Patent Publication Number: US-6990771-B2

Title: Inertial control system for opening and closing multiple sliding doors in a common direction

Description:
BACKGROUND OF THE INVENTION 
     Sliding doors are widely used in building structures. Many light weight sliding doors are opened by hand; for example, sliding patio glass doors commonly found in homes. Other sliding doors are provided in pairs which open and close by moving each door in a direction opposite that of the other door. Such conventional systems for opening and closing sliding doors do not appear to be adapted to opening a plurality of doors in a common direction. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention relates to access systems for building structures. More particularly, the invention relates to a method and apparatus for opening sliding doors by displacing multiple door panels in a common direction of travel. In a further respect, the invention relates to a method and apparatus for opening sliding doors that are difficult to open because of their extreme weight and because weather proofing seals on the doors create significant frictional resistance opposing movement of the doors. Accordingly, it would be highly desirable to provide an improved building access system for opening a plurality of sliding doors in a common direction. 
     Still a further object of the invention is to provide an improved building access system for simultaneously opening a first group of sliding doors in a first direction and a second group of sliding doors in a second direction opposite the first direction. 
    
    
     
       BRIEF DESCRIPTION TO THE DRAWINGS 
       These and other, further and more specific objects and advantages of the invention will be apparent to those of skill in the art from the following detailed description thereof, taken in conjunction with the drawings, in which: 
         FIG. 1  is a top view illustrating a single action sliding door access system constructed in accordance with the invention; 
         FIG. 2  is a perspective view illustrating a latching mechanism that causes one sliding door panel to be pulled by the another panel when an access system comprising a plurality of parallel sliding offset door panels is being closed; 
         FIG. 3  is a perspective view illustrating a latching mechanism that causes one sliding door panel to displace and pull another when an access system comprising a plurality of parallel sliding offset door panels is being opened; 
         FIG. 4  is a top view of the sliding door access system of  FIG. 1  illustrating further construction details thereof; 
         FIG. 5  is a front elevation view of the sliding door access system of  FIG. 1  illustrating the mode of operation thereof; 
         FIG. 6  is a top view illustrating a double action sliding door access system constructed in accordance with the invention; 
         FIG. 7  is a perspective view illustrating a bracket utilized in the double action sliding door access system of  FIG. 6  to secure a belt to a selected sliding door panel; 
         FIG. 8  is a top view illustrating an inertial limit switch utilized in accordance with the invention; 
         FIG. 9  is a perspective view illustrating a U-shaped channel used in the invention to conceal the belt that displaces sliding door panels; 
         FIG. 10  is a combination section view and schematic diagram illustrating the control system of the invention; 
         FIG. 11  is a perspective view illustrating further construction details of the sliding door panel access system of  FIGS. 1 and 5 ; 
         FIG. 12  is side view illustrating a guide unit used to tension and direct a drive belt; 
         FIG. 13  is a partial side section view illustrating the channeling of the drive belt through a track in the sliding door access system of the invention; 
         FIG. 14  is a bottom view illustrating the use of the guide unit of  FIG. 12  to tension a drive belt in the system of the invention; 
         FIG. 15  is a bottom view illustrating the use of the guide unit of  FIG. 12  to direct a drive belt along an arcuate path; and, 
         FIG. 16  is a top view illustrating an alternate embodiment of the invention in which sliding doors are opened and closed in directions that are canted with respect to each other. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Briefly, in accordance with the invention, I provide an improved access system for a building structure. The access system includes an access opening formed in the building structure and having first and second sides; a horizontally oriented track extending across the opening; at least first and second panels slidably mounted in the access opening on the track, each of the panels including a leading portion and a rear portion, at least the first of the panels including a catch mounted on the leading portion, the catch shaped and dimensioned to contact the leading portion of the second panel and pull the second panel simultaneously with the first panel when the first panel is moving in a selected direction; a first rotatable pulley mounted at a position lateral from the first side; a second rotatable pulley mounted at a position lateral from the second side; a belt extending around the first and second rotatable pulleys and including first and second portions; a fastener securing the first portion of the belt to the first panel; a fastener securing the second portion of the belt to the first panel; a motor for driving the first pulley: a control system for activating the motor; and, a manually operated control panel mounted on the building structure and operatively associated with the control system to generate a signal to the control system to activate the motor. 
     In a further embodiment of the invention, I provide an improved access system for a building structure. The access system includes an access opening formed in the building structure and having first and second sides; a horizontally oriented track extending across the opening and including an elongate horizontally oriented space extending along the track; at least a first panel slidably mounted in the access opening on the track, the panel including a leading portion and a rear portion; a first rotatable pulley mounted at a position lateral from the first side; a second rotatable pulley mounted at a position lateral from the second side; a belt extending around the first and second rotatable pulleys and including first and second portions, the first portion extending through the space in the track; a fastener securing the first portion to the panel; a fastener securing the second portion to the panel; a motor for driving the first pulley; and, a control system for activating the motor. 
     In another embodiment of the invention, I provide an improved access system for a building structure. The improved access system includes an access opening formed in the building structure and having first and second sides; a horizontally oriented track extending across the opening; at least a first panel slidably mounted in the access opening on the track and including a leading portion, a rear portion, a top, and a bottom; a first rotatable pulley mounted at a position lateral from the first side and from the bottom of the panel; a second rotatable pulley mounted at a position lateral from the second side and from the bottom of the panel; a belt extending around the first and second rotatable pulleys and including first and second portions; a fastener securing the first portion the bottom of the panel; a fastener securing the second portion to the bottom of the panel; a motor for driving the first pulley; and, a control system for activating the motor. 
     In still a further embodiment of the invention, I provide an improved access system for a building structure. The access system includes an access opening formed in the building structure and having first and second sides; a horizontally oriented track extending across the opening; at least first and second panels slidably mounted in the access opening on the track, each of the panels including a leading portion and a rear portion; a first rotatable pulley mounted at a position lateral from the first side; a second rotatable pulley mounted at a position lateral from the second side; a belt extending around the first and second rotatable pulleys and including first, second, and third portions; a fastener securing the first portion to the first panel; a fastener securing the second portion to the first panel; a fastener securing the third portion to the second panel; a motor for driving the first pulley such that the pulley moves the belt and the belt simultaneously moves the first and second panels in opposing directions; a control system for activating the motor; a control panel mounted on the building structure and operatively associated with the control system to generate a signal to the control system to activate the motor. 
     In still another embodiment of the invention, I provide an improved access system for a building structure. The access system includes an access opening formed in the building structure and having first and second sides; a horizontally oriented track extending across the opening; at least a first panel slidably mounted in the access opening on the track and including a leading portion, a rear portion, a top, and a bottom; a first rotatable pulley mounted at a position lateral from the first side and from the bottom of the panel; a second rotatable pulley mounted at a position lateral from the second side and from the bottom of the panel; a belt extending around the first and second rotatable pulleys and including first and second portions; a fastener securing the first portion to the bottom of the panel; a fastener securing the second portion to the bottom of the panel; guides for directing the belt along a non-linear path intermediate the pulleys; a motor for driving the first pulley; and, a control system for activating the motor. 
     In yet a further embodiment of the invention, I provide an improved method for retrofitting an access system for a building structure. The access system includes an access opening formed in the building structure and having first and second sides; a horizontally oriented track extending across the opening and including an elongate horizontally oriented space extending along the track, and at least a first panel slidably mounted in the access opening on the track. The panel includes a leading portion and a rear portion. The method including the steps of mounting a first rotatable pulley at a position lateral from the first side; mounting a second rotatable pulley at a position lateral from the second side; extending a belt through the elongate space and mounting the belt on the first and second rotatable pulleys, the belt including a first portion and a second portion; fastening the first portion of the belt to the panel; fastening the second portion of the belt to the panel; and, mounting a motor to drive the belt to move the panel along the track. 
     Turning now the drawings, which depict the presently preferred embodiments of the invention for the purpose of illustration thereof, and not by way of limitation of the invention, and in which like characters refer to corresponding elements throughout the several views,  FIG. 1  illustrates a single action sliding door access system constructed in accordance with the invention and generally indicated by reference character  10 . In a single action sliding door access system, each sliding door panel moves in the same direction when the access system is being opened, or, is being closed. 
     Access system  10  includes sliding door panels  11 ,  12 ,  13 . Each door panel  11  to  13  is parallel to and offset from the other panels and travels in a track  30  ( FIG. 5 ) in conventional fashion. The track  30  can also, if desired, be situation above—instead of below—panels  11  to  13 . Panels  11  to  13  can also, if desired, be suspended on arms or rollers or other means that move along a track positioned above panels  11  to  13  when panels  11  to  13  are being laterally displaced in, for example, the directions indicated by arrows B and F. 
     Panel  11  includes leading portion  14  and rear portion  15 . Panel  12  includes leading portion  16  and rear portion  17 . Panel  13  includes leading portion  18 . Each panel can be constructed as desired but typically includes a rectangular frame circumscribing and holding a pane of glass. 
     One end  24  of belt  21  is fastened to the leading portion  14  of panel  11 . The other end  25  of belt  21  is attached to the rear portion  15  of panel  11 . Belt  21  extends around driven pulley  23  and free-wheeling pulley  22 . Catch  19  is affixed to leading portion  14  of panel  11 . Catch  20  is affixed to leading portion  16  of panel  12 . 
     As illustrated in  FIG. 10 , pulley  23  is turned by a motor  80 . Motor  80  typically, although not necessarily, transmits motive power to pulley  23  via a gear assembly  81 . If desired, a clutch can be interposed intermediate motor  80  and pulley  23 . 
     A controller  71  receives signals from  82  a manually operated wall mounted switch, from  83  a limit switch ( FIG. 8 ), from  84  infrared sensors  26  and  27 , and/or from  85  any other desired sensors or inputs. 
     Belt  21  extends through an opening  86  formed in the wall and doorjamb  69 . 
     The limit switch mechanism illustrated in  FIG. 8  includes a plate  61  fixedly secured to the leading portion  14  of door  11 . A bolt with head  63  and externally threaded leg  64  slidably extends through opening  65  formed through plate  61 . Internally threaded nut  63 A is threaded on leg  64  and fixedly secured in position thereon. Spring  62  extends between head  63  and plate  61 . When panel  11  is moving in the direction of arrow F and head  63  contacts metal bearing  66 , head  63  is displaced in the direction of arrow V, compressing spring  62 . The force required to compress spring  62  may, if the panel  11  is light and spring  62  is stiff, slow the movement of panel  11 . More importantly, however, when head  63  contacts metal ball bearing  66 , the limit switch unit  66 A is activated and generates an electrical signal that is sent to controller  71  via wires  67 ,  68  or via other desired signal transmission means such as, but not limited to, radio waves, microwaves, fiber optic signals, etc. When controller  71  receives a signal from unit  66 A, it halts the operation of motor  80  such that the inertia of panel  11  causes panel  11  to travel in the direction of arrow F the last short distance to door jamb  69 . When the invention is utilized in connection with panels  11  to  13  weighing one hundred pounds or more, the use of the limit switch mechanism is important because it enable a panel  11  to gradually slow down and make a “soft” contact with jamb  69 . 
     In operation of the single action sliding door access system of  FIGS. 1 to 5 ,  8  and  10 , In  FIGS. 1 ,  4 ,  6  the access system is in the closed configuration. In operation of the access system of  FIGS. 1 to 5 ,  8  and  10 , the user presses the OPEN button  73 . A signal is generated which travels from switching unit  72  to controller  71 . Controller  71  activates motor  80  such that pulley  23  rotates in the direction indicated by arrow A in  FIG. 1 . When pulley  23  rotates in the direction of arrow A, section  21 A of belt  21  (extending between pulley  22  and rear portion  15 ) moves in the direction of arrow C; section  21 B of belt  21  (extending between pulleys  22 ,  23 ) moves in the direction of arrow D; and, section  21 C of belt  21  (extending between pulley  23  and leading portion  14 ) moves in the direction of arrow C. When section  21 A moves in the direction of arrow C, panel  11  is pulled in the direction of arrow B. When panel  11  has moved far enough in the direction of arrow B that the leading portion  14  of panel  11  is next to the leading portion  16  of panel  12 , latch  19  engages leading portion  16  in the manner shown in  FIG. 3  such that panel  11  pulls along panel  12  and panels  11  and  12  move simultaneously in the direction of arrow B. When panel  12  has moved far enough in the direction of arrow B that the leading portion  16  of panel  12  is next to the leading portion of panel  13 , latch  20  engages leading portion  18  such that panel  12  pulls along panel  13  and panels  11  to  13  move simultaneously in the direction of arrow B. After panels  11 ,  12 ,  13  have moved into pocket  31  ( FIG. 4 ) or to another desired position, controller  71  stops motor  80 . A sensor or any other desired means can be used to determine when panels  11  to  13  are in pocket  31  and to send a signal to controller  71  to halt motor  81 . 
     As is illustrated in  FIG. 4 , when the access system of  FIG. 1  is in the closed position and the open button  73  is depressed, causing controller  71  to activate motor  80 , panel  11  initially travels in the direction indicated by arrow B 1 . After panel  11  latches panel  12  in the manner indicated in  FIG. 3 , panels  11  and  12  travel together in the direction indicated by arrow B 2 . After panel  12  latches panel  13 , panels  11  to  13  travel together in the direction indicated by arrow B 3  and thereafter travel together into pocket  31  in the direction indicated by arrow B 4 . 
     When the access system of  FIGS. 1 and 4  is in the open position, the user can depress the CLOSE button  74 . When button  74  is depressed, switching unit  72  generates a signal to controller  71 . Controller activates motor  80  to turn driven pulley  23  in the direction of arrow G such that section  21 B of belt  21  move in the direction of arrow E and sections  21 C and  21 A move in directions opposite those in which sections  21 C and  21 A moved when the access system of  FIGS. 1 and 4  was opening. Panel  11  is, consequently, pulled in the direction of arrow F by section  21 C. After panel  11  has traveled in the direction of arrow F a distance sufficient for rear portion  15  to be next to front portion  16  of panel  12 , a latch  26  on panel  12  engages inner edge  27  of panel  11  such that panel  11  pulls panel  13  along with panel  11 , much like a train engine pulls a freight car. After panel  12  has traveled in the direction of arrow F a distance sufficient for rear portion  17  to be next to front portion  18  of panel  13 , a latch on panel  13  identical in position and shape to patch  26  engages an inner edge of panel  13  such that panel  12  pulls panel  13  along with panel  12 . When panel  11  approach jamb  29  ( FIG. 8 ), head  63  contacts bearing  66  to activate switch unit  66 A. Activating unit  66 A generates a signal  83  to controller  71 . When controller  71  receives the signal  83 , controller  71  halts motor  71  such that the inertia of panels  11  to  13  carries them the last short distance until leading portion  14  contacts or is sufficiently close to jamb  69 . 
     The user can, at any time the access system of  FIG. 1  or  FIG. 4  is opening or closing, push the STOP button  75 . Depressing button  75  causes switching unit  72  to generate a signal to controller  71 . Controller  71 , on receiving such signal, halts the operation of motor  80  and the travel of panels  11  to  13 . 
     The double action sliding door access system of  FIG. 6  includes door panels  40 ,  43 ,  46 , and,  49 . Panel  40  includes leading portion  41  and rear portion  42 . Panel  43  includes leading portion  45  and rear portion  44 . Panel  46  includes leading portion  47  and trailing portion  48 . Panel  49  includes leading portion  50  and trailing portion  51 . One end  53  of belt  52  is connected to rear portion  14 . The other end  54  of belt  52  is connected to leading portion  45 . Brackets  55  ( FIG. 7 ) are attached to leading portion  41  and rear portion  42  with metal screws or other fasteners that extend through apertures  56 ,  57 . Bolts or other fastening means fixedly secure portions of belt  52  to panel  59  of each bracket  55  via aperture  58  formed therein. 
     The control system illustrated in  FIG. 10  is used to operate the access system of  FIG. 6 . 
     The double action sliding door access system of  FIG. 6  is closed. In operation, the user depresses the OPEN button  73  to activate motor  80  to cause driven pulley  23 A to rotate in the direction of arrow J and free-wheeling pulley  22 A to rotate in the direction of arrow K. Sections  52 B and  52 C of belt  52  moves in the direction of arrow L. Section  52 A of belt  52  moves in the direction of arrow M. Consequently, section  52 A displaces panel  40  in the direction of arrow M. Section  52 C pulls panel  43  in the direction of arrow L. Leading portion  41  of panel  40  is provided with a latch equivalent to latch  19  so that when panel  40  has moved a sufficient distance in the direction of arrow M so that leading portion  41  is adjacent leading portion  50 , the latch engages leading portion  50  so that panels  40  and  49  move in unison in the direction of arrow M. Similarly, leading portion  45  of panel  43  is provided with a latch equivalent to latch  19  so that when panel  43  has moved a sufficient distance in the direction of arrow L so that leading portion  45  is adjacent leading portion  47 , the latch engages leading portion  47  so that panels  43  and  46  move in unison in the direction of arrow L. 
     Closing the double action sliding door access system of  FIG. 6  is accomplished by depressing the CLOSE button  74  such that controller  71  causes motor  80  to rotate driven pulley  23 A in a direction opposite that indicated by arrow J. 
     If desired, in  FIG. 6  belt  52  can be continuous and bracket  55  can be utilized to attach belt  52  to leading and rear portions  44 ,  45  (or to other desired portions) of panel  43 . 
     Safety and operational considerations make the speed at which panels  11  to  13  travel critical in the practice of the invention. Each panel should travel at a speed in the range of one inch to eight inches per second, preferably two inches to six inches per second. Speeds greater than eight inches per second are to be avoided because a heavy panel  11  could crush an animal or child or individual between the panel  11  and jamb  69 , causing serious injury. 
     The gear box  81  ratio used in conjunction with motor  80  is in the range of 6:1 to 100:1. When controller  71  halts motor  80  while panels  11  to  13  (or  40 ,  43 ,  46 ,  49 ) are still moving, it is important that driven pulley  23 A be permitted to free wheel such that belt  21  can continue to move around pulleys  22  and  23  while the inertia of panels  11  to  13  provides the energy to continue moving panels  11  to  13 . 
     Signal  85  can comprise a signal indicating that an individual is stuck or wedged in the access system of  FIG. 1  intermediate panel  11  and jamb  69 . Such a signal causes controller  71  to stop or reverse the operation of motor  80 . 
     Motor  80  is reversible and can be used to turn driven pulley  23  in opposing directions. If desired, two motors can be utilized. One motor would turn pulley  23  (or  22 ) in one direction. The other motor would turn pulley  23  (or  22 ) in the other opposing direction. Motor  80  can be direct drive or clutch driven. 
     If switching unit  72  is positioned inside a building structure, switching unit  72  can be designed such that depressing button  75  sends a signal to controller  71  that causes controller  71  to disable an outside switch so the outside switch will not operate the access systems of  FIGS. 1 and 6 . 
     A single action or double action sliding door access system designed in accordance with the invention can include any desired number of door panels. 
     Instead of activating controller  71  and motor  80  with the switching unit  72 , infrared sensors  26 ,  27  or other desired sensors can be utilized to generate a signal to controller  71  when an individual approaches or departs the access system of  FIG. 1  (or  FIG. 6 ). For example, when an individual walks to within a selected distance of the access system of  FIG. 1 , sensor  27  sends a signal to controller  71 . Controller  71  activates motor  80  to open the panels  11  to  13  in the manner earlier described. After the individual walks a sufficient distance away from the access system, sensor  26  sends a signal to controller  71 . Controller  71  activates motor  80  to close the panels  11  to  13  in the manner earlier described. 
     In  FIG. 5 , the panels  11  to  13  are mounted in a rectangular access opening formed in a building structure  100 . The rectangular opening includes sides  101  and  102 . 
     In  FIG. 11 , panel  11  includes glass pane  90 . The upper edge  93  of pane  90  is fixedly received by elongate bracket member  92 . Member  92  slidably moves along fixed track or head  91 . The lower edge  95  of glass pane  90  is parallel to edge  93  and is fixedly received by elongate bracket  94 . Wheel housing  96  is mounted on bracket  94  in conventional fashion. Wheel  97  is rotatably mounted in housing  96 . Wheel  97  rotates along upraised tapered member  98  when panel  11  moves laterally in the direction of arrow F or B ( FIG. 2 ) along track  99  and track  91 . 
     Panel  12  includes glass pane  100 . The upper edge  103  of pane  100  is fixedly received by elongate bracket member  102 . Member  102  slidably moves along fixed track or head  101 . The lower edge  105  of glass pane  100  is parallel to edge  103  and is fixedly received by elongate bracket  104 . Wheel housing  106  is mounted on bracket  104  in conventional fashion. Wheel  107  is rotatably mounted in housing  106 . Wheel  107  rotates along upraised tapered member  108  when panel  12  moves laterally in the direction of arrow F or B ( FIG. 2 ) along track  109  and track  101 . 
     Panel  13  includes glass pane  110 . The upper edge  113  of pane  110  is fixedly received by elongate bracket member  112 . Member  112  slidably moves along fixed track or head  111 . The lower edge  115  of glass pane  110  is parallel to edge  113  and is fixedly received by elongate bracket  114 . Wheel housing  116  is mounted on bracket  114  in conventional fashion. Wheel  117  is rotatably mounted in housing  116 . Wheel  117  rotates along upraised tapered member  118  when panel  13  moves laterally in the direction of arrow F or B ( FIG. 2 ) along track  119  and track  111 . 
     Track  91  includes elongate inner space  120  extending horizontally beneath flat top member  91 A. As can be seen in  FIG. 11 , the upper portion of bracket member  92  extends upwardly past foot  91 A into the lower part of space  120 . As will be seen with reference to  FIG. 13 , a portion of belt  21  extends through and along space  120  in one preferred embodiment of the invention. 
     The vertical end piece of panel  11  is indicated in  FIG. 11  by dashed lines  121  but has been otherwise omitted in  FIG. 11  for the sake of clarity. The vertical end pieces of panels  12  and  13  are similarly omitted in  FIG. 11 . An elongate U-shaped member is indicated by dashed lines  122  in  FIG. 11  and includes top panel  123 . While portions  21 A and  21 C of belt  21  can extend at least in part through space  120  in track  91 , another portion  21 B of belt  21  extends through member  122 . An elongate horizontally oriented member (not shown) can, if desired, be attached to the bottom of member  122  to conceal portion  21 B of belt  21  inside member  122 . 
       FIG. 12  illustrates a guide member  140  used to tension and direct the path of travel of belt  21 . Member  140  includes screw  141  including head  142  and externally threaded foot  143  extending from head  142 . Identical hollow cylindrical sleeves  144  and  145  are rotatably mounted on foot  143  with spring  146  positioned therebetween. Member  140  is mounted in top panel  123  by threading the distal end of foot  143  into panel  123  such that member  140  extends inside member  122  in the manner illustrated in  FIG. 14 .  FIG. 14  is a bottom view of member  122  with the bottom panel or cover removed so that members  140  are visible, as well as belt  21  coursing through the inner space of member  122 . When the distal end of foot  143  is turned into panel  123 , sleeve  144  is displaced toward sleeve  145 , compressing spring  146 . The distance between sleeves  144  and  145  is readily adjusted by varying the length of the distal end of foot  143  that is turned into panel  123 . Sleeves  144  and  145  can, but do not necessarily have to, free wheel in the directions of arrow Z when belt  21  moves in the directions indicated by arrows  200  and  201 . 
     In  FIG. 13 , fastener  202  secures end  25  of belt  21  to end piece  121  at the trailing edge  15  of panel  11 . Importantly, portion  21 A of belt  21  extends through space  120  in track  21 . This feature of the invention greatly simplifies installation of the motor—pulley—belt system of the invention. Prior art devices position and extend belt  21  along and above the top of track  91  and space  120 , making the retrofitting of prior art belt systems costly and impractical. 
     Retrofitting an existing sliding door system or other building access system with the motive power apparatus of the invention is accomplished by installing pulleys  22  and  23  in the wall of a building structure laterally from the sides of the opening in the building structure which the access system is installed. Pulleys  22  and  23  ordinarily can be readily installed by cutting small openings in the wall of an existing structure and fastening a pulley support structure to a two-by-four or other structure member in the wall. The pulley  23  support structure can, by way of example and not limitation, be the axle on which the pulley is mounted and which extends into and is turned by a motor. If the pulley  22  is not a driven pulley, the pulley support structure can be an axle mounted in the wall such that the pulley can freewheel on the axle and the belt  21  can freely extend around pulley  22  in the manner illustrated in  FIG. 2 . A belt  21  is fed or extended through the existing space  120  of track  91  (or through a similar space in a lower track  99 , since a panel  11  can be pulled from the bottom as well as the top), is extended around pulleys  22  and  23 , and is attached to door  11  in the manner illustrated in  FIG. 2 . A motor  80  to turn at least one of pulleys  22  and  23  is installed. A control system  71 ,  72  to turn the motor on and off is installed. The motor and control system are connected to a source of electrical or other power. The motor and control system ordinarily can be rather easily installed in the wall of an existing building structure by cutting an opening in the wall adjacent. 
     Instead of retrofitting an existing system, the belt—motor—control system of the invention can be installed along with a sliding door access system during the initial construction of a building structure. 
     When an existing sliding door access system is retrofitted with the belt—motor—control system of the invention, the existing system can be manually operated prior to the retrofit (which is usually the case), or, the existing system can include a prior art power system that is being replaced with the belt—motor—control system of the invention. 
     Belt  21  can be smooth, can be toothed, can comprise rope, can comprise chain, can comprise rubber, etc. If desired, belt  21  can be replaced by a linkage assembly or other mechanical apparatus. 
     In  FIG. 15 , guide units  140  are positioned to guide a belt  21 G along an arcuate path of travel through a track  91 C. Driven pulley  23 C moves belts  21 G around freewheeling pulley  21 C in the manner indicated by the arrows in  FIG. 15 . 
       FIG. 16  illustrates an alternate access system constructed in accordance with the invention and including sliding door panels  211 ,  212 ,  230 , and  231 . Panel  211  is parallel to and offset laterally from panel  212 . Panel  230  is parallel to and offset laterally from panel  231 . Panels  211  and  212  move in directions of travel that are at an angle to—and are not parallel to—the directions of travel in which panels  230  and  231  move. Panels  211  and  212  travel along a track that is canted with respect to the track along which panels  230  and  231  travel. 
     Panel  211  includes leading portion  214  and rear portion  215 . Panel  212  includes leading portion  216  and rear portion  217 . Panel  230  includes leading portion  233  and trailing portion  232 . Panel  231  includes leading portion  235  and trailing portion  234 . Catch  219  is affixed to the leading edge of panel  211 . Catch  220  is affixed to the leading edge of panel  230 . Brackets  281  and  282  are identical to bracket  55  and are each attached to portion  221 C of belt  221 . 
     One end  225  of belt  221  is fastened to the trailing portion  215  of panel  211 . The other end  224  is attached to the leading portion  214  of panel  211 . Belt  221  extends from trailing edge  215 , around pulley  222 , around guide unit  140 A, around driven pulley  223 , and around guide unit  140  to leading edge  214 . In  FIG. 16 , portion  221 A of belt  221  extends from edge  215  to pulley  222 ; portion  221 B of belt  221  extends from pulley  222  to guide unit  140 A; portion  221 C of belt  221  extends from guide unit  140 A to pulley  223 ; portion  221 D of belt  221  extends from pulley  223  to guide unit  140 ; and, portion  221 E extends from guide unit  140  to leading edge  214 . 
     In  FIG. 16 , the door panels are in the closed position. To open the door panels, pulley  223  is rotated in the direction indicated by arrow  280 , causing belt  221  to move in the directions indicated by arrows  250  (portion  221 A),  251  (portion  221 B),  252  (portion  221 C), and  253  (portion  221 D). When belt moves in the manner indicated by arrows  250  to  253 , belt  221  simultaneously moves panel  211  in the direction of arrow  260  and panel  230  in the direction of arrow  262 . After panel  211  moves a selected distance in the direction of arrow  260 , catch  219  contacts leading portion  216  such that panel  211  and catch  219  pull panel  212  in the direction of arrow  261  simultaneously with the movement of panel  211  in the direction of arrow  260 . Similarly, after panel  230  moves a selected distance in the direction of arrow  262 , catch  220  contacts leading portion  235  of panel  231  such that panel  230  and catch  220  pull panel  231  in the direction of arrow  263  simultaneously with the movement of panel  230  in the direction of arrow  262 . Pulley  223  is driven in the direction of arrow  280  until panels  211  and  212  are nested in pocket  271  and panels  230  and  231  are nested in pocket  270 . Pulley  223  is then stopped. Panels  211 ,  212 ,  230 ,  231  are closed by rotating pulley in the direction opposite that of arrow  280 . In  FIG. 16  panels  211  and  212  are at an angle of ninety degrees with respect to panels  230  and  231 . The angle between panels  211 ,  212  and panels  230 ,  231  can vary as desired.