Patent Publication Number: US-11040848-B2

Title: Elevator machine brake delay control

Description:
BACKGROUND 
     Elevator systems have proven useful for carrying individuals and cargo among various levels in a building. Typical elevator systems have a machine including a motor and a brake for controlling movement and position of the elevator car. Under normal operating conditions, the machine motor is controlled to slow down the elevator car and the machine brake holds the car at a landing. 
     Elevator systems typically include additional braking devices, which are often referred to as safeties, to stop elevator car movement during an overspeed condition. In some elevator systems, the machine brake is used for applying a braking force to stop the elevator car during predetermined conditions, such as when the power supply is interrupted. One of the drawbacks associated with stopping an elevator car under such conditions is that the stop tends to be very abrupt and can cause passengers discomfort or to be very uneasy. There are challenges associated with attempting to control machine brake application under such conditions to avoid an overly abrupt stop while also accounting for various other features of the elevator system that may be adversely affected, depending on how the machine brake is deployed. 
     SUMMARY 
     An illustrative elevator system includes an elevator car, a machine including a motor that provides a motive force for moving the elevator car along a travel path and a brake that resists movement of the elevator car, and a brake controller. The brake controller is configured to determine when the elevator car is within a selected range of at least one end of the travel path. The brake controller inhibits a delay in application of the brake when the elevator car is within the selected range and permits a delay in application of the brake when the elevator car is outside of the selected range. 
     An example embodiment having one or more features of the elevator system of the previous paragraph includes a detector that detects a position of the elevator car. The brake controller receives a position signal from the detector indicating that the elevator car is within the selected range. 
     In an example embodiment having one or more features of the elevator system of any of the previous paragraphs, the brake controller is configured to provide a delay command that causes the delay in application of the brake when the elevator car is outside the selected range, and the brake controller is configured to disable the delay command based on the position signal. 
     In an example embodiment having one or more features of the elevator system of any of the previous paragraphs, the selected range is configured to accommodate a latency between the elevator car entering the selected range and the brake controller receiving the position signal. 
     In an example embodiment having one or more features of the elevator system of any of the previous paragraphs, the selected range is configured based on a braking torque of the brake and a load of the elevator car. 
     In an example embodiment having one or more features of the elevator system of any of the previous paragraphs, the brake controller is configured to inhibit or permit the delay in application of the brake during an emergency braking scenario. 
     In an example embodiment having one or more features of the elevator system of any of the previous paragraphs, the detector comprises a limit switch situated near a position of the elevator car near an edge of the selected range. 
     In an example embodiment having one or more features of the elevator system of any of the previous paragraphs, the brake controller disables the delay in application of the brake when the elevator car is within the selected range. 
     An example embodiment having one or more features of the elevator system of any of the previous paragraphs includes a buffer near the at least one end of the travel path and the selected range is based on at least one characteristic of the buffer. 
     An illustrated example method of controlling a machine brake in an elevator system that includes an elevator car that moves along a travel path comprises determining when the elevator car is within a selected range of at least one end of the travel path, inhibiting a delay in application of the brake when the elevator car is within the selected range, and permitting a delay in application of the brake when the elevator car is outside of the selected range. 
     An example embodiment having one or more features of the method of the previous paragraph includes using a detector for detecting when the elevator car is within the selected range and providing a position signal from the detector indicating that the elevator car is within the selected range. 
     An example embodiment having one or more features of the method of any of the previous paragraphs includes using a brake controller to provide a delay command that causes the delay in application of the brake when the elevator car is outside the selected range. The brake controller is configured to disable the delay command based on the position signal. 
     In an example embodiment having one or more features of the method of any of the previous paragraphs, the selected range is configured to accommodate a latency between the elevator car entering the selected range and the brake controller receiving the position signal. 
     In an example embodiment having one or more features of the method of any of the previous paragraphs, the selected range is configured based on a braking torque of the brake and a load of the elevator car. 
     An example embodiment having one or more features of the method of any of the previous paragraphs includes inhibiting or permitting the delay in application of the brake during an emergency braking scenario. 
     In an example embodiment having one or more features of the method of any of the previous paragraphs, the detector comprises a limit switch situated near a position of the elevator car near an edge of the selected range. 
     An example embodiment having one or more features of the method of any of the previous paragraphs includes disabling the delay in application of the brake when the elevator car is within the selected range. 
     An example embodiment having one or more features of the method of any of the previous paragraphs includes a buffer at the end of the travel path and the selected range is based on at least one characteristic of the buffer. 
     The various features and advantages of at least one disclosed example embodiment will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates selected portions of an elevator system designed according to an embodiment of this invention. 
         FIG. 2  is a flowchart diagram summarizing an example machine brake control strategy designed according to an embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of this invention allow for controlling elevator machine brake application during overspeed conditions or emergency braking scenarios. A delay in application of the machine brake provides a smoother stop and the control technique allows for such a delay to be used under a variety of scenarios while addressing the requirements of other components within the hoistway or elevator system. 
       FIG. 1  schematically illustrates selected portions of an elevator system  20 , which is one example embodiment of this invention. An elevator car  22  and counterweight  24  are connected by a roping assembly  26 . A machine  30  includes a motor  32  that causes rotation of a traction sheave (not illustrated) to cause movement of the roping assembly  26  for moving the elevator car  22  along a travel path within a hoistway  34 . The machine  30  includes a brake  36  that applies a braking force for decelerating the elevator car  22  and holding it in place at a landing when necessary. The machine brake  36  is also useful during an overspeed condition or an emergency stop situation to prevent movement of the elevator car  22 . 
     A brake controller  40  controls operation of the machine brake  36  during an overspeed or emergency stop situation. The brake controller  40  is configured to control whether the application of a braking force by the machine brake  36  is delayed. When the machine brake  36  is used during an emergency stop situation, the application of the braking force may cause the elevator car  22  to abruptly come to a stop. The brake controller  40  facilitates including a delay in the application of the braking force to smooth out the way in which the elevator car stops. Such a delay, however, is not desirable under all conditions or for all positions of the elevator car  22  within the hoistway  34 . 
     The brake controller  40  in some embodiments is part of an elevator controller while in others the brake controller  40  is part of the elevator drive. Some embodiments include a separate or dedicated computing device or processor as the brake controller  40 . 
     The example system  20  includes at least one buffer  42  situated near a bottom  44  of the hoistway  34 , which corresponds to one end of the travel path of the elevator car  22 . The buffer  42  operates in a known manner to provide a cushion between the elevator car  22  and the bottom  44  of hoistway  34  in the event that the elevator car  22  were to descend low enough for there to be contact between the elevator car  22  and the buffer  42 . 
     The example system  20  includes another buffer  46  situated beneath the counterweight  24 . In this example, the buffers  42  and  46  are reduced stroke buffers in that they are relatively smaller and their moving components move along a reduced stroke distance during buffer activation. 
     One issue associated with including a delay in the application of the machine brake  36  is that such a delay may have an adverse affect, for example, when the elevator car  22  is within close range of the buffer  42 . The brake controller  40  is configured to selectively permit or inhibit the delay of application of the machine brake  36  based upon a position of the elevator car  22  relative to at least one end of the travel path of the elevator car  22 . 
     The brake controller  40  receives information regarding a position of the elevator car from a detector, which may be realized through a software module or physical devices within the hoistway  34 . The illustrated example system  20  includes detectors  50  and  52  situated along the hoistway  34  for detecting a position of the elevator car  22 . In particular, the detectors  50  and  52  provide an indication of a position of the elevator car  22  within a selected range of an end of the travel path of the elevator car  22 . When the elevator car  22  is within a selected range of an end of its travel path, the brake controller  40  inhibits the delay in application of the machine brake  36  so that the elevator car  22  can be brought to a stop quickly enough to compensate for at least one characteristic of the buffer  42  (or  46 ), such as the reduced stroke distance of the buffer. 
     The detectors  50  and  52  are situated along the hoistway  34  in the illustration in a way that demonstrates how the hoistway  34  or travel path of the elevator car  22  can be effectively divided into sections. In the section shown at  54 , which includes the center portion of the hoistway  34 , there is no concern with allowing for or providing a delay in the application of the machine brake  36  during an overspeed or emergency stop situation. In the section  56  beneath the detector  50 , the delay should be inhibited or prevented to avoid the elevator car  22  contacting the buffer  42  at a higher than desired speed. If the elevator car  22  is within the section  58 , which establishes a selected range near the upper end of the travel path of the elevator car  22 , inhibiting brake application delay ensures that the counterweight  24  will not strike the buffer  46  at a higher than desired speed. Additionally, inhibiting delay in the application of the machine brake  36  when the elevator car  22  is within the section  58  (i.e., within a selected range of the upper end of the travel path) protects against contact between the elevator car  22  and components situated near the top of the hoistway  34 , such as the machine  30  and the structure used for mounting or supporting the machine  30 . 
       FIG. 2  includes a flowchart diagram  60  that summarizes an example approach used by the brake controller  40  for controlling the machine brake  36 . At  62 , the brake controller  40  determines whether the elevator car  22  is within the selected range of an end of the travel path. When the elevator car  22  is within that range, the brake controller  40  inhibits the machine brake application delay at  64 . Inhibiting or preventing the delay in the brake application ensures that the machine brake  36  will apply a braking force quickly enough to bring the elevator car  22  to a stop when it is within the selected range of an end of the travel path to avoid undesired contact between the elevator car  22  and the buffer  42  or another component within the hoistway. 
     If the elevator car  22  is outside of the selected range, the brake controller  40  permits or provides the brake delay at  66 . Depending on whether the brake delay is prohibited or not, at  68  the brake controller  40  determines when the machine brake  36  is needed for an emergency stop and applies the brake  36  with or without the delay depending on the position of the elevator car  22  relative to the end of the travel path. 
     In some embodiments, the detectors  50  and  52  provide a positon signal to the brake controller  40  indicating when the elevator car  22  is within the selected range of an end of the travel path. In the illustrated example, the size of the selected range is set to accommodate or account for a latency in signal communication between the detectors  50  and  52  and the brake controller  40 . For example, there may be a latency associated with the position signal from the detector  50  being received by the brake controller  40  and interpreted in a manner that the brake controller  40  responsively prohibits delaying the brake application. The size of the selected range is set to account for any such latency. Another latency may be associated with the processing within the brake controller  40  required to inhibit the delay of the brake application. 
     Other factors that are utilized for selecting the size of the range within which brake delay will be prohibited include the brake torque of the machine brake  36 , the load of the elevator car  22 , and the size of the buffer  42 . 
     In the illustrated example, the brake controller  40  operates normally to permit or provide the delay in application of the machine brake  36 . When it is necessary to inhibit or prevent the brake delay, the brake controller  40  activates a switch, which may be realized through software. In another embodiment, a physical switch, such as a limit switch, serves as the component for changing from a condition in which brake delay is allowed to one in which brake delay is prohibited. 
     In some embodiments the brake controller  40  provides a delay command when delaying machine brake application is acceptable. The brake controller  40  disables the delay command when the elevator car  22  is within the selected range. 
     One feature of the disclosed example embodiment is that it allows for an emergency stop to be accomplished in a way that is more comfortable for passengers in the elevator car  22  without compromising control over the brake application that is required when the elevator car  22  is in specific places within the hoistway  34 , such as near an end of the travel path. The use of a reduced stroke buffer requires the use of the brake to decelerate the elevator prior to impacting the buffer. The manner in which the brake controller  40  prohibits delay in the brake application guarantees a safe buffer striking speed because whenever the elevator car  22  enters a portion of the hoistway  34  that is within a selected range of an end of the travel path, the delay in brake application will be prohibited and no further active control is required to control the timing of the brake application during an emergency stop scenario once the stop has been triggered. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.