ECE 450 Introduction to Robotics

1
ECE 450 Introduction to Robotics

• Section 50883
• Instructor Linda A. Gee
• 11/09/99
• Lecture 14

2
Perception

• Includes the following elements
• sensing
• interpretation
• cognition
• coordination

3
Robot Sensing

• Limitations
• Defined onboard sensors
• Programmed software

4
Sensors

• Sensors
• do not perceive things
• act as transducers
• convert physical phenomena to electrical signals
  for a microprocessor to use
• achievable with A/D converter onboard the
  microprocessor
• loading a value from an I/O port
• requires signal conditioning or amplification

5
Interpreting Raw Data Input

• Obtain raw data input from each sensor
• Examine/Analyze the following
• Change in resistance
• Change in voltage
• Any significant changes from low to high

6
Interfacing Sensors

• Discussion of simple sensors and how to use them
• MC68HC11A0 pins
• I/O pin
• A/D port
• Counter timer pin

7
Software Drivers

• First define and establish the sensor suite to
  use onboard the robot
• Microprocessor needs to be programmed to read the
  sensors after the sensors ingest the raw data
• Software drivers define the interface between the
  hardware device (sensor) and a program that
  accesses the device

8
Software Drivers contd

• Driver behavior
• tends to seek a trigger (e.g. polling the A/D
  pin)
• may act as an interrupt handler called only when
  a receive signal goes from high to low
• issue commands to set a flag or store data in a
  variable for future use

9
Sensitivity and Range

• Sensitivity and Range
• define a measure of the degree for which an
  output signal changes as the measured value
  changes
• physical changes in the environment of the robot
  cause a sensor to transform/amplify a signal to
  the microprocessor (using the A/D converter)
• voltage has a discrete range of values, but this
  value can be converted into one of 256 discrete
  values using the 8-bit A/D onboard the MC68HC11
• angular mappings are also possible using the A/D
  converter
• logarithmic amplifiers allow for greater range in
  the sensor

10
Light Sensors

• Light sensors include
• visible light sensors
• photoresistors
• photodiodes
• phototransistors
• infrared sensors
• Easy to interface with a microprocessor
• Easy to interpret the output of a photoresistor

11
Photodetectors

• Photoresistors also known as photocells
• Similar to variable resistors, except they change
  with the amount of light present
• Phototransistors
• Provide greater sensitivity than photocells
• Photodiodes
• Produce a linear signal over a large range of
  light levels have a rapid response to
  illumination change

12
Near-Infrared Proximity Detectors

• Sensors determine the presence or non-presence of
  an object within a cone of detection
• Often called IRs
• Sensitive to 880 nm range below visible light
• flourescent lighting sensitivity
• detect reflection from objects

13
Near-Infrared Range Sensors

• Computes range (distance) values using infrared
  sensors and triangulation
• Triangulation
• one of three methods for determining range
  (triangulation, structured light, time of flight)
• based on a source, detector and their geometries

14
Pyroelectric Sensors

• Senses small changes in temperature
• Uses a lithium tantalate crystal, where charge is
  induced with heat
• Can detect presence of the motion of a heat
  source

15
Ultraviolet Sensors

• Sensors are sensitive to radiation in the range
  185-260 nm
• Insensitive to light and heat
• Only useful in the presence of a flame