Abstract:
A railgun accelerator system powered by alternating current (AC) is disclosed. In one form, the system advantageously uses multiples of six railguns in parallel, allowing velocities of around 100 miles per hour to be imparted to a carriage of mass around 6000 pounds. Three phase AC power from a domestic grid or from a similar source may feed multiple power points along the length of the accelerator.

Description:
RELATED PATENT APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/174,467, filed Dec. 30, 1999, now abandoned and entitled “Multi-Railgun System Using Three Phase Alternating Current”. 
    
    
     TECHNICAL FIELD 
     The present invention is related to railguns and specifically to railguns powered by three phase alternating electrical current. 
     BACKGROUND OF THE INVENTION 
     Railgun macroparticle accelerators have presently impart high velocities (3 km/s and up) to launch packages or payloads with masses of a few grams to a few kilograms. There is now a large body of literature published giving details of what is required to do this. Some commercial and military applications desire launching masses of thousands of kilograms to velocities of approximately 100 m/s or so. One commercial application imparts velocities of approximately 100 miles per hour (45 m/s) to a carriage of mass 6000 pounds in the “Superman” ride at Magic Mountain, Valencia, Calif. Several military applications include launching of aircraft and “glide bombs” from naval ships and other sites such as ground based platforms. 
     FIG. 1 illustrates the general principal of a conventional railgun. During operation, electric current conducts through one rail  1  along the armature  2  and back to the power supply through the second rail  3 . Current flow is indicated by arrows drawn on the rails. The current in the rails produces magnetic fields shown as dashed ellipses  4  in FIG.  1 . The current in the armature  2  interacts with this magnetic field to give the electromagnetic (EM) railgun force on the armature  2 . The force F is generated outward regardless of current flow direction. 
     The railgun described herein is sometimes referred to as the “Bostic railgun”. The formula for calculating the railgun force, F, is: 
       F =½ L′I   2   
     where I is the current and L′ is the inductance gradient of the rail pair. The force is in Newtons when current is in amperes and L′ is in Henries per meter. Note that typically L′ is a very small number, around 0.5×10 −6  H/m, in some conventional applications. As such, large currents are needed to generate reasonable forces. 
     Two types of railgun applications include “high velocity” and “low velocity” railguns. The operating principle of both of them are substantially the same but their physical form and the means of delivering electric power to them can be quite different. High velocity railguns tend to be short with lengths of a few meters and short acceleration times of around one hundredth of a second. The accelerating current must be pretty much unidirectional because the “coasting time” at current reversal, if alternating current (AC) is used, is undesirable and leads to wasted gun length during launch. Low velocity railguns have much greater lengths and have acceleration times measured in seconds. Their allowable accelerations will be much lower because their launch packages include delicate components such as passengers. 
     The mechanical arrangement of a simple railgun is illustrated in FIGS. 2 and 3. The rails  5  are parallel and the launch package  6  and armature  7  are positioned between each rail. Rail support means and launch package guidance means are indicated at  8  as shown by the cutaway. Electrical connections are made at the breech end  9  of the rails. As is described in the case of the Bostic railgun, current goes up one rail, across the armature, and back down the other rail, as indicated by the larger arrows  10 . The railgun bore is shown as roughly square but it can be many different geometric shapes such as, rectangular, round, etc. 
     The directions of the EM forces are shown by the small arrows in FIG. 3 which is a plan view of the railgun. As well as driving the launch package or payload, the EM forces load the sliding contacts between the ends of the armature arms  11  and the rails  5 . Such loading is helpful in providing non-sparking contacts between the arm ends and the rails. Armatures are usually “sprung” between the rails to provide mechanical preloading as part of the required contact force. Electromagnetic forces also act to push the rails apart, an effect that must be resisted by the rails support structure. 
     SUMMARY OF THE INVENTION 
     In accordance with teachings of the present disclosure, a multi-railgun system using three phase alternating current is disclosed. In one form, a system operable to displace an object is provided. The system includes a housing having a pair of rails operable to conduct a current and an armature coupled between the rails and operable to conduct the current between the rails. The system includes a thrust arm coupled to the armature and extending through a slot in the housing. The thrust arm is operable to displace the object in response to the armature conducting the current and moving along the rails. 
     According to another aspect of the invention, a railgun accelerator system is disclosed. The system includes a plurality of railguns having a pair of rails operable to conduct a current and an armature positioned between the rails and operable to be displaced along the rails in response to the current. The system further includes distributed power sources positioned along the rails and operable to provide a single phase alternating current for each railgun. 
     According to a further aspect of the invention, a railgun acceleration system operable to displace an object is disclosed. The system includes a plurality of railguns having a pair of rails wherein each railgun is operable to conduct an associated single phase alternating current of a three phase alternating current. The system further includes a plurality of armatures positioned between the rails and operable to be displaced along the rails in response to the current and a thrust arm coupled to each armature and operable to displace the object. 
     One technical advantage of the present invention includes using three phase alternating current to produce a ripple free driving force for a railgun. As such, simplified embodiments for switching a railgun current “on” and “off” may be provided. 
     Another technical advantage of the present invention is to provide a railgun having plural stages. Each stage may provide a single phase of alternating current for each railgun to displace an object via thrust arms coupled to each railgun. Through using a single phase for each railgun, a substantially constant force may be realized for displacing the object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
     FIG. 1 is a general illustration of the railgun principal; 
     FIG. 2 illustrates a perspective view of a conventional railgun assembly; 
     FIG. 3 illustrates a top view of the railgun illustrated in FIG. 2; 
     FIG. 4 is a graphic illustration generally describing a current and force relationship in an AC powered railgun; 
     FIG. 5 illustrates one embodiment of a single phase AC powered railgun according to teachings of the present invention; 
     FIG. 6A illustrates a rear perspective view of one embodiment of a single phase AC powered railgun according to teachings of the present invention; 
     FIG. 6B illustrates a side perspective view of one embodiment of a single phase AC powered railgun according to teachings of the present invention; 
     FIG. 7 illustrates one embodiment of parallel array of railguns using multiple phased AC power according to teachings of the present invention; 
     FIG. 8 illustrates one embodiment of a circular array of railguns using multiple phased AC power according to teachings of the present invention; 
     FIG. 9 illustrates one embodiment of a multi-tier railgun according to teachings of the present invention; 
     FIG. 10 illustrates one embodiment of a multi-contact armature brush array according to teachings of the present invention; and 
     FIG. 11 illustrates one embodiment of a railgun using a multi-contact armature brush array according to teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the invention and its advantages are best understood by reference to FIGS. 4-11. The present invention provides multiple phase AC powered railguns operable to displace an object. In one form, the multiple phase AC powered railguns include a series of stages operable to provide a single phase to an armature. As such, a substantially constant force may be produced through reducing undesirable ripple effects produced by single phase AC powered railguns. For example, FIG. 4 illustrates one short coming of using single phase AC to drive a railgun. The force F is proportional to current squared and remains positive and sinusoidal with double the frequency of the current sine wave. As the force F rises from zero to maximum and back twice every current cycle, a large “ripple” in the force results. 
     The present invention advantageously provides multi-phased AC power to reduce the “ripple” effect caused by single phase AC power. For example, three force curves F (not expressly shown) may be provided with their phase angles 120 degrees apart through using three phase AC power. As such, three force curves F may provide a substantially constant value equal to three times the mean value of one of the F curves thereby substantially reducing ripple in the resultant total force. 
     FIG. 5 illustrates one embodiment of a single phase AC powered railgun. A railgun, illustrated generally at  50 , includes a pair of rails  12  having a first stage  13 , a second stage  14  and a third stage  15 . AC power may be provided using power lines  16  coupled to each stage of railgun  50 . First stage  13  is coupled to power lines  16  using first stage transformer  30  and first stage switch  33 , second stage  14  is coupled to power lines  16  using second stage transformer  31  and second stage switch  34 , and third stage  15  is coupled to power lines  116  using third stage transformer  32  and third stage switch  35 . Railgun  50  may also include additional stages as needed. In one embodiment, power lines  16  may be a pair of high tension AC power lines and may be electrically connected to railgun  50  using matching voltage step-down (current step-up) transformers for transformers  30 ,  31 , and  32 . 
     During operation, acceleration begins with the armature and thrust block (not expressly shown) at rest at the beginning of first stage  13 . When first stage switch  33  is closed, acceleration of the armature begins. As the armature moves into secondary stage  14 , second stage switch  34  closes and shortly thereafter first stage switch  33  opens to prevent current from second stage transformer  31  from shunting back down railgun  50 . Switching transformers continues in like manner as the armature enters subsequent stages and accelerates along rails  12 . As such, through using single phase AC power, opening and closing of switches  33 ,  34 , and  35  within plus or minus a few cycles maintains optimal performance of railgun  50  thereby reducing critical timing which may be required for accelerating an object. For example, power to an active stage remains switched “on” until the armature enters the next stage, at which time power in the next stage is switched “on” and power to the previous stage is switched “off”. 
     In one embodiment, as the velocity of the armature and thrust arm increases (not expressly shown), higher voltage may be required to maintain an operating current reasonably constant. As such, each transformer secondary for transformers  30 ,  31 , and  32  may have higher output voltages at higher stage numbers. 
     In one embodiment, standard commercial AC circuit breakers may be used to switch the AC power for each stage. Matching between the stages may be achieved using transformers and power may be provided to each stage using much higher voltage than required by railgun  50 . As such, switches  33 ,  34 , and  35  may be positioned on the primary side of the transformers due to current being lower on the primary side. 
     FIG. 6A and 6B illustrate a rear and side perspective view of a single phase AC powered railgun according to one embodiment of the present invention. A low velocity railgun is illustrated and includes a pair of rails  36  coupled to a housing  37 . An armature  18  is positioned between rails  36  and is operable to displace an object (not expressly shown) using thrust arm  17 . Housing  37  includes a continuous slot in the top portion of housing  37  to allow thrust arm  17  to provide a force F to a payload or object external to the railgun. 
     In one embodiment, housing  37  may be cantilevered from the base to offset the EM repulsion force between rails  36 . Housing  37  may be arranged such that rails  36  are positively located by the recesses within housing  37  and through use of an upper lip along the top portion of rails  36 . Additionally, the base of housing  37  and the lower surfaces of the upper lips of housing  37  provide guidance surfaces for armature  18 . 
     During use, a single phase of multiple phase AC power may be provided to rails  36  at distributed points along rails  36  (not expressly shown). Armature  18  moves along rails  36  and provides a force to thrust arm  17  to displace an object or payload. In one embodiment, three-phase AC-power may be selectively coupled to rails  36  to provide a current having a phase which is approximately 120° apart from an associated railgun (not expressly shown). As such, a substantially constant force F may be provided by armature  18  to displace an object via thrust arm  17 . 
     FIG. 7 illustrates one embodiment of a parallel array of railguns operable to displace an object or payload. Several railguns, illustrated collectively at  51 , include thrust arms  17  operably coupled to displace an object or payload (not expressly shown). Magnetic field  19  may be provided by each railgun to create a force to displace an object or payload. Railguns  51  are preferably placed far enough apart so that there is enough space between them for their magnetic fields  19  to return. 
     FIG. 7 illustrates six railguns with power supply phases arranged as indicated by the numbers,  1 ,  2 ,  3 ,  3 ,  2 ,  1 . A first phase is associated with the outer pair of railguns, a second phase is associated with adjacent inner pair railguns, and a third phase is associated with the inner pair of railguns. Other embodiments for configuring railguns  51  using associated single phase alternating current may be realized. For example, each phase for each railgun may be connected in the order  1 ,  3 ,  2 ,  2 ,  3 ,  1 . As such, the forces generated by railguns  51  may be made symmetrical about a center line to reduce yawing torque associated with displacing an object using plural railguns. 
     During use, a selective phase may be used with each associated railgun as an armature for each railgun moves along each rail. For example, each pair may accelerate an object beginning with the phase as indicated in FIG. 7 and, along various point of each railgun, several sources may be provided at predetermined locations along an associated rail pair to provide a single phase current. As such, a parallel array of railguns using multiple phase AC power having distributed power sources may be used to displace an object. 
     FIG. 8 illustrates one embodiment of a circular array of railguns operable to displace an object or payload. The circular array may be used for gun-type applications and includes several railguns  20  circularly arranged with thrust arms  22  connected to a master block  21  at their center. Railguns  20  positioned across from each other use a current having the same phase. As such, a symmetrical yaw free force on master block  21  to displace an object. During use, railguns  20  having an associated AC phased power accelerate an object coupled to master block  21  and thrust arms  22 . In one embodiment, several power sources having the same phase may be provided for each railgun  20  along distributed points of each railgun  20 . 
     FIG. 9 illustrates one embodiment of a multi-tiered railgun for displacing an object or payload. A rear perspective view of a multi-tier railgun, illustrated generally at  53 , includes plural railguns  22  coupled to a thrust arm  41  for displacing an object or payload (not expressly shown). Each railgun  22  may include a separate phase for accelerating thrust arm  41 . Additionally, the magnitude of the current used to provide a force may contribute to a cross sectional dimension for each railgun  22 . For example, a minimum rail height may be required to carry a particular magnitude of current. Higher current in general may require larger bore railguns. Additionally, if the current per unit rail height becomes too large for a square bore geometry, then rail height associated with railguns  22  may be increased. As such, through providing a multi-tier railgun the current needed to displace an object may be reduced by dividing the current among each railgun  22  in the tiered arrangement illustrated in FIG.  9 . 
     During use, each railgun  22  may be electrically coupled in series to provide current on sub-rail basis. For example, the current for each railgun  22  may be reduced by a factor of one third of a given total current needed to produce a desired force. As such, some low velocity railguns require high voltages for displacing an object may benefit from using multi-tier railgun  53 . 
     FIG. 10 illustrates one embodiment of a multi-contact armature brush array operable to contact a rail of a railgun. A multi-brush armature, illustrated generally at  54 , includes several armature arms  24  including plural brush faces  23  for contacting a rail of a railgun (not expressly shown). Through using plural brushes  23  and armature arms  24 , increased levels of current may be conducted thereby providing an increased force for a given current per brush to displace an object (not expressly shown). For example, if the total current needed is 100,000 amperes, then the current should be shared between 20 brushes as illustrated by multi-brush armature  54 . In one embodiment, high electrical conductivity brushes which may include high conductivity materials such as copper, silver, etc., may be used to contact a railgun rail. As such, high current levels may be realized without causing sparking or arching at the interface between brush  23  and a railgun rail. 
     FIG. 11 illustrates one embodiment of a railgun using a multi-contact armature brush array. A railgun, illustrated generally at  55 , includes a pair of rails  25  coupled to an armature having nested armature arms  24  with plural brush faces  23 . The armature assembly further includes a bellows  27  coupled to a pair of bellows feet  28  and resilient wedges  29 . 
     During use, brush faces  23  and nested armature arms  24  conduct current between rails  25  and produce a force to move an object or payload (not expressly shown) coupled to thrust arm  26 . Nested armature arms  24  are provided in a trailing manner such that forces act in the direction to hold brush faces  23  in contact with rails  25 . However, as an AC signal passes through zero, the EM force for railgun  55  also approaches zero. As such, bellows  27  may provide additional force to maintain brush faces  23  in contact with rails  25 . For example, bellows  27  may be cylindrically shaped and foot  28  may be attached to both end faces of bellows  27  to spread the force produced by pressure in bellows  27  to a shape and size which matches the shape and size of the brush array. In one embodiment bellows  27  may have rectangular cross section having the same shape as the brush array thereby reducing the need for foot  28 . 
     In another embodiment, wedges  29  are made of a resilient material operable to transmit the force generated by the pressure in bellows  27  to the backs of the nested armature arms  24 . A gas pressure with bellows  27  may be externally controlled (not expressly shown) so that when set to zero, the armature can be easily slid from between the rails when necessary. Contact force can be changed by changing the pressure and pressure can be increased (decreased) when brush current is increased (decreased). 
     In one embodiment, an expansion stop may be provided to prevent over-expansion of bellows  27  should the armature assembly exit rails  25  with pressure still in bellows  27 . Bellows  27 , feet  28 , and wedges  29  may be coupled such that each component may move with the whole armature assembly. For example, a double-hinged coupling element (not expressly shown) may be coupled between armature arms  24  and bellows  27 . 
     Although the present invention has been described with respect to a specific preferred embodiment thereof, various changes and modifications may be suggested to one skilled in the art and it is intended that the present invention encompass such changes and modifications fall within the scope of the appended claims.