Introduction to Robotics

Transcription

1 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 Topics Introduction Locomotion Kinematics of Mobile Robots Perception Navigation Localization Path Planning Task Planning 1

2 Locomotion is the complement of manipulation Study of actuators that generate interaction forces, and mechanisms that implement desired kinematic and dynamic properties. Locomotion and manipulation share as issues: stability, contact characteristics, and environmental type. 2

3 stability number and geometry of contact points center of gravity static/dynamic stability inclination of terrain characteristics of contact: contact point/path size and shape angle of contact friction 3

4 Type of environment Structure medium (e.g. water, air, soft or hard ground) Theory of locomotion includes: Mathematics, Mechanics Physics 4

5 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) 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 5

6 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 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 6

7 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. 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 = 2k 1 ( )! 7

8 For a mobile robot with 2 legs, there are 6 possible events : N = ( 2k 1)!= 3!= = 6 lift right leg, lift left leg release right leg, release left leg lift both legs together, release both legs together. 8

9 Static walking with six legs. A tripod formed by three legs always exists. 9

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

11 Honda Asimo HRP2, HRP3, HRP4 Sony Qrio Toyota 11

12 Aldebaran NAO and ROMEO 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 12

13 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 relatively simple mechanical implementation balance is not (usually) a problem all wheels are in ground contact Other problems: traction and stability, maneuverability, and control 13

14 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. 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. 14

15 Standard wheels and castor wheel Swedish wheels 15

16 Balls or spherical wheels Rotation x d y 16

17 Small speeds d is negligible We use odometry to estimate robot s motion Simple case, the distance traveled by the wheel is: 2πr 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 17

18 ICC A Wheeled robot in the plane has three degrees of freedom (x, y, θ) Position (x, y) Orientation θ The robot doesn t independent control over this DoF 18

19 Robot can t change arbitrary their position Changes depend on orientation Holonomic restrictions Sometimes castor wheels are required Kinematics undone We are going to focus on: Traction and stability Maneuverability Control We are not deal with balance 19

20 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. Ackerman wheel configuration (used in cars) is not a solution for mobile robots because it has poor maneuverability 20

21 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 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 21

22 Static stability it is requires 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 22

23 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 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 23

24 3 wheels Three motorized Swedish or spherical wheels arranged in a triangle; omnidirectional movement is possible Three synchronously motorized and steered wheels; the orientation is not controllable 4 wheels Two motorized wheels in the rear, 2 steered wheels in the front; steering has to be different for the 2 wheels to avoid slipping/ skidding. Two motorized and steered wheels in the front, 2 free wheels in the rear; steering has to be different for the 2 wheels to avoid slipping/skidding. 24

25 4 wheels Four steered and motorized wheels Two traction wheels (differential) in rear/front, 2 omnidirectional wheels in the front/rear 4 wheels Four omnidirectional wheels Two-wheel differential drive with 2 additional points of contact 25

26 4 wheels Four motorized and steered castor wheels 6 wheels Two motorized and steered wheels aligned in center, 1 omnidirectional wheel at each corner Two traction wheels (differential) in center, 1 omnidirectional wheel at each corner 26

27 Maneuverability Omnidireccional robots Swedish or spherical wheels Maneuverability Four drive castor wheels All controlled in traction and turn 27

28 Maneuverability Pioneer by Adept Robotics (former Active Media Robotics) PR2 by Willow Garage Maneuverability Four drive castor wheels All controlled in traction and turn 28