Failed to find Articulation in standalone python script

[ZZJzhou]

Issue

I import three robot arms from urdf and set a scene in a stand-alone python script. And then I can use the Physics Inspector in the Tool Panel to manipulate the robot like below.

But when I followed the instruction of Robot Simulation Snippets — Isaac Sim Documentation to complete the same task in the stand-alone python script, it failed.

Code

Here is key part of my code

async def set_scene():
    import omni
    import omni.kit.commands
    import omni.usd
    from isaacsim.core.api.world import World
    from isaacsim.core.prims import RigidPrim
    from isaacsim.core.api.objects import DynamicCuboid

    if World.instance():
        World.instance().clear_instance()
    world=World()
    await world.initialize_simulation_context_async()
    world.scene.add_default_ground_plane(z_position=-1.0)

    # Retrieve the path of the URDF file
    urdf_list = [
                 "/home/oem/path/isaacsim/urdf_5_0_0/rmbf8_description/urdf/instr_RMBF-8_mesh.urdf",
                 "/home/oem/path/isaacsim/urdf_5_0_0/rlnd8_description/urdf/instr_RLND-8_mesh.urdf",
                 "/home/oem/path/isaacsim/urdf_5_0_0/arm_description/robot_G2_2_2_FleshColor.urdf"
                 ]
    import_urdfs(urdf_list)
        
    # create a physical scene
    stage = omni.usd.get_context().get_stage()
    # for prim in stage.Traverse():
    #     print(prim.GetPath())



    bind_aluminum_material(stage, aluminum_path, aluminum_targets)


    import omni
    omni.timeline.get_timeline_interface().play()

    # dymical control/ robot articulation
    from omni.isaac.dynamic_control import _dynamic_control
    dc = _dynamic_control.acquire_dynamic_control_interface()

    # test log 1
    from isaacsim.core.utils.prims import get_articulation_root_api_prim_path
    root_api_prim_path = get_articulation_root_api_prim_path("/RMBF_8_G3_0")
    print("root_api_prim_path is", root_api_prim_path)

    # test log 2
    from isaacsim.core.utils.articulations import find_all_articulation_base_paths
    rootpath = find_all_articulation_base_paths()
    print("find_all_articulation_base_paths", rootpath)

    # test log 3
    stage = omni.usd.get_context().get_stage()
    for prim in stage.Traverse():
        from pxr import Gf, Sdf, Usd, UsdGeom, UsdPhysics
        if prim.HasAPI(UsdPhysics.ArticulationRootAPI):
            print(prim.GetPath(), " is articulation")
        elif prim.IsA(UsdPhysics.PrismaticJoint) or prim.IsA(UsdPhysics.RevoluteJoint) or prim.IsA(UsdPhysics.SphericalJoint):
            print(prim.GetPath(), " is joint")
            
    # test log 4
    art = dc.get_articulation("/RMBF_8_G3_0")
    if art == _dynamic_control.INVALID_HANDLE:
        print("*** '%s' is not an articulation" % "/RMBF_8_G3_0")
    else:
        # Print information about articulation
        root = dc.get_articulation_root_body(art)
        print(str("Got articulation handle %d \n" % art) + str("--- Hierarchy\n"))

        body_states = dc.get_articulation_body_states(art, _dynamic_control.STATE_ALL)
        print(str("--- Body states:\n") + str(body_states) + "\n")

        dof_states = dc.get_articulation_dof_states(art, _dynamic_control.STATE_ALL)
        print(str("--- DOF states:\n") + str(dof_states) + "\n")

        dof_props = dc.get_articulation_dof_properties(art)
        print(str("--- DOF properties:\n") + str(dof_props) + "\n")

    # test log 5
    dof_states = dc.get_articulation_dof_states(art, _dynamic_control.STATE_ALL)
    print("RMBF state", dof_states)

    # test log 6
    dof_ptr = dc.find_articulation_dof(art, "rlnd_A3_2")
    dof_state = dc.get_dof_state(dof_ptr, _dynamic_control.STATE_ALL)
    # print position for the degree of freedom
    print("rlnd_A3_2 pos", dof_state.pos)
    num_joints = dc.get_articulation_joint_count(art)
    print("number of joints", num_joints)

    world.reset()

asyncio.ensure_future(set_scene())

Here is the printed log

root_api_prim_path is /RMBF_8_G3_0/root_joint
find_all_articulation_base_paths ['/SetupArmG2_2', '/RMBF_8_G3_0', '/RLND_8_G3_0']
/RMBF_8_G3_0/joints/fixed_base  is joint
/RMBF_8_G3_0/joints/arm_joint_1  is joint
/RMBF_8_G3_0/joints/arm_joint_2  is joint
/RMBF_8_G3_0/joints/arm_joint_3  is joint
/RMBF_8_G3_0/joints/arm_joint_4  is joint
/RMBF_8_G3_0/joints/arm_joint_5  is joint
/RMBF_8_G3_0/joints/arm_joint_6  is joint
/RMBF_8_G3_0/joints/arm_joint_7  is joint
/RMBF_8_G3_0/joints/arm_joint_8  is joint
/RMBF_8_G3_0/joints/arm_joint_9  is joint
/RMBF_8_G3_0/joints/rmbf_A1  is joint
/RMBF_8_G3_0/joints/rmbf_A2  is joint
/RMBF_8_G3_0/joints/rmbf_A3_1  is joint
/RMBF_8_G3_0/joints/rmbf_A3_2  is joint
/RMBF_8_G3_0/joints/rmbf_linkA1_to_shell  is joint
/RMBF_8_G3_0/root_joint  is articulation
/RLND_8_G3_0/joints/fixed_base  is joint
/RLND_8_G3_0/joints/arm_joint_1  is joint
/RLND_8_G3_0/joints/arm_joint_2  is joint
/RLND_8_G3_0/joints/arm_joint_3  is joint
/RLND_8_G3_0/joints/arm_joint_4  is joint
/RLND_8_G3_0/joints/arm_joint_5  is joint
/RLND_8_G3_0/joints/arm_joint_6  is joint
/RLND_8_G3_0/joints/arm_joint_7  is joint
/RLND_8_G3_0/joints/arm_joint_8  is joint
/RLND_8_G3_0/joints/arm_joint_9  is joint
/RLND_8_G3_0/joints/rlnd_A1  is joint
/RLND_8_G3_0/joints/rlnd_A2  is joint
/RLND_8_G3_0/joints/rlnd_A3_1  is joint
/RLND_8_G3_0/joints/rlnd_A3_2  is joint
/RLND_8_G3_0/joints/rlnd_linkA1_to_shell  is joint
/RLND_8_G3_0/root_joint  is articulation
/SetupArmG2_2/joints/arm_joint_1  is joint
/SetupArmG2_2/joints/arm_joint_2  is joint
/SetupArmG2_2/joints/arm_joint_3  is joint
/SetupArmG2_2/joints/arm_joint_4  is joint
/SetupArmG2_2/joints/arm_joint_5  is joint
/SetupArmG2_2/joints/arm_joint_6  is joint
/SetupArmG2_2/joints/arm_joint_7  is joint
/SetupArmG2_2/joints/arm_joint_8  is joint
/SetupArmG2_2/joints/arm_joint_9  is joint
/SetupArmG2_2/joints/A1234  is joint
/SetupArmG2_2/joints/A5  is joint
/SetupArmG2_2/root_joint  is articulation
2025-08-08T07:29:38Z [17,264,764ms] [Warning] [omni.isaac.dynamic_control.plugin] Failed to find articulation at '/RMBF_8_G3_0'
*** '/RMBF_8_G3_0' is not an articulation
RMBF state None
2025-08-08T07:29:38Z [17,264,764ms] [Warning] [omni.isaac.dynamic_control.plugin] DcFindArticulationDof: Function called while not simulating
2025-08-08T07:29:38Z [17,264,764ms] [Warning] [omni.isaac.dynamic_control.plugin] DcGetDofState: Function called while not simulating
rlnd_A3_2 pos 0.0
2025-08-08T07:29:38Z [17,264,764ms] [Warning] [omni.isaac.dynamic_control.plugin] DcGetArticulationJointCount: Function called while not simulating
number of joints 0

Possible related Code

In case how I imported Urdf is also related, here is the code:

def import_urdfs(urdf_list):
    import omni.kit.commands
    import omni.usd
    from isaacsim.asset.importer.urdf import _urdf
    from isaacsim.asset.importer.urdf._urdf import UrdfJointTargetType

    # Acquire the URDF extension interface for parsing and importing URDF files
    urdf_interface = _urdf.acquire_urdf_interface()

    # Configure the settings for importing the URDF file
    import_config = _urdf.ImportConfig()
    import_config.convex_decomp = False  # Disable convex decomposition for simplicity
    import_config.fix_base = True       # Fix the base of the robot to the ground
    import_config.make_default_prim = True  # Make the robot the default prim in the scene
    import_config.self_collision = False  # Disable self-collision for performance
    import_config.distance_scale = 100     # Set distance scale for the robot
    import_config.density = 0.0          # Set density to 0 (use default values)
    import_config.default_drive_type = UrdfJointTargetType.JOINT_DRIVE_POSITION

    for urdf_path in urdf_list:
        # Parse the robot's URDF file to generate a robot model
        result, robot_model = omni.kit.commands.execute(
            "URDFParseFile",
            urdf_path=urdf_path,
            import_config=import_config
        )

        # Update the joint drive parameters for better stiffness and damping
        for joint in robot_model.joints:
            robot_model.joints[joint].drive.strength = 1047.19751  # High stiffness value
            robot_model.joints[joint].drive.damping = 52.35988    # Moderate damping value

        # Import the robot onto the current stage and retrieve its prim path
        result, prim_path = omni.kit.commands.execute(
            "URDFImportRobot",
            urdf_robot=robot_model,
            import_config=import_config,
        )
        print("result is ", result)
        print("prim path is ", prim_path)

Other Tried Out

art = dc.get_articulation("/RMBF_8_G3_0/root_joint")

[vick-yu]

Closing this discussion as a duplicate of https://forums.developer.nvidia.com/t/failed-to-query-articulation-in-python-script/341502.