Difference between revisions of "Denavit-Hartenberg parameters"

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{{Navigation|before=[[Assigning coordinate frames]]|overview=[[Denavit-Hartenberg Convention]]|next=[[A-matrices]]}}
 
{{Navigation|before=[[Assigning coordinate frames]]|overview=[[Denavit-Hartenberg Convention]]|next=[[A-matrices]]}}
 
  
 
[[File:dh-params-general.png|right|250px]]
 
[[File:dh-params-general.png|right|250px]]

Revision as of 10:50, 13 November 2015

← Back: Assigning coordinate frames Overview: Denavit-Hartenberg Convention Next: A-matrices
Dh-params-general.png

When the coordinate frames are assigned to a manipulator, the transformation between each two consecutive frames has to be described. Therefor the 4 Denavit-Hartenberg parameters \theta, d, l and \alpha are used. The figure on the right shows two coordinate frames K_{n-1} and K_n and the corresponding common normal represented by a dashed red line. The figure illustrates the Denavit-Hartenberg parameters, that are defined as follows:

\theta
The angle \theta is defined as the angle about the z_{n-1}-axis to align x_{n-1} with the new x_{n}-axis.
d
d is the offset or translation, respectively, along the z_{n-1}-axis from the origin of K_{n-1} to the intersection with the common normal.
l
The parameter l corresponds to the length of the common normal which is equivalent to the translation along it.
If the related joint J_n is a revolute joint, l can also be regarded as the radius of the rotation about the z_{n-1}-axis
\alpha
The angle \alpha corresponds to the angle about the common normal to align the z_{n-1}-axis with the new z_{n}-axis

The 4 parameters can rather be determined by just regarding the two coordinate frames, their axes and the common normal like visualized above. To completely understand the parameters and their meaning, the figure below illustrates what they actually describe. \theta, d, l and \alpha define 4 transformations that are applied consecutively to transform a coordinate frame K_{n-1} into K_n.

Dh-params-steps.png