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.

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

"""
Runs a conveyor belt in a running Isaac Sim stage for a few seconds.

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.

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

Note:
    Open Isaac Sim before running this. A stage that does not hold the
    conveyor prim gets the bundled demo belt added to it at
    /World/simple_conveyor, keeping whatever is already in the stage; to
    build a belt of your own instead, follow
    https://docs.isaacsim.omniverse.nvidia.com/6.0.1/digital_twin/warehouse_logistics/ext_isaacsim_asset_gen_conveyor.html
    and name it with --prim_path.

    If the belt connects but never moves, check that its ``ConveyorNode``
    (in ConveyorBeltGraph i.e. OmniGraphNode) has ``inputs:enabled`` set to
    true. Add an object on top of the belt beforehand to see it carried
    along.
"""

import argparse
import time

from loguru import logger

from telekinesis.medulla.conveyors import isaacsim


def main(prim_path: str,
         cargo_root: str | None,
         velocity: float,
         run_seconds: float) -> None:
    """Runs a conveyor belt for a few seconds, then stops it."""

    # ===================== Create Conveyor ======================================
    belt = isaacsim.Conveyor(name="simulated_conveyor")
    belt.set_usd("https://assets.telekinesis.ai/usd/conveyors/simple_conveyor.zip")

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

        # ==================== Run Skill ============================================
        belt.start(velocity=velocity)
        logger.info(f"Running at {belt.velocity} m/s for {run_seconds} s.")
        time.sleep(run_seconds)

        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=0.5,
                   help="Signed speed in meters per second to run the belt at")
    p.add_argument("--run_seconds", type=float, default=3.0,
                   help="How long to run the belt before stopping")
    args = p.parse_args()

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

Running the Example

python start_and_stop.py --prim_path /World/simple_conveyor

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.