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Object slips out of gripper | Gazebo 7 | UR5 | Robotiq 3 finger

asked 2016-11-20 21:06:15 -0500

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Hello,

We want to manipulate some simple objects in Gazebo 7 using UR5 and Robotiq 3 finger gripper. We are using ROS indigo on Ubuntu 14.04.

The object slips out of the gripper every time. Sample video: https://youtu.be/-YixCumWrt0

We have tried changing the mu1, mu2, kp, kd values of the gripper and the object. But no luck. We are using the Robotiq package from DRCSIM.

Have anyone faced similar issues? We will greatly appreciate a quick solution!

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answered 2016-11-21 14:46:23 -0500

nkoenig gravatar image

Here is an example tube that has been used in grasping tasks:

https://bitbucket.org/osrf/gazebo_mod...

In your world file, you can try this physics parameters:

<physics type="ode">
      <gravity>0.000000 0.000000 -9.810000</gravity>
      <ode>
        <solver>
          <type>quick</type>
          <iters>100</iters>
          <precon_iters>0</precon_iters>
          <sor>1.000000</sor>
        </solver>
        <constraints>
          <cfm>0.000000</cfm>
          <erp>0.500000</erp>
          <contact_max_correcting_vel>1000.000000</contact_max_correcting_vel>
          <contact_surface_layer>0.00000</contact_surface_layer>
        </constraints>
      </ode>
</physics>

Additionally:

  1. Check the interia value of your tube. You can visualize the inertia in the GUI.
  2. Try turning on collision visualizations, and see if the contacts are being created as you might expect.
  3. What type of control for the hand are you using, position or torque?
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answered 2016-11-21 16:22:17 -0500

ariyan.kabir gravatar image

Thanks Nate!

We have tried changing the physics parameters, its still the same issue. We are using positional control for the arm. As for the gripper, we tried to apply max. force on top of max. closing by position.

For a quick temporary solution, is there a way to attach the object with the gripper by creating an artificial link? Can we do it from the code for moving the robot? or does it require modifying the urdf manually everytime?

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Comments

Are you using a ROS controller? You can create a joint between the gripper and the object, and then disconnect the joint when you want to release the object.

nkoenig gravatar imagenkoenig ( 2016-11-21 16:36:38 -0500 )edit

Hello Nate, I am working with Ariyan on the same project. I don't think so, we are using a '.so' file compiled by the libraries provided by DRC Simulator. However, we have replaced the Robotiq gripper by the PR2 gripper on UR5 with ROS controllers. But, we are not able to control the PR2 gripper. I presume the issue to be with ROSTOPIC not able to published the gripper joints on "/joint_states" topic. Can you help us out how can we solve that issue?

brual gravatar imagebrual ( 2016-11-21 17:35:41 -0500 )edit

PS: We tried using PR2 in the same environment to pick-up objects before integrating the grippers with the UR5.

brual gravatar imagebrual ( 2016-11-21 17:36:55 -0500 )edit

Position control of a hand makes grasping difficult. Can you try using force based control? I don't have enough information about your controller to help diagnose the pr2 gripper problem. You could post some code. answers.ros.org might have better answers for ROS related questions.

nkoenig gravatar imagenkoenig ( 2016-11-22 09:31:08 -0500 )edit
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answered 2017-09-05 00:10:36 -0500

Hey, I am facing the same problem. Were you able to find a solution to it?

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Hello :) You might get an answer more quickly if you open a new question detailing what you've tried and what's your problem. An answer to another question is not the best place for this ;)

chapulina gravatar imagechapulina ( 2017-09-05 10:10:29 -0500 )edit
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Asked: 2016-11-20 21:06:15 -0500

Seen: 1,205 times

Last updated: Nov 21 '16