Patent Publication Number: US-2004055836-A1

Title: Eddy current braking apparatus with adjustable braking force

Description:
[0001] The present application is a continuation-in-part of U.S. patent application Ser. No. 09/880,353 filed Jun. 13, 2001 now U.S. Pat. No. ______ which is a continuation-in-part of U.S. patent application Ser. No. 09/447,206 filed Nov. 22, 1999 now U.S. Pat. No. 6,293,376. 
    
    
     
       [0002] The present invention is generally related to permanent magnet linear brakes and is more particularly directed to an eddy current brake and magnet system for providing adjustable braking for movable cars, for example, rail support cars, go cars, elevator cars, conveyer car, roller coaster cars among other.  
       [0003] Heretofore, eddy current braking system for providing deceleration of moving apparatus have utilized physically fixed magnets which provided no opportunity to adjust braking before or during passage of a diamagnetic member past a linear array of permanent magnets.  
       [0004] Accordingly, such prior art systems, when installed for decelerating a plurality of cars on a track, cannot accommodate for variations in car weight and size.  
       [0005] The present invention provides for a unique permanent array arrangement and apparatus for adjusting braking force before and/or during passage of a car past a selected point.  
       SUMMARY OF THE INVENTION  
       [0006] An eddy current brake in accordance with the present invention generally includes a diamagnetic or non-magnetic member, a first support wall and a separate second support wall disposed in a spaced apart relationship with the first support wall for enabling the member to pass therebetween.  
       [0007] A first linear array of permanent magnets is disposed on the first wall on the side facing the second wall and a second linear array of permanent magnets is disposed on the second wall on the side facing the first wall. The first and second arrays are parallel with one another and spaced apart from one another for allowing passage of the member therebetween and causing eddy current to be induced in the member which results in the braking force between the magnets and the member. No magnetic connection, such as a yoke, is required between the walls or the arrays of permanent magnets. This feature enables adjustability of the distance between the member and the magnet arrays.  
       [0008] In accordance with the present invention, apparatus is provided for moving a least one of the first and second walls in order to control eddy current induced in the member during the passage of the member therepast in order to adjust braking force between the magnets and the member. In one embodiment of the present invention, the apparatus includes means for moving at least one of the first and second walls in a direction perpendicular to the member, and in another embodiment of the present invention, the apparatus includes means for moving at least one of the first and second walls in a direction parallel to the member.  
       [0009] Thus, it can be seen that the apparatus in accordance with the present invention provides for changing the spaced apart relationship between the first and second walls in order to control eddy current induced in the member during passage and adjust a braking force between the magnets and member.  
       [0010] Accordingly, the amount of deceleration provided to a given car may be adjusted in accordance with the present invention. In addition, cars of various sizes and weights may be utilized and the eddy current magnetic brake in accordance with the present invention adjusted to provide the proper, or desired, deceleration. In one embodiment to the present invention, apparatus is provided for adjusting the eddy current induced in the member, and the braking force, as a function of velocity of the member between the arrays. Thus, cars having various velocities upon passing the brake, can be decelerated to a more uniform velocity exiting the brake in accordance with the present invention.  
       [0011] In this embodiment of the brake, the apparatus for adjusting eddy current includes a linkage mounting at least one of the first and second walls to a fixed foundation for enabling movement of the member therepast to change a distance between at least one of the first and second walls and the member. More particularly, the linkage may provide for changing a spaced apart relationship between the first and second walls.  
       [0012] An embodiment of the present invention includes linkage for enabling movement of the member to change a transverse relationship between at least one of the first and second walls of the member and another embodiment provides linkage for enabling movement of the member to change a parallel relationship between the first and second walls and the member.  
       [0013] Magnetic coupling and inducement of eddy current is effective through a linear array of permanent magnets which includes a channel and plurality of magnets disposed therein. The magnets may be arranged within the channel in two adjacent rows with each magnet in each row being arranged with a magnetic field at a 90° angle to adjacent magnets in each row along the channel. Each magnet in each row is also arranged with a magnetic field at an angle to another adjacent magnet in the adjacent row.  
       [0014] In yet another embodiment of the present invention eddy current brake mechanism includes a diamagnetic or non-magnetic member with a fixed linear array of permanent magnets. A moveable linear array of permanent magnets is disposed in a parallel relationship with the fixed linear array of permanent magnets for enabling passage of the member therebetween.  
       [0015] Apparatus is provided for adjusting the eddy current induced in the member, and concomitant braking force, by the lateral movement of the movable linear array of permanent magnets.  
       [0016] More specifically, this embodiment may utilize an actuator disposed in an operational relationship with a movable linear array of permanent magnets or alternatively utilize a spring attached to the movable linear array of permanent magnets for enabling the lateral movement of the movable array as a function of velocity of the member between the magnetic arrays. In this way the braking force is automatically adjusted upon relative velocity between the member and the magnet arrays.  
       [0017] Still another embodiment of the present invention includes an eddy current brake mechanism with a diamagnetic or non-magnetic member, a fixed array of permanent magnets and a rotatable array of permanent magnets disposed in a spaced apart relationship with the fixed array of permanent magnets for enabling the passage of the movement therebetween.  
       [0018] Apparatus is provided for adjusting the eddy current induced in the member, and concomitant braking force, through rotation of the rotatable array of permanent magnets. More specifically, the apparatus may include an actuator disposed in an operational relationship with the rotatable array of permanent magnets for rotation thereof. Alternatively, a spring may be attached to the rotatable array of permanent magnets for enabling rotation of the rotatable array as a function of velocity of the member between the magnetic arrays. Again, this configuration provides for automatic adjustment of braking force as a function of member velocity.  
       [0019] A further embodiment of the present invention includes an eddy current brake mechanism with a diamagnetic of non-magnetic member, a first movable linear array of permanent magnets and a second movable linear array of permanent magnets disposed in a spaced apart parallel relationship with the first array for enabling passage of the member between and within a plane established by the parallel arrays.  
       [0020] An actuator may be provided and connected to the arrays for adjusting the eddy current induced in the member, and concomitant braking force, through movement of the arrays in a direction perpendicular to the plane.  
       [0021] Yet another embodiment of the present invention provides for an eddy current braking mechanism for a car having spaced apart wheels for engagement with a pair of parallel rails. The mechanism includes a diamagnetic or non-magnetic member depending from the car between the wheels and first and second linear arrays of permanent magnets disposed in a parallel spaced apart relationship for enabling passage of the member therebetween in order to induce eddy current, and concomitant braking force, in the member upon passage of the member between the arrays.  
       [0022] Springs disposed between the car and each wheel are provided for enabling lowering of the member between the arrays as a function of car weight thereby adjusting the induced eddy current and braking force as a function of car weight.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023] The advantages and features of the present invention will be better understood by the following description when considered in conjunction with the accompanying drawings in which:  
     [0024]FIG. 1 is a perspective view of an eddy current brake in accordance with the present invention generally showing first and second spaced apart support walls and first and second linear arrays of permanent magnets along with a diamagnetic or non-magnetic member attached to moving apparatus such as a car, represented by dashed line;  
     [0025]FIG. 2 is a perspective view of a first linear array of permanent magnets disposed upon a first support wall;  
     [0026]FIG. 3 is an elevational view of the brake shown in FIG. 1;  
     [0027]FIG. 4 shows a selectively actuatable brake system disengaged;  
     [0028]FIG. 5 shows a system of FIG. 8 engaged;  
     [0029]FIG. 6 is an elevational view of an alternative embodiment according with the present invention further showing apparatus for moving at least one of the first and second walls in order to control the distance between permanent magnets and opposing walls for adjusting braking force between the magnets and a member;  
     [0030]FIG. 7 is plan view of the brake shown in FIG. 6;  
     [0031]FIG. 8 is an enlarged view of a linear array of permanent magnets in accordance with the present invention generally including a channel and a plurality of magnets disposed therein in a particular arrangement as will be hereinafter described in greater detail;  
     [0032]FIGS. 9 and 10 show embodiment of the present invention similar to that shown in FIGS. 8 and 9 and further including apparatus for adjusting eddy current induced and the member, and braking force, is a function of velocity of the member between arrays of magnets;  
     [0033] FIGS.  11 - 14  are diagrams of alternative embodiments of the present invention which provide for linkage from at least one of the first and second walls to a fixed foundation for enabling movement of the member past the first and second walls with the first and second magnet arrays thereon to change a perpendicular relationship between the first and second walls and the member;  
     [0034]FIGS. 15 and 16 are diagrams of an eddy current brake mechanism with a fixed linear array of permanent magnets, a movable linear array of permanent magnets and apparatus for adjusting eddy current induced in the member by lateral movement of the movable linear array of permanent magnets;  
     [0035]FIG. 17 is a diagram of eddy current mechanism utilizing a fixed array of permanent magnets and a rotatable array of permanent magnets and an apparatus for adjusting eddy current induced in a member passing therebetween through rotation of the rotatable array of permanent magnets;  
     [0036]FIG. 18 is a diagram of eddy current brake mechanism showing two movable linear arrays of permanent magnets and an actuator for adjusting eddy current induced in a member passing therebetween by movement of the arrays in a direction perpendicular to a plane established by the arrays of magnets; and  
     [0037]FIG. 19 is a diagram of an eddy current brake mechanism utilizing fixed magnet arrays and a spring arrangement between a car and wheels for lowering a member attached thereto in a depending fashion as a function of a car weight in order to adjust the induced eddy current in the member as the member passes between the magnet arrays.  
    
    
     DETAILED DESCRIPTION  
     [0038] For the ensuing description of a braking apparatus  10  for an object  12 , reference is made particularly to FIGS.  1 - 3 . The object  12  is shown in generalized form only and is contemplated for movement in the direction of the arrow. Affixed to the object  12  is a member, or fin,  14  which extends outwardly from the object  12  and also moves with the object in the direction of arrow  15 .  
     [0039] At some point along the path of movement there are mounted first and second laterally spaced magnet arrays  16  and  18 . Each array includes an elongated support wall  20  which may be any cross-section, such as, for example an L-shaped cross-section, and on a lateral surface thereof, there are provided a linear series of permanent magnets  22 , of any size, arrangement or configuration. For instance, the magnets may alternate in polarity as indicated by the identification letters “S” and “N”. Also, the space  26  between the arrays is dimensioned and arranged with respect to the object path of movement, that the fin  14  will move along the space directly opposite the magnets and spacers, but remain out of physical contact with either the magnets or spacers.  
     [0040] When the fin  14  passes through the magnetic field existing in the space  26 , an electric current (eddy current) is induced in the fin  14  which, in this case, reverses as the fin passes from a magnet of one polarity to a magnet of opposite polarity. These eddy currents produce a force exerted on the fin  14  (and object  12 ) of such direction as to reduce the velocity of movement of object  12  and fin  14 . It is this deceleration that produces the “braking” of the present invention.  
     [0041] Although the above-described first embodiment includes movement of the object and fin past fixedly located magnet arrays, the magnet arrays can just as well be moved past a stationary object and fin. All that is needed to achieve the braking effect is relative movement between the magnets and fin. Since usually the object is moving, in that case the magnet arrays would be carried by the object and the fin fixedly mounted adjacent the path of movement. The choice of which technique to employ depends upon the particular application.  
     [0042] In its more general aspects, the invention can be advantageously employed for braking a large variety of moving objects. As an excellent example, eddy current braking for elevators could be highly advantageous as an emergency measure where normal operation has somehow been interfered with or disrupted. Also, many amusement park rides could benefit by having eddy current braking devices to retard excessive speed as the “ride” vehicle takes a corner or drops at a severe angle.  
     [0043]FIGS. 4 and 5 illustrate an object  52  with a brake fin  54  interconnected therewith, that moves generally along a direction indicated by an arrow  56  which normally will pass by a magnet carrier  58  beyond the range of substantial magnetic interaction (FIG. 4). The object  52  and fin  54  are provided with means  60  selectively actuatable for moving them toward the magnet carrier so as to effect magnetically coupling therewith (FIG. 5) and achieve braking.  
     [0044] With reference to FIGS. 6 and 7, there is shown an alternate embodiment  100  of the eddy current brake in accordance with the present invention generally including a diamagnetic or non-magnetic member  102 , a first support wall  104  and a second support wall  106 . Walls  104 ,  106  are separate from one another and disposed in a spaced apart relationship upon a base or foundation  110  via leg portions  112 ,  114  respectively. The spaced apart relationship enables the member  102  to pass between the walls  104 ,  106  and because  104 ,  106  are not fixed with respect to one another, a distance D therebetween can be adjusted as will be hereinafter discussed in greater detail.  
     [0045] A first linear array  120  of permanent magnets  122 , see FIG. 8, is disposed on the first on a side  124  facing the second wall  106 .  
     [0046] A second linear array  130  of permanents (not individually shown) are disposed on the second wall  106  on a side  132  facing the first wall  104  with the first and second arrays  120 ,  130  being parallel with one another as shown in FIG. 10. Apparatus  140 ,  142  is provided for moving the walls  104 ,  106  and change the spaced apart relationship between the first and second walls  104 ,  106  in order to control, or adjust, eddy current induced in the member  102  during passage of the member  102  past and between the walls  104 ,  106  and magnets  120 ,  130  thereby adjusting the braking force between the magnets arrays  120 ,  130  and the member  102 .  
     [0047] The apparatus  140 ,  142  may include adjusting nuts  144 ,  146  and bolts  148 A,  148 B,  150 A,  150 B interconnected between the walls  104 ,  106  and brackets  152 ,  154  fixed to the base  110 .  
     [0048] Jam nuts  156 ,  158  prevent unwanted movement of the adjusting nuts  144 ,  146  and securing bolts  160 ,  162  extending through the base  110  and legs  112 ,  114  through slots  166 ,  168 , fix the walls  104 ,  106  in a desired spaced apart relationship after adjustment. The exact size of the walls  104 ,  106 , magnet arrays  120 ,  130 , member  102  and spacing D will be dependant upon velocity and weight of a car (not shown) attached to the member  102  and may be empirically determined.  
     [0049] It should be appreciated that the apparatus  140 ,  142  may include any number of configurations for adjustment of the walls  104 ,  106 . Such alternatives including single direction bolts, worm screws, jack screws, short in-line turn buckles, or other electrical, pneumatic, hydraulic system capable of providing the adjustment of spacing D, between the walls  104 ,  106 . Such configurations may eliminate a need for the securing bolts  160  and  162 .  
     [0050] Preferably, each magnet array  120 ,  130 , as illustrated by the array  120  in FIG. 12, includes at least 1 row  170 , each having individual magnets  180 ,  182 ,  184 ,  186 . A second row  172  may include individual magnets  188 ,  190 ,  192 ,  194  respectively.  
     [0051] The magnet rows  170 ,  172  may be disposed in a tube, or channel  200  which may be formed of any suitable material such as aluminum, stainless steel, plastic; any number of magnets (not all shown) may be used.  
     [0052] The magnets  180 ,  194  are specifically arranged within the channel  200  with a specific magnetic field pattern. While two rows  170 ,  172  are shown, it should be appreciated that any suitable number of rows (not shown) may be utilized.  
     [0053] The channel  200  may be removably attached in any suitable manner to the wall  104 . Thus, as hereinabove noted, assembly of the brake  100  is facilitated. Another advantage of the preassembly of magnets  180 - 186  is the is the fact that alternative magnet configurations may be easily exchanged on the wall  104  in order to tailor magnetic braking characteristics.  
     [0054] More particularly, a magnet  182  in a row  170  is arranged with a magnetic field (indicated by the arrow  204 ) which is at an angle to the magnetic fields  206 ,  208  of adjacent magnets  180 ,  184  in the row  170 . A number of angular relationship between the adjacent magnets  180 ,  182 ,  184  such as, for example, 15°, 30°, 45° or 90°. When the angular relationship between adjacent magnet  180 ,  182 ,  184  is 90°, they may also be arranged with the magnetic field  104  at a 90° angle to a magnetic field  210  of the magnet  190  in the adjacent row  172 .  
     [0055] Preferably, the magnets  180 - 194  are epoxied into the channel  200  and thereafter attached to the wall  104  in any suitable manner. Also, the channel  200  may be open, as shown, or closed, (not shown) and be of any suitable shape for containing the magnets. Because the magnets may be assembled in the channel  200  before installation on the wall  104 ,  106 , assembly of the brake  100  is facilitated. In addition, change of magnetic field can be easily performed by changing of channels (not shown) having different magnet configurations therein.  
     [0056] The multi-row Halbach arrangement as shown in FIG. 8, can be built with no backiron. The advantage is that most of the flux is confined to the member of fin  102  area, without needing backiron as is needed in the standard eddy current brake (not shown). The flux is concentrated between the magnet array and is small above and below the magnets. Significant weight improvements result because no backiron is used.  
     [0057] Multiple rows  170 ,  172  in proper alignment permit the use of the cubic Halbach arrangement in such a way that brakes of increasing power levels can be constructed while maintaining a fixed depth of magnet.  
     [0058] The Halbach array can achieve higher braking forces for the equivalent volume of magnetic material of a conventional ECB. The Halbach array reduces stray magnetic field through the inactive side of the array.  
     [0059] With reference to the diagrams shown in FIGS. 13 and 14, apparatus  250  including links  252 ,  254  interconnecting the wall  104  with a foundation  258  provides for changing, controlling, or adjusting eddy current induced in the member  102 , and braking force, as a function of member  102  velocity between the walls  104 ,  106  and arrays  120 ,  130 . Only one wall  104  is shown in FIGS. 13, 14 for the sake of clarity.  
     [0060] As shown by the directional arrows  260 ,  262  in FIGS. 13, 14 respectively, movement of the member  102  past the wall  104  and array  120  attached thereto provides a reaction force as shown by the arrow  266  which raises the wall  104  from stops  270 ,  272  in order to change a transverse relationship between the wall  4  and array  120  and the member  104 . This transverse movement raises  104  increasing relative penetration of  102 , which increases the induced eddy currents and braking action.  
     [0061] Because the drag force is a function of velocity, when the walls  104  are mounted for pivoting on the links  252 ,  254 , the wall  104  is raised a specific height based upon the drag force generated causing rotation of the links  250 ,  254 . Thus, the penetration of the member  102  into the magnetic flux established by the arrays  120 ,  130  is self regulated.  
     [0062] When used in one orientation, as shown in FIGS. 9, 10, the member  102  having a velocity in excess in a predetermined value would generate drag forces  266  sufficient to rotate, or pivot, the wall  104  to increase member  102  penetration and subsequently generating higher drag forces to reduce the excess velocity. As the velocity falls below the level necessary to generate drag force sufficient to fully rotate the wall  104  and pivot linkages  252 ,  254 , the wall  104  rotates back toward the default position. How far back it rotates is a self regulating function of the velocity/drag force in that instance.  
     [0063] Thus, the apparatus  250  can be utilized as an automatic “trim” brake actuating only when necessary and only with a force necessary to maintain the desired velocity of the member  102  and vehicle attached (not shown). Opposite linkages (not shown) would have the effect of lowering the wall  102  upon movement of the member  102  therepast, thereby having the effect of flattening the initial drag peak and providing flatter more uniform deceleration.  
     [0064] As diagramed in FIGS. 11 and 12, apparatus  280  including pivoting links  282 ,  284 ,  286 ,  288  interconnected between a foundation  290  and the walls  104 ,  106  enable movement of the member as indicated by the arrow  302  to pivot the links  282 ,  284 ,  286 ,  288  in direction indicated by the arrows  304 ,  306  in order to change a distance d 1  between the walls  104 ,  106 . The magnet arrays are not shown in FIGS. 15 and 16 for the sake of clarity in describing wall  104 ,  106  movement. Since the walls  104 ,  106  carry the magnet arrays  120 ,  130  the distance between the arrays  120 ,  130  is also varied. The links  282 ,  284 ,  286 ,  288  may include spring loaded pivots  310 ,  312 ,  314 ,  316  respectively in order to bias the walls  104 ,  106  against stops  320 ,  322  in a rest position.  
     [0065] As shown in FIG. 12, movement of the member between the walls  104 ,  106  decreases the distance d 1  to d 2 , thus increasing the induced eddy currents and increasing a braking action. A stop  326  defines the minimum distance d 2  Of approach between the walls  104 ,  106 .  
     [0066] Similar linkage apparatus is shown in FIGS. 13 and 14 in connection with the walls  104 ,  106  and member  102 . In this instance, links  342 ,  344 ,  346 ,  348  are interconnected so that movement indicated by the arrow  360  of the member  102  causes a spread or widening as indicated by the arrows  364 ,  366  of the walls  104 ,  106 . Stops  370 ,  372 ,  376  limit the movement of the walls  104 ,  106  in a manner similar to that described in connection with the apparatus  280  shown in FIGS. 11, 12.  
     [0067] Spring loaded pivots keep the walls  104 ,  106  initially biased against the stop  376 . This configuration lowers the magnetic coupling due to movement of the member  102  between the walls  104 ,  106  and, as hereinabove noted, has the effect of flattening the initial drag peak and provide a flatter more uniform deceleration. It should be appreciated that other means of opening and closing arrays and lowering the walls  104 ,  106  may be utilized which can include other mechanical, pneumatic, hydraulic or other components (not shown) to provide the same function.  
     [0068] With reference to FIGS. 15 and 16, there is diagramed an eddy current brake mechanism, which includes a diamagnetic or non-magnetic member  402 , as hereinbefore described for movement between a fixed linear array  404  of permanent magnets  406  and a movable linear array  408  of permanent magnets  410  which may be mounted on a rail  412  for linear movement therealong. The linear movement may be provided by, for example, a pneumatic actuator, or electric motor  414  or, as indicated in dashed line, a spring  416  which provides for automatic adjustment of eddy current induced in the member  402  and concomitant braking force, as a function of velocity of the member  402  between the arrays  404 ,  408 .  
     [0069] As illustrated in FIG. 15, the arrays  404  and  408  are positioned for optimum braking position with flux lines  420  represented in dashed format. That is, maximum braking force is achieved with the magnet arrays aligned as shown in FIG. 15.  
     [0070] As illustrated in FIG. 16, the actuator  414  has moved the movable array  408  by ½ wavelength, i.e. Δx=λ/2 and hence the flux  422  on the member  402  is minimized and accordingly braking force is minimized. While the permanent magnet arrays  404 ,  408  are shown as Halbach arrays, it should be appreciated that other magnetic arrangement of permanent magnets with or without backiron, or electromagnets may be utilized in accordance with the principle of the present invention.  
     [0071] When the spring  416  is utilized, no external motor or actuator of any kind is necessary. In this embodiment, the magnet array  408  is held in place by a spring, which offsets the force of the magnetic attraction to the adjacent magnet array  406 . When the member  406  moves between the arrays  404 ,  408  the electrodynamic braking force moves the movable array  408  to a more optimal braking position by dragging it by the effects of eddy currents.  
     [0072] At a higher speed of the member  402 , there is more drag force acting on the movable array  408  and hence more force tending to move it to an optimal braking location, i.e. greater braking force. In this manner, the brake compensates for higher input speed of the member  402  by providing more braking force.  
     [0073] With reference to FIG. 17, there is diagramed an eddy current brake mechanism  415  in accordance with the present invention utilizing a diamagnetic or non-magnetic member  452  disposed for movement between a fixed array  454  of permanent magnets  456  and a rotatable array  460  of permanent magnets  462 . The array  460  is rotatable about an axis  466  as indicated by the arrow θ, which provides maximum braking force at θ=0 and lesser braking force as the angle θ is increased.  
     [0074] Rotation of the array  460  may be provided by an actuator  470  coupled to the array in a conventional manner.  
     [0075] Alternatively, the array  460  may be spring  472  loaded in order to provide rotation of the array  466  as a function of velocity of the member  452  between the arrays  454 ,  460 . This movement is akin to the linear movement of the array  408  hereinabove described in connection with the embodiment  400  of the present invention.  
     [0076] Turning on to FIG. 18, there is diagramed eddy current brake mechanism  500  generally including a diamagnetic or non-magnetic member  502  as hereinbefore described in connection with earlier embodiments along with a first movable linear array  504  of permanent magnets  506  and a second movable linear array  508  of permanent magnets  510  disposed in a spaced apart relationship for enabling passage of the member  502  therebetween.  
     [0077] The magnet arrays  504 ,  508  establish a plane  514 , and an actuator, which may be pneumatic or electric,  516  is coupled to the arrays  504 ,  508  as indicated by the dashed line  520  in a conventional manner for adjusting the eddy current induced in the member  502 , and concomitant braking force, through movement of the arrays  504 ,  508  in a direction perpendicular to the plane  514  as indicated by the arrow  522 . Movement of the arrays  504 ,  508  in a downward direction provides for less magnetic coupling with the member  502  hence less braking action.  
     [0078]FIG. 19 diagrams another eddy current brake mechanism  550  in accordance with the present invention for a car  552  having spaced apart wheels  554 ,  556  for engagement with parallel rails  558 ,  560 . The mechanism  550  includes a diamagnetic or non-magnetic member  570  depending from the car  552  between the wheels  554 ,  556 .  
     [0079] First and second linear arrays  572 ,  574  of permanent magnets  576 ,  578  are disposed in a spaced apart relationship for enabling passage of the member  570  therebetween in order to induce eddy currents and concomitant braking force in the member  570  upon passage of the member  570  between the arrays  572 ,  574 .  
     [0080] Springs  580 ,  582 , which may have a selected spring constant k, are disposed between the car  552  and wheels  554 ,  556  in a conventional suspension manner and are operable for lowering the member  570  between the arrays  572 ,  574  as a function of car weight, thereby adjusting the induced eddy current and braking force as a function of car weight.  
     [0081] That is, when the mass of the car  552  increases (for instance, if the car is full of passengers) the car is suspended lower and the moving member  570  moves farther down inside the air gap or space  590  between the arrays  572 ,  574 . This provides more braking force which is advantageous for the heavier car.  
     [0082] Although there has been hereinabove described a specific eddy current braking apparatus with adjustable braking force in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it should be appreciated that the invention is not limited thereto. That is, the present invention may suitably comprise, consist of, or consist essentially of the recited elements. Further, the invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the present invention as defined in the appended claims.