Patent Publication Number: US-9415693-B2

Title: Selectively incrementally actuated linear eddy current braking system

Description:
CLAIM OF PRIORITY 
     This application claims priority of U.S. patent application Ser. No. 11/058,880 filed on Feb. 16, 2005, now U.S. Pat. No. 8,727,078, which claims priority of U.S. Provisional Application No. 60/575,431 filed on May 28, 2004. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a linear synchronous magnetic motor utilized primarily for braking. In particular, this invention relates to a linear synchronous magnetic motor utilized for braking that can be incrementally actuated to allow for the application of the variable braking force. 
     BACKGROUND OF THE INVENTION 
     It is known in the art to provide a linear synchronous magnetic motor as an electrodynamic brake. Such electrodynamic brakes are activated when the modules of the brake having permanent magnets of alternating polarity face one another, wherein each permanent magnet in each array faces and opposes a magnet of opposite polarity. The brakes can be deactivated by displacing one of the modules forward or backward 180 electrical degrees, which causes the magnetic field to diminish to a negligible level. 
     At present, such brakes are configured to be either fully in phase or out of phase, i.e., shifting the brakes 180 electrical degrees by fully displacing the module forward or backward or by lowering or raising a module away from the braking zone. It is also known to have such brakes configured to shift from one phase angle to another phase angle, e.g., from 180 electrical degrees to 90 electrical degrees, in order to provide an intermediate level of braking force. But no known system provides for the precise shifting of the modules to selected phase angles to provide the application of a number of selected braking forces. 
     Thus, there exists a need for an apparatus and method that provides for the incremental and precise application of braking force of an eddy current brake. For example, a brake configured to be shifted to any selected phase angle, rather than simply from one phase angle to another phase angle, would be most desirable. And there exists a need to do so with accurate metering, the type of which could not be achieved by a system that employed only double-acting piston cylinders. 
     It would be further desirable to link such a brake to a control system whereby a selected phase angle, which in turn translates to a selected braking force, could be selected on the basis of a selected condition such as velocity of the incoming vehicle and environmental factors. A system that determines the incoming velocity, for example, an object and applies a precise braking force based on that reading would be desirable. Such a system would allow for precise braking to occur in the event that the object or vehicle approaching the braking zone is not traveling at the designed or intended velocity due to external or unforeseen influences such as temperature, fluctuations in mass, or variable drag coefficients that are imposed on the moving vehicle. In most instances, achieving the desired incremental application of brake force is not possible due to the high difficulty of displacing the opposing modules forward and slightly downward brought on by mechanical interference that occurs surrounding the motor module, and due to the magnetic force between the modules which tends to push the opposing magnets in the module toward equilibrium. 
     SUMMARY AND OBJECT OF THE INVENTION 
     The invention is an incrementally actuated eddy current braking system. The system comprises first and second primary members, which further comprise arrays of permanent magnets arranged in alternating polarity. The respective magnets of the arrays face one another. A means for incremental displacement is drivingly connected to at least one of the primary members. 
     Thus, it is an object of the invention to provide an electrodynamic brake that can apply a selected brake force incrementally. 
     It is a further object of the invention to provide an electrodynamic brake that does not have simply two phases, but which can apply a plurality of selected braking forces. 
     It is still a further object of the invention to provide a system and method that provides a selected braking force based on a condition, for example, velocity or mass of an incoming vehicle, or temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of an embodiment of the present invention. 
         FIG. 2  is a side elevational view of an embodiment of the present invention. 
         FIG. 3  is a view of an embodiment of the present invention viewing the system along line AB in  FIG. 2 . 
         FIG. 4  is a top view of an embodiment of the present invention. 
         FIGS. 5A-5D  show the displacement of a module having an array of magnets relative to the other module. 
         FIGS. 6 and 7  are graphs of finite-element-analysis models of the present invention. 
         FIG. 8  is a schematic of the control system for an embodiment of the invention. 
         FIG. 9  is a flow diagram showing an embodiment of the invention. 
         FIG. 10  is a schematic of an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT OF THE INVENTION 
     The inventive system  100  is intended to operate in conjunction with a conventional type synchronous linear electrical machine operating as a motor or an electrodynamic brake. An example of such a synchronous linear electrical machine operating as a motor or an electrodynamic brake preferably comprises primary members  300 ,  500  comprising arrays of at least two permanent magnets  310 - 380 ,  510 - 580  of alternating polarity. The magnets are preferably attached to back plates  200 ,  400  which are preferably mounted on primary mounting plate  11 . The magnets along with backplate and plates  10  comprise respective modules  1000 ,  2000 . Preferably, a synchronous linear secondary stator member (not shown) accompanies the primary members to provide the synchronous linear electrical machine operating as a motor or an electrodynamic brake. A stator member can be mounted on the bottom of any incoming vehicle a fin-like protrusion that passes through the air gap  40  (shown in  FIG. 3 ) between primary members  300 ,  500  of modules  1000 ,  2000 . When the stator member and modules  1000 ,  2000  (and in turn the primary members  300 ,  500 ) move relative to one another, magneto-motive, i.e., braking force, force is created. Such is the operation of an eddy current brake. This invention, however, is concentrated on the primary members  300 ,  500  movement relative to one another and therefore discussion of a secondary stator member will be minimal. 
     The two primary members  300 ,  500  oppose each other. It is known to those skilled in the art that if the magnets in opposing primary member arrays  300 ,  500  are moved 180 electrical degrees relative to one another (as shown in  FIG. 5D ), the electrodynamic brake is fully out of phase and thereby inactive. But if the magnets in the primary member arrays  300 ,  500  are incrementally moved relative to one another (as shown in  FIGS. 5A-5C ), the magneto-motive force created will correspond to the phase angle created by said relative movement. The present invention allows for the incremental movement of a primary member relative to an opposing primary member and in this way provides for a variable electrodynamic braking force. 
     As shown in  FIGS. 1, 4 and 5A-5D , in a preferred embodiment, the invention comprises two opposing primary members  300 ,  500  each comprising arrays of permanent magnets  310 - 380 ,  510 - 580 . The first primary member  300  is preferably mounted in a stationary fashion. The second primary member  500  is mounted to a movable plate  10 . The movable plate  10  is preferably an angle weldment. The arrays are preferably mounted to a back plate  200 ,  400  which is ferromagnetic. In the completely actuated position, the magnetic array of the primary member  300  in the first stationarily mounted member directly opposes the magnetic array of the second primary member  500  with magnets of opposite polarity facing each other, for example magnets  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 , and  380  directly face and oppose magnets  510 ,  520 ,  530 ,  540 ,  550 ,  560 ,  570 , and  580  respectively. The alignment of the magnets in the arrays of the primary members  300 ,  500  when the brake is in the completely actuated position is best shown in  FIGS. 1 and 4 , which show the positive magnet of the stationary array  310  directly opposing negative magnet  510  of the movable array. As best shown in  FIG. 2 , a carriage  12  is affixed to the movable plate  10  and is slidably engaged with a linear bearing slide  14 . A bracket  16  connects the movable plate  10  to a push rod  22 , said push rod  22  being driven by a means for incremental displacement  20 . The means for incremental displacement  20  is preferably an optically encoded servo-motor operable to linearly displace the push rod  22  in direction A or B. The means for incremental displacement  20  is able to displace the push rod  22  (and therefore the movable plate  10 ) to and from a plurality points along pathway AB. The end points of the pathway are only limited by the length of the push rod  22 , the length of the linear slide bearing  14 , or the placement of the cushion bump stops  30 ,  32 . The incremental displacement in the invention differs from conventional systems, which only allow for displacement to and from only a few fixed points, most often two fixed points. Incremental displacement according to the present invention allows for modules and primary members to be moved to and from anywhere along a displacement path. Preferably, pressurized cushion bump stops  30  and  32  are affixed to the linear bearing slide  14  so as to limit the motion of the system upon contacting the bump stop supports  36 . 
     In operation, the means for incremental displacement  20 , by virtue of being drivingly attached to the movable plate  10 , and thus the modules  1000 ,  2000 , displaces the second primary member  500  a selected or a predetermined distance along direction AB. Braking force can be varied by the amount of displacement of the second primary member  500  relative to the first  300 . The predetermined displacement distance is determined based on the amount of braking force that is desired to be applied to the moving object having the secondary stator member attached. The module  1000  can be moved relative to the stationary module  2000  a plurality of distances based on the desired braking force. To deactivate the brake completely, the secondary movable module  1000  will be moved completely out of phase as discussed above and as shown in  FIG. 5D . It should be noted while that it is preferred to have one movable module and one stationary module, the invention also encompasses systems wherein both modules  1000 ,  2000 , for example, are movable with respect to one another. 
     An example of the correlation between incremental displacement of the primary members and braking power is illustrated at  FIGS. 6 and 7 .  FIG. 6  shows five finite-element-analysis models.  FIG. 6  shows velocity versus time.  FIG. 7  shows force versus time. In  FIG. 6 , series  1  shows as a function of velocity over time, a fully engaged operating set of finned modules without any actuation. Series  1  corresponds to the position of the modules shown in  FIG. 1 . It can be seen that rate of velocity reduction is greatest when the brake is fully engaged. Series  2  shows the brake&#39;s effectiveness in reducing velocity when the primary member is moved 45 electrical degrees out of phase according to the present invention. Series  2  corresponds to the position of the modules shown in Figure SA. It can be seen in Series  2  that rate of velocity reduction is lowered. Series  3  and  4  similarly show a decrease in the rate of reduction and corresponds to the position of the modules shown in  FIGS. 5B and 5C  respectively and caused by moving the member  90  and 135 electrical degrees out of phase. Finally, Series  5  shows a brake that is 180 degrees out of phase, which in this example was 5 linear inches of displacement of a primary member. Series  5  corresponds to the position of the modules shown in Figure SD. It can be seen that at this position, there is no reduction of velocity.  FIG. 7  shows corresponding levels of braking force generated by the system. 
     As schematically depicted in  FIG. 8 , another embodiment comprises, the means for incremental displacement  20  in communication with a detection device, which detects a condition, for example, the velocity of the incoming vehicle, temperature, humidity or mass of the incoming vehicle. In an example, the velocity detection device can be of the conventional kind, for example, a set of proximity switches or photo-sensors of the conventional type in a conventional arrangement that can determine velocity. 
     As shown in  FIGS. 9 and 10 , in the embodiment comprising a velocity detection device  52 , the velocity detection device  52  reads the velocity V of an incoming vehicle  60  and communicates that velocity to a data processor  54 . The data processor  54  comprises an encoded set of instructions  56  and processes the data to calculate the required displacement value DV of the movable module to achieve a desired braking force. The instructions  54  can be in the form of software or can be encoded on an embedded chip in the processor. The data processor  54  processes the data related to velocity instructs the means for incremental displacement  20  and in turn the push rod  22 , to move the desired distance X. In this way, the system provides a system and method that provides a braking level responsive to changes in velocity due to changes in mass, temperature, humidity, and other variables. 
     While the foregoing has been set forth in considerable detail, it is to be understood that the drawings and detailed embodiments are presented for elucidation and not limitation. Design variations, especially in matters of shape, size and arrangements of parts may be made but are within the principles of the invention. Those skilled in the art will realize that such changes or modifications of the invention or combinations of elements, variations, equivalents or improvements therein are still within the scope of the invention as defined in the appended claims.