Parallel Gripper Gazebo mimic close error in simulation Inbox x


mjpark
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Has any one noticed an issue with the mimic control for the Electric Parallel Gripper in the SDK simulation?
 
When we command the gripper to close, the mimic joint does not seem to fully close.  See attached screen shot showing the simulated gripped in a "closed" state.  On the real robot, we do not have this issue.
 
It could possibly be related to the logic in this code
 

Screenshot from 2018-09-06 14-52-09.png

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  • 2 weeks later...

Hello, mjpark,

We are not able to reproduce your issue, we did verify on the 16.04 machine, everything seems fine.

Few suggestions:

1, make sure to have a stable connection between the robot and your workstation.

2, make sure your gripper firmware is updated,  if you want to check your gripper firmware and update it, please go to FSM to set it up.

3, make sure your SDK checkout is the latest checkout, you can also recreate a workspace.

-Shiwei

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hi Shiwei,

I am having issues in simulation only.  The actual robot grippers are behaving fine.  I am starting to dig into the electric gripper controller link I posted above.

Here are other notes I have about the issue:

The issue does not seems to be consistent.  I just restarted the system now and now, but joints (main and mimic) open and close as they should.
 
I *do* see a delay on the order of 0.2 to 0.5 seconds between the actuation of the joints in the simulation.  I'm looking at this in RViz.  I'm now wondering if the timing of the delay has something to do with the intermittent issue.
 
I would say that 50 to 75% of the time I've seen the issue occur.  Might be processor computation resource based or networking dropped message based.
 
Mike
Edited by mjpark
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Found the issue.  Traced the main and mimic joint position values and they were all correct.  Traced the effort down to the writeSim that Gazebo reads in here:

https://github.com/RethinkRobotics/sawyer_simulator/blob/master/sawyer_gazebo/src/sawyer_robot_hw_sim.cpp

Saw when the finger joints failed, the efforts were on the order of -100, which seemed quite large to me.

Looked at

https://github.com/RethinkRobotics/intera_common/blob/master/intera_tools_description/urdf/electric_gripper/rethink_electric_gripper.xacro

and saw that the right / left effort limits are 20, which is far under the limit.  Raised the limit to 200 while also lowering the dynamics damping and friction coefficients to 10 and 50, respectively.

Issue completely gone now.  FYI still on Intera 5.2.  Did a diff to 5.3 and this configuration has not changed.  This issue with the gripper in sim has been replicated by a few developers here.

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