Navigation, Control and Robotics

Robot?

• The term "robot" is slippery. (Carol Kapek's RUR originated the term, so it's not too helpful.)

• For our purposes: an AI agent attached to some machinery for manipulating or navigating the real world

• Usual agent thing: sensors, effectors, AI director

• So not Battlebots (human remote control), but maybe a thermostat (AI?)

Sensors?

• Sensor can be most anything: thermometer, "3D" compass, 3D accelerometer, GPS, wheel rotation counter, video camera, network of sensor nodes on a farm…

  • Sensors have both systematic error (consistently measure wrong) and stochastic error (give different answers in same situation)

  • Sensors fail, which is to say you see sudden negative changes in their error pattern. In the best case they just stop reporting at all and you know that

Interpreting Sensors

• First AI problem: how to make sense of what the sensors are saying

  • Detect "useless" broken sensors and ignore them

  • Decode sensors to get salient information: easier for a thermometer than a video camera

  • Integrate information from various sensors to estimate the state of the world

Decoding Sensors

• Some sensors are more direct than others

  • Thermometer may drop voltage linear in temp: figure out linear relation and call it a day

  • GPS has lots of measurement noise: will need to do statistics to reduce stochastic error

  • 3D accelerometer has systematic bias and stochastic drift: quite hard to deal with

  • Video camera needs some serious AI to interpret the output: optical flow, neural nets, etc

• Inverting a function can be much harder than the forward direction

Integrating Sensors

• This is known as "filtering" in the literature for some reason

• Can do dumb heuristic things: "use the 'best' sensor unless the other sensors strongly disagree, then fall back to 'second best'"

• Can take a statistical approach

• Can use a more AI-ish approach

Spectral Decomposition

• Given:

  • A gamma-ray spectrum of an unknown sample

  • Known gamma-ray spectra of radioisotopes

• Problem: infer levels of radioisotopes. Why is this hard?

  • Sample spectrum will be very noisy (stochastic error)

  • Spectrometer has known bias (systematic error)

  • Continuous search space: how to adjust estimates ("weights") of radioisotopes to match sample?

A Statistical Filter

• One approach: Convex Optimization

• Extension of Linear Programming to optimization functions of various types

• I used CVXPY for this problem

• http://github.com/BartMassey/sd.git

• Is this actually AI? (I think so)

Agent Tracking

• Given:

  • A prediction about how an agent is expected to travel ("dead reckoning")

  • Sensor readings reporting the position of the agent

• Problem: Track the agent (either this robot, or some other entity). Why is this hard?

  • The prediction is likely to be dodgy

  • The sensors are hard to invert

  • The sensors have systematic and stochastic error

Kalman Filters

• Typical solution: makes best linear estimate from various sensors in the presence of noise

• There are a million "better" Kalman Filter variants

• Not a great answer given the problems listed above:

  • Dead reckoning is likely to give weird errors

  • Sensors are hard to linearize

  • Sensor errors are likely not Gaussian

• Quite cheap in CPU cost, quite small memory cost

A Bayesian Particle Filter

• Another approach: Bayesian Particle Filtering

• Basic idea: use emergent behavior of ensemble (!) of models of vehicle position

• For each model ("particle"), at each sensor reading:

  • Propagate each model forward according to dead reckoning including stochastic (random) component

  • Re-weight each model's likelihood by how well it agrees with the sensor reading

• When an estimate is needed:

  • Construct an estimate of true position from weighted model positions and likelihoods

  • Discard the least-likely models

  • Duplicate a likelihood-weighted random sample of the the rest to restore the population

• http://github.com/BartMassey/pft.git

• Is this actually AI? (I think so)

Simultaneous Localization and Mapping (SLAM)

• Produce not only good navigation but a true map of the world

• But these interact

• Variety of standard methods; typically a lot of AI-ish code

Decisions

• Assuming you know what is going on, deciding what to do about it is still hard (duh)

  • Have to predict the future (a whole 'nother area of AI)

  • Have to figure out how to achieve the desired effect

• Example: navigating an IRL maze with an IRL robot

  • What is the best algorithm for exploring a maze? (surely depends on the maze?)

  • Can the robot get stuck? Can it run out of power?

  • How much time and compute power do you have for these decisions?

• "Perfect" maze-running mice…

Effectors

• Figuring out how to operate actuators is sometimes hard

• Consider moving all the joints in a robot body to pick up a cup of tea

  • Control problem: how to apply power to the joints within their limits to get them where they should be?

  • Inverse kinematics problem: what joint motions lead to the desired path?

• Standard modern solution: machine learning (models human learning?)

• AIBO was Sony's robot pet back in 1998…

Robots Are AI+

• Lots of hard AI problems to solve in-robot

• Mixed in with problems in

  • Electronics

  • Mechanics

  • Understanding of the world