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LABOPHOT-2 (focus block)
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Smokedaddy



Joined: 07 Oct 2006
Posts: 1187
Location: Phoenix, Arizona

PostPosted: Tue Mar 06, 2018 6:08 pm    Post subject: Reply with quote

elf wrote:
Flexures Laughing


Are you the same elf on Homeshopmachinist? I'm reading about Flexures right now. Never heard of them before.

Thanks,
-JW:
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elf



Joined: 18 Nov 2007
Posts: 1357

PostPosted: Tue Mar 06, 2018 6:19 pm    Post subject: Reply with quote

Yes Very Happy

For everyone else, I posted a link to Dan Gelbarts excellent video on flexures which seem to be an ideal way to work with sub micron movements.
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Smokedaddy



Joined: 07 Oct 2006
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PostPosted: Tue Mar 06, 2018 7:41 pm    Post subject: Reply with quote

Where did you find your 3D printed model?

https://www.youtube.com/watch?v=OK_o7MRmC3s

-JW:
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mawyatt



Joined: 22 Aug 2013
Posts: 1666
Location: Clearwater

PostPosted: Wed Mar 07, 2018 6:53 am    Post subject: Reply with quote

I had completely forgot about Dan's work & video...great stuff.

BTW we used Beryllium flex pivots (same principle as Dan's video discusses) on a Laser controlled (closed loop) tiny (100mm long) moving mirror Michelson Interferrometer (8-12um) on the Remote Sensing Chemical Agent Detector (XM21) in 1980. These pivots had no backlash, no wobble, nor mechanical "noise", and worked beautifully.

Thanks for posting, and bringing back old memories!!

Best,
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1724
Location: Santa Clara, CA, USA

PostPosted: Wed Mar 07, 2018 8:21 am    Post subject: Reply with quote

These work so well because the systems are essentially springs which are highly constrained in all but the dimension intended for movement. Speaker drivers used as voice coil steppers operate similarly. The voice coil drivers sold for such purposes are not constrained, so a supporting structure is required. Speakers have these structures built-in and optimized for damping factor, so are ideal for this purpose. Most of the damping comes from the acoustics of the enclosure, but stand-alone drivers I've tested seem to be well enough damped without the enclosure to be useful for small-step stacking. I can't tell you how well an enclosure-less driver might work at high magnifications as I have not tested such a system, but up to 20-40x they seem ideal. At higher mags I do expect some sensitivity to room air movement, so there will be a limit to the step size for such a driver. Adding enclosure would greatly reduce this limit.

It's not clear to me what the ultimate limit is for step size in such a constrained system. I'd think it would be limited by the characteristics of the constraining springs. For a driver, there are two springs...the spider, and the surround. Someone much better at mechanics and materials than I might be able to tell you the limits, but I doubt there is any issue down to the nm range.

edited to add: another limit would be the noise level in the driving electronics. Not sure which wins (loses)...mechanical or electrical
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Smokedaddy



Joined: 07 Oct 2006
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Location: Phoenix, Arizona

PostPosted: Wed Mar 07, 2018 9:39 am    Post subject: Reply with quote

I have a vintage (so to speak) pair of Yamaha NS-1000M speakers but that'a all I know about Beryllium. I wasn't aware of flexures until elf mentioned it. Dan's video series is excellent as well. Seems like I learn something new every day.

Last edited by Smokedaddy on Wed Mar 07, 2018 10:21 am; edited 1 time in total
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mawyatt



Joined: 22 Aug 2013
Posts: 1666
Location: Clearwater

PostPosted: Wed Mar 07, 2018 9:59 am    Post subject: Reply with quote

Smokedaddy wrote:
Seems like I learn something new every day.


That's why science is so wonderful, the more you know the more you realize how much you don't Rolling Eyes

Best,
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mawyatt



Joined: 22 Aug 2013
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Location: Clearwater

PostPosted: Wed Mar 07, 2018 10:05 am    Post subject: Reply with quote

ray_parkhurst wrote:
These work so well because the systems are essentially springs which are highly constrained in all but the dimension intended for movement. Speaker drivers used as voice coil steppers operate similarly. The voice coil drivers sold for such purposes are not constrained, so a supporting structure is required. Speakers have these structures built-in and optimized for damping factor, so are ideal for this purpose. Most of the damping comes from the acoustics of the enclosure, but stand-alone drivers I've tested seem to be well enough damped without the enclosure to be useful for small-step stacking. I can't tell you how well an enclosure-less driver might work at high magnifications as I have not tested such a system, but up to 20-40x they seem ideal. At higher mags I do expect some sensitivity to room air movement, so there will be a limit to the step size for such a driver. Adding enclosure would greatly reduce this limit.

It's not clear to me what the ultimate limit is for step size in such a constrained system. I'd think it would be limited by the characteristics of the constraining springs. For a driver, there are two springs...the spider, and the surround. Someone much better at mechanics and materials than I might be able to tell you the limits, but I doubt there is any issue down to the nm range.

edited to add: another limit would be the noise level in the driving electronics. Not sure which wins (loses)...mechanical or electrical


Ray,

I would think with proper design the electrical noise could be made arbitrarily small since the bandwidth doesn't need to be high. A 1Hz or lower bandwidth seems reasonable for stacking, and a few nanovolt/rt(Hz) noise levels are possible. So environmental noise is probably the bigger noise source, and as you mentioned airflow is a major concern at these levels. I've even had to deal with airflow induced "noise" with ultra-precise electronics!

Best,
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ray_parkhurst



Joined: 20 Nov 2010
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PostPosted: Wed Mar 07, 2018 10:23 am    Post subject: Reply with quote

mawyatt wrote:


Ray,

I would think with proper design the electrical noise could be made arbitrarily small since the bandwidth doesn't need to be high. A 1Hz or lower bandwidth seems reasonable for stacking, and a few nanovolt/rt(Hz) noise levels are possible. So environmental noise is probably the bigger noise source, and as you mentioned airflow is a major concern at these levels. I've even had to deal with airflow induced "noise" with ultra-precise electronics!

Best,


Sure, with appropriate filtering the electrical factors could be eliminated. As we know the gain is fairly low in such a system, on order of 1mm/V, or perhaps 3 orders of magnitude below where noise would impact.
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Smokedaddy



Joined: 07 Oct 2006
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Location: Phoenix, Arizona

PostPosted: Wed Mar 07, 2018 2:26 pm    Post subject: Reply with quote

Sweet, I can't believe this arrived today. I just purchased it Monday ($75) on eBay. Looks to be in excellent condition to me. Now cut cut it down without screwing it up. <g>



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elf



Joined: 18 Nov 2007
Posts: 1357

PostPosted: Wed Mar 07, 2018 4:31 pm    Post subject: Reply with quote

Smokedaddy wrote:
Where did you find your 3D printed model?

https://www.youtube.com/watch?v=OK_o7MRmC3s

-JW:


I created it in Fusion 360. I'll have to look at the Openflexure a little more closely.
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Smokedaddy



Joined: 07 Oct 2006
Posts: 1187
Location: Phoenix, Arizona

PostPosted: Wed Mar 07, 2018 4:34 pm    Post subject: Reply with quote

elf wrote:

I created it in Fusion 360. I'll have to look at the Openflexure a little more closely.


https://github.com/rwb27/openflexure_microscope

-JW:
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Smokedaddy



Joined: 07 Oct 2006
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Location: Phoenix, Arizona

PostPosted: Thu Mar 08, 2018 4:18 pm    Post subject: Reply with quote

https://dspace.mit.edu/handle/1721.1/62511#files-area

http://www.brandonjhopkins.com/#/flexure/

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Smokedaddy



Joined: 07 Oct 2006
Posts: 1187
Location: Phoenix, Arizona

PostPosted: Wed Mar 21, 2018 8:47 pm    Post subject: Reply with quote

I thought this was rather interesting. Voice coil actuators on a X/Y Flexure. Even a range of 10mm.

https://www.youtube.com/watch?v=AJ7IHvOEr2o

-JW:
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ray_parkhurst



Joined: 20 Nov 2010
Posts: 1724
Location: Santa Clara, CA, USA

PostPosted: Thu Mar 22, 2018 9:38 am    Post subject: Reply with quote

Nice!

Voice coils are the perfect actuators for such a system. The flexure springs give the rigidity needed in the non-actuated directions to act as a proper suspension for the voice coils, similar to how the surround and spider provide this support in a speaker driver. To achieve uniform/linear stepping, force balance calibration can be done in the same way discussed in the "voice coil" thread from a while back and implemented by Peter in his VCM control software. In the example, sensors are used to achieve a closed-loop system using capacitive measurements, so essentially a PLL.

edited to add: forgot to mention that I would be a bit worried about small rotational errors in that flexure. The springs are not symmetric, so some level of rotation is inevitable.
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