introduction to robotics - universidad veracruzana · 2018-03-12 · 12/03/18 1 introduction to...

12/03/18

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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.


•  Locomotion and manipulation share as issues: – stability, – contact characteristics, and – environmental type.

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•  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

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• Type of environment

– Structure – medium (e.g. water, air, soft or hard ground)


• Theory of locomotion includes:

– Mathematics, – Mechanics – Physics

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• 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

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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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•  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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•  Honda Asimo HRP2, HRP3, HRP4


•  Sony Qrio Toyota

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•  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


•  Swedish wheels

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•  Balls or spherical wheels


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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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 •  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


•  Maneuverability •  Four drive castor wheels •  All controlled in traction and turn


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Mobile Robots: Locomotion •  Maneuverability •  Pioneer by Adept Robotics

(former Active Media Robotics)

•  PR2 by Willow Garage

•  Maneuverability •  Four drive castor wheels •  All controlled in traction and turn


introduction to robotics - universidad veracruzana · 2018-03-12 · 12/03/18 1 introduction to...

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