[Robotics] Grasping objects

[Antonio De Donno]

Good morning everybody,

this is the first time I write to this mailing list, so I briefly 
introduce myself. My name is Antonio De Donno, I'm a 3rd year PhD 
student in medical robotics at the University of Strasbourg. For my 
thesis I'm working on the kinematic control of a flexible robot for 
no-scar surgery. To test the control strategies I'm proposing, I 
realized a virtual simulator of my system. At the beginning I took a 
basic graphic environment already developed in my lab, but less than one 
year ago I discovered Blender and I decided to move to it, mainly 
because its integration with the Bullet physics engine.

After some efforts, now I have my virtual simulator working! I can 
control the virtual model of my system directly from the robot main 
application thanks to an UDP socket (at each time step I transfer the 
joint references from the application to Blender). Now my problem is 
grasping objects: I need to simulate a pick-and-place task in which the 
grasper took a ring from somewhere and move it to another place. I found 
a partial solution by creating in Python a rigid body link between 
grasper and grabbed object when a radar sensor attached to the grasper 
detect something graspable and the user is going to close the grasper. 
The problem with this method is that it seems to work only if the pivot 
point of the link is one corner of the ring bounding box: this means 
that, in many cases, the grasper is closed and the ring is some 
millimetres away from it!

Have any of you already faced this problem? I found no solutions 
searching on internet. I checked how it is performed in MORSE, but in 
that case the grabbed object is parented to the grasper. This solution 
doesn't work for me, because parenting makes grasper and ring one single 
object and doesn't permits to interact with the grabbed object.

I hope I was clear enough, thank you in advance for any suggestions you 
can give me!

Best,

Antonio


-- 
Antonio De Donno, MSBE
PhD Candidate in Medical Robotics
Equipe AVR (Automation, Vision and Robotics), ICube Lab
IRCAD - European Institute of Telesurgery, Civil Hospital
University of Strasbourg, France