Patent Publication Number: US-9406470-B2

Title: Tri-stable flexure mechanism

Description:
Embodiments presented herein relate generally to electrical circuit interruption with circuit breakers, and more particularly, to circuit breaker mechanisms that are constructed as tri-stable planar flexure mechanisms with resilient components for use in Molded Case Circuit Breakers (MCCB). 
     BACKGROUND 
     MCCBs are employed to interrupt DC or AC, single-phase or multi-phase, electrical circuits for protection of the electrical infrastructure when an electrical fault condition occurs. The electrical fault conditions can include an instantaneous current in the circuit that exceeds a predefined instantaneous current limit (i.e., an electrical short exists) or a long-term current that exceeds a predefined long-term current limit (i.e., an overload condition exists). A single-break MCCB typically comprises one pair of electrical contacts for each phase, with each pair consisting of a stationary contact mounted to a stationary current loop and a movable contact mounted to a contact arm. A dual-break MCCB comprises two pairs of electrical contacts per phase. Per phase there are two stationary contacts and a contact arm with two movable contacts. A circuit breaker mechanism interrupts the flow of electrical current by separating the movable contacts from the stationary contacts, thereby transitioning from a closed to a tripped state. 
     In conventional approaches, the circuit breaker mechanism moves from the closed to the tripped state by releasing stored elastic strain energy from a helical tension spring and converting it to kinetic energy of the mechanism links. The release of elastic strain energy begins by disengaging a cradle from a latch assembly that helps hold the spring under tension in normal operation when the circuit breaker mechanism is closed. The latch assembly can be disengaged by an automatic trip unit that senses and responds to an electrical fault or manually by an operator pressing a “push-to-trip” button. 
     The energy to separate the movable contact and contact arm from the stationary contact may also come from an electromagnetic field that develops around the stationary current loop and the contact arm due to the short circuit currents that flow through these components. The interactions between the electromagnetic field and the short circuit current result in a repulsive force between the stationary current loop and the contact arm which causes them to move apart (i.e., “blow-open”). The magnitude of the repulsive force diminishes as the current and electromagnetic field intensity drop when the contacts start to separate. The circuit breaker mechanism has to be capable of preventing the contact arm from reclosing with the stationary contact. 
     Once tripped, the circuit breaker mechanism remains tripped and indicates this state to an operator. The circuit breaker mechanism is typically resettable after being tripped by moving a handle from the tripped position to the open (i.e., off) position. This increases the elastic strain energy of the spring and engages the cradle with the latch assembly. Once reset the electrical circuit can be closed by moving the handle from the open position to the closed (i.e., on) position. MCCBs may also be used to interrupt and close electrical circuits in absence of electrical faults by moving a handle between the closed and open positions. 
     The movement of the contact arm from the closed position to the tripped position should be fast to minimize the formation of arcs that may degrade the contacts and thereby increase the overall electrical resistance of the circuit breaker. Similarly, when a handle is used to transition the circuit breaker mechanism between the closed state and the open state, the contacts have to move quickly even if the handle motion is slow. This characteristic is called “quick make-break”. The circuit breaker mechanism has to be of suitable size to fit in a predefined circuit breaker casing or electrical panel. The circuit breaker mechanism should be insensitive to wear, contamination, long-term fatigue, vibrations, temperature and humidity to prevent unintended nuisance trips or a no-trip situation. 
     Due to these design criteria, conventional circuit breaker mechanisms have a variety of moving components. Correspondingly, they are difficult to assemble and have a high number of failure modes, sources for friction and other uncertainties affecting their performance characteristics. In addition, conventional circuit breaker mechanisms may be larger than desired and still not meet all of the design criteria with regard to the opening speed or repeatability of the displacement input or force input at which they can be tripped. 
     Therefore, there is a need for circuit breaker mechanisms that are less complex, have more repeatable performance characteristics, are easier to assemble, are smaller in size, have faster opening times and more repeatable displacement or force inputs at which they can be tripped. 
     BRIEF DESCRIPTION 
     In a first embodiment, an actuation system is disclosed. In accordance with the embodiment, the actuation system includes a latch assembly configured to releasably engage a cradle. The actuation system also includes a movable arm as well as a resilient component that includes a first end having a revolute joint on the cradle and a second end connected to the movable arm. The resilient component is elastically deformed and stores elastic strain energy in one of a first stable state or a second stable state when the latch assembly is engaged with the cradle. The resilient component is in a third stable state that is not substantially elastically deformed and stores substantially no elastic strain energy when the latch assembly is not engaged with the cradle. The actuation system also includes an input link engaged with the resilient component between the first end and the second end. Movement of the input link between a first position and a second position when the latch assembly is engaged with the cradle transitions the resilient component between the first stable state and the second stable state. 
     In another embodiment, a method for actuating a movable arm is disclosed. The method includes: maintaining a resilient component under a state of elastic strain energy in a first stable state; holding a movable arm in a first stable position while the resilient component is in the first stable state; in response to a displacement input or a force input, releasing the elastic strain energy from the resilient component so that the resilient component is in a third stable state corresponding to a relaxed state; in response to the released elastic strain energy, rotating the movable arm so that it is no longer in the first stable position; and in response to the released elastic strain energy, moving an input link to a tripped position. 
     In a further embodiment, a circuit breaker assembly is disclosed. In accordance with the embodiment, the mechanism includes a latch assembly configured to releasably engage a cradle. The mechanism also includes a movable arm configured to move between a closed circuit position and an open circuit position. The mechanism also includes a leaf flexure comprising a first end having a revolute joint on the cradle and a second end connected to the movable arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying figures in which like characters represent like parts throughout the figures, wherein: 
         FIG. 1  depicts a schematic view of a single-phase, single-break MCCB mechanism having a leaf flexure element and contact arm assembly in a closed state, in accordance with aspects of the present disclosure; 
         FIG. 2  depicts a schematic view of a single-phase, single-break MCCB mechanism having a leaf flexure element and a contact arm assembly in an open state, in accordance with aspects of the present disclosure; 
         FIG. 3  depicts a schematic view of a single-phase, single-break MCCB mechanism at the bifurcation point of the leaf flexure element when transitioning from closed to open, in accordance with aspects of the present disclosure; 
         FIG. 4  depicts a schematic view of a single-phase, single-break MCCB mechanism at the bifurcation point of the leaf flexure element when transitioning from open to closed, in accordance with aspects of the present disclosure; 
         FIG. 5  depicts a schematic view of a single-phase, single-break MCCB mechanism having a leaf flexure element and contact arm assembly in a tripped state, in accordance with aspects of the present disclosure; 
         FIG. 6  depicts a schematic view of a single-phase, single-break MCCB mechanism in the closed state and having a leaf flexure element connected to a contact arm assembly by an offset revolute joint, in accordance with aspects of the present disclosure; 
         FIG. 7  depicts a schematic view of a single-phase, single-break MCCB mechanism in the closed state having a volute spring connected to a contact arm assembly by an offset revolute joint, in accordance with aspects of the present disclosure; 
         FIG. 8  depicts a schematic view of a single-phase, dual-break MCCB mechanism in the closed state and having a curled flexure element, in accordance with aspects of the present disclosure; 
         FIG. 9  depicts a schematic view of a single-phase, single-break MCCB mechanism having a compression helical spring that is collapsed to form a closed state, in accordance with aspects of the present disclosure; 
         FIG. 10  depicts a schematic view of a single-phase, single-break MCCB mechanism having a compression helical spring that is collapsed to form an open state, in accordance with aspects of the present disclosure; 
         FIG. 11  depicts a schematic view of a single-phase, single-break MCCB mechanism having a compression helical spring that is expanded to form a tripped state, in accordance with aspects of the present disclosure; and 
         FIG. 12  depicts a perspective view of a single-break, three-phase circuit breaker in a closed state, in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments presented herein relate generally to electrical circuit interruption, and more particularly, to the use of tri-stable planar flexure mechanisms that use resilient components. The mechanisms presented herein are, in one embodiment, for use in MCCBs. In certain such embodiments, the mechanisms presented herein are designed to move an electrical contact arm assembly in a single phase breaker or multiple contact arm assemblies in a multi-phase breaker in order to achieve the electrical circuit interruption. The MCCB may be configured as single-break with one stationary contact and one movable contact per phase or as dual-break with two stationary contacts and two movable contacts per phase. 
     As discussed herein, separation of the electrical contacts may be accomplished by releasing elastic strain energy stored in a resilient component and converting it to kinetic energy of the mechanism links. The resilient component may be provided as a leaf flexure element or other suitable component having a first end having a revolute joint on a cradle and a second end connected to the contact arm assembly. The release of elastic strain energy may be initiated by disengaging a cradle from a latch assembly that helps to constrain the resilient component in normal operation when there is no electrical fault. The latch assembly can be disengaged by a displacement or force input from a trip unit that senses and responds to an electrical fault or by an operator pressing a “push-to-trip” button. In certain embodiments discussed herein, the trip unit may use a bi-metallic strip that heats and deforms in an over-current situation and a magnetic flapper that deflects in the presence of electromagnetic fields that are generated in the presence of short circuit currents. 
     The energy to separate the movable contacts from the stationary contacts may also come from electromagnetic fields that develop around the stationary current loop and the contact arm due to the short circuit currents that flow through these components. The result is a repulsive force between the stationary current loop and the contact arm which causes them to move apart (i.e., “blow-open”). The magnitude of the repulsive force will diminish rapidly as the current levels drop when the electrical contacts start to separate. As discussed herein, the mechanisms disclosed are capable of preventing the movable contact arm from reclosing with the stationary contact after the repulsive force diminishes by being tripped by a trip unit and by releasing elastic strain energy to rotate the contact arm assembly so that it can no longer contact the stationary contact. 
     With the preceding in mind, the planar flexure mechanisms, as discussed herein, may be suitable for use in either residential, commercial, or industrial use MCCBs with operating voltages up to 1 kV DC or 1 kV AC at 50 Hz or 60 Hz and operating currents between 5 A and 2 kA. The rated short-circuit interrupt current can be more than tenfold higher than the rated operating current. The MCCB mechanisms, as discussed herein, may be suitable for opening times of the contact arm assembly between 1 ms and 100 ms and contact forces of 0.1 N to 100 N between the stationary and movable contacts. As discussed herein, various embodiments of the mechanism are described where resilient components are utilized that can function as both, devices that can store and release elastic strain energy and as structural components (i.e., links) in the kinematic chain (i.e., linkage) of the mechanism. As discussed herein, such resilient components can be leaf flexure elements, collapsible compression helical springs, volute springs, or curled flexure elements which are employed to maintain a contact arm assembly and a handle yoke in either a first stable closed position or a second stable open position while they have high elastic strain energy. In a third state, where the cradle is disengaged from the latch assembly and the resilient components are in a relaxed state with lower elastic strain energy, the circuit breaker mechanism may be in a tripped state distinct from the closed and open states. The resilient components as discussed herein may allow a reduction in the number of components in the circuit breaker assembly and, therefore, reduce the complexity of the circuit breaker, improve reliability and scalability of the design, and provide a lower mass and mass moment of inertia than a mechanism with conventional components, enabling higher speeds of operation. 
     As used herein, resilient components are integrated into the mechanism such that these components have a mode of higher elastic strain energy and such that the mechanism has a first stable state and a second stable state while the cradle stays engaged with a latch assembly. In the embodiments presented herein, when the mechanism is in the first stable state, reaction forces and reaction moments of the resilient components create a moment about a revolute joint of the contact arm assembly so that the movable contacts contact the stationary contacts and so that the handle yoke is held in the closed position. When the mechanism is in its second stable state, reaction forces and reaction moments of the resilient components create a moment about a revolute joint of the contact arm assembly to disconnect the movable contacts from the stationary contacts and to hold the handle yoke in the open position. A transition between the first stable state and second stable state of the mechanism can be made by means of the handle yoke that is mechanically coupled to the resilient component. The opening and closing of the stationary contacts and the movable contacts happen rapidly and are nearly independent of the handle yoke speed once the resilient component transitions through an unstable bifurcation point. This behavior is referred to as “mechanism snap-through” and provides a “quick make-break” characteristic. Furthermore, at a third stable state, where the resilient components have a mode of lower elastic strain energy, the cradle is disengaged from the latch assembly, and the mechanism is in a tripped state. The mechanism can transition from the first stable state to the third stable state by means of releasing the cradle from the latch assembly and from the third stable state to the second stable state by moving the handle yoke from tripped to closed. 
     By way of example, and as discussed in greater detail below, in a first embodiment, the resilient component is a leaf flexure element that is mounted between two ends, one of which is rigidly fixed to a crank which is part of a contact arm assembly and that forms a revolute joint with the mechanism frame. The rigid connection between the leaf flexure element and the crank is located at the revolute joint of the crank. The other end of the leaf flexure element has a revolute joint on a cradle. A handle yoke having a revolute joint on the mechanism frame connects to the leaf flexure element through a slot and a protrusion on the flexure forming a revolute joint and a prismatic pair between the handle yoke and the leaf flexure element. In this example, in normal operation, the cradle is held stationary by a latch assembly with which it engages. When the handle yoke is moved from the closed position to the open position the leaf flexure element eventually reaches a bifurcation point and transitions from the first stable position to the second stable position. The “mechanism snap-through” happens quickly and nearly independent of the speed of the handle yoke. Similarly, there is “mechanism snap-through” behavior when the handle yoke is moved from the open position to the closed position. Further, when disengaged from the latch assembly, the cradle rotates about a revolute joint on the mechanism frame as a result of the reaction forces exerted upon it by the leaf flexure element. The rotation of the cradle causes the revolute joint between the cradle and leaf flexure element to relocate with respect to the mechanism frame, and the leaf flexure element reaches its unstressed shape with low elastic strain energy content. As a result of the leaf flexure element transitioning from a mode of high elastic strain energy to a mode of low elastic strain energy, the crank and contact arm assembly as well as the handle yoke accelerate from the closed position to the tripped position. 
     With the preceding in mind, and turning to  FIG. 1 , a schematic view of certain components of the embodiment of an MCCB mechanism  100 , are depicted that are in accordance with the present disclosure. In this embodiment and as depicted, the mechanism  100  is in the closed state as can be seen by the contact between the movable contact  108  and the stationary contact  106 . Furthermore, an electrically conductive current path may exist between the stationary current loop  104 , the stationary contact  106 , the movable contact  108 , the contact arm  110 , the flexible conductor  191 , and the stationary terminal  190 . The contact arm assembly  154  comprises a crank  118  that has a crank revolute joint  117  on the mechanism frame  102 , a contact arm  110  that has a contact arm revolute joint  155  on the crank  118 , and a torsion spring  156  connected to both the crank  118  and the contact arm  110 . The leaf flexure element  150  exerts a moment on the crank  118  which is transmitted through the torsion spring  156  to the contact arm  110  resulting in a contact force normal to the contact interface between the movable contact  108  and the stationary contact  106 . 
     In the depicted example, the leaf flexure element  150  is in a first stable closed position, held in a stressed and deformed state of high elastic strain energy by the cradle  116  which is secured to the latch assembly  186 . One end of the leaf flexure element  150  has a flexure revolute joint  152  on the cradle  116  (i.e., there still can be relative rotational motion between the cradle and the leaf flexure element). The other end of the leaf flexure element  150  forms a rigid flexure connection  151  with the crank  118  (i.e., there is no relative motion possible between the crank and the leaf flexure element). The crank revolute joint  117  is in close proximity to the rigid flexure connection  151 . In one embodiment the leaf flexure element  150  consists of a 65 mm×15 mm×1 mm unidirectional fiber glass composite that has a rigid flexure connection  151  to the crank  118 . The rigid flexure connection  151  is located less than 10 mm away from the crank revolute joint  117 . 
     In the depicted embodiment, mechanism  100  includes a link in the form of a handle yoke  114  that is connected to a handle switch  112  and that has a handle yoke revolute joint  113  on the mechanism frame  102 . The handle yoke  114  has a handle yoke slot  122  that is engaged with a flexure protrusion  153 , thus forming a prismatic pair and a revolute joint, respectively, between the handle yoke  114  and the leaf flexure element  150  (i.e., a pivot is formed that can move linearly with respect to the handle yoke). In this manner, a change in state of the leaf flexure element  150 , either by operation of the latch assembly  186 , the contact arm assembly  154 , the cradle  116 , or the handle yoke  114 , may be communicated to the other interconnected parts to change the positions of those interconnected parts. 
     In the depicted example, a latch assembly  186  is also shown which, when engaged holds the mechanism in either the closed or open states. The depicted latch assembly includes a primary latch  182  that may be engaged with cradle  116  at primary latch interface  172  and with a secondary latch  178  that may be engaged with primary latch  182  at secondary latch interface  174 . In the depicted example, a latch bias spring  180  is provided between the primary latch  182  and the secondary latch  178  such that, when disengaged from one another, the latch bias spring  180  can bias the primary latch  182  and the secondary latch  178  towards one another such that the cradle  116  can be reengaged by moving the handle yoke  114  after the mechanism has been tripped. As will be appreciated, the depicted latch assembly  186  is a dual latch assembly (i.e., there are two engagements, the first between the primary latch  182  and the secondary latch  178  and the second between the primary latch  182  and the cradle  116 ). In other embodiments, the latch assembly may differ, such as being a single latch assembly between a primary latch and cradle, or a triple or greater latch assembly, having more than two latches. 
     Contact arm assembly  154  comprises a contact arm  110  that has a contact arm revolute joint  155  located on crank  118 . A contact arm torsion spring  156  creates a moment between crank  118  and movable contact arm  110 . In the depicted closed state of the MCCB mechanism  100 , the crank  118  is oriented such that the contact arm  110  is rotated away from contact arm hard stop  162  which results in a contact force between the movable contact  108  and the stationary contact  106 . The deflection of the contact arm  110  with respect to the contact arm hard stop  162  is known as “contact arm depression”. In other embodiments discussed herein, the torsion spring  156 , the contact arm revolute joint  155 , and the contact arm hard stop  162  may be absent, and the resilient component may directly attach to the contact arm  110 . In this case the resilient component directly generates the moment required for a contact force between the movable contact  108  and the stationary contact  106 . Also in this case, the leaf flexure element  150  may directly provide the necessary compliance for a “blow-open” event to occur. 
     In  FIG. 2 , mechanism  100  is shown in the second stable state or “open” position. The contact arm assembly  154  consists of a contact arm  110 , the movable contact  108 , a contact arm revolute joint  155 , the crank  118 , a contact arm torsion spring  156 , and the contact arm hard stop  162 . The contact arm  110  is rotated counter clockwise about the contact arm revolute joint  117  with respect to the crank  118  because of the moment applied by the contact arm torsion spring  156  such that the contact arm  110  is in contact with the contact arm hard stop  162 . This orientation of the contact arm assembly is typical whenever the contact arm assembly is not in contact with the stationary contact  106 . 
     In general, it may be desirable to move the circuit breaker mechanism  100  between the closed position depicted in  FIG. 1  and an open position depicted in  FIG. 2  without tripping it. That is, it may be desirable to allow an operator to open the electrical circuit in a manner distinct from tripping the circuit breaker mechanism. For example, the MCCB mechanism  100  of  FIG. 2  is depicted in an open position, as shown by the contact arm assembly  154  being separated from the stationary contact  106 . The MCCB mechanism  100  may be opened in this manner by a user or operator moving the handle yoke  114  from the position shown in  FIG. 1  to the position of the handle yoke  114  shown in  FIG. 2 . It may also be desirable to allow an operator to close the electrical circuit by moving the handle yoke  114  from the position shown in  FIG. 2  to the position shown in  FIG. 1 . 
     Turning to  FIG. 3 , the MCCB mechanism  100  is shown in a mode between the first and second stable states when the handle yoke  114  and handle switch  112  are moved from closed to open. Because the latch assembly  186  is unchanged, unmoved and remains engaged, the end of the leaf flexure element  150  connected to the cradle  116  via the flexure revolute joint  152  remains secured and stationary with respect to the mechanism frame  102 . Movement of the handle yoke  114  causes a force to be applied by the handle yoke slot  122  onto the flexure protrusion  153 . As a result of the force the leaf flexure element  150  starts to be deflected away from its first stable closed position towards its bifurcation point between the first and second stable states. Moving the handle yoke  114  even further towards the position shown in  FIG. 2  the bifurcation point of the leaf flexure element  150  is reached and the transition towards the state of the mechanism shown in  FIG. 2 . This transition happens suddenly and rapidly and is nearly independent of the speed at which the handle yoke is moved by the operator resulting in a “quick break” of the electrical circuit and minimal electrical arcing. Motion at the prismatic and revolute pair can be in the form of sliding and rotation of the leaf flexure element  150  with respect to the handle yoke  114 . Turning to  FIG. 4 , MCCB mechanism  100  is shown in a mode between the first and second stable states when handle yoke  114  is moved from the open to the closed position. This scenario is the reverse operation as described above, and the transition towards the state of the mechanism shown in  FIG. 1  results in a “quick make” of the electrical circuit. 
     As shown in  FIG. 5 , in addition to the open state and the closed state, the MCCB mechanism  100  can also be in a third stable state (i.e., a tripped state) in which there is no contact between the movable contact  108  and the stationary contact  106  and where the leaf flexure element  150  has low elastic strain energy. This state can be reached from the closed position where the leaf flexure element  150  has high elastic strain energy and such that there is a reaction force acting on the cradle  116 , which causes a counterclockwise moment of the cradle  116  about the cradle revolute joint  158 . The trip event is started when a trip unit, or a “push-to-trip” button that is pushed by an operator, initiates a rotational displacement of the secondary latch  178  about the secondary latch revolute joint  176  in the clockwise direction. This causes the secondary latch interface  174  to lose contact with the secondary latch  178 , and the reaction force at the primary latch interface  172  between the cradle  116  and the primary latch  182  causes the primary latch to rotate clockwise. This causes the primary latch  116  to lose contact with the primary latch interface  172  leaving the cradle  116  free to rotate counterclockwise about the cradle revolute joint  158 . 
     To move the MCCB mechanism  100  in  FIG. 1  from a closed state where the leaf flexure element  150  has a state of high elastic strain energy to a tripped state of the mechanism  100  in  FIG. 5  where the leaf flexure element  150  has a state of low elastic strain energy requires that the strain energy is converted to kinetic energy of the various components of the mechanism that move during the transition and which include, for example, the handle yoke  114 , the contact arm assembly  154 , the latch assembly  186 , the leaf flexure element  150 , and the cradle  116 . Relaxation of the leaf flexure element  150  results in a moment that accelerates the crank  118  from rest, allowing the contact arm assembly  154  to rotate away from the stationary contact  106 , thus opening the electrical circuit. The MCCB mechanism  100  comes to a stop in the tripped configuration once the leaf flexure element  150  has transferred its elastic strain energy to kinetic energy of the moving components and once this kinetic energy has been absorbed again by friction or inelastic collision losses at the various hard stops, for example between the yoke cam  120  and the yoke follower  160 . It should be noted that the torsion spring  156  may also contribute elastic strain energy in the trip event. 
     In the tripped state of the MCCB mechanism  100 , and as shown in  FIG. 5 , the handle yoke  114  is in a tripped position between the closed position and the open position indicating to an operator that the MCCB mechanism  100  has tripped. In the tripped state, the leaf flexure element  150  is shown in an undeformed shape due to the flexure revolute joint  152  no longer being held stationary with respect to the mechanism frame  102  by the cradle  116 . In general, to bring the contact arm assembly  154  back into contact with the stationary contact  108  after a trip event, the MCCB mechanism  100  must be moved to the open configuration (i.e., reset) prior to being moved to the closed configuration. That is, because the latch assembly  186  is disengaged when the MCCB mechanism  100  is tripped, the act of moving the handle yoke  114  from the tripped position shown in  FIG. 5  to the open position shown in  FIG. 2  causes the yoke cam  120  to exert a force on the yoke follower  160  which causes the cradle  116  to rotate clockwise towards the primary latch  182 . At the same time, the handle yoke slot  122  exerts a force on the flexure protrusion  153  to deform the leaf flexure element  150  from the tripped state with low elastic strain energy towards the open state with higher elastic strain energy shown in  FIG. 2 . When the open state of the MCCB mechanism  100  is reached, the primary latch interface  172  contacts the cradle  116 , and the secondary latch interface  174  contacts the secondary latch  178 . 
     The mechanical motions of the components described above are determined by various kinematic pairs provided as part of the assembly. For example, certain kinematic pairs may be revolute joints (i.e., pivots), prismatic pairs (i.e., sliders), or cams-followers (i.e., surface-to-surface contacts). Referring to  FIG. 1 , the kinematic pairs may or may not be fixed in location with respect to the mechanism frame  102 . Fixed kinematic pairs include revolute joints that are based on extensions or hole features of the mechanism frame  102 , the circuit breaker casing wall or surface. For example, the cradle revolute joint  158  about which the cradle  116  rotates is fixed with respect to the mechanism frame  102 , the crank revolute joint  117  about which the crank  118  rotates is fixed with respect to the mechanism frame  102 , the secondary latch revolute joint  176  about which the secondary latch  178  rotates is fixed with respect to the mechanism frame  102 , and the handle yoke revolute joint  113  about which the handle yoke  114  rotates is fixed with respect to the mechanism frame  102 . The primary latch slot  181  and the primary latch pin  184  form a prismatic pair as well as a revolute joint that allow the primary latch  178  to translate as well as rotate with respect to the mechanism frame  102 . This is used in resetting the latch assembly  186  after it has tripped. 
     Conversely, various kinematic pairs are moving with respect to the mechanism frame  102  and are defined by the structure depicted in  FIG. 1 , including the flexure revolute joint  152  defined by the interaction between the leaf flexure element  150  and the cradle  116 . Another moving kinematic pair is the contact arm revolute joint  155 , defined by the interaction between the contact arm  110  and the crank  118  (as mediated by torsion spring  156 ). The handle yoke slot  122  and the flexure protrusion  153  form a prismatic pair as well as a revolute joint that allows the leaf flexure element  150  to rotate as well as translate with respect to the handle yoke  114 . In the depicted example, the various depicted kinematic pairs define the available motions and ranges for the depicted components in response to both internally and externally applied forces and displacements. As noted above, the MCCB mechanism  100  depicted in  FIG. 1  also contains higher order kinematic pairs that are formed between surfaces of depicted components that may contact one another. For example, the yoke cam  120  may engage with the yoke follower  160  when the cradle  116  and the handle yoke  114  are in the tripped position in order to reset the mechanism from the tripped to the open configuration. 
     By way of example, in the embodiment of MCCB mechanism  100  shown in  FIG. 6 , the resilient component of the mechanism consists of a leaf flexure element  150  that is mounted such that a first end has a flexure revolute joint  152  on the cradle  116  and such that a second end has a secondary flexure revolute joint  170  on the contact arm  110 . The secondary flexure revolute joint  170  is offset from the crank revolute joint  117  by between 2 mm and 100 mm. When the mechanism moves between the closed, open, and tripped states the curvature of the leaf flexure element  150  may or may not remain deflected to one side (i.e., the curvature of the leaf flexure element may or may not change from positive to negative and vice versa). 
     By way of further example, in the embodiment of mechanism  100  shown in  FIG. 7 , the resilient component of the mechanism consists of a volute spring that is mounted such that a first end has a revolute joint  152  on the cradle  116  and a second end has a secondary revolute joint  170  on the contact arm  110 . The secondary revolute joint  170  is offset from the crank revolute joint  117 . When the mechanism moves between the closed, open, and tripped states the volute spring contacts and expands primarily in its axial direction (i.e., the curvature of the volute springs remains small). 
     Further, in the embodiment shown in  FIG. 7 , handle yoke  114  has two separate structures parallel to one another with volute spring  138  positioned between these separated structures. The interface between the volute spring  138  and the handle yoke  114  is shown in the form of a pair of crossbars  136  connecting the separated components of the handle yoke  114  through which the volute spring  138  passes. 
     In an additional example, in the embodiment of the MCCB mechanism  100  shown in  FIG. 8 , the resilient component of the mechanism consists of a curled flexure  139  that is connected at one end to the cradle  116  via a flexure revolute joint  152  and on the other end to the crank rotor  130  via a rigid flexure connection  151 . The mechanism  100  is shown as a dual-break, single phase mechanism with the contact arm assembly consisting of a crank rotor  130 , two contact arm hard stops  162 , two contact arms  110 , two movable contacts  108 , two torsion springs  156 , and two contact arm revolute joints  155 . Current flows through the first stationary current loop  104 , the first stationary contact  106 , the contact arm assembly, the second stationary contact  106 , and the second stationary current loop  104 . 
     By way of example, in the embodiment of the MCCB mechanism  100  shown in  FIG. 9  in the first stable closed state, the resilient component of the mechanism consists of a collapsible compression spring  140  (shown in cross-section) being collapsed and compressed with a first end rigidly connected to a cradle follower  144  that is contacting the cradle  116  at a cradle cam  142 . This allows in-plane rotation of the collapsible compression spring  140  with respect to the cradle  116 . A second end of the spring  140  is rigidly connected to the contact arm  110 . 
     Further, in this embodiment, the handle yoke  114  has two separate structures parallel to one another with the collapsible compression spring  140  positioned between these separated structures. The interface between the collapsible compression spring  140  and handle yoke  114  is shown in the form of a pair of crossbars  136  connecting the separated components of the handle yoke  114  through which the collapsible compression spring  140  passes. 
     Turning to  FIG. 10 , the MCCB mechanism  100  is shown in the second stable open state where the collapsible compression spring  140  is compressed and collapsed, and the contact arm assembly consisting of the contact arm  110 , the movable contact  108 , and the crank revolute joint  117  does not contact the stationary contact  106 . 
     Turning to  FIG. 11 , the MCCB mechanism  100  is depicted in its third stable tripped state. In this state the collapsible compression spring  140  is not collapsed and is less compressed than in the first and second states, having a state of lower elastic strain energy. In this example, the latch assembly  186  has been disengaged, as shown by the separation or disengagement of the cradle  116  from the primary latch  182 . In response to disengagement of the latch assembly  186 , the cradle  116  may rotate with respect to the cradle revolute joint  158 . This rotation allows the collapsible compression spring  140  to release strain energy and move towards a relaxed state by expansion and by recovering from the collapsed state. 
     The preceding examples have depicted planar, and other, flexure mechanisms for MCCBs that may be used in single-phase, single-break embodiments for simplicity and to facilitate explanation. However, it should be appreciated that any of the aforementioned approaches may be applied in other configurations, such as in multi-phase (e.g. three-phase) or dual break arrangements and in AC or DC circuits. For example, and tuning to  FIG. 12 , depicted is a three-phase, single-break MCCB mechanism  100  that comprises a torsion bar  135  that connects three contact arm assemblies to the circuit breaker mechanism. Likewise, various arrangements of latching assemblies, external trip units, as well as contact arm assemblies other than those described may be used in conjunction with resilient components which mediate the transition from open, closed, and tripped states of the MCCB mechanism. 
     Technical effects of the invention include the construction and use of a MCCB mechanism incorporating resilient components that link a cradle to a contact arm assembly. In a first embodiment, the resilient component is a leaf flexure element that is rigidly connected to a contact arm assembly. In a second embodiment the leaf flexure element has a revolute joint on the contact arm assembly that is offset from the crank revolute joint. In a third embodiment, the resilient component is a volute spring. In a fourth embodiment, the resilient component is a curled flexure, and in a fifth embodiment the resilient component is a collapsible compression spring. A handle yoke may also interface with the resilient component to transition the mechanism from a first stable closed state to a second stable open state when the cradle is held stationary. The handle yoke is moved to a tripped position by the resilient component when the mechanism is tripped to transition to a third stable tripped state. The handle yoke can be used to reset the mechanism by reengaging the cradle with the latch assembly, adding elastic strain energy to the resilient component, and transition the mechanism to the open state. The components of the mechanism may provide a low mass and mass moment of inertia allowing high angular acceleration of the contact arm assembly. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention 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 languages of the claims.