EMERGENCY TERMINAL DECELERATION IN ELEVATOR SYSTEMS

Abstract

A method of controlling a moving component (22, 24) approaching a buffer (42, 46) in a hoistway (34) of an elevator system (20) is provided. The method includes: a) calculating, based on a current velocity of the moving component (22, 24), a required braking distance to decelerate the moving component (22, 24) to a maximum buffer impact velocity; b) comparing the required braking distance to a current buffer distance between the moving component (22, 24) and the buffer (42, 46) to give a comparison result; c) repeating steps a) and b) one or more times; and d) triggering an emergency stop of the moving component (22, 24) based on the comparison result.

Claims

1. A method of controlling a moving component (22, 24) approaching a buffer (42, 46) in a hoistway (34) of an elevator system (20), the method comprising: a) calculating, based on a current velocity of the moving component (22, 24), a required braking distance to decelerate the moving component (22, 24) to a maximum buffer impact velocity; b) comparing the required braking distance to a current buffer distance between the moving component (22, 24) and the buffer (42, 46) to give a comparison result; c) repeating steps a) and b) one or more times; and d) triggering an emergency stop of the moving component (22, 24) based on the comparison result.

2. A method as claimed in claim 1, comprising repeating step a), and optionally step b), based on an updated current velocity of the moving component (22, 24).

3. A method as claimed in claim 1, comprising repeating steps a) and b) at a rate based on a measurement rate of the current velocity of the moving component (22, 24).

4. A method as claimed in claim 1, comprising repeating steps a) and b) a plurality of times when the current buffer distance between the moving component (22, 24) and the buffer (42, 46) is less than a pre-set value.

5. A method as claimed in claim 1, wherein one or more repetitions of steps a) and b) are separated by one second or less, 500 ms or less, 100 ms or less, 50 ms or less, or 10 ms or less.

6. A method as claimed in claim 1, wherein calculating the required braking distance to decelerate the moving component (22, 24) to a maximum buffer impact velocity comprises calculating the motion of the moving component (22, 24) following an emergency stop condition being met.

7. A method as claimed in claim 6, comprising calculating the required braking distance using expected constant accelerations of the moving component (22, 24) in different phases of an emergency stop.

8. A method as claimed in claim 6, wherein calculating the motion of the moving component (22, 24) comprises calculating a first distance to be travelled by the moving component (22, 24) in a reaction time between an emergency stop condition being met and one or more emergency stop actions occurring.

9. A method as claimed in claim 6, wherein calculating the motion of the moving component (22, 24) comprises calculating a second distance to be travelled by the moving component (22, 24) in a brake drop delay time between an emergency stop action occurring and a substantive braking force being generated.

10. A method as claimed in claim 6, wherein calculating the motion of the moving component (22, 24) comprises calculating a third distance to be travelled by the moving component (22, 24) in a braking time between the substantive braking force being generated and the moving component (22, 24) being decelerated to the maximum buffer impact velocity.

11. A method as claimed in claim 6, wherein calculating the motion of the moving component (22, 24) comprises using a mass of the moving component (22, 24).

12. A method as claimed in claim 1, wherein the moving component (22, 24) is an elevator car (24) or an elevator counterweight (26).

13. A method as claimed in claim 1, comprising calculating a current buffer distance from an absolute position of the moving component (22, 24) in the hoistway (34).

14. An elevator system (20) comprising: a moving component (22, 24) arranged to move along a hoistway (34); a buffer (42, 46) located in the hoistway (34) to limit the movement of the moving component (22, 24); and a controller configured to: a) calculate, based on a current velocity of the moving component (22, 24), a required braking distance to decelerate the moving component (22, 24) to a maximum buffer impact velocity; b) compare the required braking distance to a current buffer distance between the moving component (22, 24) and the buffer (42, 46) to give a comparison result; c) repeat steps a) and b) one or more times; and d) trigger an emergency stop of the moving component (22, 24) based on the comparison result.

15. An elevator system (20) as claimed in claim 14, wherein the moving component (22, 24) is an elevator car (24) or an elevator counterweight (26).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures in which:

[0037] FIG. 1 is a schematic view of an elevator system according to an example of the present disclosure;

[0038] FIG. 2 is a schematic diagram illustrating the operation of the of the elevator system in FIG. 1;

[0039] FIG. 3 is a speed-distance diagram illustrating trajectories of an elevator car operated according to an example of the present disclosure;

[0040] FIG. 4 is a speed-distance diagram illustrating another trajectory of an elevator car operated according to an example of the present disclosure and;

[0041] FIG. 5 is a speed-distance diagram illustrating a comparison between the trajectory of an elevator car operated conventionally, and an elevator car operated according to an example of the present disclosure.

DETAILED DESCRIPTION

[0042] 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. 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.

[0043] 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. The buffers 42, 46 are designed to safely withstand an impact from the elevator car 22 or counterweight 24 respectively at or below a maximum buffer impact velocity. The first and second buffers 42, 46 may have different maximum buffer impact velocities. In one example, the maximum buffer impact velocity for the first buffer 42 (i.e. the buffer for the elevator car 22) is approximately 1 ms.sup.−1.

[0044] 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. Normal operation of the drive system 30 is controlled by an elevator controller 40. In some examples, during normal operation the elevator car 22 is driven to travel at velocities exceeding the maximum buffer impact velocity for the first buffer 42 (e.g. at velocities of up to 4 ms.sup.−1 or more).

[0045] The elevator system 20 also comprises a safety controller 52, shown in more detail in FIG. 2. The safety controller comprises 52 comprises an ETS (Emergency Terminal Stop) decision node 54 and an actuator node 56, connected by a CAN bus 58. If required, the actuator node 56 can interrupt the supply of power to the drive system 30 to execute an emergency stop via a safety chain 60.

[0046] The elevator system 20 also comprises an absolute position measurement system 50 configured to determine the absolute position and velocity of the elevator car 22 in the hoistway 34. The absolute position measurement system 50 is configured to output a measurement of the absolute position and velocity of the elevator car 22 at a high rate (e.g. up to every 10 ms or faster) to the safety controller 52 over CAN bus 58. Although the absolute position measurement system 50 is shown as a separate component in FIGS. 1 and 2, in some examples it may form part of the safety controller 52 or the elevator controller 40 (or all three could be provided as one controller). The absolute position measurement system 50 comprises a coded tape extending at least part of the way along the hoistway (not shown) and two sensors (not shown) mounted on the elevator car 22 and arranged to read the coded tape to determine the position and velocity of the elevator car 22 in the hoistway 34.

[0047] At any point during normal operation an emergency stop of the elevator car 22 may be triggered, for instance if a hoistway door is opened, if a maintenance worker is present in the pit of the hoistway or, as explained in more detail below, the elevator car 22 travels too quickly on approach to the terminal landing 35. An emergency stop is triggered by an emergency stop signal from the safety chain 60 seen in FIG. 2. An emergency stop may be executed by interrupting the supply of power to the drive system 30. The loss of power triggers the brake device 36 to engage and stops the drive device 32 (i.e. removes any drive torque applied to the drive sheave). This brings the elevator car 22 (and the counterweight 24) quickly to a halt.

[0048] FIG. 3 is a speed-position diagram illustrating the normal trajectory 102 of the elevator car 22 approaching the terminal landing 35, and an improper trajectory 104 of the elevator car 22 approaching the terminal landing 35 too quickly, such that an emergency stop is triggered.

[0049] The normal trajectory 102 shows the elevator car 22 gradually slowing to a halt at the position of the terminal landing 35 (roughly 0.05 m above the buffer 42). The improper trajectory 104 shows the elevator car 22 accelerating towards the terminal landing 35.

[0050] For both trajectories 102, 104, the absolute position measurement system 50 continuously (e.g. at a high rate of up to every 10 ms or less) measures the position and velocity of the elevator car 22, and the ETS decision node 54 of the safety controller 52 repeatedly (e.g. at the same rate of the absolute position measurement system 50) calculates a required braking distance to decelerate the elevator car 22 to the maximum buffer impact velocity (1 ms.sup.−1 in this example) using the current velocity of the elevator car 22.

[0051] For instance, at point 106, at time t.sub.1, the elevator car 22 of both trajectories 102, 104 is located 1 m above the terminal landing 35 (i.e. with a current buffer distance dsbuf (tl) of approximately 1.05 m) and is travelling at 1 ms.sup.−1. The required braking distance at this moment is calculated by summing the distances that would be travelled by the elevator car 22 in three phases of an emergency stop: a first distance ds.sub.1 (t.sub.1) corresponding to the distance that would be travelled by the elevator car 22 during a reaction time dtreaction between an emergency stop condition being met at t.sub.1 and the interruption of the power supply to the drive system 30; a second distance ds.sub.2 (t.sub.1), corresponding to the distance that would be travelled by the elevator car 22 during a brake drop delay time dtdelay between the interruption of power to the brake device 36 and the generation of substantive braking force by the brake device 36 (e.g. 80% of nominal maximum braking force); and a third distance ds.sub.3(t.sub.1), corresponding to the distance that would be travelled by the elevator car 22 whilst it decelerates under braking to the maximum buffer impact velocity, for a time dtbraking. The first distance ds.sub.1(t.sub.1) is calculated according to equation (1) given above where, for this example, at time t.sub.1:

v.sub.current=1 ms.sup.−1,

dt.sub.reaction=100 ms,

a.sub.1=1 ms.sup.−2

[0052] Giving a value for ds.sub.1 of approximately 0.105 m. Similarly, the second and third distances are calculated according to equations (2)-(6), and summed to produce the total required braking distance, which in this example at time t.sub.1 is approximately 0.4 m. However, because the current buffer distance ds.sub.buf (t.sub.1) is 1.05 m, no emergency stop is triggered for either trajectory 102, 104.

[0053] However, at a second time, t.sub.2, the elevator car 22 following the improper trajectory 104 is at point 108 in FIG. 4, roughly 0.6 m above the terminal landing (i.e. with ds.sub.buf (t.sub.2)=0.605 m) and travelling at roughly 1.2 ms.sup.−1. Again, first, second and third distances ds.sub.1 (t.sub.2), ds.sub.2 (t.sub.2), ds.sub.3 (t.sub.3) are calculated and the total required braking distance calculated to be 0.605 m. Thus, an emergency stop is triggered by the actuator node 56 of the safety controller 52, cutting power to the drive system 30 and thus decelerating the elevator car 22 to below the maximum buffer impact velocity of 1 ms.sup.−1 before the elevator car 22 hits the buffer 42. The emergency stop follows the three expected phases, with the elevator car 22 accelerating to point 110 in a first phase during a reaction time, accelerating further to point 112 in a brake drop delay time and decelerating for a braking time to point 114 (where it hits the buffer 42).

[0054] For illustrative purposes, FIG. 3 shows a required braking distance 120 for a range of car velocities. However, this velocity envelope is not pre-stored by the safety controller 52 (e.g. as a look-up table) and used to trigger emergency stops, because this requires additional memory (to store the look-up table) and is more difficult to adapt to changing circumstances (e.g. a changing elevator car 22 mass). Instead, the ETS Decision node 54 simply stores a small number of parameters (e.g. maximum buffer impact velocity, terminal buffer position) and calculates analytically the required braking distance repeatedly at a high rate (e.g. up to every 10 ms or even faster) as the elevator car 22 descends towards the terminal landing 35.

[0055] FIG. 4 shows another improper trajectory 204 of the elevator car 22. It can be seen that although the elevator car 22 is decelerating towards the terminal it is doing so too slowly. At a point 206, the elevator car 22 has a current buffer distance of 0.5 m, and a current velocity of approximately 0.9 ms.sup.−1. Using the current velocity, the safety controller 52 calculates the required braking distance to be 0.5 m and thus triggers an emergency stop which brings the elevator car 22 to below the maximum buffer impact velocity before the elevator car 22 hits the buffer 42 at point 208.

[0056] FIG. 5 compares a possible trajectory of an elevator car approaching a terminal landing according to a conventional emergency terminal stop method, and according to an example of the present disclosure.

[0057] FIG. 5 shows a regular operational profile (“Drive Profile ETSD 2-point”) 302 (i.e. trajectory) for an elevator car in a system which uses a conventional emergency terminal stopping device featuring two discrete position switches 304, 306 located at 4 m and 15 m from the terminal landing (0 m) respectively. The position switches 304, 306 are arranged to trigger an emergency stop if the elevator car passes by travelling at a velocity above pre-set thresholds 308, 310 of 1.9 ms.sup.−1 and 3.4 ms.sup.−1 respectively. The dotted line connecting the pre-set thresholds 308, 310 represents the fixed velocity threshold applied across different travel distances in the hoistway.

[0058] Because, in the conventional system, emergency terminal stops can only be triggered by the discrete position switches 304, 306, the velocity threshold 310 for the upper position switch 306 must be set at a velocity it is safe for the elevator car to be travelling just prior to passing the lower position switch 304 (because the system receives no position information between these two points). This means that a large safety margin is included in the velocity threshold 310 (i.e. it must be set below what is actually safe at the position of the upper position switch 306). Similarly, the threshold for the lower position switch 304 also includes a large safety margin. The deceleration profile of the elevator car following the regular operational profile 302 must therefore be very gentle, in this example having a deceleration of approximately 0.3 ms.sup.−2.

[0059] In contrast, FIG. 5 also shows a regular operational profile (“Drive Profile”) 312 (i.e. trajectory) of an elevator car controlled according to an example of the present disclosure. In this example, the required braking distance is repeatedly calculated based on the current velocity of the elevator car and compared to the current buffer distance of the car. The calculated required braking distance (“ETS Trigger”) 320 for a range of car velocities is shown in FIG. 5 and illustrates the benefit of this continuous monitoring. The regular motion profile 312 does not need to include large safety margins and thus may be more aggressive, i.e. featuring higher velocities and a higher deceleration (1.2 ms.sup.−2 in this example) than the prior art approach. This allows for more efficient elevator operation (e.g. with shorter journey times).

[0060] 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.