Friction between gripper and stone not working properly

asked 2017-03-14 11:52:09 -0500

gocarlos gravatar image

updated 2017-03-16 00:36:19 -0500

ffurrer gravatar image

Hi there,

I'm using Gazebo to simulate a pick and place of objects with irregular shape like meshes of stones. When picking an object Gazebo does not seem to take the friction between both objects (stone and gripper ) into account.

Here is a quick video of what happens: https://www.dropbox.com/s/8svnza7dze0...

The friction coefficients of both objects are:

Stone

<gazebo reference="base_link">
  <mu1 value="1.2"/>
  <mu2 value="1.1"/>
  <kp  value="5000000.0" />
  <kd  value="1.0" />
  <fdir1 value="1 0 0"/>
  <collision>
    <surface>
      <bounce>
        <restitution_coefficient> 0.1 </restitution_coefficient>
        <threshold>0.</threshold>
      </bounce>
      <contact>
        <ode>
          <max_vel>0.1</max_vel>
          <min_depth>0.001</min_depth>
        </ode>
      </contact>
    </surface>
  </collision>
  <material name="Gray">
    <color rgba="0.8 0.8 0.8 1"/>
  </material>
  <turnGravityOff>false</turnGravityOff>
</gazebo>

and

Gripper

<!-- Link 3 -->
<link name="${prefix}link_3">
  <visual>
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <geometry>
      <mesh filename="package://robotiq_s_model_visualization/meshes/s-model_articulated/visual/link_3.STL" />
    </geometry>
    <material name="grey"/>
  </visual>
  <collision>
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <geometry>
      <mesh filename="package://robotiq_s_model_visualization/meshes/s-model_articulated/collision/link_3.STL"/>
    </geometry>
    <material name="grey"/>
  </collision>
  <inertial>
    <origin rpy="0 0 0" xyz="0.01626 0.00049 0.0002"/>
    <mass value="0.03354"/>
    <inertia ixx="0.00000305151"
             ixy="0.00000089792"
             ixz="0.00000000249"
             iyy="0.00001427978"
             iyz="-0.00000001191"
             izz="0.00001264126"/>
  </inertial>
</link>

<gazebo reference="${prefix}link_3">
  <mu1>1.1</mu1>
  <mu2>1.1</mu2>
  <minDepth>0.001</minDepth>
</gazebo>

Link_3 is the finger tip of the gripper as seen in the video above.

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Comments

Im using Gazebo 7.5, Ubuntu 14.04, ROS Indigo and ODE

gocarlos gravatar imagegocarlos ( 2017-03-14 11:54:11 -0500 )edit

Can you add a clarify statement as to why you think the friction is not being taken into account? What happens when you set the friction values significantly higher? Do you see the same behavior, or does something change?

nkoenig gravatar imagenkoenig ( 2017-03-14 17:58:31 -0500 )edit

Yes, I tried to put both at 1000 mu and mu2 in both files. The other values where unchanged. By saying that Gazebo does not take friction into account I meant that changing the friction coefficients does not make a difference in the behavior when grasping. The stone stays on the table even though the gripper presses with the maximal force.

gocarlos gravatar imagegocarlos ( 2017-03-15 10:05:09 -0500 )edit

Have you verified the stone's inertia is correct?

nkoenig gravatar imagenkoenig ( 2017-03-15 10:13:03 -0500 )edit

Im using those values: <inertial> <mass value="${mass}"/> (mass is set to 1.0 (kg)) <origin xyz="0.172716e-01 0.036106e-01 0.106380e-01"/> <inertia ixx="0.063821e-02" ixy="0.0" ixz="0.0" iyy="0.105141e-02" iyz="0.0" izz="0.110947e-02"/> </inertial> Can I check in gazebo if there is something "wrong" with those stones?

gocarlos gravatar imagegocarlos ( 2017-03-15 10:38:24 -0500 )edit
1

You can right click on your model (stone) and select View->Inertia. Your inertia should approximately surround your object's shape.

Carlos Agüero gravatar imageCarlos Agüero ( 2017-03-17 10:39:46 -0500 )edit

It looks like the gripper might not be applying enough force to hold the rock. You can test the friction by changing gravity to have an Y component and see how the rock slides against the table.

chapulina gravatar imagechapulina ( 2017-03-19 11:25:03 -0500 )edit