Introduction to Robotics

1
Introduction to Robotics

• Robot Control

2
Types of Control

• Open Loop Control
• Give a robot tasks to do without concern about
  its environment
• Closed Loop Control
• Robot gets feedback about the task as it
  progresses so it can tell if the task is being
  completed

3
Open Loop Control

• Some signal is interpreted by the microprocessor
  to drive some actuators and create some output
• Example
• Signal move left
• Microprocessor Hitachi H8 (inside the RCX
  brick)
• Actuator motor
• Output robot moves
• Note There is no link between output and
  microprocessor

4
Problems of Open Loop Control

• Robot does not know its environment or position
• Robots using only open loop control work well in
  situations that vary little and are readily
  reproducible
• Lack of Robustness
• Cannot correct for any change in environment or
  in itself
• Cannot correct for things like low battery or
  misaligned wheels
• When it strays from where the microprocessor
  thinks it is, it is lost

5
Closed Loop Control

• Same as open loop control with the addition of a
  sensor to provide information on the current
  orientation of the robot
• Example all the robots weve made

6
More on Sensors

• We know sensors can be analog or digital
• Analog Sensor Problems
• Glitchy
• Noisy
• Drifting
• Incorrect Range

7
More on Analog Errors/Solutions(when used as
digital sensors)

• Glitchy
• Usually inherent in the sensor itself
• Must be fixed in software
• Throw out values that are not in the usable range
  or look for unlikely transitions
• Noisy
• Also caused by the sensor itself
• Can be fixed by time averaging the values
• Drifting
• Can be caused by sensors retaining some sort of
  memory
• Slowly changing light sources may interfere with
  color tracking
• Option is to have the robot capable of changing
  its threshold values while running
• Important that robot knows it is on a calibrating
  surface before recalibrating
• Incorrect Range
• Rare problem because ranges are easy to change in
  software
• If readings are too small to be detected, may
  need to change the hardware in the sensor to
  amplify the readings

8
Feed Forward Control

• If we know what disturbances will appear in the
  robot, we can correct for them ahead of time
• Example dropping battery power. If we had a
  sensor to tell us the amount of battery power
  left, we could compensate when the power got low
  by running the routines for a longer period of
  time.
• Not particularly useful unless there is no time
  to correct for the know disturbance beforehand