Singularity - how to set $singul_pos[3]

I can't say I've looked at that variable before, but generally a [3] would refer to axis 3 not 4?

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Hi,

$SINGUL_POS[3] is for the third singularity a standard 6 axis robot can have (Index 1: axis one singularity, Index 2: a2-a3 singularity, Index 3 axis 5 singularity). Basically for the axis 5 singularity distance corresponds to a scaled axis 5 angle. Therefore the robot is "inside" the singularity whenever the value of $singul_dist[3] < 1.0 (about +-0.0181° a5 angle) . Did you check the value of $singul_dist[]? Otherwise the robot might still think "no singularity" and does nothing. The controller has different singularity strategies (as SkyeFire already posted), which one is chosen depends on a few system variables:

[list type=decimal]

• $CP_VEL_TYPE: reduce the axes velocities if axes get to fast: Hence check if $CP_VEL_TYPE=#VAR_ALL or #VAR_ALL_MODEL (in default case this feature is only in T1 active: $CP_VEL_TYPE=#VAR_T1)

• $ORI_TYPE = #JOINT: This is the preferred solution if orientation control is not important, because your hand axes a4-a6 are planned ptp. Hence the axis 5 singularity does not exist any more. So by cheating orientation a5- singularity is avoided

• $SINGUL_STRATEGY = 1. Try avoiding the singularity by changing orientation during interpolation (different approach than $ORI_TYPE=#joint, which already is used during planning!!!): This method is not recommended by KUKA, because the orientation change depends on the velocity (hence in T1 the orientation error might be small and in AUT/EXT much bigger)
  

• $SINGUL_POS[]: If $singul_dist[] < 1.0 the first not unique defined axis angle is set to zero.

So basically $SINGUL_POS[3] leeds inside the singularity area to a unique defined axis 4 = 0° and a axis 6 set corrspondingly. But this solves only the first problem that arises inside singularities (mathematically spoken there is a infinite number of valid axis position leading to the same cartesian position). The second problem inside singularities is the velocity problem which can be "solved" using $ORI_TYPE = #JOINT, $CP_VEL_TYPE or $SINGUL_STRATEGY .

Fubini

Hi,

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How do I check the value of $SINGUL_DIST[]?

In the menu use Display -> Variable -> Single and type $SINGUL_DIST[].

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$SINGUL_POS[3]=1 to try and prevent A4 from rotating ~180°

The axis 4 turning 180° is not only caused by the singularity but often also the wrist axis status requires turning a4 and a6 about 180°. This can be prevented (even though ist is not recommended by KUKA) by setting $POS_SWB[3] = 1 allowing a status change when driving through the axis 5 singularity.

The reason it is not recommended is that if you drive close to the singularity the status changes takes places velocity based. Hence in T1 the change might not occur but in AUT. This basically can lead to unpredictable programm behavoiur.

Fubini

Re-iterating my advice on another post somewhere in the forums:

Another strategy to avoid singularities is slight modifications of how the tool and workpiece is mounted. Most tool designers are not RobotGuys. So the designers typically design EOAT mounts and workpiece fixtures that are all square and orthogonal designs and aligned with the Robot World axes.............terrible. Add small offsets (5- 15 degrees) to your tooling to offset the axis alignments slightly. As stated before, this won't eliminate singularities, but will certainly reduce the likelihood of them occurring. And it is an inexpensive solution. I've done this many, many times over the years with great success.