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This paper discusses the approximation and feedback relevant parametric identification of a positioning mechanism present in a wafer stepper. The positioning mechanism in a wafer stepper is used in chip manufacturing processes for accurate positioning of the silicon wafer on which the chips are to be produced. The accurate positioning requires a robust and high-performance feedback controller that enables a fast throughput of silicon wafers. A control relevant set of multivariable finite dimensional linear time invariant discrete-time models is formulated and estimated on the basis of closed-loop experiments. The set of models is shown to be suitable for model-based robust control design of the positioning mechanism. This is illustrated by a successful design and implementation of a robust controller.

Large number of active vibration control systems existing in the literature has brought lot of confusion for engineers and junior researchers. This study deals with the comparison of different active control systems of a 20-storey building under seismic excitation for three control devices: Active Mass Damper (AMD), Active Bracing System (ABS) and Connected Building Control (CBC). Two different control configurations are considered to add active damping to the building. The first one employs force actuator and displacement sensor and is examined with first and second order Positive Position Feedback, Lead compensators and Direct Velocity Feedback. The second configuration employs a displacement actuator collocated with a force sensor and an Integral Force Feedback control law. A total number of 15 control cases are compared from the point of view of stability, robustness, performance and control effort. [ABSTRACT FROM AUTHOR]

• We perform in-situ acoustic detection and feedback control of boiling crisis. • Frequency spectrum of audible sound is explored across boiling regimes. • A unique and previously unreported shift in the peak frequency is noted at CHF. • A feedback controller is designed to detect CHF and power down the system. • Control strategy minimizes thermal runaway for safe operations of boiling systems. Heat transfer deteriorates and thermal runaway is observed due to the formation of a vapor blanket during boiling crisis. Such temperature excursions are undesired in practical applications and may cause device failure. Inherent complexities and the associated uncertainties with boiling systems have not allowed development of robust critical heat flux (CHF) prediction tools. Hence, a high factor of safety is adopted, limiting the practical application of boiling to low heat flux nucleate boiling regime only. Here we identify a unique feature in audible acoustic emissions wherein a sudden shift in peak frequency from ≈ 200 - 250 H z in the nucleate boiling regime to ≈ 400 - 500 H z is observed at CHF. We show that a simple threshold-based feedback control strategy with a threshold frequency can be used to accurately detect the CHF and turn off the system to minimize thermal runaway. We show that the control strategy is equally robust on smooth and nanostructured copper surfaces. We believe that the ability to detect CHF and then power down the system within one second avoids transition to the undesired film boiling regime and is critical for safety and reliability of boiling-based systems and devices. [ABSTRACT FROM AUTHOR]

We revisit the minimal time problem of in-situ decontamination of large water resources with a bioreactor, considering a recirculation flow rate in the resource as an additional control. This new problem has two manipulated inputs: the flow rate of the treatment in the bioreactor and the recirculation flow rate of the water resource between the pumping and reinjection locations. Although the velocity set of the dynamics is non convex, we show that the optimal control is reached among non-relaxed controls. The optimal strategy consists in three sequential steps: 1. do not mix and take the flow rate of treatment that maximizes the concentration decay in the resource. 2. Mix as much as possible and carry on with the flow rate that maximizes the concentration decay. 3. Carry on mixing but do not treat the water. Finally, we show in numerical simulations that a significant gain in processing time can be achieved time when controlling in addition the recirculation flow rate. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new fixed-time stability theorem. Numerical simulations show that our upper bound estimate for the settling time is much smaller than those in the existing fixed-time stability theorems. Based on the new fixed-time stability theorem, we investigate the fixed-time synchronization of memristive neural networks (MNNs) by adopting a delay-dependent feedback controller. Numerical simulations are provided to demonstrate the correctness of our theoretical results and the superiority of the new fixed-time stability theorem. [ABSTRACT FROM AUTHOR]

In the recent past, it has been observed that flexure-based microposition stages with a large workspace and high motion precision are gaining popularity for performing practical micromanipulation tasks. Thus, a piezoactuated flexible two-degrees-of-freedom micromanipulator integrated with a pair of displacement amplifiers is developed. To enhance the practical positioning performance of the micromanipulator, this paper proposes a feed-forward frictional-order proportional–integral–derivative based feedback control approach to eliminate the undesired resonant mode of a piezoactuated microposition stage to satisfy the accuracy of the system. The control approach is composed of the integration inverse feed-forward compensator, the feedback controller, and the frictional-order proportional–integral–derivative controller. The integration inverse feed-forward compensator with an extended unparallel Prandtl–Ishlinskii model is introduced for addressing the nonlinearity of the piezoactuated microposition stage, leading to an approximately linear system. When all the roots of the system characteristic equation are negative real numbers or have negative real parts, the feedback controller is guaranteed to have tracking stability. Next, a frictional-order proportional–integral–derivative controller is designed to enhance the tracking performance of the microposition stage. Finally, comparative experiments with the conventional proportional–integral–derivative controller are performed, revealing that the practical positioning performance has been increased by nearly 35%. The experimental results demonstrate that the performance with the frictional-order proportional–integral–derivative+feedback controller is improved significantly. [ABSTRACT FROM AUTHOR]

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This paper proposes a delayed feedback control strategy for a fractional ecological infectious disease system with infected predators. Firstly, for the uncontrolled system, the stability of each equilibrium is discussed. Choosing the gestational delay as the branching parameter, the conditions of Hopf bifurcation are given at the positive equilibrium. The results show that the stable domain for the fractional system is larger than that for the integer-order system. Secondly, for the controlled system, the effects of gestational delay and feedback delay on the induction of the Hopf bifurcation are investigated, respectively. In addition, we find that the feedback gain coefficient also changes the critical value at which Hopf bifurcation occurs. Selecting a suitable feedback controller can effectively extend the stable domain of the system compared to the control-free system. Finally, the accuracy and effectiveness of the delay feedback controller in controlling the bifurcation are verified through numerical simulations. • A new fractional ecological model with a delay feedback controller is proposed. • Impact of gestational delay and feedback delay on Hopf bifurcation was investigated. • A new control strategy is used to enhance the stability of the fractional system. [ABSTRACT FROM AUTHOR]

For high-fidelity quantum operations in ion traps, it is important to maintain the secular frequency of the trapped ions at a constant value. The radial secular frequency is proportional to the amplitude of the radio frequency (RF) signal applied to ion traps. Owing to the changes in the ambient temperature of a helical resonator and the minute vibration of the optical table, the amplitude can vary. Recently, a method for reducing the fluctuation in the RF signal amplitude, using a commercial universal proportional-plus-integral (PI) controller, has been introduced, which, in turn, reduces the secular frequency drift of the trapped ions. The method improves the capability to maintain the secular frequency at a constant value. However, the structure of the controller is fixed; thus, the control method cannot be changed to suit different experimental conditions, and the different feedback configuration cannot be implemented to increase the resolution. In this paper, we develop a field-programmable gate array (FPGA)-based feedback controller that allows the implementation of various automatic control methods and feedback configurations. In our experiments, the fluctuation in the amplitude of the RF signal was 1.806% using a commercial universal PI controller. The fluctuation was reduced to 0.099% using the developed FPGA-based PI controller, and to 0.102% using the developed FPGA-based lag compensator. By employing the developed FPGA control method, many other automating control methods can be applied to achieve a stable and high-performance control of the secular frequency.

Homogeneous charge compression ignition (HCCI) engine has some advantages such as high efficiency and low emissions. On the other hand, it has challenges that it is difficult to avoid knocking and misfire. Therefore, the precise control system of HCCI combustion is necessary. In this paper, firstly, a control-oriented model which was discretized to several representative points in 1 cycle of an HCCI engine was developed. Secondly, a control system based on the modern control theory was constructed. It consists of a feed-forward controller and a feedback controller with Kalman filter to estimate state variables. The controller based on only a sole linear model has a disadvantage that its performance deteriorates except when the controller works at equilibrium points. Therefore, a gain-scheduling controller was introduced to the nonlinear system. The control simulation was conducted for the nonlinear plant model with the developed gain-scheduling controllers, and both IMEP and the in-cylinder pressure rising rate were controlled over a wide range IMEP.