Author Topic: Base Frame Calculation  (Read 1851 times)

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Offline j.monteiro

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Base Frame Calculation
« on: November 18, 2016, 01:25:57 AM »
Hello,

I'm using a really old but efficially program to calculate a base frame. However I would like to know how it works, what is the mathematic expression behind it.

In the attach you can see a print of the program. Thank you in advance.
« Last Edit: November 18, 2016, 01:28:05 AM by j.monteiro »

Offline SkyeFire

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Offline j.monteiro

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Re: Base Frame Calculation
« Reply #2 on: November 20, 2016, 01:13:50 AM »
http://www.robot-forum.com/robotforum/kuka-robot-forum/abc-3-point-base-measurement-how-does-algorithm-works/msg67208/#msg67208

Thank you for your answering SkyeFire, but I'm not understanding how can I use the 3 points measured by the robot and the corresponding base frame points.

Robot Positions, Base 0, Tool 1               Base   (All data in mm)
           X          Y       Z                        X               Y                 Z
Pos 1   1536   120   -516                    3553         -610            767
Pos 2   1531   -864  -507                    2734         -610           1455
Pos 3   2474   -658  -613                    3553          610            767

Offline SkyeFire

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Re: Base Frame Calculation
« Reply #3 on: November 21, 2016, 01:28:56 PM »
What, exactly, do you not understand?  The vagueness of your question suggests that you didn't read the linked thread, or done any real research.

Offline j.monteiro

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Re: Base Frame Calculation
« Reply #4 on: November 22, 2016, 12:53:38 AM »
I'm using the algoritm from this website you shared in some thread before -> http://nghiaho.com/?page_id=671
However with the previous data I wrote before it is giving me 288mm error. Can you check if you have the same just to be sure I'm not doing nothing wrong. Thank you. 

Offline SkyeFire

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Re: Base Frame Calculation
« Reply #5 on: November 22, 2016, 01:19:37 PM »
That's b/c you data sets don't match up.  If you perform a simple 3D distance check between each pair of points, you'll find that your first two points are 1419.4mm distant in both sets.  But your distance between P2 and P3 in the robot is 971mm, while the P2-P3 distance in Base is 231mm.  The P1-P3 distance is 1661 vs 1371.  So you're trying to fit two triangles that only have one side of equal length.  For the fit algorithm to work, both triangles must be nearly perfect matches in size and shape -- the algorithm only calculates the positional and rotational differences between the two triangles.