Based on field testing and user evaluations, the Minus K 1/2-Hz vibration isolation platforms and workstations perform about 10 to 100 times better than high-performance air tables depending on the vibration isolation frequencies. They also perform better than active or electronic-cancellation systems.

The transmissibility curves, which compare top-performing air tables with the typical Minus K 1/2-Hz performance, are shown below. Minus K isolators (adjusted to 1/2 Hz) achieve 93% isolation efficiency at 2 Hz, 99% at 5 Hz, and 99.7% at 10 Hz. Isolation performance closely follows that of an ideal undamped single DOF system up to about 10 Hz and reaches a floor in the transmissibility curve with some resonances at the higher frequencies.

The Minus K curve below is typical for any Minus K 1/2-Hz system, horizontal or vertical. Measured transmissibility curves for some Minus K bench top products are also shown below.

 

Transmissibility test procedure

The transmissibility curves provided by Minus K Technology are generated using a Stanford Research Instruments SR785 Dynamic Signal Analyzer. The output source of the SR785 is set to generate a swept sine signal. This signal is fed into a Labworks PA-138 power amplifier. The amplifier drives a Labworks ET-126 electrodynamic shaker. The shaker is mounted in a heavily reinforced frame that also supports a 650BM-1 isolator. This support isolator has been adjusted to about 2.75 Hz. It has also been modified to work only in the vertical direction. This isolator supports a heavy top plate and whatever ballast weight is needed to bring the total payload including the test isolator up to around 295 Kg.

Transmissibility as it applies to our isolators is a ratio of the output signal on the top plate divided by the input signal that the base of the isolator sees. One can also think of it as the ratio of what gets through the isolator divided by what is present on the isolator support. Two similar accelerometers are used to acquire the input and output signals. The input accelerometer is attached to the heavy top plate on the 650BM-1 support isolator. The test isolator rests on the heavy top plate as well. This way the accelerometer measures the vibrations that are fed to the isolator. The output accelerometer is placed on top of the properly loaded test isolator top plate. Both accelerometers are held in place with a thin layer of seismic wax. This works quite well, providing a secure, yet easy to undo bond for measurement.

The SR785 acquires both sets of data, calculates their ratio and displays the ratio as transmissibility..

The horizontal transmissibility was acquired in much the same way. The differences were that the support isolator was allowed to move horizontally. The electrodynamic shaker was mounted horizontally. The accelerometers were mounted on their sides, which allowed the ratio of horizontal data to be calculated and displayed as horizontal transmissibility.

BM-1

The curve below shows the typical vertical 1/2 Hz performance of the BM-1. It offers 10-100 times better performance than typical high-performance air tables.

 

BM-4

The curve below shows the typical vertical 1/2 Hz performance of the BM-4. It offers 10-100 times better performance than typical high-performance air tables.

 

BM-6

The curves below demonstrate the better-than-air performance that the BM-6 delivers. Vertically, the BM-6 offers a resonant frequency that is comparable to or better than most air tables. Horizontally, the BM-6 offers much better performance than typical air tables, which can have horizontal frequencies as high as 4-5 Hz.

 

BM-8

The curve below demonstrates the vertical 1/2 Hz performance of the BM-8. The BM-8 delivers the high performance of our larger isolators in a package only 4.6 inches tall. The horizontal performance of the BM-8 is the same as that of the BM-6.

 

BM-10

The curve below shows the vertical 1/2 Hz performance of the BM-10. It offers 10-100 times better performance than an air table in a package many times smaller. The horizontal isolation performance of the BM-10 is the same as that of the BM-6.