Download - Lecture 2 Locomotion No Video 1

8/14/2019 Lecture 2 Locomotion No Video 1

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Lecture 2

Mobile Robot Locomotion

Prof. Yan Meng

Department of Electrical and Computer

EngineeringStevens Institute of Technology

CPE 521A: Introduction to Autonomous Mobile Robots


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Locomotion Concepts

Concepts

Legged Locomotion

Wheeled Locomotion

"Position"Global Map

Perception Motion Control

Cognition

Real WorldEnvironment

Localization

PathEnvironment ModelLocal Map


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Locomotion Concepts: Principles Found in Nature

2.1


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Locomotion Concepts

Concepts found in nature: difficult to imitate technically

Mechanical complexity through structural replication

Very small size and weight -> high robustnessEnergy storage system and muscular and hydraulic activation systems

-> response time, torque, and conversion efficiency

Most technical systems use wheels or small number of artificial legsLegged locomotion requires higher degrees of freedom and

mechanical complexity than the wheeled locomotion

Rolling is most efficient, but not found in nature, however, themovement of a walking biped is close to rolling


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Walking of a Biped

Biped walking mechanism

not too far from real rolling.

rolling of a polygon with side length

equal to the length of the step.

the smaller the step gets, the more the

polygon tends to a circle (wheel).

However, fully rotating joint was not

developed in nature.

2.1


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Walking or rolling?

number of actuators

structural complexity

control expense energy efficient

terrain (flat ground, soft

ground, climbing..) movement of the involved

masses

walking / runningincludes up and down

movement of COG

some extra losses


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Characterization of locomotion concept

Locomotion

physical interaction between the vehicle and its environment.

Locomotion is concerned with interaction forces, and the mechanismsand actuators that generate them.

The most important issues in locomotion are:

stability number of contact points

center of gravity

static/dynamic stabilization

inclination of terrain

characteristics of contact contact point or contact area

angle of contact

friction

type of environment

structure

medium (water, air, soft or hard

ground)


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Motion Control of Mobile Robots

Locomotion the process of causing an robot to move.

In order to produce motion, forces must be applied to the robot

Motor output, payload

Dynamics study of motion in which these forces are modeled

Deals with the relationship between force and motions.

Kinematics study of the mathematics of motion without

considering the forces that affect the motion.Deals with the geometric relationships that govern the system

Deals with the relationship between control parameters and the

behavior of a system.


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Mobile Robots with legs (walking machines)

Key advantages: adaptability and maneuverability in rough terrain

The fewer legs the more complicated becomes locomotion

stability, at least three legs are required for static stability

During walking some legs are lifted

thus loosing stability? For static walking at least 6 legs are required

babies have to learn for quite a while until they are able to stand or even walkon there two legs. (Exceptional maneuverability comes at a price: much more

complex active control to maintain balance).

mammal reptiles insects

two or four legs four legs six legs


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Number of Joints of Each Leg (DOF: degrees of freedom)

A minimum of two DOF is required to move a leg forward

a lift and a swing motion.

sliding free motion in more than only one direction not possible

Three DOF for each leg in most cases

Fourth DOF for the ankle joint

might improve walking

The ankle enables more consistent ground contact by actuating

the pose of the sole of the foot

however, additional joint (DOF) increase the complexity of the

design and especially of the locomotion control.

2 2 1


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Examples of Legs with 3 DOF

2.2.1


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The number of possible gaits

The gait is characterized as the sequence of lift and release events of

the individual legs

it depends on the number of legs.

the number of possible events N for a walking machine with k legs is:

For a biped walker (k=2) the number of possible events N is:

The 6 different events are:lift right leg / lift left leg / release right leg / release left leg / lift both legs

together / release both legs together

For a robot with 6 legs (hexapod) N is already

( )!12 = kN

( ) 6123!3!12 ==== kN

11 ! 39,916,800N = =


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Most Obvious Gaits with 4 legs

Changeover Walking Galloping

free fly


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Most Obvious Gait with 6 legs (static)


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Examples of Walking Machines

No industrial applications up to date,

but a popular research field

For an excellent overview please see:

http://www.uwe.ac.uk/clawar/

The Hopping MachineRaibert hopperHydraulic actuation


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Honda Humanoid Robots (two legs)

P2 from Honda, Japan

Enable practical mobility

in the human world of

stairs and ledges while

maintaining a

nonthreatening size and

postureMaximum Speed: 2 km/h

Autonomy: 15 min

Weight: 210 kgHeight: 1.82 m

Leg DOF: 2*6

Arm DOF: 2*7The first robot to demonstrate biomimeticbipedal stair climbing and descending


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Walking Robots with Four Legs (Quadruped)

Artificial Dog Aibo from Sony, Japan

a new robot operating system that is near real-timenew geared servomotors that are of sufficiently high torque to support therobot.a color vision system that enables AIBO to chase a brightly colored ball

emulate learning and maturation to dynamic behavior over time