Interstructural and Inertial Actuator

Abstract

Disclosed is an electrodynamic actuator that simultaneously produces a controlled linear combination of interstructural and inertial forces. Two coil pairs interact with radial or axial permanent magnets. The forces produced in the coil pairs acts between an end of the actuator and a common moveable mass. If the coil pair forces are equal and in the same direction they make the mass move and produce an inertial output force. If the coil pair forces are equal and in opposite directions the mass does not move and interstructural forces are produced between the two ends of the actuator. Combinations of inertial and interstructural forces are produced in a controlled manner by coordinating the electrical current through each coil pair. The actuator efficiency and the low frequency inertial force outputs are greatly improved compared to separate dedicated inertial and interstructural actuators.

Claims

1. An electrodynamic actuator comprising: a first coil pair; a second coil pair; a first heat conducting armature, with a first end and a second end, that supports the first coil pair; a second heat conducting armature, with a first end and a second end, that supports the second coil pair; a first actuator end plate attached to the first end of the first heat conducting armature; a second actuator end plate attached to the first end of the second heat conducting armature; an inner flux return; a first inner radial magnet ring pair attached to the inner flux return; a second inner radial magnet ring pair attached to the inner flux return; an outer flux return, attached to and surrounding the inner flux return, with a first end and a second end, wherein the first end is slidably mounted to the first actuator end plate by bearings sliding on bearing shafts mounted to the first actuator end plate and wherein the second end is slidably mounted to the second actuator end plate by bearings sliding on bearing shafts mounted to the second actuator end plate; a first outer radial magnet ring pair attached to the outer flux return; a second outer radial magnet ring pair attached to the outer flux return; and springs between the first actuator end plate and the second actuator end plate to provide a return force between the outer flux return and the actuator end plate.

2. The electrodynamic actuator of claim 1, wherein coils of the first coil pair are connected to have electric current flow equally in opposite directions.

3. The electrodynamic actuator of claim 1 wherein coils of the second coil pair are connected to have electric current flow equally in opposite directions.

4. The electrodynamic actuator of claim 1, wherein coils of the first coil pair are connected in series and coils of the second coil pair are connected in series.

5. The electrodynamic actuator of claim 1, wherein coils of the first coil pair are connected in parallel and coils of the second coil pair are connected in parallel.

6. The electrodynamic actuator of claim 1, wherein the first inner radial magnet ring pair and the first outer radial magnet ring pair are axially aligned with each other.

7. The electrodynamic actuator of claim 1, wherein the second inner radial magnet ring pair and the second outer radial magnet ring pair are axially aligned with each other.

8. The electrodynamic actuator of claim 1, wherein rings of the first inner radial magnet ring pair are polarized opposite to each other.

9. The electrodynamic actuator of claim 1, wherein rings of the second inner radial magnet ring pair are polarized opposite to each other.

10. The electrodynamic actuator of claim 1, wherein the inner flux return and the outer flux return move as a unit relative to the first and second coil pairs.

11. The electrodynamic actuator of claim 1, wherein the outer flux return, the first inner radial magnet ring pair, the second inner radial magnet ring pair, the first outer radial magnet ring pair, the second outer radial magnet ring pair, and the inner flux return constitute the inertial reaction mass of the actuator.

12. The electrodynamic actuator of claim 1, wherein forces from the first coil pair combine with same direction forces from the second coil pair to produce a controlled inertial force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

13. The electrodynamic actuator of claim 1, wherein forces from the first coil pair combine with opposite direction forces from the second coil pair to produce a controlled interstructural force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

14. The electrodynamic actuator of claim 1, wherein the heat conducting armature is made of a non-magnetic material with a high thermal conductivity.

15. The electrodynamic actuator of claim 1, wherein the heat conducting armature includes axial slots that reduce eddy current production

16. An electrodynamic actuator comprising: a first coil pair; a second coil pair; a heat conducting armature, with a first end and a second end, that supports the first coil pair and the second coil pair; a first actuator end plate attached to the first end of the heat conducting armature; a second actuator end plate attached to the second end of the second heat conducting armature; a first end support; a second end support; a center support placed between the first end support and the second end support; a first axially polarized magnet attached between the first end support and the center support; a second axially polarized magnet attached between the second end support and the center support. an outer flux return, attached to and surrounding the first end support, the second end support, the center support, the first polarized magnet and the second polarized magnet, with a first end and a second end, wherein the first end is slidably mounted to the first actuator end plate by hearings sliding on bearing shafts mounted to the first actuator end plate and the second end is slidably mounted to the second actuator end plate by bearings sliding on bearing shafts mounted to the second actuator end plate; a first outer radial magnet ring pair attached to the outer flux return; a second outer radial magnet ring pair attached to the outer flux return; and. springs separately connected to the first actuator end plate and to the second actuator end plate to provide a return force between the outer flux return and the actuator end plate,

17. The electrodynamic actuator of claim 16, wherein coils of the first coil pair are connected to have electric current flow equally in opposite directions.

18. The electrodynamic actuator of claim 16 wherein coils of the second coil pair are connected to have electric current flow equally in opposite directions.

19. The electrodynamic actuator of claim 16, wherein coils of the first coil pair are connected in series and coils of the second coil pair are connected in series.

20. The electrodynamic actuator of claim 16, wherein coils of the first coil pair are connected in parallel and coils of the second coil pair are connected in parallel.

21. The electrodynamic actuator of claim 16, wherein the first axially polarized magnet is polarized opposite the second polarized magnet.

22. The electrodynamic actuator of claim 16, wherein the magnetic flux of the first axially polarized magnet combines with the magnetic flux of the first outer radial magnet ring pair creating a strong radial magnetic field through the first coil pair.

23. The electrodynamic actuator of claim 16, wherein the magnetic flux of the second axially polarized magnet combines with the magnetic flux of the second outer radial magnetic ring pair creating a strong radial magnetic field through the second coil pair.

24. The electrodynamic actuator of claim 16, wherein forces from the first coil pair combine with same direction forces from the second coil pair to produce a controlled inertial force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

25. The electrodynamic actuator of claim 16, wherein forces from the first coil pair combine with opposite direction forces from the second coil pair to produce a controlled interstructural force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

26. The electrodynamic actuator of claim 16, wherein the heat conducting armature is made of a non-magnetic material with a high thermal conductivity.

27. The electrodynamic actuator of claim 16, wherein the heat conducting armature includes axial slots that reduce eddy current production

28. An electrodynamic actuator comprising: a first inner flux return with a first end and a second end; a first inner radial magnet ring pair attached around the first inner flux return; a second inner flux return with a first end and a second end; a second inner radial magnet ring pair attached around the second inner flux return; a first actuator end plate attached to the first end of first inner flux return; a second actuator end plate attached to the first end of the second inner flux return; a first coil pair; a second coil pair; an outer flux return, with a first end and a second end, that surrounds and supports the first and second coil pair, wherein the first end of the outer flux return is slidably mounted to the first actuator end plate by bearings sliding on bearing shafts mounted to the first actuator end plate and the second end is slidably mounted to the second actuator end plate by bearings sliding on bearing shafts mounted to the second actuator end plate; and springs separately attached to the first actuator end plate and the second actuator end plate to provide a return force between the outer flux return and the actuator end plates.

29. The electrodynamic actuator of claim 28, wherein coils of the first coil pair are connected to have electric current flow equally in opposite directions.

30. The electrodynamic actuator of claim 28, wherein coils of the second coil pair are connected to have electric current flow equally in opposite directions.

31. The electrodynamic actuator of claim 28, wherein coils of the first coil pair are connected in series and coils of the second coil pair are connected in series.

32. The electrodynamic actuator of claim 28, wherein coils of the first coil pair are connected in parallel and coils of the second coil pair are connected in parallel.

33. The electrodynamic actuator of claim 28, wherein rings of the first inner radial magnet ring pair are polarized opposite to each other.

34. The electrodynamic actuator of claim 28, wherein rings of the second inner radial magnet ring pair are polarized opposite to each other.

35. The electrodynamic actuator of claim 28 wherein the outer flux return completes a flux path for the first and second inner radial magnet ring pairs.

36. The electrodynamic actuator of claim 28, wherein the outer flux return, the first coil pair, and the second coil pair constitute an inertial reaction mass of the actuator.

37. The electrodynamic actuator of claim 28, wherein forces from the first coil pair combine with same direction forces from the second coil pair to produce a controlled inertial force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

38. The electrodynamic actuator of claim 28, wherein forces from the first coil pair combine with opposite direction forces from the second coil pair to produce a controlled interstructural force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

39. An electrodynamic actuator comprising: a first axially polarized magnet; a first end support attached to the first axially polarized magnet; a second axially polarized magnet; a second end support attached to the second axially polarized magnet; a first actuator end plate attached to the first end support; a second actuator end plate attached to the second end support; a first coil pair; a second coil pair; an outer flux return, with a first end and a second end, that surrounds and supports the first coil pair and the second coil pair, wherein the first end of the outer flux return is slidably mounted to the first actuator end plate by bearings sliding on bearing shafts mounted to the first actuator end plate and the second end is slidably mounted to the second actuator end plate s by bearings sliding on bearing shafts mounted to the second actuator end plate; and springs separately attached to the first actuator end plate and the second actuator end plate to provide a return force between the outer flux return and the actuator end plates.

40. The electrodynamic actuator of claim 39 wherein coils of the first coil pair are connected to have electric current flow equally in opposite directions.

41. The electrodynamic actuator of claim 39 wherein coils of the second coil pair are connected to have electric current flow equally in opposite directions.

42. The electrodynamic actuator of claim 39, wherein coils of the first coil pair are connected in series and coils of the second coil pair are connected in series.

43. The electrodynamic actuator of claim 39, wherein coils of the first coil pair are connected in parallel and coils of the second coil pair are connected in parallel.

44. The electrodynamic actuator of claim 39, wherein the first axially polarized magnet is polarized opposite the second axially polarized magnet.

45. The electrodynamic actuator of claim 39, wherein the outer flux return completes a flux path for the first and second axially polarized magnets.

46. The electrodynamic actuator of claim 39, wherein forces from the first coil pair combine with same direction forces from the second coil pair to produce a controlled inertial force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

47. The electrodynamic actuator of claim 39, wherein forces from the first coil pair combine with opposite direction forces from the second coil pair to produce a controlled interstructural force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

48. An electrodynamic actuator comprising; a first inner flux return; a first coil pair attached around the first inner flux return; a first end support attached to the first inner flux return; a second inner flux return; a second coil pair attached around the second inner flux return; a second end support attached to the second inner flux return; a first actuator end plate attached to the first end support; a second actuator end plate attached to the second end support; an outer flux return, with a first end and a second end, that surrounds the first coil pair, wherein the first end of the outer flux return is slidably mounted to the first actuator end plate by bearings sliding on bearing shafts mounted to the first actuator end plate and the second end is slidably mounted to the second actuator end plate by bearings sliding on bearing shafts mounted to the second actuator end plate; a first pair of outer radial magnet rings attached to the outer flux return; a second pair of outer radial magnet rings attached to the outer flux return; and springs separately attached to the first actuator end plate and the second actuator end plate to provide a return force between the outer flux return and the actuator end plates.

49. The electrodynamic actuator of claim 48, wherein coils the first coil pair are connected to have electric current flow in opposite directions.

50. The electrodynamic actuator of claim 48, wherein coils the second coil pair are connected to have electric current flow in opposite directions.

51. The electrodynamic actuator of claim 48, wherein coils of the first coil pair are connected in series and coils of the second coil pair are connected in series.

52. The electrodynamic actuator of claim 48, wherein coils of the first coil pair are connected in parallel and coils of the second coil pair are connected in parallel.

53. The electrodynamic actuator of claim 48, wherein magnet rings of the first pair of outer radial magnet rings are polarized opposite each other.

54. The electrodynamic actuator of claim 48, wherein magnet rings of the second pair of outer radial magnet rings are polarized opposite each other.

55. The electrodynamic actuator of claim 48, wherein the outer flux return, the first coil pair, and the second coil pair constitute an inertial reaction mass of the actuator.

56. The electrodynamic actuator of claim 48, wherein the first and second inner flux returns complete a flux path for the outer radial magnet ring pairs.

57. The electrodynamic actuator of claim 48, wherein forces from the first coil pair combine with same direction forces from the second coil pair to produce a controlled inertial force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

58. The electrodynamic actuator of claim 48, wherein forces from the first coil pair combine with opposite direction forces from the second coil pair to produce a controlled interstructural force at the first and second end plates, by coordinating electrical current through each coil pair through an inverted gain matrix transformation.

Description

DRAWINGS

[0016] FIG. 1 is a cross-sectional view of a first embodiment of the present invention.

[0017] FIG. 2 is an exploded component view of a first embodiment of the present invention.

[0018] FIG. 3 shows the calculated magnetic flux lines with no drive current for a first embodiment of the present invention.

[0019] FIG. 4 is a schematic of the signal and current low which illustrates how coil pair 101 and coil pair 102 are driven to achieve a linear combination of inertial and interstructural forces.

[0020] FIG. 5a shows an example random force demand for an inertial actuator.

[0021] FIG. 5b shows an example random force demand for an interstructural actuator.

[0022] FIG. 6a shows the example inertial and interstructural force demands of FIGS. 5a and 5b transformed into force demand for coil pair 101 of the present invention.

[0023] FIG. 6b shows the example inertial and interstructural force demands of FIG. 5a and 5b transformed into force demand for coil pair 102 of the present invention.

[0024] FIG. 7 shows the calculated magnetic flux lines with no drive current for a second embodiment of the present invention.

[0025] FIG. 8 is a cross-sectional view of a third embodiment of the present invention.

[0026] FIG. 9 is an exploded component view of a third embodiment of the present invention.

[0027] FIG. 10 shows the calculated magnetic flux lines with no drive current for a third embodiment of the present invention.

[0028] FIG. 11 shows the calculated magnetic flux lines with no drive current for a fourth embodiment of the present invention,

[0029] FIG. 12 shows the calculated magnetic flux lines with no drive current for a fifth embodiment of the present invention.

DETAILED DESCRIPTION

[0030] FIGS. 1 and 2 illustrate an embodiment of the interstructural and inertial actuator (actuator) of the present invention. FIG. 1 is a cross-sectional view of the actuator, while FIG. 2 is an exploded component view of the actuator. FIG. 3 shows the magnetic flux lines (F) of the same embodiment of the actuator with no drive current and with assumed magnet polarization directions shown by arrows (B).

[0031] Referring to the actuator embodiment in FIGS. 1 and 2, a coil pair (101) is supported by a heat conducting armature (107) which is attached to an actuator end plate (108) at one end of the actuator. Coil pair (102) is also supported by heat conducting armature (107) which is attached to an actuator end plate (108) at the opposite end of the actuator. Consequently, forces generated in coil pairs (101) and (102) are transferred to opposite ends of the actuator. The two coils of each pair are connected to have electric current flow in opposite directions. So, if current is flowing clockwise through one coil then it will be flowing counterclockwise in the other coil. The coils of a pair may be connected in series or parallel as long as the current flow is equal and in opposite directions.

[0032] Inner radial magnet ring pair (103) and inner radial magnet ring pair (105) are attached to inner flux return (113). Outer radial magnet ring pair (104) and outer radial magnet ring pair (106) are attached to outer flux return (112). The inner and outer flux returns (113) and (112) are attached to each other and move as a unit relative to coil pairs (101) and (102). Inner radial magnet ring pair (103) and outer radial magnet ring pair (104) are axially aligned with each other. Likewise inner radial magnet ring pair (105) and outer radial magnet ring pair (106) are axially aligned with each other. The magnet rings of each pair are polarized opposite to each other as shown in FIG. 3 by arrows B. Therefore, if one of the magnet rings of the magnet ring pair (103) is polarized outward, as shown in FIG. 3, then the other magnet ring of the pair (103) is polarized inward. The axially aligned magnetic rings are polarized in the same direction. So, if a magnet ring of pair (103) is polarized outward as shown in FIG. 3, then the magnet ring of pair (104) that is axially aligned with that ring of pair (103) is also polarized outward. The effect is to create strong radial magnetic fields, shown by lines of flux F, between the inner flux return (113) and outer flux returns (112) that pass through coil pairs (101) and (102). When current flows through the coils, axial forces are created by the Lorentz principle. The direction of magnetic flux for each coil of a pair is opposite the other coil and the direction of current flow is also opposite the other. Therefore axial forces created by each coil of a pair are in the same direction and the forces add.

[0033] Outer flux return (112) is slidably mounted onto the two actuator end plates (108) by bearings (110) sliding on bearing shafts (109). Springs (111) provide a return force between outer flux return (112) and the actuator end plates (108). The outer flux return (112), the magnet ring pairs (103), (104), (105), and (106), and the inner flux return (113) constitute the inertial reaction mass of the actuator.

[0034] The heat conducting armatures (107) are preferably made of a non-magnetic material with a high thermal conductivity such as aluminum. Such materials also have a high electrical conductivity. Therefore a solid armature would have eddy currents induced both by the fluctuating magnetic fields from the current conducting coils and by the relative motion of the permanent magnet fields. The armatures (107) of the present invention include vertical slits that prevent significant eddy currents from being induced while allowing heat flow in the axial direction.

[0035] FIG. 4 is a schematic of the signal and current flow that illustrates how coil pair (101) and coil pair (102) are driven to achieve a linear combination of inertial and interstructural forces. An input inertial force command and an input interstructural force command, which are independent and arbitrary, are multiplied by the inverted gain matrix which transforms them into coil current commands 1 and 2. Coil current command 1 goes to an amplifier that produces current through coil pair (101) and coil current command 2 goes to another amplifier that produces current through coil pair (102). The coil pairs (101) and (102) produce axial forces in response to the current. The portion of the coil pairs forces that are in the same direction produce a combined inertial output force which is equal to the input inertial force command. The portion of the coil pairs forces that are in opposite directions produce a combined interstructural output force which is equal to the input interstructural force command.

[0036] FIGS. 5a and 5b illustrate an example of random inertial and interstructural demand forces. If separate inertial and interstructural actuators were designed to produce these forces as in the current art, then the inertial actuator would have to produce an RMS force of 285N as shown in FIG. 5a and a separate interstructural actuator would have to produce an RMS force of 286 N as shown in FIG. 5b.

[0037] FIGS. 6a and 6b illustrate the effect of transforming the demand forces of FIGS. 5a and 5b to coil pair (101) and coil pair (102) of the actuator of the current invention as illustrated in FIG. 4. In this example, coil pair (101) has to produce an RMS force of 197 N as shown in FIG. 6a and coil pair (102) has to produce an RMS force of 206 N as shown in FIG. 6b. The total RMS force is 403 N for the present invention rather than the 571 N of the prior art, for an efficiency improvement of 29%.

[0038] FIG. 7 illustrates the calculated magnetic flux lines F with no drive current for a second embodiment of the present invention. The assumed magnet polarization direction is shown by arrows B. Compared to the first embodiment, this embodiment replaces the inner flux return (113) and inner radial magnet ring pairs (103) and (105) with axially polarized magnets (214), center support (215), and two end supports (216). Axially polarized magnets (214) are polarized opposite to each other as shown by arrows B. The magnetic flux of the first axially polarized magnet (214) combines with the magnetic flux of outer radial magnet ring pair (104). The magnetic flux of the second axially polarized magnet (214) combines with the magnetic flux of outer radial magnet ring pair (106). The effect is to create strong radial magnetic fields, shown by lines of flux (F), through coil pairs (101) and (102). All other aspects of this embodiment are the same as the first embodiment.

[0039] FIGS. 8 and 9 are views of a third embodiment of the present invention. FIG. 8 is a cross-sectional view of the actuator embodiment, while FIG. 9 is an exploded component view. FIG. 10 illustrates the calculated magnetic flux lines (F) with no drive current, and with assumed magnet polarization directions shown by arrows B.

[0040] Referring to FIGS. 8 and 9, coil pair (301) and coil pair (302) are supported by outer flux return (312). The two coils of each pair are connected to have electric current flow in opposite directions. So, if current is flowing clockwise through one coil of the pair (301) then it will be flowing counterclockwise in the other coil of the pair (301), as shown in FIG. 10. The coils of a pair may be connected in series or parallel as long as the current flow is equal and in opposite directions.

[0041] Inner radial magnet ring pair (303) and inner radial magnet ring pair (305) are each attached to one of the two inner flux returns (313). The Magnet rings of each pair are polarized opposite each other as shown in FIG. 10 by arrows (B). Therefore, if one magnet ring of the pair (303) is polarized outward as shown in FIG. 10 then the other magnet ring of the pair (303) is polarized inward. Outer flux return (312) completes the flux path for the inner radial magnet ring pairs (303) and (305). The effect is to create strong radial magnetic fields, shown by lines of flux (F), between the inner flux return (313) and outer flux returns (312) that pass through coil pairs (301) and (302). When current flows through the coils, axial forces are created by the Lorentz principle. The direction of magnetic flux and current flow for each coil of a pair is opposite the other coil. Therefore axial forces created by each coil of a pair are in the same direction and the forces add.

[0042] Outer flux return (312) is slidably mounted to the two actuator end plates (308) by bearings (310) sliding on bearing shafts (309). Springs (311) provide a return force between outer flux return (312) and the actuator end plates (308). The outer flux return (312) and coil pairs (301) and (302) constitute the inertial reaction mass of the actuator.

[0043] Each inner flux return (313) is attached to an end support (316) which is attached to an actuator end plate (308). When Lorentz forces are generated in coil pairs (301) and (302), equal and opposite forces are generated in the inner radial magnet ring pairs (303) and (305). These forces are transferred to the actuator end plates (308).

[0044] FIG. 11 illustrates the calculated magnetic flux lines (F) with no drive current for a fourth embodiment of the present invention. The assumed magnet polarization direction is shown by arrows B. Compared to the third embodiment, the fourth embodiment replaces the inner flux returns (313) and inner radial magnet ring pairs (303) and (305) with axially polarized magnet pair (414) and the two end supports (416). The two axially polarized magnets of the pair (414) are polarized opposite to each other as shown in FIG. 11 by arrows B. Outer flux return (312) completes the flux path for axially polarized magnets (414). The effect is to create strong radial magnetic fields as shown by the lines of flux (F) that pass through coil pairs (301) and (302). All other aspects of the fourth embodiment are the same as the third embodiment.

[0045] FIG. 12 illustrates the calculated magnetic flux lines (F) with no drive current for the fifth embodiment of the present invention. The assumed magnet polarization direction is shown by arrows B. Compared to the third embodiment, the fifth embodiment has inner coils and outer magnet rings. Coil pair (501) and coil pair (502) are each attached to one of the two inner flux returns (513). The two coils of each pair are connected to have electric current flow in opposite directions. That is, if current is flowing clockwise through one coil of the pair (501) then it will be flowing counterclockwise in the other coil of the pair (501). The coils of a pair may be connected in series or parallel as long as the current flow is equal and in opposite directions.

[0046] Outer radial magnet ring pair (504) and outer radial magnet ring pair (506) are each attached to outer flux return (512). The magnet rings of each pair are polarized opposite of each other as shown in FIG. 12 by arrows (B). If one of the magnet rings of the pair (504) is polarized outward as shown in FIG. 12, then the other magnet ring of the pair (504) is polarized inward. Inner flux returns (513) complete the flux path for the outer radial magnet ring pairs (504) and (506). The effect is to create strong radial magnetic fields, shown by lines of flux (F), between the inner and outer flux returns (513) and (512) that pass through coil pairs (501) and (502). When current flows through the coils, axial forces are created by the Lorentz principle. The direction of magnetic flux for each coil of a pair is opposite the other coil. Also, the direction of current flow for each coil of a pair is also opposite the other coil. Therefore, axial forces created by each coil of a pair are in the same direction and the forces add. Each inner flux return (513) is attached to an end support (516) which is attached to an actuator end plate (308). Therefore forces generated in coil pairs (501) and (502) are transferred to opposite ends of the actuator.

[0047] Outer flux return (512) is slidably mounted to the two actuator end plates (308) by bearings (310) sliding on bearing shafts (309). Springs (311) provide a return force between outer flux return (312) and the actuator end plates (308). The outer flux return (512) and magnet pairs (504) and (506) constitute the inertial reaction mass of the actuator.

[0048] Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is the intent of this application to cover, in the appended claims, all such modification and equivalents. The entire disclosure and all references, applications, patents and publications cited above are hereby incorporated by reference