Patent Publication Number: US-6659230-B1

Title: Safety brake for stairlifts

Description:
FIELD OF THE INVENTION 
     This invention relates to stair mounted elevators or lifts, commonly known as stairlifts. In particular, the invention relates to a governor or speed-limiting device to control or brake movement of a stairlift carriage in the event that some failure or malfunction in the drive mechanism, driving the carriage along a stairlift rail, allows the carriage to exceed a predetermined maximum speed. 
     BACKGROUND 
     Stairlifts, in the form of a carriage mounted for movement along a rail, are well known for moving aged or handicapped persons up and down staircases. Typically stairlifts incorporate a drive motor in the carriage, the output of which engages a rack, extending along the rail, via a gearbox. However, if there is a failure of or in the motor, gearbox or rack, the carriage may be left to travel down the sloping rail in an uncontrolled manner. 
     There is a requirement, at least in the United Kingdom, that stairlifts incorporate an overspeed governor to automatically apply a braking force in the event that component failure or malfunction allows the carriage to exceed a predetermined speed whilst moving down the rail. In the past these devices have tended to be quite complex in form and have only been able to apply a braking force when the carriage is moving in one direction. Thus, depending on which side of the stairway the stairlift apparatus is mounted, a different governor must be used. 
     It is an object of this invention to provide a governor for a stairlift which addresses the aforementioned problems or which at least provides a useful choice. 
     SUMMARY OF THE INVENTION 
     Broadly, the present invention concerns a governor apparatus for governing the velocity of a stairlift carriage along a stairlift rail with the stairlift carriage being movable in opposite directions along the longitudinal axis of the stairlift rail. The governor apparatus includes a braking member displaceable into contact with the stairlift rail and operating means being operable, when the speed of the stairlift carriage along the stairlift rail exceeds a predetermined maximum speed, for causing the braking member to engage the stairlift rail. The operating means comprises a guiding surface, rotatable with the movement of the carriage along the stairlift rail, and a follower, which is operatively connected to the braking member, in a sliding contact with the guiding surface for when the speed of the stairlift carriage is less than the predetermined maximum speed. 
     Said operating means is preferably constructed and arranged to trigger under the influence of a force induced centrifugally. To this end, said operating means preferably includes guide means rotatable with the movement of said carriage along said rail, and a roller in sliding contact with said guide means, said roller being connected to said braking member. 
     Said roller is preferably mounted for rotation on a first end of an operating lever, the other end of said operating lever being pivotally mounted to said braking member. 
     Preferably said braking member is mounted for rotation about the same axis of rotation as said guide means, said braking member having cam surfaces which are non-concentric with respect to said axis of rotation. 
     Preferably said guide means includes an inner guide surface and an outer guide surface, said roller contacting said inner guide surface when the speed of said carriage is below said predetermined maximum, and contacting said outer guide surface when said speed exceeds said predetermined maximum, said outer guide surface being constructed and arranged to allow the position of said roller to be locked with respect to said guide means. 
     Preferably said outer guide surface includes at least one locking notch sized to receive said roller. 
     Preferably said braking member has a central, inoperative position in which said braking member is symmetrical about an axis passing through the axis of rotation thereof. 
     Preferably said governor further includes a catch to retain said braking member, against rotation, in said central position when not under the influence of said operating means. 
     In a second aspect the invention provides a stairlift carriage including the governor as set forth above. 
     Many variations in the way the present invention may be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only and the absence of description of particular alternatives or variants should in no way be applied to limit the scope of the invention. Such description of specific elements which follows should also be interpreted as including equivalents whether existing now or in the future. The scope of the invention should be defined solely by the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One form of governor incorporating the various aspects of the invention will now be described with reference to the accompanying drawings in which: 
     FIG.  1 : Shows an elevational view of a governor according to the invention; 
     FIG.  2 : Shows a similar view to that shown in FIG. 1 but with certain detail omitted; 
     FIG.  3 : Shows a sectional view through the governor shown in FIG. 1; and 
     FIG.  4 : Shows a view along the line IV—IV in FIG.  3 . 
    
    
     DESCRIPTION OF WORKING EMBODIMENTS 
     Referring to the drawings, the present invention provides a governor  5  for a stairlift carriage (not shown), the carriage being moveable, in the conventional manner, along a rail, a surface of which is indicated by reference numeral  6  in the drawings. As will be apparent from FIG. 3 the rail surface  6 , in this embodiment, is aligned at 45° to the horizontal. 
     In the form shown, the governor  5  includes a mounting bracket  7  which forms the basis of the governor. The bracket  7  comprises an angled upper mounting section  8  so configured that when section  8  is mounted on a vertical side plate  9  of the carriage, the locking members of the governor (described in detail below) are arranged to engage rail surface  6  aligned at 45° to the horizontal. The mounting section  8  extends down into a lower section  10 . 
     Mounted on, and extending through, the lower section  10  is a bearing journal  11  in which shaft  12  is rotatably mounted. 
     Mounted at one end of the shaft  12  is a drive gear  13 . The drive gear  13  is configured and mounted so as to engage a drive rack  13   a  extending along the rail surface  6 , the drive rack forming part of the main drive system serving to power the stairlift carriage along the rail. Mounted at the opposite end of shaft  12 , so as to rotate with drive gear  13 , is a flywheel  14  forming part of an operating means which will be described in greater detail below. 
     The governor further includes a braking member  15  which is rotatable on the outer surface of the journal  11 , is thus independent of the drive gear  13 , and is displaced about journal  11  by a link arm  16 . Link arm  16  is pivotally mounted, at one end thereof, on the braking member  15  and includes, at its other end, a roller  17 . The roller  17  engages in guide track  18  [FIG.  4 ] provided on the inner surface of flywheel  14 , thereby connecting the flywheel  14  to the braking member  15 . As will be described in greater detail below, the connection is a sliding connection for so long as the speed of the carriage is below the predetermined maximum speed, but becomes a fixed connection in the event the speed of the carriage exceeds the predetermined maximum. 
     It will be appreciated that arrangement of the arm  16  and roller  17  is such that the roller normally rests, under gravity, on the inner guide surface defined by the inner central part  19  of the flywheel. The system is so configured that, at acceptable operating speeds, gravity is sufficient to maintain the roller in contact with inner central part  19 . However, should the speed of the carriage [and thus the rotational speed of shaft  12 ] exceed an acceptable level, the roller moves outwards under centrifugal action to engage outer guide surface  20 . 
     As can be seen from FIG. 4, outer guide surface  20  is adapted to lock the position of roller  17  and, to that end, preferably includes at least one, and more preferably two, braking notches  21 . It will be appreciated that, when the roller  17  enters one of the notches  21  further rolling action over the outer guide surface is prevented and the position of the roller is effectively locked with respect to the guide. In this event, the rotation of the flywheel  14  is transferred to the braking member  15  through link arm  16 . 
     As can be seen most clearly in FIG. 2, the braking member  15  has a central inoperative position in which the member  15  is substantially symmetrical about a vertical line  22  passing through the pivot axis on which the braking member is mounted. To either side of line  22  the braking member includes cam surfaces  23  arranged to engage the rail surface as the braking member is pivoted about its mounting axis. The cam surfaces may be provided with teeth  24  or the like to enhance frictional engagement with the rail as the braking member is pivoted into engagement with the rail  6 . 
     To prevent the braking member inadvertently moving into engagement with the rail  6 , catch means is preferably provided to maintain the being member in the central position as shown in FIGS. 1 and 2, when not under the influence of the flywheel  14 . However, the catch means is such that the same is overridden by flywheel effect when the roller  17  engages in one of locking notches  21 . 
     In the form shown the catch means comprises a simple leaf spring  26  mounted on bracket  7  and having a central indent (not shown) to receive one end of locking pin  27  extending from the rear face of braking member  15 . When roller  17  engages in one of notches  21 , the pin  27  is forced out of the indent in the leaf spring  26 . 
     Finally, in the form of governor depicted and described herein, electrical switch  30  is provided, the switch  30  being mounted so as to be activated by upper lobes  31  on the braking member  15 , when the barking member  15  is pivoted into an operative position, to cut power to the carriage drive motor [not shown]. 
     Since the braking member and the inner guide surface are symmetrical, the governor as described herein, will work equally effectively in both directions. This means that the same governor can be used regardless of whether the carriage is to be left or right-handed. This in turn reduces expense and the likelihood of installation-related problems. 
     It will thus be appreciated that the present invention, at least in relation to the working embodiment described herein, provides a relatively simple form of over-speed governor for a stairlift capable of effective operation regardless of the orientation of the stairlift installation.