Hall sensor—magnet geometry for large stroke linear position sensing
Position sensing units, comprising a magnetic assembly (MA) having a width W measured along a first direction and a height H measured along a second direction and including at least three magnets having respective magnetic polarizations that define along the first direction at least a left MA domain, a middle MA domain and a right MA domain, wherein the magnetic polarizations of each MA domain are different, and a magnetic flux measuring device (MFMD) for measuring a magnetic flux B, wherein the MA moves relative to the MFMD along the first direction within a stroke L that fulfils 1 mm≤L≤100 mm, stroke L beginning at a first point x 0 and ending at a final point x max , and wherein a minimum value D min of an orthogonal distance D, measured along the second direction between a particular MA domain and the MFMD, fulfills L/D min >10.
1. A position sensing unit, comprising:
a) a magnetic assembly (MA) having a width W measured along a first direction and a height H measured along a second direction and including at least three magnets having respective magnetic polarizations that define along the first direction at least a left MA domain, a middle MA domain and a right MA domain, wherein the magnetic polarizations of each MA domain are different; and
b) a magnetic flux measuring device (MFMD) for measuring a magnetic flux B,
wherein the MA is configured to move relative to the MFMD along the first direction within a stroke L that fulfils 1 mm≤L≤100 mm, stroke L beginning at a first point x 0 and ending at a final point x max over which the magnetic flux B changes, and wherein a minimum value D min of an orthogonal distance D measured along the second direction between a particular MA domain and the MFMD of the position sensing unit, fulfills L/D min >10,
wherein the at least three magnets are positioned sequentially along the first direction, and wherein adjacent magnets are separated by a gap.
2. The position sensing unit of claim 1 , wherein the MA has a symmetry axis parallel to the second direction.
3. The position sensing unit of claim 2 , wherein the symmetry axis is located at a center of the middle MA domain.
4. The position sensing unit of claim 1 , wherein D is not constant for different positions within stroke L.
5. The position sensing unit of claim 4 , wherein a value of D between the left MA domain and MFMD is D(x 0 ), wherein a value of D between the right MA domain and the MFMD is D(x max ), wherein a value of D between the middle MA domain and the MFMD is D(x max/2 ) and wherein D(x 0 )≤D(x max/2 ) and D(x max )≤D(x max/2 ).
6. The position sensing unit of claim 4 , wherein a value of D between the left MA domain and MFMD is D(x 0 ), wherein a value of D between the right MA domain and the MFMD is D(x max ), wherein a value of D between the middle MA domain and the MFMD is D(x max/2 ) and wherein D(x 0 )=D(x max )≤D(x max/2 ).
7. The position sensing unit of claim 1 , wherein L/D min >15.
8. The position sensing unit of claim 1 , wherein L/D min >20.
9. The position sensing unit of claim 1 , wherein B at x 0 is B 0 and B at x max is B max and wherein a slope S=(B 0 −B max )/L is larger than 10 mT/mm.
10. The position sensing unit of claim 1 , wherein B at x 0 is B 0 and B at x max is B max and wherein a slope S=(B 0 −B max )/L is larger than 100 mT/mm.
11. The position sensing unit of claim 1 , wherein B at x 0 is B 0 and B at x max is B max and wherein a slope S=(B 0 −B max )/L is larger than 1000 mT/mm.
12. The position sensing unit of claim 1 , wherein B at x 0 is B 0 and B at x max is B max and wherein a slope S=(B 0 −B max )/L is larger than 2500 mT/mm.
13. The position sensing unit of claim 1 , wherein the magnetic polarization of the left MA domain is directed towards the MFMD.
14. The position sensing unit of claim 1 , wherein the magnetic polarization of the right MA domain is directed away from the MFMD.
15. The position sensing unit of claim 1 , wherein the magnetic polarization of the middle MA domain is directed parallel or anti-parallel to the first direction.
16. The position sensing unit of claim 1 , included in a voice coil motor (VCM).
17. The position sensing unit of claim 16 , wherein the VCM includes four coils.
18. The position sensing unit of claim 16 , wherein the VCM is included in smartphone camera.
19. The position sensing unit of claim 1 , wherein the MFMD is a Hall sensor.
20. The position sensing unit of claim 1 , wherein the left, middle and right MA domains are rectangular.
21. The position sensing unit of claim 1 , wherein the left and right MA domains are trapezoids, and the middle MA domain is a convex pentagon.
22. The position sensing unit of claim 1 , wherein the left and right MA domains are trapezoids, and the middle MA domain is a concave pentagon.
23. The position sensing unit of claim 1 , wherein the MA additionally includes a fourth MA domain and a fifth MA domain having respective magnetic polarizations, wherein the fourth MA domain is located to the left of the left MA domain and wherein the fifth MA domain is located to the right of the right MA domain.
24. The position sensing unit of claim 23 , wherein the magnetic polarization of the fourth MA domain is directed away from the MFMD.
25. The position sensing unit of claim 23 , wherein the magnetic polarization of the fifth MA domain is directed towards the MFMD.
26. The position sensing unit of claim 1 , wherein L<20 mm.
27. The position sensing unit of claim 1 , wherein L<10 mm.
28. The position sensing unit of claim 1 , wherein L<7.5 mm.
29. The position sensing unit of claim 1 , wherein L<5 mm.
30. The position sensing unit of claim 1 , wherein L/W>0.5.
31. The position sensing unit of claim 1 , wherein L/W>0.75.
32. The position sensing unit of claim 1 , wherein L/H>3.
33. The position sensing unit of claim 1 , wherein L/H>5.
34. The position sensing unit of claim 1 , wherein the at least three magnets are made from a Neodymium based material.