EP0758622A1

EP0758622A1 - Method and system for correcting the stopping precision of an elevator car

Info

Publication number: EP0758622A1
Application number: EP96305741A
Authority: EP
Inventors: Christophe Durand; Thierry Boureux
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 1995-08-11
Filing date: 1996-08-05
Publication date: 1997-02-19
Also published as: CZ237396A3; FR2737713B1; HUP9602118A2; FR2737713A1; PL315614A1; HU9602118D0; HUP9602118A3

Abstract

This system comprises an apparatus 18, 20, 22 adapted to provide a stopping information, a logic control 26 which processes the information, and as a consequence, provides a stopping command, an apparatus 28, 30, 32 for measuring the speed of displacement of the car, a microprocessor 38 provided with a stopping management program and a memory, a calculating unit 36 for calculating a delay T and a programmable delay module 40.

Description

The present invention concerns a method which allows the stopping precision of an elevator car at different levels to be corrected.
It is known that the stopping precision is the gap which separates the level of the threshold of the elevator car and that of the threshold of the landing when the car is stopped. It is known that stopping information on descent and on ascent are given respectively for each level at the moment when a magnetic sensor fixed on the car coincides with a magnet fixed in the hoistway at the said level. The stopping information is sent to stopping command logic with which elevator installations are provided and this sends a stopping command to the drive motor of the car. In the context of the invention, the drive means may comprise a two speed motor with a drum brake (known as an AC2 motor). The motor drives the car at a first speed over practically all of its run between the floors and at a lower speed (in the order of a quarter of the first speed) over a short distance before the car stops.
Currently, the stopping precision at landings for an elevator equipped with an AC2 motor falls within a margin of + 20 mm. Such a discrepancy can lead to serious material disadvantages. For example, the user risks tripping or the load of a pallet stacker may be shaken and damaged. This poor performance however represents the limits of the current techniques with this motorisation.
The reason for the poor performance of the AC2 motor is principally due to the fact that the braking force of the motor is not adapted to the load carried by the car but it is adjusted once for all cases, to have a comfortable deceleration. The result is that with this motor, the braking distance is not controlled as a function of the load for a particular stopping information. It is estimated that the adjustment of the braking force should allow, in the case of braking on ascending at high speed with the car empty, a stopping of the car over a distance greater than or equal to 80% of the distance travelled by the car in 1 second at the nominal speed. For example, if the nominal speed is 1 m/s, the cabin should stop after having travelled a minimum distance of 0.80 m.
Another reason to explain the mediocrity in performance is found in the fact that the speed before stopping is still relatively important even though the car is travelling at the lower speed. The result is that the inertia of the moving system comprised of the car and counterweight is important and the brake must dissipate high energy. Moreover, this energy changes significantly with the load in the car.
The solutions which are currently used to resolve this problem have as their object the reduction in speed of travel before stopping so as to reduce the energy to be dissipated by the brake. In fact, modification of the braking system is avoided, as it must conform to vigorous standards (EN81). To reduce the speed of travel before stopping one can:

carry out an electric control of the speed, for example by means of a variable frequency (VF) motor which is ideal from this point of view, as it allows the stopping information to be obtained at the moment when the speed is practically zero, the brake then having a simple role of a stopping brake;
increasing the number of poles of the low speed rotor of the AC2 motor to obtain very low speed;
to use a mechanic variator.

Unfortunately, all of the solutions, and principally the first, are too onerous to be applied to a two speed AC2 motor. The costs of the solution render the selling price of the installation too high to be practical.
The present invention seeks to remedy these disadvantages and has as its object a method allowing the stopping position of the AC2 motor elevator to be corrected while keeping the costs of this motor viable.
The idea of the invention derives from two observations made by the inventor:

1. The variation curves of stopping precision of the car as a function of its load P_A = f(C), both on ascending and descending, are comparable to two straight lines, and are, therefore reproducible. One can conclude that if an apparatus has been adjusted when it was put into service with the car empty, correctly adjusting the position of the magnet in relation to the magnetic sensors serves to obtain a zero stopping precision, and if the change in stopping precision as a function of the load is known, one can estimate the stopping precision for each load.
2. The variation curves of speed of displacement of the car as a function of its load V = g(C), both on ascending and descending, are comparable to straight lines.

From these two families of curves, one can deduce the variation curves of the stopping precision as a function of the speed P_A = h (V) on ascending and descending, which are, themselves comparable to straight lines.
The advantage of taking the speed as a parameter to estimate the correction in stopping precision, rather than the load, is that the speed can be easily measured. The measurement can be carried out, for example, by means of an optical fork apparatus which is the object of French Patent Application No. 95 08428, filed in the name of the present applicant. This has the advantage of being simple and inexpensive.
As a result of the above, one can estimate from the measurement of the speed before the car stops at each level, the stopping precision, i.e. the distance at which the threshold of the car will stop above or below the threshold of the landing.
From this result, the inventor has derived a method of correction of the stopping precision according to the invention. The invention thus provides a method of correcting the stopping precision of an elevator car provided with means (18, 20, 22) providing stopping information when the car (10) is located in the vicinity of a level, and a stopping control logic (26) which provides a stopping command to the drive means of the car, said method being characterised in that it comprises:

forming variation curves V = f(C) of the speed of displacement of the car during ascent and descent as a function of the load, measuring the speed before the car stops at a given level, at least in the case when the car is empty and in the case when it carries it nominal load,
forming the variation curves P_A = g (V) of the stopping precision of the car during ascent and descent, as a function of the load, measuring the stopping precision of the car during ascent and descent in the two cases mentioned above,
deriving the variation curves P_A = h (V) of the stopping precision as a function of the displacement speed,
calculating the correction of the stopping precision in the particular case when the car arrives at a given level, with a given direction and displacement and load, carried out using the following steps,
measuring the speed of displacement V of the car at said level and with said displacement direction,
calculating a specific delay T from the formula T = P_A/v, when P_A is the value of the stopping precision taken from said curve P_A = h (V), for said measured speed value,
including this delay between the stopping information and the stopping command.

The present invention also provides a system for correcting the stopping precision, comprising

means adapted to provide a stopping information each time the elevator car arrives in the vicinity of a level,
a control logic in which the information given by said means is processed, and which outputs a stopping command as a result,
means to measure the displacement speed of the car before stopping at each level,
a microprocessor provided with a stopping management program and a memory in which the variation curves P_A = h (V) during ascent and descent are stored,
a calculating unit for calculating a delay T using the formula T = P_A/v, where P_A is the particular value of the stopping position corresponding to a specific speed V measured at a level, said value being taken from said memory,
and a programmable delay module adapted to include said delay in the stopping information given by the means for providing stopping information.

The invention will be described by the following detailed description of a preferred embodiment, given by way of example only, with reference to the attached drawings in which:

Fig. 1 is a schematic view of an elevator installation equipped with a stopping precision correcting system according to the present invention;
Fig. 2 is a graph showing the variation in the stopping precision as a function of the load, during ascent and descent;
Fig. 3 is a graph representing the variation in speed of displacement of the elevator car as a function of the load, during ascent and descent;
Fig. 4 is a graph derived from Figs. 2 and 3 and showing the variation in the stopping precision as a function of the speed of displacement, and
Fig. 5 is a flow diagram which sets out the operations carried out by the correction system of the invention.

Fig. 1 shows the elevator car 10 in a hoistway 12 at the level of a landing 14. The installation is provided with a position reference system known per se, arranged to supply stopping information at the instant when the car is located slightly before its stopping position. This system comprises a magnet 18 fixed in the hoistway at each level, and two magnetic sensors 20, 22 fixed on the car one above the other. The upper magnetic sensor 20 emits stopping information when it coincides with magnet during descent of the car, while the lower magnetic sensor 22 emits stopping information during ascent of the car.
The information emitted at each level is sent to an input 24 of a command unit which can preferably be integrated in the control logic 26 with which the elevator installation is provided. The control logic 26 provides a stopping command to the drive motor of the car and orders the brake of the motor to be released. The motor and the brake are not shown for clarity.
The elevator installation is also provided with a car speed measuring apparatus. This may be of any known type, but preferably is an optical fork apparatus by reason of its simplicity and its low cost.
It is known that this speed measuring apparatus comprises an optical fork 28 fixed on the elevator car and a plurality of flags 30, 32 fixed in the hoistway. The optical fork comprises two crossed arms in which are mounted respectively an infra-red emitter and an infra-red receiver. The arms are arranged in a horizontal plane, such that the infra-red beam 34 horizontally traverses the intervals between the arms. The flags are formed by vertical plates, opaque to infra-red beams, and these are arranged so as to cut the infra-red beam 34 each time the optical fork arrives at their level. Fig. 1 shows the two flags associated with a level. The upper flag 30 serves to measure during descent and the lower flag 32 serves to measure during ascent.
The infra-red receiver emits signals having a first logic state when the infra-red beam passes and a second logic state when the beam is cut. These signals are transmitted to a calculating unit 36, which preferably may be integrated in the control logic 26.
From these signals, the unit 36 calculates the period Δt of interruption of the infra-red beam by a flag, then the displacement speed v of the car using the formula V = h/Δt, h being the height of the flag.
Having explained how to detect the stopping information and how to measure the speed we can now disclose the procedure for correcting the stopping precision of the car.
For this, the two important observations indicated above are exploited, to know that the stopping precision varies linearly as a function of the load carried by the car and that the displacement speed of the car before stopping also varies linearly as a function of the load.
The first observation is illustrated in Fig. 2. In this figure, the load C is shown on the abscissa and the stopping precision P_A on the ordinate, in millimetres. The negative values of P_A signify that the threshold of the car is located below the threshold of the landing. Before making the measurement, the brake and the stopping precision are adjusted, with the car empty. The variation curves have been obtained by measuring only four values of the stopping precision:

stopping precision with car empty (CV) during ascent (P_A CVM),
stopping precision with car empty during descent (P_A CVD), the stopping precision in both cases, being equal to 0 (point 0 in Fig. 2), if the installation is adjusted correctly.
stopping precision with loaded car (CC) with a nominal load during ascent (P_A CCM),
stopping precision with the car loaded during descent (P_A CCD).

The second observations is shown by Fig. 3. Here, the load is represented on the abscissa and the displacement speed of the car is represented on the ordinate. To trace the curve, only four values of the speed have been measured:

speed with cabin empty during ascent (VCVM)
speed with cabin empty during descent (VCVD)
speed with cabin loaded during ascent (VCCM)
speed with cabin loaded during descent (VCCD)

From these curves, one can easily deduce the curves of the variation of the stopping precision as a function of the speed. It is sufficient to transfer onto a system of coordinates P_A = h (V) the values of the pairs (P_A, V) shown in Figs. 2 and 3 for zero load and for full load. This results in the two linear segments shown in Fig. 4
From these curves, one can estimate in advance the stopping precision which will be obtained at a given level if only the actual displacement speed of the car is known before stopping at that level, and the stopping precision can then be corrected to bring it to effectively zero.
To do this, according to the present invention, a delay T is introduced between the stopping information given by the magnetic sensors 20 and 22 and the stopping command given by the control logic of the installation. This delay is calculated from the formula T = P_A/V, in which P_A is equal to the stopping precision read from one of the curves of Fig. 4 for the load case under consideration, and thus for the speed V measured just before stopping and in the direction of displacement under consideration.
In practice, the control logic 26 comprises a microprocessor 38 provided with a stopping management program and memory in which the eight values P_ACVM, P_ACVD, P_ACCM, P_ACCD, VCMD, VCVD, VCCM and VCCD are stored, and a delay module 40 which delays the stopping information by the calculated delay T before transmitting it at the output 42 of the control logic 26.
The operations carried out by the system according to the present invention are shown in the flow diagram of Fig. 5.
At stage 50, the magnetic sensors 20, 22 detect if the cabin has arrived at a stopping level and it is verified if the displacement speed of the car has become equal to the low speed prior to stopping. If this is not the case, the program is not initialised. If yes, at stage 52 the calculating unit 36 calculates, from the information Δt which it receives, the actual speed of the car. This value is stored in memory.
Once the actual speed has been calculated, the microprocessor 38 calculates the particular stopping precision P_A which corresponds to that speed, from the curve P_A = h(V) which corresponds to the direction of displacement under consideration and is stored in the memory. This value of P_A as well as the measured speed V stored in memory is input into the calculating unit 36 which calculates the delay T. The result is stored in memory and input into the delay module 40 provided between the stopping information given by the sensor and the stopping command.
At stage 56, the system checks if the detection of the stopping information has taken place. If this is the case, the delay module 40 is triggered at stage 58.
At stage 60, the system verifies if the delay T has expired. If this is the case, the stopping information is transferred to the stopping management program at stage 62.
In order to test the system of the present invention, the inventor has used a robot connected to the control logic of the installation to realise the speed calculating program and the calculation of the stopping delay. The adjustment of the drive motor brake has been set to a suitable value to have a very poor stopping precision. However, the stopping precision obtained is + 10 mm for all loads in the two directions of displacement with the set of levels. The result is excellent, since the same elevator not equipped with the correction system of the present invention has a stopping precision during ascent of between - 60 mm and 0 mm and during descent of between - 48 mm and 0 mm. Further, the robot used had a time base of 4ms, which is too long and degrades the precision of calculating speed and the delay. By increasing the time base, a stopping precision of ± 5 mm can be obtained.

Claims

Method of correcting the stopping precision of an elevator car provided with means (18, 20, 22) providing stopping information when the car (10) is located in the vicinity of a level, and a stopping control logic (26) which provides a stopping command to the drive means of the car, said method being characterised in that it comprises:
- forming variation curves V = f(C) of the speed of displacement of the car during ascent and descent as a function of the load, measuring the speed before the car stops at a given level, at least in the case when the car is empty and in the case when it carries it nominal load,

- forming the variation curves P_A = g (V) of the stopping precision of the car during ascent and descent, as a function of the load, measuring the stopping precision of the car during ascent and descent in the two cases mentioned above,

- deriving the variation curves P_A = h (V) of the stopping precision as a function of the displacement speed,

- calculating of correction of the stopping precision in the particular case when the car arrives at a given level, with a given direction and displacement and load, carried out using the following steps,

- measuring the speed of displacement V of the car at said level and with said displacement direction,

- calculating a specific delay T from the formula T = P_A/V, when P_A is the value of the stopping precision taken from said curve P_A = h (V), for said measured speed value,

- including this delay between the stopping information and the stopping command.
A system for correcting the stopping precision according to the method of claim 1, characterised in that it comprises :
- means (18, 20, 22) adapted to provide a stopping information each time the elevator car arrives in the vicinity of a level,

- a control logic (26) in which the information given by said means (18, 20, 22) is processed, and which outputs a stopping command as a result;

- means (28, 30, 32) to measure the displacement speed of the car before stopping at each level,

- a microprocessor (38) provided with a stopping management program and a memory in which the variation curves P_A = h (V) during ascent and descent are stored.

- a calculating unit (36) for calculating a delay T using the formula T = P_A/V, where P_A is the particular value of the stopping position corresponding to a specific speed V measured at a level, said value being taken from said memory,

- and a programmable delay module (40) adapted to include said delay in the stopping information given by the means (18, 20, 22) for providing stopping information.