EECS 192: Mechatronics Design Lab Discussion 6: Velocity Control written by: Richard ”Ducky” Lin Spring 2015 1 & 2 Mar 2017 (Week 6) 1 Velocity Sensing 2 Feedback Control 3 Summary Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 1 / 11
Velocity Sensing Velocity Sensing Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 2 / 11
Velocity Sensing Basics Brainstorm! What are some ways to sense velocity? pros and cons of your methods? Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 3 / 11
Velocity Sensing Simple Encoder Optical Encoders Optical encoders... ◮ Detects when sensor lit up ◮ Reflective sensor: light up codewheel, sensor detects reflection ◮ Photointerruptors: direct light beam from transmittor to detector, interrupt by object ◮ Simple designs vulnerable to ambient light Hopefully a fairly Hamamatsu S6986... readable schematic ◮ High-pass filter and LED modulation for background light rejection ◮ Open-collector output Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 4 / 11
Velocity Sensing Simple Encoder Software Techniques Two simple ways to measure speed: Pulse width measurement ◮ Measure width between transitions Pulse counting ◮ Count number of transitions in timespan Hopefully a fairly Advantages and disadvantages of both? readable schematic Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 5 / 11
Velocity Sensing Simple Encoder Live Demo! Low speed demo see blinking LEDs! High speed demo what waveforms should you expect to see? Issues skipped pulses, inconsistent pulse lengths Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 6 / 11
Velocity Sensing Issues Uh-oh! What are some ways to deal with inconsistent pulse sizing / other issues? pros and cons of your methods? Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 7 / 11
Velocity Sensing Issues Moving Average Filter ◮ Average pulse widths over a entire revolution Hopefully a fairly readable schematic Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 8 / 11
Feedback Control Feedback Control Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 9 / 11
Feedback Control PID control PID ◮ Proportional Control ◮ Change output by p ∗ ( difference between sensor input and data ) ◮ Very intuitive- part of almost every PID scheme. ◮ Integral Control ◮ Change output by i ∗ ( integration of error over time) ◮ Overcomes offset errors (example: friction) ◮ Derivative Control ◮ Change output by d ∗ ( instantaneous derivative of the error) ◮ Helps prevent oscillation (example: steering) ◮ Video about PID control on vehicle ◮ https://www.youtube.com/watch?v=4Y7zG48uHRo ◮ Video courtesy of MIT Aerospace Controls Lab Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 10 / 11
Summary Summary ◮ Optical Encoders ◮ The way you process data affects how you acquire data. Be aware of the effects of errors/noise ◮ PID control overview Ducky (UCB EECS) Mechatronics Design Lab 1 & 2 Mar 2017 (Week 6) 11 / 11
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