This exchange pretty much sums up his expert contributions on this thread.
So what about the plinth?
- Thread starter tromba
- Start date
This exchange pretty much sums up his expert contributions on this thread.
Well, I'll throw my meager contribution in.
I have an MCS 6601 I bought that looked brand new. Light, but good direct drive, and after sliding some heat shrink over the arm, adding a M97xe Shure with M95EJ stylus, I used about 2 lbs of modeling clay inside the underside of the plinth.
Took a pretty average table and made it exceptional. Everything got tighter and cleaner.
It also drops the needle down better than any other table I have. Still need to find out what I got to do to fix that. My 1400mk2, PL-600 pio, and Sony PS-X60 all drop like a rock. Therefore, they are all fully manual now.
Those plinths are gorgeous, mfrench.
I have an MCS 6601 I bought that looked brand new. Light, but good direct drive, and after sliding some heat shrink over the arm, adding a M97xe Shure with M95EJ stylus, I used about 2 lbs of modeling clay inside the underside of the plinth.
Took a pretty average table and made it exceptional. Everything got tighter and cleaner.
It also drops the needle down better than any other table I have. Still need to find out what I got to do to fix that. My 1400mk2, PL-600 pio, and Sony PS-X60 all drop like a rock. Therefore, they are all fully manual now.
Those plinths are gorgeous, mfrench.
The following is the sort of information I would have loved to have seen from waterjetguy:
5.5.1 Vibration Critical Applications
Vibration critical applications are actually in the minority. This means the number of applications which need better vibration isolation than a passive system can provide is quite small. Passive vibration isolation systems by TMC are extremely effective at suppressing ground noise at frequencies above a few Hz. There are only two types of applications where the vibration isolation performance of a passive isolator is a problem.
First, it is possible that the level of ground noise is so high that an instrument which is functional in most environments becomes ground noise sensitive. This usually only happens in buildings with very weak floors or in tall buildings where building sway becomes an issue. This is an unusual situation, since most equipment (such as semiconductor inspection machines) usually come with a "floor spec" which vendors are very hesitant to overlook.
The second type of applications are those with the very highest degree of intrinsic sensitivity. Prime examples are atomic force and scanning tunneling microscopes (AFMs and STMs). These have atomic scale resolutions and are sensitive to the smallest payload vibrations.
In both these situations the isolation performance of passive mounts is usually adequate, except for the frequency range from about 0.7 Hz to 3 Hz where a passive mount amplifies ground motion. This is a convenient coincidence, since active systems (such as the inertial feedback scheme) are good at eliminating this resonant amplification. Again, it is important to avoid an active vibration cancellation system unless you have an application which you are sure has a vibration isolation problem that cannot be solved with passive isolators. Most semiconductor equipment today has a different issue: settling time.
Back to Technical Background Index
5.5.2 Settling Time Critical Applications
Settling time critical applications are those where the vibration isolation performance of a passive pneumatic isolator is completely adequate, but the settling time of the isolator is insufficient. It is easy to determine if yours is such a system. If it works fine after you let the payload settle from a disturbance (stage motion), then you only have a settling time issue. (See Section 5.8). Before continuing, however, it is important to understand what is meant by "settling time."
Settling Time. The term settling time is one of the most abused terms in the industry, primarily because it lacks a widely accepted definition. A physicist might define the settling time as the time for the energy in the system to drop by 1/e . This is a nice, model-independent definition. Unfortunately, it is not what anybody means when they use the term. The most common definition is the "time for the system to stop moving." This is the worst of all definitions since it is non-physical, model and payload dependent, subjective, and otherwise completely inadequate. Nonetheless, it can be used with some qualifications.
In theory, a disturbed harmonic oscillator's motion decays exponentially, which is infinitely long lived. When in the context of a vibration isolator, one could think of the time when a system "stops moving" as the time required for the RMS motion of the system to reach a constant value, where the system's motion is dominated by the feedthrough of ground vibration. This is neither what people mean by settling time, nor is it model independent, since the "time to stop moving" depends on the magnitude of the initial disturbance and the level of ground noise. In fact, there is no definition of "settling time" as a single specification which can be used to define system performance in this context – passive or otherwise.
This is the definition used by TMC: Settling time is the time required for a payload subjected to a known input to decay below a critical acceleration level. This is an exact definition that requires three numbers: The known input is the initial acceleration of the payload immediately after the disturbance (stage motion) stops. The critical acceleration level is the maximum acceleration level the payload can tolerate and still successfully perform its function. The settling time is the time required after the disturbance for the payload's motion to decay below the critical acceleration level. Notice that we use a critical acceleration level and not a maximum displacement. It is not displacement of a payload which corrupts a process, but acceleration, since acceleration is what introduces the internal stresses in a payload which distort the structure, stage positioning, optics, etc. Of the three numbers, this is the most critical to understand, since it fundamentally characterizes the rigidity of your instrument.
For the product specifications on this web site, the critical acceleration and input levels are unknowns. For this reason, we quote our settling time specifications as the time required for a 90% reduction in the initial oscillation amplitude.
This is where I found that information:
http://www.techmfg.com/techbkgd/intro.htm
5.5.1 Vibration Critical Applications
Vibration critical applications are actually in the minority. This means the number of applications which need better vibration isolation than a passive system can provide is quite small. Passive vibration isolation systems by TMC are extremely effective at suppressing ground noise at frequencies above a few Hz. There are only two types of applications where the vibration isolation performance of a passive isolator is a problem.
First, it is possible that the level of ground noise is so high that an instrument which is functional in most environments becomes ground noise sensitive. This usually only happens in buildings with very weak floors or in tall buildings where building sway becomes an issue. This is an unusual situation, since most equipment (such as semiconductor inspection machines) usually come with a "floor spec" which vendors are very hesitant to overlook.
The second type of applications are those with the very highest degree of intrinsic sensitivity. Prime examples are atomic force and scanning tunneling microscopes (AFMs and STMs). These have atomic scale resolutions and are sensitive to the smallest payload vibrations.
In both these situations the isolation performance of passive mounts is usually adequate, except for the frequency range from about 0.7 Hz to 3 Hz where a passive mount amplifies ground motion. This is a convenient coincidence, since active systems (such as the inertial feedback scheme) are good at eliminating this resonant amplification. Again, it is important to avoid an active vibration cancellation system unless you have an application which you are sure has a vibration isolation problem that cannot be solved with passive isolators. Most semiconductor equipment today has a different issue: settling time.
Back to Technical Background Index
5.5.2 Settling Time Critical Applications
Settling time critical applications are those where the vibration isolation performance of a passive pneumatic isolator is completely adequate, but the settling time of the isolator is insufficient. It is easy to determine if yours is such a system. If it works fine after you let the payload settle from a disturbance (stage motion), then you only have a settling time issue. (See Section 5.8). Before continuing, however, it is important to understand what is meant by "settling time."
Settling Time. The term settling time is one of the most abused terms in the industry, primarily because it lacks a widely accepted definition. A physicist might define the settling time as the time for the energy in the system to drop by 1/e . This is a nice, model-independent definition. Unfortunately, it is not what anybody means when they use the term. The most common definition is the "time for the system to stop moving." This is the worst of all definitions since it is non-physical, model and payload dependent, subjective, and otherwise completely inadequate. Nonetheless, it can be used with some qualifications.
In theory, a disturbed harmonic oscillator's motion decays exponentially, which is infinitely long lived. When in the context of a vibration isolator, one could think of the time when a system "stops moving" as the time required for the RMS motion of the system to reach a constant value, where the system's motion is dominated by the feedthrough of ground vibration. This is neither what people mean by settling time, nor is it model independent, since the "time to stop moving" depends on the magnitude of the initial disturbance and the level of ground noise. In fact, there is no definition of "settling time" as a single specification which can be used to define system performance in this context – passive or otherwise.
This is the definition used by TMC: Settling time is the time required for a payload subjected to a known input to decay below a critical acceleration level. This is an exact definition that requires three numbers: The known input is the initial acceleration of the payload immediately after the disturbance (stage motion) stops. The critical acceleration level is the maximum acceleration level the payload can tolerate and still successfully perform its function. The settling time is the time required after the disturbance for the payload's motion to decay below the critical acceleration level. Notice that we use a critical acceleration level and not a maximum displacement. It is not displacement of a payload which corrupts a process, but acceleration, since acceleration is what introduces the internal stresses in a payload which distort the structure, stage positioning, optics, etc. Of the three numbers, this is the most critical to understand, since it fundamentally characterizes the rigidity of your instrument.
For the product specifications on this web site, the critical acceleration and input levels are unknowns. For this reason, we quote our settling time specifications as the time required for a 90% reduction in the initial oscillation amplitude.
This is where I found that information:
http://www.techmfg.com/techbkgd/intro.htm
