Introduces a new "strain" equality mode (flex_edgeequality = 3) for flexcomps with trilinear interpolation. This mode enforces constraints on the three invariants of the Green-Lagrange strain tensor at 8 Gauss quadrature points within each flex element, resulting in 24 equality constraints per flexcomp.

Also fixes a bug when attaching a flex with constraints. PiperOrigin-RevId: 881349765 Change-Id: I8e6df8239488bfdc87d7e5b473568975e38c737e
2026-03-10 04:25:19 -07:00
parent fe6c81ed93
commit 713b5524bc
23 changed files with 899 additions and 48 deletions
@@ -0,0 +1,64 @@
+<!-- Copyright 2026 DeepMind Technologies Limited
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<mujoco model="Gripper">
+  <include file="scene.xml"/>
+
+  <option cone="elliptic" impratio="10" integrator="implicitfast"/>
+
+  <worldbody>
+    <body>
+      <freejoint/>
+      <geom type="box" size=".46 .5 .4" pos="0 0 1.5" rgba=".5 .5 0 1" condim="6"/>
+    </body>
+    <body name="column_00" pos=".7 .4 .5">
+      <geom type="box" size=".1 .1 .5" rgba=".2 .2 .2 1"/>
+      <flexcomp type="box" pos="-.24 0 .1" dim="3" spacing=".03 .01 .01"
+                radius=".001" rgba="0 .7 .7 1" mass=".5" name="left" dof="trilinear">
+        <edge equality="strain"/>
+        <contact selfcollide="none" internal="false" friction="3"/>
+        <pin id="4 5 6 7"/>
+      </flexcomp>
+    </body>
+    <body name="column_01" pos=".7 -.4 .5">
+      <geom type="box" size=".1 .1 .5" rgba=".2 .2 .2 1"/>
+      <flexcomp type="box" pos="-.24 0 .1" dim="3" spacing=".03 .01 .01"
+                radius=".001" rgba="0 .7 .7 1" mass=".5" name="right" dof="trilinear">
+        <edge equality="strain"/>
+        <contact selfcollide="none" internal="false" friction="3"/>
+        <pin id="4 5 6 7"/>
+      </flexcomp>
+    </body>
+    <body name="column_02" pos=" -.7 .4 .5">
+      <geom type="box" size=".1 .1 .5" rgba=".2 .2 .2 1"/>
+      <flexcomp type="box" pos=".24 0 .1" dim="3" spacing=".03 .01 .01"
+                radius=".001" rgba="0 .7 .7 1" mass=".5" name="bottom" dof="trilinear">
+        <edge equality="strain"/>
+        <contact selfcollide="none" internal="false" friction="3"/>
+        <pin id="0 1 2 3"/>
+      </flexcomp>
+    </body>
+    <body name="column_03" pos="-.7 -.4 .5">
+      <geom type="box" size=".1 .1 .5" rgba=".2 .2 .2 1"/>
+      <flexcomp type="box" pos=".24 0 .1" dim="3" spacing=".03 .01 .01"
+                radius=".001" rgba="0 .7 .7 1" mass=".5" name="top" dof="trilinear">
+        <edge equality="strain"/>
+        <contact selfcollide="none" internal="false" friction="3"/>
+        <pin id="0 1 2 3"/>
+      </flexcomp>
+    </body>
+  </worldbody>
+
+</mujoco>