Contact filtering on custom assets (with URDF to USD conversion)

[Johann-Huber]

Hello everyone,

I am facing an issue on Isaac Lab while trying to setup contact detection with filtering on a custom asset.
It consists of an object loaded from an urdf file.

I followed this example to build a usd file out of it. I have then loaded the asset as follow :

object_cfg: RigidObjectCfg = RigidObjectCfg(
        prim_path="/World/envs/env_.*/LoadedObject",
        spawn=UsdFileCfg(
            usd_path="root_path/ycb_mug/ycb_mug.usd",
            scale=(1.0, 1.0, 1.0),
        ),
        init_state=RigidObjectCfg.InitialStateCfg(
            pos=(0.30, 0.0, 0.0),
            rot=(1, 0, 0, 0),
        ),
    )

And then :

object = RigidObject(targeted_object_cfg)

I have loaded a franka robot on the side, and control it such that its end effector goes toward the object until it touches it.
I also added some contact sensors (following this example and that one):

contact_sensor_left_finger_cfg = ContactSensorCfg(
        prim_path="/World/envs/env_.*/Robot/panda_leftfinger", 
        filter_prim_paths_expr=["/World/envs/env_*/LoadedObject"],
        update_period=0.0,
        history_length=2,
        debug_vis=False,
    )
contact_sensor_right_finger_cfg = ContactSensorCfg(
        prim_path="/World/envs/env_.*/Robot/panda_rightfinger",
        filter_prim_paths_expr=["/World/envs/env_*/LoadedObject"],
        update_period=0.0,
        history_length=2,
        debug_vis=False,
    )
contact_sensor_hand_cfg = ContactSensorCfg(
        prim_path="/World/envs/env_.*/Robot/panda_hand", 
        filter_prim_paths_expr=["/World/envs/env_*/LoadedObject"],
        update_period=0.0,
        history_length=2,
        debug_vis=False,
    )

When I try to get the filtered contacts, I only get matrices filled with zeros.

print("Contact left forces:", self.contact_left_fingers.data.force_matrix_w.flatten())
print("Contact right forces:", self.contact_sensor_right_finger.data.force_matrix_w.flatten())
print("Contact hand forces:", self.contact_sensor_hand.data.force_matrix_w.flatten())

The exact same piece of code works fine if I replace the loaded object with a simple cube (i.e. the matrices contain non-zero values when the gripper is touching the cube) :

object_cfg = RigidObjectCfg(
        prim_path="/World/envs/env_.*/LoadedObject",
        spawn=sim_utils.CuboidCfg(
            size=(0.05, 0.05, 0.05),
            rigid_props=sim_utils.RigidBodyPropertiesCfg(),
            mass_props=sim_utils.MassPropertiesCfg(mass=100.0),
            collision_props=sim_utils.CollisionPropertiesCfg(),
            physics_material=sim_utils.RigidBodyMaterialCfg(static_friction=1.0),
            visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.0, 1.0, 0.0), metallic=0.2),
        ),
        init_state=RigidObjectCfg.InitialStateCfg(pos=(0.30, 0.0, 0.0)),
    )

I assume that the issue comes from the USD file of my object itself. Either from the conversion, or the way I load it.

I tried many changes - especially in the arguments of the spawn UsdFileCfg() (activate_contact_sensors=True, modifying rigid_props, mass_props, collision_props ...) without getting convincing results.

To generate the usd I did :

cd IsaacLab
./isaaclab.sh -p scripts/tools/convert_urdf.py \
  /path_to_urdf/ycb_mug.urdf \
  path_to_usd_to_create/ycb_mug.usd \
  --merge-joints \
  --joint-stiffness 0.0 \
  --joint-damping 0.0 \
  --joint-target-type none

Did I miss anything?

Note : I should set the parameter to avoid the convex_hull based collisions during the conversion but I guess it is not critical for the mentioned problem.

---

Here are some related files :

• zip with the URDF and OBJ files (source object coming from the YCB dataset): ycb_mug.zip
• zip with the generated USD files : ycb_mug_usd.zip. It also contains a USDA file generated with usdcat -o output.usda input.usd to debug.