Abstract:
The present invention is a power distribution assembly for distributing power about a rack mounted server system. In particular, each chassis of a rack mounted server system is provided power through a power distribution assembly that is hinged to a back of the rack of the server system. Each of the power distribution assemblies may be in either an open position or a closed position. In a closed position, each of the power distribution assemblies is rotated to lie very close to a backplane board of a chassis of the server system. In an open position, each of the power distribution assemblies is swung around so that full access may be had to the backplane boards of the chassis in the server system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to application Ser. No. 09/933,941 filed concurrently herewith. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to distributing power to rack mounted electronic devices. More particularly, the present invention is related to routing direct current power to a plurality of rack-mounted computer systems in server operation. More particularly still, the present invention is directed to placement and mounting of power bus bars, circuit breakers, and the like, for rack mounted server systems. 
     2. Background of the Invention 
     As the size of computers becomes smaller, so too does the number of computers that may be placed in one particular place. For persons and entities providing server services, e.g., Internet service providers (ISPs) and corporate computer departments, smaller computer footprints allow a smaller required area, or more computers in the same areas already allocated. 
     Given that each server is effectively just an individual computer, each of these devices must have at least a power cable and a cable to carry information to and from the server. In years past, when a single computer may have occupied an entire drawer in a rack-mounted system, having the necessary space for power and information cables was not of particular concern. However, with the increasingly smaller footprints of modem computers, the necessary space to provide adequate cabling to each of these servers becomes a major concern. The trend in the industry is to replace the cable-bundle approach to providing cable access with the use of a backplane board. 
     A backplane board is simply an electrical circuit board placed at substantially right angles to the insertion direction of rack-mounted server systems. In such a system, the act of pushing the computer into the rack physically couples the computer to the backplane board. In this way, digital signals and power may be coupled to the computer system. Further, use of the backplane board allows the rack-mounted computer system designer to move cable connections, if any, to more desirable locations. 
     While these backplane boards typically have little, if any, logic circuitry, the boards can fail. The failure modes could include failure of any onboard circuitry, as well as failure of electrical traces on the board itself caused by mechanical stresses involved in inserting and removing the computer systems. Regardless of the cause, replacing backplane boards is a major undertaking, which may include disassembly of a substantial portion, or all, of the rack-mounted system including removal of the various power distribution buses, thus disabling the entire rack-mounted system. 
     Thus, what is needed in the art is a mechanism to distribute power in a rack-mounted server system that provides necessary amperage-carrying capability for more power-intensive operations, that is easily repairable, and that need not be removed or of disassembled in the event that a backplane board of the server system needs to be replaced. 
     BRIEF SUMMARY OF THE INVENTION 
     The problems noted above are solved in large part by a main power distribution assembly for rack mounted server systems, and the like, that places the power supply and return bars in hinged non-conductive containers that extend at least the partial height of the server system. Preferably, two of these power distribution assemblies are provided on each server system for providing fully redundant power supplies. 
     In normal operation, each of the power distribution assemblies is preferably placed, by swinging it about its center of rotation, in a closed position where each of the power distribution assemblies is very close to the chassis of the rack system. When service, maintenance, or repair needs to be done to the server system, each of the power distribution assemblies is preferably rotated about its hinge away from the closed position to an open position. In the open position, each of the power distribution assemblies preferably swings at least 90 degrees away from its closed position. Thus, when both power distribution assemblies are in their open position, operators and technicians have full access to any electrical components or cables that may traverse various locations at the back of the rack, including access to each chassis within the rack. 
     Preferably, however, each of the power distribution assemblies is capable of providing power to its respective chassis in the rack whether it is in the open or closed position. This capability has two aspects: power supplied to the power distribution assembly, and power from the power distribution assembly to the various chassis. Preferably, power is supplied to power rails within the power distribution assembly by way of a set of power cables supplying appropriate direct current (DC) voltage. These voltages are preferably provided from an array of onboard DC power supplies, preferably mounted near the bottom of the rack. However, this DC voltage may also be supplied by a customer from other power systems, e.g., a battery network. By coupling the power supply to the power distribution assembly with flexible cables, current may continue to flow whether the power distribution assemblies are in their closed or open positions. Likewise, power is provided from the power distribution assembly to the various chassis by way of flexible cables that couple between circuit breakers and the power distribution assembly and power backplane boards of each particular chassis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
     FIG. 1 shows an exemplary rack mounted server system; 
     FIG. 2 shows a front perspective view of a chassis of the rack mounted server system; 
     FIG. 3 shows a back perspective view of a server system in accordance with the preferred embodiment of the present invention; 
     FIG. 4 shows an overhead view of the power distribution assemblies in the open position taken substantially along line  4 — 4  of FIG. 3; 
     FIG. 5 is an overhead view of the power distribution assemblies in the closed position; 
     FIG. 6 shows a detailed view of the right power distribution assembly; 
     FIG. 7 shows a detailed view of a circuit breaker within the power distribution assembly, and also shows the chassis supply, chassis return and cable coupler of the preferred embodiment; 
     FIG. 8 shows an elevational view of an exemplary chassis supply cable coupled to a right-angle connector; 
     FIG. 9 shows a back perspective view of the cable-end housing of the preferred embodiment; 
     FIG. 10 shows a view of the cable-end housing from the bottom; 
     FIG. 11 shows a side cut-away view of the cable-end housing; and 
     FIG. 12 shows the relationship of two electrically conductive pins and a connection guide. 
     FIG. 13 shows a cable-end housing coupled to pins of the connection area. 
    
    
     NOTATION AND NOMENCLATURE 
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, computer companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, there is shown an exemplary multiple chassis server system  100 . The exemplary server system has a rack, and four chassis  10 A-D. The rack provides a structural framework into which the chassis  10 A-D are mounted. The rack defines a front, two sides, and a back. Though the rack may not have solid structures that define these surfaces, at a minimum the rack preferably has structural members at the four comers of the server system that provide the required structural support and further define the front, back and sides. Though four chassis  10 A-D are shown in FIG. 1, any number of chassis may be a part of the server system  100 . The preferred embodiment of the present invention handles three to five such chassis, and this ability is discussed more fully below. Each of the chassis  10 A-D preferably contain a plurality of computers or servers  20 . In the preferred embodiment, eight such servers  20  may be placed within any one chassis  10 . While having eight servers in each chassis is the preferred implementation, any number of servers may be used. Thus, the server system  100  of FIG. 1 may have thirty-two servers  20 . However, one of the chassis, chassis  10 B in FIG. 1, is shown without the presence of any servers  20  to exemplify how each server  20  fits within its particular chassis  10 . In particular, each chassis preferably contains a slot  30  for each server  20 . It is within this slot  30  that a particular server  20  is installed for operation in the server system  100 . 
     Referring now to FIG. 2, there is shown a front perspective view of a chassis  10 , which also shows a backplane board  40 . Rather than having a cable bundle for each server  20 , the preferred embodiment of the present invention utilizes a backplane board  40  having a plurality of connectors which allow for electrical connection of the server  20  upon insertion into the chassis  10 . For example, the chassis  10  may comprise at least a data communication connector  42  and a power connector  44  for each of the servers  20 . Having a connector  42  for data transmission and a connector  44  for power coupling is merely exemplary, and any number of data transmission and power couplers may be present, depending upon the particular application. Further, those connections may be placed on separate backplane boards, or may be collapsed into a single connector. FIG. 2 also shows that for each of the possible servers  20  to be inserted into the particular chassis, there is preferably a slot  30  having an upper portion  32  and a lower portion  34 . Preferably, the server  20  is oriented vertically, as shown in FIG. 1, and inserted into one of the slots  30 . The server  20  is then preferably pushed back into the chassis  10  until mating connectors (not shown) on the server  20  couple to the corresponding connectors  42 ,  44  on the backplane board  40 . 
     Referring now to FIG. 3, there is shown a back perspective view of a server system  100  in accordance with the preferred embodiment of the present invention. Shown in FIG. 3 are three backplane boards  40 A-C corresponding to three chassis  10 A-C. Also shown in FIG. 3 are two power distribution assemblies  50  and  52 . Each power distribution assembly  50 ,  52  is designed and constructed to house a supply and a return power bus bar (not shown in FIG.  3 ), as well as a plurality of circuit breakers (not shown in FIG.  3 ). It is envisioned that the power distribution assemblies  50 ,  52  are substantially the same, except that they are mirror copies of each other. Though not shown in FIG. 3, in the preferred embodiment each power distribution assembly  50 ,  52  has a plurality of cables extending from the main body of the distribution assembly  50 ,  52  to each of the server chassis  10 A-C. It is through these plurality of cables that power is provided to each chassis  10 A-C in the server system  100 . 
     In addition to housing bus bars, breakers, and providing an origin point for power cables extending to the chassis  10 A-C, the power distribution assemblies  50 ,  52  are also advantageously connected to the rack of the server system  100  in such a way as to allow access to a back portion of the server system  100 , including the backplane boards  40 A-C. Referring still to FIG. 3, the power distribution assemblies  50 ,  52  are shown in their extended or open position. Referring now to FIG. 4, which is a view taken substantially along line  4 — 4  of FIG. 3, there is shown an overhead view of the power distribution assemblies  50  and  52  in their open positions, with the dashed line indicating the path of travel of each assembly. In particular, the left power distribution assembly  50  (viewed from the back of the server system  100 ) connects to the rack of the server system  100  by a hinge  58 . The power distribution assembly  50  rotates about hinge point  54  along the dashed line shown in FIG.  4 . Likewise, the right power distribution assembly  52  (again when viewed from the back of the server system  100 ) connects to the rack of the server system  100  by way of a hinge  60 , and rotates about hinge point  56  along the dashed line shown in FIG.  4 . It will be understood that the view of FIG. 4 is taken substantially along line  44  of FIG. 3, and thus only the upper-most hinges  58 ,  60  are shown. In the perspective view of FIG. 3, however, the two hinges of the right power distribution assembly  52  are shown, in particular hinges  60 A and  60 B. In the perspective view of FIG. 3, the hinges for the power distribution assembly  50  cannot be seen. 
     Referring now to FIG. 5, there is shown each of the power distribution assemblies  50  and  52  in their retracted or closed position. Referring to FIGS. 3-5 somewhat simultaneously, it may be seen that the power distribution assemblies  50 ,  52  may be either in an open position (FIG. 4) or closed position (FIG. 5) as may be necessary to perform maintenance or repair on the server system  100 . It is envisioned that for maintenance to a back portion of the server system  100 , e.g., replacement of a backplane board  40 A-C, that the power distribution assemblies  50 ,  52  would initially be in a closed position (normal operation) and then would be moved to an open position (FIG. 4) so that the operator or technician would have access to devices on the back of the server system  100 . 
     Referring now to FIG. 6, there is shown a more detailed view of the right power distribution assembly  52 . A description of only one of the power distribution assemblies is sufficient to describe them both inasmuch as they are preferably mirror copies of each other. In other words, only minor differences may exist between the left power distribution assembly  50  and the right power distribution assembly  52 . Preferably, each power distribution assembly  50 ,  52  has two bus bars mounted therein. In the preferred embodiments, these bus bars are preferably a supply bus bar  64  and a return bus bar  66 . In FIG. 6, each of these bus bars  64 ,  66  are marked in various locations so as to be discernable from the rest of the equipment. In the preferred embodiment, the supply bus bar  64  carries −48 Volt direct current (DC) voltage. Relatedly, the return bus bar  66  preferably is designated as the return or neutral. In the prior art, each chassis  10 A-C, and possibly each server  20  within each chassis has its own power supply for converting alternating current (AC) voltages to DC voltages. Because prior art power supplies were provided higher voltage AC supplies, amperage requirements were smaller. One of ordinary skill in the art is well aware that as the voltage increases, the current requirement decreases for providing the same amount of power. Thus, in the prior art, the supply of 120 Volt AC and possibly 240 Volt AC power to the supplies may require relatively small cables. However, those power supplies took up valuable space within the server system  100 . 
     In the preferred embodiments, the individual AC-DC power supplies for each server are not used, and instead each chassis  10 A-C is supplied with DC power from elsewhere. Thus, the preferred embodiments provide −48 volt DC power to each chassis. Because this lower voltage is provided, the current carrying capability must be high to provide the necessary power. Referring still to FIG. 6, each of the supply bus bar  64  and return bus bar  66  are rated for 425 amps DC. Each of these bus bars  64 ,  66  are preferably constructed of No. 110 half-hard copper. The supply and return current is preferably coupled to the supply bus bar  64  and return bus bar  66  by way of a supply and return cable  68  and  70 , respectively. These cables  68 ,  70  preferably couple to a DC power supply or some other source of power, e.g., a battery system. While in the preferred embodiment the supply cable  68  and return cable  70  couple to the power distribution assembly  50 ,  52  near the bottom, this is only exemplary and the connection point could be moved to an upper portion of the power distribution assembly  50 ,  52 , if the particular installation required. The supply cable  68  and return cable  70  preferably couple to the supply bus bar  64  and return bus bar  66  by way of a Rapid Lock™ system available from Elcon Products International Company, P.O. Box 1885, Freemont, Calif. 94538. While use of the Rapid Lock™ system is preferred for connecting the supply cables to the power distribution assemblies, any suitable means may be used, including standard lugs. 
     In the preferred embodiment, each power distribution assembly  50 ,  52  may have from three to five circuit breakers. In the exemplar drawing of FIG. 6, three such circuit breakers  72 ,  74  and  76  are shown. In the preferred embodiments, each of the circuit breakers  72 ,  74 ,  76  are rated for  70  amps DC. As can be seen in FIG. 6, each circuit breaker  72 ,  74 ,  76  preferably couples to the supply bus bar  64 . In particular, circuit breaker  72  couples to the supply bus bar  64  by way of a small copper bus branch  78 , which couples to the bus bar  64  and the circuit breaker  72  by way of a bolt. Likewise, for the uppermost circuit breakers  74 ,  76  couple to the supply bus bar  64  by way of bus branch  80 . All the hardware within the mounting cover, e.g., the bus bars, circuit breakers, bus branches, are considered power distribution hardware. On the downstream side of each circuit breaker  72 ,  74  and  76  are supply cables  82 ,  84  and  86 . Along with their respective return cables ( 83  for supply cable  82  and either of return cable  85  or  87  for supply cables  84  and  86 ), each circuit breaker  72 ,  74  and  76  preferably feeds one chassis  10 A-C. As can be seen in FIG. 6, at least a portion of each circuit breaker extends outside the hollow interior of the mounting cover. It will be understood however that although FIG. 6 shows only the right power distribution assembly  52 , the left power distribution assembly  50  is similarly constructed, including corresponding circuit breakers. In the preferred embodiments, each chassis  10 A-C is provided power through two circuit breakers, one residing in each power distribution assembly  50 ,  52 . These supplies are preferably fully redundant such that each rack may be supplied power by way of only one circuit breaker in one power distribution assembly. In this way, loss of a power supply, or maintenance required on a power distribution assembly  50  or  52 , may take place without loss of power to the particular chassis  10 A-C (so long as the second power distribution assembly  50 ,  52  is still operational). 
     Because each power distribution assembly  50 ,  52  contains relatively high voltage electrical components and currents, the electrical shroud or mounting cover  88 , which comprises the entire outer portion of the power distribution assembly  50 ,  52 , is preferably made of non-conductive material. In the preferred embodiment, this non-conductive material is Noryl FN 215X structural foam plastic. Because the supply cable  68  and return cable  70  must be connected during installation, and because some maintenance may be required, especially on the circuit breaker  72 ,  74  and  76 , the mounting cover  88  preferably comprises a removable cover  90  (FIG.  6 ). This removable cover  90  allows access to the connection points for the supply cable  68  and return cable  70 , as well as access to the breakers  72 ,  74  and  76 , and all electrical connections within the power distribution assembly  50 ,  52 . This non-conductive material also provides structural support for the power distribution hardware therein. Before moving on, it must be understood that the embodiment shown in FIG. 6 has only three circuit breakers. However, use of the power distribution assemblies  50 ,  52  may be extended to any suitable number of circuit breakers, but preferably have no fewer than three and no greater than five circuit breakers. If five circuit breakers are used, the length of the power distribution assembly  50 ,  52  is extended to accommodate the additional circuit breakers. In the preferred embodiments, the additional circuit breakers preferably mount within the power distribution assembly  50 ,  52  in a manner similar to that shown for circuit breaker  72 . 
     FIG. 7 shows a more detailed view of circuit breaker  72  within the power distribution assembly  52 , and also shows connection of the chassis supply  82  and return  83  cables within the cable-end housing  200 . In broad terms, the cable-end housing  200  is designed and constructed to house both the chassis supply  82  and chassis return  83  cables from the power distribution assembly  50 ,  52 . The cable-end housing  200 , in combination with other structures discussed subsequently, ensures that the polarity of the connection for power to a chassis  10 A-C is correct. Further, the cable-end housing  200  allows for connection of both the chassis supply  82  and chassis return  83  cables simultaneously. 
     Referring now to FIG. 8, there is shown an exemplary chassis supply cable  82  coupled to the right-angle connector  202 , which is preferably a Rapid Lock™ connector produced by Elcon, as discussed above with respect to the supply cable  68  and return cable  70 . The connector  202  preferably makes electrical contact with the conductors of the chassis supply cable  82  by way of any suitable connection device, e.g., a crimp-type coupler  204 . Electrical currents flow through the metal of the crimp-type coupler  204  to finger-like arms (not shown) within the aperture  206 . The right-angle connector  202  preferably also has two shoulders  208 A and  208 B. The importance of these shoulders becomes clear with regard to a discussion of the cable-end housing  200 . 
     Referring now to FIG. 9, there is shown a back perspective view of the cable-end housing  200 . In particular, FIG. 9 shows that the two major portions of the cable-end housing  200  are the front cover  210  and back cover  212 . Assembly of the cable-end housing  200  preferably involves placing an end of each of the chassis supply cable  82  and rack return cable  83  into the cable-end housing. In particular, the right-angle connector  202  associated with each of the chassis supply and chassis return cable  82 ,  83  are preferably placed through one of the bottom apertures  214 A, B. Preferably, each right-angle cable connector  202  associated with each supply or return cable  82 ,  83  slides into the connector mating portion  216 A or  216 B. The cable associated with that connector  202  then protrudes through the interior aperture  218 A, B and out of the cable-end housing  200  by means of the bottom apertures  214 A, B. Each of the connector mating portions  216 A, B of the front cover  210  have interior shoulders  220  ( 220 A, B for portion  216 A, and  220 C, D for connector mating portion  216 B). Preferably, each shoulder  208 A, B of the right-angle connector  202  (FIG. 8) contacts the shoulders  220  in such a way as to retain the right-angle connector  202  and corresponding cable  82 ,  83  within the cable-end housing  200 . Finally, back cover  212  is connected to the front cover  210  in such a way as to retain the respective cables within the cable-end housing  200  from being pulled in a direction generally perpendicular to that of the cable direction. The combination of the front cover  210  and back cover  212  also provide stress relief for the respective cables, especially through the apertures  214 A, B. 
     Also shown in FIG. 9 are two features that aid in the installation and removal of the cable-end housing  200  generally. In particular, FIG. 9 shows a semi-circular protrusion  222 . This semi-circular protrusion  222 , and the corresponding protrusion on the opposite side (not shown in FIG.  9 ), provide a location for an operator or technician to grasp the cable-end housing  200  during installation and removal. The semi-circular protrusion preferably has its open side directed toward the back cover  212 . Further, the front cover  210  also preferably comprises a pry aperture  224 . This aperture is preferably located such that during removal of the cable-end housing  200 , an operator or technician may place the flat blade of a screwdriver within this pry aperture  224 , and in combination with other components to be discussed below, aid in the removal of the cable-end housing  200 . 
     The perspective view of the cable-end housing  200  shown in FIG. 9 is simplified with respect to the back cover  212  and the apertures  214  and  218 . Referring to FIG. 10, there is shown a view of the cable-end housing  200  from the bottom, i.e., the direction through which the cables  82 ,  83  extend into the cable-end housing  200 . Preferably, the front cover  210  and the back cover  212  form substantially circular apertures  214 A, B. The radius of these apertures is preferably sized to be just slightly larger than the outer diameter of the particular cable used. Though not shown in FIG. 10, the internal apertures  218 A, B are also preferably circular in nature. However, the diameter of the internal apertures  218 A, B may be larger to accommodate the crimp coupler  204 . 
     Referring now to FIG. 11, there is shown a side view cutaway drawing of the cable-end housing  200 . In particular, the front cover  210  has a side cutaway to show how the back cover  212  connects to the front cover  210 . In particular, the back cover  212  connects by “toe-in” to the front cover  210 . This toe-in mechanism is accomplished by means of a rectangular protrusion  225  on the front surface of the back cover  212 , and a mating latch structure  226  on the front cover  210 . The directional arrow in FIG. 11 shows the direction that the back cover  212  is mated with the front cover  210  which involves pushing the back cover  212  such that the protrusion  225  and the latch  226  mate. Once these devices are mated, the back cover  212  then rotates, with its point of rotation being the interface between the rectangular protrusion  225  and the latch  226  until the cover is properly in place. Using the protrusion  225  and latch  226  on the back cover  212 , the preferred embodiment requires only one screw (not shown) to hold the cover  212  in place. This screw extends through reinforcing member  228  of the back cover and into reinforcing member  230  of the front cover  210 . 
     Referring now to FIG. 12, there is shown a connection area  231  including a set of electrical contact pins  232 A and B. This connection area  231  may be part of a backplane board  40 A-C, or may be mounted on a structural member on the rack, e.g., a metal brace extending across the back of the rack. Regardless of its location, the connection area  231  is where the cable-end housing  231  preferably couples to transfer DC power to the racks  10 A-C. The pins  232 A, B are preferably sized to fit within the aperture  206  of the right-angle connector  202  (see FIG.  8 ). Fingers within the aperture  206  (not shown) contact the pins  232 A, B in such a way as to allow electrical current to flow, whether that current is from the supply to the servers of the server system  100  or the return current through ground or neutral. Also shown in FIG. 12 is connection guide  236 . Connection guide  236  preferably performs two functions. First, its placement above the pins  232 A, B acts as a safety mechanism for the connecting of the cable-end housing  200  to the system. Because of lip  238  of the connection guide  236 , the cable-end housing  200  may only be placed onto the pins  232 A, B in one orientation. Referring to FIG. 13, there is shown the cable-end housing  200  connected to the pins  232  (only one of which is shown in FIG.  13 ). As can be seen, the apertures leading to the right-angle connectors of the cable-end housing  200  are off center such that a top portion  240  of the cable-end housing  200  lies near the lip  238  of the connection guide  236  when coupled to the pins  232 A, B. Referring generally to FIGS. 9 and 13, it is seen that the cable-end housing  200  will only fit onto the pins  232 A, B in one direction. If an operator or technician tries to turn the cable connector upside down to install it, the lip  238  does not allow for proper installation, thus negating the possibility of inadvertently connecting the cable coupler wrong, which could result in reversing the polarity of the power supply and subsequent damage to downstream equipment. 
     The second function of the connection guide  236  was mentioned with respect to the pry aperture  224  (see FIG.  9 ). During removal or disconnection of the cable-end housing  200 , it is envisioned that an operator or technician may take a flat blade screwdriver and place the blade of that screwdriver within the pry aperture  224 . The portion of the screwdriver contacting the lip  238  acts as a hinge point, and the blade portion of the screw driver within the pry aperture acts as force application point. Thus, by pushing a portion of the screw driver opposite the pry aperture, mechanical advantage is obtained in the removal of the cable-end housing  200 . 
     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.