dh parameter questions

[baxelrod]

I was wondering if anyone has a plugin for OpenRave that allows specification of the robot’s kinematics with DH parameters.  This seems like a really useful addition. 

 

I am planning on doing some arm calibration and would like to pull out the DH parameters for my arm.  However, I noticed that when I call planningutils.GetDHParameters(robot) with different joint angles, I get different parameters.  d, a, and alpha change, not just theta as I was expecting.  At first I thought that I wouldn’t be able to use this at all and would need to specify the parameters by hand.  But now I think I can still use them for the calibration procedure.  Does anyone know if this is ok?  (I am planning on following the procedure laid out in "Robotics: Modelling, Planning and Control" by Bruno Siciliano, Lorenzo Sciavicco, Luigi Villani, Giuseppe Oriolo, chapter 2.11 unless someone knows of a better method).

 

Lastly which DH parameter convention does OpenRave use?  There are a few, and it would really help to know which convention is being followed.

 

Thanks,

Ben

 

 

Ben Axelrod
Sr. Robotics Software Engineer
Technology Organization

iRobot
8 Crosby Drive 8-1
Bedford, MA 01730
t: 781.430.3315
[hidden email]

 

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[Rosen Diankov]

Dear Ben,

DH parameters also allow you to recover the current pose of the robot, which will also become the zero of the robot, so the theta and alpha will change. I don't think d and a changes though...

If you want the standardized parameters such that the zero of the robot doesn't change, then always set the robot to all zeros before calling GetDHParameters.

As you already noticed, DH parameters are ambiguous. The same DH parameters can point to the same robot structure and there are conventions to resolve the ambiguities.

The one I followed is from wikipedia, I'm not sure which convention that is.... the code is in planningutils.cpp

Hope this helps,

Rosen,

2015-07-29 6:39 GMT+09:00 Axelrod, Ben <[hidden email]>:

I was wondering if anyone has a plugin for OpenRave that allows specification of the robot’s kinematics with DH parameters.  This seems like a really useful addition. 

 

I am planning on doing some arm calibration and would like to pull out the DH parameters for my arm.  However, I noticed that when I call planningutils.GetDHParameters(robot) with different joint angles, I get different parameters.  d, a, and alpha change, not just theta as I was expecting.  At first I thought that I wouldn’t be able to use this at all and would need to specify the parameters by hand.  But now I think I can still use them for the calibration procedure.  Does anyone know if this is ok?  (I am planning on following the procedure laid out in "Robotics: Modelling, Planning and Control" by Bruno Siciliano, Lorenzo Sciavicco, Luigi Villani, Giuseppe Oriolo, chapter 2.11 unless someone knows of a better method).

 

Lastly which DH parameter convention does OpenRave use?  There are a few, and it would really help to know which convention is being followed.

 

Thanks,

Ben

 

 

Ben Axelrod
Sr. Robotics Software Engineer
Technology Organization

iRobot
8 Crosby Drive 8-1
Bedford, MA 01730
t: <a href="tel:[phone]" value="[phone]" target="_blank">781.430.3315
[hidden email]

 

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