Inventing Hybrid Control The basic idea is simple: we want the best of both worlds (if possible). The goal is to combine closed-loop and open-loop execution. That means to combine reactive and deliberative control. This implies combining the different time-scales and representations. This mix is called hybrid control. Hybrid robotic architectures believe that a union of deliberative and behavior-based approaches can potentially yield the best of both worlds.

Strategic Global Planning Tactical Intermediate Planning Short-Term Local Planning Actuator Control Actions Global Knowledge Local World Model Intermediate Sensor Interpretations Sensing Real - Time Time Horizon Long - Term Spatial Scope Global Immediate Vicinity Hierarchical Planner World Model 4

Organizing Hybrid Systems Planning and reaction can be tied: A: hierarchical integration - planning and reaction are involved with different activities, time scales Level N Level 2 Level 1 Level 0 More Reactive More Deliberative A Deliberation  Projection Planner Reactor B Behavioral Advice Configurations Parameters B: Planning to guide reaction - configure and set parameters for the reactive control system. C: coupled - concurrent activities PlannerReactor C 11

Example: AuRA R. Arkin (1986)  Planning is viewed as configuration.  Initial A* planner integrated with schema-based controller.  Provides modularity, flexibility, and adaptability. LearningUser Input Plan Recognition User Profile User Intentions Spatial LearningSpatial Goals Opportunism ( סתגלנות ) On-line Adaptation Teleautonomy Mission Alterations Mission Planner Spatial Reasoner Plan Sequencer RE PRE SEN TA TI ON Schema Controller Motor Perceptual ActuationSensing Hierarchical Component Reactive Component 23

Example: Atlantis  E. Gat (1991)  Three layers: controller, sequencer, deliberator.  Asynchronous, heterogeneous: reactivity and deliberation  Planning as advice giving, not as command.  Tested on NASA rovers. Control SensorsActuators Deliberative Sequencing Results ActivationStatus Invocation 26

Example: AuRA R. Arkin (1986)  Planning is viewed as configuration.  Initial A* planner integrated with schema-based controller.  Provides modularity, flexibility, and adaptability. LearningUser Input Plan Recognition User Profile User Intentions Spatial LearningSpatial Goals Opportunism ( סתגלנות ) On-line Adaptation Teleautonomy Mission Alterations Mission Planner Spatial Reasoner Plan Sequencer RE PRE SEN TA TI ON Schema Controller Motor Perceptual ActuationSensing Hierarchical Component Reactive Component 23

Example: Planner-Reactor D. Lyons (1992)  Continuous modification of a reactive control system (sub-optimal).  Planning is a form of reactor adaptation.  Adaptation is on-line rather than off-line deliberation.  Planning is used to remove performance errors when they occur.  Uses Robot Schema (RS) model.  Tested in both assembly cell and grasp planning. Goals Planner World Adaptation Perceptions Reactions REACTOR Action Sensing Perception 29

Planner-Reactor Adaptation: a) a reactor executes under a set of operating assumptions. b) if any assumptions are violated, the planner modifies the reactor’s control system to remove the violation. –Each assumption has a monitor associated with it during run time to ensure its validity. Reactor Performance with Monitoring Reactor Adapted by Planner and Assumptions Relaxed. Assumptions violation detected. Adapt Reactor Restore Initial Reactor. Violation assumptions Restored. Completed Initial Reactor Construction Adapt ReactorStart Execution Normal Performance 31

 Georgeff and A. Lansky (1987)  PRS = Procedural Reasoning System  Reactivity refers to postponement of the elaboration of plans until it is necessary:  a least commitment strategy.  Tested on SRI Flakey Example: PRS INTERPRETER ACTUATORSSENSORS MONITOR BELIEFS DESIRESPLANS INTENTIONS COMMAND GENERATOR OPERATOR INTRFACE 32