D cmotortutorial
- 1. Motor Tutorial Kevin M. Lynch Laboratory for Intelligent Mechanical Systems Northwestern University Evanston, IL USA
- 2. Types of Motors • DC (brushed) • Stepper • RC Servo • Solenoid
- 3. Types of Motors • DC (brushed) • Stepper • RC Servo • Solenoid Workhorse, high power Simple to use, two wires Torque proportional to current, steady state constant-load speed proportional to voltage Requires gearing Requires feedback
- 4. Types of Motors • DC (brushed) • Stepper • RC Servo • Solenoid Useful for low-torque applications with no surprises No feedback required One step per pulse More involved driving circuit
- 5. Types of Motors • DC (brushed) • Stepper • RC Servo • Solenoid High torque, useful for positioning applications Feedback and gearing built in Position commanded by persistent pulse train Limited motion (less than 1 revolution)
- 6. Types of Motors • DC (brushed) • Stepper • RC Servo • Solenoid For on-off applications Simple to use Short stroke Powered in only one direction; requires external spring for return
- 7. DC Motors Lorentz Force Law: F = I x B F = force on wire I = current B = magnetic field Right hand rule: index finger along I, middle finger along B, thumb along F N S
- 8. Inside a DC Motor
- 9. DC Motors V = IR + L (dI/dt) + k e = k t I V voltage I current R resistance L inductance speed torque k e electrical constant k t torque constant speed-torque curves for two voltages 2 - permanent magnet 3 - housing (magnetic return) 4 - shaft 5 - winding
- 10. DC Motor Specs
- 11. Driving a DC Motor Switches and relays Transistors Linear push-pull stage with op amp Ideally: H-bridge and PWM
- 12. H-bridge and PWM PWM: Rapidly switch between S1-S4 closed and S2-S3 closed Averages to effective voltage across motor between -V and +V depending on time spent in S1-S4 and S2-S3 states Switch control signals are simply digital signals Use an H-bridge chip or build out of transistors
- 14. Practical Issues flyback diodes for “inductive kick” heat sinks for transistors capacitors to smooth voltage spikes other noise issues, isolation
- 15. Gears Gear ratio G out = in / G out = G in ( = efficiency) Many types spur, planetary, worm, lead/ball screw, bevel, harmonic...
- 16. Encoder Feedback Another option: potentiometer US Digital
- 17. Feedback Control Proportional (Integral-Derivative) Control Multiply position/velocity error by a gain to get control signal (and perhaps add integral and derivative of that error multiplied by other gains) Usually implemented on computer Can be implemented with op amps
- 18. Stepper Motor Bipolar: 4 wires Unipolar: 5 or 6 wires +V alternately ground one end of coil or other 1 4 2 3 A B A B R R R R L L L L L L R R R L
- 19. Animation of Unipolar Taken fro m http://www.cs.uiowa.edu/~jones/step/
- 20. Driving a Stepper Use logic on/off signals at 2, 7, 10, 15.
- 21. RC Servo Motor 3 wires: power, ground, control Control signal sets the position. High pulse every ~20 ms determines set angle; pulse width between ~0.5 ms and ~2 ms, indicating the two ends of angle range Internal gearing, potentiometer, and feedback control.
- 22. Solenoid Plunger attracted or repelled by current through a coil. May be driven by a relay or transistor.