Object Gripping and picking

Omniverse Isaac Sim
,
1

Hello guys, as a new comer, I have a question regarding gripping an object in Isaac Sim.
I have 2 panda arms, when they pick an object, they cannot hold it firmly and it slips and falls down. what would be the problem? it is a very simple cubic shape object. It seems that they may count it as a collision and avoid touching it completely … I even made the object a little bigger, but the fingers will also open bigger and cannot hold the object firmly.

3 Likes
2

Also having the same issue in robotiq 3f gripper also object is getting out of gripper

3

Hi,
just another user passing by. I think that the slipping object is a problem that occurs very often. I would suggest few things:

  • Try modifying the solver_position_iteration_count as suggested here
  • Try not to use the set_joint_positions() function (try instead the your_gripper_articulation.apply_action(ArticulationAction(joint_positions=[TARGET_POS, TARGET_POS]))) and play around with friction parameters as suggested here
  • Have a look also at the damping and stiffness settings as they may play a role if you are trying to do either a position, velocity or effort control. See here

If the gripper is not touching the object completely it may be a problem of collision settings. Check this topic.

4

I found that I can make my gripper pick up something if the weight is very small (1g). However, I’m struggling to pick up my intended object weight of around 500 g. Is there any settings besides the ones above that will allow me to pick up heavier objects?

5

@alireza.delavari - this should not be an issue to simulate. I agree with @altick’s point about using joint drives vs. setting the joint positions kinematically.

Is there a way for you to read out the contact normal forces between the gripper fingers and the cube? The normal forces need to be large enough to be able to hold the cube given the static friction coefficient, i.e. you need Fnormal * static_friction_coef >= 0.5 * m_cube * gravity (0.5 from two fingers holding the cube).

You can also analyze contact forces using PVD: OmniPVD - PhysX Visual Debugger — Omniverse Extensions latest documentation

Or share here and I can have a look, too.

6

The example I’m using is:

  • Launch Isaac Sim, then select Isaac Examples > Manipulation > Simple Stack
  • Click on one of the cubes and increase the mass to 0.5
  • Press Start Stacking

I tried to use the OmniPVD, but not sure how to play it back / view the contact forces. I posted a related question here on how to load OmniPVD in case I was doing it wrong.