www.photomacrography.net :: View topic - Voice Coil Rail
www.photomacrography.net Forum Index
An online community dedicated to the practices of photomacrography, close-up and macro photography, and photomicrography.
Photomacrography Front Page Amateurmicrography Front Page
Old Forums/Galleries
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Voice Coil Rail
Goto page Previous  1, 2, 3 ... 16, 17, 18
 
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Equipment Discussions
View previous topic :: View next topic  
Author Message
ray_parkhurst



Joined: 20 Nov 2010
Posts: 2372
Location: Santa Clara, CA, USA

PostPosted: Sun Jun 25, 2017 6:28 pm    Post subject: Reply with quote

Finally found time to assemble the voice coil system as I had originally planned. My concept was to integrate a speaker mounted horizontally within a B&L B-stand base. This can then be added to any B&L A-stand to enable narrow-range but high precision stacking. Here are pics of the result with the 1.5" speaker I tested earlier:



And here is a closeup showing a coin on a sub-stage above the voice coil stage:



Peter's software works similarly for use with voice coil as with a stepper, and at my request he has enabled both to work simultaneously. This may help folks who would use a stepper system for coarse focusing, and the voice coil for the actual stack. I've tried this and it does work.

The only noticeable difference in the software is its range of max 4096 positions, which I assume means the DAC he used is 12-bit. Peter has included a software adjustment for the reference voltage, so this gives a sort of "gain control" to the system. I initially did not see this feature, and was limited to ~100um range from the speaker (which was marginal for coin stacking), then discovered the default reference voltage is 0.125. I upped it to 0.5 and now have plenty of range (about 500um) for coin stacks. The maximum reference voltage is 0.875V.

I have not tried calibrating my speaker, as I really don't see a need to do so. It's probably a good feature if you push the speaker into strong nonlinearity, but the linearity over the range I am interested seems good enough.

The version of hardware I have from Peter is unidirectional. I don't know status of his bidirectional efforts.

The system is a real pleasure to use and has much the same adjustment feel, and all the precision, of my analog power supply shown earlier in this thread.
Back to top
View user's profile Send private message Visit poster's website
ray_parkhurst



Joined: 20 Nov 2010
Posts: 2372
Location: Santa Clara, CA, USA

PostPosted: Mon Jun 26, 2017 9:58 pm    Post subject: Reply with quote

One thing I see that is very different with the voice coil rail vs stepper-based systems is the stable alignment. All the stepper-based rails I've tried move the stage side to side a little as it moves up/down. The voice coil rail does not do this. It's a bit odd to look through a stack of images taken with a telecentric lens using the voice coil rail. The images don't change in scale or position, just in focus from highest to lowest feature. If anyone is interested I can send or post some source pics from a stack to show this effect.
Back to top
View user's profile Send private message Visit poster's website
mawyatt



Joined: 22 Aug 2013
Posts: 2167
Location: Clearwater

PostPosted: Tue Jun 27, 2017 5:50 am    Post subject: Reply with quote

Ray,

Nice work with Peter's controller and your setup! Get on Peter to supply you with a Current Mode Bidirectional Controller/Driver Very Happy

The rails I have do exhibit some stage wobble as I call it (side to side movement) except the THK KR20 which seem free from any wobble. The "Off Axis Loading" concept significantly reduces this wobble if applied correctly (normal to the screw thread face). It certainly made an improvement in mine and others rail systems, and for a few rubber bands and bolt doesn't cost much either.

Looking forward to see your coin images from this and your best 1~2X lens.

Best,

Mike
Back to top
View user's profile Send private message
ray_parkhurst



Joined: 20 Nov 2010
Posts: 2372
Location: Santa Clara, CA, USA

PostPosted: Tue Jun 27, 2017 7:03 am    Post subject: Reply with quote

I have a KR26 that I just finished integrating (with Peter's conversion kit) but have not fully evaluated yet. Hopefully it has minimal wobble. I have a couple KR20's that will be integrated as well. I wonder if the KR20 has lower wobble given the 1mm pitch vs 2mm of the KR26. We'll see once I get something built.
Back to top
View user's profile Send private message Visit poster's website
lothman



Joined: 14 Feb 2009
Posts: 376
Location: Stuttgart/Germany

PostPosted: Tue Jun 27, 2017 8:14 am    Post subject: Reply with quote

ray_parkhurst wrote:
I wonder if the KR20 has lower wobble given the 1mm pitch vs 2mm of the KR26. We'll see once I get something built.


since the KR26 has a much higher load capacity than the KR20, I think it should wobble lesser. On the other hand friction (needed torque) for moving should be smaller on the KR20, but since all the THK rail move so smooth that should be no problem.
Back to top
View user's profile Send private message
mawyatt



Joined: 22 Aug 2013
Posts: 2167
Location: Clearwater

PostPosted: Wed Jun 28, 2017 5:23 am    Post subject: Reply with quote

My KR20 has no discernible wobble at 10X, I haven't tried beyond that though. I specifically got the KR20 because of the 1mm thread pitch, with 400 step motor gives a fundamental 2.5 micron step before engaging micro-stepping, however I suspect the KR26 will be just as good at 2mm pitch.

Mike
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Equipment Discussions All times are GMT - 7 Hours
Goto page Previous  1, 2, 3 ... 16, 17, 18
Page 18 of 18

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group