10/29/08 15-494 Cognitive Robotics 1State Machines15-494 Cognitive RoboticsDavid S. Touretzky &Ethan Tira-ThompsonCarnegie MellonSpring 200810/29/08 15-494 Cognitive Robotics 2Robot Control Architectures●State machines are the simplest and most widely used robot control architecture.●Easy to implement; easy to understand.●Not very powerful:–Action sequences must be laid out in advance, as a series of state nodes.–No dynamic planning.–Failure handling must be programmed explicitly.●But a good place to start.10/29/08 15-494 Cognitive Robotics 3Basic Idea●Robot moves from state to state.●Each state has an associated action: speak, move, etc.●Transitions triggered by sensory events or timers.10/29/08 15-494 Cognitive Robotics 4Extensions●For convenience, we can extend the basic state machine idea to make programming easier.●Extension 1: multi-states.–Several states can be active at once. –Provides for parallel processing.●Extension 2: hierarchical structure.–State machines can nest inside other state machines.–Invocation sort of like a subroutine call.10/29/08 15-494 Cognitive Robotics 5Tekkotsu State Nodes●In Tekkotsu, state machine nodes are behaviors.●StateNode is a child of BehaviorBase.●To enter a state, call its DoStart() method.●To leave a state, call its DoStop() method.●StateNodes can listen for and process events just like any other behavior.10/29/08 15-494 Cognitive Robotics 6Types of State NodesBehaviorBaseStateNodeMCNode<T>MotionSequenceNodeWalkToTargetNodeSoundNodeLedNode WalkEngineNodeTailWagNode10/29/08 15-494 Cognitive Robotics 7Transitions●Transitions in Tekkotsu are also behaviors.–Transition and StateNode are both subclasses of BehaviorBase.●A transition's DoStart() is called whenever its source state node becomes active.●Transitions listen for sensor, timer, or other events, and when their conditions are met, they fire.●When a transition fires, it deactivates its source node(s) and activates its target note(s).10/29/08 15-494 Cognitive Robotics 8Transition TypesRandomTransLostTargetTransSmoothCompareTrans<T>10/29/08 15-494 Cognitive Robotics 9Programs As State MachinesYour program is the parent StateNode:#include “Behaviors/StateNode.h”#include “Behaviors/Nodes/SoundNode.h”#include “Behaviors/Transitions/CompletionTrans.h”#include “Behaviors/Transitions/EventTrans.h”#include “Behaviors/Transitions/TimeOutTrans.h”class DstBehavior : public StateNode {public: DstBehavior() : StateNode("DstBehavior") {}10/29/08 15-494 Cognitive Robotics 10Setup and Teardown●Programs must include a setup() function to construct the state machine as a child of the parent state node.●setup() is called automatically the first time the parent's DoStart() is called.●Each node created by setup() must be registered with the parent using the addNode() method.●Transitions are registered with their source nodes.●A teardown() function is automatically provided to destroy the state machine. Called by ~StateNode().10/29/08 15-494 Cognitive Robotics 11Setup Examplevirtual void setup() { StateNode::setup(); cout << getName() << " setting up the state machine." << endl; SoundNode *bark_node = new SoundNode("bark","barkmed.wav"); SoundNode *howl_node = new SoundNode("howl","howl.wav"); StateNode *wait_node = new StateNode("wait"); addNode(bark_node); addNode(howl_node); addNode(wait_node); EventTrans *btrans = new EventTrans(wait_node, EventBase::buttonEGID, RobotInfo::HeadFrButOffset, EventBase::activateETID); btrans->setSound("ping.wav"); bark_node->addTransition(btrans); bark_node->addTransition(new TimeOutTrans(howl_node,5000)); howl_node->addTransition(new CompletionTrans(wait_node)); wait_node->addTransition(new TimeOutTrans(bark_node,15000)); startnode = bark_node; }10/29/08 15-494 Cognitive Robotics 12Parent's DoStart and DoStop virtual void DoStart() { cout << getName() << " is starting up." << endl; StateNode::DoStart(); } virtual void DoStop() { StateNode::DoStop(); cout << getName() << " is shutting down." << endl; }private: // Dummy functions to satisfy the compiler DstBehavior(const DstBehavior&); DstBehavior& operator=(const DstBehavior&);10/29/08 15-494 Cognitive Robotics 13State Machine Events●Entering or leaving a state generates a stateMachineEGID event.–activateETID for entering–deactivateETID for leaving●Firing of a transition generates a stateTransitionEGID event.●You can use the Tekkotsu Event Logger to monitor these events: Root Control > Status Reports > Event Logger10/29/08 15-494 Cognitive Robotics 14Multi-State Machines10/29/08 15-494 Cognitive Robotics 15Blink Using LedEngine::cycle()●The cycle() motion command never completes.●When the howl completes, we want to leave both the howl state and the blink state.●We can do this by telling CompletionTrans that only one of its source nodes needs to signal a completion in order for the transition to fire.●When it does fire, it will deactivate both source nodes.10/29/08 15-494 Cognitive Robotics 16Setting Up the Blink#include “Behaviors/Nodes/LedNode.h”LedNode *blink_node = new LedNode(“blink”);addNode(blink_node);blink_node->getMC()->cycle(RobotInfo::FaceLEDMask,1500,1.0);TimeOutTrans *htrans = new TimeOutTrans(howl_node,5000);htrans->addDestination(blink_node);bark_node->addTransition(htrans);CompletionTrans *ctrans = new CompletionTrans(wait_node,1);howl_node->addTransition(ctrans);blink_node->addTransition(ctrans);htrans ctrans10/29/08 15-494 Cognitive Robotics 17Cleaning Up the Blink:Turn Face LEDs OffLedNode *noblink = new LedNode(“noblink”);noblink->getMC()->set(RobotInfo::FaceLEDMask, 0.0);noblink->setPriority(MotionManager::kBackgroundPriority);StateNode *launcher = new Statenode(“launcher”);NullTrans *ntrans = new NullTrans(bark_node);ntrans->addDestination(noblink);launcher->addTransition(ntrans);10/29/08 15-494 Cognitive Robotics 18Shorthand Notation●Node definition:nodename: NodeClass(constructor_args)[initializers]●Transition definition: source >==Transition==> targetsourcenode >== transname: TransitionClass(constructor_args)[initializers] ==> targetnode●Multiple sources/targets:source >==Transition==> {targ1name, targ2name, ...}●10/29/08 15-494 Cognitive Robotics 19$ and $$●Use $ to refer to the name of the current node or transition, e.g., these are equivalent:foo: Statenode --- foo: StateNode($) bar: SoundNode($,”howl.wav”)foo: