[Question] Gripper disassembly

[jsbae-RL]

Hello. I am trying to do reinforcement learning using iassac lab. Before starting reinforcement learning, I am working on checking if the movement is appropriate. So I created a custom usd (manipulator), and when I ran the python code below, the gripper was disassembled. I will attach the actual gripper image on rviz2. Please help me with the problem.

---------------------------------python code---------------------------------
import argparse
from isaaclab.app import AppLauncher

parser = argparse.ArgumentParser(description="M0609 roboto + RG2 gripper control")
parser.add_argument("--num_envs", type=int, default=1, help="num env")
AppLauncher.add_app_launcher_args(parser)
args_cli = parser.parse_args()

app_launcher = AppLauncher(args_cli)
simulation_app = app_launcher.app

import numpy as np
import isaaclab.sim as sim_utils
from isaaclab.actuators import ImplicitActuatorCfg
from isaaclab.assets.articulation import ArticulationCfg
from isaaclab.scene import InteractiveScene, InteractiveSceneCfg
from isaaclab.assets import AssetBaseCfg, RigidObjectCfg

robot

M0609_CONFIG = ArticulationCfg(
spawn=sim_utils.UsdFileCfg(
usd_path="/home/jsbae/IsaacLab/source/isaaclab_assets/data/Robots/M0609_6th/m0609.usd",
rigid_props=sim_utils.RigidBodyPropertiesCfg(disable_gravity=False),
articulation_props=sim_utils.ArticulationRootPropertiesCfg(
enabled_self_collisions=True,
solver_position_iteration_count=8,
solver_velocity_iteration_count=0,
),
),
init_state=ArticulationCfg.InitialStateCfg(
joint_pos={
"joint_1": 0.0, "joint_2": 0.0, "joint_3": 1.57,
"joint_4": 0.0, "joint_5": 1.57, "joint_6": 0.0,
"gripper_joint": 0.0,
"r_finger_1_joint": 0.0, "l_finger_2_joint": 0.0,
"r_finger_2_joint": 0.0, "l_finger_passive_joint": 0.0,
"r_finger_passive_joint": 0.0,
},
pos=(0.25, -0.25, 0.0),
),
actuators={
**{
f"joint{i}act": ImplicitActuatorCfg(
joint_names_expr=[f"joint{i}"],
effort_limit_sim=100.0, velocity_limit_sim=100.0,
stiffness=10000.0, damping=100.0,
) for i in range(1, 7)
},
"gripper_joint_act": ImplicitActuatorCfg(joint_names_expr=["gripper_joint"], stiffness=20000, damping=200),
"r_finger_1_joint_act": ImplicitActuatorCfg(joint_names_expr=["r_finger_1_joint"], stiffness=20000, damping=200),
"l_finger_2_joint_act": ImplicitActuatorCfg(joint_names_expr=["l_finger_2_joint"], stiffness=20000, damping=200),
"r_finger_2_joint_act": ImplicitActuatorCfg(joint_names_expr=["r_finger_2_joint"], stiffness=20000, damping=200),
"l_finger_passive_joint_act": ImplicitActuatorCfg(joint_names_expr=["l_finger_passive_joint"], stiffness=20000, damping=200),
"r_finger_passive_joint_act": ImplicitActuatorCfg(joint_names_expr=["r_finger_passive_joint"], stiffness=20000, damping=200),
},
)

class NewRobotsSceneCfg(InteractiveSceneCfg):
ground = AssetBaseCfg(
prim_path="/World/defaultGroundPlane",
spawn=sim_utils.GroundPlaneCfg()
)

dome_light = AssetBaseCfg(
    prim_path="/World/Light",
    spawn=sim_utils.DomeLightCfg(intensity=3000.0, color=(0.75, 0.75, 0.75))
)

m0609bot = M0609_CONFIG.replace(prim_path="{ENV_REGEX_NS}/m0609bot")

oreo = AssetBaseCfg(
    prim_path="{ENV_REGEX_NS}/oreo",
    spawn=sim_utils.CuboidCfg(
        size=(0.22, 0.052, 0.052),
        visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.0, 0.0, 1.0)),
        mass_props=sim_utils.MassPropertiesCfg(mass=0.5),
        rigid_props=sim_utils.RigidBodyPropertiesCfg(disable_gravity=False),
        collision_props=sim_utils.CollisionPropertiesCfg(),
    ),
    init_state=RigidObjectCfg.InitialStateCfg(
        pos=(0.55, -0.25, 0.15),
        rot=(0.7071, 0, 0, 0.7071),
    ),
)

plate = AssetBaseCfg(
    prim_path="{ENV_REGEX_NS}/plate",
    spawn=sim_utils.CuboidCfg(
        size=(0.4, 0.4, 0.05),
        visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(1.0, 1.0, 0.0)),
        mass_props=sim_utils.MassPropertiesCfg(mass=0.0),
        rigid_props=sim_utils.RigidBodyPropertiesCfg(disable_gravity=True),
        collision_props=sim_utils.CollisionPropertiesCfg(),
    ),
    init_state=RigidObjectCfg.InitialStateCfg(pos=(0.615, -0.25, 0.025))
)

def run_simulator(sim: sim_utils.SimulationContext, scene: InteractiveScene):
sim_dt = sim.get_physics_dt()
sim_time = 0.0
count = 0

for actuator_name, actuator in scene["m0609bot"].actuators.items():
    actuator.stiffness = 50000.0
    actuator.damping = 500.0
    actuator.effort_limit_sim = 1000.0  # force limit 충분히 크게
    actuator.velocity_limit_sim = 100.0

while simulation_app.is_running():
    # print(scene["m0609bot"].data.joint_names)

    if count % 500 == 0:
        count = 0
        root_state = scene["m0609bot"].data.default_root_state.clone()
        root_state[:, :3] += scene.env_origins

        scene["m0609bot"].write_root_pose_to_sim(root_state[:, :7])
        scene["m0609bot"].write_root_velocity_to_sim(root_state[:, 7:])
        joint_pos = scene["m0609bot"].data.default_joint_pos.clone()
        joint_vel = scene["m0609bot"].data.default_joint_vel.clone()
        scene["m0609bot"].write_joint_state_to_sim(joint_pos, joint_vel)
        scene.reset()
        print("[INFO]: Resetting m0609bot state...")

    # sinusoidal open/close control
    amp = 0.4
    freq = 0.5
    gripper_pos = amp * 0.5 * (1 + np.sin(2 * np.pi * freq * sim_time))

    joint_names = scene["m0609bot"].data.joint_names
    wave_action = scene["m0609bot"].data.default_joint_pos.clone()

    name_to_val = {
        "gripper_joint": gripper_pos,
        "r_finger_1_joint": -gripper_pos,
        "l_finger_2_joint": -gripper_pos,
        "r_finger_2_joint": gripper_pos,
        "l_finger_passive_joint": gripper_pos,
        "r_finger_passive_joint": -gripper_pos,
    }

    for name, val in name_to_val.items():
        if name in joint_names:
            idx = joint_names.index(name)
            wave_action[:, idx] = val

    scene["m0609bot"].set_joint_position_target(wave_action)
    scene.write_data_to_sim()
    sim.step()
    sim_time += sim_dt
    count += 1
    scene.update(sim_dt)

def main():
sim_cfg = sim_utils.SimulationCfg(device=args_cli.device)
sim = sim_utils.SimulationContext(sim_cfg)
sim.set_camera_view([3.5, 0.0, 3.2], [0.0, 0.0, 0.5])

scene_cfg = NewRobotsSceneCfg(args_cli.num_envs, env_spacing=2.0)
scene = InteractiveScene(scene_cfg)

sim.reset()
print("[INFO]: Setup complete...")

run_simulator(sim, scene)

if name == "main":
main()
simulation_app.close()

[RandomOakForest]

Thank you for posting this. I'll move your question to our Discussions section for follow up. In the meantime, here are a few steps to consider that may help:

1. Verify Gripper Joint Names

Your USD file's gripper joint names must exactly match the names in your code. Common issues:

# Check actual joint names in USD:
print(scene["m0609bot"].data.joint_names)  

• If names differ (e.g., "gripper_joint" vs "RG2_gripper_joint"), update name_to_val dictionary and init_state accordingly.

2. Simplify Gripper Control

Most robotic grippers use 1 DOF control (not individual finger joints). Modify your control logic:

# Replace name_to_val with this simplified version:
name_to_val = {"gripper_joint": gripper_pos}  # Control only the main actuator

# Remove finger/passive joint actuators from M0609_CONFIG:
actuators={
    **{f"joint{i}act": ... for i in range(1,7)},  # Arm joints
    "gripper_act": ImplicitActuatorCfg(  # Single actuator
        joint_names_expr=["gripper_joint"], 
        stiffness=20000, 
        damping=200
    )
}

3. Check USD File Structure

Open your USD in Isaac Sim's Scene Inspector:

1. Ensure gripper meshes are child prims of the robot's end-effector link
2. Verify joints connect links correctly (e.g., gripper_joint should parent to arm_link_6)

4. Adjust Physics Settings

Add solver stabilization to M0609_CONFIG:

articulation_props=sim_utils.ArticulationRootPropertiesCfg(
    enabled_self_collisions=True,
    solver_position_iteration_count=32,  # Increase for stability
    solver_velocity_iteration_count=4,
    stabilization_threshold=0.001,  # Add this line
),

[jsbae-RL]

Thank you for your detailed answer.
I have a few additional questions.

• First, I have checked several times whether the names are the same for item 1. Therefore, I am sure that they are the same names.

• In my project, I am using urdf converted to usd file. At this time, the gripper gripper is configured separately on the right and left in urdf, and this gripper is connected to mimic. However, isaaclab confirmed that this setting is released when mimic is used. Therefore, I removed mimic from urdf and converted it to usd. (I decided that it is safer to delete mimic from urdf.) Even if I applied it like this, can I simplify gripper control?

• In case 3, there may be an error in the process of converting urdf to usd, so I will check and leave a post on this issue.

• I will also add 4 and check.