Lecture 2 Locomotion No Video 1
Transcript of 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