Pioneers in Engineering

1. Pioneers in Engineering Week 8: Sensors and Feedback

2. Announcements • T-Shirts – Order by tomorrow! • Zipcards/Badges – contact us if you still need them • Zipcar voting contest starts tonight

3. Lesson Agenda • Definition of systems • Overview of controls • Introduction to sensors

4. Lesson Agenda • Definition of systems • Overview of controls • Introduction to sensors

5. Systems • A system is a function. SYSTEM INPUT OUTPUT

6. Example of Systems • F1 Car INPUT? OUTPUT?

7. Lesson Agenda • Definition of systems • Overview of controls • Introduction to sensors

8. What is controls theory? • The study of how to choose the input to a system to give the desired output. • The entity which generates the input is called a controller

9. Cruise Control Example Pedal Position Vehicle speed Desired speed CONTROLLER

10. Open-Loop Control • No measurements of system output, y (i.e. no feedback) CONTROLLER SYSTEM y u r

11. Open-Loop Control-Cruise Control Example Pedal Position Vehicle speed Desired speed CONTROLLER

12. Open-Loop Control - Implementation • Suppose system is invertible function f • Choose controller to be f -1 CONTROLLERf-1(r) SYSTEM f(u) y=r u r

13. Open-Loop Control - Brainstorm

14. Open-Loop Control - Problems • Usually we don’t know what the system is exactly • Model Mismatch–Model not the same as real car Laboratory Model Reality • Disturbances–gravity, wind, etc.

15. Solution: Feedback Control r • Measure output and send to controller • Controller usually acts on the error e=r-y’ CONTROLLER u SYSTEM y y’ SENSOR

16. Feedback Control-Cruise Control Example Controller Input CONTROLLER Desired speed Vehicle speed

17. Videos • Inverted Pendulum • Line Following Car • Quadrotors

18. Feedback Control r CONTROLLER u SYSTEM y y’ SENSOR

19. Lesson Agenda • Definition of systems • Overview of controls • Introduction to sensors

20. Sensor Input Types • Analog • Continuum of values • Digital • Value is 0 or 1

21. Digital Switch Sensor • DigitalSensorclass • Can be wired Normally Closed (NC) or Normally Open (NO) • Uses • Collision detection • Limit switch(limiting a mechanism’s range of motion) • Price: $2

22. IR Rangefinder • AnalogIRDistanceSensor class • Measures distance to object directly in front • Uses • Better collision detection • Navigation in a narrowpassageway • Cautions • Watch out for minimum detection distance • Price: $10/15

23. IR Rangefinder (Digital) • DigitalDistanceSensor class • Outputs LOW if an object is within its detection range (e.g. 4-10 cm) • Price:$2

24. Sonar Rangefinder • AnalogSonarSensor class • Pros • More accurate • Robust to sunlight • Cons • More expensive • Not good with absorbent objects • Cautions • Do not cross two beams (sonar may pick up its neighbor’s pulses) • Price:$30

25. Potentiometers • AnalogPotentiometer class • Available in linear and rotary forms • Uses • Detect mechanism position (e.g. jointed arm, lifts) • Price:$2

26. Encoders • GrizzlyEncoder class • Continuous rotation • Measures rotation; can calculate distance, velocity

27. Encoders • Uses • Detect mechanism position • Drive for a set distance • Set wheel velocity (i.e. driving straight) • Cautions • Wheel slipping (around turns and in collisions) • Price:$15 more than motors without encoders

28. RFID Sensor • Rfid class • Returns the ID of the current item scanned and the last item scanned.

29. Where do I get them? • Everything is available in Kit Extension for Panda points! • You can buy and return them for full refund if they are unaltered • Request parts via the forum