Damping of structural vibrations with piezoelectric materials and passive electrical networks

Dynamics of Phononic Materials and Structures: Historical Origins, Recent Progress, and Future Outlook

Nanotechnology is the science of understanding matter and the control of matter at dimensions of 100 nm or less. Encompassing nanoscale science, engineering, and technology, nanotechnology involves imaging, measuring, modeling, and manipulation of matter at this level of precision. An important aspect of research in nanotechnology involves precision control and manipulation of devices and materials at a nanoscale, i.e., nanopositioning. Nanopositioners are precision mechatronic systems designed to move objects over a small range with a resolution down to a fraction of an atomic diameter. The desired attributes of a nanopositioner are extremely high resolution, accuracy, stability, and fast response. The key to successful nanopositioning is accurate position sensing and feedback control of the motion. This paper presents an overview of nanopositioning technologies and devices emphasizing the key role of advanced control techniques in improving precision, accuracy, and speed of operation of these systems.

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A Survey of Control Issues in Nanopositioning

Active noise control exploits the long wavelengths associated with low frequency sound. It works on the principle of destructive interference between the sound fields generated by the original primary sound source and that due to other secondary sources, acoustic outputs of which can be controlled. The acoustic objectives of different active noise control systems and the electrical control methodologies that are used to achieve these objectives are examined. The importance of having a clear understanding of the principles behind both the acoustics and the electrical control in order to appreciate the advantages and limitations of active noise control is emphasized. A brief discussion of the physical basis of active sound control that concentrates on three-dimensional sound fields is presented. >

Active noise control

Recent advances in nonlinear passive vibration isolators

In many industrial and defense applications noise and vibration are important problems. The conventional method of treatment is to use passive damping techniques or to redesign the system. However, passive damping techniques are primarily effective at higher frequencies, and redesign is often costly and ineffective. In the last decade, active control of sound and vibration (at audio frequencies) has emerged as a viable technology to bridge this low-frequency technology gap. Recent developments have been propelled by the rapid technology growth in affordable and practical digital signal processing chips and, to a smaller degree, improvements in control transducers. In this article the authors overview the active sound and vibration control field, first by putting it into a historical context, then by outlining the relevant control theory and implementations, and finally by describing some current practical applications.

Active control of sound and vibration

This paper describes theoretical and experimental work performed on the modelling and vibration control of a hanging flexible beam. The synthesis and laboratory implementation of low-authority controllers based upon feedback of local velocity to actuator force has been the subject of previous studies. This paper extends this work with the design and laboratory implementation of low-authority controllers based upon concepts of disturbance propagation and reflection. Control forces are applied to the lower end of the hanging beam. Compensators are derived which feed back local deflection and slope to control force and moment with the goal of minimizing the reflection of energy at the lower end. Several of these compensators are approximated by analog electronic filters for laboratory implementaipn. The performance of these wave-absorbing compensators is compared with that of velocity feedback.

Wave absorbing. controllers for a flexible beam

Techniques for designing and implementing algorithms for the control of periodic narrowband disturbances are discussed, and the strong similarities between the different methodologies are shown. The analysis of linear time invariant feedback systems results in a suggestion of how to extend two of the LQ-based multiple-input, multiple-output methodologies to achieve improved performance and stability robustness properties. In the analysis of the adaptive feedforward methods, it is concluded that the popular filtered-x LMS algorithm is useful for implementation, but is best analyzed from a classical linear time invariant feedback perspective. This perspective results in a suggestion of how to extend the multiple error LMS algorithm to achieve improved performance and stability robustness. Stability bounds of the adaptive feedforward approaches are derived in terms of allowable model error. >

Comparison and extensions of control methods for narrow-band disturbance rejection

This paper introduces the point of view that elastic deformations in large spacecraft structures may be aptly viewed in terms of propagating disturbances. Since the main topic of this paper is the control concepts, which result from such a viewpoint, the required structural dynamic description in terms of travelling disturbances is described only briefly, with reference to previously published works. The active control of these structures is approached from the point of view of actively modifying the natural disturbance propagation paths. Elastic energy is shunted into unimportant portions of the structure or is absorbed by an active "wave absorber." Several computational examples demonstrate the remarkable theoretical performance achievable by propagation-based controllers. Some discussion of practical difficulties in the implementation of such controllers is included.

A.H. von Flotow

Papers

Damping of structural vibrations with piezoelectric materials and passive electrical networks

Active control of sound and vibration

Wave absorbing. controllers for a flexible beam

Comparison and extensions of control methods for narrow-band disturbance rejection

Traveling wave control for large spacecraft structures