Keeping Optical Tables Steady Tech
lenge for precision experiments and manufacturing processes in optoelectronics. Optical tables and breadboards in various shapes and forms are the de facto standard of vibration control. They rest on soft isola-tors that effectively filter out vibration from the floor. However, other sources of disturbance – acoustic noise, atmospheric turbulence and onboard sources – still exist and may become prevalent vibration sources at higher frequencies. These disturbances can have a significant negative impact on the optomechanical performance if their spectral contents are close to the resonance frequencies of the platform. For this reason, internal damping, or dissipation of mechanical energy, that mitigates the effect of resonance is very important for high-quality vibration-isolated platforms. Active vibration damping that involves electromechanical sensors, actua-tors and control systems has proved most effective for suppressing resonance vibrations. Recent extension of this technology by Newport with add-on SmartTable ADD active dampers expands the limits of applications beyond standard optical tables to virtually any vibration-isolated platform that can experience unwanted resonance vibrations. The theory of active vibration control predicts that a small number of active dampers placed near antinodes of the main vibration modes suffice to suppress resonance vibration over the whole structure. In the case of a typical rectangular platform, two dampers placed at adjacent corners do the job. This has been confirmed by theoretical analysis and by multiple measurements of the dynamic reaction at remote locations on the table by highly sensitive seismic ac-celerometers. 3 To illustrate this in a more vivid demonstration, researchers at New-port Corporation turned to the powerful experimental means provided by the scanning laser Doppler vibrometer from Polytec Inc. The experiment also promised valuable information about the proper tuning of the active control feedback loops. A custom all-steel optical breadboard was chosen for testing the effect of add-on active dampers (Figure 1). The breadboard, whose size was 4 ft × 5 ft × 4.5 in., was supported by four spring-based vibration isolators, so that the " rigid body " natural frequency of the suspension equaled 5.25 Hz. Two SmartTable ADD dampers were bolted onto the two front corners of the breadboard. To obtain a consistent stationary vibration signal, the breadboard was excited by a stationary random force. A miniature electromagnetic shaker was used for this purpose; it is seen at the far left corner of the breadboard in Figure 1. The resulting vibration of the bread-board did not exceed the levels routinely …
Evolving criteria for research facilities: vibration
The paper presents a review of generic vibration criteria used for vibration-sensitive technical facilities. The paper reviews the logic behind and evolution of the Vibration Criterion (VC) curves, originally known as the "BBN" criteria, and discusses the background of a generic criterion in common usage for nanotechnology, currently denoted NIST-A. The criteria are compared with representative types of research equipment and activities.
Maturation of the Vibration Environment in Advanced Technology Facilities
Semiconductor production and other advanced technology facilities are often designed in two states, the “base-build” state and the “hook-up” state. The base-build state, which after completion is termed “as-built” by the International Organization for Standardization (ISO) 1 , includes the design and construction of the shell structure and all architectural, mechanical, electrical, and process systems needed for building operation. The hook-up state includes the installation of the production tools and their local support equipment (dry pumps, piping attachments, etc.). During the project design, cleanroom environment vibration and noise requirements are often assigned for compliance in the asbuilt state only (before tool hook up), since often a different design team or construction team or both is involved in the hook-up state and the base-build design team has little control of operational vibration and noise levels. This paper discusses typical changes, or maturation, in the production vibration environment after the as-built state. In these mature states, identified by ISO as “at rest” and “operational,” there is usually an increase in environmental vibration and noise levels with the addition of tools and tool support equipment. This paper also discusses the role of maturation in building mechanical equipment as well as the means of controlling the increase in vibration.