Abstract:
A rotary actuated overspeed safety device for elevators. The overspeed safety device comprises a pair of pivotally mounted counterweights linked by a pivotally attached coupling rod and a wheel that rollably engages a guide rail. The counterweights are pivotally mounted to the wheel in a parallel plane configuration. Centrifugal force causes the pivotally mounted counterweights to pivot outward toward an actuator as the wheel spins. The overspeed safety device is triggered when the pair of pivotally mounted counterweights engages an actuator. The actuator is a housing that is engagably connected to an elevator safety.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to elevator braking systems. More particularly, the present invention relates to a rotary actuator that replaces a conventional elevator governor and maintains the function of the governor. The invention provides the actuation that allows a braking system to prevent the elevator car from overspeeding.  
         BACKGROUND OF THE INVENTION  
         [0002]    Elevator systems generally comprise an elevator car suspended by a rope system including a traction drive. The car is guided along guide rails so that relatively little lateral motion is imparted to the car during use. In passenger elevators, at least, it is conventional to provide a braking system to halt the elevator car in the event of an overspeed condition. Braking systems include actuation devices commonly known as governors.  
           [0003]    Most elevators of the prior art employ governors. In such an elevator system, the governor detects an excessive speed of the car and actuates emergency stop devices in the event the car experiences an overspeed condition. Conventional governors include a governor pulley at an upper end of the governor system, a tension sheave at the lower end of the governor system, and an endless governor rope passed around and between the pulley and the sheave and extending substantially throughout the length of the governor system. A part of the governor rope is connected to a safety link that is mounted on the car frame. As the car ascends or descends, the governor rope travels so that the governor pulley is rotated.  
           [0004]    In an elevator constructed in this manner, if the car travels at a speed higher than the predetermined speed for any reason, the governor pulley correspondingly rotates at a speed higher than its predetermined speed. As the governor pulley rotates at this higher speed, paired flyweights or flyballs rotating on a spindle are accelerated outwardly by centrifugal force. As the flyweights or flyballs are accelerated outwardly, an overspeed switch is tripped and power is removed from the machine motor, a brake is actuated, and, if further overspeed occurs, a clutching device is activated that will clamp down on the governor rope to activate the safeties. The result is that the elevator is brought to an abrupt, although safe, halt.  
           [0005]    If the path of the elevator is very long, a very long governor rope is required. As the rope length increases, both the weight of the rope and the force of inertia produced during acceleration of the rope increase. Consequently, as these things increase, so does the requirement for larger and more powerful equipment to slow down the governor rope. Likewise, larger equipment would require more space.  
           [0006]    More modern governing devices omit the stationary governor pulley and rope and fit each elevator car with its own smaller governor. Nakagawa, in U.S. Pat. No. 5,377,786, discloses a governor that includes a rotating member mounted on an elevator car so as to rollably contact the guide rail along which the elevator travels. This rotating member is looped by a belt to an actuator means which actuates the stop mechanism when the rotating speed of the rotating member exceeds a predetermined speed.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is drawn to a rotary actuated overspeed safety device for elevators. The rotary actuated overspeed device comprises a pair of pivotally mounted counterweights fixedly attached to a wheel that rollably engages an elevator guide rail. The pair of counterweights is positioned in a parallel planar relationship with the wheel. Centrifugal force causes the pivotally mounted counterweights to pivot outward toward the edge of the wheel as the wheel spins. An elevator safety is triggered when the pivotally mounted counterweights engage a clutch housing that is movably connected to the elevator safety.  
           [0008]    A pivotally attached connecting rod may connect the pair of counterweights. This rod causes the counterweights to pivot in unison. One of the counterweights is spring-biased against an application of centrifugal force. Springs of various spring rates can be used to adjust the amount of centrifugal force needed to cause the counterweights to pivot.  
           [0009]    The counterweights may be pivotally mounted on a base. This base is preferably positioned in a parallel planar relationship with the wheel and is fixedly connected to the wheel. The base is rotatably supported within the clutch housing by bearings. Bearings may be interposed on the base plate beneath the counterweights to facilitate the pivoting of the counterweights.  
           [0010]    The clutch housing is movably connected to an arm that causes the elevator safety to engage when torque is transferred from the moving counterweights to the clutch housing. The clutch housing is dimensioned, configured, and positioned to be engaged by the counterweights when the counterweights pivot outwardly.  
           [0011]    The invention also comprises a rotary actuated safety device having a wheel that rollably engages a guide rail, two pairs of pivotally mounted counterweights, and a clutch housing to actuate an elevator safety. This embodiment is substantially the same as the previous embodiment; however, the second pair of counterweights is configured to pivot under an application of centrifugal force caused by overspeed rotation in the opposite direction. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The present invention will now be described with reference to the accompanying drawings, which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several figures, in which:  
         [0013]    [0013]FIG. 1 is an exploded view of the clutch housing, tire, and rotary actuator;  
         [0014]    [0014]FIG. 2 is a side cutaway view of the clutch housing, the base plate, the bearings supporting the base plate, and the counterweights;  
         [0015]    [0015]FIG. 3 is an isometric view of the rotary actuator;  
         [0016]    [0016]FIG. 4A is an isometric view of an alternate embodiment showing low-friction bearings interposed between the counterweight and the base plate;  
         [0017]    [0017]FIG. 4B is a side view of the alternate embodiment showing low-friction bearings interposed between the counterweight and the base plate;  
         [0018]    [0018]FIG. 5 is a plan view of the rotary actuator;  
         [0019]    [0019]FIG. 6 is a plan view of the counterweight and its contact point with clutch housing; and  
         [0020]    [0020]FIG. 7 is an exploded view of an alternate embodiment of the rotary actuator showing two sets of counterweights on a base plate as they would be fitted inside a housing. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The invention summarized above and defined by the enumerated claims will be better understood by referring to the following detailed description, which should be read in conjunction with the accompanying drawings.  
         [0022]    [0022]FIG. 1 illustrates a rotary actuator  10 . Rotary actuator  10  comprises a pair of counterweights  12  mounted on a base plate  14  and connected together by a coupling rod  16 . Base plate  14  is rotatably mounted inside a clutch housing  22  and fixedly attached to an end of a shaft  28 . An opposing end of shaft  28  is fixedly mounted to a rotatable tire  20 . Tire  20  rollably engages the nose portion of a T-shaped guide rail.  
         [0023]    Base plate  14  freely spins inside clutch housing  22 , as shown in FIG. 2, providing counterweights  12  are not centrifugally driven into contact with clutch housing  22 . Shaft  28  is fixedly attached to base plate  14 . Base plate rod  30  is fixedly attached to the back of base plate  14  and is positioned in the space of shaft  28 . Bearings  15  are housed inside a bearing housing  17  thus allowing base plate  14  to freely spin inside clutch housing  22 . Axial rotation of clutch housing  22  causes an arm (not shown) to activate elevator safeties.  
         [0024]    Referring now to FIG. 3, rotary actuator  10  is described in greater detail. Each counterweight  12  is generally cylindrical in shape and dimensioned and configured to fit within clutch housing  22 . The surface of counterweight  12  that slides across the surface of base plate  14  is polished to the same smooth finish as the surface of base plate  14  to minimize the frictional resistance during operation of rotary actuator  10 . In a preferred embodiment, referring to FIGS. 4A and 4B, low-friction bushings  33  are interposed between base plate  14  and counterweights  12  for improved friction reduction. The preferred material of construction for low-friction bushing  33  is polytetrafluoroethane or a similar material. The sides of counterweights  12  should not be polished, but should instead be of a rougher texture in order to maximize the frictional resistance when counterweights  12  engage a braking surface on the inside of clutch housing  22  during operation of rotary actuator  10 . The operation of rotary actuator  10  is described in greater detail below.  
         [0025]    As illustrated in FIG. 5, counterweights  12  are mounted on diametrically opposing sides of base plate  14 . Each counterweight  12  is pivotally mounted to base plate  14  at a point that is not the center of gravity of counterweight  12 .  
         [0026]    Each end of coupling rod  16  is pivotally connected to a point near the outer edge of the cross sectional area of each counterweight  12 . Coupling rod  16  is connected to counterweights  12  in such a manner as to allow pivoting of each counterweight  12  in unison. Furthermore, the distance and travel path of each counterweight  12  is symmetrical with respect to the other. It is preferred that the counterweight  12  and connecting rod  16  assembly be precisely balanced to offset gravitational effects.  
         [0027]    A spring  34  is used to hold counterweights  12  in the unactuated position. One end of spring  34  is pivotally attached to one of the counterweights  12  of the pair at a point proximate the outer edge of the counterweight  12 . The other end of spring  34  is fixedly attached to base plate  14 . Spring  34  has a tension that corresponds to the speed required to trigger rotary actuator  10 . In the fully unactuated position, the distance between the outermost edge of counterweight  12  and an inner wall  36  of clutch housing  22  defines a clearance  37 .  
         [0028]    Operation of rotary actuator  10  is dependent upon the rotational speed of tire  20  along the guide rail. Rotary actuator  10  is triggered by its rotation about an axial center of gravity  32  at such an angular speed that spring  34  extends and counterweights  12  pivot eccentrically outward in unison from their respective pivot points  40  to simultaneously engage inner wall  36  of clutch housing  22 . Referring now to FIG. 6, a first line  48  passes through a contact point  54  of counterweight  12  with inner wall  36  of clutch housing  22  and extends to axial center of gravity  32  of actuator  10 . A second line  50  passes through the same contact point  54  and extends to a pivot point  40 . First line  48  and second line  50  define an angle  38  that causes counterweights  12  to “wedge” against inner wall  36  of clutch housing  22  and remain engaged against inner wall  36 .  
         [0029]    Rotary actuator  10  rotates at some angular velocity about axial center of gravity  32 . As counterweights  12  pivot and engage inner wall  36  of clutch housing  22 , torque is transferred to clutch housing  22  as a result of the angular velocity and the load on tire  20 . The transfer of torque to clutch housing  22  in turn triggers engagement of the elevator safeties through a connector (not shown), thereby causing the elevator car to come to a halt.  
         [0030]    In order to disengage the elevator safeties, once they are engaged as a result of rotary actuator  10  being triggered, the elevator car must be moved in the opposite direction. Movement of the elevator car in the opposite direction allows tire  20  to roll in the direction opposite of the direction it was rolling during the overspeed that caused rotary actuator  10  to trigger and engage the elevator safeties. Once tire  20  begins to roll in the opposite direction, counterweights  12  become “unwedged” from inner wall  36  and the spring  34  is released thereby biasing one counterweight  12  (directly) back into its pre-pivot position. As the first counterweight  12  returns to its pre-pivot position, connecting rod  16  moves and pulls second counterweight  12  back into its pre-pivot position. Both counterweights  12  are unwedged, and inner wall  36  of clutch housing  22  is disengaged and moves freely relative to base plate  14 . This movement in the opposite direction also disengages the elevator safeties.  
         [0031]    One pair of counterweights  12  is arranged so that it can halt the elevator car from either the ascent or the descent. A second pair of counterweights  42  can also be pivotally connected to each end of a second connecting rod  46  and mounted on base plate  14  as shown in FIG. 7. The second pair of counterweights  42  is configured to fit around the first set of counterweights  12  and inside clutch housing  22 . The second pair of counterweights has the same properties and dimensions as the first pair of counterweights  12 , but the configuration of the individual weights on base plate  14  is “backwards”. In other words, counterweights  42  are mounted in such a way that the rolling of tire  20  in the same direction that caused first set of counterweights  12  to actuate and engage inner wall  36  of clutch housing  22  does not allow counterweights  42  to wedge against clutch housing  22 . This is because the angle defined by a line extending from the contact point of counterweight  42  and housing  22  and pivot  40  and a radial line passing through the contact point is not proper for counterweights  42  to wedge in this direction. Tire  20  turns in the same direction that a second spring  44  is biased; therefore, the second set of counterweights  42  will never be actuated. In order to actuate the second set of counterweights  42 , tire  20  must turn in the opposite direction. For example, previously if the elevator was descending, an overspeed would cause the first set of counterweights  12  to pivot and engage inner wall  36  of clutch housing  22 . Now, the elevator would have to ascend and overspeed to cause the second set of counterweights  42  to pivot and engage inner wall  36  of clutch housing  22 .  
         [0032]    Having thus described several exemplary embodiments of the invention, it will be apparent that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements, though not expressly described above, are nonetheless intended and implied to be within the spirit and scope of the invention. Accordingly, the foregoing discussion is intended to be illustrative only; the invention is limited and defined only by the following claims.