Robotics

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Sensors
Sensors that tell the robot position/change of joints: odometers, speedometers, etc.
Force sensing. Enables compliant motion--robot just maintains contact with object (video: compliant)
Sonar. Send out sound waves and measure how long it takes for it to be reflected back. Good for obstacle avoidance.
Vision systems
Effectors
Converts software commands into physical motion
Typically electrical motors or hydraulic/pneumatic cylinders
Two main types of effectors:
locomotion
manipulation
Locomotion
Legs!
traditional (video: honda human)
Other types
Statically stable locomotion: can pause at any stage during its gate without falling
Dynamically stable locomotion: stable only as long as it keeps moving (video: hopper)
Still, wheeled or tread locomotion like Shakey is still most practical for typical environments
Other methods: reconfigurable robots, fish robots, snake-like robots. (video: mod-robot)
Manipulation
Manipulation of objects
Typical manipulators allow for:
Prismatic motion (linear movement)
Rotary motion (around a fixed hub)
Robot hands go from complex anthromorphic models to simpler ones that are just graspers
(video: manipulation)
(video: heart surgery)
Localization: Where Am I?
Use probabilistic inference: compute current location and orientation (pose) given observations
Motion Planning
Simplest task that a robot needs to accomplish
Two aspects:
Finding a path robot should follow
Adjusting motors to follow that path
Goal: move robot from one configuration to another
Configuration space
Describe robot’s configuration using a set of real numbers
Flatland -- robot in 2D -- how to describe?
Degrees of freedom: a robot has k degrees of freedom if it can be described fully by a set of k real numbers
e.g. robot arm (slide)
Want minimum-dimension parameterization
Set of all possible configurations of the robot in the k-dimensional space is called the configuration space of the robot.
Example
workspace for 2-D robot that can only translate, not rotate
configuration space describes legal configurations
free-space
obstacles
Configuration space depends on how big robot is—need reference point
Path planning
Goal: move the robot from an initial configuration to a goal position
path must be contained entirely in free space
assumptions:
robot can follow any path (as long as avoids obstacles)
dynamics are completely reliable
obstacles known in advance
obstacles don’t move
Assumption #1
robot can follow any path
what about a car?
degrees of freedom vs. controllable degrees of freedom
holonomic (same)
nonholonomic
(video: holonomic)
Motion planning
reduces to problem of finding a path from an initial state to a goal in robot’s configuration space
why is this hard?
Reformulate as discrete search
finely discretized grid
cell decomposition: decompose the space into large cells where each cell is simple, motion planning in each cell is trivial
roadmap (skeletonization) methods: come up with a set of major “landmarks” in the space and a set of roads between them
Issues in Search
Complete
Optimality
Computational Complexity
Motion planning algorithms
grid
cell decomposition
exact
approximate
roadmap (skeletonization) methods:
visibility graphs
randomized path planning
Robotics: Summary
We’ve just seen a brief introduction…
Issues:
sensors, effectors
Locomotion, manipulation
Some problems:
Localization
Motion Planning
Lots more!!