Minus K Technology


Q. I want the 1/2 Hz vibration isolation performance. Is there a standard bench top platform or workstation suitable for my application?

A. Yes, provided your application satisfies the following:

  1. You need vibration isolation from floor, building or ground vibrations, not vibrations on the payload itself.
  2. Your payload weight is nearly static.
  3. Your payload weight is within the recommended range specified for the isolator. 
  4. Your payload will fit the top plate of the appropriate bench top or workstation model with the payload center-of-mass centered on the top plate (See specs for dimensions).
  5. There are no stiff lines, hoses, cables, etc., that would “short-circuit" our low-stiffness, low-frequency vibration isolation system. Typical electrical cables and computer cables are usually acceptable.

There are various products to choose from.  The BM-1 and BM-4 bench top platforms and the MK26 workstations provide 1/2 Hz vertical and horizontal.  The BM-8 and BM-10 low-height platforms provide 1/2 Hz vertical.

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Q. 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.

A. If the moving part of your stage weighs less than a few percent of the total payload weight and the maximum stage displacement is less than a few percent of the minimum footprint dimension of your payload, the standard system will probably work without any modifications. If the stages are heavier and the displacements are greater than this, we can usually accommodate this by simple modifications to the isolator such as increasing the tilt stiffness and increasing the displacement range. In cases where the stage weight is a significant part of the payload weight, and/or the maximum displacement is a significant fraction of the footprint dimension, we can make other custom modifications including increasing the vertical and horizontal natural frequencies. For example, we have modified a 350 lb capacity 350BM-1 to handle a 90-lb stage moving +/- 6 or 7 inches while keeping the natural frequencies around 1 Hz or less.

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Q. Will the Minus K isolator work if my payload weight is outside the weight range given in the specs?

A. No. Your payload weight must be within the range specified or the isolator will not work. If you need the 1/2 Hz horizontal frequency you need to be loaded near the nominal load capacity of the isolator. If your payload weight is close to the minimum weight specified, you could add sufficient ballast weight to get 1/2 Hz horizontal frequency. Another option is to use the next lowest weight capacity model with a custom modification to increase the weight capacity. This might be more cost-effective and more practical than adding a lot of ballast weight.

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Q. Can I place a larger plate or breadboard on the isolator to increase its working surface?

A. Yes, this is a common practice. We have customers who place breadboards as large as 3 ft. x 4 ft. on top of our 2 ft. x 2 ft. BM-1 bench top platform. We also can provide larger custom top plates on our bench top platforms and workstations.  Our MK26 workstation has standard sizes of 30" x 36" and 36" x 48" and we can provide larger custom units.

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Q. Can I use multiple bench top isolators or workstations to support a larger load?

A. Yes, this is a common practice. For example, two 650 lb. capacity 650BM-1 bench top isolators can be used to support a 4 ft. x 8 ft breadboard and a total payload weight as high as 1,400 lb., including the weight of the breadboard.

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Q. Do I need a special table to support a bench top platform?

A. No. Any reasonably sturdy bench or table will work, even one made of wood.

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Q. How do I determine if the cables or lines going to my payload are too stiff for a 1/2 Hz system?

A.The total stiffness of cables, lines, hoses, etc., connected to the payload should not exceed about 20% of the effective isolator stiffness in any direction. For a 1/2 Hz system, the isolator vertical or horizontal stiffness is approximately equal to the total payload weight divided by 40 in. or 100 cm. For example, the stiffness of a 100 lb (45 kg) 1/2 Hz system is approximately 100 lb/40 in.=2.5 lb/in. or 45 kg/100 cm=0.45 kg/cm. For this system the stiffness of the cables, lines, etc., should not exceed about 0.5 lb/in. or 0.09 kg/cm. Estimate the cables/lines stiffness as follows: Imagine disconnecting the cables/lines at the payload and estimate the force required to translate the payload ends of the cables/lines unit distance. For example, if it took 0.25 lb to translate the payload ends of the cables/lines 1 in., the stiffness would be 0.25 lb/in. This would be acceptable for a 100 lb capacity system. For a particular instrument or payload, using a larger weight capacity system and ballast weight reduces the effects of cables and lines on performance.

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Q. What is the most cost-effective Minus K product for my application?

A. See “Tips for Selecting the Most Cost-Effective Minus K Product."

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Q. Will a higher weight capacity isolator perform better than a lower weight capacity isolator?

A. Generally, no. However, if cables, lines or other connections to the payload are stiff enough to affect the isolator performance, then a higher capacity isolator with ballast weight will reduce this effect and give better results.

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Q. Is there any performance difference between the MK26 workstation and the BM-1 bench top platform?

A. No, provided a reasonably sturdy support is used for the BM-1 since the MK26 uses the same isolator as the BM-1.

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Q. Does the isolator have a “service life" and is any maintenance required?

A. When properly used a Minus K isolator will last for many years with no maintenance required.

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Q. How long does it take to set up a standard bench top platform or workstation?

A. For a payload that can easily be moved by one or two people it typically takes 10-15 minutes to set up. Heavier payloads requiring lifting equipment take longer.

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Q. When do you recommend the more expensive auto adjust system?

A. For remote or automated applications where it is not practical for an operator to adjust the vertical-motion isolator for changes in weight load or to correct for temperature changes.

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Q. 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?

A. A good practice is to keep the CM height of the payload within about half the minimum lateral dimension of the top plate, e.g., 12" for the BM-1, 8" for the BM-4, and 9" for the BM-6. However, we have been able to stiffen the isolator in tilt and exceed these heights by a factor of two or three.

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Q. I don’t know if I’m getting natural frequencies of 1/2 Hz. How do I determine this?

A. First, make sure the isolator is floating freely vertically and horizontally, both front-back and side-side. When you check the vertical, press down on the top plate while keeping it level until it bottoms or hits the down stop. Then release it and estimate the time for a complete cycle, up and down, which should be two seconds. You can check this with the second hand of a clock or watch. If the frequency is higher than 1/2 Hz you can reduce it using the vertical stiffness adjustment screw. Review the User Manual for the procedure. Repeat the procedure for the horizontal frequencies. Note: The horizontal frequency can only be reduced by increasing the payload weight.

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Q. Is the typical 1/2 Hz performance curve shown on the website for both vertical and horizontal behavior?

A.Yes.

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Q. When I try to adjust the vertical position, the pin stays above or below the line.  What should I do?

A. There is too much negative stiffness.  Turn the vertical stiffness adjustment screw a few degrees counter-clockwise and readjust the vertical position.  Repeat until the pin can be positioned on the line.

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Q. What are the typical frequencies of vibrations in a laboratory environment?

A. Below are the typical frequencies of vibrations in laboratory environments:

Vehicles on the streets outside 5-30 Hz
Trains and subways <10 Hz at a distance
Wind against the building 1-13 Hz
Rocking of tall building (upper floors, horizontal vibration) 1-5 Hz
Structural resonances within the building 1-40 Hz
Acoustic excitation (airborne or structural) 20+ Hz
HVAC systems 7-350 Hz
Seismic waves from ocean waves, etc. ~1 Hz
People walking in the building 1-5 Hz
Elevators <40 Hz
Transformers 40+ Hz
Machines and motors 4+ Hz
Raised floors (e.g. in clean room) 12-50 Hz resonance
   
Sources: Melles Griot and Colin Gordon & Associates.

 

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