Patent Publication Number: US-9892837-B2

Title: Energy efficient actuator

Description:
STATEMENT OF GOVERNMENT SUPPORT 
     The subject matter of the present application was made with Government support from the National Science Foundation under contract number IIP-1152605. The Government may have rights to the subject matter of the present application. 
    
    
     FIELD OF THE INVENTION 
     The present application for patent is in the field of actuators and more specifically is in the field of actuators for mechanical or electromechanical devices such as, but not limited to orthotic devices. 
     BACKGROUND 
     In general, mechanical or electromechanical actuators are used to apply a stimulus to a device in order to switch its function between or among functional states. The required actuation may depend on the characteristics of the device being switched. For example, a device may be able to hold its state without further assistance from the actuator. In another example, the device may require actuator assistance to hold its state. Actuators may simply make electrical connections or they may apply a required mechanical force. The latter actuators may work using any phenomenon that generates or transmits a force; wherein the force can be applied actively or passively. Such forces include hydraulic, pneumatic, electric, electrostatic, electromagnetic, thermal, such as might be encountered in materials having shape memory, and mechanical forces. Such forces may be converted into motion. 
     Actuators may provide unstable states of operation that require the supply of energy to hold one state or another in actuation. However, in applications where it is desirable to conserve energy, such as in devices that use batteries, it is often desirable to for an actuator to provide one or more stable states. In such actuators, little or no energy input is required to hold a state in, for example, “engaged” or “disengaged” positions. Moreover, actuators may have more than two states of operation when, for example, they are used to switch among different states of a device. 
     In certain circumstances it may be desirable for an actuator to switch between or among states using minimal energy, hold its state without further expenditure of energy, and apply mechanical forces characteristic of each state to the device being actuated. For example, such a device may be desirable for actuating a clutch with a high mechanical advantage. 
     Various attempts have been made to provide such an actuator. For example, U.S. Pat. No. 8,702,133 to Sun et al provides an actuator for an electronic door lock that includes “a stationary first magnet assembly, a beam, and a second magnet assembly,” wherein the first magnet “includes at least one magnet stationarily positioned within the electronic door lock. The beam is movable relative to the first magnet assembly to a first position and a second position. The second magnet assembly is connected to the beam and is configured to be magnetically repulsed away from the first magnet assembly. The repulsion of the second magnet assembly maintains the beam in either the first or second position until the beam is selectively actuated therefrom.” However, in this configuration, the forces applied in each of the two states are symmetrical such that the magnet on the movable beam is “magnetically repulsed” about equally in both states of actuation. Many devices to be actuated, such as, for example, clutches with high mechanical advantage, require a “pull” in one state and a “push” in the other state, without drawing power from a power source when in either state. Therefore, there remains a need for actuators having the characteristics hereinabove described. The present application for patent discloses an actuator that addresses these needs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an “exploded view” embodiment of an actuator having a linear range of motion. 
         FIG. 2  illustrates a portion of the actuator of  FIG. 1  in exploded view with certain hardware removed, showing a linkage to a control arm. 
         FIG. 3  illustrates a portion of a coil subassembly. 
         FIG. 4  shows an embodiment of an actuator with various cutaway views.  FIG. 4( a )  illustrates a slider, as in  FIGS. 1 and 2  with portions of the actuator removed to show the configuration of the magnetic holder.  FIG. 4( b )  illustrates a slider, as in  FIGS. 1 and 2  with portions of the actuator removed to show the configuration of the magnetic holder.  FIG. 4( c )  shows an example of the arrangement of the holder magnets with a single static magnet.  FIG. 4( d )  shows an example of the arrangement of the holder magnets with two static magnets. In  FIGS. 4( a ) and 4( b ) , the slider is shown in its left-most stable position. 
         FIG. 5  shows an embodiment of an actuator with various cutaway views.  FIG. 5( a )  illustrates a slider, as in  FIG. 4( a )  with portions of the actuator removed to show the configuration of the magnetic holder.  FIG. 5( b )  illustrates a slider, as in  FIG. 4( b )  with portions of the actuator removed to show the configuration of the magnetic holder.  FIG. 5( c )  shows an example of the arrangement of the holder magnets with a single static magnet.  FIG. 5( d )  shows an example of the arrangement of the holder magnets with two static magnets. In  FIGS. 5( a ) and 5( b ) , the slider is shown in its midrange position. 
         FIG. 6  shows an embodiment of an actuator with various cutaway views.  FIG. 6( a )  illustrates a slider, as in  FIG. 4( a )  with portions of the actuator removed to show the configuration of the magnetic holder.  FIG. 6( b )  illustrates a slider, as in  FIG. 4( b )  with portions of the actuator removed to show the configuration of the magnetic holder.  FIG. 6( c )  shows an example of the arrangement of the holder magnets with a single static magnet.  FIG. 6( d )  shows an example of the arrangement of the holder magnets with two static magnets. In  FIGS. 6( a ) and 6( b ) , the slider is shown in its right-most stable position. 
         FIG. 7  illustrates another example of an actuator with the slider configured to pivot on an axis. The slider is shown in its right-most stable position. 
         FIG. 8  illustrates another example of an actuator with the slider configured to pivot on an axis. The slider is shown in its left-most stable position. 
         FIG. 9  illustrates another example of an actuator with the slider configured to pivot on an axis. The slider is shown in its midrange position. 
         FIG. 10  illustrates results of static force tests of the actuator shown in  FIG. 1 . The graphs show force as a function of slider displacement, wherein the forces are exerted by the magnets on the holder. 
         FIG. 11  illustrates a portion of a coil subassembly wherein the conducting pathways form an essentially flat facing side and can be wired for three-phase operation. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an “exploded view” embodiment of an actuator having a linear range of motion. Shown are two coil subassemblies, each having a substantially flat facing side, each having a frame on which the coils are mounted,  101  and  102 . Conducting pathways  103 - 105 , indicated, for example, on the top coil subassembly (shown in the inset), are configured or wired for three-phase operation and are similar to the conducting pathways in the bottom coil subassembly (not numbered). Shading does not indicate instantaneous electromagnetic polarity or current. Rather, shadings of  103 - 105  indicate how the conducting pathways are arranged when configured for multiphase operation. The slider of  FIG. 1, 106  has a plurality of drive magnets, exemplified by  107  and  108 , polarized along a vertical direction, with the vertical direction configured so that the pole faces are the flat top and bottom, and arranged with alternately opposite pole faces, wherein the pole faces face the conducting pathways on the coil subassemblies. In this illustration, the magnetic holder assembly comprises stationary magnets, exemplified by  110 - 111 , and  130 - 131 , and a magnet on the slider  109 , which may be either attracted or repelled by the stationary magnets. The mounting hardware  117 ,  118  or the coil subassembly frame may include bearing assemblies  116 , comprising ball bearings and slots as guides. A linkage arm,  121 , couples the slider  106 , to the device being actuated. A platform  119  for electronic control circuitry exemplified by  122  is shown configured to be connected at  123  to the coil subassemblies  101  and  102  via a series of conductors, illustrated by  120 , mating connectors  126  and via holes, exemplified by  124 ,  125 . A limiter or “stop” exemplified by  135 , may be used to limit the range of motion of the slider. 
       FIG. 2  illustrates an embodiment of a portion of the actuator of  FIG. 1  in exploded view with certain hardware removed, showing a linkage to a control arm  220 . Mounting hardware is removed. Shown are two coil subassemblies, each having a substantially flat facing side, and each having a frame,  201  and  202 . Conducting pathways  203 - 205 , indicated on the top coil subassembly, are configured or wired for three-phase operation and are similar to the conducting pathways in the bottom coil subassembly (not numbered). Shading does not indicate instantaneous electromagnetic polarity or current. Rather, shadings of  203 - 205  indicate how the conducting pathways are arranged when configured for multiphase operation. The slider of  FIG. 2, 206  has a plurality of drive magnets, exemplified by  207  and  208 , polarized along a vertical direction, and arranged with alternately opposing pole faces, wherein the pole faces face the conducting pathways on the coil subassemblies. In this illustration, the magnetic holder assembly comprises stationary magnets, exemplified by  210 - 213 , similar to those masked by other hardware on the actuator, and a magnet on the edge of the slider  209 , which may be either attracted or repelled by the stationary magnets. Motion of the slider may be facilitated by a bearing assembly  216 . 
       FIG. 3  illustrates an embodiment of a portion of a coil subassembly  301  configured or wired for three phase operation. The coil comprises three serpentine patterns, electrically isolated from one another. In this embodiment, an alternating current (AC) signal having a first phase flows in a first conducting pathway  303  between contact  325  and  326 . The arrows superimposed on the conducting pathway between those two points show the relative direction of the current in each segment. In a similar manner, an AC having a second phase flows in a second conducting pathway  304  between contacts  327  and  328 . Finally, an AC having a third phase flows in a third conducting pathway  305  between contacts  329  and  330 . 
       FIGS. 4( a ) and ( b )  each illustrate an embodiment of a slider, as in  FIGS. 1 and 2  with mounting hardware and coil assemblies partially removed to show exemplary configurations of the magnetic holder. The frame for the coil,  402 , supports a plurality of conducting pathways, exemplified by  403 - 405 . The slider,  406  has a plurality of drive magnets, exemplified by  407  and  408 . In these embodiments, the magnetic holder assemblies comprise stationary magnet(s), exemplified by  452  in  FIG. 4( a )  and by  410 - 413  in  FIG. 4( b ) , and a magnet  449  on the edge of the slider in  FIG. 4( a )  and  409  in  FIG. 4( b ) , each of which may be either attracted or repelled by the stationary magnet(s). Similar magnetic holders may be configured on both sides of the slider to balance forces that may arise perpendicular to the direction of motion.  FIG. 4( c )  shows an example of a holder magnet arrangement with holder magnets  449  and  452  arranged as shown. The magnet  449 , mounted on the slider which is positioned in the left-most slider position is repelled as shown in net force vector  450  by the stationary magnet  452 , mounted on or near the frames of the coil assemblies. The slider is shown in its left-most stable position wherein a force, represented by net force vector  450 , is applied to the actuator linkage arm  420  (shown in  FIGS. 4( a ) and ( b ) ).  FIG. 4( d )  shows an example of a holder magnet arrangement with holder magnets  409 - 413  arranged as shown. The magnet  409  mounted on the slider, positioned in the left-most slider position is repelled as shown in net force vector  440  by the stationary magnets  410 - 413 , mounted on or near the frames of the coil assemblies. The slider is shown in its left-most stable position wherein a force, represented by net force vector  440 , is applied to the actuator linkage arm  420  (shown in  FIGS. 4( a ) and ( b ) ). 
       FIGS. 5( a ) and ( b )  each illustrate an embodiment of a slider, as in  FIGS. 1 and 2  with mounting hardware and coil assemblies partially removed to show exemplary configurations of the magnetic holder. The frame for the coil,  502 , supports a plurality of conducting pathways, exemplified by  503 - 505 . The slider,  506 , shown in its intermediate position, has a plurality of drive magnets, exemplified by  507  and  508 . In this illustration, embodiments of the magnetic holder assemblies comprise stationary magnet(s), exemplified by  552  in  FIG. 5( a )  and  510 - 513  in  FIG. 5( b ) , and a magnet  549  in  FIG. 5( a )  and  509  in  FIG. 5( b )  on the edge of the slider, each of which may be either attracted or repelled by the stationary magnet(s). Similar magnetic holders may be configured on both sides of the slider to balance forces on the slider that may arise perpendicular to the direction of motion.  FIG. 5( c )  provides an example of a holder magnet arrangement with holder magnets  549  and  552  arranged as shown. The magnet  549  mounted on the slider, is positioned in an intermediate position, which position may be unstable, wherein a force, represented by net force vector  550 , or by net force vector  551 , depending transitionally on its position, is applied to the actuator linkage arm  520  by interacting with the stationary magnet  552 , mounted on or near the frames of the coil assemblies.  FIG. 5( d )  shows an example of a holder magnet arrangement with holder magnets  509 - 513  arranged as shown. The magnet  509  mounted on the slider, is positioned in an intermediate position, which position may be unstable, wherein a force, represented by net force vector  540 , or, by net force vector  541 , depending transitionally on its position, is applied to the actuator linkage arm  520  by interacting with the stationary magnets  510 - 513 , mounted on or near the frames of the coil assemblies. The slider is shown in an intermediate position wherein a force, represented by net force vector  540  or  541 , is applied to the actuator linkage arm  520  (shown in  FIGS. 5( a ) and ( b ) ). 
       FIGS. 6( a ) and ( b )  each illustrate an embodiment of a slider, as in  FIGS. 1 and 2  with mounting hardware and coil assemblies partially removed to show exemplary configurations of the magnetic holder. The frame for the coil,  602 , supports a plurality of conducting pathways, exemplified by  603 - 605 . The slider,  606  has a plurality of drive magnets, exemplified by  607  and  608 . In this illustration, embodiments of the magnetic holder assemblies comprise stationary magnet(s), exemplified by  652  in  FIG. 6( a )  and  610 - 613  in  FIG. 6( b ) , and a magnet  649  on the edge of the slider in  FIG. 6( a )  and  609  in  FIG. 6( b ) , each of which may be either attracted or repelled by the stationary magnet(s). Similar magnetic holders may be configured on both sides of the slider to balance forces on the slider that may arise perpendicular to the direction of motion.  FIG. 6( c )  shows an example of a holder magnet arrangement with holder magnets  649  and  652  arranged as shown. The magnet  649  mounted on the slider, positioned in the right-most slider position is repelled as shown in net force vector  650  by the stationary magnet  652 , mounted on or near the frames of the coil assemblies. The slider is shown in its right-most stable position wherein a force, represented by net force vector  650 , is applied to the actuator linkage arm  620  (shown in  FIGS. 6( a ) and ( b ) ).  FIG. 6( d )  shows an example of a holder magnet arrangement with holder magnets  609 - 613  arranged as shown. The magnet  609  mounted on the slider, positioned in the right-most slider position is repelled as shown in net force vector  640  by the stationary magnets  610 - 613 , mounted on or near the frames of the coil assemblies. The slider is shown in its right-most stable position wherein a force, represented by net force vector  640 , is applied to the actuator linkage arm  620  (shown in  FIGS. 6( a ) and ( b ) ). 
       FIG. 7  illustrates another embodiment of an actuator with the slider configured to pivot on an axis. The slider  706  is shown in its right-most stable position. In this embodiment, the coil may present two flat faces back to back on the same frame,  701 . Conducting pathways, exemplified by  703 - 705 , indicated on one side of the coil subassembly, are configured or wired for three-phase operation and are similar to the conducting pathways which may comprise the face the opposite side of the coil subassembly (not shown). Shading does not indicate instantaneous electromagnetic polarity or current. Rather, shadings of  703 - 705  indicate how the conducting pathways are arranged when configured for multiphase operation. The slider of  FIG. 7, 706  may have a “sandwich” structure  702 , wherein each layer has a plurality of drive magnets, exemplified by  707  and  708 , polarized in a direction normal to the side shown, and arranged with alternately opposite pole faces, wherein the pole faces face the conducting pathways on the coil subassembly. The magnetic holder assembly comprises stationary magnets, exemplified by  710 - 713 , and a magnet on each face of the slider, if applicable,  709 , which may be either attracted or repelled by the stationary magnets. The slider is shown in its right-most stable position wherein a force is applied to the actuator linkage arm  720 . 
       FIG. 8  illustrates another view of the actuator of  FIG. 7  with the slider configured to pivot on an axis. The slider  806  is shown in its left-most stable position. In this embodiment, the coil may present two flat faces back to back on the same frame,  801 . Conducting pathways  803 - 805 , indicated on one side of the coil subassembly, are configured or wired for three-phase operation and are similar to the conducting pathways which may comprise the face the opposite side of the coil subassembly (not shown). Shading does not indicate instantaneous electromagnetic polarity or current. Rather, shadings of  803 - 805  indicate how the conducting pathways are arranged when configured for multiphase operation. The slider of  FIG. 8, 806  may have a “sandwich” structure  802 , wherein each layer has a plurality of drive magnets, exemplified by  807  and  808 , polarized in a direction normal to the side shown, and arranged with alternately opposite pole faces, wherein the pole faces face the conducting pathways on the coil subassembly. The magnetic holder assembly comprises stationary magnets, exemplified by  812 - 813 , and a magnet on each face of the slider, if applicable,  809 , which may be either attracted or repelled by the stationary magnets. Not shown are the stationary magnets  810 - 811  shown as  710 - 711  in  FIG. 7  because they are obscured by the position of the slider. The slider is shown in its left-most stable position wherein a force is applied to the actuator linkage arm  820 . 
       FIG. 9  illustrates another view of the actuator of  FIGS. 7-8  with the slider configured to pivot on an axis. The slider  906  is shown in an intermediate position. In this embodiment, the coil may present two flat faces back to back on the same frame,  901 . Conducting pathways  903 - 905 , indicated on one side of the coil subassembly, are configured or wired for three-phase operation and are similar to the conducting pathways which may comprise the face the opposite side of the coil subassembly (not shown). Shading does not indicate instantaneous electromagnetic polarity or current. Rather, shadings of  903 - 905  indicate how the conducting pathways are arranged when configured for multiphase operation. The slider of  FIG. 9, 906  may have a “sandwich” structure  902 , wherein each layer has a plurality of drive magnets, exemplified by  907  and  908 , polarized in a direction normal to the side shown, and arranged with alternately opposite pole faces, wherein the pole faces face the conducting pathways on the coil subassembly. The magnetic holder assembly comprises stationary magnets, exemplified by  912 - 913 , and a magnet on each face of the slider, if applicable (shown in  FIG. 8  as  809 , obscured in this view), which may be either attracted or repelled by the stationary magnets. Not shown are the stationary magnets  910 - 911 , shown as  710 - 711  in  FIG. 7  and the magnet on the slider  909 , shown as  809  in  FIG. 8  because they are obscured by the position of the slider. The slider is shown in an intermediate position wherein a force is applied to the actuator linkage arm  920 . Depending on the intermediate position of magnet  909 , the force applied to the linkage arm may be in either direction, as shown by analogy with  FIG. 10 , infra. 
       FIG. 10  illustrates results of static force tests of the actuator shown in  FIG. 1 . The graphs show gram equivalent force as a function of slider displacement in cm, wherein the forces are a function of displacement and are exerted by interactions among the stationary magnets and the magnet mounted on the slider as shown in  FIGS. 4( b ) and 4( d ) . When the slider is in its left-most position, a force to the left  1001  is imposed. When the slider is in its right-most position, a force to the right  1002  is imposed. When in use, the magnetic force holding assembly maintains the slider in substantial repulsion at the left position and substantial attraction at the right position. When the slider is in an intermediate position, the force  1003  depends transitionally on the position. 
       FIG. 11  illustrates another embodiment a portion of a coil subassembly wherein the conducting pathways form an essentially flat facing side and can be wired for three-phase operation. In this figure, the conducting pathways comprise wire wrappings, exemplified by  1103 - 1105 , wrapped on a frame  1101  to form an essentially flat facing side. 
     DETAILED DESCRIPTION 
     As used herein, the conjunction “and” is intended to be inclusive and the conjunction “or” is not intended to be exclusive unless otherwise indicated. For example, the phrase “or, alternatively” is intended to be exclusive. As used herein, the descriptor “exemplary” is understood as a pointer to an example and is not intended to indicate preference. As used herein, the term “essentially flat” is intended to describe a roughly planar facing which may or may not exhibit topography. For example, an essentially flat facing side may be seen in  FIG. 11  and may be distinguished from a coil formed on a curved substrate. As used herein, the terms “holder” and “magnetic force holding assembly” are understood to be interchangeable. 
     Disclosed herein is an actuator, comprising: (a) a frame; (b) a slider, wherein the slider is displaceable over a range of travel between a first position and a second position; and (c) a magnetic force holding assembly, comprising: (i) at least one permanent magnet on the slider; and; (ii) at least one permanent magnet on the frame proximally positioned to the permanent magnet on the slider; wherein, when in use, the magnetic force holding assembly maintains the slider in substantial repulsion at the first position and substantial attraction at the second position. 
     The actuator may further comprise an actuation mechanism, powered by an electrical power source, said actuation mechanism comprising: (a) one or more coil subassemblies, affixed to the frame, wherein each coil subassembly is configured for multiphase operation, and wherein each coil subassembly comprises: a plurality of conducting pathways, comprising a conductor, wherein the conducting pathways are mounted at least partially on the facing side of the coil subassembly, and wherein each conducting pathway is electrically isolated from the others; and (b) a slider comprising: (i) a frame; and (ii) two or more drive magnets attached to the frame, wherein each of the drive magnets is arrayed so that its nearest neighbor(s) have opposing magnetic polarity. 
     Further disclosed herein is an actuator, comprising: (a) one or more coil subassemblies, each coil subassembly having a substantially flat facing side, wherein each coil subassembly is configured for multiphase operation, and wherein each coil subassembly comprises: a substrate; and a plurality of conducting pathways, each comprising a conductor, wherein the conducting pathways are mounted at least partially on the facing side of the coil subassembly, and wherein each conducting pathway is electrically isolated from the others; (b) a slider comprising: (i) a frame; M drive magnets attached to the frame, wherein each of the drive magnets is arrayed so that its nearest neighbor(s) have opposing magnetic polarity, and wherein M is an integer from 2 to 20; and (c) at least one magnetic holder, for holding the slider in one of two opposing states without expending additional energy from the electrical power source; wherein the actuator is powered by an electrical power source, when in use. 
     The magnetic holder of the further disclosed embodiment, supra, may also comprise (i) at least one permanent magnet on the slider; and; (ii) at least one permanent magnet on the frame proximally positioned to the at least one permanent magnet on the slider; wherein, when in use, the magnetic holder maintains the slider in substantial repulsion at the first opposing state and substantial attraction at the second opposing state without drawing power from the electrical power source. 
     In addition to the above embodiments, further embodiments may also include features that facilitate design and operation. For example, displacement limiters or stops may be used to prevent the slider from moving out of its operating range. Displacement limiters may comprise mechanical stops such as cushioned or hard posts, springs, narrowed channels in which increased friction may arise, hydraulic or pneumatic devices as well as magnetic stops, electromagnetic stops, ferroelectric or electrostrictive stops, friction braking devices and the like. 
     In addition, modifications such as guide structures, bearings and bushings may be used to facilitate movement of the slider and reduce friction and noise. Bearing assemblies may be built into the coil body and slider by way of slots or the like. Lubricants like oils, greases, graphite combinations of oils and water, polymers such as poly tetrafluoroethylene and polymerized ethylenically unsaturated fluoroethers, alone or in combination with protic or non-protic lubricants may also be used. In addition, non contact devices may be used. These include, without limitation, magnetic guides, electrostatic guides and the like. 
     Electrical power sources may be used to provide the necessary power to the actuator and may comprise rechargeable and non rechargeable batteries, capacitors, supercapacitors, inductive devices, RF devices, external generators, AC current and the like. 
     Coils may comprise conductors, semiconductors and superconductors. Conductors may include, without limitation, metals such as copper, silver, gold, platinum, palladium aluminum or other metal. In situations where cooling is available and low power dissipation is desired, superconducting materials may be used. Exemplary superconducting materials may include, without limitation, YBa 2 Cu 3 O 7 , Bi 2 Sr 2 CuO 6 , Bi 2 Sr 2 CaCu 2 O 8 , Tl 2 Ba 2 CuO 6 , HgBa 2 Ca 2 Cu 3 O 8 , Tl 2 Ba 2 CaCu 2 O 8 , Tl 2 Ba 2 Ca 2 Cu 3 O 10 , TlBa 2 Ca 3 Cu 4 O 11 , HgBa 2 CuO 4 , HgBa 2 CaCu 2 O 6 , HgBa 2 Ca 2 Cu 3 O 8 . The coil may be in the form of wires of cylindrical or ribbon shape. Exemplary wire cross sectional dimensions (diameters, rectangular lengths, etc.) may be from about 0.05 mm to about 5 mm. Further exemplary wire cross sections may be from about 0.1 mm to about 1 mm. Further, the coil, may comprise wires wrapped in manner hereinabove described or may comprise printed features on a substrate. Printed wiring features may have exemplary thicknesses of from about 0.001 mm to about 5 mm. Further exemplary thicknesses may be from 0.01 mm to 2 mm. Exemplary widths may from about 0.001 mm to about 5 mm. Further exemplary widths may be from 0.01 mm to 3 mm. The conducting pathways printed on a substrate may be arranged in a serpentine pattern with the conducting pathways interdigitated with one another. The topography on the coil assembly may comprise thickness variations due to placement of the conductive pathways and is not intended to detract from the coil assembly being “essentially flat” in the portion proximal to the drive magnets. 
     When wired for N-phase operation, N conducting pathways, isolated from one another as in  FIGS. 3 and 11 . Shown in those Figures are coil assemblies that are wired for three-phase operation because there are three isolated conducting pathways in each. In addition, a preferred configuration is one in which the drive magnet array is cast on approximately the same pitch as the arrangement of the coils on the coil assembly. In one embodiment, a slider having an even number of drive magnets faces a single side (or facing region) of a coil assembly. In another embodiment, a slider having an even number of drive magnets with both poles available for interaction, faces two coils, one on each side as in  FIG. 1 . In still another embodiment, the slider with an even number of drive magnets may sandwich a coil such that two sliders coupled together move past a two-sided coil as shown in  FIGS. 7-9 . In still another embodiment, the slider with an odd number of drive magnets may sandwich a coil such that two sliders coupled together move past a two-sided coil. 
     Multiphase signals to the coils may be supplied by known methods. In one embodiment, the phased current is provided to the coils by a multichannel pulse-width modulator, such as might be available, for example, as the MSP430F1232, F1222, F1132 or F1122, integrated circuit devices available from Texas Instruments. In another embodiment, a multiphase signal may be generated according to the method set forth by Dooghabadi, et al. “Multiphase Signal Generation Using Capacitive Coupling of LC-VCOs,” Electronics, Circuits and Systems, 2007. ICECS 2007. 14th IEEE International Conference on, vol., no., pp. 1087, 1090, 11-14 Dec. 2007. 
     Conducting pathways using wires or features printed on circuit boards may be used for coils wired for multiphase operation. Wires may be isolated from each other by using a suitable insulation material such as polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene or other insulating polymer. In addition wires may be coated with insulating materials such as varnishes, lacquers, or shellacs. Conducting pathways formed on printed circuit boards, such as depicted in FIG.  3 , may be electrically isolated according to known methods of making multi-layer printed circuit boards. Multi-layer printed circuit boards have trace layers inside the board, achieved by laminating a stack of boards with circuits etched on them in a press and applying pressure and heat. For example, a four-layer PCB can be fabricated starting from a two-sided copper-clad laminate, etching the circuitry on one or both sides, and laminating the top and bottom layers to one another. The resulting workpiece may then be drilled, plated, and etched again to get traces on top and bottom layers. 
     Further embodiments of the actuators described herein include magnetic position sensors to allow monitoring of the position of the slider. Such monitoring may be used for error correction, determination of the state of the actuator, and/or mechanical switching rate, as well as closed-loop operation and field control. Magnetic position sensors may be on a linear or rotary scale. Moreover, the resolution of the position sensor may be determined by the number of bits in the digital signal. Sensors are available in 8-16 bit resolutions. Such devices may be obtained from AMS Corporation of Raleigh, N.C. 
     Suitable permanent magnets for the embodiments of this disclosure may include, without limitation, rare earth magnets such as samarium-cobalt and neodymium-iron-boron, specific examples of which include Nd 2 Fe 14 B (sintered), Nd 2 Fe 14 B (bonded), SmCo 5  (sintered), Sm(Co,Fe,Cu,Zr) 7  (sintered), Sr-ferrite (sintered), which generate high field strengths per unit volume. Weaker magnets such as Alnico or ceramic may also be utilized. Bar magnets may be polarized along the thin dimension so that, for example, the top comprises the north pole and the bottom comprises the south pole such as, for example  409  in  FIG. 4( d ) . Bar magnets may be polarized along the thick dimension so that, for example, one side comprises the north pole and the opposite side comprises the south pole, such as in  552  in  FIG. 5( c ) . In systems wired for multiphase operation, the drive magnet array may be formed from a plurality of magnets which are conveniently though not necessarily attached to the slider. In particular, M drive magnets attached to the slider, wherein each of the drive magnets is arrayed so that its nearest neighbor(s) have opposing magnetic polarity, and wherein, for example, M is an integer from 2 to 20. As a further example, M can be from 2 to 10. A preferred configuration is one in which M is an even number. 
     Although the present invention has been shown and described with reference to particular examples, various changes and modifications which are obvious to persons skilled in the art to which the invention pertains are deemed to lie within the spirit, scope and contemplation of the subject matter set forth in the appended claims.