WO2007026270A1

WO2007026270A1 - Ironless magnetic linear motors having levitating and transversal force capacities

Info

Publication number: WO2007026270A1
Application number: PCT/IB2006/052772
Authority: WO
Inventors: Georgo Angelis; David Biloen
Original assignee: Koninklijke Philips Electronics, N.V.; U.S. Philips Corporation
Priority date: 2005-08-29
Filing date: 2006-08-10
Publication date: 2007-03-08
Also published as: US20140312717A1; EP1927180B1; KR101270048B1; JP5329222B2; US8803372B2; CN101253673A; EP1927180A1; US20080246348A1; KR20080046642A; JP2009506747A; CN101253673B

Abstract

A ironless magnetic motor (21-23) employs a magnetic track (30) and a forcer (40). The forcer (40) is orientated a magnetic field (β) across a linear air gap of the magnetic track (30) to generate a drive force (Fx) parallel to the X drive axis and orthogonal to the Z levitation axis in response to a commutation drive current (Ix) and to generate a force (Fz, Fy) orthogonal to the X drive axis in response to a commutation coil current (Iz, Iy) being superimposed on and phase shifted from the commutation drive current (Ix). To this end, a set of levitating turns of the coil (41) parallel to the X drive axis and orthogonal to the Z levitation axis may be internal or external to magnetic field (β), and the forcer (40) may be centered or offset from a center X-Z longitudinal axis (CP) of the linear air gap.

Description

IRONLESS MAGNETIC LINEAR MOTORS HAVING LEVITATING AND TRANSVERSAL FORCE CAPACITIES

The present invention generally relates to ironless magnetic linear motors. The present invention specifically relates to generating two or more controllable orthogonal forces in a ironless magnetic linear motor.

FIGS. 1-4 illustrate a ironless magnetic linear motor 20 employing a magnetic track 30 and a forcer 40. Magnetic track 30 includes a linear magnetic array 31 and a linear magnetic array 32 for generating a magnetic field β across a linear air gap as best shown in FIG. 3. Linear magnetic arrays 31 and 32 have 180° degree spatial separation between adjacent magnets.

Forcer 40 is disposed within the linear air gap along a center X-Z longitudinal plane CP of the linear air gap as best shown in FIG. 2, and includes three (3) coils 41-43 with a 120°+n*360 degree spatial separation (n is an arbitrary integer) between adjacent coils. As shown in FIG. 4, coil 41 is represented by its flow path for a commutation drive current Ix₁, coil 42 is represented by its flow path for a commutation drive current Ix₂ and coil 43 is represented by its flow path for a commutation drive current Ix₃.

Opposing sets of drive turns of coils 41-43 orthogonal to a X drive axis of linear air gap and parallel to a Z levitation axis of linear air gap are internal to magnetic field β as best shown in FIGS. 2 and 4. Opposing sets of levitating turns of coils 41-43 parallel to the X drive axis and orthogonal to the Z levitation axis are external to magnetic field β as best shown in FIG. As a result, an application of a 120° phase shift PSl of commutation drive currents Ix₁, Ix₂ and Ix₃ to coils 41-43, respectively, exclusively generates a drive force F_x parallel to the X drive axis as best shown in FIG. 5.

A drawback of the structural configuration of ironless magnetic linear motor 20 is its inability to generate a substantially independent levitating force F_z parallel to the Z levitating axis as best shown in FIG. 5 and its inability to generate a substantially independent transversal force F_γ parallel to the Y transversal axis of the linear air gap as best shown in FIG. 5. To overcome these drawbacks, the present invention provides a new and improved ironless magnetic linear motor implementing a new orientation of forcer 40 within the linear air gap of magnetic track 30 to thereby facilitate a superimposition of a commutation levitation current Iz and/or a commutation transversal current Iγ on the commutation drive current Iχ for each coil of forcer 40.

In a first form of the present invention, one set of levitating turns of a coil parallel to the X drive axis and orthogonal to the Z levitation axis is internal to magnetic field, and an opposing set of levitating turns of a coil parallel to the X drive axis and orthogonal to the Z levitation axis is external to magnetic field. A commutation drive current is applied to the coil to generate a drive force parallel to the X drive axis and orthogonal to the Z levitation axis. A commutation levitating current is superimposed on and phase shifted from the commutation drive current to generate a levitating force orthogonal to the X drive axis and parallel to the Z levitation axis.

In a second form of the present invention, a coil of the forcer is offset from a center X- Z longitudinal plane of the linear air gap. A commutation drive current is applied to the coil to generate a drive force parallel to the X drive axis and orthogonal to the Y transversal axis. A commutation transversal current is superimposed on and phase shifted from the commutation drive current to generate a transversal force orthogonal to the X drive axis and parallel to the Y transversal axis.

In a third form of the present invention, a commutation drive current is applied to a coil of the forcer to generate a drive force parallel to the X drive axis. The forcer is orientated with the linear air gap to generate a force orthogonal to the X drive axis in response to an additional commutation coil current being superimposed on and phase shifted from the commutation drive current.

The foregoing forms and other forms of the present invention as well as various features and advantages of the present invention will become further apparent from the following detailed description of various embodiments of the present invention read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.

FIGS. 1 illustrates a view of an ironless magnetic linear motor in a X-Z plane as known in the art; FIG. 2 illustrates a view of the ironless magnetic linear motor of FIG. 1 in a Y-Z plane; FIG. 3 illustrates a view of a linear air gap of a magnetic track of FIG. 1 in a X-Y plane;

FIG. 4 illustrates a view of an application of commutation drive currents to coils of a forcer of FIG. 1 in a X-Z plane; FIG. 5 illustrates exemplary commutation drive currents applied to a forcer of FIG. 1 and an exemplary drive force generated by the forcer in response to the commutation drive currents as known in the art;

FIG. 6 illustrates a view of an ironless magnetic linear motor in a Y-Z plane in accordance with a first embodiment of the present invention; FIG. 7 illustrates a view of an application of commutation levitating currents to a forcer of FIG. 6 in a X-Z plane in accordance with the present invention;

FIG. 8 illustrates exemplary commutation levitating currents applied to the forcer of FIG. 7 and an exemplar levitation force generated by the forcer in response to the commutation levitating currents in accordance with the present invention; FIG. 9 illustrates a view of an application of superimposed commutation drive currents and commutation levitating currents to the forcer of FIG. 7 in a X-Z plane in accordance with the present invention;

FIG. 10 illustrates exemplary phase shifting of commutation drive currents and commutation levitating currents as applied to the forcer of FIG. 9 in accordance with the present invention;

FIG. 11 illustrates a view of an ironless magnetic linear motor in a Y-Z plane in accordance with a second embodiment of the present invention;

FIG. 12 illustrates a view of an application of superimposed commutation drive currents and commutation levitating currents to a forcer of FIG. 11 in a X-Z plane in accordance with the present invention;

FIGS. 13 and 14 illustrate views of an ironless magnetic linear motor in a Y-Z plane in accordance with a third embodiment of the present invention;

FIG. 15 illustrates a view of an application of commutation transversal currents to a forcer of FIGS. 13 and 14 in a X-Z plane in accordance with the present invention; - A -

FIG. 16 illustrates exemplary commutation transversal currents applied to a forcer of FIG. 15 and an exemplary transversal force generated by the forcer in response to the commutation transversal currents in accordance with the present invention;

FIG. 17 illustrates a view of an application of superimposed commutation drive currents and commutation transversal currents to the forcer of FIG. 2 in a X-Z plane in accordance with the present invention;

FIG. 18 illustrates exemplary phase shifting of commutation drive currents and commutation transversal currents as applied to the forcer of FIG. 17;

FIG. 19 illustrates a commutation current superimposition/phase shifting control system in accordance with a fourth embodiment of the present invention;

FIG. 20 illustrates a first exemplary mechanical coupling of a pair of ironless magnetic linear motor of the present invention to an object;

FIG. 21 illustrates a second exemplary mechanical coupling a pair of ironless magnetic linear motor of the present invention to an object; FIG. 22 illustrates a view of an ironless magnetic linear motor of FIG. 21 in a X-Z plane;

FIG. 23 illustrates a third exemplary mechanical coupling a pair of ironless magnetic linear motor of the present invention to an object; and

FIG. 24 illustrates a view of a mechanical coupling of a pair of ironless magnetic linear motor of FIG. 23 in a X-Z plane.

Referring to FIG. 6, an ironless magnetic linear motor 21 of the present invention employing magnetic track 30 and forcer 40 with forcer 40 having a new and unique orientation within the linear air gap. Specifically, forcer 40 is disposed within the linear air gap along a center X-Z longitudinal plane CP of the linear air gap as best shown in FIG. 6. As shown in FIG. 7, coil 41 of forcer 40 is represented by its flow path for a commutation levitating current Iz₁, coil 42 is of forcer 40 is represented by its flow path for a commutation levitating current Iz₂, coil 43 of forcer 40 is represented by its flow path for a commutation levitating current Iz₃.

Opposing sets of drive turns of coils 41-43 orthogonal to the X drive axis and parallel to the Z levitation axis are internal to magnetic field β as best shown in FIG. 7. One set of levitating turns of coils 41-43 parallel to the X drive axis and orthogonal to the Z levitation axis from a bottom perspective of FIG. 7 is external to magnetic field β, while the opposing set of levitating turns of coils 41-43 parallel to the X drive axis and orthogonal to the Z levitation axis from a top perspective of FIG. 7 is internal to magnetic field β. As a result, an application of a 120° phase shift PSl of commutation levitating currents Iz₁, Iz2 and Iz₃ to coils 41-43, respectively, generates a levitating force F_z parallel to the Z levitating axis as best shown in FIG. 8.

The present invention provides for a phase shifting of a superimposition of commutation levitating currents Iz₁, Iz2 and Iz₃ on commutation drive currents Ix₁, Ix₂ and Ix₃, respectively, to facilitate a maximum decoupling, if not a complete decoupling, of drive force F_x (FIG. 5) and levitating force F_z (FIG. 8). Specifically, as shown in FIG. 9, coil 41 of forcer 40 is represented by its flow path for a superimposition of commutation levitating current Iz₁ on commutation drive coil Ix₁, coil 42 of forcer 40 is represented by its flow path for a superimposition of commutation levitating current Iz₂ on commutation drive coil Ix₂, and coil 43 of forcer 40 is represented by its flow path for a superimposition of commutation levitating current Iz₃ on commutation drive coil Ix₃. As shown in FIG. 10, commutation levitating current Iz₁ is phase shifted from commutation drive coil Ix₁ by a 90° phase shift PS2, commutation levitating current Iz2 is phase shifted from commutation drive coil Ix₂ by 90° phase shift PS2, and commutation levitating current Iz₃ is phase shifted from commutation drive coil Ix₃ by 90° phase shift PS2. Referring to FIG. 11, an ironless magnetic linear motor 22 of the present invention employing magnetic track 30 and forcer 40 with forcer 40 having a opposite orientation within the linear air gap as compared to the forcer 40 orientation of the linear air gap of motor 21 (FIG. 6). Specifically, opposing sets of drive turns of coils 41-43 orthogonal to the X drive axis and parallel to the Z levitation axis are internal to magnetic field β as best shown in FIG. 12. One set of levitating turns of coils 41-43 parallel to the X drive axis and orthogonal to the Z levitation axis from a top perspective of FIG. 12 is external to magnetic field β, while the opposing set of levitating turns of coils 41 -43 parallel to the X drive axis and orthogonal to the Z levitation axis from a bottom perspective of FIG. 12 is internal to magnetic field β. As a result, an application of a 120° phase shift PSl of commutation levitating currents Iz₁, Iz2and Iz₃ to coils 41-43, respectively, generates a levitating force F_z parallel to the Z levitating axis as best shown in FIG. 8. The present invention provides for a phase shifting of a superimposition of commutation levitating currents Iz₁, Iz2 and Iz₃ on commutation drive currents Ix₁, Ix₂ and Ix₃, respectively, to facilitate a minimal decoupling, if not a complete decoupling, of drive force F_x (FIG. 5) and levitating force F_z (FIG. 8). Specifically, as shown in FIG. 12, coil 41 of forcer 40 is represented by its flow path for a superimposition of commutation levitating current Iz₁ on commutation drive coil Ix₁, coil 42 of forcer 40 is represented by its flow path for a superimposition of commutation levitating current Iz₂ on commutation drive coil Ix₂, and coil 43 of forcer 40 is represented by its flow path for a superimposition of commutation levitating current Iz₃ on commutation drive coil Ix₃. As shown in FIG. 10, commutation levitating current Iz₁ is phase shifted from commutation drive coil Ix₁ by a 90° phase shift PS2, commutation levitating current Iz2 is phase shifted from commutation drive coil Ix₂ by 90° phase shift PS2, and commutation levitating current Iz₃ is phase shifted from commutation drive coil Ix₃ by 90° phase shift PS2.

Referring to FIGS. 13-15, an ironless magnetic linear motor 23 of the present invention employing magnetic track 30 and forcer 40 with forcer 40 having a new and unique orientation within the linear air gap. Specifically, forcer 40 is disposed within the linear air gap at an offset to center X-Z longitudinal plane CP of the linear air gap as best shown in FIGS. 13 and 14. As shown in FIG. 15, coil 41 of forcer 40 is represented by its flow path for a commutation levitating current Iy₁, coil 42 is of forcer 40 is represented by its flow path for a commutation levitating current Iγ2, coil 43 of forcer 40 is represented by its flow path for a commutation levitating current Iy₃.

Opposing sets of drive turns of coils 41-43 orthogonal to the X drive axis and parallel to the Z levitation axis are internal to magnetic field β as best shown in FIG. 15. Opposing sets of levitating turns of coils 41-43 parallel to the X drive axis and orthogonal to the Z levitation axis are external to magnetic field β as best shown in FIG. 15. As a result, an application of a 120° phase shift PSl of commutation transversal currents Iy₁, Iy₂ and Iy₃ to coils 41-43, respectively, generates a transversal force F_γ parallel to the Y transversal axis as best shown in FIG. 16.

The present invention provides for a phase shifting of a superimposition of commutation transversal currents Iy₁, Iy₂ and Iy₃ on commutation drive currents Ix₁, Ix₂ and Ix₃, respectively, to facilitate a minimal decoupling, if not a complete decoupling, of drive force F_x (FIG. 5) and transversal force F_γ (FIG. 16). Specifically, as shown in FIG. 17, coil 41 of forcer 40 is represented by its flow path for a superimposition of commutation transversal current Iy₁ on commutation drive coil Ix₁, coil 42 of forcer 40 is represented by its flow path for a superimposition of commutation transversal current Iy₂ on commutation drive coil Ix₂, and coil 43 of forcer 40 is represented by its flow path for a superimposition of commutation transversal current Iy₃ on commutation drive coil Ix₃. As shown in FIG. 18, commutation transversal current Iy₁ is phase shifted from commutation drive coil Ix₁ by a 90° phase shift PS2, commutation transversal current Iy₂ is phase shifted from commutation drive coil Ix₂ by 90° phase shift PS2, and commutation transversal current Iy₃ is phase shifted from commutation drive coil Ix₃ by 90° phase shift PS2.

In practice, the present invention does not impose any limitations or any restrictions as a system for controlling a ironless magnetic linear motor of the present invention. In one embodiment as illustrated in FIG. 19, a commutation current superimposition/phase shifting control system 50 of the present invention employing M number of forcer position sensors 51, where M > 1, and a commutation current generator 52. Sensor(s) 51 operate to measure the relative position (up to 360 spatial degrees) of coils of a forcer within the magnetic field generated by the linear arrays of magnets within the linear air gap of the magnetic track. In one embodiment, sensor(s) 51 are position transducers strategically positioned relative to the forcer to thereby provide signals FPS indicative of a position of coils of a forcer within the magnetic field in view of the structural configurations of the magnetic track and the force. In a second embodiment, sensor(s) 51 are magnetic flux sensors (e.g., Hall sensors) strategically positioned relative to the forcer within the magnetic field to thereby provide signals FPS indicative of a position of coils of a forcer within the magnetic field in view of the structural configurations of the magnetic track and the forcer. Commutation current generator 52 operates to provide a phase shifting of a N number of superimposition of commutation levitating currents Iz on respective commutation drive currents Iχ and/or a phase shifting of a N number of superimposition of commutation transversals currents Iy on respective commutation drive currents Iχ as shown in FIG. 19. This operation of generator 52 is in accordance with new and unique superimposition/phase shifting commutation algorithm designed in view of the structural configurations and relative orientations of the magnetic track, the forcer and sensors 51. Referring to FIGS. 6-19, those having ordinary skill in the art will appreciate numerous advantages of the present invention including, but not limited to, addressing the drawbacks of the background art previously described herein. Furthermore, those having ordinary skill in the art will appreciate how to apply the phase shifting/superimposition inventive principles of the present invention to ironless magnetic liner motors in addition to motors 21-23 shown in FIGS. 6, 11, 13 and 14, respectively. In particular, those having ordinary skill in the art will appreciate how to apply the phase shifting/superimposition inventive principles of the present invention in the context of (1) the numerous variations in a structural configuration of a magnetic track, (2) the numerous variations in a structural configuration of a forcer, (3) the numerous variations in the orientation of a forcer in a linear air gap of a magnetic track in accordance with the present invention, (4) the numerous variations in a structural configuration of forcer position sensors, (5) the phase shifting range for commutation coil currents of the same type, (6) the phase shifting range for commutation coil currents of a dissimilar types and (7) the implementation of a positive slope and/or a negative slope for the commutation coil currents. The result is numerous variations of combinations of ironless magnetic linear motors in accordance with the inventive principles of the present invention, such as, for example, the utilization of one ore more magnetic tracks to build a more degree of freedom (position and/or orientation) stage/manipulator as will now be exemplary described herein in the context of FIGS. 20-24. Referring to FIG. 20, a pair of ironless magnetic linear motors 23 (FIGS. 13-15) are mechanically coupled in an eccentric to opposing sides of an object 60 whereby motors 23 can be operated to selectively move object 60 in an X drive direction of their respective linear air gaps and in a Y transversal direction of their respective linear air gaps.

Referring to FIGS. 21 and 22, a pair of ironless magnetic linear motors 24 are mechanically coupled in an eccentric to opposing sides of an object 61. Each motor 24 includes a pair of magnetic tracks 30 mechanically coupled to align their respective linear air gaps as a an integrated linear air gap. Each motor 24 further includes pair of outside forcers 40(O) within the integrated linear air gap to selectively generate a drive force F_x, a levitation force Fz, a drive torque Rx, a levitating torque Ry and a transversal torque Rz. Each motor 24 further includes an internal forcer 40(1) within the integrated linear air gap to selectively generate a drive force F_x, a transversal force F_γ, and levitating torque Rz. The result is a six (6) degree of freedom control of object 61 relative to a coordinate system of object 61 with a long stroke of object 61 along the X drive axis of the integrated linear air gaps of motors 24 and shorts strokes of object 61 along the Z levitating axes and the Y transversal axes of the integrated linear air gaps of motors 24. Referring to FIGS. 23 and 24, a pair of ironless magnetic linear motors 25 of the present invention are mechanically coupled in an eccentric to opposing sides of an object 62 with each motor 25 having an ironless magnetic linear motor 26 of the present invention being mechanically coupled thereto. Each motor 25 and motor 26 includes a pair of magnetic tracks 30 mechanically coupled to align their respective linear air gaps as a an integrated linear air gap. Each motor 25 further includes pair of forces 40 within the integrated linear air gap to selectively generate a drive force F_x, a levitation force F_z, a drive torque Rx, a levitating torque Ry and a transversal torque Rz. Each motor 26 further includes a single forcer 40 within the integrated linear air gap to selectively generate a drive force F_x, and a transversal force F_γ. The result is a six (6) degree of freedom control of object 62 relative to a coordinate system of object 62 with a long stroke of object 62 along the X drive axis of the integrated linear air gaps of motors 24 and shorts strokes of object 62 along the Z levitating axes and the Y transversal axes of the integrated linear air gaps of motors 24.

While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

Claims

1. A ironless magnetic motor (21, 22), comprising: a magnetic track (30) generating a magnetic field (β) across a linear air gap having a X drive axis, a Y transversal axis and a Z levitation axis; and a forcer (40) including a coil (41) disposed within the linear air gap, wherein a first set of levitating turns of the coil (41) parallel to the X drive axis and orthogonal to the Z levitation axis is internal to magnetic field (β), wherein a second set of levitating turns of the coil (41) parallel to the X drive axis and orthogonal to the Z levitation axis is external to magnetic field (β), wherein a commutation drive current (Iχ) is applied to the coil (41) to generate a drive force (F_x) parallel to the X drive axis and orthogonal to the Z levitation axis, and wherein a commutation levitating current (Iz) is superimposed on and phase shifted from the commutation drive current (Iχ) to generate a levitating force (F_z) orthogonal to the X drive axis and parallel to the Z levitation axis.

2. The ironless magnetic motor (21, 22) of claim 1, wherein the levitating force (F_z) is at least substantial decoupled from the drive force (F_x).

3. The ironless magnetic motor (21, 22) of claim 1, wherein the phase shifting of commutation levitating current (Iz) from the commutation drive current (Iχ) is 90°.

4. The ironless magnetic motor (21, 22) of claim 1, wherein the forcer (40) is centered on a center X-Z longitudinal plane (CP) of the linear air gap.

5. The ironless magnetic motor (21, 22) of claim 1, wherein the first set of levitating turns of the coil (41) is a top set of levitating turns of the coil (41).

6. The ironless magnetic motor (21, 22) of claim 1, wherein the second set of levitating turns of the coil (41) is a top set of levitating turns of the coil (41).

7. A ironless magnetic motor (23), comprising: a magnetic track (30) generating a magnetic field (β) across a linear air gap having a X drive axis, a Y transversal axis and a Z levitation axis; and a forcer (40) disposed including a coil (41) disposed within the linear air gap, wherein the forcer (40) is offset from a center X-Z longitudinal plane (CP) of the linear air gap, wherein a commutation drive current (Iχ) is applied to the coil (41) to generate a drive force (F_x) parallel to the X drive axis and orthogonal to the Y transversal axis, and wherein a commutation transversal current (Iγ) is superimposed on and phase shifted from the commutation drive current (Iχ) to generate a transversal force (Fy) orthogonal to the X drive axis and parallel to the Y transversal axis.

8. The ironless magnetic motor (23) of claim 7, wherein the transversal force (Fy) is at least substantial decoupled from the drive force (F_x).

9. The ironless magnetic motor (23) of claim 7, wherein the phase shifting of commutation transversal current (Iy) from the commutation drive current (Iχ) is 90°.

10. The ironless magnetic motor (23) of claim 7, wherein a first set of levitating turns of the coil (41) parallel to a X drive axis and orthogonal to a Z levitation axis is external to magnetic field (β).

11. The ironless magnetic motor (23) of claim 10, wherein a second set of levitating turns of the coil (41) parallel to the X drive axis and orthogonal to the Z levitation axis is external to magnetic field (β),

12. A ironless magnetic motor (21-23), comprising: a magnetic track (30) generating a magnetic field (β) across a linear air gap having a X drive axis, a Y transversal axis and a Z levitation axis; and a forcer (40) disposed including a coil (41) disposed within linear air gap, wherein a commutation drive current (Iχ) is applied to the coil (41) to generate a drive force (F_x) parallel to the X drive axis, and wherein the forcer (40) is orientated within the linear air gap to generate a force (Fz, F_γ) orthogonal to the X drive axis in response to a commutation coil current (Iz, Iγ) being superimposed on and phase shifted from the commutation drive current (Iχ).

13. The ironless magnetic motor (21-23) of claim 12, wherein the force (Fz, F_γ) is a levitating force (F_z) that is at least substantial decoupled from the drive force (F_x).

14. The ironless magnetic motor (21-23) of claim 12, wherein the force (Fz, F_γ) is a transversal force (Fy) that is at least substantial decoupled from the drive force (F_x).

15. The ironless magnetic motor (21-23) of claim 12, wherein the phase shifting of commutation coil current (Iz, Iγ) from the commutation drive current (Iχ) is 90°.

16. The ironless magnetic motor (21-23) of claim 12, wherein a set of levitating turns of the coil (41) parallel to a X drive axis and orthogonal to a Z levitation axis is external to magnetic field (β).

17. The ironless magnetic motor (21-23) of claim 12, wherein a set of levitating turns of the coil (41) parallel to the X drive axis and orthogonal to the Z levitation axis is internal to magnetic field (β).

18. The ironless magnetic motor (21-23) of claim 12, wherein the forcer (40) is centered on a center X-Z longitudinal plane (CP) of the linear air gap.

19. The ironless magnetic motor (21-23) of claim 12, wherein the forcer (40) is offset from a center X-Z longitudinal plane (CP) of the linear air gap.