Abstract:
A compact automatic shutter mechanism in an electrical enclosure provides enhanced protection against inadvertent electrical contact for personnel working within and around the electrical enclosure, and also makes it possible to install more equipment in the electrical enclosure than could have been accommodated using prior automatic shutter mechanisms.

Description:
FIELD OF THE INVENTION 
     My invention is directed to enclosures for electrical equipment, such as motor control centers, and more particularly to a shutter mechanism which automatically closes off access to bus bars used in such enclosures to reduce the risk of inadvertent electrical contact by a technician installing or removing equipment from the enclosure. 
     BACKGROUND OF THE INVENTION 
     Protecting people working within or around electrical equipment such as motor control centers against inadvertent electrical contact is a concern for designers of such equipment. A typical motor control center includes an enclosure for mounting and housing three bus bars capable of carrying high current side-by-side in the enclosure with their longitudinal axes running from bottom to top of the enclosure. A mounting panel is typically provided adjacent the bus bars and includes provisions for mounting various electrical devices, such as control units, on a mounting surface of the panel opposite the bus bars. These electrical devices and control units typically include an electrical connector for connecting the device or control unit to one or more of the bus bars. The mounting panel typically includes a connector opening over each bus bar for passage of the connector through the panel and into electrical contact with the bus bar when the electrical device or control unit is mounted on the mounting surface. While the electrical device or control unit is mounted on the mounting panel, the openings over the bus bars are typically covered by the control unit or device in a manner precluding inadvertent contact with the bus bars. Prior to installation of or the removal of the device or control unit, however, the bus bars are exposed through the openings in the mounting panel. 
     Many prior approaches to protecting against electrical contact have been utilized. In one approach, the bus bars are simply left exposed when an electrical device is not mounted over one or more of the connector openings in the panel, and people are simply given verbal warnings or tags are attached to the enclosure warning people against touching the exposed bus bars. This prior approach is not very satisfactory in that it really does not inhibit physical contact with exposed bus bars. 
     In other prior electrical enclosures, a device known as a manual shutter has been provided. The shutter typically includes a shutter panel having holes matching those of the mounting panel when the shutter is placed in an open position, so that an electrical device may be installed through the shutter and panel into contact with the bus bars. The shutters typically include one or more web areas between the holes which cover the electrical connector openings in the panel when the shutter is in the closed position. However, bus bars are exposed before the shutter is manually closed, and during any time period when the shutter has been manually opened but the electrical device has not yet been installed. 
     There have also been many different approaches utilized in the past aimed at providing an automatic shutter mechanism that will close on its own as an electrical device in contact with the bus bars is removed from the enclosure, without any action being taken by a technician or operator and automatically open the shutter as a replacement electrical device is inserted back into the enclosure to make contact with the bus bars. Prior approaches to providing such an automatic shutter mechanism have spanned the range from a very simple shutter operating under the force of gravity via an inclined plane, to shutters which are pushed, pulled, or otherwise forced into an open or closed position respectively upon installation or removal of an electrical device using a shutter actuation system which often includes complex arrangements of cams, levers, chains and sprockets, and the like. Such prior automatic shutter actuation systems have tended to be bulky and complex, and often extend beyond the top and bottom sides of the electrical device, thereby consuming space inside the enclosure which could more advantageously be used to mount additional electrical devices connected to the bus bars. 
     It is an object of my invention, therefore, to provide an improved electrical enclosure through utilization of an improved shutter mechanism. It is also an object of my invention to provide a shutter mechanism which is straight forward in its construction and operation, and very compact with little or no extension of the shutter mechanism above and below an electrical device with contacts protected by my shutter mechanism. 
     SUMMARY OF THE INVENTION 
     My invention meets the above objects by providing an improved shutter actuator including a lever having one end hinged to the shutter and extending outward from the shutter to a distal outer end of the lever configured for engaging a control unit or electrical device having electrical contacts configured to connect with bus bars within the enclosure. My improved actuator further includes a spring mechanism operably attaching the lever to the shutter for urging the distal end of the lever to pivot outward from the shutter while simultaneously urging the shutter toward a first, closed position wherein web portions of the shutter close off access to the bus bars protected by the shutter. As an electrical device is installed, a lever engaging surface of the electrical device contacts the outer end of the lever. As the electrical device is pushed into place, the lever and spring mechanism pull the shutter open to expose the bus bars for electrical connection to the electrical connectors on the electrical device. When the electrical device is removed, the spring mechanism causes the lever to pivot outward from the shutter, thereby allowing the shutter to return to a closed position. 
     In a preferred embodiment of my invention, a single constant force spring in the form of an extendable, coiled, tape spring is utilized for simultaneously urging the lever to spring outward and the shutter to return to the closed position. This aspect of my invention can be utilized in many different embodiments meeting the needs of a particular electrical enclosure with an elegantly simple actuator having only a few, e.g., two or three parts. 
     According to another aspect of my invention, an embodiment of an actuator according to my invention does not protrude above or below the top or bottom edges respectively of a control unit or electrical device connected to bus bars in an enclosure. 
     According to another aspect of my invention, the lever and spring mechanisms of an actuator mechanism are connected to a pusher plate operably connected to the shutter in such a manner that as the lever is pushed inward, by installing a control unit, or pulled outward by the spring, the pusher plate pushes or pulls the shutter from a closed to an open position. In a highly preferred embodiment according to this aspect of my invention, the pusher plate includes key-shaped slots for receipt of a mating key-shaped projection of the shutter. Making the operable connection between the pusher plate and shutter in this manner allows a single pusher plate configuration to be used with shutters of differing thickness or shape, thereby providing the advantage of reducing the inventory of parts which must be carried to manufacture or repair a line of equipment enclosures having different shutter configurations. The slotted shape also allows the pusher plate and shutter to be utilized on panels wherein the shutter and pusher plate are mounted for sliding movement in a different plane. 
     The compact size, together with simple construction and operation, allow a shutter mechanism according to my invention to be readily retrofitted into existing enclosures which formerly utilized other types of shutter mechanisms. The compact size of my shutter mechanism also makes it possible to install more equipment in the same electrical enclosure due to the fact that my shutter mechanism does not extend above or below the control unit or electrical device mounted through the shutter of my invention. 
     Other aspects and advantages of my invention will be apparent to those having skill in the art upon review of the attached drawings and the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts an exemplary embodiment of my invention with the shutter in the closed position; 
     FIG. 2 depicts the exemplary embodiment of FIG. 1 with the shutter in an open position; 
     FIG. 3 is a cross-section of the embodiment in FIG. 1 showing a control unit engaging a shutter actuator of my invention, and the shutter in a closed position; 
     FIG. 4 is a sectional depiction of the control unit installed on an electrical enclosure according to my invention and the shutter in an open position; 
     FIG. 5 is an enlarged view of a portion of a shutter actuator according to my invention; 
     FIG. 6 a  depicts a keyed, slidable connection between a shutter and a pusher plate according to my invention; 
     FIGS. 6 b - 6   e  depict an alternate embodiment of the connection between the shutter and the pusher plate; 
     FIG. 7 depicts an embodiment of my invention wherein the shutter actuating mechanism is mounted on the shutter itself, and the pusher plate and associated guide and retaining track are eliminated; 
     FIG. 8 is a partial sectional view taken along a centerline of FIG. 6 a  depicting a flexible joint formed by engaging a T-shaped tang with a mating T-shaped slot, to allow shutter mechanisms of varying thicknesses and shapes to be used with a single pusher plate configuration, or alternatively, allowing the shutter mechanism and pusher plate to be mounted on a stepped mounting plate having a first and a second mounting surface not lying in a common plane; and 
     FIG. 9 illustrates an alternate exemplary embodiment of a shutter actuator including a first and a second spring. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-4 depict an exemplary embodiment of an electrical enclosure according to my invention in the form of a motor control center  10  including three bus bars  12   a ,  12   b ,  12   c  having longitudinal axes  14  mounted in parallel with one another and the longitudinal axes extending in a generally vertical up-down direction as indicated in FIG.  2 . The motor control center  10  includes a mounting panel  16  having a control unit mounting surface  18  opposite the bus bars  12   a ,  12   b ,  12   c  for receiving a control unit  20 , as shown in FIGS. 3 and 4. 
     As shown in FIGS. 3 and 4, the control unit  20  includes three stab-on electrical connectors  22   a ,  22   b ,  22   c  for connecting the control unit  20  to the bus bars  12   a ,  12   b ,  12   c.    
     As shown in FIG. 1, the mounting panel  16  includes connector openings  24   a ,  24   b ,  24   c , as indicated by dashed lines, for passage of the electrical connectors  22   a ,  22   b ,  22   c  through the panel  16  and into electrical contact with the bus bars  12   a ,  12   b ,  12   c  when the control unit  20  is mounted on the mounting surface  18 , as shown in FIG.  4 . 
     A shutter mechanism  26  includes a shutter panel  28 , and a shutter actuator  30 . The shutter panel  28  is slidably mounted by elongated slots  29  and fasteners in the form of plastic rivets or retaining bolts  31  on the mounting surface  18  for movement along a path generally transverse to the longitudinal axes  14  between a first or closed position, as shown in FIG. 1, and a second or open position, as shown in FIG.  2 . The retaining bolts  31  and slots are configured such that the bolts  31  also function as stops limiting travel of the shutter panel. 
     The shutter panel  28  includes three webs  32   a ,  32   b ,  32   c  respectively covering the connector openings  24   a ,  24   b ,  24   c  in the mounting panel  16  when the shutter panel  28  is in the closed position as depicted in FIG.  1 . The shutter panel  28  also includes two holes  34   a ,  34   b  configured to align with the connector openings  24   a ,  24   b  in the mounting panel  16  for passage of electrical connectors  22   a ,  22   b  of the control unit  20  when the shutter panel  28  is in the second or open position as depicted in FIG.  2 . Only two holes  34   a ,  34   b  are required in the shutter panel  28  as depicted in FIGS. 1-4 because the length of the shutter panel  28  has been judiciously selected so that when the shutter panel  28  moves right to left from the closed to the open position as seen by comparing FIGS. 1 and 2, the right end  36  of the shutter panel  28 , as shown in FIG. 2 clears the hole  24   c  allowing access to bus bar  12   c.    
     The shutter actuator  30  includes a shutter pusher plate  38  operably connected at arrow  40  by a flexible connection to the left end of the shutter  28  for movement with the shutter  28  along the path generally transverse to the longitudinal axis  14  of the bus bars  12  between the open and closed positions of the shutter  28 . The actuator  30  also includes a track  42  mounted on the mounting surface  18  for retaining and guiding the pusher plate  38  along the path as the shutter  28  moves from the open and closed positions. 
     As shown in FIGS. 3 and 4, the actuator  30  includes a lever  44  having one end  46  pivoted by a pivot pin shown schematically at  47  to the pusher plate  38  and extending outward from the pusher plate  38  to a distal end  48  of the lever  44  configured for engaging the control unit  20 . As shown in FIG. 5, the shutter actuator  30  further includes a spring mechanism in the form of a constant force spring  50  conventionally including an extendable, coiled, tape spring having a first end  52  thereof attached to the lever  44  at a point on the lever outward from the pivot  47  and a second end  54  attached simultaneously to the track  42  and the mounting panel  16  by a single screw  56 , as shown in FIG. 5. A portion  58  of the constant force spring extending between the first and second ends  52 ,  56  of the spring  50  slidably engages the pusher plate  38  at an end  60  opposite the end  40  of the pusher plate  38  attached to the shutter panel  28 . The lever  44  includes a flat  74  configured to bear against a stop surface  76  of the pusher plate  38  to form a stop limiting outward pivoting of the lever  44  to a desired angle less than 90□ from the shutter panel, as shown in FIG. 3, when the shutter panel  28  is in the closed position. 
     Operation of the embodiment of a shutter mechanism  26  as described thus far, may now be readily seen by examination of FIGS. 1 through 5. Prior to installation of the control unit  20 , the constant force spring  50  causes the lever  44  to swing outward and the pusher plate  38  to pull the shutter panel  28  into a closed position as indicated by FIGS. 1 and 5. As the control unit  20  is brought into position for engaging the electrical contacts  22   a ,  22   b ,  22   c  with the bus bars  12   a ,  12   b ,  12   c , as shown in FIG. 3, the distal end  48  of the lever  44  comes into contact with a surface  62  of the control unit  20  configured to receive the distal end  48  of the lever  44 . The surface  62  may be in the form of a V-shaped notch. As the control unit  20  is pushed toward the mounting panel  16  and bus bars  12   a ,  12   b ,  12   c , the lever  44  is pushed toward the pusher plate as shown in FIG. 4, and the lever  44  pulls the shutter panel  28  from the closed position of FIG. 1 to the open position of FIG. 2, thereby allowing the electrical connectors  22   a ,  22   b ,  22   c  of the control unit  20  to engage the bus bars  12   a ,  12   b ,  12   c  as shown in FIG.  4 . 
     When the control unit is removed, the procedure described above is reversed, and the constant force spring  50  returns the lever  44  to its extended position and simultaneously pulls the shutter and pusher plate back into the closed position indicated in FIG.  1 . 
     FIG. 6 a  depicts an exemplary embodiment for making the flexible connection between the pusher plate  38  and shutter panel  28 . According to this embodiment of my invention, the pusher plate  38  includes a flexible joint  63  formed by engaging a T-shaped tang  64  of the shutter  28  in a mating T-shaped slot  66  in the pusher plate  38 . This arrangement allows shutter mechanisms of varying thicknesses and shapes to be used with a single standard pusher plate  38 . Alternatively, the flexible connection  63  formed by the T-shaped tang end slot  64 ,  66  allows the shutter panel  28  and pusher plate  38  to be mounted on a mounting plate  16  having a first mounting surface  67  and a second mounting surface  68  not lying in a common plane, as shown in FIG. 8, thereby allowing greater flexibility for designing the enclosure. This feature also allows the pusher plate  38  and shutter panel  28  to “float” with respect to one another to accommodate non-uniformity in the mounting panel, and reduce the need for highly toleranced parts. 
     FIGS. 6 b - 6   e  depict an alternate embodiment for making the flexible connection between the pusher plate  38  and the shutter panel  28 . FIG. 6 b  is a sectional view of the pusher plate  38  taken along lines  6   b — 6   b  in FIG.  1 . The pusher plate of the embodiment depicted in FIG. 6 b  includes a rectangular opening  80  in an end of the pusher plate  38  adjacent the shutter panel  28 . As shown in FIGS. 6 c - 6   e , the shutter panel  28  includes a Z-shaped tab  82  extending upward from the remainder of the shutter panel  28  and terminating in a T-shaped bar  84 . In this embodiment of my invention, the configuration of the Z-shaped tab  82 , T-shaped bar  84  and the dimensions of the rectangular opening  80  in the pusher plate  38  are judiciously selected such that when the T-shaped bar  84  is inserted into the rectangular opening  80  in the pusher plate  38 , and both the pusher plate  38  and shutter panel  28  are installed in the motor control center  10 , the shutter panel  28  is locked into the pusher plate  38  in such a manner that the pusher plate  38  and shutter panel  28  cannot be separated by merely lifting the shutter panel  28  straight up off of the mounting surface  18 . This construction provides an advantage in that any friction or binding in operation of the shutter panel  28  is less likely to cause a separation of the flexible joint. In a highly preferred version of this embodiment of my invention, the dimensions of the Z-shaped tab  82 , the T-shaped bar  84  and the rectangular opening  80  in the pusher plate  38  are selected and configured such that the shutter panel  28  may be installed or removed from the motor control center  10  after removal of the screws  31 , with the shutter actuator  30  affixed to the mounting surface  18 . 
     FIG. 7 depicts an alternate embodiment of my invention in which the shutter actuator  30  is mounted on the shutter panel  28 , thereby allowing the track  42  of the embodiments described above to be eliminated. In the embodiment of FIG. 7, the shutter actuator includes a lever  44  having one end  46  hinged to the shutter  28  as in the embodiment of FIGS. 1-4. A constant force spring  50  is attached at a first end  52  to the lever  44  and at a second end  54 , at a point underneath the shutter panel  28  to the mounting panel  16  with a screw  56 . The portion  58  between the first and second ends  52 ,  54  of the constant force spring  50  slidingly contacts an end  60  of the shutter panel in a manner similar to that described above and shown in FIG. 5, for embodiments of my invention utilizing a pusher plate. Operation of the alternate embodiment of FIG. 7 is essentially identical to that described above for the embodiments depicted in FIGS. 1-5 utilizing a pusher plate  38 . This embodiment provides an advantage in that the track  42 , pusher plate  38 , and the connection  40  between the actuator  30  and shutter panel  28  can be eliminated, thereby further reducing cost, size, and complexity of my shutter mechanism. 
     FIG. 9 illustrates an exemplary embodiment of my invention in which the spring mechanism includes a first spring in the form of a constant force spring  70  attached at a first end to the pusher plate  38 , and attached at a second end to the track or mounting panel  16  by a screw  56  in such a manner that, absent other forces being exerted on the pusher plate, the constant force spring  70  will pull the pusher  38  and shutter  28  into a closed position as indicated at FIG. 1. A second spring in the form of a torsion spring  72  operably connects a lever  44  to the pusher plate  38  for urging the lever  44  to rotate outward from the pusher plate  38 , as shown in FIG.  9 . 
     Although I have described certain exemplary embodiments of my invention in the description above and the attached drawings, those having skill in the art will recognize that many other alternate embodiments of my invention are possible and contemplated by me within the scope of the appended claims.