Centering object on spinning platform
Centering object on spinning platform
(OP)
I've been trying to come up with a good solution to a unique problem. I have a spinning shaft with a plate attached, and i need to place an object on that plate and have it be centered.
The shaft spin is controlled via a laptop and is used for photography - the problem we haven't been able to find a solution for is trying to perfectly center that product on the plate. Right now when the shaft spins, if the product isn't centered up exactly it is very obvious in the photos.
Objects placed on the plate very greatly, sometimes they are cylindrical and sometimes they aren't even a standard geometrical shape. I'm looking for any suggestions on how to solve this problem - we've tried several different methods and haven't came up with anything good.
The shaft spin is controlled via a laptop and is used for photography - the problem we haven't been able to find a solution for is trying to perfectly center that product on the plate. Right now when the shaft spins, if the product isn't centered up exactly it is very obvious in the photos.
Objects placed on the plate very greatly, sometimes they are cylindrical and sometimes they aren't even a standard geometrical shape. I'm looking for any suggestions on how to solve this problem - we've tried several different methods and haven't came up with anything good.





RE: Centering object on spinning platform
There could be a number of different meanings, center of gravity, optical centroid, etc.
TTFN
RE: Centering object on spinning platform
I suspect, as IRstuff hints, that in practice what you mean by 'centre' is not a definable thing.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Centering object on spinning platform
RE: Centering object on spinning platform
Since the objects we're taking photos of aren't always square or cylindrical, we can't really keep the lense a constant distance from the object. Picture something like a sculpture of a horse with a base and trying to take photos from every angle.
Bottom line is we just need these series of photo's to look fluid and pleasing for people. Whatever achieves that result is what we're looking for. Thanks for all your suggestions thus far.
RE: Centering object on spinning platform
RE: Centering object on spinning platform
RE: Centering object on spinning platform
RE: Centering object on spinning platform
RE: Centering object on spinning platform
TTFN
RE: Centering object on spinning platform
eg take the letter C. You want the centre of the circle, not its mass centroid, or its geometrical centre.
I'd think about a remote controlled x y table if this is a big deal.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Centering object on spinning platform
I can't find a decent one anywhere. However, I seems that not all objects have one.
Greg's suggestion of an X-Y table is where I was headed when I asked about constant distance.
RE: Centering object on spinning platform
TTFN
RE: Centering object on spinning platform
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Centering object on spinning platform
RE: Centering object on spinning platform
TTFN
RE: Centering object on spinning platform
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Centering object on spinning platform
TTFN
RE: Centering object on spinning platform
* Use a small aperture so that depth of field is large
* put a large thin "x" on the table
* put vertical marks every 90deg on the edges of a "coaster"
* put the coaster on the x so that the marks align
* put your object on the coaster
* turn the table and take one photo each time the x has an arm pointing at the camera (4 photos)
* Superimpose pairs of photos from 180deg orientations so that they appear to show rotation about the "correct" axis
* measure the distance between the marks on the coaster
* move the coaster 1/2 that distance relative to the marks on the table
* re-check
RE: Centering object on spinning platform
If you did your vertical marks in different colors for 180deg orientations (ie red opposite green), then you should be able to figure out the right way to move the object based on whether the red vertical mark was on the left or the right of the green vertical mark when you'd aligned the photos properly.
RE: Centering object on spinning platform
Instead of rotating the subject, revolve the camera around the subject and use an auto focus feature to manage the depth issue.
Griffy
RE: Centering object on spinning platform
RE: Centering object on spinning platform
RE: Centering object on spinning platform
RE: Centering object on spinning platform
TTFN
RE: Centering object on spinning platform
RE: Centering object on spinning platform
TTFN
RE: Centering object on spinning platform
RE: Centering object on spinning platform
Try this; Mount a camera vertically above the table, centered on the rotational axis of the table. From a scientific supply company, you can get assorted filters that provide a geometric pattern such as a series of concentric rings, for mounting on the camera. Adjust the X&Y location of the workpiece until it is entirely within the same / smallest ring on the grid.
If you are in a high-volume situation, I'd suggest using a vision-inspection system for the overhead camera; the software can generate the smallest circumscribed cylinder and give X/Y coordinates of the cylinder center relative to the center of the rotary table. You should even be able to tie in an encoded bed to automatically center it based on the feedback from the vision system.
It would be appreciated if you let the group know how you make out on this. Tks. Jim
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
www.profileservices.ca
RE: Centering object on spinning platform
For an automated solution, an idea I had was instead of moving the component around on the table, can you put the camera on a slide and move the camera closer or further from the component using some kind of range finder? As the component rotates, the range finder tells the camera to move closer to or further from the piece to maintain a set distance. Or have an 'electric eye' that looks across the table perpendicular to the camera. If the object blocks the beam, the camera and eye move out together until the beam is no long blocked by the object. The camera could take a picture and it would always be the same distance from the side of the object nearest the camera.
Or what about using image editing software to crop the photos to make it look like the photo was taken from the same distance from center? I assume some kind of 'auto-crop' feature could be used to make the object fill the same amount of space in all photos.
Bob
Bob