Centering object on spinning platform

[segment3]

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.

 

[griffengm]

segment3,
Instead of rotating the subject, revolve the camera around the subject and use an auto focus feature to manage the depth issue.

Griffy

 

[ivymike]

I thought about that one too, but you have the same fundamental problem (selecting an appropriate axis of rotation).

 

[BobM3]

Mount camera on x-y table. Make a plate that mounts onto the existing plate with legs so that the camera is between the two plates. Mark o center point and graduation lines on the second plate. Take a picture and take a look at it and adjust the x-y table based on how far off the mark is in the photo.

 

[ivymike]

I think you'd still end up with an object that turns about the wrong axis... unless I'm missing something here.

 

[IRstuff]

You would need to put the object on the x-y table, which is put on the turntable.

TTFN

 

[BobM3]

Second plate is rigidly mounted (but removable) above the rotary table surface. Its center mark is aligned with the axis of rotation of the rotary table. The camera is mounted in-between on an xy table which is mounted to the rotary table.

 

[IRstuff]

If the camera is ultimately mounted on the rotary table, then there is no relative rotation between the camera and the object.

TTFN

 

[BobM3]

Camera is mounted on xy table. Second plate is not.

 

[MechNorth]

Interesting problem. I think your solution lies in a plane that is perpendicular to your photographic plane. Basically, what I'd suggest is to find the smallest cylinder that can circumscribe the object; the center of that cylinder should be your center of rotation of the subject piece. You then align the center of the cylinder with the center of the rotary table. For situations where you want the rotational center to be the dominant feature, such as the rim of the teacup, then you'd use the body of the cup (excluding the handle) as the object to be circumscribed.

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

http://www.profileservices.ca

 

[Ataloss]

Are you photographing so many differently shaped components that it's worth the hassle and expense of coming up with some automated solution rather than the photographer simply adjusting the position of the component until it looks good?

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