The effect of vibration isolation (antivibration) is numerically determined with the ratio of a vibration frequency of the floor vibration f and the natural vibration frequency of vibration-proofing materials indicated by the system fn.
The smaller the natural vibration frequency fn of a supporting system, that is, the larger the vibration frequency ratio f/fn, the more favorable the vibration isolation effect generally is.

The antivibration supporting system has six types of natural vibrations as shown in Figure 2, each of which has a natural vibration frequency. In calculating vibration transmissibility, note that the natural vibration frequency of rotation becomes more than double of the natural vibration frequency in vertical direction of the formula above, .although it is determined by the shape, etc. of a supporting instrument, generally it becomes more than double of the natural vibration frequency in vertical direction of the formula above. The theoretical value of the relationship between vibration frequency f/fn and vibration transmissibility is shown in Figure 3 (Note that actual transmissibility curves become corrupted due to natural elastic vibration of instrument itself, surrounding acoustic pressure, influence of wind, etc. instead of becoming as the theoretical value).

An example of the basic configuration of the servo system is shown below. The surface plate is supported with a servo mount (air spring) installed on the frame. The basic piping system is shown in Figure 1. Compressed air supplied to the vibration-isolation base from the air source through the filter regulator is supplied to the air spring passing through the automatic pressure regulators at three places. The level of the surface plate is detected with the automatic pressure regulator, and the level is set automatically.

　
1. Automatic pressure regulator
There are various types of automatic pressure regulators, and the type used in standard vibration-isolation bases is shown in Figure 2. This automatic pressure regulator has in inside an extremely small diaphragm built-in as a sealing part of air. Since there are no sliding parts such as an O-ring, it has semipermanent life. When a coarse motion adjustment bolt or a fine motion adjustment bolt is turned clockwise, and the cantilever is displaced downward, air is supplied to the air spring, and the level of the surface plate goes up (counterclockwise for going down). When the level of the surface plate is set in this adjustment, even when variation of the level occurs to the surface plate due to variation of load, etc., the level is automatically corrected.

2. Air source and piping
The air spring system generally need an air source up to 0.5MPa. Air source of the plant, etc. can be utilized, and a baby air-compressor is used as necessary. When a tilt occurs to a vibration-isolation base, air is supplied or discharge to/from the automatic pressure regulator, the amount of consumption is increased A filter regulator with draining mechanism is installed at the air supply port of the air spring system. Since the upper limit of air supply pressure to this filter regulator is up to 1MPa, if the air source pressure is more than this, please reduce the pressure.. Use PT-1/8 female screw for the supply port from the air source of the plant, etc.

In order to respond to user needs required for precision vibration-isolation bases, and to develop higher performance vibration-isolation bases, various high performance vibration gauges, vibration structure analyzer (FFT, modal analyzer), computer, etc. are utilized for analysis. Figure 1 to Figure 3 below show examples of the analysis.

Vibration transmissibility
Figure 1 shows vibration transmissibility measured using a large vibration experiment base. This analysis method can measure vibration transmissibility, etc. in high precision. When mounted on actual machines, there is a benefit of being able to confirm modal analysis or vibration tolerance, etc. and frequency, acceleration, or amplitude, etc. can be freely controlled. Because of this, under any circumstances, measurement can be performed with good precision and reproducibility not influenced by the surrounding environment.

　
Figure 2 shows a spectrum of acceleration on the floor of the vibration-isolation base and on the surface plate in an example of an experiment performed by setting a vibration-isolation base on the floor and measuring in background vibration. In this analysis method, the average value of a spectrum in certain time is determined with FFT, in which the acceleration level on the vibration-isolation base shows lower levels than the acceleration level on the floor except for in the vicinity of resonance point.
Figure 3 shows the vibration transmissibility of the background vibration measurement shown in Figure 2. This Figure shows the features of the air spring, which is effective in dumping in low resonance magnification also at the resonance point. Also, the part lower than 0 decibel shows the vibration isolation area, proving more effective in low frequency.

1. Features of each surface plate

We provide four types, a. Steel core surface plate, b. Stone surface plate, c. Cast iron surface plate, and d. steel + concrete surface plate for surface plates of precision vibration-isolation bases.
Of these, steel core surface plates are mainly used for optical experiments, stone surface plates and cast iron surface plates are used for assembly of precision machines or components.
Also, of steel core surface plates, if you want to restrain the compliance (dynamic characteristics) of a surface plate, please use the Steel core surface plate SHD series with attenuation. Similarly, in order to increase the resonance frequency, light-weight surface plate with the same bending stiffness will be necessary, but the mass of the core is light-weight, being 5 to 10% of the surface plate mass, it is possible that rather than making the top and bottom face plates thicker, increasing the core height (surface plate thickness) will be necessary (please contact us for what is not included in this catalog)

	Advantages	Disadvantages
Steel core surface plate	1) Light-weight, 2) High static and dynamic stiffness (with attenuation)	1) Flatness
	3) Shape freedom degree 4) Polarization	2) Susceptible to disturbance (wind pressure, acoustic pressure)
	5) Tap processing 6) Attenuation can be added in a composite way
Stone surface plate	1) Flatness 2) Mass effect	1) Polarization
	3) Prolonged stability 4) Abrasion resistance	2) Tap processing is expensive
Cast iron surface plate	1) Inexpensive 2) Flatness	1) Attenuation
	3) Shape freedom degree 4) Tap processing	2) Rust
	5) Mass effect 6) Polarization
Concrete surface plate	1) Inexpensive 2) Large construction 3) Mass effect	1) Homogeneity 2) Hygroscopicity 3) Aging

Figure 1 shows the comparison of bending stiffness between the cast iron box surface plate and the black granite stone surface plate when the bending stiffness E (I bend in the longer direction) of the SHD type steel core surface plate is 1 (one).

Figure 2 shows the values of the primary natural vibration frequency of the SHD type steel core surface plate in the cross direction, and the primary natural vibrations of other surface plates. The numerical values in () in the Figure are the thickness of the surface plates used for calculation, indicating representative values of generic product.

The vibration attenuation characteristics of various materials in the table below are shown. These characteristic values are measurement comparison values with test pieces. In actual products, reductions are indicated. In addition, SH type steel core surface plate without attenuation characteristics become almost equal to the values of SPCC.

◆Vibration attenuation characteristics of various materials

	SHD type surface plate	Black	Cast iron (FC-20)	Steel material (SPCC)
		granite stone
Coefficient of loss	0.23	0.04	0.02	0.04
Resonance magnification	4.3	25	50	250

Figure 3 shows examples of mass of various surface plate per 1 m of surface plate depth. For the thickness of the surface plates, numerical values in ( ) of the graph of the primary natural vibration frequencies.