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Seismological Research Letters; November/December 2006; v. 77; no. 6; p. 684-690; DOI: 10.1785/gssrl.77.6.684
© 2006 Seismological Society of America
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Implementation of a Linear Shaker Using the Zero Friction Air Bearings

Nebojsa Vrcelj, Gagandip Grewal, Martin Williams, and Iain Weir-Jones
Terrascience Systems Ltd./Weir-Jones Group of Companies

The first 20% of the full text of this article appears below.


   INTRODUCTION
 
To qualify a new generation of high-resolution strong-motion recording equipment, Terrascience Systems Ltd. initiated development of a precise linear shaker for automated verification and calibration of seismic instrumentation. Current electromagnetic (EM) and hydraulic shakers are unable to generate signals of high purity at very low frequencies; this poses a problem in qualification of the seismic instrumentation. In addition to their nonlinearity and static friction, most shaker systems today cannot be optimally adjusted at different loads and movement profiles. This introduces signal distortion, thus reducing the accuracy of important instrument parameters measured at different frequencies: dynamic range, linearity, flatness of the amplitude frequency response, etc. Furthermore, typical calibration methods, such as static tests based on the force of gravity as a reference signal, present an additional significant limitation, as there is no possibility of precisely calibrating an instrument at acceleration levels higher than 1 g. The overall objective of the project was to design a system to address the problems discussed above that would be capable of precisely generating specific movement profiles required for seismic instrumentation testing. With these objectives in mind, we designed a system with an air-bearing stage, which offers well known advantages compared to the rolling element bearings and hydraulic systems, such as zero friction, zero wear, silent and smooth operation, stability, etc. This paper describes the project's three distinct phases: installation, tuning, and post-test data analysis.

The shaker is not in commercial development and is used in internal engineering qualification testing. The purpose of this paper is primarily to share our experience and knowledge.


   INSTALLATION
 
System Description

The core of the application is a stage based on air bearings. Air bearings function on a controlled film of pressurized air between two closely matched surfaces. The air bearings supply air pressure equally across the whole face by diffusing the air through . . . [Full Text of this Article]

Terrascience Systems Ltd.
2040 West 10th Avenue
Vancouver, British Columbia
V6J 2B4, Canada
wjgroup@weir-jones.com






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