G. J. Sheu

Vibration Control of Composite Smart Structures by Feedforward Adaptive Filter in Digital Signal Processor

Intelligent structures with built-in piezoelectric sensors and actuators have been found to be preferable in vibration control. However, it is difficult to model the uncertainties of interfaces between the composite lamina and the embedded sensor/actuator. This article presents an adaptive filter design for system dynamics identification of composite laminated smart structures. A feedforward adaptive controller based on an adaptive filter with dynamic convergence is also developed for vibration suppression. Both the adaptive filter for system identification and the adaptive controller for vibration suppression are implemented in TMS320C32 digital signal processor for real-time applications. Experimental verifications show that the adaptive control is superior to active damping control and it is effective and robust to vibration suppression of smart structures.

Design of Experiments for the Controller of Rotor Systems With a Magnetic Bearing

A new design methodology for the vibration control of rotor systems with a magnetic bearing is developed in this paper. The methodology combines the experimental design method in quality control engineering and the conventional PD control technique such that their advantages in implementation feasibility and performance-robustness can be integrated together. A quality loss index defined by the summation of the infinity norm of unbalanced vibration is used to characterize the system dynamics. By using the location of the magnetic bearing and PD feedback gains as design parameters, the controller can be determined by a small number ofmatrix experiments to achieve the best system performance. In addition, it is robust to the vibration modes within a desired speed range. A rotor system consisting of rigid disks, 3 isotropic bearings, and l magnetic bearing is applied to illustrate the feasibility and effectiveness of the experiment-aided controller design.

Simulating Displacement and Velocity Signals by Piezoelectric Sensor in Vibration Control Applications

Intelligent structures with built-in piezoelectric sensor and actuator that can actively change their physical geometry and/or properties have been known preferable in vibration control. However, it is often arguable to determine if measurement of piezoelectric sensor is strain rate, displacement, or velocity signal. This paper presents a neural sensor design to simulate the sensor dynamics. An artificial neural network with error backpropagation algorithm is developed such that the embedded and attached piezoelectric sensor can faithfully measure the displacement and velocity without any signal conditioning circuitry. Experimental verification shows that the neural sensor is effective to vibration suppression of a smart structure by embedded sensor/actuator and a building structure by surface-attached piezoelectric sensor and active mass damper.

Vibration Control of Rotor Systems With Noncollocated Sensor/Actuator by Experimental Design

This paper presents a controller design methodology for vibration suppression of rotor systems in noncollocated sensor/actuator configuration. The methodology combines the experimental design method of quality engineering and the active damping control technique such that their advantages in implementation feasibility and performance-robustness can be integrated together. By using the locations of sensor/actuator and the feedback gains as design parameters, the controller design is shown to achieve a near optimal performance within the two-sigma confidence among all possible parameter combinations. Compared with LQ-based designs, the controller order is smaller and it is applicable to systems in an operation speed range. In addition, neither preselected sensor/actuator location(s) nor state measurement/ estimation is needed.

Vibration Control of a Rotating Shaft: An Analytical Solution

It has been shown that a rotating shaft in the Rayleigh beam model has only a finite number of whirl speeds and vibration modes when the rotating speed is higher than half of the whirl speed. The systems unbalanced response can therefore be written analytically by the vibration modes and the generalized coordinates. This paper presents an analytical controller design of optimal sensor/actuator location and feedback gain for minimizing the steady-state unbalanced response. Because all of the critical speeds and vibration modes are included in the controller design, there will be no residual mode, hence no spillover. An example is used to illustrate that the controller design in collocated or noncollocated configuration not only guarantees the closed-loop stability but also effectively suppresses the unbalanced response.

On the Spillover of Steady State Unbalance Response of a Rotating Shaft Under Velocity Feedback

It has been stated that a uniform rotating shaft in the Rayleigh beam model has only a finite number of critical speeds and precession modes. This paper presents a controller design of optimal sensor/actuator location and feedback gain for steady state unbalance response of a rotating shaft operating in a speed range. For systems under order-limit constraint such that only part of the precession modes can be included in the reduced-order controller design, the system stability can be evaluated. The example of a hinged-hinged rotating shaft is employed to illustrate the controller design of velocity feedback in collocated and noncollocated senor/actuator configuration. Analyses show that the reduced-order controller not only guarantees the closed loop system stability but also effectively suppress the unbalance response.

Synthesis of Reference Signal in Adaptive Feedback Controller for Structure Vibration Suppression

Adaptive control has been known to be desirable to accommodate the system parameter variations and adapt to operational requirements in smart (intelligent) structures. Conventional feedforward controller requires both the reference sensor to measure the disturbance and the error sensor to measure the residual vibration; however, the reference sensor measurement may be impractical because the disturbance is often not known a priori in structural vibration. This study presents an adaptive feedback controller design in which the reference signal is synthesized by the error sensor measurement and the system dynamics identification, which is a prerequisite also in adaptive feedforward controller design. The infinite impulse response (IIR) adaptive filter for system identification and the finite impulse response (FIR) adaptive filter for feedback controller are implemented on digital signal processor for effective on-line vibration suppression. Experimental results show that the controller performance is strongly influenced by the accuracy of system identification. The controller achieves broadband attenuation and remains robust under parameter variations.

Analytical Solution of Whirl Speed and Mode Shape for Rotating Shafts

The analytical solution of whirl speed and mode shape of a rotating shaft in six boundary conditions is presented in this paper. The shaft is modelled by a Rayleigh beam with rotatory inertia and gyroscopic effects, and the boundary conditions are (1) short-short, (2) long-long, (3) long-free, (4) free-free, (5) long-short, and (6) short-free bearings. It is shown that the whirl speed can be written analytically by a function of the whirl ratio (λ) defined by the rotating speed over the whirl speed and the slenderness ratio (l) defined by the length of the shaft over its radius. The number of whirl speeds, contrary to common belief, is finite when λ > 1/2. For the first time, the rotating system’s unbalanced response can be written analytically in an exact form by a finite number of vibration modes with the corresponding generalized coordinates.Copyright

Experiment-Aided Controller Design of Rotor Systems With a Magnetic Bearing

A new design methodology for the vibration control of rotor systems with a magnetic bearing is developed in this paper. The methodology combines the experimental design method in quality control engineering and the conventional PD control technique such that their advantages in implementation feasibility and performance-robustness can be integrated together. A quality loss index defined by the summation of the infinity norm of unbalanced vibration is used to characterize the system dynamics. By using the location of the magnetic bearing and PD feedback gains as design parameters, the controller of experiment-aided design achieves the best system performance. In addition, it is robust to operating speed variations. A rotor system consisting of 4 rigid disks, 3 isotropic bearings, and 1 magnetic bearing is applied to illustrate the feasibility and effectiveness of the experiment-aided controller design.© 1995 ASME

Design of quantum well thermoelectric energy harvester by CMOS process

This work aims at improving the energy harvester performance by using low-dimensional thermoelectric materials. A micro-thermoelectric generator with quantum well thermocouples is developed by state-of-the-art CMOS (Complementary metal-oxide semiconductor) process. A relaxation-time model is applied to analyze the characteristic length of silicon germanium quantum well, and a thermal model is also applied to calculate the thermocouple size for optimal performance by matching the thermal/electrical resistance. Analysis based on TSMC 0.35μm 3P3M (3-poly and 3-metal layers) BiCMOS process shows that the quantum well thermocouples (0.05 μm Si0.9Ge0.1 quantum well on 0.300 μm P-thermoleg and 0.280 μm N-thermoleg) has the best performance. that the power factor and voltage factor is 0.241 μW/cm2K2 and 10.442 V/cm2K.