introduction to robotics - universidad veracruzana · 2018-03-12 · 12/03/18 1 introduction to...
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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
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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.
Mobile Robots: Locomotion
• Locomotion and manipulation share as issues: – stability, – contact characteristics, and – environmental type.
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Mobile Robots: Locomotion
• stability – number and geometry of contact points
– center of gravity – static/dynamic stability – inclination of terrain
Mobile Robots: Locomotion
• characteristics of contact: – contact point/path size and shape
– angle of contact – friction
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Mobile Robots: Locomotion
• Type of environment
– Structure – medium (e.g. water, air, soft or hard ground)
Mobile Robots: Locomotion
• Theory of locomotion includes:
– Mathematics, – Mechanics – Physics
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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)
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
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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
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
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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.
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 = 2k −1( )!
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Mobile Robots: Locomotion • Legged Robots • For a mobile robot with 2 legs, there are 6
possible events :
• lift right leg, lift left leg • release right leg, release left leg • lift both legs together, release both legs
together. €
N = 2k −1( )!= 3!= 3⋅ 2⋅ 1 = 6
Mobile Robots: Locomotion • Legged Robots
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Mobile Robots: Locomotion • Legged Robots
Mobile Robots: Locomotion • Legged Robots
• Static walking with six legs. • A tripod formed by three legs always exists.
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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
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
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Mobile Robots: Locomotion • Legged Robots
• Honda Asimo HRP2, HRP3, HRP4
Mobile Robots: Locomotion • Legged Robots
• Sony Qrio Toyota
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Mobile Robots: Locomotion • Legged Robots
• Aldebaran NAO and ROMEO
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
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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
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
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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.
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.
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Mobile Robots: Locomotion • Wheeled Mobile Robots
• Standard wheels and castor wheel
Mobile Robots: Locomotion • Wheeled Mobile Robots
• Swedish wheels
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Mobile Robots: Locomotion • Wheeled Mobile Robots
• Balls or spherical wheels
Mobile Robots: Locomotion
x
Rotation
y d
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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: – 2πr
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
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Mobile Robots: Locomotion
ICC
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 independent control over
this DoF
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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
Mobile Robots: Locomotion • Wheeled Mobile Robots • We are going to focus on:
– Traction and stability – Maneuverability – Control
• We are not deal with balance
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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.
•
Mobile Robots: Locomotion • Wheeled Mobile Robots • Ackerman wheel configuration (used in
cars) is not a solution for mobile robots because it has poor maneuverability
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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
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
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Mobile Robots: Locomotion • Wheeled Mobile Robots
Mobile Robots: Locomotion • Wheeled Mobile Robots • 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
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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
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
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Mobile Robots: Locomotion • Wheeled Mobile Robots • 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
Mobile Robots: Locomotion • Wheeled Mobile Robots • 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.
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Mobile Robots: Locomotion • Wheeled Mobile Robots • 4 wheels • Four steered and motorized
wheels • Two traction wheels
(differential) in rear/front, 2 omnidirectional wheels in the front/rear
Mobile Robots: Locomotion • Wheeled Mobile Robots • 4 wheels • Four omnidirectional wheels
• Two-wheel differential drive with 2 additional points of contact
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Mobile Robots: Locomotion • Wheeled Mobile Robots • 4 wheels • Four motorized and steered
castor wheels
Mobile Robots: Locomotion • Wheeled Mobile Robots • 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
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• Maneuverability • Omnidireccional robots • Swedish or spherical wheels
Mobile Robots: Locomotion
• Maneuverability • Four drive castor wheels • All controlled in traction and turn
Mobile Robots: Locomotion