Post on 27-Apr-2015
description
Snake Motion inspired Robots
Outline
• Robot Motion Models
• Snake Locomotion
• Snake Robot Model
• Proposed Model
• Design and Technical Concerns
• Implications and Future Work
Motivation
• Occupy a wide variety of ecological niches
• Movement without limbs
• Small cross section to length ratio
• Ability to change the shape of their body
"To walk is human, to slither divine"
Other Models
Applied AI Systems, Inc., Canada
Ijspeert et al
Science 315, 1416
2007
Advantages of Serpentine Locomotion
STABILITY• Potential Energy low in most situations
• Less probable failure points
TERRAINABILTY• Can climb heights many times it’s own girth
• No possibility of getting stuck
Advantages of Serpentine Locomotion
TRACTION• Moving Snake can exert a force upto a 3rd of
it’s own weight
• Large contact area results in greater traction
EFFICIENCY• Reduced costs due to low COG, elimination of
acceleration and decceleration of limbs
Advantages of Serpentine Locomotion
SIZE & SHAPE• Small frontal area
• Slender design implies better maneuverabilty
REDUNDANCY• Employs simple motion actuators in sequence
• Failure/Defect could be easily replaced
Snake Locomotion
Scales & Weight distribution.
Scales have similar design as Wheels and Ice
skates.
•Lateral undulation S-shaped wave travelling from head to tail, it is the
most common and efficient mode, and used by almost all snakes. Snake’s
body moves back and forth causing lateral waves that force longitudinal
motion.
Used mostly in areas with uneven or variable terrain . e.g swimming
snakes, anguilliform swimming lampreys eels.
•Rectilinear locomotion ("inchworm" )employed by the heavyweights snake
like boas & pythons. By cyclically “fixing” parts of the skin to the ground
using scales, and then moving the backbone forward with respect to the skin,
and finally releasing the scales allowing the skin to move forward. Stabbing
and pushing mechanism of the scales. Very slow motion used while
stalking its prey.
•Concertina mode: can be thought of as snake taking steps. Part of the
snake’s body is pushed against a surface forming a small number of waves:
by moving these waves, and the corresponding contact points, the snake
progresses.
The only place where concertina progression is primarily used is by arboreal
snakes on tree limbs as one part is always attached to the tree ,here LU and
RP are difficult.
•Sidewinding is used by desert snakes that need to move on sand; Fastest
mode of locomotion can be thought of as equivalent to horse galloping. In this
mode, the snake lifts a part of the body to maintain only a few contact points
with the ground, using them to move the rest of the body.
Other types of locomotion:
Climbing:The two most common ways of ascent are LU and RP. Hard to
believe a snake lashing itself up a tree, but it does work and ascent is fluid.
When on branches the much safer concertina mode is used in place of the other
two
Swimming:The horizontal undulatory progression lends itself well to moving
through water and is employed by most aquatic serpents. Even large snakes
like Python reticulatus and Eunectes murinus are known to use HUP in the
water (something large boids generally avoid doing on land).
Flying:Flying snakes have longitudinal hinges on their ventral scales which
allows them to create a concavity which creates more surface area for air to
pass through which creates drag, which slows descent and voila, we have flight.
Simulation of Motion
Miller et. Al.
Simulation Implementation
Which Gait should we choose??
Factors influencing Selection
• Speed
• Terrain
• Ability to maneuver
• Energetic efficiency
Lateral Undulation
Configuration Parameters
•Design
•Morphology
•Control System
Design
• Segments – “vertebrae”
• Actuators – “Muscles”
Morphological Segments connected by universal joints
Actuator is a mechanical device for controlling a mechanism.
Takes Energy and converts into motion
Mechanism was proposed by Dr. Hirose and is called Active Cord
Mechanism5
Design Optimization
• Number of Scales and Angle of rotation
For Speed Number Of Segments
But , Number Of Segments Design Complexion
Earlier Models –
Dr. Hirose et. Al.
10 Segments – 20
actuators
S5 – Miller et. Al.
Closest to natural snake
locomotion
32 Segment – 64
actuators
Snakes usually have 100-400 segments
Morphology
Low friction force -in the direction of forward
movement
High friction force - in lateral directions
Achieved By Directionality of scales
Dowling et. al.
Fiber Skins with
various surface
treatments
Control System
“Follow the Head”
Travelling Wave
propagated from head to
tail
Generated from predefined gait
patterns, usually computed as sine
waves
Works pretty well for uniform terrains
Velocity changes with friction
coefficients
What will happen when the terrain changes??
phase difference between the head and tail
joints will not remain constant – Snake will wriggle in
place
Jae-Kwan Ryu et all.
Central Pattern Generators (CPG)
Matsuoka’s neural oscillators on each joints –
take velocity as input and modulate frequency
can be defined as neural networks that can endogenously produce
rhythmic patterned outputs
Jae-Kwan Ryu et
al.
Work On
Feedback
Mechanis
m
Existing Models
1. Robots that move using powered wheels
http://zedomax.com/blog/wp-content/uploads/2007/04/servo-snakebot.jpg
Existing Models
2. Robots that move by applying torques on the joints between the segments. Can have passive wheels.
Ref : Hirose et. al
Technical Concerns
• For search and rescue missions, and possible medical applications.
Waterproofing.
Completely autonomous.
Distributed control
Different type of movement for different terrains.
Remote controlled - GSM against radio-
waves
Degree of freedom
Falling over
The movement patterns obtained with the
robot have to be compared to biological
data.
Proposed Design
Multiple identical elements – same algorithm, easy to replace , redundancy
Distributed actuation, power and control
Each individual element is made waterproof
The center of gravity is placed below the geometrical center.
Large lateral surfaces for good swimming efficiency.
Asymmetric friction for the lateral undulatorylocomotion
Controlled by a CPG mechanism
Remotely controlled in terms of speed and direction commands, but otherwise have an onboard locomotion controller for coordinating its multiple degrees of freedom.
For better control – servo motors in head and tail with paddles.
Sensing – points of contact with the ground.
Miniaturization – use of bionic arm like mechanism. 70 % weight is due to motors.
Proposed Model
Linker Design and mechanism
Ref : Dowling et. al.
Expected outcome
• Based on the work plan we will get a fully functional robotic snake which should be capable of autonomous motion in a 3d environment by mimicking the snake movement of lateral undulation.
• The robot will be easy to control and will be able to traverse through rough terrain, rubble, sand, fluids or over obstacles with ease.
• Making the robot design simple(bionic arm method) , we should be successfully be able to miniaturize it thus giving us a lot more interesting applications like medical applications.
Amphibious ACM R5 robot snake –
Hirose Fukushima Robotics Lab
Snake Bot – Sacros designs,
Utah
Applications
• Can be used to detect leaks in oil pipes
• Can be used in search and exploration missions during earthquakes and floods.
• Essentially can be used to reach or explore places which are not easily accessible.
• If scaled down significantly, it could even be used for a very specific drug delivery system.
Anna Konda – a fire fighting robot, SINTEF Norway
Robot motion in a fluid
Future work
• With advancement in technology, we should be able to make smaller motors which will enable us to make smaller robot snakes with good control.
• By studying all the methods of movement, we can design a robot snake to change its motion from serpentine to concertina to side-winding, simply by providing different inputs to each segment.
• The material used to make the robot must be improved upon to better mimic the scales and stretchable skin of the snake.
Take home message…
• Motivation/Background
•Motion of the snake
•Models and Work plan
•Applications and challenges