[Error] Please ensure that there is only one articulation in the prim path tree

Hi, I am currently working on Stretch3 robot with issac lab and issac sim(4.2.0 ver). I’m trying to import the robot and as I have XML file, I converted in the sim.
Conversion worked but I think the joint isn’t connects the link accordingly.
Joints are all gathered under base_link, not in individual parent links.


When running a code to excert effort to the joint, I encounter the error. Can anybody give me a single clue in this ??

Traceback (most recent call last):
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/asset_base.py”, line 92, in
lambda event, obj=weakref.proxy(self): obj._initialize_callback(event),
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/asset_base.py”, line 263, in _initialize_callback
self._initialize_impl()
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py”, line 904, in initialize_impl
raise RuntimeError(
RuntimeError: Failed to find a single articulation when resolving '/World/envs/env
.*/Robot’. Found multiple ‘[Usd.Prim(</World/envs/env_0/Robot/base_link>), Usd.Prim(</World/envs/env_0/Robot/worldBody>)]’ under ‘/World/envs/env_0/Robot’. Please ensure that there is only one articulation in the prim path tree.
[INFO]: Time taken for simulation start : 1.760487 seconds
Creating window for environment.
[INFO]: Completed setting up the environment…
Error executing job with overrides:
Traceback (most recent call last):
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab_tasks/omni/isaac/lab_tasks/utils/hydra.py”, line 91, in hydra_main
func(env_cfg, agent_cfg, *args, **kwargs)
File “/home/portal/Isaac/IsaacLab/…/Isaac_stretch/train_skrl.py”, line 146, in main
env = gym.make(args_cli.task, cfg=env_cfg, render_mode=“rgb_array” if args_cli.video else None)
File “/home/portal/Isaac/IsaacLab/_isaac_sim/kit/python/lib/python3.10/site-packages/gymnasium/envs/registration.py”, line 802, in make
env = env_creator(**env_spec_kwargs)
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab_tasks/omni/isaac/lab_tasks/direct/stretch/stretch_env.py”, line 151, in init
self._arm_dof_idx, _ = self.stretch.find_joints(self.cfg.arm_dof_name)
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py”, line 241, in find_joints
joint_subset = self.joint_names
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py”, line 136, in joint_names
return self.root_physx_view.shared_metatype.dof_names
File “/home/portal/Isaac/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py”, line 155, in root_physx_view
return self._root_physx_view
AttributeError: ‘Articulation’ object has no attribute ‘_root_physx_view’

Set the environment variable HYDRA_FULL_ERROR=1 for a complete stack trace.

What format is the xml file? Is the flat structure also present in the XML file?

Sorry for the late reply, No the xml isn’t flat. Here is the xml file that I’m using right now.