Mindboards

doc-helmut wrote:

I find it strange that you are unable to increase the distance

aswin, actually I'm curious why you're asking this, do you suppose me to be not sure about my own requirements?

No, that is not the reason. I thought you had to do this in a confined space.

But as I understand it you want to align a grabber more or less exactly with an object to be able to pick it up. You might be able to align your grabber much better than the resolution of your sensor! Let me try to explain. Suppose your sensor has a no detection angle. The goal is to find the center of an object. (we assume the object is square, this makes it easy to define he center.) the way to do this is to detect both the left and the right edge of the object. If you take the mean of these two you get the center. Now suppose the sensor is not perfect, it has a beam with some width. As a resulting detects the edge of an object a bit to soon. How much to soon is a function of distance and width of the beam. let say it is X. This means that the left edge is detected X too much to the left (-X), the right edges detected X too much to the right (+X). But if you take the average of the two to calculate the center you will see that the two X values cancel each other out. So, even when the sensor is not very precise you can still get precise measurements.

Hope this helps you.

As I already wrote, I already tried out using the sharp GP2D120 sensors (6-20 cm) looking like the ones used by MS.
No way to get satisfactory results for approching and centering the different sized chess pieces (different diameter, different height, different shaped tops) while approaching them by the claw from over the top. The centering has to be done simultaneously when lowering the claw (about 5 cm within 3 seconds).
So I still will need 3 (or maybe even 4) of them with
a distance range: 1-10 cm (whole range needed at least)
a detection angle: < 10° (not bigger)

the center detection algorithm will be designed for them in the moment I'll have them.

Have you considered a camera? What about re-designing it to not need to be centered?

yes I did, I even have one (MS cam) (v2? v3?), but
1st, I can't handle the commands: far too complicated, far too poor documented, far too troubled image, far too many blobs flurrying over the screen
2nd, I don't know how to attach it in a straight vertical way targtting the center of a square or a piece
3rd, if attached diagonally, the center of the cam screen moves away from the centered piece when moving closer
4th, the pieces are light browm to black with lots of shadows, no idea how to recognise the center of the top of the piece anyway,
5th, the pieces are standing on differnet coloured squares from light brown to dark brown which interfere with the pieces itself

so - no chance.

It's impossible for you to learn how to use it?
It's impossible for you to redesign the grabber?
You can't use lights to illuminate the area?
You have to use that specific game set? Why not a B&W set?

Or (at the risk of you thinking I am ultimately radical in my suggestions), what about putting small stickers on the tops of the peices? Or what about magnets (and the use of at least one magnet sensor)?


Seriously, these forums are a place people come for help, suggestions, and inspiration. This is not a place to come with a huge list of problems you need other people to solve, when you aren't willing to expand your thinking and knowledge. If this project is too complicated for you, you either need to step up to the plate and learn how to solve the problems you run into, or move on to a different project. I have been trying to give helpful suggestions, that might or might not work, but none-the-less should be inspirational. If you aren't willing to consider anything that doesn't perfectly fit your mental ideal, I won't continue to offer suggestions for you.

no chance to do it in another way, it must be small sensors, probably smaller than Lego sensors, it's a small claw by fischertechnik.
No inspiration needed, just small sensors for 1...10 cm, <10° as described in the TOP ;)

I'm afraid you won't find such a sensor. It's time to go back to the drawing board.