Preventing Two Geoms from Penetrating in a Model Gripper? #2062

kurtenkera · 2024-09-19T00:23:53Z

kurtenkera
Sep 19, 2024

Intro

Hi!

I am an Australian PhD researcher at the University of Queensland, and I use MuJoCo for my robotics research.

My setup

I currently use MuJoCo via the Python bindings.

My question

I'm trying to create a simple XML model of the gripper seen below.

I want the lower platform to be fixed in space, and the upper platform to be able to slide. Furthermore, I want the two platforms to be able to slide in sync when lifting up a gripped test object. Currently, I have enabled the upper platform to slide via a slide joint, and both platforms can slide in sync via a slide joint. I have damped both joints significantly to prevent the platforms from dropping to the ground due to gravity (ideally, I want them to remain fixed in space unless I actuate them).

My issue is this: If I run the model in the interactive GUI, the two platforms are allowed to penetrate: why (see the initial model configuration and the 'penetrating platforms' configuration below)? How can I prevent them from penetrating? Also, is there a nice method to stop my platforms from sliding due to gravity (but only slide via my motors/actuators) rather than via applying high damping to the slide joints?

Initial configuration:

Penetrating platforms:

Minimal model and/or code that explain my question

I have created a minimal XML file containing the two platforms seen in the attached gripper image, as well as a test object.

<mujoco>
	
  <option gravity = "0 0 -9.81"/>

  <worldbody>
    <light pos="0 0 1.5" dir="0 0 -1" directional="true"/>
   
    <geom name="floor" size="0 0 0.05" type="plane" rgba = "1 1 1 1"/>

    <!-- GANTRY-GRIPPER ASSEMBLY -->
    <body name="gantry_gripper" pos = "0 0 0.3">
    
      <joint name = "lift_gripper" type = "slide" axis = "0 0 1" damping = "5000"/>
      
      <!-- UPPER SLIDING PLATFORM -->
      <body name = "movingplatform">
        <joint name = "close_gripper" type = "slide" axis = "0 0 -1" damping = "5000"/>
        <geom name="movingplatform" type="box" euler = "0 0 0" size="0.2 0.1 0.05" pos="0 0 0.45" rgba="1 0 0 1"/>
      </body>
      
      <!-- FIXED LOWER PLATFORM -->
      <body name = "fixedplatform">
        <geom name="fixedplatform" type="box" euler = "0 0 0" size="0.2 0.1 0.05" pos="0 0 0.25" rgba="0 1 0 1"/>
      </body>
    </body>
    
    <!-- test object -->
    <body pos="0 0 0.2">
      <joint type = "free"/>
      <geom name="testobject" type="box" size="0.1 0.1 0.2" rgba="1 1 0 1"/>
    </body>
    
  </worldbody>
  
  <actuator>
    <motor name="close_gripper" joint="close_gripper" gear="1000"/>
    <motor name="lift_gripper" joint="lift_gripper" gear="1000"/>
  </actuator>
  
</mujoco>

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Preventing Two Geoms from Penetrating in a Model Gripper? #2062

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Preventing Two Geoms from Penetrating in a Model Gripper? #2062

kurtenkera Sep 19, 2024

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 0 comments

kurtenkera
Sep 19, 2024