Robot 6-Axis

This Article is about bringing a Standard 6-Axis industry robot into FreeCAD for simulation

The description follows the Denavit-Hartenberg Parameter system, as also described in John J. Craigs book "Introduction to Robotics".

Example Kuka

**The Kuka KR-16**

Kinematic

**3D applications**
Segment	Parameter	Description
		Base konfiguration
	$\theta _{1}=q_{1}$ $d_{1}=675mm$ $a_{1}=260mm$ Failed to parse (syntax error): {\displaystyle \alpha_{1} = −90} °	Segment 1
	$\theta _{2}=q_{2}-90$ ° $d_{2}=0mm$ $a_{2}=680mm$ $\alpha _{2}=0$ °	Segment 2
	$\theta _{3}=q_{3}$ $d_{3}=0mm$ $a_{3}=0mm$ $\alpha _{3}=90$ °	Segment 3
	$\theta _{4}=q_{4}$ $d_{4}=-670mm$ $a_{4}=0mm$ $\alpha _{4}=-90$ °	Segment 4
	$\theta _{5}=q_{5}$ $d_{5}=0mm$ $a_{5}=0mm$ $\alpha _{5}=90$ °	Segment 5
	$\theta _{6}=q_{6}$ $d_{6}=0mm$ $a_{6}=-158mm$ $\alpha _{6}=180$ °	Segment 6

This leads to following table:

**Kinematik table**
$i$	$\theta$	$d$	$a$	$\alpha$
1	q1	675 mm	260 mm	-90°
2	q2 - 90°	0 mm	680 mm	0°
3	q3	0 mm	0 mm	90°
4	q4	-670 mm	0 mm	-90°
5	q5	0 mm	0 mm	90°
6	q6	-158 mm	0 mm	180°

Since the Kuka robots do not have all Axis to 0 in the drawn L-Position, we have to change Axis 2 & 3 by 90°.

**Kinematik table**
$i$	$\theta$	$d$	$a$	$\alpha$
1	q1	675 mm	260 mm	-90°
2	q2	0 mm	680 mm	0°
3	q3 - 90°	0 mm	0 mm	90°
4	q4	-670 mm	0 mm	-90°
5	q5	0 mm	0 mm	90°
6	q6	-158 mm	0 mm	180°

In the Data sheet we find additional information about the Axis:

That leads to this complete Table:

**Kinematik table**
$i$	$\theta$	$d$	$a$	$\alpha$	$\theta _{min}$	$\theta _{max}$	Axis Speed
1	0	575	260	-90	-185	185	156
2	0	0	680	0	-155	35	156
3	- 90	0	0	90	-130	154	156
4	0	-670	0	-90	-350	350	330
5	0	0	0	90	-130	130	330
6	q6	-158	0	180	-350	350	615

Visual representation

FreeCAD can generate a rough visual out of the kinematic table. But if you want closer to reallity you can use a VRML file with the robot shape for the simulation. E.g. Kuka delivers for its model VRML files. The VRML file gets loaded while the creation of the specific robot in FreeCAD. In order to allow FreeCAD to move the axis we have to edit the VRML file and insert special transformation nodes FreeCAD can find and manipulate.

Again shown by the example Kuka KR 16. Beginning from line 1:

#VRML V2.0 utf8
#
# This VRML97 file was exported using eM-Workplace
# (c) Tecnomatix Technologies GmbH & Co. KG
#     Heisenberg-Bogen 1
#     D-85609 Aschheim-Dornach
#     GERMANY
#
#Background
#{
#   skyColor   [0.752941 0.752941 0.752941]
#}
Transform
{
   #rotation 1 0 0 -1.5707963
   #scale .001 .001 .001
   children
   [
           DEF AOBJ_0001_000_TRAFO Transform
           {
              children
              [
...

You see this file is exported with a robot simulation software called Tecnomatix. Remove this notice and put in a URL were you get this file, because Tecnomatix has no copyright in the file content. Its only an converter! First of all we remove the Background node. Then remove the rotation and scale node to get the model to mm and upright Z.