METHOD OF PREVENTING GRAVITY JUMP AT EMERGENCY STOP IN ELEVATOR SYSTEMS

Abstract

A method of controlling an elevator car (22) includes driving the elevator car (22) with a drive system (30) including a drive device (32) and a brake device (36); detecting an emergency stop condition; triggering the brake device (36) in response to detecting an emergency stop condition; determining a delay to be applied between triggering the brake device (36) and stopping the drive device (32); and waiting for a time period corresponding to the delay before stopping the drive device (32).

Claims

1. A method of controlling an elevator car (22), the method comprising: driving the elevator car (22) with a drive system (30) including a drive device (32) and a brake device (36); detecting an emergency stop condition; triggering the brake device (36) in response to detecting an emergency stop condition; determining a delay to be applied between triggering the brake device (36) and stopping the drive device (32); and waiting for a time period corresponding to the delay before stopping the drive device (32).

2. A method as claimed in claim 1, comprising determining whether the detected emergency stop condition is a motion-hazard emergency stop condition, and only waiting for the time period corresponding to the delay before stopping the drive device (32) if the emergency stop condition is a motion-hazard emergency stop condition.

3. A method as claimed in claim 1, wherein the delay to be applied between triggering the brake device (36) and stopping the drive device (32) is predetermined.

4. A method as claimed in claim 3, wherein the predetermined delay to be applied between triggering the brake device (36) and stopping the drive device (32) corresponds to an expected brake drop delay of the brake device (36).

5. A method as claimed in claim 1, comprising determining the delay to be applied by measuring a level of braking force that is applied in use by the brake device (36).

6. A method as claimed in claim 5, wherein measuring a level of braking force that is applied in use by the brake device (36) comprises monitoring motion of the elevator car (22) after the brake device (36) has been triggered.

7. A method as claimed in claim 1, comprising controlling the drive device (32) to decelerate the elevator car (22) after the brake device (36) is triggered.

8. A method as claimed in claim 1, wherein detecting an emergency stop condition comprises opening a safety chain.

9. An elevator system (20) comprising: an elevator car (22); and a drive system comprising a drive device (32) and a brake device, the drive system (32) arranged to drive the elevator car (22); and a safety system (47) configured to: detect an emergency stop condition; trigger the brake device (36) in response to detecting an emergency stop condition; determine a delay to be applied between triggering the brake device (36) and stopping the drive device (32); and wait for a time period corresponding to the delay before stopping the drive device (32).

10. An elevator system (20) as claimed in claim 9, wherein the safety system (47) comprises a safety controller (40) configured to: determine the delay to be applied between triggering the brake device (36) and stopping the drive device (32); and wait for the time period corresponding to the delay before stopping the drive device (32).

11. An elevator system (20) as claimed in claim 9, wherein the safety system (47) comprises a safety chain (43) configured to detect an emergency stop condition.

12. An elevator system (20) as claimed in claim 9, comprising an absolute position measurement system (41) arranged to determine elevator car (22) position and/or velocity.

13. An elevator system (20) as claimed in claim 12, wherein the safety system (47) is arranged to determine the delay to be applied by monitoring motion of the elevator car (22), after the brake device (36) has been triggered, using the absolute position measurement system (41).

Description

DRAWING DESCRIPTION

[0027] One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures in which:

[0028] FIG. 1 is a schematic view of an elevator system;

[0029] FIG. 2 is a velocity-distance diagram illustrating the trajectory of a conventional emergency stop; and

[0030] FIG. 3 is a velocity-distance diagram illustrating the trajectory of an emergency stop carried out according to an example of the present disclosure.

DETAILED DESCRIPTION

[0031] As shown in FIG. 1, an elevator system 20 comprises an elevator car 22 that runs in a hoistway 34 between various floors of a building. The elevator car 22 is suspended in the hoistway 34 by a tension member 26 (e.g. comprising one or more ropes or belts). The other end of the tension member 26 is connected to a counterweight 24. The elevator car 22 and the counterweight 24 are moving components in the elevator system 20. However, it will be appreciated that in other examples the elevator system may be ropeless.

[0032] The bottom of the hoistway 34 includes a first buffer 42 located underneath the elevator car 22 and a second buffer 46 located underneath the counterweight 24. The buffers 42, 46 are located just below a terminal landing 35 of the elevator system 20 (i.e. stopping point for the lowermost floor in the building) and are arranged to act as shock absorbers to bring the elevator car 22 and/or counterweight 24 quickly but gently to a halt if it should overrun the terminal landing 35. An emergency terminal stopping device (ETSD) 37 is arranged to detect if the elevator car 22 or the counterweight 24 is travelling too quickly on approach to the terminal landing 35, and to trigger an emergency stop if so. The ETSD 37 may, for instance, comprise a series of sensors located at points in the hoistway near to the terminal landing 35. If the elevator car 22 passes one of the sensors travelling above a pre-set speed threshold, an emergency stop is triggered. A permissible motion profile (“ETS trigger”) 103 that falls just within these speed thresholds is shown in FIG. 2.

[0033] During normal operation, the elevator car 22 travels up and down in the hoistway to transport passengers and/or cargo between floors of the building. The elevator car 22 is driven by a drive system 30 comprising a drive device 32 and a brake device 36. The tension member 26 passes over a drive sheave (not shown) that is driven to rotate by the drive device 32 and braked by the brake device 36.

[0034] In an emergency stop situation, the drive device 32 and the brake device 36 are controlled by a safety controller 40. Normal operation of the drive system 30 may be controlled by a separate elevator controller (not shown). The safety controller 40 may be connected to an absolute position measurement system 41. The safety controller 40 may comprise a PESSRAL node. The elevator system 20 also comprises a safety chain 43 configured to detect emergency stop conditions. The safety chain 43 is connected to the safety controller 40 (which may be considered part of the safety chain) and together they form a safety system 47.

[0035] The conventional approach to emergency stops is illustrated in FIG. 2, which shows a normal trajectory (“drive profile”) 102 of the elevator car 22 approaching the terminal landing 35, and an improper trajectory (“start at wrong pos”) 104 of the elevator car 22 approaching the terminal landing 35 too quickly, such that a conventional emergency stop is triggered.

[0036] The normal trajectory 102 shows the elevator 22 gradually slowing to a halt at the position of the terminal landing 35. However, the improper trajectory 104 shows the elevator car 22 accelerating towards the terminal landing 35, such that at a point 106 approximately 0.45 m above the terminal landing 35, the elevator car 22 is travelling at approximately 1 ms.sup.−1. After a short electronic reaction time (“PES response time”), in which the elevator car 22 continues to travel and accelerate to point 108, this causes the emergency terminal stopping device 37 to trigger an emergency stop of the elevator car 22 by opening the safety chain 43 and interrupting the supply of power to the whole drive system 30 (i.e. cutting power to the drive device 32 and the brake device 36).

[0037] The drive device 32 immediately stops driving the drive sheave, and the brake device 36 is triggered to engage. However, due to the inherent brake-drop delay of the brake device 36, for a short period of time immediately after the emergency stop is triggered, little or no braking force is actually generated by the brake device 36. Because the power supply to the drive device 32 has also been interrupted, there is also no driving force applied to the elevator car 22. Thus, the elevator car 22 continues to travel and accelerate to point 110 on a brake deceleration profile, roughly level with the terminal landing 35 (i.e. still slightly above the buffer position 42) and travelling at approximately 1.4 ms.sup.−1. Only after this brake drop delay does the brake device 36 start to generate a substantial level of braking force and the elevator car 22 begins to decelerate, slowing slightly before impacting the buffer 42 at point 112 at a speed of approximately 1.3 ms.sup.−1.

[0038] FIG. 3 illustrates a method of controlling the elevator car 22 according to an example of the present disclosure. FIG. 3 again shows the normal trajectory (“drive profile”) 102 of the elevator car 22 approaching the terminal landing 35, and an improper trajectory (“start at wrong pos”) 104 of the elevator car 22 approaching the terminal landing 35 too quickly, such that an emergency stop is triggered when the improper trajectory 104 intersects a permissible motion profile (“ETS trigger”) 203. It will be appreciated that the permissible motion profile 203 represents the maximum permitted speed at any given point in the hoistway, above which an emergency stop will be triggered. The safety controller 40 may use information from the absolute position measurement system 41 to compare the speed of the elevator car 22 to the permissible motion profile 203, as well as or instead of relying on the ETSD 37. An emergency stop is triggered by opening the safety chain 43.

[0039] The normal trajectory 102 again comprises a gradual deceleration before stopping at the terminal landing 35. However, the improper trajectory 104 shows the elevator car 22 accelerating towards the terminal landing 35, such that at a point 206 approximately 0.4 m above the terminal landing 35, the elevator car 22 is travelling at approximately 1.1 ms.sup.−1, which is above the permitted threshold speed for that position. Therefore, after a short electronic reaction time (“PES response time”) (e.g. a reaction time of the emergency terminal stopping device 37 and/or the safety chain 43) in which the elevator car 22 continues to travel and accelerate to point 208, the emergency terminal stopping device 37 triggers an emergency stop of the elevator car 22 by opening the safety chain 43. This triggers the safety controller 40 to immediately interrupt the supply of power to the brake device 36, triggering the brake device 36. However, the drive device 32 continues to be powered and to drive the elevator car 22 via the drive sheave.

[0040] The safety controller 40 then determines a delay to be applied between triggering the brake device 36 (at point 208) and stopping the drive device 32, for instance by retrieving from memory an expected brake-drop delay for the brake device 36. The safety controller 40 then waits for a for a time period corresponding to the delay before stopping the drive device 32 at point 210 (e.g. by interrupting a power supply to an inverter of the drive device 32). During the delay time period, the safety controller 40 controls the drive device 32 to decelerate the elevator car 22, such that at the end of the delay time period at point 210, the elevator car 22 is located just above the terminal landing 35 and travelling at approximately 0.8 ms.sup.−1.

[0041] Because the delay time period corresponds to the expected brake drop delay for the brake device 36, at this point 210 the brake device 36 starts to generate a substantial level of braking force and the deceleration of the elevator car 22 increases, slowing the elevator car 22 to approximately 0.5 ms.sup.−1 before impacting the buffer 42 at point 212.

[0042] Thus, by delaying the stopping of the drive device 32 after the brake device 36 is triggered, not only is a gravity jump avoided but the eventual impact velocity with the buffer 42 is also reduced even when the emergency stop is triggered closer to the terminal landing 35. This means the ETSD emergency stop threshold speeds can be increased and/or the threshold positions moved closer to the terminal landing 35, allowing more efficient elevator motion profiles to be used (e.g. with higher operating speeds and/or higher deceleration profiles). For instance, in the example shown in FIG. 3, the example permissible motion profile (“ETS trigger”) 203 involves generally higher speeds at the same positions than the comparable motion profile 103 in FIG. 2.

[0043] While the disclosure has been described in detail in connection with only a limited number of examples, it should be readily understood that the disclosure is not limited to such disclosed examples. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of the disclosure. Additionally, while various examples of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described examples. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.