1. Taming the Electromagnetic Solenoid: Building a System That Achieves a Soft Landing Gary Bergstrom Magnesense

2. Gary Bergstrom, Magnesense Simplified valve

3. Gary Bergstrom, Magnesense Flux in an E-core

4. Gary Bergstrom, Magnesense Electrical Rtotal=Rdrive+Rsolenoid L is inductance of solenoid Rsolenoid is a function of temperature Inductance is a strong function of position + - Drive Solenoid L Rsolenoid Rdrive

5. Gary Bergstrom, Magnesense Inductance vs. Position

6. Gary Bergstrom, Magnesense Mass, spring damper – mechanical model x m mass, Kg c damping coeff k spring coeff, N M F force, N x displacement, M x velocity, M/S x acceleration, M/S^2 m is all moving mass, including part of springs k is the net restoring force from all springs F is the net electromagnetic force from both stators c is damping from mechanical friction and gas flow x is displacement, symbolized by a pointer moving along scale m x + c x + k x = F k c m F

7. Gary Bergstrom, Magnesense Force vs. Position, various flux densities 0 200 400 600 800 1000 1200 0.000000.001000.002000.003000.004000.005000.006000.007000.00800 gap in meters force in N 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 1.7 1.5

8. Gary Bergstrom, Magnesense Force vs. Flux density, various gaps 0 200 400 600 800 1000 1200 00.20.40.60.811.21.41.61.82 Flux density in T Force in N 0.00000 0.00117 0.00218 0.00400 gap 0.00000 0.00117 0.00218 0.00400

9. Gary Bergstrom, Magnesense Flux summary Flux resists changes V=L*dI/dt only when: –x doesn’t change –no eddy current –no saturation Flux is the integral of inductive voltage Force goes as the square of flux and is a non-linear function of position

10. Gary Bergstrom, Magnesense Excel spreadsheet of simulation

11. Gary Bergstrom, Magnesense Voltage drive I=V/Rtotal if V=40V and Rtotal=.25 then I=160 Amps This can occur at saturation Power lost is I^2 * Rtotal so we want to minimize R

12. Gary Bergstrom, Magnesense Position, voltage and current

13. Gary Bergstrom, Magnesense Flux density and force

14. Gary Bergstrom, Magnesense Voltage drive details Time is in seconds Position 4.5 mm to 0 mm (plot starts near “middle”) Voltage 0 to 40 volts Flux density in Teslas Force is in Newtons Flux must = ~1.65 T to hold in this example “bounce” was set to 70% of the incoming velocity (or ½ the energy) Flux goes as integral of applied inductive voltage Force is function of position and square of flux

15. Gary Bergstrom, Magnesense Position, voltage and current

16. Gary Bergstrom, Magnesense Flux density and force

17. Gary Bergstrom, Magnesense Position, voltage and current

18. Gary Bergstrom, Magnesense Position, voltage and current

19. Gary Bergstrom, Magnesense Position, voltage and current 30V supply

20. Gary Bergstrom, Magnesense Voltage drive summary Sensitive to changes in power supply Very prone to saturating core, but need to run close to saturation due to size considerations No good correlation between applied voltage and resulting force Cannot always achieve soft landing and holding flux level at same time with simple drive Landing time very sensitive to changes in initial energy

21. Gary Bergstrom, Magnesense Current drive Rs (current sense) should be small (more I^2 * R loss) R1/R2 gain circuit is to reduce noise Diode must include both Solenoid and Rs in loop

22. Gary Bergstrom, Magnesense Position, voltage and current

23. Gary Bergstrom, Magnesense Flux density and force

24. Gary Bergstrom, Magnesense Position, voltage and current

25. Gary Bergstrom, Magnesense Position, voltage and current

26. Gary Bergstrom, Magnesense Position, voltage and current 30V supply

27. Gary Bergstrom, Magnesense Current drive summary Not very sensitive to power supply changes Saturation is not as big a problem (current is limited, saturation still occurs) Unstable – the current changes in the opposite direction from what is needed for a soft landing Back EMF forces the current around in counter-intuitive ways

28. Gary Bergstrom, Magnesense Flux drive Flux sensor needed This design uses full bridge drive More parts, more performance

29. Gary Bergstrom, Magnesense Position, voltage and current

30. Gary Bergstrom, Magnesense Flux density and force

31. Gary Bergstrom, Magnesense Position, voltage and current

32. Gary Bergstrom, Magnesense Position, voltage and current

33. Gary Bergstrom, Magnesense Position, voltage and current 30V supply

34. Gary Bergstrom, Magnesense Flux drive summary Less sensitive than voltage drive to changes in power supply Stable like voltage drive but without the saturation problem Flux, therefore force is known (if position is known) Allows position to be calculated since: x ~ current / flux Position PID loop can now be closed giving us closed loop position drive, with a well behaved open loop system

35. Gary Bergstrom, Magnesense So how do we sense flux? Hall effect sensor Sense coil “Sensorless”

36. Gary Bergstrom, Magnesense Hall effect sensor Good points: Simple DC response Low cost Small Bad points: Temperature (reliability) Some cost Extra wires Measurement position

37. Gary Bergstrom, Magnesense Sense coil Good points: Simple circuit Rugged Low cost No temperature problems Bad points: More parts Higher cost Takes up core area Extra wires

38. Gary Bergstrom, Magnesense “Sensorless” Good points: No wires Reliable No size (at valve) Can be done in software Bad points: Small temperature sensitivity Even more parts Difficult to develop Difficult to understand Flux existing drive Rtotal MULT Rsense INT