View
516
Download
0
Tags:
Embed Size (px)
Citation preview
Introduction to RoboticsLocomotion
CSCI 4830/7000January 11, 2010
Nikolaus Correll
What is locomotion?
• Latin: moving from place to place
Crawling Sliding Running
Jumping Walking Rolling
Other forms of locomotion
Gliding Flying Swimming
Propulsion
Locomotion relationships
• Swimming to walking• Walking to rolling• Gliding to flying• Running to jumping
A.J. Ijspeert, A. Crespi, D. Ryczko, and J.M. Cabelguen. From swimming to walking with a salamander robot driven by a spinal cord model. Science, 9 March 2007, Vol. 315. no. 5817, pp. 1416 - 1420, 2007.
Nature vs. Technology
• Robots become more and more capable of imitating natural locomotion schemes
• Nature did not evolve rotating shafts / rotational joints
Hinge joint Ball and socket joint
Walking vs. rolling
• If the terrain allows, rolling is more efficient
• Walking requires more– Structural complexity– Joints– Control
Characterization of locomotion
• Stability– Number of contact points– Center of gravity– Static/Dynamic Stabilization– Inclination of terrain
• Contact– Point vs. Area– Friction vs. grasp
3-Point rule
3 legs : static stability6 legs : static walking
Walking
2-DOF 4-DOF 6-DOF
How many DOF are needed?
Gait
• Sequence of event sequence
• Event: leg up or down• Possible number of
gaits N=(2k-1)!• Most efficient gait is a
function of speed!
Horse Gait (Gallop)
167 different gaits observed in a horse!
Industry
• 2-legged locomotion– popular because suited to
human environment– hardest to control– Commercial prototypes
• 4-legged locomotion– Not statically stable– Commercial prototypes
• 6-legged locomotion– Statically stable– Forestry
http://www.youtube.com/watch?v=CD2V8GFqk_Y
http://www.youtube.com/watch?v=FAcgSi6pzv4
Wheeled locomotion
• Most appropriate for most applications
• Stable with at least 3 wheels• Steered wheels make
control more complex pretty quickly
Stable zone
Wheel suspension
• Suspension consists of a spring and damper
• The damper absorbs shock
• The spring counteracts the shock
• Result: – wheel remains on ground– Better traction– Better control
Omni-Directional Drive
• Swedish Wheel– Rotation around wheel axle– Rotation around the rollers– Rotation around contact point
Uranus, CMU
Climbing with wheels
Friction-based Center-of-gravitybased
Suspension-based
Dynamic Stability
• The system has to move in order not to fall over
• Active balance• Inertia is used to
overcome unstable states
• Examples are– Running– Getting up
Inverted Pendulum
Part II: Practice
Brushed DC Motor
• Directly driven by DC current• Self-commutating• Speed regulated by voltage• Needs gear-box to generate useful speed/torque
Stepper Motor
• Requires dedicated circuitry to generate activation sequence
• Speed of sequence controls motor speed• Motor stops at precise increments
Brushless DC Motor
• Commutation done electronically• Requires speed controller• More efficient then brushed DC Motor
Encoders
• Required to estimate axis position
• Optical encoders– Differential– Quadrature– Absolute
• Hall-Effect
Servos
• Servo =motor + encoder + gearbox + controller
• Low-End:– Pulse-Width Modulation
(PWM):rate regulates position
• High-End:– Digital control allows
setting and querying position, speed and torque
Linear Actuators
• Rotation-based• Hydraulic / Pneumatic• Solenoid• Piezo-Electric• Shape-Memory Alloy
(SMA) wires
Design
• Lets design robots that– Crawl– Slide– Gallop– Jump– Walk– Roll
Crawling Sliding Running
Jumping Walking Rolling
Crawling
Mechanics of Soft Materials Laboratoryhttp://ase.tufts.edu/msml/researchInchBot.asp
Sliding
Hirose-Fukushima labhttp://www-robot.mes.titech.ac.jp/robot_e.html
Gavin Miller
Running
Scout II, McGill Universityhttp://www.youtube.com/watch?v=SRIU7PtyGOw
Jumping
Laboratory of Intelligent Systems, EPFLhttp://lis.epfl.ch/?content=research/projects/SelfDeployingMicroglider/
Homework
• Chapter 3– Required for next week’s exercise– Hints
• read the questions first• Skip: 3.2.3.4-5• Skim: 3.2.4-3.3.3• Understand what Maneuverability (Mobility and
Steerability is) conceptionally
• Goal: calculate the speed of your robot’s motors so that it can follow a desired trajectory
Next exercise
• Locomotion (1 week)• Play with different locomotion concepts in
Webots• Understand various gaits• Come up with a “stand-up-gait” for the Soccer
robot