Abstract:
An electromagnetic actuator includes a plunger, an armature, and a coil. The plunger is moveable between a first position and a second position. The armature includes a first armature portion proximally disposed about the first position, and a second armature portion proximally disposed about the second position. The coil is proximally disposed with the first armature portion and, when energized, is configured to generate a magnetic field. The magnetic field causes the plunger to move toward the first position by a magnetic flux through a magnetic circuit. The magnetic circuit includes the first armature portion, the plunger, a main air gap, and a variable air gap. The main air gap and variable air gap are between the first armature portion and the plunger. The main air gap diminishes as the plunger moves toward the first position. The variable air gap enlarges as the plunger moves toward the first position.

Description:
BACKGROUND 
     The field of the disclosure relates generally to electromagnetic actuators and, more particularly, to an electromagnetic actuator with multiple air gaps and pole shaping and a method of use. 
     Most known electromagnetic actuators convert electric power into magnetic force to move a push pin. The push pin is coupled to a plunger that moves freely within a cavity in the actuator, generally within a guiding structure. Current passes through a coil in the electromagnetic actuator and generates an electromagnetic field and, more specifically, an electromagnetic flux. 
     For many of these known electromagnetic actuators, certain surfaces of the plunger operate as poles that are attracted to the electromagnetic flux, pulling the plunger toward the coil. A flux circuit is formed around the coil by the plunger, the poles, and a yoke. An air gap between the poles and the yoke dictates the magnetic force with which the plunger is pulled toward the coil. The air gap is a region of high magnetic reluctance, which can be air, a vacuum, or another non-magnetic material. The push pin transfers the magnetic force to an external object. When the plunger reaches a stable position, the plunger is latched in place by one or more permanent magnets. 
     Such known electromagnetic actuators often replace mechanical spring mechanisms in various applications. A force-stroke relationship, which is frequently represented as a force-stroke curve, for a spring does not always meet the requirements of a given application, for example, and without limitation, a vacuum circuit breaker. Electromagnetic actuators have a force-stroke relationship that matches the mechanical characteristics of vacuum circuit breakers. Electromagnetic actuators are also available at a lower cost, require less maintenance, have a reduced footprint, and greater endurance. However, certain applications, e.g., certain vacuum circuit breakers, call for unique force-stroke relationships depending on the stroke direction. For vacuum circuit breakers, a closing force-stroke curve and an opening force-stroke curve are often different. Additionally, some vacuum circuit breakers also utilize a spring effect of the contacts themselves to achieve a desired force-stroke curve. 
     BRIEF DESCRIPTION 
     In one aspect, an electromagnetic actuator is provided. The electromagnetic actuator includes a plunger, a first yoke portion, a second yoke portion, and a coil. The plunger is moveable between a first position and a second position. The first yoke portion is proximally disposed about the first position, and the second yoke portion is proximally disposed about the second position. The coil is proximally disposed with the first yoke portion and, when energized, is configured to generate a magnetic field. The magnetic field causes the plunger to move toward the first position by a magnetic flux through a magnetic circuit. The magnetic circuit includes the first yoke portion, the plunger, a first air gap, and a variable air gap. The first air gap and variable air gap are at least partially defined by the first yoke portion and the plunger. The first air gap diminishes as the plunger moves toward the first position. The variable air gap enlarges as the plunger moves toward the first position. 
     In another aspect, a method of operating an electromagnetic actuator is provided. The method includes latching a plunger in a position. The method also includes energizing a first coil to generate a first magnetic flux. The magnetic flux flows through the plunger, a first yoke portion, a first air gap, and a variable air gap. The method also includes generating an electromotive force corresponding to the first magnetic flux. The electromotive force is applied to the plunger, causing the plunger to travel toward the first yoke portion. The method also includes reducing a length of the first air gap and enlarging a cross-section of the variable air gap to regulate the electromotive force upon the plunger. 
     In yet another aspect, a vacuum circuit breaker is provided. The vacuum circuit breaker includes a first contact, a second contact, and an electromagnetic actuator. The second contact is configured to translate between an open position and a closed position in which the second contact is further configured to engage the first contact. The electromagnetic actuator includes a plunger, a first yoke, a second yoke, and an opening coil. The plunger includes at least one permanent magnet and is coupled to the second contact. The plunger is moveable between the open position and the closed position. The first yoke is proximally disposed about the closed position. The second yoke is proximally disposed about the open position. The opening coil is proximally disposed with the second yoke. When energized, the opening coil is configured to generate an opening magnetic field that causes the plunger to move toward the open position. The opening coil is further configured to generate an opening magnetic flux through an opening magnetic circuit. The opening magnetic circuit includes the second yoke, the plunger, a first air gap, and a variable air gap. The first air gap and variable air gap are defined at least partially by the second yoke and the plunger. The first air gap is configured to diminish as the plunger moves toward the open position. The variable air gap is configured to enlarge as the plunger moves toward the open position. The plunger moves toward the open position with an opening force corresponding to the first air gap and the variable air gap. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a cross-sectional diagram of an exemplary vacuum circuit breaker; 
         FIG. 2  is a cross-sectional diagram of an exemplary electromagnetic actuator that may be used with the vacuum circuit breaker shown in  FIG. 1 , illustrated in a stable position; 
         FIG. 3  is a cross-sectional diagram of an exemplary electromagnetic actuator that may be used with the vacuum circuit breaker shown in  FIG. 1 , illustrated in another stable position; and 
         FIG. 4  is a flow diagram of an exemplary method of operating an electromagnetic actuator shown in  FIGS. 2 and 3 . 
     
    
    
     Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
     DETAILED DESCRIPTION 
     In the following specification and the claims, a number of terms are referenced that have the following meanings. 
     The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise 
     The electromagnetic actuators described herein provide unique pole shaping that facilitates unique force-stroke relationships depending on the stroke direction. More specifically, the embodiments of electromagnetic actuators described herein include multiple air gaps for storing magnetic energy. Pole shaping is a process by which surfaces of the electromagnetic actuator plunger and yoke that define an air gap are configured to form a particular air gap. One or more of the multiple air gaps may vary with stroke, facilitating custom force-stroke relationships. Some of the electromagnetic actuators described herein include permanent magnetics disposed in the mobile portion of the actuator, further facilitating variable air gaps. 
       FIG. 1  is a cross-sectional diagram of an exemplary vacuum circuit breaker  100 . Vacuum circuit breaker  100  includes an electromagnetic actuator  102 , a push pin  104 , a vacuum cylinder  106 , and terminals  108  and  110 . Vacuum cylinder  106  includes a first contact  112  and a second contact  114 . First contact  112  is electrically coupled to terminal  108  by a terminal interface  116 . Second contact  114  is electrically coupled to terminal  110  by a terminal interface  118 . Vacuum cylinder  106 , push pin  104 , and terminal interfaces  116  and  118  are contained within a vacuum circuit breaker body  120 . 
     Electromagnetic actuator  102  has a linear range of travel, i.e., a stroke  122 , that translates push pin  104  up and down. As push pin  104  translates up and down, terminals  108  and  110  are coupled and decoupled, respectively. When terminals  108  and  110  are coupled, vacuum circuit breaker  100  is closed. Conversely, when terminals  108  and  110  are decoupled, vacuum circuit breaker  100  is open. 
       FIG. 2  is a cross-sectional diagram of the exemplary electromagnetic actuator  102  (shown in  FIG. 1 ). Electromagnetic actuator  102  includes a plunger  202  coupled to push pin  104  (also shown in  FIG. 1 ) and disposed within a first yoke portion  206  and a second yoke portion  204 . Electromagnetic actuator  102  also includes a first coil  210  and a second coil  208 . First yoke portion  206  includes poles  212 . Plunger  202  includes permanent magnets  214  and  216 , and poles  218 . 
     Electromagnetic actuator  102  is illustrated in a stable position. More specifically, plunger  202  is latched by permanent magnets  214  and  216  in a first position near first yoke portion  206 . Plunger  202  is also latchable by permanent magnets  214  and  216  in a second position near second yoke portion  204 . 
     Second coil  208  is energized to move plunger  202  from the first position to the second position. As illustrated, energizing second coil  208  pulls plunger  202  up toward second yoke portion  204 . When energized, a second-coil current  220  flows through windings of second coil  208 . Second-coil current  220  generates an electromagnetic field (not shown) and, more specifically, creates a second magnetic circuit  222 . A direction of second-coil current  220  is configured such that a direction of the magnetic field is aligned with an orientation of permanent magnets  214  and  216 , thus avoiding demagnetizing permanent magnets  214  and  216 . Second-coil current  220  flows out of the page on the right side of second coil  208 , indicated by circles and solid dots. Second-coil current  220  flows into the page on the left side of second coil  208 , indicated by circles and Xs. The direction of second-coil current  220  results in a clockwise magnetic flux direction on the left side of second magnetic circuit  222  and a counter-clockwise magnetic flux direction on the right side of second magnetic circuit  222 . 
     Second magnetic circuit  222  includes second yoke portion  204 , plunger  202 , a second primary air gap  224 , and a second secondary air gap  226 . Second yoke portion  204  and plunger  202  at least partially define second primary air gap  224  and second secondary air gap  226 . The magnetic field resulting from energizing second coil  208  is strong and concentrated in second yoke portion  204  and plunger  202  due to their respective low reluctances. Second primary air gap  224  and second secondary air gap  226  have a high reluctance relative to second yoke portion  204  and plunger  202 . Consequently, second primary air gap  224  and second secondary air gap  226  store most of the magnetic energy of the generated magnetic field and impact the amount of magnetic flux through second magnetic circuit  222 . The amount of magnetic flux is directly related to an electromotive force  228  applied to plunger  202 . The amount of magnetic flux is inversely related to squares of respective lengths of second primary air gap  224  and second secondary air gap  226 . Therefore, as the respective lengths of second primary air gap  224  and second secondary air gap  226  decrease, electromotive force  228  applied to plunger  202  increases. As plunger  202  moves, under electromotive force  228 , toward second yoke portion  204 , the respective lengths of second primary air gap  224  and second secondary air gap  226  decrease, and electromotive force  228  increases. Likewise, electromotive force  228  decreases as the respective lengths of second primary air gap  224  and second secondary air gap  226  increase, which occurs when plunger  202  moves toward first yoke portion  206 . 
       FIG. 3  is a cross-sectional diagram of electromagnetic actuator  102  (shown in  FIG. 1 ) illustrated with plunger  202  in the second position near second yoke portion  204 . Permanent magnets  214  and  216  latch plunger  202  in the second position. First coil  210  is energized to move plunger  202  from the second position near second yoke portion  204  to the first position near first yoke portion  206 . When first coil  210  is energized, a first-coil current  302  flows through first coil  210  in a direction such that a corresponding magnetic field is aligned with the orientation of permanent magnets  214  and  216 . First-coil current  302  flows out of the page on the left side of first coil  210 , indicated by the circles and solid dots, and flows into the page on the right side of first coil  210 , indicated by the circles and Xs. First-coil current  302  generates an electromagnetic field and, more specifically, creates a first magnetic circuit  304 . The direction of first-coil current  302  results in a counter-clockwise magnetic flux on the left side of first magnetic circuit  304  and a clockwise magnetic flux on the right side of first magnetic circuit  304 . 
     First magnetic circuit  304  includes first yoke portion  206 , plunger  202 , a first primary air gap  306 , a first secondary air gap  308 , and a variable air gap  310 . First primary air gap  306  is formed at the center of plunger  202 , between plunger  202  and poles  212  of first yoke portion  206 . First secondary air gap  308  is formed at the periphery of plunger  202 , between poles  218  of plunger  202  and poles  212  of first yoke portion  206 . Variable air gap  310  is formed tangentially to plunger  202 , between plunger  202  and an interior surface of first yoke portion  206 . 
     The magnetic field resulting from energizing first coil  210  is strong and concentrated in first yoke portion  206  and plunger  202  due to their respective low reluctances. First primary air gap  306 , first secondary air gap  308 , and variable air gap  310  have high reluctances relative to first yoke portion  206  and plunger  202 . Consequently, first air gap  306 , second air gap  308 , and variable air gap  310  store most of the magnetic energy of the generated magnetic field and impact the amount of magnetic flux through first magnetic circuit  304 . The amount of magnetic flux is directly related to an electromotive force  312  applied to plunger  202 . 
     The amount of magnetic flux through first magnetic circuit  304  is inversely related to the size of first primary air gap  306 , first secondary air gap  308 , and variable air gap  310 . As plunger  202  moves, due to electromotive force  312 , toward first yoke portion  206 , respective lengths of first primary air gap  306  and first secondary air gap  308  decrease until poles  218  and plunger  202  meet poles  212 , which increases the magnetic flux. As first primary air gap  306  and first secondary air gap  308  reduce in size, variable air gap  310  increases in size, which stores magnetic energy and reduces the amount of magnetic flux through first magnetic circuit  304 . Plunger  202 , poles  218 , and poles  212  are configured to form variable air gap  310  as a variable air gap that facilitates a customizable force-stroke relationship for electromagnetic actuator  102 . Moreover, the customizable force-stroke relationship is different per direction of travel of plunger  202 . 
       FIG. 4  is a flow diagram of an exemplary method  400  of operating electromagnetic actuator  102  (shown in  FIG. 1 ). Method  400  begins at a start step  410 . At a latching step  420 , plunger  202  of electromagnetic actuator  102  (shown in  FIGS. 2 and 3 ) is latched in a stable position by permanent magnets  214  and  216  (also shown in  FIGS. 2 and 3 ). At an energizing step  430 , first coil  210  (shown in  FIGS. 2 and 3 ) is energized, generating a magnetic flux through first magnetic circuit  304  (shown in  FIG. 3 ). First magnetic circuit  304  passes through plunger  202 , first yoke portion  206 , first primary air gap  306 , first secondary air gap  308 , and variable air gap  310  (all shown in  FIG. 3 ). 
     At a translation step  440 , the magnetic flux through first magnetic circuit  304  generates electromotive force  312  (shown in  FIG. 3 ) upon plunger  202 . Plunger  202  then travels linearly toward first yoke portion  206 . In an air gap varying step  450 , as plunger  202  travels toward first yoke portion  206 , lengths of first primary air gap  306  and first secondary air gap  308  are reduced. As plunger  202  travels toward first yoke portion  206 , a cross-section of variable air gap  310  increases. The variance in air gap size facilitates regulation of electromotive force  312  upon plunger  202  by regulating the amount of flux through first magnetic circuit  304 . 
     In certain embodiments, plunger  202  is locked in another stable position near first yoke portion  206  by permanent magnets  214  and  216 . When second coil  208  is energized, a magnetic flux is generated through second magnetic circuit  222  (all shown in  FIG. 2 ). Second magnetic circuit  222  passes through second yoke portion  204 , plunger  202 , second primary air gap  224 , and second secondary air gap  226  (all shown in  FIG. 2 ). The magnetic flux generates electromotive force  228  (shown in  FIG. 2 ) upon plunger  202 . Electromotive force  228  pulls plunger  202  linearly toward second yoke portion  204 , closing second primary air gap  224  and second secondary air gap  226 . The method then ends at an end step  460 . 
     The above-discussed electromagnetic actuators provide unique pole shaping that facilitates unique force-stroke relationships depending on the stroke direction. More specifically, the embodiments of electromagnetic actuators described herein include multiple air gaps for storing magnetic energy. One or more of the multiple air gaps may vary with stroke, facilitating custom force-stroke relationships. Some of the electromagnetic actuators described herein include permanent magnetics disposed in the mobile portion of the actuator, further facilitating variable air gaps. 
     An exemplary technical effect of the methods, systems, and apparatus described herein includes at least: (a) an electromagnetic actuator having unique force-stroke relationships achieved through multiple air gaps, at least one of which is a variable air gap formed by pole shaping; (b) a reduced foot-print relative to mechanical spring mechanisms; and (c) a reduced cost over mechanical spring mechanisms. 
     Exemplary embodiments of methods, systems, and apparatus for electromagnetic actuators are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may also be used in combination with other non-conventional electromagnetic actuators, and are not limited to practice with only the systems and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other applications, equipment, and systems that may benefit from unique force-stroke relationships. 
     Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.