Denavit-Hartenberg parameters

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Overview: Denavit-Hartenberg Convention

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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