January 16, 2019, 12:38:22 PM
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 Transformation from DH algorithm angles to physical angles


Author Topic:  Transformation from DH algorithm angles to physical angles  (Read 952 times)

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April 10, 2018, 10:38:39 AM
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maria


Hello,

I am new to industrial manipulators and I have maybe a silly question. Can anyone explain me why we should transform the theta parameter in DH algorithm (such as in the atteched photo) to the robot's physical angles? And what is the meaning of robot's physical angles?

Thank you!

Linkback: https://www.robot-forum.com/robotforum/index.php?topic=26441.0
« Last Edit: April 10, 2018, 10:49:52 AM by maria »

Today at 12:38:22 PM
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April 11, 2018, 03:34:32 PM
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SkyeFire

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This is probably the best explanation of DH parameters that I've ever come across:

https://www.youtube.com/watch?v=rA9tm0gTln8

Put simply, DH is simply a (mostly) standardized method of describing a serial chain of kinematic linkages.  It is theoretically possible to build a DH model for any serial kinematic chain, of any kind, with any number of linkages, and from the DH model derive a single matrix that will serve as the entire forward kinematic formula for the TCP.

This may be one of the best books explaining the underlying mathematics that I've ever seen -- I really wish someone would write an updated as thorough: 
https://www.amazon.com/gp/product/026216082X/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

April 16, 2018, 05:17:14 PM
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robotero



Dear Maria

It has to do with the Manufacture┬┤s convention on were the angles si measure from (were is the zero) and positive/negative direction
For joint 2 for example most manufacturers use Link 2 vertical position as the zero location
Hence the DH parameter requires an adjustment of 90 degrees to account for the rotation transformation from the horizontal plane to the vertical plane

That is why the formula adds Pi/2 to the theta value


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