Abstract:
An emergency braking assembly that stops the rotation of a shaft in the event that the speed of the shaft exceeds a predetermined speed. The braking assembly includes a flanged mounting ring that is mounted to a housing where the shaft extends through the ring, and a braking ring threadably mounted to the mounting ring. An insert is mounted to the shaft within the braking ring. The braking assembly insert includes a pair of symmetrical weights that tend to move outward upon rotation of the shaft. Pins mounted to the weights and the insert prevent the weights form moving outward until the speed of the shaft exceeds the predetermined speed. A locking mechanism that locks the pin to the insert releases causing the pins to extend outside of the insert and engage stops mounted to an inside surface of the braking ring, which stops the shaft from rotating.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a braking assembly for stopping the rotation of a shaft and, more particularly, to an emergency braking assembly for stopping the rotation of a shaft if the speed of the shaft exceeds a predetermined speed, where the braking assembly employs weights that slide outward under centrifugal force and cause pins to engage a rotating braking ring. 
     2. Discussion of the Related Art 
     Many critical operations in elevating, hoisting, material handling and transfer operations require the use of braking mechanisms to prevent fatalities, injury and damage to property. Typical examples include elevators, man lifts, hoists, locks, conveyers and other machinery designed to overpower gravity, water or wind energy. Failure of these braking mechanisms can lead to a potential runaway condition that can be avoided by the use of redundant braking mechanisms. 
     Existing systems designed to provide redundant braking are typically powered or released by the same power source that the machine uses, such as electricity, pneumatic pressure or hydraulic pressure. This means that the reliability of these redundant braking systems can only be as reliable as the power source itself. 
     One application where emergency braking is critical is for overhead hoists and winches. An overhead hoist or winch typically lifts and lowers a load by using a motor that winds and unwinds a cable onto a cylindrical cable drum rotating upon a shaft. The motor includes an output shaft that is coupled to a gear box having an output shaft. The gear box output shaft is coupled to the cable drum shaft so that the gears control the speed and power provided by the motor to the cable drum. 
     In a typical hoist or winch design, a braking device is attached to the motor. In one design, the braking device includes a spring loaded plate that applies a force against a stationary plate. When the motor shaft is to be rotated, an electrical signal controls an electromagnetic coil that releases the spring loaded plate against the bias of the springs to allow the motor shaft to rotate. Thus, if power is not available to operate the motor, the springs that maintain the motor in the locked position prevent it from rotating. 
     If the motor brake is not periodically inspected and maintained, contamination and normal wear can affect the ability of the braking device to prevent the motor shaft from rotating. Thus, if the hoist or winch is carrying a load and power is disrupted, the motor brake may not be able to prevent the load from falling. Further, these types of hoists and winches typically do not include a braking device downstream of the motor. Particularly, failure of any of the several gears in the gear box may allow the cable drum shaft to rotate independently of the rotation of the motor shaft. Thus, a potential hazardous condition exists where a gear box failure could cause a suspended load on the hoist or winch to drop, possibly causing injury or worse. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, an emergency braking assembly is disclosed that stops the rotation of a shaft in the event that the speed of the shaft exceeds a predetermined speed. The braking assembly includes a flanged mounting ring that is mounted to a housing where the shaft extends through the ring, and a braking ring threadably mounted to the mounting ring. An insert is mounted to the shaft within the braking ring. The insert includes a pair of symmetrical weights that tend to move outward upon rotation of the shaft. Pins mounted to the weights and the insert prevent the weights form moving outward until the speed of the shaft exceeds the predetermined speed. When the speed of the shaft does reach the predetermined speed, a locking mechanism that locks the pins to the insert releases causing the pins to extend outside of the insert and engage stops mounted to an inside surface of the braking ring. Further rotation of the insert causes the braking ring to rotate on the mounting ring, which stops the shaft from rotating. 
     Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a hoist or winch including a braking assembly, according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the braking assembly shown in  FIG. 1 ; 
         FIG. 3  is a blown-apart perspective view of the braking assembly; 
         FIG. 4  is a front view of the braking assembly; 
         FIG. 5  is a cross-sectional view of an insert within the braking assembly; 
         FIG. 6  is a perspective view of a braking pin used in the braking assembly; 
         FIG. 7  is a back view of the braking assembly showing the braking pins in a retracted position; and 
         FIG. 8  is a back view of the braking assembly showing the braking pins in an extended braking position. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discussion of the embodiments of the invention directed to a braking assembly for stopping the rotation of a shaft is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. Particularly, any reference below of the braking assembly of the invention being used for a particular application, such as an overhead hoist or winch, is merely for illustration purposes in that the braking assembly of the invention has application for stopping any suitable shaft. 
       FIG. 1  is a side view of an overhead hoist or winch  12  including a braking assembly  10 , according to an embodiment of the present invention. The hoist or winch  12  includes a motor  18  that rotates a cable drum  20  including a cable drum shaft  16  through a gear box  14 . A cable  22  is wound and unwound onto the cable drum  20  by the motor  18  to lift and lower a load in a manner that is well understood in the art. As discussed above, the motor  18  would include its own braking mechanism that would prevent the motor  18  from rotating in the event of power loss or motor control failure. However, if a failure occurred within the gear box  14 , the motor brake controls or the motor  18  itself, then the shaft  16  could continue rotating independent of the braking power of the motor  18 . As will be discussed in detail below, the braking assembly  10  engages the shaft  16  if the shaft  16  exceeds a calibrated rotational speed, indicating a failure, to stop the shaft  16  from rotating. 
       FIG. 2  is a cross-sectional view of the braking assembly  10  mounted on the hoist or winch  12 ,  FIG. 3  is a broken-apart perspective view of the braking assembly  10  and  FIG. 4  is a front view of the braking assembly  10 . The braking assembly  10  includes a mounting ring  24  having a mounting flange  26  and a threaded center cylinder  28  extending therefrom. The mounting ring  24  is bolted to a mounting platform  36  of the hoist or winch  12  by a plurality of bolts  30  theadily engaged through threaded openings  32  in the flange  26 . The shaft  16  extends through a central opening  34  in the cylinder  28 . 
     The braking assembly  10  also includes a braking ring  40  having a flange  42  and a center cylinder  44 . In this non-limiting embodiment, the braking ring  40  and the mounting ring  24  have about the same diameter. The cylinder  44  includes a cylindrical opening  46  having a threaded portion that theadily engages the outer threads of the cylinder  28  so that the braking ring  40  can rotate on the mounting ring  24 . A plurality of pins  50  are threaded through openings  52  in the flange  42  so that a tip  54  of each pin  50  extends out a back of the flange  42  a calibrated distance. When the braking ring  40  is threaded to the mounting ring  24 , the tips  54  of the pin  50  will contact an outer surface of the flange  26 . For reasons that will become apparent from the discussion below, the pins  50  are made of a softer metal than the mounting ring  24 . In one embodiment, the pins  50  are made of brass and the mounting ring  24 , as well as most of the components of the braking assembly  10 , are made of steel. Opposing brake stops  58  and  60  are mounted within the cylinder  44  by bolts  62  also for reasons that will become apparent from the discussion below. 
     The braking assembly  10  also includes a cylindrical braking insert  70  that is positioned within the opening  46 , and is shown in cross-section in  FIG. 5 . The braking insert  70  includes a side wall  72 , a front plate  74  and a center cylinder  76 . A cylindrical bore  78  is provided through the center cylinder  76 , and a cylindrical chamber  80  is provided within the insert  70  between the sidewall  72  and the center cylinder  76 . The shaft  16  extends through the bore  78  in a suitable fit so that it is able to rotate relative thereto. A key channel  82  is provided within the bore  78  and excepts a half-moon type key  84  that is fitted within a channel  86  in the shaft  16  so that the shaft  16  is locked to the insert  70 . Therefore, upon rotation of the shaft  16 , the insert  70  will also rotate. 
     Opposing half-cylindrical weights  90  and  92  are positioned within the chamber  80  in a loose configuration so that the weights  90  and  92  can slide a set distance toward and away form each other within the chamber  80 . The weight  90  includes a half-cylindrical opening  94  and the weight  92  includes a half-cylindrical opening  96  that conform to the shape of the center cylinder  76  of the insert  70  so that when the weights  90  and  92  are in a completely retracted position, they are in contact with each other and form a bore through which the center cylinder  76  extends. 
     The weight  90  includes a pair of control pins  98  and  100  extending from opposite ends, and the weight  92  includes a pair of control pins  102  and  104  extending from opposite ends. A back ring  106  is positioned within channels  108  and  110  in a back-end of the weights  90  and  92  so that the pin  98  is positioned within a slot  112  on the ring  106  and the pin  102  is positioned within a slot  114  on the ring  106 . Likewise, a front ring  120  is positioned within a channel  122  in the weight  90  and a channel  124  in the weight  92  so that the pin  100  is positioned within a slot  126  of the ring  120  and the pin  104  is positioned within a slot  128  of the ring  120 . 
     When the weights  90  and  92  are in their retracted position and in contact with each other, the pins  98  and  102  are at one end of the slots  112  and  114 , respectively, and the pins  100  and  104  are at one end of the slots  126  and  128 , respectively. When the weights  90  and  92  move away from each other under centrifugal force to engage the braking mechanism of the assembly  10 , as will be discussed in more detail below, the rings  106  and  120  rotate so that the pin  98  slides in the slot  112 , the pin  102  slides in the slot  114 , the pin  100  slides in the slot  126  and the pin  104  slides in the slot  128  so that the weights  90  and  92  move in a smooth and symmetrical fashion relative to each other. 
     A locking ring  136  is positioned within a groove  132  in the center cylinder  76  of the insert  70  to hold the ring  120  within the channels  122  and  124  and the ring  106  within the channels  108  and  110 . A locking ring  130  is positioned within a groove  134  in the end of the shaft  16  to hold the assembly  10  on the shaft  16 . 
     Opposing braking pins  140  and  142  are positioned within the insert  70 . The braking pin  140  is positioned within the insert  70  so that it extends through a bore  144  of the sidewall  72  of the insert  70 , a bore  146  in the center cylinder  76  of the insert  70  and a bore  148  in the weight  90 . Likewise, the braking pin  142  extends through a bore  150  in the sidewall  72  of the insert  70 , a bore  152  in the center cylinder  76  of the insert  70  and a bore  154  in the weight  92 . 
       FIG. 6  is a perspective view of the pin  140 , where the pin  142  is identical. The pin  140  includes a head portion  160  and a body portion  162  defining a V-shaped groove  164  therebetween. A rounded indentation  166  is provided in the body portion  162 , and is aligned with a threaded hole  168  in the weight  90 . A locking screw  170  is threaded through the hole  168  so that it contacts and is inserted within the indentation  166  so as to lock the pin  140  to the weight  90 . A locking screw  172  is also provided to lock the braking pin  142  to the weight  92 . 
     An end of the body portion  162  opposite to the head portion  160  includes a cut-out portion  174  that conforms to the shape of the shaft  16 . When the braking pins  140  and  142  are extended to provide the braking, as will be discussed in detail below, the V-shaped groove  164  engages conforming angled edges  178  and  180  on the braking stops  58  and  60 , respectively. A resilient bumper  176  is mounted within the indentation  174  by a suitable screw to prevent the pins  140  and  142  from vibrating on the shaft  16  as the assembly  10  rotates. 
     The braking assembly  10  is engaged by the operation of centrifugal force from rotation of the shaft  16 . Particularly, once the speed of the shaft  16  exceeds a calibrated speed, where a failure has likely occurred, the weights  90  and  92  slide outward under centrifugal force so that the head portions  160  of the pins  140  and  142  extend out of the sidewall  72  of the insert  70 . The calibration speed is set by a calibrating screw  190  that is threaded into an opening  192  in the plate  74  and the side wall  72 . First, a ball  194  is placed in the opening  192  and a spring  196  is positioned against the ball  194 . The calibrating screw  190  is threaded into the opening  192  the appropriate distance so that the ball  194  is positioned within the V-groove  164  of the pin  140  with the desired force provided by the spring  196 . As the shaft  16  rotates at normal speed, the tension provided by the ball  194  in the groove  164  holds the pin  140  in place, which in turn holds the weight  90  in the retracted position. The rings  106  and  120  in turn hold the weight  92  in the retracted position.  FIG. 7  is a back view of the braking assembly  10  showing the weights  90  and  92  in the non-braking or retracted position with the mounting ring  24  removed. 
     As the speed of the shaft  16  increases beyond the calibration speed, the groove  164  pushes the ball  194  against the spring  196  so that the ball  194  will be released from the groove  164 . The centrifugal force on the weight  90  and  92  will cause the weights  90  and  92  to slide outward in the chamber  80  until they contact the inside edge of the sidewall  72 .  FIG. 8  is a back view of the braking assembly  10  showing the weights  90  and  92  in the braking or extended position with the mounting ring  24  removed. In this position, the head portions  160  of the pins  140  and  142  extend outward into the inside surface of the cylinder  44 . 
     As the shaft  16  continues to rotate, the head portions  160  and the grooves  164  of the pins  140  and  142  will contact the edges  178  and  180  of the braking stops  58  and  60 , respectively, causing the braking ring  40  to rotate with the shaft  16 . As the braking ring  40  rotates, it is further threaded onto the mounting ring  24  driving the tips  54  of the pins  50  into the flange  26 . Because the tips  54  of the pins  50  are relatively soft compared to the steel of the ring  24 , the engagement between the braking ring  40  and the mounting ring  24  provides a controlled brake to the shaft  16 , preventing it from rotating further. 
     Once the hoist or winch  12  is in a safe configuration, and the braking assembly  10  can be released, rotation of the braking ring  40  in an opposite direction by rotating the shaft  16  will cause the head portions  160  of the pins  140  and  142  to be release from the angled edges  178  and  180  and contact an angled edge  200  and  202  of the braking stops  58  and  60 , respectively, once the braking ring  40  has rotated one complete revolution. The shape of the head portion  160  and the orientation of the angled edges  200  and  202  pushes the pins  140  and  142  back into the insert  70  to reset the brake assembly  10 . The pins  50  can then be replaced with new pins, and the assembly  10  will be operational again. 
     The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.