Start and Stop

SUMMARY

Start runs the belt, and wakes cargo resting under the connection's cargo_root so a box that came to rest is picked up again. Stop halts it again without changing its configured speed, so a later start() with no velocity resumes at that same speed.

Available on: IsaacSim Conveyor.

The Skill

belt.start()
belt.stop()

Pass a signed speed to override the belt's own configured speed; negative runs the belt backwards along its installed travel direction:

belt.start(velocity=0.5)

The Code

"""
Demonstrates starting and stopping a conveyor belt in a running Isaac Sim
stage.

Supports Isaac Sim only. The belt runs at the speed the scene authored
unless ``start()`` is given one, and a negative speed runs it backwards. It
keeps that speed once stopped, so starting it again without a velocity
resumes at the same speed.

Usage:
    python start_and_stop.py --prim_path <PRIM_PATH>
    python start_and_stop.py --prim_path <PRIM_PATH> --velocity -0.5
    python start_and_stop.py --prim_path <PRIM_PATH> --load_usd

Note:
    Open Isaac Sim and add a conveyor prim before running this. If there is
    none in the stage yet, follow
    https://docs.isaacsim.omniverse.nvidia.com/6.0.1/digital_twin/warehouse_logistics/ext_isaacsim_asset_gen_conveyor.html
    to create one, or pass --load_usd to add one to the open stage -- this
    keeps whatever is already in the stage. If the belt connects but never
    moves, check that its ``ConveyorNode`` has ``inputs:enabled`` set to
    true. Add an object on top of the belt beforehand to see it carried
    along.
"""

import argparse

from loguru import logger

from telekinesis.medulla.conveyors import isaacsim


def main(prim_path: str, cargo_root: str | None, velocity: float | None,
         load_usd: bool) -> None:
    """Starts a conveyor belt, then stops it."""

    if load_usd:
        # ===================== Load Demo Scene (Optional) ===========================
        from telekinesis import datatypes, isaacsim_client

        client = isaacsim_client.IsaacSimClient(
            api_key="",
            base_url="http://127.0.0.1:8766",
            websocket_base_url="ws://127.0.0.1:8766",
        )
        asset = datatypes.USD.from_url(
            "https://assets.telekinesis.ai/usd/conveyors/simple_conveyor.zip"
        )
        client.stage.add_to_scene(uri=asset.path.as_posix(),
                                  prim_path="/World/simple_conveyor")

    # ===================== Create Conveyor ======================================
    belt = isaacsim.Conveyor(name="my_simulated_conveyor")

    try:
        # ===================== Connect Conveyor ==================================
        belt.connect(simulation_prim_path=prim_path, cargo_root=cargo_root)

        # ==================== Run Skill ============================================
        belt.start(velocity=velocity)
        logger.success(f"Running at {belt.velocity} m/s. Running: {belt.is_running}.")

        belt.stop()
        logger.success(f"Stopped. Running: {belt.is_running}.")
    except (ConnectionError, RuntimeError) as e:
        logger.error(f"Error occurred: {e}")
    finally:
        belt.disconnect()


if __name__ == "__main__":
    p = argparse.ArgumentParser(description="Start and stop a conveyor belt in Isaac Sim")
    p.add_argument("--prim_path", type=str, default="/World/simple_conveyor",
                   help='Isaac Sim conveyor prim path, e.g. "/World/simple_conveyor"')
    p.add_argument("--cargo_root", type=str, default="/World",
                   help="USD path whose rigid bodies are woken when the belt starts")
    p.add_argument("--velocity", type=float, default=None,
                   help="Signed speed in meters per second to run the belt at. "
                        "Defaults to the belt's own configured speed")
    p.add_argument("--load_usd", action=argparse.BooleanOptionalAction, default=False,
                   help="Add the bundled demo conveyor to the open stage at "
                        "/World/simple_conveyor before connecting. Use this "
                        "if you don't already have one in the stage.")
    args = p.parse_args()

    main(prim_path=args.prim_path, cargo_root=args.cargo_root, velocity=args.velocity,
         load_usd=args.load_usd)

Running the Example

python start_and_stop.py --prim_path /World/simple_conveyor

To load the bundled demo conveyor into the stage first:

python start_and_stop.py --load_usd

For all options:

python start_and_stop.py --help

Parameter Configuration

start

Parameter	Type	Default	Description
velocity	float | None	None	Signed speed in meters per second along the belt's installed travel direction; negative runs the belt backwards. None runs it at the belt's own configured speed.

stop

Takes no parameters.

Returns

Method	Type	Description
start	None	Returns nothing.
stop	None	Returns nothing.

Raises

Method	Exception	Condition
start	RuntimeError	The conveyor is not connected, or the belt rejects the command.
stop	RuntimeError	The conveyor is not connected, or the belt rejects the command.

Where to Use the Skill

Start and Stop require an active connection — see Connection and Disconnection.