Introduction to Robotics Ph.D. Antonio Marin-Hernandez Artificial - PDF document

4/15/20 Introduction to Robotics Ph.D. Antonio Marin-Hernandez Artificial Intelligence Research Center Universidad Veracruzana Sebastian Camacho # 5 Xalapa, Veracruz Robotics Action and Perception LAAS-CNRS 7, av du colonel Roche Toulouse, France 1 Topics • Introduction • Locomotion • Kinematics of Mobile Robots • Perception • Navigation • Localization • Path Planning • Task Planning 2 1

4/15/20 Mobile Robots: Locomotion • Locomotion is the complement of manipulation • Study of actuators that generate interaction forces, and mechanisms that implement desired kinematic and dynamic properties. 3 Mobile Robots: Locomotion • Locomotion and manipulation share as issues: –stability, –contact characteristics, and –environmental type. 4 2

4/15/20 Mobile Robots: Locomotion • stability –number and geometry of contact points –center of gravity –static/dynamic stability –inclination of terrain 5 Mobile Robots: Locomotion • characteristics of contact: –contact point/path size and shape –angle of contact –friction 6 3

4/15/20 Mobile Robots: Locomotion • Type of environment –Structure –medium (e.g. water, air, soft or hard ground) 7 Mobile Robots: Locomotion • Theory of locomotion includes: –Mathematics, –Mechanics –Physics 8 4

4/15/20 Mobile Robots: Locomotion • To be able to do certain task a robot must be able to move in the environment • Two main problems –Given some inputs how the robot is going to move ? (kinematics) –Which inputs are required to move a robot to a given position or with desirable movement ? (inverse kinematics) 9 Mobile Robots: Locomotion • The field of study where the forces involved are modeled is Dynamics –Energy and Forces associated with movements • Different Mobile Robots in: –Terrestrial –Aquatic –Aerial –Space 10 5

4/15/20 Mobile Robots: Locomotion • Legged Robots • Characterized by a series of contact points between the robot and the ground. • Advantages: include adaptability and maneuverability in rough terrain. • Disadvantages of legged locomotion include power and mechanical complexity 11 Mobile Robots: Locomotion • Legged Robots • Insects –6 or more legs • Mammals and reptiles –4 legs • Some mammals (Humans) –2 legs • Humans can jump in one leg –complex active control to maintain balance 12 6

4/15/20 Mobile Robots: Locomotion • Legged Robots • Adding degrees of freedom to a robot leg increases the maneuverability of the robot • Disadvantages: – energy, control, and mass. • Additional actuators require energy and control, and they also add to leg mass, further increasing power and load requirements on existing actuators. 13 Mobile Robots: Locomotion • Legged Robots • The number of possible gaits depends on the number of legs • The gait is a sequence of lift and release events for the individual legs. • For a mobile robot with k legs, the total number of possible events N for a walking machine is: ( ) ! N = 2 k − 1 14 7

4/15/20 Mobile Robots: Locomotion • Legged Robots • For a mobile robot with 2 legs, there are 6 possible events : ( ) ! = 3! = 3 ⋅ 2 ⋅ 1 = 6 N = 2 k − 1 • lift right leg, lift left leg • release right leg, release left leg • lift both legs together, release both legs together. 15 Mobile Robots: Locomotion • Legged Robots 16 8

4/15/20 Mobile Robots: Locomotion • Legged Robots 17 Mobile Robots: Locomotion • Legged Robots • Static walking with six legs. • A tripod formed by three legs always exists. 18 9

4/15/20 Mobile Robots: Locomotion • Legged Robots • Minimize the number of legs –Mass –Legs coordination • Legged robots can cross a gap –Easier when they have less legs –Jump and running 19 Mobile Robots: Locomotion • Legged Robots • Two legged robots have been shown to: –run, –jump, –travel up and down stairways, –and even do aerial tricks such as somersaults 20 10

4/15/20 Mobile Robots: Locomotion • Legged Robots • Honda Asimo HRP2, HRP3, HRP4 21 Mobile Robots: Locomotion • Legged Robots • Sony Qrio Toyota 22 11

4/15/20 Mobile Robots: Locomotion • Legged Robots • Aldebaran NAO and ROMEO 23 Mobile Robots: Locomotion • Legged Robots • Four legs • Standing is passively stable • Walking is challenging because to remain stable the robot’s center of gravity must be actively shifted during the gait 24 12

4/15/20 Mobile Robots: Locomotion • Legged Robots • Six legs • Static stability reducing the control complexity • In most cases, each leg has three degrees of freedom, including hip flexion, knee flexion, and hip abduction 25 Mobile Robots: Locomotion • Wheeled Mobile Robots • relatively simple mechanical implementation • balance is not (usually) a problem • all wheels are in ground contact • Other problems: –traction and stability, –maneuverability, and –control 26 13

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • The four basic wheel types: • (a) Standard wheel: two degrees of freedom; rotation around the (motorized) wheel axle and the contact point. • (b) castor wheel: two degrees of freedom; rotation around an offset steering joint. 27 Mobile Robots: Locomotion • Wheeled Mobile Robots • The four basic wheel types: • (c) Swedish wheel: three degrees of freedom; rotation around the (motorized) wheel axle, around the rollers, and around the contact point. • (d) Ball or spherical wheel: realization technically difficult. 28 14

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • Standard wheels and castor wheel 29 Mobile Robots: Locomotion • Wheeled Mobile Robots • Swedish wheels 30 15

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • Balls or spherical wheels 31 Mobile Robots: Locomotion Rotation x y d 32 16

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • Small speeds d is negligible • We use odometry to estimate robot’s motion • Simple case, the distance traveled by the wheel is: –2 πr 33 Mobile Robots: Locomotion • Wheeled Mobile Robots • The Instantaneous Center of Curvature (ICC) must coincide with the axes of rotation of each wheel in contact • ICC should not only exist, but each wheel must describe a movement consistent with a rotation of the vehicle around the ICC 34 17

4/15/20 Mobile Robots: Locomotion ICC 35 Mobile Robots: Locomotion • Wheeled Mobile Robots • A Wheeled robot in the plane has three degrees of freedom –( x , y , θ ) • Position ( x , y ) • Orientation θ • The robot doesn’t have independent control over this DoF 36 18

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • Robot can’t change arbitrary their position • Changes depend on orientation –Holonomic restrictions • Sometimes castor wheels are required –Kinematics undone 37 Mobile Robots: Locomotion • Wheeled Mobile Robots • We are going to focus on: –Traction and stability –Maneuverability –Control • We are not deal with balance 38 19

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • The choice of wheel types for a mobile robot is strongly linked to the choice of wheel arrangement, or wheel geometry • When design –What type of wheels? and –Which geometry ? • The choices are in function of: maneuverability, controllability, and stability. 39 Mobile Robots: Locomotion • Wheeled Mobile Robots • Ackerman wheel configuration (used in cars) is not a solution for mobile robots because it has poor maneuverability 40 20

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • 2 wheels • One steering wheel in the front, one traction wheel in the rear • Two-wheel differential drive with the center of mass (COM) below the axle 41 Mobile Robots: Locomotion • Wheeled Mobile Robots • The minimum of wheel required to have stability is two • Stability is achieved if the center of mass is below the axis of the wheels • Under ordinary conditions, wheel diameter is impractical • Robots with two wheels can hit the ground due to torque 42 21

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots 43 Mobile Robots: Locomotion • Wheeled Mobile Robots • Static stability it is required 3 wheels • The center of gravity must be contained in the triangle formed by the three contact points • Stability can be improved by adding more wheels –The hyper-static nature of geometry requires flexible suspension on roughly terrain 44 22

4/15/20 Mobile Robots: Locomotion • Wheeled Mobile Robots • 3 wheels • Two-wheel centered differential drive with a third point of contact • Two independently driven wheels in the rear/front, 1 unpowered omnidirectional wheel in the front/rear 45 Mobile Robots: Locomotion • Wheeled Mobile Robots • 3 wheels • Two connected traction wheels (differential) in rear, 1 steered free wheel in front • Two free wheels in rear, 1 steered traction wheel in front 46 23