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moving camera over Z-axis  

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diep
Posts: 7
 diep
(@diep)
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Joined: 4 weeks ago

If i put the lightning of fabscan with the camera on some cheap SBR16 rails with 4 carriages, which i have left here (actually shortest i have are 400mm length) then would the camera also photograph the top which this German reviewer on youtube saw hollow as it was above camera the object - would this work?

In short i do not know the angle the camera takes pictures - i would point it directly towards the rotary table.

Now of course a scan takes way longer then - but that's not a problem at all.

Is there a simple way to get this working?

Please note - not as important as the nema34 motor for a larger rotary table - as the objects we want to scan (friend of mine has made a few objects - he is a talented artist/painter - and he likes to scan them) do not fit on the current rotary table. The linear movement i would do with a nema23 that rotates a simplistic cheap chinese C7 ballscrew which i have left. All this is overkill to move a lightweight camera and lightning board yet i happen to have it here so why not use it. 

Driving the nema34 and nema23 then would be done by linuxcnc preferably as it steers those motors so nice.

Note i also have other electronics that can do the job like smoothieboards and similar yet price of that parallel breakout board is dirt cheap. Like 5 dollar or so on ebay including shipment and old computers are for free. Whereas those other electronics boards i have are ranging in price from 120 to 200 dollar/euro. Too much in case someone else also wants to build something similar.

 

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diep
Posts: 7
 diep
(@diep)
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Joined: 4 weeks ago

thinking about this plan - it might require more than 2 lasers in total such setup. 2 that are low in the case and 2 that are quite a tad higher. one wouldn't want to move the lasers i guess as those are accurately pointed. And the linear movement is not so accurate. Especially the leadscrew or ballscrews are notoriously seriously bad quality. Accurate movement with ball screws is too expensive obviously for a cheap scanner project. So the question is not so much how much lasers and linear movement is needed - the question is whether the software is so clever to fit different point clouds together from different Z-heights taken - and we have a rough guess what the Z-height is - yet ball screw (C7) will be off easily 0.08 mm from the ideal path in absolute error. Please note German C7 quality ball screws use a different errortable so one would guess there absolute path error is 0.04mm roughly. The question and discussion here is of course the software like Meshlab. Does it try to testfit in clever manner point clouds and determine what the position of the camera was? Kind Regards, Vincent Diepeveen

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m.marino
Posts: 24
(@m-marino)
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Joined: 12 months ago

I have been working on a design that uses four lasers, trapizodal screw and Nema 23's to drive the motion. The Turn table has been up graded to be supported by a pin bearing to aid in motion and allow better bearing of heavier objects. The link is here:

https://www.thingiverse.com/thing:4023019

That was the last update I posted as have been working on multiple projects and trying to get business and family items dealt with first. Would be glad for help in the design and also in upgrading the current Fabscan board to being able to handle 4 lasers and only having to motor drives or the ability to off load the drives to a higher voltage driver for smoothness and control.

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diep
Posts: 7
 diep
(@diep)
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Joined: 4 weeks ago

Yes much appreciated effort. The design seems little bit overcomplex to me. Now of course i have some experience designing machines. Fixed positions for lasers - so to speak also 2 lasers might be possible initially. 1 low position and 1 high position. Only move Camera over Z-axis. The distance i do not understand. If you have such tiny turntable of just 150mm why put the camera at a whopping 360 mm (-70 = 290mm) distance from it? If camera moves over Z-axis why not put the turntable closer say at 100mm distance. Moving camera over Z-axis i see the same weird thing you see in many 3d printers. huge leadscrew and small diameter smooth rods and both are way too long. You only want to move the camera over Z-axis. Then i see 2 smoothroads connected to turntable which doesn't make sense to me. As those smoothrods do not really give stiffness to the construction. Of course i assume the thing itself you want to put in a box like fabscan has one. Yet the real problem of this setup might be the turntable. It seems from plastic and using plastic as a bearing. That will rotate around like a pancake of course. You cannot expect software to correct for pancake-rotating mistakes of the turntable. Many bearings, especially in the stronger motors cause the shafts to have no visible 'runout' -  if i measure it here it's order of less than a micrometer at the stronger stepper motors - you cannot buy those bearings easily in the shops by the way - the internal radial clearances are much better than you canbuy for example from SKF which best radial internal clearance is bearings C2 which is roughly until 0.011mm 'runout'. And if i buy those from SKF they go for 9+ euro a piece here or more. Which is why i suggested using a nema34. Then the turntable platform you cannot use selfprinted 3d plastic for this. That i say as someone who designs professional 3d printers. It's simply not flat like a mirror is - and the way how you connect the turntable to the steppershaft there must be manners of adjusting that in X,Y,Z directions. Any micrometer type mistake of the shaft - in case of nema23 that's usually 6.35mm or 8mm diameter. At R=75mm then any error at a 8mm shaft translates to an error that multiplicates by: 75 / 4 = factor 18.75. Now using default bearings is no good idea either as those have a radial internal clearance by default of 0.03mm roughly. 0.03mm * 18.75 = 0.5623mm deviations just by the turntable. Which is why i suggested taking a Nema34 which is 14mm diameter the ones i got here. As then R=7, big improvement over R=4. A turntable that's very level and adjusted to run precisely - then things you put on there do not fall off easily. Seeing all the folks tying objects to the turntable in order to not fall off doesn't come over as very professional. Cheap solution there is using mirrors - even square ones there of 20x20 cm are very flat and then have some adjustable arms attached to the motors shaft that allow adjusting. As for the linear movement i would keep it simple. As short as possible smoothrods and a simple 8mm leadscrew that's also very short. Just moving the camera at most 200mm or so. What's drawn here is 500mm high that's way too ambitious. Of course the leadscrew, turning it around with a motor like drawn here is possible yet i wouldn't do it like this. Yet that's not so relevant compared to the other points above. 

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m.marino
Posts: 24
(@m-marino)
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Joined: 12 months ago

No metal bearings and my background on the industrial side is CNC and Industrial construction (former Industrial Pipefitter in Detroit area). I have designed and built a few CNC Gantry routers that had the major fault of over build on many of them. The reasons for the height and distance is the intentions of adding additional cameras. As I stated this is a early prototype design and the function is to look at ideas and be able to build from there. The moving lasers is due to the fact that I hope to be able to get near 300-500mm height volume available for the scanning area. the major issue with that is being able to offload the image data effectively during the scan as at that volume the Pi would slow down a good bit. The 10mm smooth rods will add enough stability to the arms to allow the lasers to move with the camera which will be needed if the design is able to get the vertical volume I am hoping for. Though as stated this is a beginning design and things will move from there. If you have any designs ideas you wish to share please do. File wise I work with Solidworks, so most file formats are able to be dealt with. Just prefer not dealing with .stl or .3mf for actual design work (output for parts great, design not so much). Looking at a 1205 lead screw as it will allow very smooth motion, reasonable microstepping without loss of positional accuracy and a small amount of structural rigidity. May be over kill but rigidity that still allows for smooth and controlled motion is never a bad thing.

Anyhow thanks for the feed back.

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