Down the anti-vibration rabbit hole again...

[Beatsy]

I mentioned before that my macro rig had a vibration problem at high mag caused by cars hitting speed-bumps on a nearby road. This limited me to taking hi-mag stacks late at night until I fixed it with Godox AD200 flashes. But I still prefer multiple continuous sources for control of overall lighting, so I continued trying to solve this "speed bump" niggle. Happy to say I kind of fixed it by bolting my rig to a large 10mm-thick steel plate supported on short columns of Sorbothane discs. It's a nice, tidy and stable setup that plays well with my penchant for supporting everything else on magnetic Noga stands. Prior to that, the rig itself was stood (balanced) directly on a mixture of cork and sorbothane pads. Unfortunately, although the rig is completely immune to speed-bumps now (yay), it's no longer immune to my fidgeting about on the chair (boo). It's not too bad as I've no control over the speed-bumps, but can control my own fidgeting Yet the niggle remains so I'm still looking to improve things further.

I think I found most posts to do with anti-vibration measures, but they're a bit scattered and I 'd like to prompt some discussion over a couple of ideas I'm considering. I'm pretty sure the issue is frequency; my rig has been "detuned" away from speed-bumps but "tuned" to floor vibrations caused by my moving in the chair. So I wondered if adding a second steel plate under the first, with taller Sorbothane columns under that, might solve the problem. I found a source for chunky hemispherical Sorbothane feet that look like they'd so the job (50mm diameter, rated to >50kg for 5). The idea being that each layer would be tuned to absorb a different range of vibration frequencies while preserving the flat and stable base. It's an easy, incremental change to what I have now, but...

While searching for info, I came across the idea of suspending everything from bungee cords. Now that actually looks a very promising and attractive solution! I'm intrigued. The rig is sat on a table dedicated to the task so it's no problem to attach (say) four posts to hang the bungees on. I'm sorely tempted to try this instead - suspending the steel plate and attached rig just above the table by it's corners. Has anyone else done this? Does it work well? How long/thick/stretched should the bungees be in order to absorb the widest range of "nuisance" frequencies? Thanks in advance for any insights.

[enricosavazzi]

I must stress that the following is guesswork, not a tried and tested solution.

What you are proposing to build (two rigid sheets stacked atop each other, each sheet with sorbothane feet underneath) should be more effective than a single sheet, on condition that the resonance frequencies of the two sheets differ, and are not harmonics of each other.

You could start the way you propose, with the equipment placed on the top sheet (you want to start with the final mass on the top sheet). Test for vibrations. Best would be with a vibration analyzer, or at least a motion transducer (inertial sensor) on each of the two plates, coupled to an oscilloscope to get visual results and compare the vibration frequencies and amplitudes of the two layers. A far simpler, but less sensitive, solution is a plastic Petri dish filled with water (if vibrations are strong enough to see).

Increase the mass of the lower sheet, for example by stacking two sheets together. You might try replacing the lower steel sheet with a (heavier) stone or concrete plate. Repeat a few times with different masses, trying to home in on a configuration that approaches minimum vibration of the top layer. If this proves difficult, you might even try increasing the mass on the top layer and lowering the mass of the bottom layer.

There are some unknowns. For example, I should expect that the optimal configuration will have different masses on the top and bottom layers of the stack, and different resonating frequencies, but I am not sure how the two layers will couple together when you change the mass of the lower layer. This is why I am suggesting using transducers and a two-channel oscilloscope to see what is really happening. An additional uncertainty is that the source of vibration may not be repeatable, e.g. local street traffic or construction sites may vary in frequency.

If the above seems overly complicated, just try the above without transducers and oscilloscope, and judge by the photographic results.

[Pau]

What about isolating the table from the floor? Or maybe the chair?

There are isolating tables for microscopes that time to time pop up at Ebay, like
http://www.ebay.com/itm/Newport-Vistek- ... SwwvZZRESh
I'm always tempted but shipping and customs costs are stopping me.

[Lou Jost]

I'm working on the bungee cord solution for my work, to fight vibrations from passing cars and trucks, and from my neighborhood volcano (which thankfully has been quiet lately). I will mix it with Sorbothane solutions. The system will not simply hang but will be under lateral stress so that the whole thing doesn't sway. It may be a while until I manage this....will report when I do.

[Beatsy]

I must stress that the following is guesswork, not a tried and tested solution.

What you are proposing to build (two rigid sheets stacked atop each other, each sheet with sorbothane feet underneath) should be more effective than a single sheet, on condition that the resonance frequencies of the two sheets differ, and are not harmonics of each other...

Thanks for this - helps me know I'm on the right track. For visualising vibration I'll use the rig by focussing a 50x Mitty on a small, high contrast detail, zoom in 100% on the camera and watch the live image on a monitor. I only need to kill vibration that affects the image (assuming some may not make it all the way from baseplate to camera/specimen) and even a half-pixel wobble is easily detectable this way.

Thanks Lou and Pau for your comments too. I expect to try the bungee thing at some point, but think I'll chase this "two plates" solution first as it's closer to what I have now and alters fewer variables at once. If it doesn't work well enough then I can try suspending the whole shebang as a next step.

[lothman]

your setup should be heavy in order to gather inertia and be isolated via soft springs (low frequencies) to your building. So I would try to increase mass (sand filled sacks, lead balls...) and put the whole thing an tennis balls and see how things work out. Sand and tennis balls should dampen energy.

[Smokedaddy]

I just finished my horizontal setup. Of course I still may revise a few things. It weighs in about 260 pounds now. I covered the top of my surface plate with Sorbothane sheet and used Sorbothane disks under the surface plate. It all mounted on a super old solid Oak teachers desk. Seems pretty solid to me.

[Smokedaddy]

Best would be with a vibration analyzer, or at least a motion transducer (inertial sensor) on each of the two plates, coupled to an oscilloscope to get visual results and compare the vibration frequencies and amplitudes of the two layers.

Personally I would love to know how to accomplish what you are describing. I have an oscilloscope that I just took in trade for a couple of astronomy eyepieces. Of course I am a novice oscilloscope wise.

[enricosavazzi]

That oscilloscope seems to have four channels, so it should be more than adequate for the task.

What you need next is a transducer that transforms vibration to an analog signal. The following module incorporates XYZ vibration transducers, and judging from the data sheet, would seem suitable (it measures between 1Hz-500Hz or 1Hz-100Hz for different models, which is plenty enough), but I have no information about price:
http://signalquest.com/download/Vibrati ... SQ-SVS.pdf

This module outputs 2 analog RMS readings, averaged over 1s time span. These output should be suitable for direct connection to the oscilloscope. They do not output the actual vibration waveform, only an RMS reading within the specified vibration frequency bandwidth. For constant vibration readings, a mV meter may actually be enough, but the readout value likely requires some post-processing (and you also need a constant source of artificial vibration of adjustable frequency).

Since you are mainly interested in achieving the lowest amount of vibration, you don't really need to differentiate among vibration about different axes (although it might be nice to know), and only a total figure is strictly necessary.

I am sure there are other products available as well. There might even be something available for the Arduino and Raspberry Pi boards. However, make sure that you are purchasing a transducer that gives an analog readout of vibration intensity, not just an on-off binary signal. The cheapest transducers are of the latter type, but are not useful if you need a quantitative measurement.

[Lou Jost]

Smokedaddy, that looks very impressive. But it also looks quite tall. All else being equal, you can expect the amplitude of horizontal vibrations to increase more or less in proportion to the height above the vibrating surface. On the other hand, I see your even taller vertical set-up behind it, and if you haven't had problems with that, then your new set-up should be fine too (assuming the connections between each layer of your set-up are completely solid).

[Olympusman]

This reminds me of an encounter I had about 15 years ago with a woman who was a consultant on early digital imaging in New York City.
She set up all of these studios with digital scanning camera backs which were awesome. They made three passes Y/C/M of a tabletop setup and saved the passes to a computer. The resolution was remarkable. Large format stuff.
The problem was that many of the trendy lofts these photographers were using were above the subway system, so the scanning backs were pretty much useless because of the ambient vibration. None of the scans were even remotely in register.
Needless to say, the three-pass system (as high as the resolution was) was impractical - at least in a major metropolis.

Mike

[elf]

While steel weighs a lot for a specific size, it's really not very good at dampening vibrations. Cast iron is much better. Granite would also be a better choice. Concrete is also better than steel for dampening vibrations.

Sorbothane also needs to be tuned to the specific vibration frequency you're trying to dampen. While it works if you just use some, it will work better when properly tuned.

Here's an interesting DIY cable vibration dampener based on commercial dampeners.

[ChrisR]

Nice 'scope.
Vibration transducer? Microphone or loudspeaker.


Humblingly good though, is a mobile phone. They have very good sensors, and some apps will output the data, though snapping a picture of the screen is good.
Start with "Sensor Kinetics", but there are many apps.

[Smokedaddy]

Thanks, yea we've talked a 'little' about this via PM once before. I don't have the skills most of you have on the forum so everything is a learning curve, huge in most cases. I wanted to use my oscilloscope since I have one now and learn something about them.

[mawyatt]

Smokedaddy,

Like Chris said "Nice Scope". Get yourself a signal generator and start playing around, lots of fun stuff ahead with your new scope!!

Best,

Mike