Modular Vibration Control Systems: Passive and Active Isolation Solutions for Dynamic Workspaces

Understanding Horizontal Vibration

Ideally, an optical table’s vertical vibration response on isolators would be a single-degree-of-freedom system. The system would be symmetrical around the vertical axis, and a vertical force through the table’s c.g. creates only translation motion. Just one linear deflection parameter is needed to positionally define the table in space. When it comes to horizontal motion and forces, the isolators are under the table so there is no symmetry in relation to the c.g. Horizontal force through the table’s c.g. will cause rotation and translation simultaneously.

Two deflection parameters are needed, so the horizontal system (in one plane) has two resonant frequencies and two degrees of freedom. The translation and rotation occur at the same time, so it can be demonstrated that these are “coupled” to the vertical resonance with one marginally higher (upper rocking mode) and one marginally lower (lower rocking mode).¹ These coupled resonances result from the table’s inertia properties and load. There are infinite variances in possible loads in service, so test data from horizontal isolation can vary slightly between applications.

KSI horizontal data reflect common service conditions and are offered with no edits. The KSI vertical natural frequency is as low as is workable to ensure a negligible effect of the inherent horizontal coupling on high-frequency isolation.

Image Credit: Visicon Inspection Technologies, LLC

Passive-Air™ Vibration Isolation

For less crucial applications and where low-frequency vibration below 10 Hz is not anticipated, the Model 500P Passive-Air™ module provides exceptional high-frequency vibration isolation.

The simple, free balloon-type omnidirectional airspring has been designed for the Model 500 Modular Legstand. A “tire valve” offers inflation using a bicycle hand air pump without a pressure gauge. Correct inflation is reached when the table floats freely.

Figure 29.1. Model 500 Series Supports Exploded view showing four modular isolation options. Image Credit: Kinetic Systems, Inc.

Rigid-Passive-Active Modular Support System

If the budget is modest or changing needs are anticipated, the Model 500 modular support system is recommended. It begins as Model 500R rigid leg units with 3" (76 mm) adjustable height screw jacks and a load limit of 2000 lb per leg.

This model can be upgraded with leg braces, 500P “add-on” passive-air mounts, 500RC retractable casters, 500A “drop-in” active-air vibration isolation, or 500AP active-air pendulum isolators.

For passive-air add-on isolators, the maximum load is 1600 lb (726 kg) per leg; active-air drop-in isolators have two load ranges: 500 lb (227 kg) and 1000 lb (454 kg) per leg. The maximum load of the Model 500AP active-air pendulum is 1000 lb (454 kg) per leg.

Figure 29.2. Model 505 Series modular legstand. Image Credit: Kinetic Systems, Inc.

500 Series Modular Isolation Legstands for Optical Table

For Load Ranges up to 2000 lbs Per Mount

Features/Benefits:

• Optional casters and braces
• Isolation components can be upgraded

Modular legstands can be ordered for the full-size optical tables when purchasing or later on. The Model 500R offers rigid leg units that can be upgraded to include leg braces (LB), add-on Passive-Air isolation (500P), drop-in Active-Air vibration isolation (500A), retractable casters (RC), or Active-Air pendulum (500AP). With the ability to be upgraded, the 500 Series is ideal for smaller budgets or when requirement changes are expected. Load capacities vary from 500 to 2000 lb per leg.

Specifications

Source: Kinetic Systems, Inc.

Note: Typical performance efficiencies are for microdisturbances

Performance Data

Measured Horizontal and Vertical Transmissibility for Model 500A Active-Air Isolation Leg Stand. Image Credit: Kinetic Systems, Inc.

Measured Horizontal and Vertical Transmissibility for Model 500AP-1000-28 Isolation Leg Stand. Image Credit: Kinetic Systems, Inc.

References and Further Reading

1. Himmelblau, H. and S. Rubin, “Vibration of a Resiliently Supported Rigid Body”, Chap. 3, Vol. 1, Shock and Vibration Handbook, edited by C.M. Harris and C.E. Crede, pub. McGraw Hill, 1961.

This information has been sourced, reviewed and adapted from materials provided by Kinetic Systems, Inc.

For more information on this source, please visit Kinetic Systems, Inc.