TMC's Technical Background
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g these sources ofvibration can be done passively, with TMCs MaxDamp > Ү For over 30 years, TMC has specialized in providin g isolators must be desi g ned to addressthe central issue: control of environmental noise. g precision workin g surfaces and vibration isolation systemsfor precision measurement laboratories and industry. To provide optimal performance, both precision topsӔ and their supportin line of isolators or actively usin g feedback or feedforwardtechniques (active systems are discussed be g innin g onpa g e 112). Payload- g enerated noise sources are usually ofa well-known...

in acceleration (see section 1.2.2 below). Amplitude spec-trums can also be expressed as velocity or position ampli- tudes as a function of frequency. Most spectrum analyzers use the Fast Fourier Transform, or FFT. An FFT analyzer finds the amplitude of each frequency in the input data and plots it. This includes the amplitudes and frequencies of any periodic noise sources. The amplitudes of periodic noise sources measured using an amplitude spectrum are independent of the length of the data record. > Hz , where [units]may be acceleration, velocity, or position. This normaliza-tion for the...

Since most locations have a combination of both random and periodic noise sources, it is often desirable to come up with a single number which characterizes noise levels. This is usually done by quoting an RMS (Root-Mean-Squared) noise level within a specified range of frequencies.Fortunately, this is easily done by integrating the powerspectral density or PSD over the frequency range ofinterest. The PSD is the square of the amplitude spectral density. This gives the following expression for the RMS motion between the frequencies f > 1 and f > 2 :This formula correctly calculates the RMS...

is just the fraction of the systems dampingto critical damping. We use Q rather than because T Q system to rest. It does this by producing a force on the payload proportional and opposite to its velocity relative to the earth:The presence of at = > , for Q s above about 2. There are several featureswhich characterize the transmissibility shown in Figure 3: ҕIn the region > ( X > e in both of these equations showsthat vibration of the earth is transmitted as a force to the payload by both the spring ( k ) and the damper ( b ). Ratherthan use the parameters ( M ), ( k ), and ( b ) to describe...

Figure 4a plots this function versus frequency. Unlike Figure 3, decreasing the > Q reduces the response of the payload at all frequencies, including the region >> Figure 5 shows a simplified pneumatic isolator. The isolator works by the pressure in the volume ( > . TMCs MaxDamp V ) acting on the area of a piston ( A ) to support the load against the force of gravity. A reinforced rolling rubber diaphragmforms a seal between the air tank and the piston. The pressure in the isolator is controlled by a height control valve which senses the height of the payload and inflates the isolator until...

load disk, which transfersits burden to the bottom of the piston well through the load pin. The load pin contacts the bottom of the well with a pivoting thrust bearing. As the payload moves sideways, the piston well pivots like a gimbal in the plane of the diaphragm. Thus a pendulum is formed, whose length is equal to the vertical distance from the roll in the diaphragm to the bottom of the load pin.TMCs CSP Figure 6 shows a cutaway view of TMCҒs Gimbal Piston > isolator. It uses two air chambers instead of one. Theseare connected by a small orifice. As the piston moves up and down, air is...

by onboard disturbances, and improves both the leveling and settling times for the system. Leveling time is thetime for the valving system to bring the payload to the correct height and tilt. Settling time 0.5 inch travel range, and thisprovides enough flexibility for almost all applications. Some systems also provide leveling feet. If a floor is extremely uneven, piers for the isolators may be required. Some free- standing isolators or other types of supports (like rigid tripods) must be grouted to the floor if the floors surface has a poor surface quality. Quick-setting ғready-mix...

control triangle is formed by the three pointswhere the valves contact the payload. Like the loadtriangle, the system will have the greatest stability and best positioning accuracyif the COM is inside this triangle. Thevalves should be mounted and their armsӔ rotated such that this triangle has the largest possible area.7.Sometimes following the above rules results in a system with poor height and tilt positioning accuracy. In this case, an alternate choice for the master/slave combination(s) might be required. In addition to valve location, there are several differenttypes of valves which...

The condition for absolute stability is: And the formula for H < An > p W > p 2 VW > Tot.Tot. 2 X > p [12] [13] [14][15] and 2 + X > p AnVW W > ֮ H < r X > r r X > r isolators use a single air chamber, they are more stable, and the rule becomes:Note that the effective support point for TMCs GimbalPiston 2 Җ 2 + > absolute instability is: with the volume between being possiblyӔ or marginallyӔstable. The ratios H > An2VW > TopTop p X > and W > p X > p p isolators is approximately 7 in. below the top of the isolator. For lightly loaded isolators, these rules underestimate system stability. If...