Overview

The Behavior Engine (BE) is a layer for development, execution, and monitoring of robot behaviors.

Information on the ROS port of the BE can be found at ​http://www.ros.org/wiki/behavior_engine.

The general idea is to have a fawkes thread maintain a user-defined hybrid state machine which is implemented in a ​LUA framework. The current state is maintained in the fawkes thread, which periodically re-evaluates transition conditions and advances the state accordingly. The BE is split into a purely reactive layer (the Skiller) and a higher-level layer (the Agent), which is meant to implement long-shot and strategic decisions. The main difference between them is the agent's ability to execute multiple skills concurrently in a single state. For a more in-depth conceptual description of the BE see ​this presentation.

The ​luadoc for the entire BE is currently in the GIT branch containing the new skiller backported from ROS.

Papers

Developing A Behavior Engine for the Fawkes Robot-Control Software and its Adaptation to the Humanoid Platform Nao

Diploma thesis describing the original Behavior Engine for Fawkes and its design principles.

A Lua-based Behavior Engine for Controlling the Humanoid Robot Nao

Conference paper describing the BE more concise, but less practical.

HERB 2.0: Lessons Learned from Developing a Mobile Manipulator for the Home

Journal article describing the bi-manual mobile manipulator HERB 2.0. Section V describes the BE ported to ROS.

Skills

Skills are aggregated into a common Skillspace, which needs to be defined in the /skiller/skillspace setting, for example:

INSERT INTO "config" VALUES('/skiller/skillspace','string','test','Skill space');

The skillspace is then initialized as a LUA module with the regular search order, usually in src/lua/skills. Since a skillspace will normally be comprised of multiple skills, it's common practice to put the skillspace module into a folder, e.g. src/lua/skills/test/, containing an init.lua which pulls in the other skill modules, e.g.:

-- init.lua: require all skill modules. Make sure the load order reflects their dependencies.
require('testskill')
require('some_skill_depending_on_testskill')
-- [...]

Each skill module requires a header which initializes it and defines dependencies:

module(..., skillenv.module_init)
name               = "fetch_puck"
fsm                = SkillHSM:new{name=name, start="INITIAL_STATE", debug=true}
depends_skills     = { "some_skill", "some_other_skill" -- [...]
}
depends_interfaces = {
   {v = "skill_variable_representing_interface", type="IfaceClassName", id="iface_config_id"}
   -- [...]
}

documentation      = [==[This is displayed in the skillgui.
Explain parameter names and their meaning.]==]

skillenv.skill_module(_M)

State types with their required and optional arguments:

State Class	Required Args	Optional Args
JumpState?	none	timeout
SkillJumpState	skills, final_to	fail_to