Author Topic: Denavit-Hartenberg convention  (Read 211 times)

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Offline dequeiroz

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Denavit-Hartenberg convention
« on: August 02, 2018, 02:00:41 PM »
How are the coordinate frames and DH parameters determined in industry? Does one use the CAD drawing of the arm or take physical measurements on the actual arm?

Offline SkyeFire

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Re: Denavit-Hartenberg convention
« Reply #1 on: August 03, 2018, 11:59:47 AM »
Yes.

More specifically, most robots generally operate on an "ideal" DH model that is built into their controllers.  The robot is built to match this model, within certain build tolerances.  In most applications, the differences between the as-built robot and the ideal model are of little concern, since 90% of robot uses depend on repeatability rather than accuracy.

For applications that require higher accuracy, there are various services and options to "tune" the DH model of the controller to more closely match the as-built condition of the robot.  These methods vary between brands.  Usually, these methods do not measure the robot directly, but rather measure the TCP location error of the robot over a specified volume, and reverse-engineer the DH corrections from there.

There are 3rd-party applications (New River Kinematics' SARCA, for example) that, lacking access to the controller's internal DH parameters, perform similar measurements of TCP location error throughout the robot's motion volume, and then create a massive weighted-sum correction algorithm that can provide Cartesian corrections for any given location&orientation throughout the volume while the robot is running.  It's a bit of a hack, but has been proven to work quite well, when used properly.