Abstract:
An operating mechanism for a circuit breaker is provided. The operating mechanism includes a holder assembly being positioned to receive a portion of an operating handle of the circuit breaker. The holder assembly is capable of movement between a first position and a second position wherein the first position corresponds to a closed position of the circuit breaker and the second position corresponds to an open position of the circuit breaker. The operating mechanism further includes a drive plate being movably mounted to a support structure of the operating mechanism. The drive plate is coupled to the holder assembly. The operating mechanism also includes an energy storage mechanism for assuming a plurality of states, each state having a prescribed amount of energy stored in the energy storage mechanism. When the energy stored in the energy storage mechanism is released it provides an urging force to the drive plate causing the holder assembly to travel in the range defined by the first position to the second position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit of Provisional Application No. 60/190,298 filed on Mar. 17, 2000, and Provisional Application No. 60/190,765 filed on Mar. 20, 2000, the contents of which are incorporated herein by reference thereto. This application is a continuation-in-part of U.S. application Ser. No. 09/595,278 filed on Jun. 15, 2000, the contents of which are incorporated herein by reference thereto. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    This invention relates to a method and apparatus for storing energy in a circuit breaker.  
           [0003]    Electric circuit breakers are generally used to disengage an electrical system under certain operating conditions. Therefore, it is required to provide a mechanism whereby a quantum of stored energy, utilized in opening, closing and resetting the circuit breaker after trip, is capable of being conveniently adjusted with a minimum of effort and without additional or special tools, in the field or in the manufacturing process. Conventional systems use a portion of stored energy to close the circuit breaker or circuit interrupter mechanism. This energy is wasted in overcoming resistance presented by components used in charging systems.  
           [0004]    It is desired to provide a mechanism that minimizes the stored energy required for opening, closing, and resetting the breaker mechanism, as well as reducing the operational time to achieve quick closing of breaker (within 50 ms), using minimum signal power and with high reliability, thus optimizing the mechanism size, and cost.  
         SUMMARY OF INVENTION  
         [0005]    An operating mechanism for a circuit breaker is provided. The operating mechanism includes a holder assembly being configured, dimensioned and positioned to receive a portion of an operating handle of the circuit breaker where the holder assembly is capable of movement between a first position and a second position wherein the first position corresponds to a closed position of the handle and the second position corresponds to an open position of the handle.  
           [0006]    The operating mechanism further includes a drive plate being movably mounted to a support structure of the operating mechanism where the drive plate is being coupled to the holder assembly. The operating mechanism also includes an energy storage mechanism for assuming a plurality of states, each state having a prescribed amount of energy stored in the energy storage mechanism, the energy storage mechanism providing an urging force to the drive plate when the holder assembly is in the second position and the urging force causing the holder assembly to travel from the first position to the second position. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]    [0007]FIG. 1 is an exploded three-dimensional view of the energy storage mechanism of the present invention;  
         [0008]    [0008]FIG. 2 is a view of the auxiliary spring guide of the energy storage mechanism of FIG. 1;  
         [0009]    [0009]FIG. 3 is a view of the main spring guide of the energy storage mechanism of FIG. 1;  
         [0010]    [0010]FIG. 4 is a view of the assembled energy storage mechanism of FIG. 1;  
         [0011]    [0011]FIG. 5 is a view of the assembled energy storage mechanism of FIG. 1 showing the movement of the auxiliary spring guide relative to the main spring guide and the assembled energy storage mechanism engaged to a side plate pin;  
         [0012]    [0012]FIG. 6 is a more detailed view of a segment of the assembled energy storage mechanism of FIG. 5 showing the assembled energy storage mechanism engaged to a drive plate pin;  
         [0013]    [0013]FIG. 7 is a three dimensional view of the energy storage mechanism of FIG. 1 including a second spring, coaxial with the main spring of FIG. 1;  
         [0014]    [0014]FIG. 8 is a view of the locking member of the energy storage mechanism of FIG. 1;  
         [0015]    [0015]FIG. 9 is a side view of the circuit breaker motor operator of the present invention in the CLOSED position;  
         [0016]    [0016]FIG. 10 is a side view of the circuit breaker motor operator of FIG. 9 passing from the closed position of FIG. 9 to the OPEN position;  
         [0017]    [0017]FIG. 11 is a side view of the circuit breaker motor operator of FIG. 9 passing from the closed position of FIG. 9 to the OPEN position;  
         [0018]    [0018]FIG. 12 is a side view of the circuit breaker motor operator of FIG. 9 passing from the closed position of FIG. 9 to the OPEN position;  
         [0019]    [0019]FIG. 13 is a side view of the circuit breaker motor operator of FIG. 9 in the OPEN position;  
         [0020]    [0020]FIG. 14 is a first three dimensional view of the circuit breaker motor operator of FIG. 9;  
         [0021]    [0021]FIG. 15 is a second three dimensional view of the circuit breaker motor operator of FIG. 9;  
         [0022]    [0022]FIG. 16 is a third three dimensional view of the circuit breaker motor operator of FIG. 9;  
         [0023]    [0023]FIG. 17 is a view of the cam of the circuit breaker motor operator of FIG. 9;  
         [0024]    [0024]FIG. 18 is a view of the drive plate of the circuit breaker motor operator of FIG. 9;  
         [0025]    [0025]FIG. 19 is a view of the latch plate of the circuit breaker motor operator of FIG. 9;  
         [0026]    [0026]FIG. 20 is a view of the first latch link of the circuit breaker motor operator of FIG. 9;  
         [0027]    [0027]FIG. 21 is a view of the second latch link of the circuit breaker motor operator of FIG. 9;  
         [0028]    [0028]FIG. 22 is a view of the connection of the first and second latch links of the circuit breaker motor operator of FIG. 9;  
         [0029]    [0029]FIG. 23 is a three dimensional view of the circuit breaker motor operator of FIG. 9 including the motor drive assembly;  
         [0030]    [0030]FIG. 24 is a three dimensional view of the circuit breaker motor operator of FIG. 9, excluding a side plate;  
         [0031]    [0031]FIG. 25 is a view of the ratcheting mechanism of the motor drive assembly of the circuit breaker motor operator of FIG. 9; and  
         [0032]    [0032]FIG. 26 is a force and moment diagram of the circuit breaker motor operator of FIG. 9. 
     
    
     DETAILED DESCRIPTION  
       [0033]    Referring to FIG. 1, an energy storage mechanism is shown generally at  300 . Energy storage mechanism  300  comprises a main spring guide  304  (seen also in FIG. 3), a generally flat, bar-like fixture having a first closed slot  312  and a second closed slot  314  therein. Main spring guide  304  includes a semi-circular receptacle  320  at one end thereof and an open slot  316  at the opposing end. Main spring guide  304  includes a pair of flanges  318  extending outward a distance “h” (FIG. 3) from a pair of fork-like members  338  at the end of main spring guide  304  containing open slot  316 . Fork-like members  338  are generally in the plane of main spring guide  304 . Energy storage mechanism  300  further comprises an auxiliary spring guide  308 . Auxiliary spring guide  308  (seen also in FIG. 2) is a generally flat fixture having a first frame member  330  and a second frame member  332  generally parallel to one another and joined by way of a base member  336 . A beam member  326  extends generally perpendicular from first frame member  330  in the plane of auxiliary spring guide  308  nearly to second frame member  332  so as to create a clearance  340  (as seen in FIG. 2) between the end of beam member  326  and second frame member  332 . Clearance  340  (as seen in FIG. 2) allows beam member  326 , and thus auxiliary spring guide  308 , to engage main spring guide  304  at second closed slot  314 . Beam member  326 , first frame member  330 , second frame member  332  and base member  336  are placed into an aperture  334 .  
         [0034]    A tongue  328  extends from base member  336  into aperture  334 . Tongue  328  is operative to receive an auxiliary spring  306 , having a spring constant of k a . whereby auxiliary spring  306  is retained within aperture  334 . The combination of auxiliary spring  306 , retained within aperture  334 , and auxiliary spring guide  308  is coupled to main spring guide  304  in such a manner that beam member  326  is engaged with, and allowed to move along the length of second closed slot  314 . Auxiliary spring guide  308  is thereby allowed to move relative to main spring guide  304  by the application of a force to base member  336  of auxiliary spring guide  308 . Auxiliary spring  306  is thus retained simultaneously within open slot  316  by fork-like members  338  and in aperture  334  by first frame member  330  and second frame member  332 .  
         [0035]    Energy storage mechanism  300  further comprises a main spring  302  having a spring constant k m . Main spring guide  304 , along with auxiliary spring guide  308  and auxiliary spring  306  engaged thereto, is positioned within the interior part of main spring  302  such that one end of main spring  302  abuts flanges  318 . A locking pin  310  (FIG. 7) is passed through first closed slot  312  such that the opposing end of main spring  302  abuts locking pin  310  so as to capture and lock main spring  302  between locking pin  310  and flanges  318 . As seen in FIG. 4, the assembled arrangement of main spring  302 , main spring guide  304 , auxiliary spring  306 , auxiliary spring guide  308  and locking pin  310  form a cooperative mechanical unit. In the interest of clarity in the description of energy storage mechanism  300  in FIGS. 1 and 4, reference is made to FIGS. 2 and 3 showing auxiliary spring guide  308  and the main spring guide  304  respectively.  
         [0036]    Reference is now made to FIGS. 5 and 6. FIG. 5 depicts the assembled energy storage mechanism  300 . A side plate pin  418 , affixed to a side plate (not shown), is retained within receptacle  320  so as to allow energy storage mechanism  300  to rotate about a spring assembly axis  322 . In FIG. 6, a drive plate pin  406 , affixed to a drive plate (not shown), is retained against auxiliary spring guide  308  and between fork-like members  338  in the end of main spring guide  304  containing open slot  316 . Drive plate pin  406  is so retained in open slot  316  at an initial displacement “D” with respect to the ends of flanges  318 . Thus, as seen in FIGS. 5 and 6, the assembled energy storage mechanism  300  is captured between side plate pin  418 , drive plate pin  406 , receptacle  320  and open slot  316 .  
         [0037]    Energy storage mechanism  300  is held firmly therebetween due to the force of auxiliary spring  306  acting against auxiliary spring guide  308 , against drive plate pin  406 , against main spring guide  304  and against side plate pin  418 . As seen in FIG. 5, auxiliary spring guide  308  is operative to move independent of main spring  302  over a distance “L” relative to main spring guide  304  by the application of a force acting along a line  342  in FIG. 6. When auxiliary spring guide  308  has traversed the distance “L,” side plate pin  418  comes clear of receptacle  320  and energy storage mechanism  300  may be disengaged from side plate pin  418  and drive plate pin  406 .  
         [0038]    As best understood from FIGS. 5 and 6, the spring constant, k a,  for auxiliary spring  306  is sufficient to firmly retain the assembled energy storage mechanism  300  between side plate pin  418  and drive plate pin  406 , but also such that only a minimal amount of effort is required to compress auxiliary spring  306  and allow auxiliary spring guide  308  to move the distance “L.” This allows energy storage mechanism  300  to be easily removed by hand from between side plate pin  418  and drive plate pin  406 .  
         [0039]    Referring now to FIG. 7, a coaxial spring  324 , having a spring constant k c  and aligned coaxially with main spring  302 , is shown. Coaxial spring  324  may be engaged to main spring guide  304  between flanges  318  and locking pin  310  (not shown) in the same manner depicted in FIG. 4 for main spring  302 , thus providing energy storage mechanism  300  with a total spring constant of k T =k m +k c . Flanges  318  extend a distance “h” sufficient to accommodate main spring  302  and coaxial spring  324 . Thus, energy storage mechanism  300  of the present invention is a modular unit that can be easily removed and replaced in the field or in the factory with a new or additional main spring  302 . This allows for varying the amount of energy that can be stored in energy storage mechanism  300  without the need for special or additional tools.  
         [0040]    Referring now to FIGS.  9 - 14 , a circuit breaker (MCCB) is shown generally at  100 . Circuit breaker  100  includes a circuit breaker handle  102  extending therefrom is coupled to a set of circuit breaker contacts (not shown). The components of the circuit breaker motor operator of the present invention are shown in FIGS.  9 - 14  generally at  200 . Motor operator  200  generally comprises a holder, such as a carriage  202  coupled to circuit breaker handle  102 , energy storage mechanism  300 , as described above, and a mechanical linkage system  400 .  
         [0041]    Mechanical linkage system  400  is connected to energy storage mechanism  300 , carriage  202  and a motor drive assembly  500  (FIG. 24). Carriage  202 , energy storage mechanism  300  and mechanical linkage system  400  act as a cooperative mechanical unit responsive to the action of motor drive assembly  500  and circuit breaker handle  102  to assume a plurality of configurations. In particular, the action of motor operator  200  is operative to disengage or reengage the set of circuit breaker contacts coupled to circuit breaker handle  102 . Disengagement (i.e., opening) of the set of circuit breaker contacts interrupts the flow of electrical current through circuit breaker  100 . Reengagement (i.e., closing) of the circuit breaker contacts allows electrical current to flow through the circuit breaker  100 .  
         [0042]    Referring to FIG. 8, in conjunction with FIGS. 15, 16 and  17 , mechanical linkage system  400  comprises a pair of side plates  416  held substantially parallel to one another by a set of braces  602 ,  604  and connected to circuit breaker  100 . A pair of drive plates  402  (FIG. 18) are positioned interior, and substantially parallel to the pair of side plates  416 . Drive plates  402  are connected to one another by way of, and are rotatable about, a drive plate axis  408 . Drive plate axis  408  is connected to the pair of side plates  416 . The pair of drive plates  402  include a drive plate pin  406  connected therebetween and engaged to energy storage mechanism  300  at open slot  316  of main spring guide  304 . A connecting rod  414  connects the pair of drive plates  402  and is rotatably connected to carriage  202  at axis  210 .  
         [0043]    A cam  420 , rotatable on a cam shaft  422 , includes a first cam surface  424  and a second cam surface  426  (FIG. 17). Cam  420  is, in general, of a nautilus shape wherein second cam surface  426  is a concavely arced surface and first cam surface  424  is a convexly arced surface. Cam shaft  422  passes through a slot  404  in each of the pair of drive plates  402  and is supported by the pair of side plates  416 . Mechanical linkage system  400  minimizes the stored energy required for closing the breaker mechanism and reduces the closing time, thereby optimizing the mechanism size and cost. Cam shaft  422  is further connected to motor drive assembly  500  (FIGS. 24 and 25) from which cam  420  is driven in rotation.  
         [0044]    Carriage  202  is connected to drive plate  402  by way of the connecting rod  414  of axis  210  and is rotatable thereabout. Carriage  202  comprises a set of retaining springs  204 , a first retaining bar  206  and a second retaining bar  208 . Retaining springs  204 , disposed within carriage  202  and acting against first retaining bar  206 , retain circuit breaker handle  102  firmly between first retaining bar  206  and second retaining bar  208 . Carriage  202  is allowed to move laterally with respect to side plates  416  by way of first retaining bar  206  coupled to a slot  214  in each of side plates  416 . Carriage  202  moves back and forth along slots  214  to toggle circuit breaker handle  102  back and forth between the position of FIG. 9 and that of FIG. 13.  
         [0045]    In FIG. 9, circuit breaker  100  is in the closed position (i.e., electrical contacts closed) and no energy is stored in main spring  302 . Motor operator  200  operates to move circuit breaker handle  102  between the closed position of FIG. 9 and the open position (i.e., electrical contacts open) of FIG. 13. In addition, when circuit breaker  100  trips due for example to an overcurrent condition in an associated electrical system, motor operator  200  operates to reset an operating mechanism (not shown) within circuit breaker  100  by moving the handle to the open position of FIG. 13.  
         [0046]    To move the handle from the closed position of FIG. 9 to the open position of FIG. 13, motor drive assembly  500  rotates cam  420  clockwise as viewed on cam shaft  422  such that mechanical linkage system  400  is sequentially and continuously driven through the configurations of FIGS. 10, 11 and  12 . As best seen in FIG. 10, cam  420  rotates clockwise about cam shaft  422 . Drive plates  402  are allowed to move due to slot  404  in drive plates  402 . Roller  444  on roller axis  410  moves along first cam surface  424  of cam  420 . The counterclockwise rotation of drive plates  402  drives drive plate pin  406  along open slot  316  thereby compressing main spring  302  and storing energy therein. Energy storage mechanism  300  rotates clockwise about spring assembly axis  322  and side plate pin  418 . Latch plate  430 , abutting brace  604 , remains fixed with respect to side plates  416 .  
         [0047]    Referring now to FIG. 11, drive plate  402  rotates further counterclockwise causing drive plate pin  406  to further compress main spring  302 . Cam  420  continues to rotate clockwise. Rolling pin  446  moves from second concave surface  436  of latch plate  430  partially to first concave surface  434  and latch plate  430  rotates clockwise away from brace  604 . Drive plate pin  406  compresses main spring  302  further along open slot  316 .  
         [0048]    In FIG. 12, latch plate  430  rotates clockwise until rolling pin  446  rests fully within first concave surface  434 . Roller  444  remains in intimate contact with first cam surface  424  as cam  420  continues to turn in the clockwise direction. In FIG. 13, cam  420  has completed its clockwise rotation and roller  444  is disengaged from cam  420 . Rolling pin  446  remains in contact with first concave surface  434  of latch plate  430 .  
         [0049]    Mechanical linkage system  400  thence comes to rest in the configuration of FIG. 13. In proceeding from the configuration of FIG. 9 to that of FIG. 13, main spring  302  is compressed a distance “x” by drive plate pin  406  due to counterclockwise rotation of drive plates  402  about drive plate axis  408 . The compression of main spring  302  thus stores energy in main spring  302  according to the equation 
           E= ½ k   m   x   2 , 
         [0050]    where x is the displacement of main spring  302 . Motor operator  200 , energy storage mechanism  300  and mechanical linkage system  400  are held in the stable position of FIG. 13 by first latch link  442 , second latch link  450  and latch plate  430 . The positioning of first latch link  442  and second latch link  450  with respect to one another and with respect to latch plate  430  and cam  420  is such as to prevent the expansion of the compressed main spring  302 , and thus to prevent the release of the energy stored therein. Referring to FIGS.  20 - 22 , a pair of first latch links  442  are coupled to a pair of second latch links  450 , about a link axis  412 . Second latch link  450  is also rotatable about cam shaft  422 . First latch links  442  and second latch links  450  are interior to and parallel with drive plates  402 . A roller  444  is coupled to a roller axis  410  connecting first latch links  442  to drive plate  402 . Roller  444  is rotatable about roller axis  410 . Roller axis  410  is connected to drive plates  402  and roller  444  abuts, and is in intimate contact with, second cam surface  426  of cam  420 . A brace  456  connects the pair of second latch links  450 . An energy release mechanism, such as a latch plate  430 , is rotatable about drive plate axis  408  and is in intimate contact with a rolling pin  446  rotatable about the link axis  412 . Rolling pin  446  moves along a first concave surface  434  and a second concave surface  436  of latch plate  430 . First concave surface  434  and second concave surface  436  of latch plate  430  are arc-like, recessed segments along the perimeter of latch plate  430  operative to receive rolling pin  446  and allow rolling pin  446  to be seated therein as latch plate  430  rotates about drive plate axis  408 . Latch plate  430  includes a releasing lever  458  to which a force may be applied to rotate latch plate  430  about drive plate axis  408 . In FIG. 9, latch plate  430  is also in contact with the brace  604 .  
         [0051]    As seen in FIG. 26, this is accomplished due to the fact that although there is a force acting along the line  462  caused by the compressed main spring  302 , which tends to rotate drive plates  402  and first latch link  442  clockwise about drive plate axis  408 , cam shaft  422  is fixed with respect to side plates  41   6  which are in turn affixed to circuit breaker  100 . Thus, in the configuration FIG. 13 first latch link  442  and second latch line  450  form a rigid linkage. There is a tendency for the linkage of first latch link  442  and second latch link  450  to rotate about link axis  412  and collapse. However, this is prevented by a force acting along line  470  countering the force acting along line  468 . The reaction force acting along line  472  at the cam shaft counters the moment caused by the spring force acting along line  462 . Thus forces and moments acting upon motor operator  200  in the configuration of FIG. 13 are balanced and no rotation of mechanical linkage system  400  may be had.  
         [0052]    In FIG. 13, circuit breaker  100  is in the open position. To proceed from the configuration of FIG. 13 and return to the configuration of FIG. 9 (i.e., electrical contacts closed), a force is applied to latch plate  430  on latch plate lever  458  at  460 . The application of this force acts so as to rotate latch plate  430  counterclockwise about drive plate axis  408  and allow rolling pin  446  to move from first concave surface  434  as in FIG. 13 to second concave surface  436  as in FIG. 9. This action releases the energy stored in main spring  302  and the force acting on drive plate pin  406  causes drive plate  402  to rotate clockwise about drive plate axis  408 . The clockwise rotation of drive plate  402  applies a force to circuit breaker handle  102  at second retaining bar  208  throwing circuit breaker handle  102  leftward, with main spring  302 , latch plate  430  and mechanical linkage system  400  coming to rest in the position of FIG. 9.  
         [0053]    Referring to FIG. 25, motor drive assembly  500  is shown engaged to motor operator  200 , energy storage mechanism  300  and mechanical linkage system  400 . Motor drive assembly  500  comprises a motor  502  geared to a gear train  504 . Gear train  504  comprises a plurality of gears  506 ,  508 ,  510 ,  512 ,  514 . One of the gears  514  of gear train  504  is rotatable about an axis  526  and is connected to a disc  516  at the axis  516 . Disc  516  is rotatable about axis  526 . However, axis  526  is displaced from the center of disc  516 . Thus, when disc  516  rotates due to the action of motor  502  and gear train  504 , disc  516  acts in a cam-like manner providing eccentric rotation of disc  516  about axis  526 .  
         [0054]    Motor drive assembly  500  further comprises a unidirectional bearing  522  coupled to cam shaft  422  and a charging plate  520  connected to a ratchet lever  518 . A roller  530  is rotatably connected to one end of ratchet lever  518  and rests against disc  516  (FIG. 26). Thus, as disc  516  rotates about axis  526 , ratchet lever  518  toggles back and forth as seen at  528  in FIG. 26. This back and forth action ratchets the unidirectional bearing  522  a prescribed angular displacement, θ, about the cam shaft  422  which in turn ratchets cam  420  by a like angular displacement. Referring to FIG. 24, motor drive assembly  500  further comprises a manual handle  524  coupled to unidirectional bearing  522  whereby unidirectional bearing  522 , and thus cam  420 , may be manually ratcheted by repeatedly depressing manual handle  524 .  
         [0055]    The method and system of an exemplary embodiment stores energy in one or more springs  302  which are driven to compression by at least one drive plate  402  during rotation of at least one recharging cam  420  mounted on a common shaft  422 . The drive plate is hinged between two side plates  416  of the energy storage mechanism and there is at least one roller follower  444  mounted on the drive plate which cooperates with the recharging cam during the charging cycle. The circuit breaker handle is actuated by the stored energy system by a linear rack  202  coupled to the drive plate. The drive plate is also connected to at least one compression spring  302  in which the energy is stored. The stored energy mechanism is mounted in front of the breaker cover  100  and is secured to the cover by screws.  
         [0056]    The recharging cam  420  is driven in rotation about its axis by a motor  502  connected to one end of the shaft by a reducing gear train  504  and a unidirectional clutch bearing assembly  522  in the auto mode and by a manual handle  524  connected to the same charging plate  520  in the manual mode.  
         [0057]    At the end of the charging cycle the recharging cam  420  disengages completely from the drive plate  420  and the drive plate  402  is latched in the charged state by a latch plate  430  and the latch links. The stored energy is releases by the actuation of a closing solenoid trip coil in the auto mode, activated by a solenoid, and by an ON pushbutton in the manual mode on the latch plate which pushes it in rotation about its axis setting free the drive plate to rotate about the hinge to its initial position. The advantage of such a system is that because of the complete disengagement of the recharging cam and the drive plate, there is no resistance offered by the charging system when the drive plate is released by the delatching of the latch plate. This ensures minimum wasteage of stored energy while closing the breaker, less wear on the recharging cam and roller follower. There is also much lower closing time of the breaker. Thus, the drive plate holding the stored energy required to close the breaker is disengaged from the recharging cam and shaft used for charging, thus allowing for the quick closing of the breaker using a minimum signal power and with high reliability. The system minimizes the stored energy required for closing the breaker mechanism and reduces the closing time, thereby optimizing the mechanism size and cost.  
         [0058]    At the end of charging cycle, the control cam mounted on the common shaft pushes the drive lever in rotation about its axis and the drive lever, in turn, pushes the charging plate away from the eccentric charging gear, thereby disconnecting the motor from the kinematic link and allowing free rotation of the motor. During discharge of the main spring the control cam allows the drive lever to come back to its normal position by a bias spring and hence the charging plate is connected again to the eccentric charging gear to complete the kinematic link for a fresh charging cycle.  
         [0059]    In motor operator, motor power it is disengaged from the charging mechanism by direct cam action, thereby eliminating excessive stress on the charging mechanism and avoiding overloading the motor. The cam assembly achieves this using a few mechanical components and therefore, decreases the cost of the motor operator and enhances its longevity.  
         [0060]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.