014 Robot Control Architectures

Information about 014 Robot Control Architectures

Published on May 2, 2008

Author: Jolene

Source: authorstream.com

Content

Artificial Intelligence versus classical Robotics:  Artificial Intelligence versus classical Robotics All robot control architectures are build on some ideas of Artificial Intelligence They form also, what the AI considered now, in contrast to classical AI AL is the best example Robot control architectures Is AI Engineering or Science?:  Is AI Engineering or Science? Construction ==> Engineering all scientific problems solved representative: Feigenbaum Science more scientific principles to be discoverer representative: McCarthy Is Robotics Engineering or Science? What is a robot? More definitions….:  What is a robot? More definitions…. An intelligent robot is a machine able to extract information from its environment and use knowledge about its world to move safely in a meaningful and purposeful manner. A robot is a system which exists in the physical world and autonomously senses its environment and acts in it. Robotics is the intelligent connection of perception to action (M. Brady) Slide4:  Alternative terms we will use: UAV: unmanned aerial vehicle UGV: unmanned ground vehicle UUV: unmanned undersea vehicle What makes a robot? sensors effectors/actuators locomotion system on-board computer system controllers for all of the above (smart methods everywhere) How these definitions relate to AI? Compare to classical robot definitions. Sensing::  Sensing: What can be sensed? depends on the sensors on the robot the robot exists in its sensor space (i.e., all possible values of its sensory readings, also called perceptual space) robotic sensors are very different from biological sensors; a designer needs to put his mind into the robot's sensor space a roboticist has to try to imagine the world in the robot’s sensor space What needs to be sensed?:  What needs to be sensed? depends on the robot's task State: a sufficient description of the system:  State: a sufficient description of the system observable: the robot knows its state at all times hidden/inaccessible/unobservable: the robot does not know its state partially-observable: the robot knows some part of its state discrete (e.g., up, down, blue, red) or continuous (e.g., 3.765 mph) State space: all the states a system can be in External state: state of the world night/day, raining/sunny, at home, etc. sensed using the robot's sensors Internal state: state of the robot:  Internal state: state of the robot happy/sad, stalled/moving, battery level, velocity, etc. can be sensed (e.g., velocity) can be stored/remembered (e.g., happy/sad) The robot's state is a combination of its external and internal state. How intelligent the robot appears will strongly depend on how much and quickly it can sense its environment and itself. We will talk more about sensors in next lectures. Internal state can be used to remember information about the world (e.g., remember paths to the goal, remember maps, remember friends versus enemies, etc.) This is called a representation or an internal model. Representations/models have a lot to do with how complex a controller is! Acting::  Acting: A robot acts through the use of its actuators, also called effectors Robotic actuators are very different from biological ones, both are used for: locomotion (moving around, going places) manipulation (handling objects) This divides robotics into three areas: mobile robotics manipulator robotics communication robotics (theatre, toys) Acting::  Acting: Action versus Behavior : Behavior is what an external observer sees a robot doing. Robots are programmed to display desired behavior. Behavior is a result of a sequence of robot actions. Observing behavior may not tell us much about the internal control of a robot. Control can be a black box. Mobile robots can move around, using wheels, tracks, or legs, and usually move in 2-dimensions. However, swimming and flying robots are also mobile robots, and they move in 3-dimensions (and are therefore even harder to control) Manipulators are various robot arms; they can move in 1 or more dimensions. the number of dimensions are called the robot's degrees of freedom (DOF). we will learn much more about actuators/effectors later. Autonomy::  Autonomy: What is autonomy? the ability to make one's own decisions and act on them for robots, the ability to sense the situation and act on it appropriately Autonomy can be complete, as in autonomous robots, or partial, as in tele-operated robots. examples of autonomous robots: R2D2 examples of tele-operated robots: NASA's robots before Pathfinder Exo-skeletons are not robots, according to our definition. (E.g., Ripley's exo-skeleton in the movie Alien.) Fundamentals of Robot Control Architectures:  Fundamentals of Robot Control Architectures Distinguish the classical control used in robots and the Robot Control Architectures that have more to do with AI Control::  Control: Robot control refers to the way in which the sensing and action of a robot are coordinated. The many different ways in which robots can be controlled all fall along a well-defined spectrum of control. Control Approaches: Reactive Control : Don’t think, (re)act. Behavior-Based Control : Think the way you act. Deliberative Control : Think hard, act later. Hybrid Control : Think and act independently, in parallel. Control Trade-offs::  Control Trade-offs: Thinking is slow. Reaction must be fast. Thinking enables looking ahead (planning) to avoid bad solutions. Thinking too long can be dangerous (e.g., falling off a cliff, being run over). To think, the robot needs (a lot of) accurate information => world models. Food for Thought::  Food for Thought: Many robots you build in this class will use reactive control. What more can you build on top of it? Your dream robot?! Are exo-skeletons (e.g., Ripley’s in the movie Alien) robots? Is HAL (in the movie 2001) a robot? Some intelligent Web agents are called "softbots". Are they robots? Please review::  Please review: 1. The concept of a Finite State Machine (a sequential system) 2. The design of a reactive system may include using design automation tools (FPGA, EPLD) that you learn from other classes. 3. Review the stages of designing FSMs 4. Recall examples of FSMs 5. Reactive machine may include counters, shifters, adders, sequence generators, sequence recognizers or other that we covered in ECE 271. Slide17:  Reactive Systems: Don’t think, react! Reactive control is a technique for tightly coupling perception (sensing) and action, to produce timely robotic response in dynamic and unstructured worlds. Think of it as "stimulus-response". A powerful method: many animals are largely reactive. Limitations: Minimal (if any) state. No memory. No learning. No internal models / representations of the world. Reactive Robot Systems Reactive versus Deliberative Systems:  Reactive versus Deliberative Systems Reactive Systems Collections of sense-act (stimulus-response) rules rules implemented as assembly code, C++ code, EPLD combinational logic, FPGA state machine, state machine with stacks (memory), etc Inherently concurrent (parallel) Very fast and reactive Unable to plan ahead Reactive versus Deliberative Systems:  Reactive versus Deliberative Systems Deliberative Systems Based on the sense->plan->act model Inherently sequential Planning requires search, which is slow Search requires a world model World models become outdated Search and planning takes too long Hybrid Systems:  Hybrid Systems Combine the two extremes reactive system on the bottom deliberative system on the top connected by some intermediate layer Often called 3-layer systems Layers must operate concurrently Different representations and time-scales between the layers The best or the worst of both worlds??? Behavior-Based Systems:  Behavior-Based Systems An alternative to hybrid systems Have the same capabilities the ability to act reactively the ability to act deliberatively There is no intermediate layer A unified, consistent representation is used in the whole system => concurrent behaviors That resolves issues of time-scale Feedback Control:  Feedback Control Feedback: continuous monitoring of the sensors and reacting to their changes. Feedback control = self-regulation Two kinds of feedback: Positive Negative The basis of control theory - and + Feedback Negative feedback acts to regulate the state/output of the system e.g., if too high, turn down, if too low, turn up thermostats, toilets, bodies, robots... Positive feedback acts to amplify the state/output of the system e.g., the more there is, the more is added lynch mobs, stock market, ant trails... Feedback and Cybernetics:  Feedback and Cybernetics Uses of Feedback Invention of feedback as the first simple robotics (does it work with our definition)? The first example came from ancient Greek water systems (toilets) Forgotten and re-invented in the Renaissance for ovens/furnaces Really made a splash in Watt's steam engine Cybernetics Pioneered by Norbert Wiener (1940s) (From Greek "steersman" of steam engine) Marriage of control theory (feedback control), information science and biology Seeks principles common to animals and machines, especially for control and communication Coupling an organism and its environment (situatedness) W. Grey Walter’s Tortoise:  W. Grey Walter’s Tortoise Machina Speculatrix 1 photocell & 1 bump sensor, 1 motor Behaviors: seek light head to weak light back from bright light turn and push recharge battery Reactive control Turtle World (homework 2):  Turtle World (homework 2) Turtle Principles Parsimony: simple is better (e.g., clever recharging strategy) Exploration/speculation: keeps moving (except when charging) Attraction (positive tropism): motivation to approach light Aversion (negative tropism): motivation to avoid obstacles, slopes Discernment: ability to distinguish and make choices, i.e., to adapt Turtle World (homework 2):  Turtle World (homework 2) Braitenberg Vehicles Valentino Braitenberg (early 1980s) Extended Walter’s model in a series of thought experiments Also based on analog circuits Direct connections (excitatory or inhibitory) between light sensors and motors Complex behaviors from very simple mechanisms By varying the connections and their strengths, numerous behaviors result, e.g.: "fear/cowardice" - flees light "aggression" - charges into light "love" - following/hugging many others, up to memory and learning! Reactive control Later implemented on real robots Artificial Intelligence:  Artificial Intelligence Early Artificial Intelligence "Born" in 1955 at Dartmouth (thus both traditions are old!) "Intelligent machine" would use internal models to search for solutions and then try them out (M. Minsky) => deliberative model! Planning became the tradition Explicit symbolic representations Hierarchical system organization Sequential execution Artificial Intelligence (AI) Early AI had a strong impact on early robotics Focused on knowledge, internal models, and reasoning/planning Eventually (1980s) robotics developed improved and innovative approaches => behavior-based and hybrid control AI itself has also evolved... But before that, early robots used deliberative control Early Robots:  Early Robots Early Robots: SHAKEY At Stanford Research Institute (late 1960s) Vision and contact sensors STRIPS planner Visual navigation in a special world Deliberative Early Robots: HILARE LAAS in Toulouse, France (late 1970s) Video, ultrasound, laser range-finder Still in use! Multi-level spatial representations Deliberative -> Hybrid Control Early Robots: CART/Rover:  Early Robots: CART/Rover Hans Moravec Stanford Cart (1977) followed by CMU rover (1983) Sonar and vision Deliberative control Robotics Today:  Robotics Today Assembly and manufacturing (most numbers of robots, least autonomous) Materials handling Gophers (hospitals, security guards) Hazardous environments (Chernobyl) Remote environments (Pathfinder) Surgery (brain, hips) Tele-presence and virtual reality Entertainment Both approaches represented Why is Robotics hard?:  Why is Robotics hard? Sensors are limited and crude Effectors are limited and crude State (internal and external, but mostly external) is partially-observable Environment is dynamic (changing over time) Environment is full of potentially-useful information Key Issues of Robotics vs. AI:  Key Issues of Robotics vs. AI Grounding in reality: not just planning in an abstract world Situatedness (ecological dynamics): tight connection with the environment Embodiment: having a body Emergent behavior: interaction with the environment Scalability: increasing task and environment complexity Food for thought. And Exam?...:  Food for thought. And Exam?... Argumentation: Try to argue that robotics is an engineering and not science Try to argue on the opposite Write an Eliza-like program with two robots arguing on this topic Sensing: Based on your knowledge from other classes, try to invent a new sensor that has so far not been used much in robotics, such as smell sensor, polarized light sensor or radiation sensor. Some sensors may need a lot of processing. What computer software and algorithms may be useful. Think for instance of having an array of directed microphones. Food for thought. And Exam?...:  Food for thought. And Exam?... State: Give examples of various types of states for your Turtle robot from homework 2. Using the concept of finite state machines and verification of them, how can you verify the correctness of actions of your robot, for instance that it reaches the goal or does not bump to the obstacle. What can be proven ? How to design a program that will analyze the reachability of your robot in certain space? Food for thought. And Exam?...:  Control: Using example of your Turtle, show examples of positive and negative feedback. Do you have to redesign your control to be able to demonstrate both? Control Architectures: Using your Turtle, give examples what behaviors are reactive and what are deliberative. Perhaps most of your Turtle behavior is reactive. How can you add planning on top of reactive behaviors? What kind of plans will be the robot able to execute. If a plan fails, what is the simple solution, using the concepts that you learned so far? Food for thought. And Exam?... Food for thought. And Exam?...:  Learning As you remember, any kind of behavior that transforms the stored knowledge to a new form in result of which the new behavior is more efficient, can be categorized as learning, for instance, modifying the table of a reactive state machine. Add one more layer to your Turtle, the level of learning. How will you evaluate the quality of learning? Can GA be a learning mechanism? How learning can be introduced in the framework of tree search? Applications: Think about all possible practical applications for your Turtle. What should be added to it that it will remove mines from a former battlefield? That it will be finding weeds and destroying them? Give characterization of every task in terms of basic control architectures from the class Food for thought. And Exam?...

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