WO2009083870A2

WO2009083870A2 - Six degrees of freedom direct drive induction motor apparatus and method

Info

Publication number: WO2009083870A2
Application number: PCT/IB2008/055373
Authority: WO
Inventors: Peter Hoekstra
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-12-26
Filing date: 2008-12-17
Publication date: 2009-07-09
Also published as: WO2009083870A3

Abstract

A direct drive induction motor apparatus (10) featuring six degrees of freedom comprises a conductor plate (16) and a rotor (12). The rotor is moveably coupled with respect to the conductor plate via a direct drive repulsive force configuration. The rotor includes a principal member having a number of N linear induction motors (20,22,24) arranged proximate side edges thereof, where N is an integer number greater than or equal to three. Each of the linear induction motors comprises a plurality of electromagnets (14), wherein responsive to an application of AC control currents of three different phases, the plurality of electromagnets of each linear induction motor produce both thrust force and normal force for realizing six degrees of freedom.

Description

Six degrees of freedom direct drive induction motor apparatus and method

FIELD OF THE INVENTION

The present embodiments relate generally to stage systems and more particularly, to a direct drive induction motor featuring six degrees of freedom and method.

BACKGROUND OF THE INVENTION

Automated construction of items frequently requires that the item under construction be moved from one part or section of a machine to another for further processing. One solution for transferring items is to place them on a moveable, horizontal plate (known in the art as a 'stage') driven by a motor arrangement, translating the plate between machine sections and thereby transporting the carried item. Most existing moving plate mechanisms offer good control of lateral movement but less control of rotational movement. Existing solutions for improved rotational torque include use of a separate rotary table placed onto the stage. This introduces extra weight into the system. Improved rotational control, using less weight, would allow further degrees of freedom in the design of automated machinery.

In addition, moving of items in automated machine construction include use of various stage concepts. Most stage concepts are based on Lorentz forces on current carrying wires in magnetic fields created by permanent magnets (e.g., using Lorentz motors or reluctance motors). In addition, most stages offer a very limited in-plane rotation stroke (Rz). If a bigger Rz is needed, a separate rotary table is added to the system. Such a stacked configuration introduces undesirable extra weight and dynamics. Also, the moving part of a stage has a big mass compared to the part that is to be manipulated.

Accordingly, an improved method and system for overcoming the problems in the art is desired.

SUMMARY OF THE INVENTION

The present embodiments advantageously provide for a direct drive induction motor arrangement comprising a plurality of linear induction motors configured in a manner to allow rotational motion. In addition, rotational symmetry of a conductor plate provides the ability for the direct drive induction motor apparatus to rotate without the stage "noticing it". The induction aspect of the embodiments herein advantageously allows for symmetry, which enables the achievement of long strokes. By using both the thrust and normal forces of a linear induction motor, according to the embodiments disclosed herein, a full 6 degrees of freedom stage can advantageously be realized.

In particular, linear induction motors can generate forces in the thrust direction and in the normal direction. These forces can be controlled independently, as discussed herein. In addition, these forces can also be combined to control a stage in 6 degrees of freedom, i.e. 3 linear directions and 3 rotations about the 3 linear directions, according to the requirements of a given moveable stage implementation.

The embodiments of the present disclosure advantageously enable an unlimited stroke in Rz. In addition, the embodiments of the present disclosure advantageously allow for fabrication of a light-weight mover for use in moving a part or section of a machine to another for further processing.

BRIEF DESCRIPTION OF THE EMBODIMENTS

Figure 1 is a perspective diagram view of a six degrees of freedom (6 DoF) direct drive induction motor apparatus according to an embodiment of the present disclosure;

Figure 2 is a simplified top diagram view of the 6 DoF direct drive induction motor apparatus of Figure 1 according to one embodiment of the present disclosure;

Figure 3 is a cross-sectional diagram view illustrating electromotive forces of one of the linear induction motors and its corresponding electromagnets of the 6 DoF direct drive induction motor apparatus of Figure 1 with the B-field moving to the left, taken along line A-A, according to one embodiment of the present disclosure; Figure 4 is a cross-sectional diagram view illustrating electromotive forces of one of the linear induction motors and its corresponding electromagnets of the 6 DoF direct drive induction motor apparatus of Figure 1 with the B-field moving to the right, taken along line A-A, according to one embodiment of the present disclosure;

Figure 5 is a block diagram view of the 6 DoF direct drive induction motor apparatus according to another embodiment of the present disclosure;

Figure 6 is a perspective diagram view of a 6 DoF direct drive induction motor apparatus according to another embodiment of the present disclosure; and

Figure 7 is a perspective diagram view of a 6 DoF direct drive induction motor apparatus according to yet another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

In the figures, like reference numerals refer to like elements. In addition, it is to be noted that the figures may not be drawn to scale. Turning now to the figures, Figure 1 is a perspective diagram view of six degrees of freedom (6 DoF) direct drive induction motor apparatus 10 according to one embodiment of the present disclosure. The direct drive induction motor apparatus 10 includes a rotor/translator 12 and a conductor plate 16. In one embodiment, the rotor/translator 12 includes a triangular configuration of linear induction motors and electromagnets 14. In one embodiment, the conductor plate comprises non-magnetic conductive material. The 6 DoF for the induction motor is represented by the coordinate axes 18, which illustrates translation in x, y, and z directions and rotation θx, θy, and θz about the respective axes. Rotation θx, θy, and θz may also be designated Rx, Ry, and Rz, respectively.

Figure 2 is a simplified top diagram view of the 6 DoF direct drive induction motor apparatus 10 of Figure 1 according to one embodiment of the present disclosure. In particular, the rotor/translator 12 includes a triangular configuration of linear induction motors, generally indicated by reference numerals 20, 22, and 24, respectively. Each of the linear induction motors 20, 22, and 24 include a plurality of electromagnets 14. In one embodiment, the plurality of electromagnets comprises a number of electromagnets that is a multiple of three, as will be explained further herein with reference to Figures 3 and 4. In one embodiment, the linear induction motors 20, 22, and 24 each include nine electromagnets, arranged in a row. In addition, the plurality of electromagnets of each of the three linear induction motors is further arranged along side edges of a triangle shaped rotor/translator 12 in a triangular configuration. In operation, the plurality of electromagnets 14 of the first linear induction motor 20 are controlled with three phases, as indicted in the figures with the letter designations R, S, and T. In a similar manner, the plurality of electromagnets 14 of the second linear induction motor 22 are controlled with three phases, as indicted in the figures with the letter designations R, S, and T. Furthermore, the plurality of electromagnets 14 of the third linear induction motor 24 are controlled with three phases, as indicted in the figures with the letter designations R, S, and T. With use of suitable control signals (e.g., current(s) applied to the electromagnets) of the respective linear induction motors, linear induction motor 20 produces one or both normal force 26 and thrust force 28, linear induction motor 22 produces one or both normal force 30 and thrust force 32, and linear induction motor 24 produces one or both normal force 34 and thrust force 36.

Stated in a slightly different manner, regarding the 6 DoF direct drive induction motor apparatus 10 of Figure 2, the letters U, V, and W are labels for three (3) forcers. The letters R, S and T designate three (3) phases. The currents in the phases are 120 degrees shifted in phase. Currents are induced in the conductor plate 16 by the changing magnetic field. In addition, AC currents in the electromagnets induce electric fields in the conductor plate 16 which results in induced currents in the conductor plate 16. For low frequent currents (i.e., frequencies less than or equal to a threshold amount), the conductor plate 16 is mainly resistive and the current is in phase with the electric field. The electric field is 90 degrees phase shifted to the currents in the electromagnets 14, resulting in a thrust force (e.g., thrust forces 28, 32, and 36). For higher frequencies (i.e., frequencies more than a threshold amount), the conductor plate 16 becomes more and more inductive and the phase of the induced currents is shifted towards the phase in the electromagnets 14, resulting in a normal force (e.g., normal forces 26, 30, and 34). In one embodiment, the triangular configuration of the 6 DoF direct drive induction motor apparatus 10 of Figure 2 is configured to provide long horizontal strokes and short vertical strokes.

Figure 3 is a cross-sectional diagram view illustrating electromotive forces of one of the linear induction motors and its corresponding electromagnets of the 6 DoF direct drive induction motor apparatus of Figure 1 with the B-field (magnetic force) moving to the left, taken along line A-A, according to one embodiment of the present disclosure. In particular, the figure illustrates an origin of thrust and normal forces. The primary B-field 40 moves to the left 42 with respect to the conductor plate 16. The induced field 44 (with a minus sign) lags 90 degrees behind for a pure resistive plate, creating a force to the left on the primary field. If the self- inductance is dominant, the induced field 46 is in phase with the primary field creating an upwards force on the primary field.

Figure 4 is a cross-sectional diagram view illustrating electromotive forces of one of the linear induction motors and its corresponding electromagnets of the 6 DoF direct drive induction motor apparatus of Figure 1 with the B-field (magnetic force) moving to the right, taken along line A-A, according to one embodiment of the present disclosure. In particular, the figure illustrates an origin of thrust and normal forces. The primary B-field 50 moves to the right 52 with respect to the conductor plate 16. The induced field 54 is 90 degrees ahead for a pure resistive plate 16, creating a force to the right on the primary field. If the self- inductance is dominant, the induced field 56 is out of phase with the primary field creating a downwards force on the primary field.

Figure 4 also includes several equations suitable for use in obtaining a measure of the primary magnetic field (B_pnmary) (B(50)), the induced magnetic field (B_md_Uced) (B(54,56)), electromotive force (emf) and current (i), which are repeated herein below.

The measure of the primary magnetic field (Bprimary) is given by:

^B _pnmary = ∞^ (kχ - ωt) .

The measure of the induced magnetic field (Binduced) is given by: ^_B<w = -cos (£x - (ωt + Δθ )) . The measure of electromotive force (emf) is given by: emf = -dφ I dt .

The measure of current (i) is given by: i = l/LJμdt .

Accordingly, in one embodiment, the direct drive linear induction motor comprises a triangular arrangement of three linear induction motors which create forces on a conductor plate. Each linear motor can generate a thrust force and a normal force. The thrust forces can be combined to generate forces in the plane (x, y, Rz), and the normal forces can be combined to generate forces perpendicular to the plane (z, Rx, Ry). Because the magnetic field is induced, a long stroke Rz (infinitely many turns possible), and of course x and y, is achieved. The system is truly direct drive.

The embodiments of the direct drive motor disclosed herein thus advantageously use repulsive forces to keep the mover located above the conductive plate (or vice versa in the embodiment which includes the conductive plate as the movable part). High-frequency currents are used to provide the necessary levitation forces. In one embodiment, the triangle arrangement of three (3) linear induction motors is configured to move over the conductor plate 16. Three (3) linear induction motors represents a minimum number for obtaining six degrees of freedom (6 DoF), because each linear induction motor can generate two (2) independent forces, corresponding to thrust force and normal force. Figure 5 is a block diagram view of the 6 DoF direct drive induction motor apparatus 60 according to another embodiment of the present disclosure. Apparatus 60 comprises a rotor/translator arrangement 62 including a number N of linear induction motors 64, 66, 68 (indicated by "..."), and 70, wherein the value N comprises an integer number. The number of linear induction motors, as well as the number of electromagnets of respective linear induction motors is selected according to the requirements of a given direct drive induction motor implementation/application. In addition, each linear induction motor comprises a plurality of electromagnets 14, similarly as discussed herein with respect to Figures 1 and 2.

The 6 DoF direct drive induction motor apparatus 60 further comprises a controller 72. Controller 72 couples via suitable signal lines 74 (only one line has been illustrated for simplicity of illustration) to each of the linear induction motors (64, 66, 68, and 70) of the rotor/translator arrangement 62. More particularly, the signal lines 74 couple to electromagnets 14 of the respective linear induction motors. Controller 72 comprises any suitable computer, microprocessor, and/or microcontroller, with appropriate interface circuitry, and being programmed with software instructions for performing a desired motor control in a given implementation. Controller 72 is configured to provide appropriate AC current signals for generating primary magnetic fields (Bprimary), and which produce desired induced magnetic fields (Binduced) in the conductor 16, wherein responsive to the induced magnetic fields, corresponding thrust forces and normal forces are produced. Accordingly, the 6 DoF direct drive induction motor apparatus 60 can be configured to operate with a desired horizontal long stroke and desired vertical short stroke in response to appropriate thrust and normal forces as controlled by controller 72. Figure 6 is a perspective diagram view of a 6 DoF direct drive induction motor apparatus 80 according to another embodiment of the present disclosure. The direct drive induction motor apparatus 80 includes a rotor/translator 82 and a conductor plate 86. In one embodiment, the rotor/translator 82 includes a rectangular configuration of linear induction motors and electromagnets 84. The 6 DoF for the induction motor is represented by the coordinate axes 88, which illustrates translation in x, y, and z directions and rotation θx, θy, and θz about the respective axes. In the embodiment of Figure 6, the rectangle configuration of four (4) linear induction motors are configured and operated for moving over stationary conductor plate 86. While the embodiment comprises four (4) linear induction motors, the mover 82 may also comprise a mover embodied as one part. Figure 7 is a perspective diagram view of a 6 DoF direct drive induction motor apparatus 90 according to yet another embodiment of the present disclosure. The direct drive induction motor apparatus 90 includes a stationary rotor/translator 92 and a movable conductor plate 96. With respect to the embodiment of Figure 7, instead of moving electromagnets and a stationary conductor plate, the electromagnets are rendered stationary and the conductor plate is configured for being movable. In this embodiment, air-bearings can be used to create passive gravity compensation.

Further with respect to the embodiment of Figure 7, the rotor/translator 92 comprises an embedded configuration of linear induction motors and electromagnets 94. The embedded configuration can include, for example, a triangular configuration, a rectangular configuration, a grid arrangement, or other geometric configuration according to the requirements of a given implementation. In addition, the 6 DoF for the induction motor is represented by the coordinate axes 98, which illustrates translation in x, y, and z directions and rotation θx, θy, and θz about the respective axes. In the embodiment of Figure 7, the linear induction motors are configured and operated to move the conductor plate 96 over the stationary rotor/translator 92 according to the requirements of a given implementation, for example, a high-performance stage.

By now it should be appreciated that there has been disclosed a direct drive induction motor apparatus featuring six degrees of freedom, comprising a conductor plate and a rotor. The rotor is moveably coupled with respect to the conductor plate via a direct drive repulsive force configuration. The rotor includes a principal member having a number of N linear induction motors arranged proximate side edges thereof, where N is an integer number greater than or equal to three. In addition, each of the linear induction motors comprises a plurality of electromagnets, wherein responsive to an application of AC control currents of three different phases, the plurality of electromagnets of each linear induction motor produce both thrust force and normal force for realizing six degrees of freedom. In one embodiment, the plurality of electromagnets of each linear induction motor includes a number of electromagnets that comprises a multiple of three.

According to another embodiment, the principal member includes a geometric shape. For example, the geometric shape can include one of a triangular shape and a rectangular shape. In addition, the rotor is further configured to provide long horizontal strokes and short vertical strokes. In another embodiment, the principal member of the rotor comprises a triangular arrangement of three linear induction motors. In another embodiment, the principal member of the rotor comprises a rectangular arrangement of four linear induction motors. In a further embodiment, the conductor plate is stationary and the rotor is movable. In a still further embodiment, the conductor plate is movable and the rotor is stationary.

In another embodiment, the direct drive induction motor apparatus further comprises a controller configured to provide AC control currents of three different phases. The controller provides AC current control signals of three different phases to independently control one or both (i) thrust forces and (ii) normal forces produced by one or more of the plurality of electromagnets of the respective linear induction motors. The AC control currents in the electromagnets induce electric fields in the conductor plate, which further results in induced currents in the conductor plate, wherein (i) for low frequent currents corresponding to frequencies less than or equal to a threshold amount, the conductor plate takes on a mainly resistive characteristic and the induced current is in phase with the electric field, the electric field being 90 degrees phase shifted to the currents in the electromagnets, resulting in a thrust force; and (ii) for higher frequencies corresponding to frequencies more than a threshold amount, the conductor plate takes on a more inductive characteristic and a phase of the induced currents is shifted towards the phase in the electromagnets, resulting in a normal force.

According to another embodiment, a direct drive induction motor apparatus featuring six degrees of freedom comprises a conductor plate, a rotor, and a controller. The rotor is moveably coupled with respect to the conductor plate via a direct drive repulsive force configuration. The rotor includes a principal member having a number of N linear induction motors arranged proximate side edges thereof, where N is an integer number greater than or equal to three, and wherein each of the linear induction motors comprises a plurality of electromagnets, wherein the plurality of electromagnets of each linear induction motor includes a number of electromagnets that comprises a multiple of three, wherein responsive to an application of AC control currents of three different phases, the plurality of electromagnets of each linear induction motor are further configured to produce both thrust force and normal force for realizing six degrees of freedom. The controller is configured to provide AC control currents of three different phases, wherein the controller is further configured to provide AC current control signals of three different phases to independently control one or both (i) thrust forces and (ii) normal forces produced by one or more of the plurality of electromagnets of the respective linear induction motors.

In a further embodiment, the geometric shape includes one of a triangular shape and a rectangular shape, the rotor further being configured to provide long horizontal strokes and short vertical strokes. In another embodiment, the AC control currents in the electromagnets induce electric fields in the conductor plate and further which results in induced currents in the conductor plate, wherein (i) for low frequent currents corresponding to frequencies less than or equal to a threshold amount, the conductor plate takes on a mainly resistive characteristic and the induced current is in phase with the electric field, the electric field being 90 degrees phase shifted to the currents in the electromagnets, resulting in a thrust force; and (ii) for higher frequencies corresponding to frequencies more than a threshold amount, the conductor plate takes on a more inductive characteristic and a phase of the induced currents is shifted towards the phase in the electromagnets, resulting in a normal force.

In yet another embodiment, the principal member of the rotor comprises one selected from the group consisting of (i) a triangular arrangement of three linear induction motors and (ii) a rectangular arrangement of four linear induction motors. In a further embodiment, the conductor plate is stationary and the rotor is movable. In a still further embodiment, the conductor plate is movable and the rotor is stationary.

In another embodiment, a method of implementing six degrees of freedom in a direct drive induction motor comprises: providing a conductor plate; moveably coupling a rotor with respect to the conductor plate in a direct drive repulsive force configuration, the rotor including a principal member having a number of N linear induction motors arranged proximate side edges thereof, where N is an integer number greater than or equal to three, and wherein each of the linear induction motors comprises a plurality of electromagnets, wherein responsive to an application of AC control currents of three different phases, the plurality of electromagnets of each linear induction motor are further configured to produce both thrust force and normal force for realizing six degrees of freedom; and providing AC current control signals of three different phases to independently control one or both (i) thrust forces and (ii) normal forces produced by one or more of the plurality of electromagnets of the respective linear induction motors.

Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the embodiments of the present disclosure. For example, the embodiments of the present disclosure can be applied to high-performance stages. Accordingly, all such modifications are intended to be included within the scope of the embodiments of the present disclosure as defined in the following claims. In the claims, means-plus- function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.

In addition, any reference signs placed in parentheses in one or more claims shall not be construed as limiting the claims. The word "comprising" and "comprises," and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural references of such elements and vice- versa. One or more of the embodiments may be implemented by means of hardware comprising several distinct elements, and/or by means of a suitably programmed computer. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to an advantage.

Claims

CLAIMS:

1. A direct drive induction motor apparatus (10) featuring six degrees of freedom, comprising: a conductor plate (16); and a rotor moveably coupled with respect to the conductor plate (16) via a direct drive repulsive force configuration, the rotor including a principal member having a number of N linear induction motors (20, 22, 24) arranged proximate side edges thereof, where N is an integer number greater than or equal to three, and wherein each of the linear induction motors (20, 22, 24) comprises a plurality of electromagnets (14), wherein responsive to an application of AC control currents of three different phases, the plurality of electromagnets (14) of each linear induction motor are further configured to produce both thrust force and normal force for realizing six degrees of freedom.

2. The apparatus of claim 1, wherein the plurality of electromagnets (14) of each linear induction motor includes a number of electromagnets (14) that comprises a multiple of three.

3. The apparatus of claim 1, wherein the principal member includes a geometric shape.

4. The apparatus of claim 3, further wherein the geometric shape includes a triangular shape.

5. The apparatus of claim 3, further wherein the geometric shape includes a rectangular shape.

6. The apparatus of claim 1, the rotor further being configured to provide long horizontal strokes and short vertical strokes.

7. The apparatus of claim 1, further comprising: a controller (72) configured to provide AC control currents of three different phases.

8. The apparatus of claim 7, wherein the controller (72) is further configured to provide AC current control signals of three different phases to independently control one or both (i) thrust forces and (ii) normal forces produced by one or more of the plurality of electromagnets (14) of the respective linear induction motors (20, 22, 24).

9. The apparatus of claim 7, wherein AC control currents in the electromagnets

(14) induce electric fields in the conductor plate (16) and further which results in induced currents in the conductor plate (16), wherein (i) for low frequent currents corresponding to frequencies less than or equal to a threshold amount, the conductor plate (16) takes on a mainly resistive characteristic and the induced current is in phase with the electric field, the electric field being 90 degrees phase shifted to the currents in the electromagnets (14), resulting in a thrust force; and (ii) for higher frequencies corresponding to frequencies more than a threshold amount, the conductor plate (16) takes on a more inductive characteristic and a phase of the induced currents is shifted towards the phase in the electromagnets (14), resulting in a normal force.

10. The apparatus of claim 1, wherein the principal member of the rotor comprises a triangular arrangement of three linear induction motors (20, 22, 24).

11. The apparatus of claim 1 , wherein the principal member of the rotor comprises a rectangular arrangement of four linear induction motors.

12. The apparatus of claim 1, wherein the conductor plate (16) is stationary and the rotor is movable.

13. The apparatus of claim 1, wherein the conductor plate (16) is movable and the rotor is stationary.

14. A direct drive induction motor apparatus (10) featuring six degrees of freedom, comprising: a 16; a rotor moveably coupled with respect to the conductor plate (16 via a direct drive repulsive force configuration, the rotor including a principal member having a number of N linear induction motors (20, 22, 24) arranged proximate side edges thereof, where N is an integer number greater than or equal to three, and wherein each of the linear induction motors (20, 22, 24) comprises a plurality of electromagnets (14), wherein the plurality of electromagnets (14) of each linear induction motor includes a number of electromagnets (14) that comprises a multiple of three, wherein responsive to an application of AC control currents of three different phases, the plurality of electromagnets (14) of each linear induction motor are further configured to produce both thrust force and normal force for realizing six degrees of freedom; and a controller (72) configured to provide AC control currents of three different phases, wherein the controller (72) is further configured to provide AC current control signals of three different phases to independently control one or both (i) thrust forces and (ii) normal forces produced by one or more of the plurality of electromagnets (14) of the respective linear induction motors (20, 22, 24).

15. The apparatus of claim 14, further wherein the geometric shape includes one of a triangular shape and a rectangular shape, the rotor further being configured to provide long horizontal strokes and short vertical strokes.

16. The apparatus of claim 14, wherein AC control currents in the electromagnets (14) induce electric fields in the conductor plate (16) and further which results in induced currents in the conductor plate (16), wherein (i) for low frequent currents corresponding to frequencies less than or equal to a threshold amount, the conductor plate (16) takes on a mainly resistive characteristic and the induced current is in phase with the electric field, the electric field being 90 degrees phase shifted to the currents in the electromagnets (14), resulting in a thrust force; and (ii) for higher frequencies corresponding to frequencies more than a threshold amount, the conductor plate (16) takes on a more inductive characteristic and a phase of the induced currents is shifted towards the phase in the electromagnets (14), resulting in a normal force.

17. The apparatus of claim 14, wherein the principal member of the rotor comprises one selected from the group consisting of (i) a triangular arrangement of three linear induction motors (20, 22, 24) and (ii) a rectangular arrangement of four linear induction motors (20, 22, 24).

18. The apparatus of claim 14, wherein the conductor plate (16) is stationary and the rotor is movable.

19. The apparatus of claim 14, wherein the conductor plate (16) is movable and the rotor is stationary.

20. A method of implementing six degrees of freedom in a direct drive induction motor comprising: providing a conductor plate (16); moveably coupling a rotor with respect to the conductor plate (16) in a direct drive repulsive force configuration, the rotor including a principal member having a number of N linear induction motors (20, 22, 24) arranged proximate side edges thereof, where N is an integer number greater than or equal to three, and wherein each of the linear induction motors (20, 22, 24) comprises a plurality of electromagnets (14), wherein responsive to an application of AC control currents of three different phases, the plurality of electromagnets (14) of each linear induction motor are further configured to produce both thrust force and normal force for realizing six degrees of freedom; and providing AC current control signals of three different phases to independently control one or both (i) thrust forces and (ii) normal forces produced by one or more of the plurality of electromagnets (14) of the respective linear induction motors (20, 22, 24).