Behavior Executor - NVIDIA Docs

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Isaac AMR Behavior Executor

The behavior executor is responsible for coordination of on-robot behaviors.

Overview

It receives and processes mission actions from the on-robot mission client. It then uses a behavior tree to manage downstream modules like path planner to realize specific behaviors needed to accomplish missions. It also monitors important health signals such as, the localization health, and feedback from planners to decide the robot’s mode of operation.

Inputs

PoseTree: This library provides the pose frame transform queries.
Action: The relevant actions from the currently being executed mission from mission control.
Localization Result: The assessment of localization quality as either good or bad.
Path Planner Health: The status of path planner’s last cycle as success or failure, plus contextual information.
Trajectory Solver Status: The status of trajectory planner solver, indicating relevant failures if any.
Semantic regions: Relevant semantic regions, i.e. navigable surfaces and regions of interest, for passing down to the planners.

It also loads up a behavior tree from file, using nodes implemented in the manager component described hereinafter.

Outputs

Planner Operation Mode: The selected mode for path planner to operation on, including whether to idle.
Route Request: When necessary a request for the onboard route planner to generate a new route.
Maneuver: The local planning task, sent to regional path planner and the speed decision maker.
Action Feedback: Collected feedback detailing the status of execution of the action received from mission client.
Localization Reset Signal: Signal to reset localization when needed, e.g. when map changes
Route Planner Reset Signal: Signal to reset onboard route planner when needed, e.g. when map changes
Map Republish Signal: Signal to request publishing of maps after loading of new tiles.
Entity Enablers/Disablers: Set of enabler/disablers for certain modules (RPP, TP, SDM, etc)

Core Components

The module is implemented using a collection of Graph eXecution Format (GXF) components, each in charge of key decision making aspect. These include:

Planner Manager

Responsible for consuming and processing feedback from path and trajectory planners, and deciding which operation mode to run next. It uses the planner health and trajectory solver status as inputs and generate planner operation mode as output.

Action Manager

Receives and processes actions from the mission client. It also checks for changes in the goal pose transform to update the target goal if necessary. Internally it decides when the robot has reached the goal, and requests for new routes when needed.

System Health Manager

Receives health signals and determines if the robot can navigate or not. For example, when the localization result indicates bad localization, the robot is set to idle. Also resets localization when needed.

Entity Enabler

Defined behavior tree nodes that allows GXF codelets to be enabled or disabled. When disabled, codelet ticking is stopped, and on resumption of ticking, the start method is called before continuing with ticking.

Autonomy Level Manager

Handles switching between autonomy levels, i.e. manual, teleoperation and autonomous. Useful for integration with remote controllers, and a deadman switch mechanism.

Maneuver Generator

Uses the route waypoints to construct a polyline, thereby building a Frenet coordinate frame. It then uses the robot’s position and regional planning horizon to slice a portion of the route polyline. It then constructs a maneuver using the waypoints in this slice and optionally, semantic objects. This maneuver repesents the next task for the regional planners. The goal is taken at the projection of the robot’s horizon onto the polyline.

Map Manager

Responsible to coordinating map (tile) loading and map changes. When a new request to load a map is received, it disables map-dependent codelets, asks Map Loader to load the new map, resets localization, and then finally enabled the codelets again. The flow of data is shown below

sequenceDiagram Behavior Executor->>+Map Loader: LoadTileRequest Map Loader-->>-Behavior Executor: LoadTileResult Behavior Executor->>+Localization: Reset Signal Localization-->>-Behavior Executor: Localization Result

Behavior Tree

The coordination of behavior is realized using a behavior tree, loaded from XML files at startup. This behavior tree is implemented using the popular behaviortreecpp library. The files are split to represent functional subtrees. For example, the subtree to check and make sure there is a route before running path and trajectory planners is shown below.

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            <root BTCPP_format="4">
  <BehaviorTree ID="SUBTREE_pre_planning_checks">
    <Sequence>
      <!-- Localization must be ready and good -->
      <Condition ID="localizationIsReady" name="CONDITION_localization_is_good?"/>
      <Fallback name="FALLBACK_check_route_or_request_one">
        <!-- Either a route is already available -->
        <Condition ID="newRouteAvailable" name="CONDITION_route_available?"/>
        <!-- Else, request one -->
        <Action ID="requestNewRouteOnBoard" name="ACTION_request_new_route"/>
      </Fallback>
    </Sequence>
  </BehaviorTree>
</root>

The nodes used in the trees are implemented in the components described above. The tree is loaded and ticked from the main behavior executor codelet. As a convention we prepend node type information in the node names, e.g. ACTION_doSomething to make it easy to read the tree when rendered on the terminal.

GXF

All the components above are put together in the behavior executor codelet. This codelet takes as inputs, the above components and a filename for the behavior tree to load. For example,

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             # Setup components, input and output channels
 #...
- name: behavior_executor
  type: nvidia::isaac::BehaviorExecutor
  parameters:
    managers:
      - system_health_manager
      - planner_manager
      - action_manager
      - classical_egm_enabler
      - map_manager
      - rpp_enabler
      - sdm_enabler
      #- MODULE_X_enabler
    feedback_collector: feedback_collector
    behavior_tree_file: "{PATH_TO_TREE_FILES}/navigation_classic.xml"
    save_tree_nodes: false  # Save tree models for use with Groot2 behavior tree visualization tool
    use_tile_loader: false  # Load map tiles dynamically on demand
    execution_time: execution_metrics/execution_time
 - type: nvidia::gxf::PeriodicSchedulingTerm
   parameters:
     recess_period: 2hz
 # ...
 # Additional component like metrics

API Documentation

NvIsaacBehaviorExecutorExtension

Extension containing behavior execution module.

nvidia::isaac::behavior_execution::Maneuver

Holds a maneuver send from behavior executor to path planner.

Parameters:

nvidia::isaac::MessageCache

A component that handles localization result input.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::BehaviorManager

A generic behavior manager.

Parameters:

nvidia::isaac::SystemHealthManager

A behavior tree component that checks localization status.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::MessageCache

A component that handles the route input.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::MessageCache

A component that handles action input.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::MessageCache

A component that handles load tile requests.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::MessageCache

A component that handles load tile results.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::ActionManager

A behavior tree component that manages the processing of actions from mission client.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
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type
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name
lookup_name
description
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type
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name
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description
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type
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name
lookup_name
description
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type
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name
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description
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type
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name
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type
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name
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name
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type
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name
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type
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name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::MessageCache

A component that handles path planner health input.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::PlannerManager

A behavior tree component that manages the path planner.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
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name
lookup_name
description
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type
default

name
lookup_name
description
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type
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name
lookup_name
description
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type
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name
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description
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type
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name
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type
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name
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type
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name
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description
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type
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name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::MapManager

A behavior tree component that manages map loading and usage.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::FeedbackCollector

A component that collects feedback from the navigation stack and publishing to the mission client.

Parameters:

name
lookup_name
description
flags
type
default

nvidia::isaac::EntityManager

A behavior tree manager that allows to dis-/enable an entity.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::AutonomyLevelManager

A component that manages the remote control.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::LocalActionGenerator

Codelet that translates local routes into actions.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

nvidia::isaac::BehaviorExecutor

The executor for the navigation behavior tree.

Parameters:

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default

name
lookup_name
description
flags
type
default