Advice with motorized rail

[mawyatt]

I went for a THK rail, but not the small KR20 but the bigger KR26.

Peter (mjkzz) provides a KR26 conversion Kit with all you need:
http://www.mjkzz.com/product-page/thk-k ... ersion-kit

He also provides the control software for free :-) what lets you choose pitch, stepping width, number of frames, settle time, triggers camera, start and end point...

The THK rails are not only much stiffer, have more precise guides for the block, they also have a ball screw. This has no backlash and low friction, so ideal for constant small steps. You can find the KR26 wit a 2mm pitch what will allow steps of about 0,5 µm (Peter correct me) with fine stepping mode.

So with a used THK Rail in good shape (100-250$) and the conversion kit for 96$ you get a rail solution which is far superior (IMHO as a mechanical engineer) than all the other stuff around.


P.S.: what might occur, the low friction THK rails with ball srews are no longer self locking, so on a vertical setup the camera might slide down when the stepper is powered off.

Lothman,

I went with the smaller KR 20 style because I wanted a 1mm thread pitch, and Peter's (MJKZZ) kit. Either way these are very well designed and built rail....but you still need some sort of controller. I have the option of the Stackshot controller (which I prefer mainly because of the direct interface to Zerene), the WeMacro controller or Peter's.

Best,

Mike

[lothman]

....but you still need some sort of controller. I have the option of the Stackshot controller (which I prefer mainly because of the direct interface to Zerene), the WeMacro controller or Peter's.

you are right I forgot the controller, so another 50$ für Peters controller.

[ray_parkhurst]

I went for a THK rail, but not the small KR20 but the bigger KR26.

Peter (mjkzz) provides a KR26 conversion Kit with all you need:
http://www.mjkzz.com/product-page/thk-k ... ersion-kit

He also provides the control software for free :-) what lets you choose pitch, stepping width, number of frames, settle time, triggers camera, start and end point...

The THK rails are not only much stiffer, have more precise guides for the block, they also have a ball screw. This has no backlash and low friction, so ideal for constant small steps. You can find the KR26 wit a 2mm pitch what will allow steps of about 0,5 µm (Peter correct me) with fine stepping mode.

So with a used THK Rail in good shape (100-250$) and the conversion kit for 96$ you get a rail solution which is far superior (IMHO as a mechanical engineer) than all the other stuff around.


P.S.: what might occur, the low friction THK rails with ball srews are no longer self locking, so on a vertical setup the camera might slide down when the stepper is powered off.

Thanks for the info and link. I was not aware Peter was offering this as an option. I have a couple of the THK rails so this is a great way to automate them. I also have a couple of his controllers. Good stuff!

[Chris S.]

Albert,

Lest ChrisR's comment gets lost in the shuffle, let me repeat it:

It would be worth seriously looking at microscope focus blocks if much of your work will be 10x and up, they're much better.

You've expressed particular interest in working at 20x. At this magnification, a focus block repurposed from a microscope works very well, and is perhaps your best option. I use a microscope focus block from 1x to 100x, and find that it easily handles this entire range.

Going this route, however, requires some do-it-yourself work. In brief, you purchase a surplus microscope stand from a set of "known good" models; you cut the focus block out of the stand; you mount some hardware on the block to hold your camera and affix the block to a base; you mount a stepper motor to the focus mechanism; you build or buy a controller to address the motor.

If this path interests you, say so, and we can provide some useful links.

--Chris S.

[ray_parkhurst]

Judging from my results so far with the voice coil rail, I would judge this path will turn out to be the superior solution at 20x and above. The control electronics are still being developed, but likely it will be a simpler and cheaper overall solution for a specific range of applications requiring <1mm of total travel. I urge you to follow the voice coil stepper thread before investing in any other approach for high magnification.

Of course, if you need larger travel for deep stacks, then the microscope focus block will be superior.

[rjlittlefield]

for a specific range of applications requiring <1mm of total travel

Just from reading the thread, it seems to me that mounting the subject on the voice coil stage will be a significant limitation.

I can see that coins will sit very nicely on a horizontal stage in a vertical setup. But in quickly reviewing my own portfolio, I don't see anything that looks like it would have been suitable.

What are your thoughts on that issue?

--Rik

[lothman]

What are your thoughts on that issue?

--Rik

I think with a high quality rail we can get 0,5µm steps done properly and be able to move the whole camera. So the subject can be tiny or big that doesn't matter and gives much flexibility. Steps in the <1µm range should be OK for up to 50x.

The speaker coil is very flexible like a soft spring, therefore any vibrations of the lab/house may cause more problems than the benefit small of smaller steps might bring. And also there will be a problem at higher loads (heavier specimen).

For micro movement why not using a piezo actuator (see used items on ebay) or a thermal stepping like Kurt Wirz did and presented, but almost got no interest for that easy and clever solution.

http://www.photomacrography.net/forum/v ... ht=pandora

[mawyatt]

Chris,

I tend to agree with Lothman. Certainly the microscope base is a proven and well tested solution with great range and precision.

However, these THK rails are really well designed and made and just may be able to reach precise micron or sub-micron stepping. Anyway, that's why I jumped on a couple KR-20s when they popped up on eBay awhile back. The design is kind of like the Stackshot or WeMacro rail except for two major differences, 1st the guide rails and base are all one piece from a precise extrusion that is machined for the guide bearings, 2nd all the bearings and the screw nut have ball bearings which produces a very smooth movement with no apparent backlash. I suspect the rail wobble that has been bothering my rails will be eliminated or significantly reduced with the THK rails.

If these work, they should be as useful as the microscope base IMO, and maybe slightly easier to implement a precise wide range capable stacking system.

I'm using a 1mm thread pitch with a 400 step motor which will allow 2.5 micron basic steps and 1.25 micron with just half-microstepping, and 0.625 microns with quarter steps. Soon I hope to find out just how good these THK rails are.

Best,

Mike

[ray_parkhurst]

Just from reading the thread, it seems to me that mounting the subject on the voice coil stage will be a significant limitation.

I can see that coins will sit very nicely on a horizontal stage in a vertical setup. But in quickly reviewing my own portfolio, I don't see anything that looks like it would have been suitable.

What are your thoughts on that issue?

--Rik

The 1mm limitation I was referring to was for the small speakers I tested. A larger driver, and bi-directional travel, could push the displacement much further if desired. Speakers are available with throws measured in inches.

I also don't see a reason for the vertical limitation. The speaker could be mounted to move the subject horizontally.

I think with a high quality rail we can get 0,5µm steps done properly and be able to move the whole camera. So the subject can be tiny or big that doesn't matter and gives much flexibility. Steps in the <1µm range should be OK for up to 50x.

The speaker coil also is very flexible like a soft spring, therefore any vibrations of the lab/house may cause more problems than the benefit small of smaller steps. And also there will be a problem at higher loads (heavier specimen).

I saw no difference, or perhaps even a small improvement, in vibration dampening using the speaker. Speakers are designed to be well damped to control resonances, so are not like soft springs.

I do agree that a high quality rail should do the job well, but the more I use the voice coil system the more negatively I look at stepper and rail mechanics for moving the subject. That said, for lack of proper electronics and software, I still can't do an automated stack.

The voice coil system (at least one that is speaker-based) of course can't move the camera.

[rjlittlefield]

I also don't see a reason for the vertical limitation. The speaker could be mounted to move the subject horizontally.

Sure, but then all the solutions that appear in my mind involve adhering the subject or some holding device to the speaker.

In any case the speaker appears to cover a large area close behind the subject, which restricts possibilities for lighting.

Have I overlooked some possibilities here?

--Rik

[Irisoratoria]

Albert,

Lest ChrisR's comment gets lost in the shuffle, let me repeat it:

It would be worth seriously looking at microscope focus blocks if much of your work will be 10x and up, they're much better.

You've expressed particular interest in working at 20x. At this magnification, a focus block repurposed from a microscope works very well, and is perhaps your best option. I use a microscope focus block from 1x to 100x, and find that it easily handles this entire range.

Going this route, however, requires some do-it-yourself work. In brief, you purchase a surplus microscope stand from a set of "known good" models; you cut the focus block out of the stand; you mount some hardware on the block to hold your camera and affix the block to a base; you mount a stepper motor to the focus mechanism; you build or buy a controller to address the motor.

If this path interests you, say so, and we can provide some useful links.

--Chris S.

Yes i'm shure a microscope block is the most precise option, but i'm not keen on fixing, mounting , etc. To automatize the block i must I should have some knowledge that I have not (mechanical, etc). Honestly, I was scared if after spending a lot of time looking for a microscope block, motorizing it and spending money for finally getting unsatisfactory results (because of my ignorance).

[Irisoratoria]

Thank you guys for this information as accurate as useful. I'll think about and I'll try to decide something.

[ray_parkhurst]

I also don't see a reason for the vertical limitation. The speaker could be mounted to move the subject horizontally.

Sure, but then all the solutions that appear in my mind involve adhering the subject or some holding device to the speaker.

In any case the speaker appears to cover a large area close behind the subject, which restricts possibilities for lighting.

Have I overlooked some possibilities here?

--Rik

A stage must be adhered to the speaker. For the small speaker I tested, I glued a wood block to the center cone/plug that covers the magnetic pole piece and voice coil proper. This stage can be of any configuration desired, within reason. For vertical use with coins, the stage is all that is needed, but for horizontal use with bugs and such a specimen holder could be attached as well. This could put the specimen well in front of the speaker surface such that lighting is not an issue.

[rjlittlefield]

This stage can be of any configuration desired, within reason.

Speaking for myself, I was very pleased by gaining fine control over specimen positioning through the use of rotary table and goniometers, versus the various contraptions that I used in prior years. I would not like to give up that capability, and I don't see how to get the same capability using the voice coil approach, given the relatively sizes of various parts.

Have I overlooked a possibility?

--Rik

[ray_parkhurst]

This stage can be of any configuration desired, within reason.

Speaking for myself, I was very pleased by gaining fine control over specimen positioning through the use of rotary table and goniometers, versus the various contraptions that I used in prior years. I would not like to give up that capability, and I don't see how to get the same capability using the voice coil approach, given the relatively sizes of various parts.

Have I overlooked a possibility?

--Rik

Certainly the goniometers will be too heavy to mount on a small speaker in a horizontal setup. I initially thought to mount the speaker to the goniometers but the stacking axis would be incorrect. A large speaker could handle the weight, so all is not lost, but if you're using automated goniometers, I'd think the system would be too bulky for even a large speaker, so only manual ones would work.

edited to add: I'm envisioning 40mm or even 60mm stage size goniometers and theta tables. The ones I have are certainly not light but I doubt they'd stress the cone of a 6" or 8" woofer that would have the kind of displacement you are probably looking for.