Introduction to Robotics

Transcription

1 Marcello Restelli Dipartimento di Elettronica e Informazione Politecnico di Milano restelli@elet.polimi.it tel: Introduction to Robotics Robotica for Computer Engineering students A.A. 2006/2007

2 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1920: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Bishop Albertus Magnus holds banquet at which guests were served by metal attendants. Upon seeing this, Saint Thomas Aquinas smashed the attendants to bits and called the bishop a sorcerer. 2

3 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1920: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Descartes builds a female automaton which he calls Ma fille Francine. She accompanied Descartes on a voyage and was thrown overboard by the captain, who thought she was the work of Satan 3

4 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1920: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Jacques de Vaucanson builds (1738) a mechanical duck made of more that 4,000 parts. The duck could quack, bathe, drink water, eat grain, digest it and void it. Whereabouts of the duck are unknown today. 4

5 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1920: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Jacques de Vaucanson builds (1738) a mechanical duck made of more that 4,000 parts. The duck could quack, bathe, drink water, eat grain, digest it and void it. Whereabouts of the duck are unknown today. 5

6 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1921: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Karel Capek coins the term robot in his play Rossum s Universal Robots (R.U.R). Robot comes from the Czech word robota, which means servitude, forced labor. 6

7 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1921: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Sparko, the Westinghouse dog, uses both mechanical and electrical components. 7

8 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1921: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Industrial Robots created. Robotic Industries Association states that an industrial robot is a re-programmable, multi-functional manipulator designed to move materials, parts, tools, or specialized devices through variable programmed motions to perform a variety of tasks. 8

9 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1921: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age Shakey is made at Stanford Research Institute International. It contained a television camera, range finder, onboard logic, bump sensors, camera control unit, and an antenna for a radio link. Shakey was controlled by a computer in a different room. 9

10 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1921: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age In 1986, LEGO and the MIT Media Lab collaborate to bring the first LEGO based educational products to market. LEGO tc Logo is used by in the classrooms of thousands of elementary school teachers. 10

11 Historical Overview ~1250: first trials 1640: automatons : mechanics age 1921: fiction age 1940: cybernetics age 1960: automation age 1980: computer science age 1990: artificial intelligence age 11

12 Definition of Robot There is no widely accepted definition of what a robot is. The word robot comes from Czech robota, that means obligatory work Most real-world robots today do perform such obligatory work in highly controlled environments Factory automation (car assembly) But that is not what robotics research about; the trends and the future look much more interesting 12

13 Definition of Robot In the past, a robot was a clever mechanical deviceautomaton ISO definition for industrial robots: A robot is a re-programmable, multi-functional manipulator designed to move materials, parts, tools, or specialized devices through variable programmed motions to perform a variety of tasks. A robot must have at least 3 axes. It can be either fixed or move along rails. A mobile robot is a system able to move in environments that can be differently structured through different locomotions devices (wheels or legs). Usually these robots are equipped with sensors that allow to explore the environment. 13

14 Definition of Robot The previous definitions missing some important aspects: thought reasoning problem solving emotion consciousness A robot is a machine able to extract information from its environment and use knowledge about its world to act safely in a meaningful and purposeful manner (R.Arkin, 1998) A robot is an autonomous system which exists in the physical world, can sense its environment, and can act on it to achieve some goals. 14

15 Definition of Robotics Robotics is the study of robots, autonomous embodied systems interacting with the physical world Robotics is that science that aims at smartly integrating perceptions and actions in the physical world. Robotics is not limited to build robots. Robotics is not limited to use robots. 15

16 Robot Taxonomy Robots can be classified along many different dimensions. According to the environment they operate in: industrial robots indoor robots outdoor robots: UAV (unmanned aerial vehicle) UGV (unmanned ground vehicle) UUV (unmanned undersea vehicle) Space Robotics According to the way they move fixed robots wheeled robots legged robots humanoid robots 16

17 Robotic Applications Up to now industrial robots have been the main commercial product from robotics (also in Italy) Other applicative domains: edutainment surveillance domestic use exploration tour guides 17

18 The Main Components of a Robot Sensors Effectors and actuators used for locomotion and manipulation Controllers coordinating information from sensors with commands for the robot's actuators Environment Internal Perceptions Actions External Perceptions 18

19 Sensors A sensor is a physical device that provides information about the world the process is called sensing or perception The sensors required by a robot depend on the tasks it has to face Sensor (perceptual) space: contains all the possible combinations of sensor readings the number of possible combinations grows exponentially with the number of sensors 19

20 Sensors Perceptual level world state actions consequences World level building of the geometrical model sensor fusion Measure level signal conversion Physical level transductor 20

21 State The state of a robot is a complete description of the world that allows to determine how to act The state can be: Observable / Partially Observable / Hidden Discrete / Continuous External / Internal State space contains all the possible states a robot could be in state space perceptual space The intelligence of a robot is strongly dependent on how much and how fast it can sense its environment and about itself 21

22 Action Effectors: devices of the robot that have impact on the environment (legs, wings, propeller,...) Actuators: mechanisms that allow the effectors to do their work (muscles, motors) Actuators are used for: locomotion => Mobile robotics manipulation => Manipulator robotics Traditional actuators have high stiffness: pro: accuracy, stability,... contra: large, friction, inertia, noiser New actuators: elastic, light high ratios force/mass, power/mass 22

23 Autonomy Autonomy is the ability to make one's own decisions and act on them. Autonomy can be complete or partial (teleoperated robots) The robot become autonomous thanks to controllers: play the role of the brain in animals typically more than one controller is employed the interaction of all the controllers is challenging 23

24 Control Architectures Robot control is the means by which the sensing and action of a robot are coordinated Control architecture Guiding principles and constraints for organizing a robot s control system Robot control may be implemented: In hardware: programmable logic arrays In software Controllers need not (should not) be a single program 24

25 Languages for Programming Robots There is no best language The choice of the programming language depends on: the task faced the hardware used the knowledge of the programmer General purpose languages (C, JAVA) Robotic languages (the Behavior Language, the Subsumption Language) 25

26 Robot Control Approaches Reactive control Don't think, (re)act Deliberative (Planner-based) Control Think hard, act later Hybrid control Think and act separately and concurrently Behavior-Based Control (BBC) Think the way you act 26

27 Spectrum of Robot Control 27

28 Thinking vs Acting Thinking/Deliberating slow, speed decreases with complexity involves planning (looking into the future) to avoid bad solutions thinking too long may be dangerous requires (a lot of) accurate information flexible for increasing complexity Acting/Reaction fast, regardless of complexity innate/built-in or learned (from looking into the past) limited flexibility for increasing complexity 28

29 Mechanical Parts of a Robot A robot has a fixed base (typical of manipulators) or a mobile base. On the base of manipulators there is the arm of the robot. The arm is made up by joints and links At the end of the arm there is the hand Nearby the hand there are some joints (called wrist) that allow to reach any orientation 29

30 Types of Joints and Links There are three main categories: Revolute joints Prismatic joints Spherical joints There are many different types of links with different geometries 30

31 Degrees of Freedom DEFINITION How many degrees of freedom do we have on a plane? 3 (x,y,θ) How many degrees of freedom do we have in the space? 6 (x,y,z,ρ,θ,φ,φ) 31

32 Mechanisms A mechanism is a chain with a link fixed to the ground How many degrees of freedom has a structure with N links? Since each object has 6 degrees in the space, the number of degrees of freedom should be 6*N This is not true since there are some constraints For a manipulator the number of degrees of freedom is equal to the number of independent joint variables that must be specified to define the position of all the links Given an N link chain DOF = 6N Number_of_constraints DOF = 3(N-1) - 2#P1 - #P2 (Gruebler) 32

33 Degrees of Freedom and Manipulation To reach points of a 3D space we need at least 3 DOF To reach any point with any orientation we need 6 DOF Typical solution: 3 DOF for the arm 3 DOF for the wrist 33

34 Manipulators A manipulator is an open sequential kinematic chain made up by links coupled by joints It should have 6 DOF industrial robots may use less DOF for better performance more DOF may be used 34

35 Workspace The workspace of a robot is the set of points in the space that the robot can reach with its hand For a correct functioning each point should be reachable with any orientation of the hand workspace dexterous space Manipulators can be classified according to their workspace... 35

36 Cartesian Robot (TTT) A Cartesian robot has 3 prismatic joints Each joint is orthogonal with respect to the other two Its workspace is a right regular rectangular prism Pros: stiff structure, decoupled Used for assembly in highly structured environments 36

37 Cylindric Robot (RTT) A cylindric robot has 1 revolute joint at the base and 2 prismatic joints placed orthogonally Its workspace is a cylinder Less freedom of movement w.r.t. a Cartesian robot Building a revolute joints is easier 37

38 Spheric Robot (RRT) A spheric robot has 2 revolute joints starting from its base and 1 prismatic joint Its workspace is half a sphere Typically used for welding operations that require the hand externally oriented 38

39 Hinged Robot (RRR) A hinged robot has 3 revolute joints Its workspace is part of half a sphere It is called also anthropomorphic It is cheap and nimble since it uses only revolute joints The transformation between the actuation space and the real-world space is complex 39

40 SCARA A SCARA (Selective Compliant Assembly Robot Arm) is a robot with 3 parallel revolute joints and 1 prismatic joints heading towards the bottom Vertical descends (performed by moving only the prismatic joint) are typical of assembly operations The control is simplified 40

41 Parallel Robot A parallel robot is characterized by closed kinematic chains that allow to move a hand placed on a platform It is derived by flight simulation systems Its kinematics is typical complex It has good precision and speed Several different architectures 41

42 Human arm A human arm has 7 DOF (3 in the shoulder, 1 in the elbow, and 3 in the wrist) Furthermore, the hand has about 20 DOF The forces that can be wielded are significant 42

43 The Wrist of Industrial Robots The wrist of a manipulator are the last three joints of the arm It gives the revolute DOF required to reach any position with any orientation Typically the wrist is quite compact The names for the wrist movements are taken form the aeronautical jargon: Yaw, Pitch, Roll 43

44 Manipulator Hand The hand of a manipulator is a device that allows to grasp objects for manipulation Simple hand: it must grant to stably moving objects (for instance a hand with two fingers PINZA) Complex hand: it is required when a simple hand would lead to too complex operations. In general, it is built for a specific task, thus being hardly reusable Hands with more than two fingers are built for research purposes, since their application is very complex 44