Patent Publication Number: US-11643870-B2

Title: Covering for an architectural opening having nested rollers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 15/895,061, filed Feb. 13, 2018, and entitled “Covering for an Architectural Opening Having Nested Rollers”, which is a continuation of U.S. patent application Ser. No. 15/412,366, now U.S. Pat. No. 9,909,361, filed Jan. 23, 2017, and entitled “Covering for an Architectural Opening Having Nested Rollers”, which is a continuation of U.S. patent application Ser. No. 14/212,387, now U.S. Pat. No. 9,567,802, filed Mar. 14, 2014, and entitled “Covering for an Architectural Opening Having Nested Rollers”, which claims the benefit under 35 U.S.C. 119(e) of the earlier filing dates of U.S. Provisional Application No. 61/801,811, filed Mar. 15, 2013, and entitled “Covering for an Architectural Opening having Nested Rollers”, and U.S. Provisional Application No. 61/834,080, filed Jun. 12, 2013, and entitled “Covering for an Architectural Opening Having Nested Rollers”, which are all hereby incorporated by reference into the patent application in their entireties. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to coverings for architectural openings, and more particularly to apparatus and methods for operating a covering for an architectural opening having nested rollers. 
     BACKGROUND 
     Coverings for architectural openings, such as windows, doors, archways, and the like, have taken numerous forms for many years. Some coverings include a retractable shade that is movable between an extended position and a retracted position. In the extended position, the shade of the covering may be positioned across the opening. In the retracted position, the shade of the covering may be positioned adjacent one or more sides of the opening. 
     Some coverings, when in the fully extended position, transmit light through the material from which the covering is constructed. In some instances, even when the covering has operable vanes that open and close to control the amount of light passing through the covering, a greater amount of darkening is desired. Additionally, or alternatively, in some instances a user may desire a different pattern or appearance of the covering when in the fully extended position. Typically, these goals are accomplished by having a separate roller positioned behind the primary roller for separate actuation by the user. These separate rollers for the supplemental function or appearance increase the size of the head rail, and may require the use of a second set of control cords and operating mechanisms, thus increasing size and weight of the covering structure. 
     SUMMARY 
     Examples of the disclosure may include a covering for an architectural opening having nested rollers. In some examples, the covering may include a rotatable outer roller defining an elongated slot extending along a length of the outer roller and opening to an interior of the outer roller, a rotatable inner roller received within the outer roller and defining a central longitudinal axis, a first shade secured to the outer roller, the first shade retractable onto and extendable from the outer roller, and a second shade secured to the inner roller, with the second shade extending through the elongated slot and retractable onto and extendable from the inner roller. The elongated slot may be substantially horizontally aligned with the central longitudinal axis of the inner roller when the first shade is in a fully extended position. 
     In some examples, the inner and outer rollers are concentric about the central longitudinal axis of the inner roller. In some examples, the first and second shades have the same width. In some examples, the width of the first shade extends along the entire length of the outer roller, and the width of the second shade extends along the entire length of the inner roller. In some examples, the slot is oriented orthogonally to a direction of extension of the first shade. 
     In some examples, the covering includes a bottom rail secured to the second shade and engaging the outer roller when the second shade is in a fully retracted position. In some examples, the outer roller defines a longitudinal seat formed along the slot, and the bottom rail is received in the seat when the second shade is in the fully retracted position. In some examples, the covering includes a mounting system supporting the inner and outer rollers for rotative movement about the central longitudinal axis of the inner roller. In some examples, the covering includes an operating mechanism for selectively rotating the inner roller. 
     In some examples, the outer roller includes a first shell and a second shell each having a longitudinally-extending terminal edge, and the edges of the first and second shells are peripherally spaced apart from one another to define the elongated slot. In some examples, the covering includes a first bushing locked into one end of the first and second shells, and a second bushing locked into an opposing end of the first and second shells; wherein the first and second bushings maintain a constant width of the slot. 
     In some examples, the covering includes a lock mechanism movable between a first position restricting the rotation of the outer roller and a second position permitting rotation of the outer roller. In some examples, the lock mechanism moves from the first position to the second position upon engagement of the bottom rail with the lock mechanism. In some examples, the outer roller defines an elongated groove formed in the sidewall, the lock mechanism includes a bearing, and in the first position of the lock mechanism, the bearing is received in the groove. In some examples, the lock mechanism includes a pin, and the lock mechanism is actuated upon engagement of the pin by the bottom rail to remove the bearing from the groove. In some examples, the bearing movably engages the outer surface of the outer roller in the second position. 
     In some examples, the lock mechanism includes a locking member that pivots between the first and second positions. In some examples, the lock mechanism includes a locking member that axially translates between the first and second positions. In some examples, the lock mechanism includes a rotatable shaft positioned external to the outer roller and oriented substantially parallel to the central longitudinal axis of the inner roller. In some examples, the covering includes an end cap, the inner and outer rollers are rotatably coupled to the end cap, the lock mechanism includes a housing cantilevered from the end cap, and the rotatable shaft is journaled to the housing. In some examples, the lock mechanism includes a gear mechanism that couples rotation of the rotatable shaft and the outer roller. 
     In some examples, the covering may include a rotatable outer roller defining an elongated slot, a first shade secured to and wrappable around the outer roller, a lock mechanism positioned external to the outer roller and at least partially defining a bottom stop for the first shade, a rotatable inner roller received within the outer roller, a second shade secured to and wrappable around the inner roller, the second shade extendable and retractable through the elongated slot, and a non-rotatable shaft extending within the inner roller and at least partially defining a bottom stop for the second shade. 
     In some examples, the lock mechanism includes a rotatable shaft positioned external to the outer roller, and a locking member that axially translates along the rotatable shaft. In some examples, the lock mechanism includes a pivotable locking member positioned external to the outer roller. 
     Examples of the disclosure may include a method of operating a covering for an architectural opening. In some examples, the method includes unwrapping a first shade from a periphery of an outer roller, upon the first shade reaching a fully extended position, unwrapping a second shade from a periphery of an inner roller positioned within the outer roller, wherein unwrapping the second shade comprises extending the second shade through an elongated slot formed in the outer roller and positioned in substantial horizontal alignment with a central longitudinal axis of the inner roller. 
     In some examples, the method includes pivoting a locking member into locking engagement with the outer roller to lock rotation of the outer roller, rotating the inner roller relative to the outer roller to retract the second shade onto the inner roller through the elongated slot formed in the outer roller, pivoting the locking member out of locking engagement with the outer roller at a fully retracted position of the inner roller to allow the outer roller to rotate, and rotating the outer roller by driving the inner roller to retract the first shade onto the outer roller. 
     In some examples, the method includes during extension of the first shade, axially traversing a locking member external to the periphery of the outer roller, restricting rotation of the outer roller with the locking member upon the first shade reaching the fully extended position, during extension of the second shade, axially traversing a nut positioned within the inner roller, and restricting rotation of the inner roller with the nut upon the second shade reaching a fully extended position. 
     The disclosure is given to aid understanding, and one of skill in the art will understand that each of the various aspects and features of the disclosure may advantageously be used separately in some instances, or in combination with other aspects and features of the disclosure in other instances. Accordingly, while the disclosure is presented in terms of examples, it should be appreciated that individual aspects of any example can be claimed separately or in combination with aspects and features of that example or any other example. 
     The present disclosure is set forth in various levels of detail in this application and no limitation as to the scope of the claimed subject matter is intended by either the inclusion or non-inclusion of elements, components, or the like in this summary. In certain instances, details that are not necessary for an understanding of the disclosure or that render other details difficult to perceive may have been omitted. It should be understood that the claimed subject matter is not necessarily limited to the particular examples or arrangements illustrated herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate examples of the disclosure and, together with the general description given above and the detailed description given below, serve to explain the principles of these examples. 
         FIG.  1    is an isometric view of a covering with first and second shades in fully-retracted positions in accordance with some examples of the present disclosure. 
         FIG.  2    is an isometric view of the covering of  FIG.  1    with a first shade in a partially-extended position and a second shade in a fully-retracted position in accordance with some examples of the present disclosure. 
         FIG.  3    is an isometric view of the covering of  FIG.  1    with a first shade in a fully-extended position and a second shade in a fully-retracted position in accordance with some examples of the present disclosure. 
         FIG.  4    is an isometric view of the covering of  FIG.  1    with a first shade in a fully-extended position and a second shade in a partially-extended position in accordance with some examples of the present disclosure. 
         FIG.  5    is an isometric view of the covering of  FIG.  1    with first and second shades in fully-extended positions in accordance with some examples of the present disclosure. 
         FIG.  6    is an isometric, partially-exploded view of head rail components of a covering in accordance with some examples of the present disclosure. The head rail cover and the first and second shades are not shown for clarity. 
         FIG.  7    is a lengthwise cross-sectional view of a covering taken along line  7 - 7  of  FIG.  1    with the head rail components of  FIG.  6    in accordance with some examples of the present disclosure. 
         FIG.  8    is a transverse cross-sectional view of a covering taken along line  8 - 8  of  FIG.  2    with the head rail components of  FIG.  6    in accordance with some examples of the present disclosure. 
         FIG.  9    is a transverse cross-sectional view of a covering taken along line  9 - 9  of  FIG.  3    with the head rail components of  FIG.  6    in accordance with some examples of the present disclosure. 
         FIG.  10    is a transverse cross-sectional view of a covering taken along line  10 - 10  of  FIG.  4    with the head rail components of  FIG.  6    in accordance with some examples of the present disclosure. 
         FIG.  11    is a transverse cross-sectional view of a covering taken along line  11 - 11  of  FIG.  5    with the head rail components of  FIG.  6    in accordance with some examples of the present disclosure. 
         FIG.  12    is an isometric view of head rail components of a covering in accordance with some examples of the present disclosure. The head rail cover is not shown for clarity. 
         FIG.  13    is an isometric, partially-exploded view of the head rail components of  FIG.  12    in accordance with some examples of the present disclosure. 
         FIG.  14    is a transverse cross-sectional view of the head rail components of  FIG.  12    taken along line  14 - 14  of  FIG.  12    in accordance with some examples of the present disclosure. 
         FIG.  15    is a side elevation view of some of the head rail components of  FIG.  12    depicting three intermeshed gears rotatably supported on an end cap of a covering in accordance with some examples of the present disclosure. 
         FIG.  16    is an isometric view of a lock mechanism of the head rail components of  FIG.  12    in accordance with some examples of the present disclosure. 
         FIG.  17    is a side elevation view of the lock mechanism of  FIG.  16    in accordance with some examples of the present disclosure. 
         FIG.  18    is another isometric view of the lock mechanism of  FIG.  16    in accordance with some examples of the present disclosure. 
         FIG.  19    is a side elevation view of a dual roller unit attached to the lock mechanism of  FIG.  16    in accordance with some examples of the present disclosure. 
         FIG.  20    is a detail view of a locking interface between first and second shells of an outer roller of the dual roller unit of  FIG.  19    in accordance with some examples of the present disclosure. 
         FIG.  21    is a front elevation view of a housing of the lock mechanism of  FIG.  16    in accordance with some examples of the present disclosure. 
         FIG.  22    is a side elevation view of the housing of  FIG.  21    in accordance with some examples of the present disclosure. 
         FIG.  23    is a shaft of the lock mechanism of  FIG.  16    in accordance with some examples of the present disclosure. 
         FIG.  24    is an isometric view of a nut of the lock mechanism of  FIG.  16    in accordance with some examples of the present disclosure. 
         FIG.  25    is another isometric view of the nut of  FIG.  24    in accordance with some examples of the present disclosure. 
         FIG.  26    is a front elevation view of the shaft of  FIG.  23    rotatably supported in the housing of  FIG.  21    and the nut of  FIG.  24    threadedly mounted onto the shaft, with the housing and nut shown in lengthwise cross-section, in accordance with some examples of the present disclosure. 
         FIG.  27    is a transverse cross-sectional view of the housing, the nut, and the shaft of  FIG.  26    taken along line  27 - 27  of  FIG.  26    in accordance with some examples of the present disclosure. 
         FIG.  28    is an isometric, partially-exploded view of head rail components of a covering in accordance with some examples of the present disclosure. The head rail cover and the second shade are not shown for clarity. 
         FIG.  29    is another isometric, partially-exploded view of the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
         FIG.  30    is a transverse cross-sectional view of a covering taken along line  30 - 30  of  FIG.  5    with the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
         FIG.  31    is a transverse cross-sectional view of a covering taken along line  31 - 31  of  FIG.  3    with the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
         FIG.  32    is a transverse cross-sectional view of the covering of  FIG.  31    with a bottom rail seated against the outer roller and a lock mechanism unseated from the outer roller in accordance with some examples of the present disclosure. 
         FIG.  33    is a transverse cross-sectional view of the covering of  FIG.  32    with the outer roller rotated counterclockwise relative to the position of the outer roller in  FIG.  32    in accordance with some examples of the present disclosure. 
         FIG.  34    is a transverse cross-sectional view of a covering taken along line  34 - 34  of  FIG.  4    with the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
         FIG.  35    is a transverse cross-sectional view of the covering of  FIG.  31    with the inner roller and second shade removed for clarity in accordance with some examples of the present disclosure. 
         FIG.  36    is a transverse cross-sectional view of the covering of  FIG.  32    with the inner roller and second shade removed for clarity in accordance with some examples of the present disclosure. 
         FIG.  37    is a transverse cross-sectional view of the covering of  FIG.  33    with the inner roller and second shade removed for clarity in accordance with some examples of the present disclosure. 
         FIG.  38    is an isometric view of a lock mechanism of the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
         FIG.  39    is another isometric view of the lock mechanism of  FIG.  38    in accordance with some examples of the present disclosure. 
         FIG.  40    is an isometric view of a bracket of the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
         FIG.  41    is an isometric view of the lock mechanism of  FIG.  38    rotatably mounted onto the bracket of  FIG.  40    in accordance with some examples of the present disclosure. 
         FIG.  42    is a fragmentary isometric view of some of the head rail components of  FIG.  28    and depicts the interface of the lock mechanism of  FIG.  38    with a bottom rail of the covering in accordance with some examples of the present disclosure. 
         FIG.  43    is a fragmentary isometric view of some of the head rail components of  FIG.  28    and depicts the interface of the lock mechanism of  FIG.  38    with a bottom rail of the covering in accordance with some examples of the present disclosure. 
         FIG.  44    is a fragmentary view of an end of the bottom rail of  FIGS.  42  and  43    in accordance with some examples of the present disclosure. 
         FIG.  45    is an isometric view of an actuator rim of the bottom rail of  FIG.  44    in accordance with some examples of the present disclosure. 
         FIG.  46    is a lengthwise cross-sectional view of one end of a covering taken along line  7 - 7  of  FIG.  1    with the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
         FIG.  47    is a lengthwise cross-sectional view of another end of a covering taken along line  7 - 7  of  FIG.  1    with the head rail components of  FIG.  28    in accordance with some examples of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure provides a covering for an architectural opening. In general, the covering may include a first shade and a second shade both suspended from the same head rail by a pair of nested rollers forming a dual roller unit. The first shade (front shade in this configuration) is engaged with an outer roller for retraction onto and extension therefrom by wrapping around and unwrapping from the outer roller as actuated by a user. The second shade (rear shade in this configuration) is engaged with an inner roller, which is positioned inside the outer roller, for retraction onto and extension therefrom by wrapping around and unwrapping from the inner roller as actuated by the user. The inner roller may be positioned inside the outer roller and collectively the inner and outer rollers may form a roller unit, as further described below. The second shade may be extended and retracted as directed by the user when the first shade is in the fully extended position. The operating unit that causes the rollers to rotate as directed by the user may be operated by, for example, a motor or a single control cord. The operating unit may engage and control the rotation of the inner roller, which in turn may control the rotation of the outer tube. 
     Referring to  FIGS.  1 - 5   , a retractable covering  10  for an architectural opening is provided. The retractable covering  10  may include a head rail  14 , a first bottom rail  18 , a second bottom rail  20 , a first shade  22 , and a second shade  24 . The first shade  22  may extend between the head rail  14  and the first bottom rail  18 . The second shade  24  may extend between the head rail  14  and the second bottom rail  20 . The head rail  14  may include two opposing end caps  26   a ,  26   b , which may enclose the ends of the head rail  14  to provide a finished appearance. The first bottom rail  18  may extend horizontally along a lower edge of the first shade  22  and may function as a ballast to maintain the first shade  22  in a taut condition. The second bottom rail  20  may extend horizontally along a lower edge of the second shade  24  and may function as a ballast to maintain the second shade  24  in a taut condition. 
     The first shade  22  may include vertically suspended front  30  and rear  34  sheets of flexible material (such as sheer fabric) and a plurality of horizontally-extending, vertically-spaced flexible vanes  38 . Each of the vanes  38  may be secured along horizontal lines of attachment with a front edge attached to the front sheet  30  and a rear edge attached to the rear sheet  34 . The sheets  30 ,  34  and vanes  38  may form a plurality of elongated, vertically-aligned, longitudinally-extending cells, which collectively may be referred to as a cellular panel. The sheets  30 ,  34  and/or the vanes  38  may be constructed of continuous lengths of material or may be constructed of strips of material attached or joined together in an edge-to-edge, overlapping, or other suitable relationship. The second shade  24  may be a single panel and may be constructed of strips of material attached or joined together in an edge-to-edge, overlapping, or other suitable relationship. 
     The first and second shades  22 ,  24  may be constructed of substantially any type of material. For example, the shades  22 ,  24  may be constructed from natural and/or synthetic materials, including fabrics, polymers, and/or other suitable materials. Fabric materials may include woven, non-woven, knits, or other suitable fabric types. The shades  22 ,  24  may have any suitable level of light transmissivity. For example, the first and second shades  22 ,  24  may be constructed of transparent, translucent, and/or opaque materials to provide a desired ambience or decor in an associated room. In some examples, the first shade  22  includes sheets  30 ,  34  that are transparent and/or translucent, and vanes  38  that are translucent and/or opaque. In some examples, the second shade  24  is made of a single sheet of material with zero light transmissivity, often referred to as a black-out shade. The second shade  24  may include patterns or designs so that when the second shade  24  is extended behind the first shade  22 , the second shade  24  creates a different aesthetic appearance than the first shade  22  by itself. 
     Referring to  FIGS.  1 - 6   , the covering  10  may include a drive or operating mechanism  40  configured to raise or retract the first shade  22 , the second shade  24 , or both. The operating mechanism  40  may be controlled mechanically and/or electrically. The operating mechanism  40  may include a speed governing device to control or regulate the extension or lowering speed of the shades  22 ,  24 . 
     In some examples, the operating mechanism  40  may include an operating element  42  (such as a ball chain, a cord, or a wand) to allow the user to extend or retract the first and/or second shades  22 ,  24 . To move the shades  22 ,  24 , an operator may manipulate the operating element  42 . For example, to raise or retract the shades  22 ,  24  from an extended position, the operator may pull the operating element  40  in a downward direction. To extend or lower the shades  22 ,  24  from a retracted position, the operator may manipulate the operating element  42  to release a brake, which may allow the shades  22 ,  24  to automatically lower under the influence of gravity. 
     Additionally, or alternatively, the operating mechanism  40  may include an electric motor  44  configured to extend or retract the shades  22 ,  24  upon receiving an extension or retraction command. The motor  44  may be hard-wired to a switch and/or operably coupled to a receiver that is operable to communicate with a transmitter, such as a remote control unit  46 , to permit a user to control the motor  44  and thus the extension and retraction of the shades  22 ,  24 . The motor  44  may include a gravity lower state to permit the shades  22 ,  24  to lower via gravity without motor intervention, thereby reducing power consumption. 
     Referring to  FIG.  6   , the covering  10  may include a dual roller unit  46 , which may be disposed within the head rail  14 . The dual roller unit  46  may include an inner roller  48  and an outer roller  50 . The inner roller  48  may be positioned inside the outer roller  50 , and the rollers  48 ,  50  may be coaxially aligned about the same rotational axis  52 . The rollers  48 ,  50  may be concentric about a central axis of the inner roller  48 . 
     Referring to  FIGS.  6  and  7   , the inner roller  48  may be generally cylindrical in shape and may be formed as a tube. The second shade  24  may be attached at a top edge to the inner roller  48  by adhesive, corresponding retention features, or other suitable attachment means. In some examples, a longitudinally-extending recess  52  is formed in the circumferential wall of the inner roller  48  and may receive an adhesive bead configured to adhere the top edge of the second shade  24  to the inner roller  48 . 
     The outer roller  50  may be generally cylindrical in shape and may surround the inner roller  48 . The outer roller  50  may be formed of two pieces that interlock with one another. Referring to  FIG.  6   , the outer roller  50  may include a first shell  54  and a second shell  56  that nest together. Referring to  FIGS.  6  and  8 - 11   , longitudinally-extending edge portions  58 ,  60  of the first and second shells  54 ,  56 , respectively, may overlap and interlock with one another. The first shade  22  may be attached at a top edge to the outer roller  50  by adhesive, corresponding retention features, or other suitable attachment means. In some examples, a pair of channels  62  is formed in the circumferential wall of the outer roller  50  and configured to receive and secure the top edges of the first shade  22 . Referring to  FIGS.  8 - 11   , inserts  64  may be positioned in a hem formed on each of the top edges and may act to retain the top edges in the respective channels  62 . 
     Referring to  FIG.  7   , the inner and outer rollers  48 ,  50  may extend substantially the entire distance between the right and left end caps  26   a ,  26   b . The inner and outer rollers  48 ,  50  may have the same or substantially the same length. The first and second shades  22 ,  24  may have the same or substantially the same width, which may be equivalent to the length of the rollers  48 ,  50 . In some examples, the first and second shades  22 ,  24  have equivalent widths that match the length of the inner and outer rollers  48 ,  50 , which may eliminate the existence of a light gap between the edges of the shades  22 ,  24  and the sides of the architectural opening. 
     Referring to  FIGS.  6  and  7   , the dual roller unit  50  may be rotatably supported by the opposing end caps  26   a ,  26   b . The operating mechanism  40  may be anchored to the right end cap  26   a  and may be actuated, for example, by the operating element  42  or the remote control unit  46 . The operating mechanism  40  may be operably associated with the inner roller  48  to cause it to rotate. The operating mechanism  40  may include an internal fitting  64 , which may be received within the inner roller  48  and may tightly engage the wall of the inner roller  48 . The internal fitting  64  may be driven in rotation by the operating mechanism  40 , such as the motor  44 , and thus may drive the inner roller  48  in rotation. The operating mechanism  40  may include a planetary gear drive often utilized in window covering applications. 
     Continuing with  FIGS.  6  and  7   , a limit screw  66  may be positioned inside the inner roller  48  and may be fixed to the left end cap  26   b  such that the limit screw  66  does not rotate. A limit nut  68  may be threadedly engaged with the limit screw  66  and may be rotationally keyed to the wall of the inner roller  48 . The key structure may allow movement of the limit nut  68  along the length of the inner roller  48 . As the inner roller  48  rotates, the limit nut  68  may move along the threaded limit screw  66 , and may engage a limit stop formed on the limit screw  66  to define the lowermost extended position of the second shade  24  (see  FIG.  5   ). Additionally, or alternatively, a top limit stop may be employed on the limit screw  66  if desired. 
     Referring to  FIG.  6   , right and left bushings  70   a ,  70   b  may be axially aligned with the inner roller  48  and may be disposed adjacent opposing ends of the inner roller  48 . The right bushing  70   a  may be rotatably mounted onto the operating mechanism  40 , and the left bushing  70   b  may be rotatably mounted onto the limit screw  66 . The bushings  70   a ,  70   b  may lock into the ends of the outer roller  50  to maintain a desired spatial relationship between the shells  54 ,  56 . The bushings  70   a ,  70   b  each may include a pair of axial projections  72   a ,  72   b . One of the projections  72   a  may engage the first shell  54 , and the other projection  72   b  may engage the second shell  56 . When the bushings  70   a ,  70   b  are engaged with the opposing ends of the outer roller  50 , the bushings  70   a ,  70   b  and the outer roller  50  may rotate in unison about the rotation axis  52  of the inner and outer rollers  48 ,  50 . 
     Referring to  FIGS.  8 - 11   , the first and second shells  54 ,  56  of the outer roller  50  each may define a retention feature that snugly receives the axial projections  72   a ,  72   b  of the bushings  70   a ,  70   b . The retention feature may be formed as circumjacently-spaced shelves  74  that extend inwardly from the outer roller  50  into an interior space defined by the outer roller  50 . When the bushings  70   a ,  70   b  are engaged with the ends of the outer roller  50 , the axial projections  72   a ,  72   b  may be snugly received between the shelves  74  and the circumferential wall of the outer roller  50  to prevent relative movement between the first and second shells  54 ,  56 . 
     Continuing with  FIGS.  8 - 11   , the first and second shells  54 ,  56  may define a slot  76  extending along a length of the outer roller  50  and in communication with the interior of the outer roller  50 . The slot  76  permits passage of the second shade  24  during extension and retraction of the second shade  24 . When the first end portions  58 ,  60  of the first and second shells  54 ,  56 , respectively, are interlocked together, second longitudinally-extending edge portions  78 ,  80  of the first and second shells  54 ,  56  may be peripherally spaced apart from one another to define the slot  76 . The confronting second edge portions  78 ,  80  of the first and second shells  54 ,  56  may be spaced a sufficient distance from one another to permit passage of the second shade  24  yet prevent passage of the bottom rail  20  of the second shade  24 . The axial projections  72   a ,  72   b  of the bushings  70   a ,  70   b  may maintain the width of the slot  76  during operation of the covering  10 . The slot  76  may be positioned on the outer roller  50  so as to be located above and adjacent to the rearward most of the pair of channels  62  when the first shade  22  is in its extended, vane-open configuration. 
     With continued reference to  FIGS.  8 - 11   , the outer roller  50  may define a recessed seat  81  in the circumferential wall on both sides of the slot  76 . The seat  81  may be formed as a recess extending along the length of the slot  76 . The seat  81  may include a generally vertically-oriented base wall  84  spanning the slot  76  and formed by the opposing edge portions  78 ,  80  of the outer roller  50 . The seat  81  may be configured to receive the second bottom rail  20  when the second shade  24  is in the fully retracted position (see  FIG.  8   ). The base wall  84  may allow a relatively vertical-tangential engagement and disengagement between the second bottom rail  20  and the outer roller  50 . The slot  76  and the seat  81  may be positioned on the circumference of the outer roller  50  above the attachment point  62  of the rear sheet  34  of the first shade  22 , and the position of the slot  76  and the seat  81  may be referred to in  FIGS.  9 - 11    as 3 o&#39;clock. The location of the seat  81  and the slot  76  near the furthest rearward position on the circumference of the outer roller  50 , along with the shape of the seat  81 , may allow for secure receipt of the second bottom rail  20  as it is pulled vertically up and into the seat  81  during retraction (see  FIGS.  8 - 10   ). 
     The shape of the seat  81  and its orientation on the outer roller  50  may encourage smooth and predictable disengagement of the second bottom rail  20  from the seat  81  to begin the extension of the second shade  24 . The shape and orientation of the seat  81  may allow the bottom rail  20  to drop vertically out of the seat  81 , which takes advantage of the force of gravity on the relatively heavy bottom rail  20 . The generally tangential orientation of the seat  81  on the outer roller  50  may assist in this regard. The lower free edge of the slot  76  (defined by the edge portion  80  of the second shell  56  of the outer roller  50 ) may be curved or rounded to allow for smooth travel of the second shade  24  over the edge portion  80  as the second shade  24  is extended and retracted through the slot  76 . 
     The second bottom rail  20  may be an elongated member, having relatively high mass, and defining a groove running along its length to receive and retain a lower edge of the second shade  24 . The lower edge of the second shade  24  may be held in the groove of the bottom rail  20  by an insert  82  positioned in a hem formed in the lower edge of the second shade  24 . A portion of the profile of the second bottom rail  20  may generally match the shape of the seat  81  formed in the outer roller  50  to conform thereto when the second shade  24  is in the retracted position. 
     Referring to  FIGS.  7 - 11   , the first shade  22  may be coupled to and wrappable about the outer roller  50 . An upper edge of each of the front and rear sheets  30 ,  34  may be attached to the outer roller  50  at circumferentially-spaced locations. The first shade  22  may be wrapped about or unwrapped from a rear side of the outer roller  50 , with the rear side of the roller  50  positioned between a front side of the roller  50  and a street side of an associated architectural opening (in  FIGS.  8 - 11   , the rear side of the roller  50  is to the right). Generally, rotation of the outer roller  50  in a first direction (counterclockwise in  FIGS.  8 - 11   ) retracts the first shade  22  by winding it about the outer roller  50  to a position adjacent one or more sides (such as the top side) of an associated architectural opening, and rotation of the outer roller  50  in a second, opposite direction extends the first shade  22  across the opening (such as to the bottom side). 
     Referring still to  FIGS.  7 - 11   , the second shade  24  may be coupled to and wrappable about the inner roller  48 . An upper edge of second shade  24  may be attached to the inner roller  48 , as discussed previously. The second shade  24  may be wrapped about or unwrapped from a rear side of the roller unit  46 , with the rear side of the roller unit  46  positioned between a front side of the roller unit  46  and a street side of an associated architectural opening (in  FIGS.  8 - 11   , the rear side of the roller unit  46  is to the right). Generally, rotation of the inner roller  48  in a first direction (counterclockwise in  FIGS.  8 - 11   ) retracts the second shade  24  by winding it about the inner roller  48  to a position adjacent one or more sides (such as the top side) of an associated architectural opening, and rotation of the inner roller  48  in a second, opposite direction extends the second shade  24  across the opening (such as to the bottom side). 
     The operation of the covering is described below with reference to  FIGS.  1 - 5  and  7 - 11   . As shown in  FIGS.  1  and  7   , the first and second shades  22 ,  24  are in fully-retracted positions and concealed within the head rail  14 . In this configuration (see  FIG.  7   ), the second shade  24  is fully wrapped about the inner roller  48  and the first shade  22  is fully wrapped about the outer roller  50 . In some examples, the first bottom rail  18  engages a portion of the head rail  14  to define a top limit stop. 
     To extend the first shade  22  from the head rail  14 , the user may actuate the operating mechanism  40  to cause the inner roller  48  to rotate in an extension direction (clockwise in  FIGS.  8 - 11   ), which in turn causes the outer roller  50  to rotate in an extension direction (clockwise in  FIGS.  8 - 11   ) due at least in part to the weight of the first bottom rail  18  applying a downward force to the first shade  22 . As the first shade  22  extends off of the rear of the outer roller  50 , the outer roller  50  generally rotates in unison with the inner roller  48 . The dual roller unit  46  generally rotates in the direction the user controls the inner roller  48  to rotate. 
     Referring to  FIGS.  2  and  8   , the first shade  22  extends off of the rear of the outer roller  50  in a closed or collapsed configuration in which the front and rear sheets  30 ,  34  are relatively close together and the vanes  38  extend vertically in an approximately coplanar, contiguous relationship with the front and rear sheets  30 ,  34 . Once the first shade  22  is substantially unwrapped from the outer roller  50 , continued rotation of the outer roller  50  in the extension direction moves the front and rear sheets  30 ,  34  generally vertically relative to each other to shift the vanes  38  from a closed position ( FIGS.  2  and  8   ) to an open position ( FIGS.  3  and  9   ). A rear portion of the first bottom rail  18  may be weighted more than a front portion of the bottom rail  18  to facilitate the full opening of the vanes  38 . 
     Referring to  FIGS.  3  and  9   , the covering  10  is shown with the first shade  24  in a fully extended position with the vanes  38  in an open or expanded configuration. In this position, the front and rear sheets  30 ,  34  are horizontally spaced with the vanes  38  extending substantially horizontally therebetween, and the attachment points  62  of the front and rear sheets  30 ,  34  with the outer roller  50  may be disposed at the same height. In  FIG.  9   , for instance, the positions of the attachment points  62  may be referred to as being at 4 o&#39;clock and 8 o&#39;clock, and are disposed at substantially the same level with each other. Rotation of the outer roller  50  in either direction from that shown in  FIG.  9    causes the front and rear sheets  30 ,  34  to move toward one another and the vanes  38  to re-orient into more vertical alignment. 
     When the first shade  22  is fully unwrapped from the outer roller  50 , the slot  76  in the outer roller  50  is rotationally oriented within the head rail  14  such that the bottom rail  20  of the second shade  24  may drop vertically out of the seat  81  upon further rotation of the inner roller  48  in the extension direction. The generally tangential orientation and generally vertical positioning of the seat  81 , with a relatively vertical base wall  84  (see  FIGS.  10  and  11   ), allows the weight of the second bottom rail  20  to unseat the bottom rail  20  from the outer roller  50  when the tension in the second shade  24  is decreased due to continued rotation of the inner roller  48  in the extension direction. The operating mechanism  40  may include a brake system operably coupled to the inner roller  48  to restrict unwanted downward movement of the second shade  24 , and thus of the first shade  22 . 
     In order to extend the second shade  24 , the operating mechanism  40  is further actuated by the user to rotate the inner roller  48  in the extension direction. During extension of the second shade  24  (see  FIGS.  4  and  10   ), the outer roller  50  and the first shade  22  may remain stationary due to the weight of the first shade  22  and the weight of the first bottom rail  18  maintaining the rotational position of the outer roller  50 , without a positive lock. In some examples, as discussed below, a positive lock may be used to prevent rotation of the outer roller  50  upon full extension of the first shade  22 . As shown in  FIGS.  10  and  11   , during extension of the second shade  24 , the slot  76  defined in the outer roller  50  may be directed rearwardly and may be substantially horizontally aligned with the rotational axis  52  (see  FIG.  6   ) of the inner and outer rollers  48 ,  50 . In other words, the second shade  24  may deploy off of the rear side of the inner and outer rollers  48 ,  50 . 
     During extension of the second shade  24 , the inner roller  48  rotates relative to the outer roller  50 , with the fitting  64  and the limit nut  68  supporting the respective ends of the inner roller  48 . As the inner roller  48  rotates in the extension direction, the second shade  48  is unwound from the inner roller  48  as it is extended through the slot  76  formed in the outer roller  50 . The rotation of the inner roller  48  in the extension direction moves the limit nut  68  along the limit screw  66  towards the bottom limit stop. 
     Referring to  FIGS.  5  and  11   , the covering  10  is shown with the first and second shades  22 ,  24  both in the fully extended positions with the vanes  38  in an open or expanded configuration. In this position, the front and rear sheets  30 ,  34  are horizontally spaced with the vanes  38  extending substantially horizontally therebetween. The second shade  24  may be a blackout shade and inhibit light from passing through the second shade  24 , and thus through the first shade  22 . When the second shade  24  is fully extended (see  FIGS.  5  and  11   ), the second shade  24  may be offset rearwardly from the first shade  22 , but may extend coextensively in length and width with the first shade  22 . To control the amount of light passing through the first shade  22 , the second shade  24  may be withdrawn into the head rail  14  and wrapped about the inner roller  48  of the dual roller unit  46 . 
     When the second shade  24  is in the fully extended position (lowermost extension), the limit nut  68  may be positioned on the limit screw  66  (see  FIG.  6   ) in engagement with a lower limit stop formed on the limit screw  66  to prevent further rotation of the inner roller  48 . The limit screw  66  also may include an upper limit stop to define the upper limit of the covering  10 . Alternatively, the bottom rail  18  of the first shade  22  may engage a portion of the head rail  14  when the first shade  22  is fully retracted to serve as the upper limit stop of the covering  10 . 
     At any point during the extension process, the user may stop the operating mechanism  40  or reverse the direction of the operating mechanism  40  to move the first and second shades  22 ,  24  into a desired position. In examples including a motorized covering  10 , pre-programmed commands may be used to control the motor  44  and thus control the position of the first and second shades  22 ,  24 . The commands may instruct the motor  44  to move the first and second shades  22 ,  24  into predetermined shade positions, such as a first position in which the first and second shades  22 ,  24  are fully retracted, a second position in which the first shade  22  is fully extended and the second shade  24  is fully retracted, and a third position in which the first and second shades  22 ,  24  are fully extended. The commands may be transmitted to the motor  44  by the remote control unit  46 . 
     Retraction of the first and second shades  22 ,  24  may be accomplished in reverse order as compared to the extension sequence described above, such as generally following  FIG.  11    to  FIG.  8   . In  FIGS.  5  and  11   , the first and second shades  22 ,  24  are disposed in fully extended positions. When both the first and second shades  22 ,  24  are in the fully extended position, the limit nut  68  (see  FIG.  6   ) may be engaged with a lower limit stop, which may be formed on the limit screw  66 . Actuation of the operating mechanism  40 , such as by the operating element  42  and/or the motor  44 , from this position moves the limit nut  68  axially away from the lower limit stop and begins the retraction process of the covering  10 . The retraction process generally involves actuation of the operating mechanism  40  to first rotate the inner roller  48  in a retraction direction (counterclockwise in  FIG.  11   ) to retract the second shade  24 , and when the second shade  24  is fully retracted, the outer roller  50  is then rotated in a retraction direction (counterclockwise in  FIG.  11   ) to retract the first shade  22  onto the outer roller  50 . This sequence is described further below. 
     To retract the second shade  24  from the fully extended position of  FIGS.  5  and  11   , the user actuates the operating mechanism  40  to cause the inner roller  48  to rotate in a retraction direction (counterclockwise in  FIGS.  8 - 11   ), which in turn wraps the second shade  24  about the inner roller  48  and raises the second bottom rail  20  upwardly along a rear face of the rear sheet  34  of the first shade  22 . During retraction of the second shade  24 , the inner roller  48  rotates relative to the outer roller  50 , with the fitting  64  and the limit nut  68  supporting the respective ends of the inner roller  48 . As the inner roller  48  rotates in the retraction direction, the second shade  24  is wound onto the inner roller  48  as it is pulled through the slot  76  formed in the outer roller  50 . The rotation of the inner roller  48  in the retraction direction moves the limit nut  68  along the limit screw  66  towards the opposite end of the limit screw  66 . Also during the retraction of the second shade  24 , the first shade  22  remains in the fully extended, open position due to the weight of the first bottom rail  18  and the weight of the portion of the first shade  22  suspended from the outer roller  50  acting upon the outer roller  50  to inhibit rotation of the outer roller  50 . This allows the user to move the second shade  24  between fully extended and fully retracted positions without affecting the position or orientation of the first shade  22 . 
     Referring to  FIGS.  9  and  10    in reverse order, as the second shade  24  is further withdrawn into the outer roller  50 , the second bottom rail  20  becomes securely positioned in the seat  81 . Upon the bottom rail  20  engaging the seat  81  of the outer roller  50 , the driving force of the operating mechanism  40  may be transferred through the second shade  24  to the outer roller  50 . That is, the operating mechanism  40  may apply a rotational force to the inner roller  48 , which in turn may be applied to the outer roller  50  through the engagement of the bottom rail  20  in the seat  81  under the tension of the second shade  24 . Referring to  FIGS.  8  and  9   , when the second shade  24  is fully wrapped onto the inner roller  48  and the second bottom rail  20  is received in the seat  81  of the outer roller  50 , the outer roller  50  may be driven in a retraction direction (counterclockwise in  FIGS.  8  and  9   ) by the operating mechanism  40 , through rotation of the inner roller  48  in the same retraction direction. As such, when the bottom rail  20  is received in the seat  81  and a retraction force (counterclockwise in  FIGS.  8  and  9   ) is applied to the inner roller  48  by the operating mechanism  40 , the outer roller  50  generally rotates in conjunction with the inner roller  48 . 
     Referring to  FIG.  8   , as the outer roller  50  continues to rotate in the retraction direction, the first shade  22  wraps around the outer roller  50 . The first shade  22  is under tension as it is wrapped around the outer roller  50  due to the suspended portion of the first shade  22  and the weight of the bottom rail  18 . 
     When the first shade  22  is fully retracted, the first bottom rail  18  may engage a portion of the head rail  14 , such as an abutment, to serve as a top limit stop for the dual roller unit  46 . It is contemplated that other mechanisms may be utilized to define the top retraction position, including a top limit stop positioned on the limit screw  66  opposite the bottom limit stop. For example, a top limit stop may be formed on the limit screw  66  and positioned along the screw  66  such that the nut  68  engages the top limit stop upon full retraction of the first shade  22 . 
     As explained above, the retraction of the second shade  24  and then the first shade  22  from the fully extended position occurs with the user actuating a single operating element  42  or a motor  44  for the retraction of both shades  22 ,  24 . The limit screw  66  includes a sufficient length to allow the limit nut  68  to move along the screw  66  from the bottom limit stop until the top retracted position is attained. It is contemplated that the first shade  22  may be wrapped about or unwrapped from the front side of the outer roller  42 . Accompanying modifications to the structure described herein would be necessary to facilitate the implementation of the dual roller shade technology as applied to a front-descending shade structure. 
     The covering may include a lock mechanism that restricts rotation of the outer roller  50  when the first shade  22  is in the fully extended position, thereby ensuring the first shade  22  remains in the fully extended position and is substantially unaffected by rotation of the inner roller  48  during extension of the second shade  24 . The lock mechanism may be movable (such as pivotable, translatable, or other suitable movements) between a first position that restricts rotation of the outer roller  50  and a second position that permits rotation of the outer roller  50 . In one example, the lock mechanism includes a locking member positioned external to the outer roller  50  that translates longitudinally along an outer periphery of the outer roller  50  and engages a stop to restrict rotation of the outer roller  50 . In another example, the lock mechanism includes a locking member positioned external to the outer roller  50  that pivots into engagement with the outer roller  50  to restrict rotation of the outer roller  50 . 
     Referring to  FIGS.  12 - 27   , a covering for an architectural opening is provided that uses a lock mechanism to positively lock rotation of the outer roller upon full extension of the first shade  22 . With the exception of a lock mechanism and retaining clips, the covering depicted in  FIGS.  12 - 27    generally has the same features and operation as the covering depicted in  FIGS.  1 - 11   . Accordingly, the preceding discussion of the features and operation of the covering depicted in  FIGS.  1 - 11    should be considered generally applicable to the covering depicted in  FIGS.  12 - 27   , except as noted in the following discussion. The reference numerals used in  FIGS.  12 - 27    generally correspond to the reference numerals used in  FIGS.  1 - 11    to reflect the similar parts and components, except the reference numerals are incremented by one hundred. 
     Referring to  FIG.  12   , the covering  110  includes an axially movable lock mechanism  186  that, similar to the pivotally movable lock mechanism discussed below in connection with  FIGS.  28 - 47   , restricts rotation of the outer roller  50  when the first shade  22  is in the fully extended position. The axially movable lock mechanism  186  may include a housing  187 , a rotatable shaft  188  journaled to the housing  187 , and a nut  189  threadedly engaged with and travelable axially along the shaft  188 . Although the axially movable lock mechanism  186  is depicted in conjunction with the left end cap  126   b , the lock mechanism  186  may be used in conjunction with the right end cap  126   a.    
     Referring to  FIGS.  12 ,  16 , and  18   , the housing  187  may be cantilevered from the left end cap  126   b  and extend axially away from the left end cap  126   b  along an outer periphery of the outer roller  150  towards the right end cap  126   a . One end  187   a  of the housing  187  may be removably connected to the left end cap  126   b  with a fastener  190 , and an opposing, free end  187   b  of the housing  187  may be positioned laterally outward of the outer roller  150 . The housing  187  may be laterally separated from the periphery of the outer roller  150  by a sufficient distance so as to not interfere with the wrapping or unwrapping of the first shade (not shown) about or from the outer roller  150 . The housing  187  may be laterally separated from the periphery of the outer roller  150  by a uniform distance. 
     With reference to  FIGS.  16 ,  18 ,  21 , and  26   , the opposing end portions  187   a ,  187   b  of the housing  187  may include axially-extending collars  191  and abutment flanges  192  extending outward from the collars  191 . The collars  191  may include an internal wall  193  (see  FIGS.  22  and  26   ) that defines a shaft aperture  194  that receives a journal portion  195  of the rotatable shaft  188 , which rotatably bears against the internal wall  193 . The internal wall  193  of the collar  191  also may define a key hole  196  that permits passage of the rotatable shaft  188  (particularly the stops  197  formed on the rotatable shaft  188 ) during axial insertion or removal of the shaft  188  into or out of the housing  187 . The abutment flanges  192  each may define a fastener aperture configured to receive a fastener  190  that connects the housing  187  to a respective end cap  126   a ,  126   b  (see  FIGS.  12 ,  14 ,  16 ,  18 , and  22   ). The end portions  187   a ,  187   b  of the housing  187  may be mirror images of one another to facilitate interconnection of the housing  187  to either the left or right end caps  126   a ,  126   b.    
     With continued reference to  FIGS.  12 ,  16 ,  18 ,  21 , and  26   , the housing  187  may include an intermediate portion  187   c  that interconnects the end portions  187   a ,  187   b . The intermediate portion  187   c  may extend longitudinally along an outer periphery of the outer roller  150  in a laterally spaced relationship. The intermediate portion  187   c  of the housing  187  may include a base  198  and a guide rail  199  each spanning the distance between the opposing end portions  187   a ,  187   b  of the housing  187 . The base  198  of the housing  187  may define stop receiving apertures  200  proximate to the end portions  187   a ,  187   b  to permit passage of the shaft  188  stops during rotation of the shaft  188  relative to the housing  187 , thereby reducing the transverse profile of the housing  187 . The base  198  of the housing  187  also may include a stiffening rib  201  extending longitudinally between the end portions  187   a ,  187   b  that stiffens the housing  187  and reduces lateral displacement or buckling of the intermediate portion  187   c  of the housing  187 . As shown in  FIG.  27   , the stiffening rib  201  may include at least one transversely-extending buttress  202  that further increases the stiffness of the longitudinally-extending rib  201 . 
     Referring to  FIGS.  12 ,  16 - 19 ,  23 , and  26   , the shaft  188  of the axially movable lock mechanism  186  may be offset from, but parallel or substantially parallel to, a rotation axis  152  of the inner roller  148 . The shaft  188  may be positioned external to the outer roller  150  and extend longitudinally along an outer periphery of the outer roller  150  in a spaced relationship. The shaft  188  may include journal portions  195  rotatably received within the collars  191  of the housing  187 . The journal portions  195  of the shaft  188  may include recessed circumferential areas that reduce the contact areas (and thus the friction) between the bearing surface  193  of the collars  191  and the journal portions  195  of the shaft  188 . The shaft  188  may include a threaded portion  203  extending between the journal portions  195  of the shaft  188  and between the collars  191  of the housing  187 . Stops  197  may be formed on the shaft  188  near the terminal ends of the threaded portion  203  of the shaft  188 . The stops  197  may extend radially outward from the shaft  188  and may be axially aligned with the apertures  200  formed in the base  198  of the housing  187  (see  FIG.  21   ) so that during rotation of the shaft  188  relative to the housing  187  the stops  197  rotationally pass in and out of the apertures  200 . A gear  204  may be non-rotatably attached to one end of the shaft  188  and may define a central cavity for laterally locating the gear (and thus the shaft  188 ) relative to the end cap  126   b.    
     Referring to  FIGS.  12 ,  16 ,  18 , and  24 - 27   , the nut  189  of the axially movable lock mechanism  186  is positioned at least partially within the housing  187  and travels axially along the shaft  188  within the intermediate portion  187   c  of the housing  187 . The nut  189  is keyed to the housing  187  so that as the shaft  188  rotates the nut  189  translates along, rather than rotates about, the shaft  188 . The nut  189  includes a body  205  that extends only partially around the shaft  188  and may be referred to as a half-nut  189 . In an alternative design, the nut  189  may extend around the entire circumference of the shaft  188 . 
     Referring to  FIGS.  24  and  25   , the nut  189  includes an internal thread  206  that projects inward from the body  205  and threadedly engages the external thread of the threaded portion  203  of the shaft  188 . To maintain engagement of the threads and restrict rotation of the nut  189  about the shaft  188 , the nut  189  may include two longitudinally-extending wings  207  that project radially outward from the body of the nut  189 . The wings  207  may include axially-extending fins  208  that slidably contact confronting faces of the base  198  of the housing  187  (see  FIG.  27   ) and guide the nut  189  axially along the intermediate portion  187   c  of the housing  187  while reducing the contact area (and thus the friction) between the nut  189  and the housing  187 . 
     One of the wings  207  may define a longitudinally-extending slot  208  that at least partially receives the guide rail  199 . As shown in  FIG.  27   , portions of the wing  207  defining the slot  208  may slidably abut different sides of the guide rail  199 . As such, the wings  207  of the nut  189  may substantially prevent the nut  189  from rotating about the shaft  188 , thereby facilitating translation of the nut  189  along the shaft  188  during rotation of the shaft  188  relative to the housing  187 . To laterally stiffen the wings  207 , the nut  189  may include a transversely-extending rib  209  positioned outwardly of the internal thread  206  and extending between the wings  207 . In an alternative design, the nut  189  and the housing  187  may include various other corresponding keying structures so that the nut  189  travels axially along the shaft  188  upon rotation of the shaft  188  relative to the housing  187 . 
     As described, rotation of the shaft  188  relative to the housing  187  generally moves or translates the nut  189  axially along the shaft  188 . To limit the axial range of the nut  189 , the shaft  188  may include stops  197  extending outward from a periphery of the shaft  188 . Upon contact with the nut  189 , the stops  197  generally restrict or limit translation of the nut  189  relative to the shaft  188 , thereby restricting or limiting further rotation of the shaft  188  relative to the housing  187 . To ensure a solid engagement between the nut  189  and a respective stop  197 , the nut  189  may include a longitudinally-extending abutment wall  211  that interacts with the shaft  188  stop upon the nut  189  reaching a desired stopping position corresponding to a full extension of the first shade  22 . As shown in  FIG.  24   , the abutment wall  211  may be formed at a terminal end of the internal thread  206  of the nut  189 . 
     Additionally or alternatively, the body  205  of the nut  189  (which may resemble an axially-extending sleeve) may abut the abutment flange  192  of the housing  187  to stop translation of the nut  189  along the shaft  188 . The body  205  of the nut  189  may be radially spaced from an outer periphery of the shaft  188  by a sufficient distance to permit passage of the shaft stop  197  in an annular space defined between the shaft  188  and the body  205 . The shaft  188  and the nut  189  may include two stops  197  and abutment walls  211 , respectively, to facilitate interoperability of the lock mechanism  186  with the right or left end caps  126   a ,  126   b , thereby providing a robust design capable of accommodating left and right hand assemblies. 
     Referring to  FIGS.  15 - 17   , the axially movable lock mechanism  186  may include a gear mechanism or train  213  positioned external to the inner and outer rollers  148 ,  150 . The gear mechanism or train  213  may include a first gear  215  non-rotatably coupled to the outer roller  150 , a second gear  204  non-rotatably coupled to the shaft  188 , and an idler gear  217  intermeshed with the first and second gears  215 ,  204 . The idler gear  217  may be rotatably supported on a mounting plate  219  that includes locator pins  221  projecting axially from the mounting plate  219  (see  FIG.  17   ) toward the associated end cap  126 . The locator pins  221  may be receivable within the end cap  126  to restrict rotation of the mounting plate  219  relative to the end cap  126 . 
     The gear mechanism  213  may be altered depending on the size, weight, or other characteristics of the shade members. In one example, the gear mechanism  213  provides a three-to-one gear ratio between the first and second gears  215 ,  204 . That is, for every revolution of the outer roller  150 , the shaft  188  completes three revolutions. In one example, the external thread of the shaft  188  has sixteen threads per inch (or a pitch of 1/16 of an inch). Generally, the length of the threaded portion  203  of the shaft  188  may be oversized relative to the operative range of the nut  189  so that the shaft  188  may accommodate many different shade lengths. Thus, in some examples, the nut  189  only interacts with one of the stops  197  on the rotatable shaft  188  during operation and the other stop is provided so that the lock mechanism  186  may be used with either of the right or left end caps  126   a ,  126   b.    
     Referring to  FIG.  15   , the gear mechanism  213  is depicted in association with the left end cap  126   b . The external gears  204 ,  215 ,  217  are rotatably supported by stub shafts projecting axially from the left end cap  126   b . The idler gear  217  is positioned forwardly of the first gear  215 , and the second gear  204  is positioned forwardly of the idler gear  217 , with all three gears  215 ,  204 ,  217  disposed in the same plane adjacent to the end cap. The idler gear  217  is positioned upwardly of the first gear  215 , and the second gear  204  is positioned upwardly of the idler gear  217 . The first gear  215  and the idler gear  217  may be received within a rim  223  projecting axially from the end cap  126   b.    
     Referring to  FIG.  13   , a partially exploded view of the head rail components (with the exception of the right side components which are generally the same as those shown and discussed in relation to  FIGS.  6 - 11   ) is provided. The components include a left end cap  126   b , a non-rotatable limit screw  166  that attaches to the left end cap  126   b , a left bushing  170   b  that mounts onto and rotates relative to a bearing surface of the limit screw  166 , an inner roller  148  that internally receives a portion of the limit screw  166  (including the limit nut  168 ) and mounts onto a boss  167  of the left and right bushings  170   a ,  170   b , an outer roller  150  that internally receives the inner roller  148 , and the axially movable lock mechanism  186  that attaches to the left end cap  126   b.    
     Referring to  FIGS.  13 ,  14 ,  19 , and  20   , the outer roller  150  may include a split shell design. In particular, the outer roller  150  may include first and second shells  154 ,  156 . To secure the first and second shells  154 ,  156  together and maintain a desired spatial relationship relative to one another, the first and second shells  154 ,  156  of the outer roller  150  each may snugly receive an axial projection  172   a ,  172   b  of the left and right bushings  170   a ,  170   b  (see  FIGS.  14 ,  18 , and  19   ). The axial projections  172   a ,  172   b  may couple the outer roller  150  to the bushings  170   a ,  170   b  so that the outer roller  150  and bushings  170   a ,  170   b  rotate in unison about a rotation axis  152  of the outer roller  150 . The first gear  215  may be non-rotatably secured to an opposing face of the left bushing  170   b  relative to the axial projections  172   a ,  172   b , thereby ensuring the first gear  215  rotates in unison with the outer roller  150 . To further secure the first and second shells  154 ,  156  together, the shells  154 ,  156  may be clamped together by at least one retaining clip  225  ( FIGS.  12 - 13    depict two retaining clips, although more or less clips may be used as desired to securely fasten the shells together). As shown in  FIG.  20   , the retaining clip  225  may be resiliently snapped around an interlocked region  227  of the first and second shells  154 ,  156 . 
     Referring to  FIG.  20   , the end portions  158 ,  160  of the first and second shells  154 ,  156  may overlap one another and extend into corresponding longitudinally-extending receiving channels  229 ,  231  defined at least partially by longitudinally-extending lips  233 ,  235 . The lip  233  of the first shell  158  may be positioned internal to a terminal, longitudinally-extending edge  237  of the second shell  160 , while the lip  235  of the second shell  160  may be positioned external to a terminal, longitudinally-extending edge  239  of the first shell  158  (although this arrangement may be flipped). The retaining clip  225  may resiliently snap around external detents  241 ,  243  formed in the interlocked region of the first and second shells  154 ,  156 , respectively, to clamp the first and second shells  154 ,  156  together. 
     Referring to  FIGS.  14  and  19   , the split-shell design of the outer roller  150  defines a longitudinally-extending slot  176  that permits passage of the second shade  24  during extension and retraction of the second shade  24 . When the edge portions  158 ,  160  of the first and second shells  154 ,  156  are interlocked together, opposing or second longitudinally-extending terminal edge portions  178 ,  180  of the first and second shells  154 ,  156  are peripherally spaced apart from one another and define the longitudinally-extending slot  176 . The confronting second terminal edge portions  158 ,  160  of the first and second shells  154 ,  156  may be spaced a sufficient distance from one another to permit passage of the second shade  24  yet prevent passage of the bottom rail  20  of the second shade  24 . The function of the outer roller  150  is generally the same as that discussed in relation to  FIGS.  6 - 11    and thus will not be repeated here for the sake of brevity. 
     During operation of the covering, as the outer roller  150  extends the first shade  22  across the architectural opening, the first gear  215  drives the idler gear  217 , which in turn drives the second gear  204 , which traverses the nut  189  axially along the shaft  188  toward a bottom end position. Once the nut  189  reaches the bottom end position (which may be defined by a stop  197  on the shaft  188 ), the nut  189  restricts further rotation of the shaft  188  in the extension direction of the first shade  22 , which in turn inhibits further rotation of the outer roller  150  in the extension direction. With the outer roller  150  restricted from further rotation in the extension direction and the first shade  22  unwrapped from the periphery of the outer roller  150 , the second shade  24  may be unwrapped from the inner roller  148 , passed through the slot  176  in the outer roller  150 , and extended across the architectural opening. As the inner roller  148  rotates during extension of the second shade  24 , the internal limit nut  168  rotates in unison with the inner roller  148  and travels axially along the limit screw  166  toward a bottom end stop formed on the non-rotatable limit screw  166 . The internal limit nut  166  generally contacts the bottom end stop upon the second shade  24  being fully extended across the architectural opening to define a bottom stop of the dual roller unit  146 . 
     During retraction of the covering from a fully extended position, the inner roller  148  pulls the second shade  24  through the slot  176  defined between the opposing longitudinally-extending edge portions  178 ,  180  of the shells  154 ,  156  of the outer roller  150  and wraps the second shade  24  about a periphery of the inner roller  148  until the bottom rail  20  of the second shade  24  seats against an outer periphery of the outer roller  150 . During retraction of the second shade  24 , the weight of bottom rail  18  of the first shade  22  maintains the bushings  170   a ,  170   b  in a stationary condition and thus the inner roller  148  rotates relative to the bushings  170   a ,  170   b  and the outer roller  150 . 
     Once seated, the bottom rail  20  of the second shade  24  transfers the rotational torque from the inner roller  148  to the outer roller  150 , thereby rotating the outer roller  150  in a retraction direction and wrapping the first shade  22  about a periphery of the outer roller  150 . The inner and outer rollers  148 ,  150  continue to rotate in a retraction direction until the bottom rail  18  of the first shade  22  contacts a top limit stop, which may be associated with one or both of the end caps  126 , at which point the covering is retracted into a fully retracted position. During rotation of the inner roller  148  in the retraction direction, the internal limit nut  168  traverses along the non-rotatable limit screw  166  within the inner roller  148  away from the bottom stop of the second shade  24 . During rotation of the outer roller  150  in the retraction direction, the external nut  189  traverses along the rotatable shaft  188  away from the bottom stop of the first shade  22 . 
     Referring to  FIGS.  28 - 47   , a covering for an architectural opening is provided that includes a pivotable lock mechanism. With the exception of the pivotable lock mechanism and the multiple-piece outer roller, the covering depicted in  FIGS.  28 - 47    generally has the same features and operation as the covering depicted in  FIGS.  6 - 27   . Accordingly, the preceding discussion of the features and operation of the covering depicted in  FIGS.  6 - 27    should be considered generally applicable to the covering depicted in  FIGS.  28 - 47   , except as noted in the following discussion. The reference numerals used in  FIGS.  28 - 47    generally correspond to the reference numerals used in  FIGS.  12 - 27    to reflect the similar parts and components, except the reference numerals are incremented by one hundred. 
     Referring to  FIGS.  28 - 34   , the inner roller  248  is generally cylindrical in shape, and forms a retaining member for securing the top edge of the second shade  24  thereto. As noted above, the inner roller  248  is positioned inside the outer roller  250  to define the dual roller unit, and in this example both rollers  248 ,  250  are coextensive about the same rotational axis  252 . An upper edge of the second shade  24  is attached to the inner roller  248 , and a lower edge of the second shade  24  is received in a slot formed in the second bottom rail  220 , and held in the slot by an insert  282  positioned in a hem formed on the bottom edge of the second shade  24 . Other attachment structures may be used to attach the bottom rail  220  to the second shade  24 . 
     Continuing with  FIGS.  28 - 34   , the second bottom rail  220  is an elongated member, having relatively high mass, and defining a slot running along its length to receive and retain, as noted above, the bottom edge of the second shade  24 . The second bottom rail  220  has a generally triangular cross section, a portion of which generally matches the shape of the seat  281  formed on the outer roller  250  to conform thereto when the second shade  24  is in the retracted position. An actuator rim  247  is defined at one end of the second rail  220 , and engages the lock mechanism  286  to disengage the lock mechanism  286  from the outer roller  250 , as is described in more detail below. 
     The outer roller  250  in this example is generally cylindrical, and defines several features in its circumferential wall. The outer roller  250  defines a longitudinal central axis  252  about which it rotates, and about which the inner roller  248  is coextensively positioned also. A pair of channels  262  is formed to receive and secure the top edges of the first shade  22 , with the inserts  264  each being positioned in a hem formed on each of the top edges, the inserts  264  acting to retain the top edge in the respective channel  262 . An anchor groove  245  is formed along the length of the outer roller  250  for receipt of a roller lock bearing, as is described below. A slot  276  is formed along the length of the outer roller  250  and is in communication with the interior of the outer roller  250 , which may be formed as a tube. A recessed seat  281  is formed on either side of the slot  276 . The second shade  24  is extended and retracted through the slot  276 , and when in the fully retracted position, the second bottom rail  220  is received in the seat  281  and nests therein for at least one of many purposes, as is described below. The slot  276  is positioned on the outer roller  250  so as to be located above and adjacent to the rearward most of the two channels  262  when the first shade  22  is in its extended position and vane-open configuration. 
     Referring to  FIGS.  28 ,  29 ,  46 , and  47   , the dual roller unit is rotatably supported between the right end cap  226   a  and the left end cap  226   b , and the operating mechanism  240  is operably associated with the inner roller tube  248  to cause it to rotate. The operating mechanism  240  is anchored to the right end cap  226   a  and is actuated by, in one example, the operating element  242  as noted above. The operating mechanism  240  may, in one example, include a planetary gear drive often utilized in window covering applications. The operating mechanism  240  may include an internal fitting  264  which is rotated by the operating mechanism  240 . The fitting  264  is sized to be received within the inner roller  248 , and tightly engages the inner wall of the inner roller  248 . The inner roller  248  is driven in rotation by the internal fitting  264  as the fitting is driven by the operating mechanism  240 . The open right end of the outer roller  250  receives a right end roller cap  270   a , which includes a central aperture having an axially extending collar rotatably receiving an axial bearing surface formed on the housing of the operating mechanism  240 . The bearing surface supports the right end roller cap  270   a  as it rotates when the outer roller  250  rotates. The inner roller  248  is rotatably received on the collar. The collar rotatably supports the right end of the inner tube  248  as it is driven by the operating mechanism  240  to rotate. 
     As shown in  FIG.  46   , right ends  248   a ,  250   a  of the inner and outer rollers  248 ,  250 , respectively, may be aligned with one another, and a right side edge  24   a  of the second shade  24  may be aligned with the right ends  248   a ,  250   a  of the rollers  248 ,  250 . As shown in  FIG.  47   , left ends  248   b ,  250   b  of the inner and outer rollers  248 ,  250 , respectively, may be aligned with one another, and a left side edge  24   b  of the second shade  24  may be aligned with the left ends  248   b ,  250   b  of the rollers  248 ,  250 . The first shade  22  may be wrapped about the outer roller  250 , and the edges of the first shade  22  may be aligned with the ends of the rollers  248 ,  250  and the edges of the second shade  24 . The alignment of the ends of the rollers  248 ,  250  and the edges of the shades  22 ,  24  may reduce or eliminate light gaps between the edges of the shades and corresponding sides of the architectural opening. 
     The outer roller  250  is driven in rotation by the inner roller  248  when the second shade  24  is fully retracted onto the inner roller  248  and the second end rail  220  is received in the seat  281  of the outer tube  250 . In this condition, as the inner roller  248  rotates, the second shade  24  tensions the second end rail  220 , which in turn applies a force to the outer roller  250  at the interface between the second end rail  220  and the seat  281 . Thus the outer roller  250  is caused to rotate in conjunction with the inner roller  248 . The outer roller  250  does not rotate along with the inner roller  248  unless the second shade  24  is fully retracted about the inner roller  248 . As noted above, the operating mechanism  240  may be actuated by an operating element  242  to extend or retract the first and second shades  22 ,  24  as desired by the user. Many types of mechanisms for causing the rotation of the inner roller tube  248  upon actuation of the operating element  242  are acceptable. 
     Continuing with  FIGS.  28  and  29   , a limit screw  266  is positioned inside the inner roller  248 , and is operably fixed to the left end cap  226   b  by a screw. The limit screw  266  does not rotate. A limit nut  268  is threadedly engaged with the limit screw  266 , and is rotationally keyed to the inside of the inner roller  248 , the key structure allowing movement of the limit nut  268  along the length of the inner roller  248 . As the inner roller  248  rotates, the limit nut  268  moves along the threaded limit shaft  266 , and engages a limit stop defining the bottom most extended position of the second shade  24  (see  FIG.  5   ). The retracted position of the first shade  22  is defined by the first shade  22 , in this example, being wrapped entirely around the outer roller  250 . In some examples, the first bottom rail  18  engages a portion of the head rail  14  to define this position. Alternatively or additionally, while a top limit stop on the limit screw  266  is not used in this example, one may be employed on the limit screw  266  if desired. The left end cap  226   b , as best seen in  FIGS.  28 ,  29 , and  47   , rotatably supports the inner roller  248  and the outer roller  250 . 
     Referring to  FIGS.  28 ,  29 , and  40   , a pivot bracket  249  is attached to the inside surface of the left end cap  226   b  and defines a centrally positioned annular boss  251  and a post  253  extending toward the right end cap  226   a  that serves as an axle on which the roller lock  255  is pivotally mounted. The annular boss  251  on the pivot bracket  249  is rotatably received in the central aperture of the left outer roller cap  270   b , which is itself received in the open left end of the outer roller  250 . A collar extends axially from around the central aperture of the cap  270   b , and serves as a bearing surface for the relative rotation between the outer roller  250  and the left end bracket. The open left end of the inner roller  248  is rotatably received upon the outer surface of the collar, which acts as a bearing surface for the rotation of the roller  248  relative to the collar, which rotation is under the selective control through the operating mechanism  240 . 
     The roller lock  255 , as shown in  FIGS.  28 ,  29 ,  38 , and  39   , is pivotally attached to the post  253  on the pivot bracket  249  (see  FIGS.  40  and  41   ), and secured thereto by a fastener  257  (see  FIG.  41   ). The roller lock  255  is pivotable relative to the pivot bracket  249  about the axis defined by the post  253 . A spring member  259  (see  FIG.  43   ) is positioned around the post  253  of the pivot bracket  249 , the spring  259  having two legs, one of which engages the roller lock  255  to bias the roller lock  255  into engagement with the outer surface of the outer roller  250 , and the other leg operably engages a portion of the left end cap  226   b.    
     Referring to  FIGS.  38  and  39   , the roller lock  255  includes a frame plate  261  having a central body  263  from which extend an upper leg  265  and a lower leg  267 , each leg  265 ,  267  lying in the same plane as the central body  263 . The upper and lower legs  265 ,  267  extend at near right angles to one another, and it is contemplated that this relative positioning may be adjusted as needed given the geometry of the particular usage. The end of the lower leg  267  includes a pin  269  extending orthogonally from the plate  261  toward the opposite end cap, the pin  269  having a cylindrical shape and being relatively short. For instance, the pin  269  does not extend far enough to interfere with the rotation of the roller  250 . The length and shape of the pin  269  facilitate the moving engagement between the pin  269  and the actuator rim  247  on the second end rail  220  as described below. 
     Continuing to refer to  FIGS.  38  and  39   , the end of the upper leg  265  rotatably supports a relatively long cylindrical bearing  271  which extends orthogonally from the upper leg  265  towards the opposite end cap  226   a . The bearing  271  is rotatably supported at its opposite end by an arm  273  extending at an angle from the central plate  261 . The arm  273  supports the distal end of the bearing  271  from a top side only, and does not extend much beyond the center of the bearing  271 . This configuration leaves the lower portion of the bearing  271 , along its length, unencumbered and able to be received in the anchor groove  245  formed in the outer roller  250 , as well as to engage the outer surface of the outer roller  250  and ride along its surface, as described further below. 
     The operation of one example of the covering is described below with primary reference to  FIGS.  30 - 34   . As shown in  FIG.  30   , both the first and second shades  22 ,  24  are in the extended position, and the vanes  38  are in an open configuration. With brief reference to  FIG.  30   , the first shade  22  may be coupled to and wrappable about the outer roller  42 . An upper edge of each of the front and rear sheets  30 ,  34  may be coupled to an inwardly-directed, longitudinally extending gland or rib  275 . The gland  275  may define an internal cavity  262  that opens through a periphery of the outer roller  250 . The shade  22  may be wrapped about or unwrapped from a rear side of the roller  250 , with the rear side of the roller  250  positioned between a front side of the roller  250  and a street side of an associated architectural opening (in  FIG.  30   , the rear side of the roller is to the right). Generally, rotation of the roller  250  in a first direction (counterclockwise in  FIG.  30   ) retracts the shade  22  by winding it about the outer roller  250  to a position adjacent one or more sides (such as the top side) of an associated architectural opening and rotation of the roller  250  in a second, opposite direction may extend the shade  22  across the opening (such as to the bottom side). 
     The first shade  22  is maintained in this open position by positioning the engagement points  262  of the rear and front sheets  30 ,  34  of the first shade  22  with the outer roller  250  at the same height. In  FIG.  30   , for instance, the positions of these attachment points  262  may be referred to as being at 4 o&#39;clock and 8 o&#39;clock, which puts them at close to the same level with each other. If the outer roller  250  is rotated either direction from that shown in  FIG.  30   , the front and rear sheets  30 ,  34  would move toward one another and the vanes  38  would re-orient into more vertical alignment. 
     At this position with both the first and second shades  22 ,  24  at the fully extended position, the limit nut  268  (see generally  FIGS.  28  and  29   ) is engaged with the lower limit. Actuation of the operating mechanism  240 , such as by the operating element  242 , from this position begins the retraction of the second shade  24  into the head rail  14 . The operating mechanism  240  first rotates the inner roller  248  in a counterclockwise direction in  FIG.  30    to retract the second shade  24 , and when the second shade  24  is fully retracted, the outer roller  250  is then actuated to retract the first shade  22  onto the outer roller  250 . This sequence is described further herein and below. 
     As noted above, and referring still to  FIG.  30   , the inner roller  248  is positioned within the outer roller  250  to define the dual roller unit  246 . The outer roller  250  defines an axis of rotation  252  defined by the portion of the outer roller  250  having a circular shape (such as from 9 o&#39;clock to 2 o&#39;clock). The inner roller  248  is positioned so as to be coextensive with or concentric about the same axis  252  as the outer roller  250 . 
     During retraction of the second shade  24 , the inner roller  248  rotates relative to the outer roller  250 , with the opposing collars in the left and right roller end caps  270   a ,  270   b  supporting the respective ends of the inner roller  248 . The outer roller  250  is held in fixed rotational position relative to the inner roller  248  by the roller lock  255 . The roller lock  255  is oriented such that the bearing  271  is biased by the spring  259  to be received in the anchor groove  245  (See  FIGS.  28 - 30   ). This position of the bearing  271  inhibits the rotation of the outer roller  250 . As the inner roller  248  rotates in the retraction direction, the second shade  24  is wound onto the inner roller  248  as it is pulled through the slot  276  formed in the outer roller  250 . This retraction rotation moves the limit nut  268  along the limit screw  266  towards the opposite end of the limit screw  266 . 
     The slot  276  through which the second shade  24  extends, and the seat  281  for receiving the second end rail  220  is positioned on the circumference of the outer roller  250  above the attachment point  262  of the rear sheet  34  of the first shade  22 . This may be referred to in  FIG.  30    as 3 o&#39;clock. The slot  276  is defined by opposing free edges formed in the seat  281 . The seat  281  is a recess formed along the length of the slot  276 , and includes two outer edges that define the boundaries of the seat  281  on the circumference of the outer roller  250 . The shape of the recess, as oriented in  FIG.  30   , is somewhat angular overall, with a generally vertically oriented base wall  284  allowing a relatively vertical-tangential engagement and disengagement between the second bottom rail  220  and the outer roller  250 . The location of the seat  281  and slot  276  near the furthest rearward position on the circumference of the outer roller  250 , along with the shape of the seat  281 , allows for secure receipt of the second bottom rail  220  as it is pulled vertically up and into the seat  281  during retraction (see  FIGS.  31  and  32   ). 
     The shape of the seat  281  and its orientation on the outer roller  250  encourages smooth and predictable disengagement of the second bottom rail  220  from the seat  281  to begin the extension of the second shade  24  (from the position shown in  FIG.  32   ). The shape and orientation of the seat  281  allows the bottom rail  220  to drop vertically out of the seat  281 , which takes advantage of the force of gravity on the relatively heavy bottom rail  220 . The generally tangential orientation of the seat  281  on the outer roller  250  assists in this regard. Referring to  FIG.  35   , the upper wall  277   a  extends from the top edge of the recess downwardly and radially inwardly to a lip  277   b , which extends directly downwardly to an upper free edge  277   c . This portion of the seat  281  is the deepest (as measured from the circumference toward the center of the outer roller). The lower wall  279   a  extends from the bottom edge of the recess upwardly and inwardly at a shallow angle, and transitions to a lip  279   b  which defines the lower free edge  279   c  of the slot  276 . The lower wall  279   a  is relatively vertical, and remains so even in combination with the upper lip  277   b . The lower free edge  279   c  of the slot  276  is curved or rounded to allow for the smooth travel of the second shade  24  over this feature as it is retracted onto the inner roller  248 . 
     The secure engagement of the second bottom rail  220  in the seat  281  aids in consistent actuation of the roller lock  255  to disengage the bearing  271  from the anchor groove  245 . Referring to  FIG.  31   , when the second shade  24  is near fully wound around the inner roller  248 , the bottom rail  220  of the second shade  24  engages the roller lock  255  to disengage the roller lock  255  from the outside of the outer roller  250 . The second bottom rail  220  is shown in dash in  FIGS.  31  and  35   . At this position, the actuator rim  247 , which extends axially from the end of the second bottom rail  220 , contacts the pin  269  formed on the lower leg  267  of the roller lock  255 . As the second bottom rail  220  is pulled into the seat  281  by the second shade  24  being retracted, the actuator rim  247  moves the pin  269  relative to the pivot axis of the post  253 . The pin  269  is moved radially inwardly relative to the inner roller  248 , and is moved circumferentially relative to the pivot axis of the roller lock  255 . The movement of the roller lock  255  about the post  253  moves the upper arm  265 , which begins the movement of the bearing  271  upwardly and out of engagement with the anchor groove  245 , which frees the outer roller  250  to rotate (see  FIGS.  32 ,  36 , and  43   ). 
     As shown in  FIGS.  42  and  43   , the actuator rim  247  extends off of the end of the second bottom rail  220  adjacent the roller lock  255 . With reference to  FIGS.  44  and  45   , the rim  247  is a thin, curved element that in this example conforms to the curved shape of the bottom side of the second bottom rail  220 . The rim  247  is curved along a dimension consistent with the bottom side of the second bottom rail  220 , and extends axially away from the second bottom rail  220 . As best seen in  FIG.  43   , the rim  247  extends a distance sufficient to engage the pin  269  on the roller lock  255  but not contact the central plate  261  of the roller lock  255 . The inside, concave surface of the fin  247  engages the round outer surface of the pin  269 . As the second bottom rail  220  is further retracted, the pin  269  and fin  247  maintain a sliding engagement. This further movement of the second end rail  220  causes the roller lock  255  to pivot further about the pivot axis of the post  253  and thus moves the roller lock bearing  271  out of the anchor groove  245 . 
     Referring to  FIGS.  32  and  36   , as the second shade  24  is further withdrawn into the outer roller  250 , the bottom rail  220  becomes securely positioned in the seat  281  and the fin  247  moves the pin  269  a sufficient amount inwardly to fully remove the bearing  271  from the anchor groove  245 , which frees the outer roller  250  to rotate. Further actuation of the operating mechanism  240  applies the rotational motion of the inner roller  248  to the outer roller  250 , through the engagement of the bottom rail  220  in the seat  281  under the tension of the second shade  24 . This engagement causes the outer roller  250  to rotate in conjunction with the rotation of the inner roller  248 . As the outer roller  250  begins to rotate in the retraction direction, the actuator rim  247  on the second bottom rail  220  disengages from the pin  269  on the roller lock  255 . Referring to  FIGS.  33  and  37   , upon release the roller lock  255  is biased by the spring  259  to cause the bearing  271  to contact the outer surface of the outer roller  250  at a circumferential location spaced away from the anchor groove  245 . 
     Referring to  FIG.  34   , as the outer roller  250  continues to rotate in the retraction direction, the first shade  22  wraps around the outer roller  250 , covering the anchor groove  245 . When the roller lock bearing  271  nears the anchor groove  245  as the outer roller  250  continues to rotate, the roller lock bearing  271  passes over the groove  245  by riding on the first shade  22  which spans the groove  245 . The first shade  22  is under tension as it is wrapped around the outer roller  250 , thus making the span of the shade  22  extending over the groove  245  relatively taut. The bearing  271  may depress somewhat into the anchor groove  245  when only a single wrap of the first shade  22  is positioned over the anchor groove  245 , but after another full rotation the bearing  271  rides over the surface of the first shade  22  wrapped around the outer roller  250  without interference from the anchor groove  245 . 
     As the first shade  22  continues to retract, it wraps around the outer roller  250  many times, and the roller lock bearing  271  continues to ride on the outer surface of the shade  22 . The dual roller unit  246  reaches the top retraction position when the first bottom rail  18  contacts an abutment on the head rail housing, for example. It is contemplated that other mechanisms may be utilized to define the top retraction position, including a top limit stop positioned on the limit screw  266  opposite the bottom limit stop. As explained above, the retraction of the second shade  24  and first shade  22  from the fully extended position may occur with the user actuating one operating element (manually or automatically) for the retraction of both shades  22 ,  24 . The limit screw  266  is of sufficient length to allow the limit nut  268  to move from the bottom limit stop until the top retracted position is attained. 
     Extension of the first shade  22  and the second shade  24 , if desired, is accomplished in reverse order as described above, such as generally following  FIGS.  34  to  30   . This allows the user to select whether to have just the first shade  22  extended or to also have the second shade  24  extended (between fully retracted and fully extended). During extension of the first shade  22 , the user actuates the operating mechanism  240  to cause the inner roller  248  to rotate in an extension direction (clockwise in  FIGS.  34 - 30   ), which in turn causes the outer roller  250  to rotate in an extension direction. The dual roller unit  246  rotates, in this example, in the direction the user controls the inner roller  248  to rotate. As the first shade  22  extends off of the rear of the outer roller  250 , the roller lock bearing  271  rides on the outer surface of the outer roller  250  until the first shade  22  is nearly fully extended. At this point, the outer surface of the outer roller  250  is exposed. 
     As the outer roller  250  continues to rotate, the roller lock bearing  271  rides on the outer surface of the outer roller  250  until it meets the anchor groove  245 . The bearing  271  is biased downwardly by the spring  259  to be positioned in the groove  245  and inhibit the rotation of the outer roller  250  and allow the continued rotation of the inner roller  248  (if desired by the user). Since the roller lock  255  is biased in a direction against the outer surface of the outer roller  250 , the bearing  271  moves into the anchor groove  245  without further urging. At this point the first shade  22  is at its most extended position across the opening. It is contemplated that the roller lock  255  may be biased by means other than a spring  259  in these examples. For instance, the top arm  273  of the roller lock  255  may be weighted such that the roller lock  255  pivots as desired automatically under the weight of the top arm  273 . Where a spring  259  is used, it may be a wire spring, coil spring, resilient material spring (such as rubber, elastic, and/or plastic) or the like. 
     When the bearing  271  of the roller lock  255  is seated in the anchor groove  245 , the slot  276  in the outer roller  250  is rotationally oriented within the head rail  14  such that the bottom rail  220  of the second shade  24  may drop vertically out of the seat  281  when the tension in the second shade  24  is lessened by the operating system  240 . The generally tangential orientation and generally vertical positioning of the seat  281 , with a relatively vertical base wall  284 , allows the weight of the second bottom rail  220  to be effective to extract the bottom rail  220  from the seat  281  when the tension in the second shade  24  is released in the retraction position. However, if the user does not intend to extend the second shade  24 , then the second shade  24  may remain retracted. The operating mechanism  240  may include a brake system to restrict unwanted downward movement of the second or first shades  24 ,  22 . 
     In order to extend the second shade  24 , the operating system  240  is further actuated to the level as desired by the user. When the user extends the second shade  24  to the lowest position (most extension), the limit nut  268  is positioned on the limit screw  266  in engagement with the lower limit stop. Thus a single limit screw  266  may be utilized to define the upper limit of the retracted first shade  22  attached to the outer roller  250 , and to define the lower limit of the extended second shade  24  attached to the inner roller  248 . 
     It is contemplated that the first shade  22  of  FIGS.  30 - 34    (which may be the same as or different than that shown in  FIGS.  1 - 5   ) may be wrapped about or unwrapped from the front side of the outer roller  250 . Accompanying modifications to the structure described herein would be necessary to facilitate the implementation of the dual roller shade technology as applied to a front-descending shade structure. It is also contemplated that the roller lock mechanism and accompanying elements necessary for it to operate may be employed on the right end of the head rail, in affiliation with the right end cap  226   a , either in conjunction with a roller lock mechanism on the left end of the head rail, or by itself. Also, the second bottom rail  220  may have an actuating rim  247  on either end thereof. 
     The foregoing description has broad application. While the provided examples describe a silhouette-type shade and a black-out type shade, it should be appreciated that the concepts disclosed herein may equally apply to many types of shades. Accordingly, the discussion of any embodiment is meant only to be explanatory and is not intended to suggest that the scope of the disclosure, including the claims, is limited to these examples. In other words, while illustrative embodiments of the disclosure have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art. 
     The foregoing discussion has been presented for purposes of illustration and description and is not intended to limit the disclosure to the form or forms disclosed herein. For example, various features of the disclosure are grouped together in one or more aspects, embodiments, or configurations for the purpose of streamlining the disclosure. However, it should be understood that various features of the certain aspects, embodiments, or configurations of the disclosure may be combined in alternate aspects, embodiments, or configurations. Moreover, the following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure. 
     The phrases “at least one”, “one or more”, and “and/or”, as used herein, are open-ended expressions that are both conjunctive and disjunctive in operation. 
     The term “a” or “an” entity, as used herein, refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. 
     All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, back, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of this disclosure. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. Identification references (e.g., primary, secondary, first, second, third, fourth, etc.) are not intended to connote importance or priority, but are used to distinguish one feature from another. The drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto may vary.