Making Optics module OpenFlexure-compatible

[beniroquai]

The problem @theosanderson mentioned about the optics is, that it is a lot of tinkering. The voicecoil-based focus is very hacky and requires a lot of DIY knowledge. Perhaps it's indeed a better idea to adapt the beatiful optics assembly for finite corrected objective lenses from the openflexure ecosystem. Nevertheless, I like the idea of having a fast autofocus using the VCM-based actuator. So the joint approach would be something like this:

It is a UC2 flexure stage + the openflexure optics module (potentially with fluorescence LED) + Voicecoil (reproducible):

What do you think?

[theosanderson]

Hey! This sounds really great!

Just to say, don't change on my account - I'm sure that your original design would be really useful to a ton of people (though I think you're right that some might get scared off by the [incredibly cool] diy coil).

The solenoid is a cool idea for easy building. From googling I think technically it's not a "voice coil" unless it has a permanent magnet (sorry if I've misunderstood your set up, and obviously the name doesn't matter!).

Stream of consciousness.. I was googling and thinking of my experience of solenoids, which is generally that because of how magnetic fields work they do tend to be fairly all or nothing. I think the first thing would be to really confirm that they can be used to set a fixed position. Or is the idea to always move through a full Z-stack pretty fast? That seems to not allow so much flexibility?

Thanks for thinking about this and for all your awesome prototypes

[beniroquai]

Yes, you are totally right, it's not a VCM in the classical sense. I would rather keep it in a closed-loop system. So that with the PWM signal you can tune the focus. First contrast-based. Maybe later with a quandrant diode - but this is fancy stuff ;)

Are you aware of any low-cost /DIY VCMs or simply copper coils one could use to build up the conductivity? I haven't found any and I'm really surprised since you will see that in every speaker: Amazon stuff

I would like to avoid letting people winding their own. It's a lot of effort I guess. Just screwing together standard parts is more fun.

It would work like this here: I'll make a quick mock-up to see how it works, but I agree, having proper VCMs like in cellphones would be the key!

[theosanderson]

No I couldn't find cheap VCMs (also had a look). I was wondering if with the right solenoid one could replace the slug with a stack of cylindrical magnets? (and would likely need a stronger spring too).

I don't actually have a strong intuition about whether or not the VCM will give more fine-grained control than the traditional solenoid (physics was a while ago :) )

Awesome demo piece

[theosanderson]

Random research: Halbach array as another potential possibility? https://www.instructables.com/Linear-Direct-3D-Printer-Extruder-Drive-Fusion-360/

[beniroquai]

This looks really fascinating. But 15 A sounds tough :-)

What do you think about this:

Flexure bearing with folded beam.

[theosanderson]

Hah, I'd missed that minor detail :)

Looks cool! To check if I'm parsing it right - black thing at left is VCM/solenoid?

[beniroquai]

This is how it looks like - in action ;-)

I still like the single VCM solution a bit more. Do you think it would be worth a try to wind a larger coil in order to move a standard objective lens? The OFM mechanism is nice but too slow.

[theosanderson]

Super cool! You're saying this is a lighter lens than typical?

I guess just a heavier-duty solenoid might work? Or two?

[beniroquai]

Yes, that's a good idea. I may buy a few of these solenoids. But I'd guess, that indeed it is hard to control. Your comment about VCMs is definitely worth thinking about.

The force over the stroke tells us why (and I guess you had this in mind already:  I found some larger ring-magnets with 24,0mm inner diameter. With this, you could use the RMS 10x objective you can get on the cheap. The open actuator project shows how to make nice DIY VCMs. I'll give it a try and aim for a larger VCM for standard objective lenses in parallel.

Nevertheless, the solenoid-based z-focus is worth testing, but probably very hard to control.

A few comments about the design you see above:

• the solenoid pushes the level arm which reduces the moving distance by ~2.5 => more precise focusing (Yaiy!)
• Camera is fixed
• there is room for a dichroic
• A folding mirror is placed directly after the objective
• Currently, there is no room for an LED for fluorescent imaging (yet)

[theosanderson]

Apologies for a slow reply!

Yeah exactly the linearity of the VCM based system seems good.

So I do think if we can avoid having to wind our own coils that would be a big advantage. I got pretty interested in the idea of replacing the steel slug in a solenoid with a cylindrical magnet. I'm really surprised this hasn't been described before (as far as I can see) and that it isn't available as a cheap commercial device. One problem that I encountered is that most solenoids seem to be encased in a structure made from a steel-containing alloy. But if you cut that off they are still wrapped in a nice plastic casing.

https://photos.app.goo.gl/Rw3dyJKimo6mduap9

Here is just playing with the voltage on that with a neodymium magnet. This isn't a particularly stiff spring (was a weak solenoid from a valve) so there isn't all that much force but I think there is something to the idea potentially.

[beniroquai]

Fantastic! :)) I was thinking about it and was directly worried about the following:

• Heat: The Coil gets hot 60-80 °C - not good for neodym magnets
• Space?
• Fragile, neoym magnets seem to be very spongy and I had many ring magnets broken over time. Mechanical stress? Any feelings? :p

I assembled the whole thing and added an extra layer for the base (the solenoid limits the height a bit..)

It works ok-ish, but the neodym hack is insane! which magnet did you use? Did you need to glue it or "just" magnetic force? Will directly buy the magnets once I know the source :p

Cheers

PS: The 10x right in front of the whole thing is an attempt to wind a larger coil. But for this you would need higher voltage - not an option. Also heating up lenses is probably not a very nice idea anyway ;)

[theosanderson]

This vid is beautiful - congrats!!

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Great point on heat - I hadn't realised neodymium is especially sensitive to that. Not sure exactly how hot this gets, but defs could be an issue over time. Maybe that's why it hasn't been done :)

I think the one I'm using here is: https://www.amazon.co.uk/gp/product/B010DOPDEA/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Just held on by magnetic force. Its diameter is a little too small for the coil I've got here. But I guess if this got off the ground one would put it in some kind of 3D printed sleeve, and there are a lot of diameters available (can always stack multiple magnets up)

If the solenoid is working I would definitely stick with that - much less fuss. Honestly for my applications speed of focusing is less of an issue so again don't overly focus on me :) but hopefully bouncing ideas is sometimes useful.

[RainerHeintzmann]

I have some that are more heat resistance up to 150 C. But maybe it’s a different alloy and they are not rings.

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Rainer Heintzmann Institute of Physical Chemistry, Friedrich-Schiller-Universität Jena, Helmholtzweg 4, 07743 Jena, Germany Leibniz Institute of Photonic Technology, Albert-Einstein Str. 9, 07745 Jena, Germany Tel.: +49 (0) 3641 206 431

Am 24.11.2020 um 20:56 schrieb Benedict Diederich notifications@github.com:

Fantastic! :)) I was thinking about it and was directly worried about the following:

Heat: The Coil gets hot 60-80 °C - not good for neodym magnets Space? Fragile, neoym magnets seem to be very spongy and I had many ring magnets broken over time. Mechanical stress? Any feelings? :p I assembled the whole thing and added an extra layer for the base (the solenoid limits the height a bit..)

It works ok-ish, but the neodym hack is insane! which magnet did you use? Did you need to glue it or "just" magnetic force? Will directly buy the magnets once I know the source :p

Cheers

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[beniroquai]

@theosanderson May I quickly ask you which solenoid and magnet combination you have used for you voice coil motor? Foot some reason I cannot get it to work. Either to much or too little play in the moving parts. Thanks :)

[theosanderson]

Oh man, I don't think I'm going to be able to sort this out right now, sorry. The magnets are the Amazon ones above. The coil I got out of a solenoid I had lying around, I think actually randomly from a solenoid valve. Probably bought off eBay 5 years ago.. And I don't have physical access to it right now. The play was probably a few mm for mine, so too much. I'd have needed a 3D printed shroud or something to use it properly. Sorry if I misled you there, not intentionally!

[beniroquai]

No worries at all! I'll sort that out somehow :-) Thanks for your help. I hope everything is alright in UK! Keeping finger crossed, that the situation is calming down during next year.. Cheers.

Am So., 20. Dez. 2020 um 17:27 Uhr schrieb Theo Sanderson < notifications@github.com>:

Oh man, I don't think I'm going to be able to sort this out right now, sorry. The magnets are the Amazon ones above. The coil I got out of a solenoid I had lying around, I think actually randomly from a solenoid valve. Probably bought off eBay 5 years ago.. And I don't have physical access to it right now. The play was probably a few mm for mine, so too much. I'd have needed a 3D printed shroud or something to use it properly. Sorry if I misled you there, not intentionally!

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