Voice Coil Rail

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mjkzz
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Post by mjkzz »

Here is the result with a weight (shown in optical setup in previous post). The total travel is (1388/3456*14.8)/7.5 = 0.7925mm or 792.5um.

Will do some stacking if I got time, too busy lately, but I think this is out of the way. :D

Image

ray_parkhurst
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Post by ray_parkhurst »

The linearity looks surprisingly good over that displacement. Nice test method as well.

mjkzz
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Post by mjkzz »

Thanks Ray! The truth is, I am actually trying to drive this thing. Too bad, this one seems to be a custom version, the threaded holes is not the same as their specification sheet, therefore the rubber band, but no time for this ...

Image

mawyatt
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Post by mawyatt »

mjkzz wrote:Finally ran a test of my circuit (see previous image)

This one is done without a weight on the speaker, total current change is roughly 230ma (always has problem at the end, maybe I should not have set the end point to 4095). The objective is an Olympus 10x clone and tube lens is Zhongyi 135, so actual magnification on sensor is 7.5x. From the image, we can see total travel distance is 1532 pixel, the vertical size of the sensor is 14.8mm with total of 3456 pixels. So total physical travel is (1532/3456*14.8)/7.5 = 0.8747mm!!!

Result
Image

Optical setup
Image

Stacking parameters
Image
Nice Peter!! Linearity does look pretty good at this level. Maybe a stack session is a good way to get better resolution on the stage movement. Then a simple error correction table should make very linear.

Best,

Mike

mjkzz
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Post by mjkzz »

Thanks Mike.

Yes, a lookup table can translate current to actual positioning. My design allows setting of maximum current with full 12 bits resolution. In the tests, I set max current to be 256 ma (well a bit less), so with full 12 bits, minimum step is 256/4096 = 1/16 ma or 0.0625 ma. With this, I think the lookup table can be very accurate, if necessary at all :D

rjlittlefield
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Post by rjlittlefield »

Let me offer a bit of counterpoint.

I am actually very surprised at how non-linear is the movement shown at http://www.photomacrography.net/forum/v ... 745#211745 . Stepping from the bottom up, I see step sizes (measured in Photoshop from the posted image) of 33 pixels, 32 pixels, 38 pixels, 29 pixels, then 31, 34, 37, and 49. The smooth progression of the upper part from 29 up to 49 is pretty much what I expected, but the overall pattern of medium/big/small/medium/big/bigger just cries out for explanation.

Is there any possibility that the fourth-from-bottom position was specified incorrectly and is too high as a result? Having that one position be too high would go a long way to restoring smoothness.

--Rik

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Post by ray_parkhurst »

I would see no reason to linearize this response. IMO the main reason to linearize would be if there is a significant distortion (like on the first 4" speaker I showed data for) that would cause issues with 3D rendering.

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Post by ray_parkhurst »

rjlittlefield wrote:Let me offer a bit of counterpoint.

I am actually very surprised at how non-linear is the movement shown at http://www.photomacrography.net/forum/v ... 745#211745 . Stepping from the bottom up, I see step sizes (measured in Photoshop from the posted image) of 33 pixels, 32 pixels, 38 pixels, 29 pixels, then 31, 34, 37, and 49. The smooth progression of the upper part from 29 up to 49 is pretty much what I expected, but the overall pattern of medium/big/small/medium/big/bigger just cries out for explanation.

Is there any possibility that the fourth-from-bottom position was specified incorrectly and is too high as a result? Having that one position be too high would go a long way to restoring smoothness.

--Rik
It looks an exaggerated version of the 4" speaker I published, where there was an initial compression, then expansion, but we don't see the final severe compression. This speaker has a rubber surround, making me expect it is designed for very long throws compared with the speaker I tested, hence the lack of final compression. I'd expect if the current was increased to 400-500mA we'd see that final compression as it nears end of travel.

mjkzz
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Post by mjkzz »

rjlittlefield wrote:Let me offer a bit of counterpoint.

I am actually very surprised at how non-linear is the movement shown at http://www.photomacrography.net/forum/v ... 745#211745 . Stepping from the bottom up, I see step sizes (measured in Photoshop from the posted image) of 33 pixels, 32 pixels, 38 pixels, 29 pixels, then 31, 34, 37, and 49. The smooth progression of the upper part from 29 up to 49 is pretty much what I expected, but the overall pattern of medium/big/small/medium/big/bigger just cries out for explanation.

Is there any possibility that the fourth-from-bottom position was specified incorrectly and is too high as a result? Having that one position be too high would go a long way to restoring smoothness.

--Rik
Hi Rik, here is what I did: start with first image, add a layer, copy the second image into this layer, set blend mode to "additive", merge down layer, then do the same to 3rd, 4th, etc. There is no positioning.

Here are all the files If you follow my steps, you will get exactly the same images. :D

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Post by rjlittlefield »

mjkzz wrote:
rjlittlefield wrote:Is there any possibility that the fourth-from-bottom position was specified incorrectly and is too high as a result? ...
...add...merge down...do the same... There is no positioning.
Yes, I assumed that the images were simply overlaid. When I spoke of the position being "specified", I was actually talking about the drive currents. I thought perhaps you were setting the 9 different drive currents with some manual process, and the wrong value got entered for that fourth-from-the-bottom position.
ray_parkhurst wrote:I would see no reason to linearize this response.
Interesting. Clearly I have no good idea what your concerns and priorities are, and I guess there's really no reason I need to.

But to make sure that I'm following the plot line of this somewhat convoluted movie...

Did you just transition from worrying about part-per-million nonlinearity around crossover, to not worrying about a 29:49 ratio of step sizes as shown in mjkzz's data?

--Rik

ray_parkhurst
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Post by ray_parkhurst »

rjlittlefield wrote:
ray_parkhurst wrote:I would see no reason to linearize this response.
Interesting. Clearly I have no good idea what your concerns and priorities are, and I guess there's really no reason I need to.

But to make sure that I'm following the plot line of this somewhat convoluted movie...

Did you just transition from worrying about part-per-million nonlinearity around crossover, to not worrying about a 29:49 ratio of step sizes as shown in mjkzz's data?

--Rik
I of course expected that question. The issue with the speaker nonlinearity is calculated as the INL, Integrated Non Linearity, which basically tells you how straight the overall line is. This assumes there is no strangeness going on when the speaker is at equilibrium and is then pushed or pulled, but this sort of issue is guaranteed not a problem due to the design of the spider. Basically, the speaker has a slow and gently-changing slope to its displacement, and as I stated this has little effect on 3D rendering.

The issue with the driving electronics that I was concerned about is calculated as the DNL, the Differential Non Linearity. This looks at each step vs the next step. If there is a localized discrepancy in step size, there can be a problem with rendering small displacements. My concern was that there would be a large step at an unpredictable place in the stack that would cause 3D rendering issues. I see this problem with my mechanical rail, and it causes some odd distortions in mildly-sloped surfaces. I saw none of these issues when I used the speaker as a rail using the uni-directional voltage source to drive it, and was loathe to introduce such a distortion with the bi-directional source current.

mjkzz
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Post by mjkzz »

rjlittlefield wrote:
mjkzz wrote:
rjlittlefield wrote:Is there any possibility that the fourth-from-bottom position was specified incorrectly and is too high as a result? ...
...add...merge down...do the same... There is no positioning.
Yes, I assumed that the images were simply overlaid. When I spoke of the position being "specified", I was actually talking about the drive currents. I thought perhaps you were setting the 9 different drive currents with some manual process, and the wrong value got entered for that fourth-from-the-bottom position.
ray_parkhurst wrote:I would see no reason to linearize this response.
Interesting. Clearly I have no good idea what your concerns and priorities are, and I guess there's really no reason I need to.

But to make sure that I'm following the plot line of this somewhat convoluted movie...

Did you just transition from worrying about part-per-million nonlinearity around crossover, to not worrying about a 29:49 ratio of step sizes as shown in mjkzz's data?

--Rik
Oh, OK, everything is automatic, no manual intervention, hit the "Stack" button, it will just go from Start to End (0 to 4095 or 0 ma to 256ma) at even space.

mjkzz
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Post by mjkzz »

ray_parkhurst wrote:
rjlittlefield wrote:Let me offer a bit of counterpoint.

I am actually very surprised at how non-linear is the movement shown at http://www.photomacrography.net/forum/v ... 745#211745 . Stepping from the bottom up, I see step sizes (measured in Photoshop from the posted image) of 33 pixels, 32 pixels, 38 pixels, 29 pixels, then 31, 34, 37, and 49. The smooth progression of the upper part from 29 up to 49 is pretty much what I expected, but the overall pattern of medium/big/small/medium/big/bigger just cries out for explanation.

Is there any possibility that the fourth-from-bottom position was specified incorrectly and is too high as a result? Having that one position be too high would go a long way to restoring smoothness.

--Rik
It looks an exaggerated version of the 4" speaker I published, where there was an initial compression, then expansion, but we don't see the final severe compression. This speaker has a rubber surround, making me expect it is designed for very long throws compared with the speaker I tested, hence the lack of final compression. I'd expect if the current was increased to 400-500mA we'd see that final compression as it nears end of travel.
Ray, yes, it is a long throw speaker. I will try 375ma when I get a chance, just to see how it performs.

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Post by ChrisR »

very surprised at how non-linear is the movement shown
Looks a bit horrible to me - was there some loud music playing? :shock:
Chris R

mawyatt
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Post by mawyatt »

ray_parkhurst wrote:
rjlittlefield wrote:
ray_parkhurst wrote:I would see no reason to linearize this response.
Interesting. Clearly I have no good idea what your concerns and priorities are, and I guess there's really no reason I need to.

But to make sure that I'm following the plot line of this somewhat convoluted movie...

Did you just transition from worrying about part-per-million nonlinearity around crossover, to not worrying about a 29:49 ratio of step sizes as shown in mjkzz's data?

--Rik
I of course expected that question. The issue with the speaker nonlinearity is calculated as the INL, Integrated Non Linearity, which basically tells you how straight the overall line is. This assumes there is no strangeness going on when the speaker is at equilibrium and is then pushed or pulled, but this sort of issue is guaranteed not a problem due to the design of the spider. Basically, the speaker has a slow and gently-changing slope to its displacement, and as I stated this has little effect on 3D rendering.

The issue with the driving electronics that I was concerned about is calculated as the DNL, the Differential Non Linearity. This looks at each step vs the next step. If there is a localized discrepancy in step size, there can be a problem with rendering small displacements. My concern was that there would be a large step at an unpredictable place in the stack that would cause 3D rendering issues. I see this problem with my mechanical rail, and it causes some odd distortions in mildly-sloped surfaces. I saw none of these issues when I used the speaker as a rail using the uni-directional voltage source to drive it, and was loathe to introduce such a distortion with the bi-directional source current.

Ray,

I took a look at the PS pixel data Rik presented and looked at the Pixel Difference between steps.

+1, +6, -9, +2, +3, +4, +12.

The overall Integrated response looks OK to me but not the Diiferenal between steps.

Either should be correctable within reason with Peter's error correction table.

Best,

Mike

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