Peng Yan

Control of Subsonic Cavity Flows by Neural Networks - Analytical Models and Experimental Validation

Flow control is attracting an increasing attention of researchers from a wide spectrum of specialties because of its interdisciplinary nature and the associated challenges. One of the main goals of The Collaborative Center of Control Science at The Ohio State University is to bring together researchers from different disciplines to advance the science and technology of flow control. This paper approaches the control of subsonic cavity flow, a study case we have selected, from a computational intelligence point of view, and offers a solution that displays an interconnected neural architecture. The structures of identification and control, together with the experimental implementation are discussed. The model and the controller have very simple structural configurations indicating that a significant saving on computation is possible. Experimental testing of a neural emulator and of a directlysynthesized neurocontroller indicates that the emulator can accurately reproduce a reference signal measured in the cavity floor under different operating conditions. Based on preliminary results, the neurocontroller appears to be marginally effective and produces spectral peak reductions analogous to those previously observed by the authors using linearcontrol techniques. The current research will continue to improve the capability of the neural emulator and of the neurocontroller.

Design and analysis of an X–Y parallel nanopositioner supporting large-stroke servomechanism:

In this paper, we consider the design and analysis of an X–Y parallel piezoelectric-actuator-driven nanopositioner with a novel two-stage amplifying mechanism, where the mechanical design is optimized to achieve a large stroke and high-natural frequency for the purpose of high-performance servomechanism. The parallel kinematic X–Y flexure mechanism provides good geometric decoupling. The kinematic and dynamic analysis shows that the proposed design has a large work space and high bandwidth, which is further verified by finite-element analysis. The analysis results demonstrate that the designed nanopositioner has a large workspace more than 200 µm and a high-natural frequency at about 760 Hz. Furthermore, the dynamical model of the nanopositioner, including the dynamics of the PZT actuators, is also generated from the perspective of input/output transfer functions, and the parameters are identified by frequency-response experiments, which can be used for nano precision servomechanism.

CONTROLLER DESIGN FOR ACTIVE CLOSED-LOOP CONTROL OF CAVITY FLOWS

In this paper we discuss feedback controller design issues for active control of shallow cavity flows. Linear controllers, such as H ∞ , PID, and Smith predictor based controllers are designed and tested experimentally. The ineffectiveness of using fixed linear models in the design of linear controllers for the cavity flows is demonstrated via experimental results. In order to better address this problem, we are in the process of developing a nonlinear model of the cavity flow dynamics using Proper Orthogonal Decomposition (POD). We briefly discuss control issues related to the class of feedback systems involving this type of nonlinear plants.

An Experimental Study of Subsonic Cavity Flow - Physical Understanding and Control

We present the results of an experimental investigation that uses two different techniques for controlling a shallow cavity flow in the Mach number range 0.25-0.5. The first method is basically an open-loop design that relies on zero-net-mass forcing at an optimal frequency for suppressing the cavity flow resonance. The second method is a parallel-proportional with time delay controller, a linear control design that relies on real-time feedback from the flow to counteract the resonance. With properly tuned parameters, both methods are successful in reducing the cavity resonance for flows in the Mach number range explored. However the parallel-proportional controller exhibits a superior robustness with respect to departure of the Mach number from the design conditions, a signature of feedback control designs that are naturally more capable to handle changes of the open-loop plant. An additional benefit of the feedback control method is the lower power requirement to achieve comparable suppression of the resonance. An interpretation is presented of the physical mechanisms by which the optimal forcing frequency and the parallel-proportional with time delay controller reduce the cavity flow resonance. The results support the idea that the optimal forcing frequency control induces in the system a rapid switching between modes competing for the available energy that can be extracted from the mean flow. In the case of parallelproportional control mode switching is also observed which involves a larger range of frequencies and spreads more the extracted energy thus producing a flow with a quieter, more broadband spectral signature.

A disturbance observer-based adaptive control approach for flexure beam nano manipulators.

This paper presents a systematic modeling and control methodology for a two-dimensional flexure beam-based servo stage supporting micro/nano manipulations. Compared with conventional mechatronic systems, such systems have major control challenges including cross-axis coupling, dynamical uncertainties, as well as input saturations, which may have adverse effects on system performance unless effectively eliminated. A novel disturbance observer-based adaptive backstepping-like control approach is developed for high precision servo manipulation purposes, which effectively accommodates model uncertainties and coupling dynamics. An auxiliary system is also introduced, on top of the proposed control scheme, to compensate the input saturations. The proposed control architecture is deployed on a customized-designed nano manipulating system featured with a flexure beam structure and voice coil actuators (VCA). Real time experiments on various manipulating tasks, such as trajectory/contour tracking, demonstrate precision errors of less than 1%.

Time-varying internal model-based tracking control for a voice coil motor servo gantry

This paper presents a time-varying internal model-based control algorithm for high precision tracking of frequency-varying trajectories on a Voice Coil Motor (VCM) actuated servo gantry system. A new internal model control structure is proposed with a parallel connection of the stabilizer, which facilitates the design of a low order time-varying stabilizer for the augmented time-varying system. Effectiveness of the proposed control design is validated with simulations and experiments on the VCM servo gantry system. The resulting controller demonstrates good tracking performance with tracking error around 2 μm (RMS) for frequency varying periodic signals with RMS value of 354 μm.

Modeling and control of a novel X–Y parallel piezoelectric-actuator driven nanopositioner

In this paper, a novel X-Y parallel piezoelectric-actuator driven nanopositioner is studied from the perspectives of design optimization, dynamical modeling, as well as controller synthesis for high precision positioning. FEM (Finite Element Method) and dynamical modeling are provided to analyze the mechatronic structure of the proposed two-dimensional nano-stage, where the system model, including the hysteresis loop, is derived analytically and further verified experimentally. A robust control architecture incorporating an H∞ controller and an anti-windup compensator is then developed to deal with the hysteresis and saturation nonlinearities of the piezoelectric actuators. Real time experiments on the nano-stage platform demonstrate good robustness, high precision positioning and tracking performance, as well as recovery speed in the presence of saturation.

High precision tracking control of a servo gantry with dynamic friction compensation

This paper is concerned with the tracking control problem of a voice coil motor (VCM) actuated servo gantry system. By utilizing an adaptive control technique combined with a sliding mode approach, an adaptive sliding mode control (ASMC) law with friction compensation scheme is proposed in presence of both frictions and external disturbances. Based on the LuGre dynamic friction model, a dual-observer structure is used to estimate the unmeasurable friction state, and an adaptive control law is synthesized to effectively handle the unknown friction model parameters as well as the bound of the disturbances. Moreover, the proposed control law is also implemented on a VCM servo gantry system for motion tracking. Simulations and experimental results demonstrate good tracking performance, which outperform traditional control approaches.

A discrete time-varying internal model-based approach for high precision tracking of a multi-axis servo gantry

In this paper, we consider the discrete time case of a time-varying internal model-based control design for high precision tracking of frequency-varying reference trajectories. Thanks to a recently proposed parallel time-varying internal model structure, the asymptotic tracking conditions for the design of internal model units are developed, and a low order robust stabilizer is synthesized. In a discrete time setting, the high precision tracking control architecture is deployed on a Voice Coil Motor (VCM) actuated servo gantry system, where numerical simulation and real time experimental results are given to validate the proposed method.

Design, modeling and control of a novel parallel kinematics servo gantry for high precision tracking

In this paper we present the design, modeling and control of a high-precision, two-axis servo gantry by using a novel parallel kinematics XY stage. The parallel mechanism is based on a set of linear guideways for the motion decoupling. The advantages of the proposed design lie in low inertia and symmetric dynamics. Moreover the design of the stage makes the overall actuation system well suited for high-speed contouring in an XY plane. The contact of the rolling interface of the linear guideways are modeled by linear springs, and simulated via a finite element analysis, and partially verified by experiments. Furthermore to deal with feedrate variations, a time-varying internal model-based controller is adopted for the designed actuation system to track trajectories, and the experimental results demonstrate that the proposed design and control offers a good performance for the proposed design.