Vibration Criterion (VC) Curves-Lab Analysis
Codes and curve descriptions for different vibration environments and solutions.

The VC (Vibration Criteria) curves were developed in the early 1980s by Eric Ungar and Colin Gordon. They were originally developed as a generic vibration criteria for vibration-sensitive equipment for use in the semiconductor, medical and biopharmaceutical industries, but have found application in a wide variety of technological applications.

The criteria takes the form of a set of one-third octave band velocity spectra, together with the International Standards Organization (ISO) guidelines for the effects of vibration on people in buildings. The criteria apply to vibration as measured in the vertical and two horizontal directions.

full vc curve details...

Featured Product: WS-4 Compact Vibration Isolation Table

• Vertical natural frequency of 1/2 Hz or less can be achieved over the entire load range.
  
• Horizontal natural frequency is load dependent. 1/2 Hz or less can be achieved at or near the nominal load.
  
• Horizontal natural frequency is load dependent. 1/2 Hz or less can be achieved at or near the nominal load.
  
• Dimensions: 24" W x 24" D x 23" H
  (610mm W x 610mm D x 533mm H)
  

A cost effective vibration isolation table for weight loads up to 1000 lb. and 1/2 Hz performance vertical and horizontal.

The stand has been designed with a damped Phenolic top which includes locating holes for the leveling feet of the BM-1 and BM-4.

Pricing & Specifications

FAQs>>Frequently Asked Questions About Vibration Isolation

• I want the 1/2 Hz vibration isolation performance. Is there a standard bench top platform or workstation suitable for my application?
  
  
• How “static" must the payload be to use a standard 1/2 Hz system? I have stages that cause some redistribution of the payload weight.
  
  
• Will the Minus K isolator work if my payload weight is outside the weight range given in the specs?
  
  
• Can I place a larger plate or breadboard on the isolator to increase its working surface?
  
  
• Can I use multiple bench top isolators or workstations to support a larger load?
  
  
• Do I need a special table to support a bench top platform?
  
  
• How do I determine if the cables or lines going to my payload are too stiff for a 1/2 Hz system?
  
  
• Will a higher weight capacity isolator perform better than a lower weight capacity isolator?
  
  
• Is there any performance difference between the MK26 workstation and the BM-1 bench top platform?
  
  
• Does the isolator have a “service life" and is any maintenance required?
  
  
• How long does it take to set up a standard bench top platform or workstation?
  
  
• When do you recommend the more expensive auto adjust system?
  
  
• Is there a limit on the center-of-mass (CM) height of the payload for the standard 1/2 Hz bench top platform or workstation?
  
  
• I don’t know if I’m getting natural frequencies of 1/2 Hz. How do I determine this?
  
  
• Is the typical 1/2 Hz performance curve shown on the website for both vertical and horizontal behavior?
  
  
• When I try to adjust the vertical position, the pin stays above or below the line. What should I do?
  
  
• What is the most cost-effective Minus K product for my application?
  
  
• What are the typical frequencies of vibrations in a laboratory environment?
  
  

How They Work>>Negative-Stiffness Vibration Isolators

Minus K® vibration isolators employ a revolutionary concept in low-frequency vibration isolation. Vertical-motion isolation is provided by a stiff spring that supports a weight load, combined with a negative-stiffness mechanism (NSM). The net vertical stiffness is made very low without affecting the static load-supporting capability of the spring. Beam-columns connected in series with the vertical-motion isolator provide horizontal-motion isolation. The horizontal stiffness of the beam-columns is reduced by the "beam-column" effect. (A beam-column behaves as a spring combined with an NSM.) The result is a compact passive isolator capable of very low vertical and horizontal natural frequencies and very high internal structural frequencies.

Figure 1

Minus K® isolators typically use three isolators stacked in series: A tilt-motion isolator on top of a horizontal-motion isolator on top of a vertical-motion isolator. A vertical-motion isolator is shown in Figure 1. It uses a conventional spring connected to an NSM consisting of two flexures connected at their inner ends to the spring and supported at their outer ends, and loaded in compression by forces P. The spring is compressed by weight W to the operating position of the isolator, as shown in Figure 1. The stiffness of the isolator is K=KS-KN where KS is the spring stiffness and KN is the magnitude of a negative stiffness which is a function of the design of the flexures and the load P. The isolator stiffness can be made to approach zero while the spring supports the weight W.

A horizontal-motion isolation system consisting of two beam-column isolators is shown in Figure 2. Each isolator behaves like two fixed-free beam columns loaded axially by a weight load W. Without the weight load the beam-columns have horizontal stiffness KS. With the weight load the lateral bending stiffness is reduced by the "beam-column" effect. This behavior is equivalent to a horizontal spring combined with an NSM so that the horizontal stiffness is K=KS-KN, and KN is the magnitude of the beam-column effect. Horizontal stiffness can be made to approach zero by loading the beam-columns to approach their critical buckling load.

Figure 2

Full article + more images...

Performance...

Minus K engineers can design a variety of custom vibration isolation systems. Frequently these are modifications of other designs such as changing the load capacity of an SM-1 isolator, or the capacity, size and isolator locations on a FP-1.