon the identified nominal model and evaluated on the VVT test bench. Performance of the designed OCC controller was compared with that of the well-tuned baseline proportional-integral (PI) controller on the test bench. Results show that the OCC controller uses less control effort and has significant lower overshoot than those of PI ones.

Commentary by Dr. Valentin Fuster

### Technology Reviews

J. Dyn. Sys., Meas., Control. 2011;133(2):024001-024001-7. doi:10.1115/1.4003369.

This paper compares some of the common tools and techniques that enable state-of-the-art systems to provide high-level control of mobile sensor networks. There is currently a great deal of interest in employing unmanned and autonomous vehicles in intelligence, surveillance, and reconnaissance operations. Although this paper addresses issues common to all mobile sensor networks, the applications presented are typically associated with autonomous vehicles. We focus specifically on three high-level areas: 1. mission definition languages that allow human users to compose missions defined in terms of tasks, 2. communication-addressing degradation and loss and relationship to underlying system architecture design, and 3. task allocation among the assets.

Commentary by Dr. Valentin Fuster

### Technical Briefs

J. Dyn. Sys., Meas., Control. 2011;133(2):024501-024501-7. doi:10.1115/1.4003260.

This paper deals with controller design for gentle physical human-robot interaction. Two objectives are set up. The first is to establish an analytical framework in order to justify the good features of state of the art controller, recently designed by numerical search of parameter space. The second is to investigate the possibilities to improve the performance of such controller. Our method ensures “prescribed” admittance behavior of the robot, similar to natural admittance controller design but with both more realistic model of the robot and more realistic target admittance. Joining natural admittance approach with the concept of complementary stability allows reaping the benefits of both. Limited knowledge about the environment via structured uncertainty allows a very simple worst-case analysis using elementary tools such as Routh–Hurwitz stability criterion. Consequent relation within the parameters determines an allowed region in the parameter space, where the contact stability is guaranteed. Not surprisingly, on one border of this region, the system behaves exactly the same as when the state of the art controller is employed. In addition, unexpected stability regions are discovered, suggesting theoretical performance improvements.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):024502-024502-6. doi:10.1115/1.4003265.

In this paper, a robust control strategy based on the uncertainty and disturbance estimator (UDE) is proposed for uncertain Linear Time Invariant-Single Input Single Output (LTI-SISO) systems with state delays. The knowledge of the bounds of uncertainties and disturbances is not needed during the design process although it is required for the stability analysis. Both the cases with known and unknown delays are considered. In the case of unknown delays, the terms involving the delays are treated as additional disturbances to the system. The robust stability of the closed-loop system is analyzed in detail, and a stability condition is proposed. Simulations are given to demonstrate the excellent tracking and disturbance rejection capabilities of the UDE-based control strategy.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):024503-024503-8. doi:10.1115/1.4003374.

This brief proposes a numerical approach for simultaneous prediction of stability lobe diagrams and surface location error in low radial immersion milling based on the direct integration scheme and the precise time-integration method. First, the mathematical model of the milling dynamics considering the regenerative effect is presented in a state space form. With the cutter tooth passing period being divided equally into a finite number of elements, the response of the system is formulated on the basis of the direct integration scheme. Then, the four involved time-variant items, i.e., the time-periodic coefficient item, system state item, time delay item, and static force item in the integration terms of the response, are discretized via linear approximations, respectively. The corresponding matrix exponential related functions are all calculated by using the precise time-integration method. After the state transition expression on one small time interval being constructed, an explicit form for the discrete dynamic map of the system on one tooth passing period is established. Thereafter, the milling stability is predicted via Floquet theory and the surface location error is calculated from the fixed point of the dynamic map. The proposed method is verified by the benchmark theoretical and experimental results in published literature. The high efficiency of the algorithm is also demonstrated.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):024504-024504-7. doi:10.1115/1.4003206.

A common problem pertaining to linear or nonlinear systems is the design of a combined robust control and estimation strategy that can effectively deal with noise and uncertainties. The variable structure control (VSC) and its special form of sliding mode control (SMC) demonstrate robustness with regard to uncertainties, although their performance can be severely degraded by noise. As such they can benefit from using state estimates obtained from filters. In this regard, this paper considers the use of a recently proposed robust state and parameter estimation strategy referred to as the variable structure filter (VSF) in conjunction with SMC. The contribution of this paper is a new strategy that combines sliding mode control with the variable structure filter. In the presence of bounded parametric uncertainties and noise, this combined method demonstrates robust stability both in terms of control and state estimation. Furthermore, the combined strategy can be used to achieve high regulation rates or short settling time. The combined VSF and SMC strategy is demonstrated by its application to a high precision hydrostatic system, referred to as the electrohydraulic actuator system.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2011;133(2):024505-024505-6. doi:10.1115/1.4003094.

This paper presents procedures to handle time delays in a feedback control loop in which both measurement and control signals are sent through a network, where random time delays occur. Even when time stamps are utilized, for example, the control signal time delay still must be estimated. Using a Padé approximation and a Kalman filter, we can estimate the mean time delay. Furthermore, methods are described to estimate the time delay of every packet instead of the mean for the measurement channel, which greatly enhances the performance of the Padé approximation approach. This is done by matching the measurements to the expected measurements provided by the filter with maximum likelihood. The methods are applied to an inverted pendulum to assess performance.

Commentary by Dr. Valentin Fuster