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