[Question] Failure to parse the configuration of grouped articulations in one usd file with ArticulationCfg class

[YitianShi]

Hi everyone, recently I've built a simple manipulator with robotiq 2f 85 mounted on the end effector of ur10e and tried to load it into the ArticulationCfg class and instantiate a scene with it as a robot. But it seems like only one articulation root is able to be replaced into the scene (As I have two seperate articulation roots as gripper and robot arm).

The following is my usd hierarchy (ManipulatorMounted.usd):

My configuration code is:

MOUNTED_CFG = ArticulationCfg(
    spawn=sim_utils.UsdFileCfg(
        usd_path=f"{USD_PATH}/ManipulatorMounted.usd",
        rigid_props=sim_utils.RigidBodyPropertiesCfg(
            disable_gravity=False,
            max_depenetration_velocity=5.0,
        ),
        activate_contact_sensors=False,
    ),
    init_state=ArticulationCfg.InitialStateCfg(
        joint_pos={
            "shoulder_pan_joint": 0,
            "shoulder_lift_joint": -1.2,
            "elbow_joint": 1.1,
            "wrist_1_joint": 0,
            "wrist_2_joint": 0,
            "wrist_3_joint": 0.0,
        },
         pos = (0.5, 1, 0.9)
    ),
    actuators={
        "arm": ImplicitActuatorCfg(
            joint_names_expr=[
            "shoulder_pan_joint",
            "shoulder_lift_joint",
            "elbow_joint",
            "wrist_1_joint",
            "wrist_2_joint",
            "wrist_3_joint"],
            velocity_limit=100.0,
            effort_limit=800.0,
            stiffness=800.0,
            damping=50.0,
        ),
    },
)

Notice that the data are adapted from the UR10 tutorials and the joints in the gripper were not set up due to the current failure of running my code.

And configured through:

class CellSceneCfg(InteractiveSceneCfg):
    """Configuration for a cell scene."""

    robot: ArticulationCfg = MOUNTED_CFG.replace(prim_path="{ENV_REGEX_NS}/Robot")

Following is my RL environment configuration:

@configclass
class CellEnvCfg(RLTaskEnvCfg):
    """Configuration for the locomotion velocity-tracking environment."""

    # Scene settings
    scene: CellSceneCfg = CellSceneCfg(num_envs=4096, env_spacing=3.0, replicate_physics=True)
    # Basic settings
    observations: ObservationsCfg = ObservationsCfg()
    actions: ActionsCfg = ActionsCfg()
    randomization: RandomizationCfg = RandomizationCfg()
    # MDP settings
    curriculum: CurriculumCfg = CurriculumCfg()
    rewards: RewardsCfg = RewardsCfg()
    terminations: TerminationsCfg = TerminationsCfg()
    # No command generator
    commands: CommandsCfg = CommandsCfg()

    # Post initialization
    def __post_init__(self) -> None:
        """Post initialization."""
        # general settings
        self.decimation = 2
        self.episode_length_s = 5
        # viewer settings
        self.viewer.eye = (8.0, 0.0, 5.0)
        # simulation settings
        self.sim.dt = 1 / 120

It shows the following error if both the robotiq gripper and robot arm are articulation roots:

2024-01-21 23:56:04 [15,490ms] [Error] [carb.events.python] RuntimeError: Failed to find a single articulation root when resolving '/World/envs/env_.*/Robot'. Found roots '[Usd.Prim(</World/envs/env_0/Robot/UR10e>), Usd.Prim(</World/envs/env_0/Robot/robotiq_arg2f_85_model>)]' under '/World/envs/env_0/Robot'.

It shows the following error if I remove the seperate articulation roots while set the Root path as the articulation root:

2024-01-21 23:11:42 [17,913ms] [Error] [omni.physx.tensors.plugin] Pattern '/World/envs/env_*/Robot/(base_link|base|base_link_inertia|shoulder_link|upper_arm_link|forearm_link|wrist_1_link|wrist_2_link|wrist_3_link|flange|tool0|robotiq_arg2f_base_link|left_outer_knuckle|left_inner_knuckle|right_inner_knuckle|right_outer_knuckle|left_outer_finger|right_outer_finger|left_inner_finger|right_inner_finger|left_inner_finger_pad|right_inner_finger_pad)' did not match any rigid bodies

2024-01-21 23:11:42 [17,913ms] [Error] [carb.events.python] AttributeError: 'NoneType' object has no attribute 'prim_paths'

Does anyone have idea how to mount such a gripper on the robot properly so that it can be parsed by the InteractiveSceneCfg class properly?

[SantiDiazC]

Hi, I'm trying a similar thing as you describe in your case, I set the robot config as:

UR5_ROBOTIQ_CFG = ArticulationCfg(
    spawn=sim_utils.UsdFileCfg(
        # usd_path= get_assets_root_path() + "/Isaac/Robots/UniversalRobots/ur5/ur5.usd",
        usd_path = "/home/hri-david/Omniverse/Orbit/Santi_tests/assets/ur5_robotiq_2f_140.usd",
        rigid_props=sim_utils.RigidBodyPropertiesCfg(
            disable_gravity=False,
            max_depenetration_velocity=5.0,
        ),
        activate_contact_sensors=False,
    ),
    init_state=ArticulationCfg.InitialStateCfg(
        joint_pos={
            "shoulder_pan_joint": 0.0,
            "shoulder_lift_joint": -1.712,
            "elbow_joint": 1.712,
            "wrist_1_joint": 0.0,
            "wrist_2_joint": 0.0,
            "wrist_3_joint": 0.0,
            "body_f1_.*": 0.0,
            "f1_f2_.*": 0.0,
        },
    ),
    actuators={
        "shoulder": ImplicitActuatorCfg(
            joint_names_expr=["shoulder_.*"],
            velocity_limit=100.0,
            effort_limit=87.0,
            stiffness=800.0,
            damping=40.0,
        ),
        "elbow": ImplicitActuatorCfg(
            joint_names_expr=["elbow_joint"],
            velocity_limit=100.0,
            effort_limit=87.0,
            stiffness=800.0,
            damping=40.0,
        ),
        "wrist": ImplicitActuatorCfg(
            joint_names_expr=["wrist_.*"],
            velocity_limit=100.0,
            effort_limit=87.0,
            stiffness=800.0,
            damping=40.0,
        ),
        "gripper_out": ImplicitActuatorCfg(
            joint_names_expr=["body_f1_.*"],
            velocity_limit=100.0,
            effort_limit=87.0,
            stiffness=800.0,
            damping=40.0,
        ),
        "gripper_in": ImplicitActuatorCfg(
            joint_names_expr=["f1_f2_.*"],
            velocity_limit=100.0,
            effort_limit=87.0,
            stiffness=800.0,
            damping=40.0,
        ),
    },
)

and my usd file hierarchy is:

However, I have a similar error as you:

2024-04-03 12:13:35 [12,858ms] [Error] [carb.events.python] RuntimeError: Failed to find a single articulation root when resolving '/World/Origin4/Robot/ur5'. Found roots '[]' under '/World/Origin4/Robot/ur5'.

At:
  /home/hri-david/Omniverse/Orbit/source/extensions/omni.isaac.orbit/omni/isaac/orbit/assets/articulation/articulation.py(487): _initialize_impl
  /home/hri-david/Omniverse/Orbit/source/extensions/omni.isaac.orbit/omni/isaac/orbit/assets/asset_base.py(255): _initialize_callback
  /home/hri-david/Omniverse/Orbit/source/extensions/omni.isaac.orbit/omni/isaac/orbit/assets/asset_base.py(92): <lambda>
  /home/hri-david/Omniverse/Orbit/source/extensions/omni.isaac.orbit/omni/isaac/orbit/sim/simulation_context.py(440): render
  /home/hri-david/.local/share/ov/pkg/isaac_sim-2023.1.1/exts/omni.isaac.core/omni/isaac/core/simulation_context/simulation_context.py(889): play
  /home/hri-david/.local/share/ov/pkg/isaac_sim-2023.1.1/exts/omni.isaac.core/omni/isaac/core/simulation_context/simulation_context.py(592): initialize_physics
  /home/hri-david/.local/share/ov/pkg/isaac_sim-2023.1.1/exts/omni.isaac.core/omni/isaac/core/simulation_context/simulation_context.py(624): reset
  /home/hri-david/Omniverse/Orbit/source/extensions/omni.isaac.orbit/omni/isaac/orbit/sim/simulation_context.py(369): reset
  /home/hri-david/Omniverse/Orbit/Santi_tests/test_robot_manipulator.py(173): main
  /home/hri-david/Omniverse/Orbit/Santi_tests/test_robot_manipulator.py(182): <module>

I wonder if you find a solution to make it work,

Thank you in advance!