Abstract:
A main drive shaft brake for a passenger conveyor includes a braking element, an actuator, and a counter-actuator. The actuator is de-energized to release the braking element and halt operation of the passenger conveyor during an abnormal or emergency condition. An energized counter-actuator permits release of the braking element but, when de-energized, inhibits release of the braking element by the actuator to prevent unintentional release of the braking element caused by, for example, an accidental loss of power to the actuator.

Description:
BACKGROUND 
     The present invention relates to braking systems for passenger conveyors. More particularly, the present invention relates to main drive shaft brakes used to halt passenger conveyors in the event of an emergency or otherwise abnormal condition. 
     Conventional passenger conveyors, such as moving walkways or escalators, include a series of pallets or steps that move in a closed loop. Passenger conveyors allow people to stand or walk along the steps while being transported across a distance. The steps are typically attached to a step chain, which provides forward movement to the steps. More specifically, a drive sheave imparts motion to step chains thereby moving the steps, and any people located on the steps, along a predetermined track. For escalators, the track extends between a lower elevation and a higher elevation and back to the lower elevation in a closed loop. Moving walkways can have inclined, declined, or substantially flat tracks and sometimes include a pair of oppositely traveling, parallel walkways. 
     For some reasons passenger conveyors include both a machine brake and a main drive shaft brake. The machine brake is activated to prevent further movement of the step chain under normal conditions. For example, if the passenger conveyor is shut down for the evening or if repairs are needed, the machine brake will stop the step chain and hold the passenger steps in a stationary condition. The main drive shaft brake, or “auxiliary brake” as it is sometimes referred to, is an additional braking system that can be activated to halt movement of the step chain to avoid damage to the passenger conveyor and/or prevent passenger injury. 
     SUMMARY 
     An embodiment of the present invention is a main drive shaft brake for a passenger conveyor. The main drive shaft brake includes a braking element, an actuator, and a counter-actuator. The braking element halts movement of the driving mechanism in the passenger conveyor system. The actuator is connected to the braking element and controls activation of the braking element. The actuator is movable between an energized mode, in which power supplied to the actuator keeps the braking element in a ready position, and an un-energized mode, in which a lack of power supplied to the actuator causes the actuator to release the braking element, thereby halting movement of the driving mechanism in the passenger conveyor system. The counter-actuator is connected to the actuator. The counter-actuator is movable between an energized mode in which power supplied to the counter-actuator keeps the counter-actuator from interfering with the actuator, and an un-energized mode, in which a lack of power causes the counter-actuator to block the release of the braking element. 
     In another embodiment, the main drive shaft brake includes a braking element, a release lever, an actuator, and a counter-actuator. The release lever is connected to the braking element for holding the braking element in a lifted and ready position or releasing the braking element to halt movement of the conveyor. The actuator has a first coil adjacent to the release lever and a first stroke extending into the first coil. The first stroke is capable of moving further into the first coil to enable the release lever to release the braking element. The counter-actuator is opposite to the actuator. The counter-actuator has a second coil and a second stroke extending into the second coil. The second stroke is biased by a spring such that a loss of power causes the second stroke to block the first stroke from moving further into the first coil, thereby preventing release of the braking element. 
     Another embodiment of the present invention is a method of controlling a main drive shaft brake for a passenger conveyor. The method includes controlling a brake actuator in either an energized state, such that the brake actuator holds the main drive shaft brake in lifted position, or a de-energized state to cause the brake actuator to release the main drive shaft brake to a dropped position. The method also includes inhibiting the brake actuator from releasing the main drive shaft brake in response to a loss of line power. 
     Another embodiment of the present invention is a passenger conveyor including a driving mechanism, a drive sheave, and a main drive shaft brake. The drive sheave is in contact with the driving mechanism for imparting motion thereto. The main drive shaft brake is associated with the drive sheave. The main drive shaft brake including a braking element for halting rotation of the drive sheave, an actuator for controlling activation of the braking element, and a counter-actuator for blocking an unintentional activation of the braking element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a passenger conveyor with a portion shown in phantom to show a driving sheave applied to a main drive shaft brake in accordance with the present invention. 
         FIG. 2  is a side view of one embodiment of a main drive shaft brake. 
         FIG. 3  is a cross-sectional view of the embodiment of the main drive shaft brake from  FIG. 2  in a ready to brake or lifted position. 
         FIG. 4  is a cross-sectional view of the embodiment of the main drive shaft brake from  FIG. 3  in a released or dropped position. 
         FIG. 5  is a cross-sectional view of the embodiment of the main drive shaft brake from  FIGS. 3 and 4  in a brake blocked or inhibited position. 
         FIG. 6  is a cross-sectional view of an alternative embodiment of a main drive shaft brake in a ready to brake or lifted position. 
         FIG. 7  is a cross-sectional view of the embodiment of the main drive shaft brake from  FIG. 6  in a released or dropped position. 
         FIG. 8  is a cross-sectional view of the embodiment of the main drive shaft brake from  FIGS. 6 and 7  in a brake blocked or inhibited position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of passenger conveyor  10  with a portion shown in broken lines to show drive sheave  12 A having auxiliary braking system or main drive shaft brake  14 . Depicted in  FIG. 1  are passenger conveyor  10 , drive sheave  12 A, guide sheave  12 B, main drive shaft brake  14 , step chain  16 , and steps  18 . Drive sheave  12 A imparts forward motion to step chain  16 , which propels steps  18  of passenger conveyor  10  along a closed loop. If an emergency condition or otherwise abnormal situation should occur, main drive shaft brake  14  halts down motion of passenger conveyor  10  by directly stopping movement of drive sheave  12 A. 
     In the depicted embodiment, passenger conveyor  10  is an escalator having drive sheave  12 A and guide sheave  12 B. Drive sheave  12 A is located in an upper landing of passenger conveyor  10  and is connected to a motor. Guide sheave  12 B is located in a lower landing of passenger conveyor  10  and is not directly associated with a motor. Main drive shaft brake  14  is located adjacent and connected to drive sheave  12 A in the upper landing. Step chain  16  extends around an outer surface of both drive sheave  12 A and guide sheave  12 B to form a closed loop extending from the upper landing to the lower landing. Sheave  12 A has teeth or sprockets that match the chain links of step chain  16  and provide for secure engagement of step chain  16 . A plurality of steps  18  have a top surface for carrying passengers and a bottom surface connected to step chain  16  for propulsion along with step chain  16  around the closed loop. Although passenger conveyor  10  is illustrated as an escalator, main drive shaft brake  14  is not so limited and is appropriate for other systems such as, but not limited to, moving walkways. 
     During normal operation of passenger conveyor  10 , drive sheave  12 A rotates and engages step chain  16 . The forward motion imparted to step chain  16  propels step chain  16 , as well as steps  18 , between the upper landing and the lower landing. Steps  18  travel in a closed loop between the upper landing and the lower landing. When located above step chain  16 , and moving in the selected direction of travel, steps  18  carry passengers either up or down passenger conveyor  10 . When located beneath step chain  16 , or otherwise not exposed for use by passengers and moving in a return direction between the upper and lower landings, steps  18  are free of passengers and simply return to the beginning of the loop on the passenger side. If an abnormal condition occurs, such as over-speed or an unintentional reversal in direction, main drive shaft brake  14  is activated. Actuation of main drive shaft brake  14  halts downward movement of drive sheave  12 A, thereby stopping movement of step chain  16  and steps  18 . 
       FIG. 2  is a side view of one embodiment of main drive shaft brake  14 A. Depicted in  FIG. 2  are drive sheave  12 A, main drive shaft brake  14 A, brake disk  20 , brake wedge  22 , release lever  24 , release solenoid  26 , line solenoid  28 , first spring  30 , second spring  32 , and third spring  33 . Main drive shaft brake  14 A is a dual solenoid electromechanical system configured to stop passenger conveyor  10  during abnormal conditions. 
     Brake disk  20  is mounted to main drive shaft sheave  12 A. Located on one side of brake disk  20  and drive sheave  12 A, is main drive shaft brake  14 A including brake wedge  22 , release lever  24 , release solenoid  26 , line solenoid  28 , and springs  30 ,  32 ,  33 . Brake wedge  22  has a first side adjacent to drive sheave  12 A and a second side connected to release lever  24 . Release lever  24  has a pivoting base near drive sheave  12 A and brake wedge  22 , and an arm extending away from its base to connect with release solenoid  26 . Release solenoid  26  is beneath the arm of release lever  24  and above line solenoid  28 . Release solenoid  26  and line solenoid  28  are connected to each other and can share a common solenoid housing, although other configurations are contemplated. First spring  30  is connected to the base of release lever  24 , second spring  32  is connected to a bottom of line solenoid  28 , and third spring  33  is connected to a bottom of brake wedge  22  where it is adjacent to first spring  30 . 
     Main drive shaft brake  14 A is a spring loaded system biased toward brake release and countered by release solenoid  26 . First spring  30  is biased to pivot release lever  24  and third spring  33  is biased to thrust brake wedge  22  into interference with drive sheave  12 A. Release lever  24  has a latch which engages brake wedge  22  thereby holding brake wedge  22  in a lifted or “ready to brake” position. With brake wedge  22  held out of the way, drive sheave  12 A is free to rotate and engage step chain  16  (not depicted). Release lever  24  is held horizontally in the lifted position by release solenoid  26 . Power supplied to release solenoid  26  keeps release lever  24  horizontal, which keeps brake wedge  22  in the lifted position. As will be described in more detail below with reference to  FIGS. 3 and 4 , when an emergency or otherwise abnormal condition occurs and actuation of main drive shaft brake  14  is desired, power to release solenoid  26  is intentionally interrupted. Without power, release solenoid  26  no longer holds release lever  24  in the horizontal position and therefore, first spring  30  pivots release lever  24 . Once release lever  24  pivots, it is no longer holding brake wedge  22  out of the way of drive sheave  12 A. Third spring  33  thrusts brake wedge  22  into engagement with drive sheave  12 A, thereby halting movement of the step chain  16  of passenger conveyor  10 . 
     In prior art systems, both an intentional loss of power due to an abnormal condition and an unintentional loss of power due to power failure would cut off power to release solenoid  26  and therefore, cause release lever  24  to drop brake wedge  22 . The unintentional actuation of main drive shaft brake system  14 A is undesirable. The addition of line solenoid  28  and second spring  32  in the present invention allows main drive shaft brake system  14 A to operate normally when cessation of power to release solenoid  26  is intentional, but inhibits the unintentional release of release lever  24 . In the case of an unintentional loss of power such as a power outage or power interruption, line solenoid  28 , biased by second spring  32 , will prevent release solenoid  26  from disengaging release lever  24 . Details of the interaction between release solenoid  26  and line solenoid  28  are described below with reference to  FIGS. 3-5 . 
       FIG. 3  is a cross-sectional view of main drive shaft brake system  14 A in a ready to brake position. Depicted are the components of main drive shaft brake system  14 A: release lever  24 , release solenoid  26 , line solenoid  28 , first spring  30 , second spring  32 , first stroke or plunger  34 , second stroke or plunger  36 A, first coil  38 , second coil  40 , first side  42 , second side  44 , aperture  46 , space  48 A, buffer  50 A, arm  52 , and base  54 . In  FIG. 3 , the bias of first spring  30  is countered by electromagnetism from release solenoid  26  holding main drive shaft brake  14 A in the ready to brake position illustrated. 
     Extending between release lever  24  and release solenoid  26  is first stroke  34 . Opposite to release solenoid  26  and first stroke  34 , and creating a mirror image thereof, are line solenoid  28  and second stroke  36 A. First stroke  34  is adjacent release lever  24  and extends into first coil  38 . Second stroke  36 A extends from second spring  32  into second coil  40 . First coil  38  and second coil  40  are adjacent to one another thereby connecting release solenoid  26  to line solenoid  28 . First stroke  34  enters first coil  38  on first side  42  and second stroke  36  enters second coil  40  on second side  44 , such that both first stroke  34  and second stroke  36  extend into aperture  46  running though a center of first coil  38  and second coil  40 . In an approximate center of aperture  46  is space  48 A. Buffer  50 A is attached to second stroke  36 A adjacent to space  48 A. Buffer  50 A comprises a non-magnetic material, such as but not limited to, plastic. Release lever  24  has arm  52  extending from one side of base  54 , where arm  52  is located above and adjacent to first stroke  34  and base  54  is attached to first spring  30 . 
     In  FIG. 3 , power is independently supplied to both first coil  38  of release solenoid  26  and second coil  40  of line solenoid  28 . Power received by first coil  38  is used to pull first stroke  34  outward and away from line solenoid  28 . Similarly, power received by second coil  40  is used to pull second stroke  36 A outward and away from release solenoid  26 . Energizing release solenoid  26  and line solenoid  28  frees up space  48 A of aperture  46 , thereby bringing main drive shaft brake system  14 A into the ready to brake position. The electromagnetic force of first coil  38  pulls first stroke  34  upwardly through first side  42  to hold arm  52  in a horizontal and approximately perpendicular position. When arm  52  is held in this perpendicular position, spring forces of first spring  30  and of third spring  33  are countered. In a similar fashion, the electromagnetic force of second coil  40  pulls second stroke  36 A downwardly through second side  44  toward second spring  32  to counter spring force of second spring  32 . In this lifted position, both release solenoid  26  and line solenoid  28  are energized and ready to change states should the power supply be interrupted. 
       FIG. 4  is a cross-sectional view of main drive shaft brake system  14 A in a brake released or dropped position. Depicted are the components of main drive shaft brake system  14 A: release lever  24 , release solenoid  26 , line solenoid  28 , first spring  30 , second spring  32 , first stroke  34 , second stroke  36 A, first coil  38 , second coil  40 , first side  42 , second side  44 , aperture  46 , space  48 A, buffer  50 A, arm  52 , and base  54 . The components of main drive shaft brake system  14 A depicted in  FIG. 4  are connected as described above with reference to  FIG. 3 . Main drive shaft brake system  14 A is an active system where power supplied to first coil  38  of release solenoid  26  counters first spring  30  and third spring  33  to keep brake wedge  22  lifted. In  FIG. 4 , power to first coil  38  of release solenoid  26  is interrupted so that first spring  30  pivots release lever  24 , freeing third spring  33  to thrust brake wedge  22  into interference with drive sheave  12 A. 
     When it is desirable to stop the operation of passenger conveyor  10 , the power supplied to first coil  38  of release solenoid  26  is intentionally terminated. Termination of power to first coil  38  extinguishes the electromagnetic counterforce and therefore, allows first stroke  34  to fall further into aperture  46  toward line solenoid  28  where it occupies space  48 A. More or less simultaneously, first spring  30  pushes base  54  upward, which causes lever  24  to pivot and arm  52  to move downwardly out of its horizontal and perpendicular alignment. This in turn allows third spring  33  to apply its bias to brake wedge  22 . When release solenoid  26  is intentionally de-energized to apply main drive shaft brake system  14 A, power continues to be supplied to second coil  40  of line solenoid  28 . Thus, application of brake wedge  22  is dependent on termination of power to release solenoid  26  and the continuation of power to line solenoid  28 . Main drive shaft brake system  14 A, including the dropping of brake wedge  22  by release lever  24 , is resettable. When release solenoid  26  is energized once again, first coil  38  pushes first stroke  34  upwards so that arm  52  is perpendicular to first stroke  34 , brake wedge  22  is lifted and main drive shaft brake system  14 A is ready to brake again. 
       FIG. 5  is a cross-sectional view of main drive shaft brake system  14 A in a brake blocked position. Depicted are the components of main drive shaft brake system  14 A: release lever  24 , release solenoid  26 , line solenoid  28 , first spring  30 , second spring  32 , first stroke  34 , second stroke  36 A, first coil  38 , second coil  40 , first side  42 , second side  44 , aperture  46 , space  48 A, buffer  50 A, arm  52 , and base  54 . The components of main drive shaft brake system  14 A depicted in  FIG. 5  are connected as described above with reference to  FIG. 3 . Main drive shaft brake system  14 A is equipped with line solenoid  28  to prevent an unintentional release of release solenoid  26 . In  FIG. 5 , an approximately simultaneous interruption or loss of power to both release solenoid  26  and line solenoid  28  causes second spring  32  and second stroke  36 A to inhibit the movement of release lever  24  caused by the release of first stroke  34  into space  48 A of aperture  46 . 
     In the case of power failure, power is unintentionally terminated to both release solenoid  26  and line solenoid  28 . In prior art systems that lack line solenoid  28 , a power failure mimics an intentional termination of power in that release solenoid  26  is de-energized, which drops release lever  24 , allowing brake wedge  22  to stop rotation of drive sheave  12 A and operation of passenger conveyor  10 . In main drive shaft brake system  14 A, an approximately simultaneous loss of power to both release solenoid  26  and line solenoid  28  extinguishes the electromagnetic counterforce of both first coil  38  and second coil  40 . First stroke  34  is no longer prevented by first coil  38  from falling into aperture  46 . Second stroke  36 A, however, moves into space  48 A more quickly and more forcefully than first stroke  34 . More specifically, the bias of second spring  32  pushes second stroke  36 A upwardly into aperture  46  toward release solenoid  26 . Buffer  50 A of second stroke  36 A occupies space  48 A and prevents first stroke  34  from occupying space  48 A. As a result, release lever  24  stays in its lifted position where arm  52  is substantially perpendicular to first stroke  34  and base  54  continues to latch brake wedge  22 . Space  48 A is dimensioned so that either first stroke  34  or buffer  50 A on second stroke  36 A can occupy space  48 A, but not both. The bias of second spring  32  is greater than that of first spring  30 , so that second stroke  36 A will block and inhibit the movement of first stroke  34  in the case of power failure. Second stroke  36 A will have a faster reaction time than first stroke  34  so that second stroke  36 A will always beat first stroke  34  by occupying space  48 A first. Line solenoid  28 , therefore, comprises a fail safe system that prevents the unintentional dropping of release lever  24  and application of brake wedge  22 . 
       FIG. 6  is a cross-sectional view of an alternative embodiment of main drive shaft brake  14 B in a ready to brake or lifted position. Depicted are the components of main drive shaft brake  14 B: release lever  24 , release solenoid  26 , line solenoid  28 , first spring  30 , second spring  32 , first stroke or plunger  34 , second stroke or plunger  36 B, stroke extension  37 , first coil  38 , second coil  40 , first side  42 , second side  44 , aperture  46 , space  48 B, buffer  50 B, arm  52 , and base  54 . The components of main drive shaft brake  14 B are arranged and functioning similar to the components of main drive shaft brake  14 A described above. In fact,  FIGS. 6-9  are in large part explained by the above description of  FIGS. 3-5  where like numbers correspond to like components. In the interest of brevity, the differences between main drive shaft brake  14 B and main drive shaft brake  14 A will be highlighted below. 
     The structural differences of main drive shaft brake  14 B are best understood from second stroke  36 B having stroke extension  37  and the location of space  48 B and buffer  50 B. In main drive shaft brake  14 B shown in  FIG. 6 , stroke extension  37  has a reverse “L”-shape, first extending horizontally from one end of second stroke  36 B away from second coil  40  and then extending vertically in the direction of arm  52  and substantially parallel to second stroke  36 B, adjacent an outside of both line solenoid  28  and release solenoid  26 . Stroke extension  37  is substantially parallel to and spaced apart from first stroke  34  as it approaches a bottom surface of arm  52 . Located at a top of stroke extension  37 , adjacent a bottom surface of arm  52 , is buffer  50 B. Like buffer  50 A, buffer  50 B comprises a non-magnetic material such as but not limited to plastic. Located between buffer  50 B and the bottom surface of arm  52  is space  48 B. Space  48 B is dimensioned such that either buffer  50 B or a portion of arm  52  can occupy space  48 B, but not both. 
     The functional differences of main drive shaft brake  14 B arise from the location of space  48 B and buffer  50 B. Energizing release solenoid  26  and line solenoid  28  brings main drive shaft brake system  14 B into the ready to brake position. The electromagnetic force of second coil  40  pulls second stroke  36 B downwardly through second side  44  toward second spring  32  to counter spring force of second spring  32 . By pushing second stroke  36 B downwardly, stroke extension  37  and attached buffer  50 B are also held down thereby, freeing up space  48 B between buffer  50 B and arm  52 . In this lifted position, both release solenoid  26  and line solenoid  28  are energized and ready to change states should the power supply be interrupted. 
       FIG. 7  is a cross-sectional view of the embodiment of main drive shaft brake  14 B from  FIG. 6  in a released or dropped position. Depicted are the components of main drive shaft brake system  14 B: release lever  24 , release solenoid  26 , line solenoid  28 , first spring  30 , second spring  32 , first stroke  34 , second stroke  36 B, stroke extension  37 , first coil  38 , second coil  40 , first side  42 , second side  44 , aperture  46 , space  48 B, buffer  50 B, arm  52 , and base  54 . The components of main drive shaft brake system  14 B depicted in  FIG. 7  are connected as described above with reference to  FIGS. 3 and 6 . 
     Termination of power to first coil  38  extinguishes the electromagnetic counterforce and therefore, allows first stroke  34  to fall further into aperture  46  toward line solenoid  28 . More or less simultaneously, first spring  30  pushes arm  52  downwardly out of its horizontal and perpendicular alignment and into space  48 B to contact buffer  50 B. More or less simultaneously, first spring  30  pushes base  54  upward, which causes lever  24  to pivot and arm  52  to move downwardly out of its horizontal and perpendicular alignment. This in turn allows third spring  33  to apply its bias to brake wedge  22 . When release solenoid  26  is intentionally de-energized to apply main drive shaft brake system  14 B, power continues to be supplied to the second coil  40  of line solenoid  28 . Thus, as in main drive shaft brake system  14 A shown in  FIG. 4 , application of brake wedge  22  is dependent on termination of power to release solenoid  26  and the continuation of power to line solenoid  28 . Main drive shaft brake system  14 B is also resettable. When release solenoid  26  is energized once again, first coil  38  pushes first stroke  34  upwards so that arm  52  is perpendicular to first stroke  34  and no longer occupying space  48 B. So positioned, main drive shaft brake system  14 B is once again ready to brake and holds brake wedge  22  in the lifted and ready position. 
       FIG. 8  is a cross-sectional view of the embodiment of main drive shaft brake  14 B from  FIGS. 6 and 7  in a brake blocked or inhibited position. Depicted are the components of main drive shaft brake system  14 B: release lever  24 , release solenoid  26 , line solenoid  28 , first spring  30 , second spring  32 , first stroke  34 , second stroke  36 B, stroke extension  37 , first coil  38 , second coil  40 , first side  42 , second side  44 , aperture  46 , space  48 B, buffer  50 B, arm  52 , and base  54 . The components of main drive shaft brake system  14 B depicted in  FIG. 8  are connected as described above with reference to  FIGS. 3 and 6 . 
     In main drive shaft brake system  14 B, an approximately simultaneous loss of power to both release solenoid  26  and line solenoid  28  extinguishes the electromagnetic counterforce of both first coil  38  and second coil  40 , and first stroke  34  is no longer prevented by first coil  38  from moving further into aperture  46 . Buffer  50 B attached to stroke extension  37 , however, moves into space  48 B and prevents arm  52  from occupying space  48 B. More specifically, the bias of second spring  32  pushes second stroke  36 B, including stroke extension  37  having buffer  50 B attached thereto, upwardly. Since arm  52  is prevented from falling into space  48 B, now occupied by buffer  50 B, lever  24  continues to latch brake wedge  22  and hold it in a lifted position. The bias of second spring  32  is greater than that of first spring  30 , so that second stroke  36 B will block and inhibit the movement of lever arm  52  in the case of power failure. Second stroke  36 B will have a faster reaction time than first spring  30  or lever  24 , so that second stroke  36 B will always beat release lever  24  by occupying space  48 B first. Line solenoid  28 , therefore, comprises a fail safe system that prevents the unintentional dropping of release lever  24  and application of brake wedge  22 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.