Singularity ..what it is , how can we avoid this of arm robot

Hi All,

I am working on xARm7 Ufactory Robot which has DOF=7 .

I have following queries:

a) While using Move IT , I observed object was just kept vertical down to gripper , but moveIt return fraction of 15% and xArm could not pick the object as we have checked if fraction>90% it should not pick , and sometime also I feel that the trajectory from this position is quite easy and can pick by robot but then I found fraction is <90% . What might be the issue, and what needs to be done for this ? How can I check trajectory and why move it is returning fraction (computeCartesianPath) which is <90% for simple locations?

I suspect this issue occur due to singularity position in Arm. But I dont know how to avoid singularities and what type of singularity occurred.

b) I observe xarm_straight_plan service which is wrapper function to plan the path using move_group.computeCartesianPath() , I can understand it fails sometime if fraction < 90% .But sometime I could not find any error logs , it just randomly failed. May I know the reason of it? I observed this type of behavior for other service server call as well.
If anyone has observed the same issue, please share your findings that would be really helpful.

c) xarm_exec_plan also wrapper function using which call move_group.execute(), It did not returns any string for failed service call . How can it return the string and we can know the precise error for it fail.


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