F/T Sensors in Isaac Sim

Omniverse Isaac Sim
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1

Hello everyone,

I have recently added a force/torque sensor to my cobot .usd file in Isaac Sim. Thus, I can read the forces applied to it through forces = db.state.robot.get_measured_joint_forces() (checked Articulation State — Isaac Sim and Articulation Joint Sensors — Isaac Sim Documentation ).

The Python script I wrote is as follows:

import omni.graph.core as og
from omni.isaac.core.articulations import Articulation
from omni.isaac.core.utils.prims import get_prim_at_path

def setup(db: og.Database):
    # Crear el articulation del robot
    db.state.robot = Articulation("/World/xarm6")

    # Joint del sensor
    # sensor_joint_prim_path = "/UF_ROBOT/TorqSensor/ft_sensor_root_joint"
    sensor_joint_prim_path = "/World/JoinedTorqueSensor/FixedJoint_TorqueSensor_Link6"
    sensor_joint_prim = get_prim_at_path(sensor_joint_prim_path)
    sensor_joint_name = sensor_joint_prim.GetName()

    # Metadata del articulation
    metadata = db.state.robot._articulation_view._metadata
    joint_indices = metadata.joint_indices
    joint_names = metadata.joint_names

    # Índice interno de la joint
    sensor_joint_index = joint_indices[sensor_joint_name]

    print("Joint indices: ", joint_indices)
    print("Joint names: ", joint_names)
    print("sensor_joint_prim_path: ", sensor_joint_prim_path)
    print("sensor_joint_name: ", sensor_joint_name)
    print("sensor_joint_index: ", sensor_joint_index)

    # Fila real en get_measured_joint_forces()
    db.state.row_index = sensor_joint_index + 1

    db.log_info(f"F/T sensor joint: {sensor_joint_name}, row index: {db.state.row_index}")

    # db.state.initialized = True

def compute(db: og.Database):
    # if not db.state.initialized:
    #    setup(db)
    
    # Leer fuerzas cada frame
    forces = db.state.robot.get_measured_joint_forces()
    fx, fy, fz, tx, ty, tz = forces[db.state.row_index]

    # Output double[6]
    #db.outputs.Forces = [float(fx), float(fy), float(fz),
    #                     float(tx), float(ty), float(tz)]

    db.outputs.Fx = fx
    db.outputs.Fy = fy
    db.outputs.Fz = fz
    db.outputs.Tx = tx
    db.outputs.Ty = ty
    db.outputs.Tz = tz

    return True


def cleanup(db: og.Database):
    db.log_info("F/T Script Node cleaned up")

def cleanup(db: og.Database):
    db.state.robot = None
    db.state.row_index = None
    # db.state.initialized = False
    db.log_info("F/T Script Node cleaned up")

And that Python script is run inside an OmniGraph as shown in the following screenshot:

imagen
imagen1920×1080 261 KB

However, after the simulation runs for the first time, I have to click on “Reload script” within the “Script node” block for it to work again. Otherwise, the warning 2026-03-02 07:30:47 [Warning] [isaacsim.core.prims.impl.articulation] Physics Simulation View is not created yet in order to use get_measured_joint_forces appears, and when I read the values, I get the last values read from the first simulation run and not those corresponding to the current run.

Has anyone else encountered this situation, and how did you resolve it? Having to click on reload script every time the execution is launched is tedious, considering that there may be several action graphs where you have to click.

2

Closing this topic as a duplicate of F/T Sensor (force/torque sensor) · isaac-sim/IsaacSim · Discussion #513 · GitHub. We will continue the conversation and share updates that discussion.