Abstract:
A method and system for transportation using a magnetic bearing structure is disclosed. In one aspect, an apparatus for carrying a load comprises a source of magnetic flux and a controller configured to control the position of the source of magnetic flux relative to a magnetizable structure. The source of magnetic flux comprises a first upper portion and a first lower portion of opposite polarities. The first portions are spaced apart horizontally from a first side of the magnetizable structure. The source of magnetic flux further comprises a second upper portion and a second lower portion of opposite polarities. The second portions are spaced apart horizontally from a second side of the magnetizable structure. The second side is opposite the first side. The first and second upper portions are magnetically attracted to an upper portion of the magnetizable structure and the first and second lower portions are magnetically attracted to a lower portion of the magnetizable structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) of provisional application 61/163,778 filed Mar. 26, 2009, which is hereby incorporated by reference. This application also relates to U.S. Pat. Nos. 7,617,779; 3,569,804; and 6,977,451 each of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
     Field 
       [0002]    The invention generally relates to a method and system for transportation using a magnetic bearing structure. More particularly, the invention generally applies to levitation of a load for transportation. 
       SUMMARY 
       [0003]    In one aspect, an apparatus for carrying a load comprises a source of magnetic flux and a controller configured to control the position of the source of magnetic flux relative to a magnetizable structure. The source of magnetic flux comprises a first upper portion and a first lower portion of opposite polarities. The first portions are spaced apart horizontally from a first side of the magnetizable structure. The source of magnetic flux further comprises a second upper portion and a second lower portion of opposite polarities. The second portions are spaced apart horizontally from a second side of the magnetizable structure. The second side is opposite the first side. The first and second upper portions are magnetically attracted to an upper portion of the magnetizable structure and the first and second lower portions are magnetically attracted to a lower portion of the magnetizable structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1A  is a perspective view of a system comprising a tubular magnetic bearing structure positioned proximally to a rail. 
           [0005]      FIG. 1B  is a cross-sectional view of the system of  FIG. 1A  illustrating a plurality of magnetic field lines representing a magnetic field. 
           [0006]      FIG. 2A  is a front view of a system comprising a tubular magnetic bearing structure having a control coil. 
           [0007]      FIG. 2B  is a functional block diagram of a horizontal positioning system. 
           [0008]      FIG. 2C  is a flowchart illustrating a method of providing a current to a control coil based on received sensor data. 
           [0009]      FIG. 3  is a cross-sectional view of a system comprising a vehicle with magnetic bearing structures positioned proximally to rails. 
           [0010]      FIG. 4  is a cross-sectional view of a system comprising a prismatic magnetic bearing structure. 
           [0011]      FIG. 5  is a cross-sectional view of a system comprising a magnetic bearing structure with a plurality of magnets. 
           [0012]      FIG. 6  is a cross-sectional view of a system comprising a magnetic bearing structure with two magnets. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The following detailed description is directed to certain specific aspects of the invention. However, the invention may be embodied in a multitude of different ways, for example, as defined and covered by the claims. It should be apparent that the aspects herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative. Based on the teachings herein one skilled in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. Similarly, methods disclosed herein may be performed by one or more computer processors configured to execute instructions retrieved from a computer-readable storage medium. A computer-readable storage medium stores information, such as data or instructions, for some interval of time, such that the information may be read by a computer during that interval of time. Examples of computer-readable storage media are memory, such as random access memory (RAM), and storage, such as hard drives, optical discs, flash memory, floppy disks, magnetic tape, paper tape, and punch cards. 
         [0014]      FIG. 1  is a perspective view of a system  10  comprising a tubular magnetic bearing structure  100  positioned proximally to a rail  120 . The magnetic bearing structure  100  comprises a source of magnetic flux  104  between an inner shell  106  and an outer shell  102 . In one embodiment, the outer shell  102  has a C-shaped cross-section and is positioned concentrically about the inner shell  106 , which has a similarly C-shaped cross-section. Both the inner shell  106  and outer shell  102  are preferably made from a magnetizable material, such as iron or steel. The shells  102 ,  106  may guide the magnetic flux of the source of magnetic flux  104  along the inner and outer perimeter of the magnetic bearing structure  100  and thereby assist in containing and concentrating the magnetic flux of the source of magnetic flux  104 . 
         [0015]    Because of the magnetic attraction between the magnetic bearing structure  100  and the rail  120 , the magnetic bearing structure  100  may support a load without contacting the rail  120 . As described further with respect to  FIG. 3 , such a magnetic bearing structure  100  may be used to provide a levitative force countering the force of gravity upon a vehicle thereby reducing friction as the vehicle moves along the rail. 
         [0016]    In one embodiment, the source of magnetic flux  104  comprises a single permanent magnet. Permanent magnets may comprise rare earth magnets, samarium-cobalt magnets, alnico magnets and neodymium magnets. The use of permanent magnets allows the bearing  100  to provide “always on” levitation forces which do not require an electric power source. In other embodiments, the source of magnetic flux  104  may comprise one or more permanent magnets and/or one or more electromagnets. In one embodiment, the source of magnetic flux  104  is uniformly radially magnetized, such that edge surfaces of the source of magnetic flux  104  contacting the outer shell  102  are of one polarity and edge surfaces of the source of magnetic flux  104  contacting the inner shell  106  are of an opposite polarity. The source of magnetic flux  104  may be a bonded magnet. In one embodiment, a bonded magnet comprises a magnetic powder blended together with a thermoplastic resin to form injection molded, compression, or flexible magnets. The magnetic powder may be aligned in a preferred direction while the resin is liquid and be maintained in this preferred direction by the resin when it is hardened. A bonded magnet may be used to minimize stray flux, e.g., flux projecting outside the desired boundaries of the magnetic bearing  10 . 
         [0017]      FIG. 1B  is a cross-sectional view of the system of  FIG. 1A  illustrating a plurality of magnetic field lines  190 . Although only six field lines  190  are illustrated, it is to be appreciated that the magnetic field is a continuous field and more or fewer field lines  190  could be used to represent it. The outer shell  102  comprises a first end  152  and a second end  154  located proximally to protrusions of the rail  120 . The inner shell  106  also comprises a first end  162  and a second end  164  similarly located proximally to protrusions of the rail  120 . In one embodiment, the source of magnetic flux  104  generates a magnetic field represented by a plurality of magnetic field lines  190  beginning and ending at the source of magnetic flux  104 . The outer shell  102  guides each field line  190  along the outer shell  102  to the first end  152  or second end  154  where it crosses the gap between the outer shell  102  and the rail  120 . Each field line  190  continues via the rail  120  and exits the rail  120  by crossing the gap between the rail  120  and the first end  162  or second end  164  of the inner shell  106 . The inner shell  106  guides each field line  190  along the inner shell  106  and each field line  190  ends back at the source of magnetic flux  104 . Depending on the polarity of the source of magnetic flux  104 , this order may be reversed. 
         [0018]    In one embodiment, the length of the bearing  100  in the axial direction (along the rail  120 ) is larger than the radial thickness of the shell. This configuration minimizes non-suspensive flux and reduces stray fields as the lowest reluctance paths between the outer shell  102  and inner shell  106  are through the rail  120  via the gaps between the bearing  100  and the rail  120 . 
         [0019]    The rail  120  illustrated in  FIG. 1  positioned between the first and second ends of the inner and outer shell has an I-shaped cross-section. In other embodiments, other shapes may be used. In one embodiment, the rail  120  is narrow enough to fit between the gaps between the first ends  152 ,  154  and second ends  162 ,  164 . In one embodiment, the rail  120  is narrow enough to fit between the gaps between the first ends  152 ,  154  and second ends  162 ,  164  without contacting the magnetic bearing  100 . The rail  120  may be of any axial length to allow propulsion in addition to levitation. 
         [0020]    In one embodiment, the rail  120  comprises magnetizable material such as steel or iron. In another embodiment, the rail  120  comprises a magnetic material. The bearing  100  may “capture and restrain” the rail  120  since any vertical movement of the magnetic bearing structure  100  is resisted by magnetic forces generated by the source of magnetic flux  104  which tend to minimize the length of the magnetic field lines  190 . 
         [0021]    In one embodiment, the rail  120  comprises at least two substantially parallel rails separated by a gauge, each rail having a generally I-shaped profile with a head and a foot separated by a web. In one embodiment, the rail  120  comprises standard or international gauge rails, e.g., the gauge is approximately 1,435 mm. The gauge may be smaller or larger than 1,435 mm. In one embodiment, the rail  120  allow flanged wheels to ride along the head of the rail. Accordingly, embodiments described herein may be compatible with existing rail technology and other rolling stock. 
         [0022]      FIG. 2A  is a front view of a system comprising a tubular magnetic bearing structure  200  having a control coil  225 . The magnetic bearing structure  200  comprises a source of magnetic flux  204  between an inner shell  206  and an outer shell  202 . As described above with respect to the system  10  of  FIG. 1 , the bearing  200  may “capture and restrain” the rail  220 . As described further below, control current in the control coil  225  changes the amount of flux and therefore force on each side of the gaps between the source of magnetic flux  204  and the rail  220  such that lateral forces may produced or controlled and contact prevented. 
         [0023]    A horizontal positioning system  210  may comprises a controller, processor, or other circuit, and may be configured to horizontally center the bearing  200  with respect to the rail  220 . The horizontal positioning system  210  may comprise or be operatively coupled to a sensor  290  and a control coil  225 . The control coil  225  may carry an electric current which generates a magnetic flux within the coil  225 . Accordingly, the control coil  225  operates as an electromagnet, which converts an electric current into magnetic flux. The generated magnetic flux may bias the magnetic field described above with respect to  FIG. 1B , thereby providing a horizontal force to the magnetic bearing structure  200  through differential flux control. Accordingly, the amount of magnetic flux is differentially modulated by adding the bias magnetic flux generated by the control coil  225  to the magnetic flux generated by the source of magnetic flux  104 . As can be seen in  FIG. 1B , the flux direction in the gap  187  between the rail and the outer shell  102  and the flux direction in the gap  188  between the rail and the inner shell  106  are in opposite directions because of the polarity and orientation of the source of magnetic flux. Accordingly, more than one control coil  225 , where the direction of the coil winding for each coil is known or predetermined, may be used in series or parallel to appropriately produce net lateral force in the same direction. 
         [0024]    Through control of the current through the control coil  225 , the horizontal positioning system  210  may horizontally center the bearing  200  on the rail  220 . In one embodiment, the horizontal positioning system  210  preserves a constant total air gap between the source of magnetic flux  204  and the rail  220  by balancing attractive horizontal forces between the source of magnetic flux  204  and the rail  220 . In particular, because the magnetic attraction pulls both ends of each shell  202 ,  206  towards the rail  220 , the effectiveness of the control is enhanced. In one embodiment, the horizontal positioning system  210  operates to equalizes the magnetic flux on both sides of the rail  220 . 
         [0025]    In order to determine the horizontal position, one or more sensors  290  may be used. The sensor  290  may generate sensor data indicative of a distance from the sensor  290  to an object or to a predefined reference point. For example, the sensor  290  may generate sensor data indicative of a horizontal position of the magnetic bearing structure  200  with respect to the rail  220 . The sensor  290  may comprise, but is not limited to, an inductive proximity sensor, a capacitive displacement sensor, or a laser rangefinder. In one embodiment, the sensor  290  emits a light or acoustic signal and measures changes in a returned field. In another embodiment, the sensor  290  may also generate sensor data indicative of a rate of change of a distance from the sensor  290  to an object. For example, the sensor  290  may generate sensor data indicative of how fast a magnetic bearing structure  200  is approaching a rail  220 . The sensor  290  may comprise a Doppler-based sensor. In one embodiment, the sensor  290  emits a light or acoustic signal and measures a change in the wavelength of a returned signal. 
         [0026]    In one embodiment, the current carried by the control coil  225  as provided by the horizontal positioning system  210  is based on the horizontal position as determined by the sensor  290 . In one embodiment, the current is amplified based on a linear equation in which the current is linearly proportional to a distance indicated by the sensor  290 . In another embodiment, the current is amplified based on an inverse quadratic equation in which the current is proportional to the inverse of a square of a distance indicated by the sensor  290 . In another embodiment, the current is proportional, either linearly or non-linearly, to a difference in distances indicated by two sensors on opposite sides of the rail  220 . Because the current is based, at least in part, on a measurement from the sensor  290 , which is based, at least in part on the current provided, the horizontal positioning system  210  may comprise a servo drive to efficiently perform in this feedback situation. In general, a servo drive receives a command signal from a control system, amplifies the signal, and transmits electric current in order to produce motion proportional to the command signal. 
         [0027]    In one embodiment, the control coil  225  is wound around the outer shell  202 . In another embodiment, the control coil  225  is wound around the inner shell  206 . In another embodiment, multiple control coils may be wound around at least one of the outer shell  202  and inner shell  206 . For example, in one embodiment, a first control coil is wound around the outer shell  202  and a second coil is wound around the inner shell  206 . The control coil  225  may be physically separated from the outer shell  202 , the source of magnetic flux  204 , and the inner shell  206  by an electrically insulating material. 
         [0028]      FIG. 2B  is a functional block diagram of a horizontal positioning system  210  according to one embodiment. The horizontal positioning system  210  receives a signal from the sensor  290  indicating the horizontal position of a bearing  200  with respect to a rail  220 . A controller  212  processes the signal from the sensor  290  to determine the appropriate correcting current to provide to the control coil  225 . The controller  212  controls (and may be powered by) a power source  216  such as a battery or other source of electric current. The controller  212  controls the power source  216  so as to provide a current to the control coil  225 . In one embodiment, the horizontal positioning system  210  comprises a memory  214  for storing an algorithm for determining an appropriate current based on the signal received from the sensor  290 . 
         [0029]    The controller  212  may be a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any suitable combination thereof designed to perform the functions described herein. The controller  212  may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
         [0030]    The controller  212  may be coupled, via one or more buses, to read information from or write information to the memory  214 . The controller  214  may additionally, or in the alternative, contain memory, such as processor registers. The memory  214  may include processor cache, including a multi-level hierarchical cache in which different levels have different capacities and access speeds. The memory  214  may also include random access memory (RAM), other volatile storage devices, or non-volatile storage devices. 
         [0031]      FIG. 2C  is flowchart illustrating a method  270  of providing a current to a control coil. The method  270  may be performed, for example, by the horizontal positioning system  210  of  FIG. 2B . The method  270  begins, in block  271 , with the reception of sensor data indicative of a horizontal position. In one embodiment, the sensor data is indicative of a distance from a sensor to an object or a predefined reference point. For example, in one embodiment, the sensor data is indicative of a horizontal position of a magnetic bearing with respect to a rail. In one embodiment, the sensor data is indicative of a rate of change of a distance from a sensor to an object. For example, in one embodiment, the sensor data is indicative of how fast a magnetic bearing structure is approaching a rail. In another embodiment, the sensor data comprises data from multiple sensors, each indicative of a distance or a rate of change of a distance. 
         [0032]    Next, in block  272 , it is determined whether the sensor data is indicative of a distance or speed greater than a predetermined threshold. The determination may be performed, for example, by the controller  212  of  FIG. 2B . In one embodiment, the predetermined threshold may be zero. If the distance or speed is less than the predetermined threshold, the method  200  moves to block  273  where the method  200  pauses for a predetermined amount of time. By including blocks  272  and  273 , the method  270  does not perform a continuous adjustment which may be energy inefficient or may result in excess jerk. 
         [0033]    If it is determined that the sensor data is indicative of a distance or speed greater than the predetermined threshold, the method  200  continues to block  274 , where a current corresponding to the received sensor data is determined. The determination may be performed, for example, by the controller  212  of  FIG. 2B . In one embodiment, the current is amplified based on a linear equation in which the current is linearly proportional to a distance indicated by the sensor. In another embodiment, the current is amplified based on an inverse quadratic equation in which the current is proportional to the inverse of a square of a distance indicated by the sensor. In another embodiment, the current is proportional, either linearly or non-linearly, to a difference in distances indicated by two sensors on opposite sides of a rail. In yet another embodiment, the current is amplified based on a look-up table. Such a look-up table may be stored, for example, in the memory  214  of  FIG. 2B . In one embodiment, the current is determined proportional to a speed indicated by the sensor. In another embodiment, the current is determined based on a distance and a speed indicated by the sensor. 
         [0034]    Continuing to block  275 , the determined current is provided to one or more control coils. The current may be provided, for example, by the power source  216  as controlled by the controller  212  of  FIG. 2B . The current provided to the control coils may generate a magnetic flux within the control coil and thereby bias the magnetic field described above with respect to  FIG. 1B  so as to provide a horizontal force and horizontally center the bearing on the rail. It is to be appreciated that in some embodiments, the determined current may be zero. For example, the determined current may be zero when a magnetic bearing is centered with respect to a rail in the absence of external forces. 
         [0035]    After block  275 , the method  270  returns to block  271  and repeats. Thus, the method  270  continually provides a current based on sensor data. In one embodiment, the horizontal positioning system  210  continually centers a magnetic bearing with respect to a rail. 
         [0036]      FIG. 3  is a cross-sectional view of a system  30  comprising a vehicle  330  having a load  360  coupled to magnetic bearing structures  310 ,  312  positioned proximally to rails  320 ,  322 . By using two rails rather than a single rail, rotation of the vehicle with respect to the rail may be inhibited. The vehicle comprises a first bearing  310  positioned proximally to the first rail  320  and a second bearing  312  positioned proximally to the second rail  322 . The bearings  310 ,  312  provide a suspensive or levitative force counteracting the force of gravity acting upon the vehicle  330  and the load  360 , thereby reducing friction along the rails. The bearings  310 ,  312  are attached to the load  360  via one or more support structures  362 . The bearings may be attached via welding, screws, or other affixing techniques. 
         [0037]    A horizontal position system (not shown) comprising one or more position sensors and one or more control coils may keep the bearings horizontally centered such that the bearings do not contact the rails, further reducing friction. In one embodiment, the horizontal positioning system comprises one or more control coils configured to respectively carry one or more electrical currents so as to provide a horizontal force as described above with respect to  FIG. 2 . 
         [0038]    In one embodiment, the system may use asymmetrical air gaps as described in U.S. patent application Ser. No. 12/048,062, herein incorporated by reference in its entirety. In one embodiment, the inner gaps  380  between the bearings  310 ,  312  and the rails  320 ,  322  are of a different size than the outer gaps  382  between the bearings  310 ,  312  and the rails  320 ,  322 . Thus, if the vehicle  330  is displaced horizontally, only one of the bearings would contact the rails. 
         [0039]    Whereas the system  30  may comprise bearings which provide a force in the vertical direction and a horizontal positioning system which provides a horizontal force, the system  30  may also comprise an engine which provides a propulsive force in the direction of the rails  320 ,  322 . Accordingly, the system  30  may be provided six degrees of freedom. In one embodiment, the engine comprises a conventional, wheeled locomotive engine connected to the vehicle  330 . In another embodiment, the engine comprises a linear motor as described in U.S. patent application Ser. No. 12/048,062 or U.S. Pat. No. 7,617,779, herein incorporated by reference in its entirety. 
         [0040]    Although only two bearings  310 ,  312  are shown in  FIG. 3 , it is to be appreciated that a vehicle or system could contain additional independent bearings in various configurations. For example, bearings may be approximately positioned at four corners of a vehicle. As another example, bearings having an approximate axial length similar to that of the vehicle may be positioned on each side of the vehicle. In one embodiment, multiple vehicles having bearings may be pulled or pushed by one or more wheeled or levitating engines. 
         [0041]    Some of the benefits of levitating platforms, such as the vehicle  330  of  FIG. 3 , as opposed to wheeled carts are, among other things, the reduction of wear on mechanical parts, the reduction of extraneous heat produced, and the reduction of noise. A hybrid levitation system has the potential to be more energy efficient than conventional systems by virtue of the reduced friction. One embodiment of the invention comprises a MagLev system comprising one or more magnetic bearings. 
         [0042]      FIG. 4  is a cross-sectional view of a system  40  comprising a prismatic magnetic bearing structure  400 . The system  40  differs from the embodiments described above in that the magnetic bearing structure  400  is not tubular, but rather shaped as a prism. Although a rectangular prism is shown in  FIG. 4 , other shapes may be used. For example, in one embodiment, the cross-section of the magnetic bearing structure  400  is triangular. Otherwise, the structure and functionality of the system  40  may be as the system  20  of  FIG. 2  as described above. Because the magnetic bearing structure  400  is prismatic, the bearing  400  may be more easily attached to a vehicle or more easily stored. Because a prismatic structure generally contains flat surfaces, manufacture of a source of magnetic flux may be simplified and control coils may be more easily installed. 
         [0043]      FIG. 5  is a cross-sectional view of another system  50  comprising a magnetic bearing structure  500 . The system  50  differs from the embodiments described above in that the source of magnetic flux  504  comprises a plurality of magnets  504  arranged such that one polarity faces the outer shell  502  and the other polarity faces the inner shell  506 . Between the magnets  504 , there is a non-magnetizable substance  515 , such as glass, wood, resin, or air and offering more space and potentially suitable locations for placement of control windings. Otherwise, the structure and functionality of the system  50  may be as the system  20  of  FIG. 2  as described above. Because the magnetic bearing structure  500  comprises a plurality of magnets  504  rather than a single magnet, the source of magnetic flux  504  may be less expensive. However, if the plurality of magnets  504  are too spaced apart, magnetic field lines may exist through the non-magnetizable material rather than through the rail  520  thereby decreasing the levitative force. 
         [0044]      FIG. 6  is a cross-sectional view of a system comprising a magnetic bearing structure with two magnets The magnetic bearing structure  600  comprises a support structure  630  and a source of magnetic flux comprising two magnets  604   a ,  604   b  arranged on either side of the rail  620 . The magnets  604   a ,  604   b  are arranged such that the top of each magnet  604   a ,  604   b  is of one polarity and the bottom of each magnet  604   a ,  604   b  is of the other polarity. In one embodiment, the support structure  360  fixes the location of the magnets  604   a ,  604   b  with respect to each other. Otherwise, the structure and functionality of the system  60  may be as the system  20  of  FIG. 2  as described above. Because the magnetic bearing structure  600  has only two magnets, production may be simplified or costs may be reduced. However, magnetic field lines may exist to the left of the left magnet  604   a  or to the right of the right magnet  604   b  rather than through the rail  620  thereby decreasing the levitative force. 
         [0045]    In one embodiment, the source of magnetic flux positioned proximally to the rail may be narrow in the vertical direction or may comprise narrow protrusions towards the rail so as to provide resistance to vertical displacement by reluctance changes. 
         [0046]    While the above description has pointed out novel features of the invention as applied to various embodiments, the skilled person will understand that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made without departing from the scope of the invention.