Device for measuring speed of an elevator car

Abstract: This speed measuring device comprises: an optical fork (10) fixed on the elevator car (26), the said fork comprising two hollow arms disposed in a horizontal plane and housing respectively an emitter and a receiver of infra-red radiation, such that the infra-red beam (16) crosses horizontally the space between the said arms, a plurality of vertical flags, (20,22) opaque with respect to infra-red rays, having a predetermined height h, fixed in the elevator shaft (26) at positions where one wishes to know the speed of displacement of the car and disposed in such a manner that they cut the infrared beam (16) each time the fork (10) passes their level, the receiver giving out electrical signals which have a first logical state when the infra-red beam passes and a second logical state when the beam is cut, and a calculating unit (30) which receives from the receiver when positioned at each level information on the duration Δt during which the infra-red beam is interrupted by the flag mounted at that level, and which calculates the speed of the car by means of the formula V=h/Δt.

Description: The present invention concerns a device for measuring the speed of displacement of an elevator car. Knowledge of the speed of displacement parameter of an elevator car is very important because it can be used particularly to improve the precision of stopping of the car at the different landings served. Low cost European elevators, such as two-speed elevators and service elevators, are not generally equipped with a system for measuring speed because the system is too costly and their installation would increase the overall cost of sale of the lift. US-A-5,349,854 discloses a speed control system in an elevator using a gear wheel mounted to the elevator cabin and cooperating with a perforated metal band provided in the hoistway. In effect, these known systems, such as optical coders mounted on one of the axes of rotating of the installation, dynamo tachometers, accelerometers, laser measuring devices, etc., imply a significant expense and necessitate special inputs for rapid counting or analogue signals. They are therefore exclusively used in upper-range elevators provided with an electronic speed control. The present invention seeks to remedy this disadvantage by proposing a speed measuring device of which the relatively modest cost is compatible with the quality standard of commercial elevators. FR-A-2,601,142 discloses a device for measuring the speed of a train including a plurality of vertical flags which are opaque with respect to infra-red rays and which are mounted on the track. A light barrier is arranged on the train in such a way that it is interrupted by the flag when the train passes over a flag. The speed of the train can be calculated from the time the infra-red beam is interrupted by the flag. The speed measuring device according to the invention comprises: an optical fork fixed on the elevator car, said fork comprising two hollow arms disposed in a horizontal plane and housing respectively an emitter and a receiver of infra-red radiation, in a manner such that the infra-red beam crosses horizontally the space between the said arms, a plurality of vertical flags, opaque with respect to infra-red rays, having a predetermined height h, fixed in the elevator hoistway at positions where one wishes to know the speed of displacement of the car and disposed in such a manner that they cut the infra-red beam each time the fork passes their level, the receiver giving out electrical signals which have a first logical state when the infra-red beam passes and a second logical state when the beam is cut, and a calculating unit which receives from the receiver when positioned at each level information on the duration At during which the infra-red beam is interrupted by the flag mounted at that level, and which calculates the speed of the car by means of the formula V=h/Δt. The flags can be constituted by plates or tapes of thin steel sheet, for example of the order of lmm, and several centimetres high. These are thus cheap commercial elements. The same applies to the optical fork which is an accessory currently sold in commerce. A big advantage of the invention lies in the fact that one can use as the calculating unit the electronic control card with which the elevator is already equipped. The logical elements to be added to this card need not increase the manufacturing cost. Similarly, the input for the electrical signals sent by the receiver already exists in the electronic control card. Another advantage of the invention lies in the good precision of the speed measurement. Further, given that the measurement can be made without mechanical contact, the lifetime of the electronic fork can be several decades. The device according to the invention can thus be used in mid-range elevators. One way of implementing the invention will now be described, by way of a non-limiting example, and with reference to the annexed drawings in which: Fig. 1 is a perspective view of an optical fork and a flag; Fig. 2 is a schematic view illustrating the whole of the speed measuring device according to the invention; Fig. 3 is a flow chart showing the operations carried out by the electronic control card; Fig. 4 is a schematic view of the mounting of the flags in the hoistway of an elevator; Fig. 5 is a diagram representing the speed of the car as a function of time. In Fig. 1 is represented an optical fork 10 in the form of a U known per se. The parallel branches 12,14 of the optical fork are hollow and house respectively an infra-red emitter and receiver, not shown. Infra-red beam 16 emitted by the emitter leaves through a hole 18, transversely crosses the space between the two branches and is received by the receiver. The optical fork is fixed on the object of which one wishes to measure the speed of displacement, for example on an elevator cabin, and it thus moves at the same time as the object. On the path of travel of the optical fork, at the points where one wishes to measure the speed, are disposed flags 20 each comprising a plate of material opaque to infra-red, for example of sheet steel. Each flag is able to cut the infra-red beam 16 when the optical fork arrives at its level. The receiver provides at its output 28 an electrical signal having a certain logical state when the beam passes freely and another logical state when the beam is cut. According to the form of the electrical signal taken from the output of the receiver, one can thus deduce the duration At of the interruption of the beam by a flag. Knowing the height h of the flag and assuming that the speed of displacement is constant, the speed can be calculated by the formula V=h/Δt. We refer now to Fig. 2 which illustrates the application of the device of Fig. 1 to calculating the speed of an elevator car 24. The optical fork 10 is fixed on an exterior wall of the car, and is oriented in such a manner that its arms are in the same horizontal plane. In the hoistway 26 are fixed the plurality of flags 20,22 disposed in the same vertical plane at the different levels where one wishes to measure the speed of displacement of the car and in such a manner that they pass between the branches of the optical fork when the latter arrives at their level. The electrical signal taken from the output of the receiver is sent via the conductor 28 to a calculating unit 30. For economic reasons this can be constituted by the electronic control card with which every elevator installation is provided. But it goes without saying that the calculating unit can equally be constituted by a specific electronic card based on a microcontroller. The electronic control card comprises a simple static input 32 which is disposable on the card or which can be shared with another data processing device, a counter 34, a clock 36, a calculator 38, a memory 40, a program store 42 and an output 44. The information concerning the speed of displacement is displayed on a screen 46. The flow chart of Fig. 3 illustrates the sequence of operations for calculating speed. The information received from the receiver is introduced at the input 32. The program determines at step 1 if the beam of the fork is cut. In the affirmative, the program passes to the step 2 where a counting of the duration of the cutting takes place. Then, at step 3, the program determines if the beam has been re-established. If this is not the case, the counting continues. If reestablishment of the beam is determined, the counting of time is stopped and the value of the duration of the interruption of the beam At is memorised in the step 4. Then, at the step 5, the speed is calculated from the measured duration At and the height h of the flag. Fig. 4 shows a practical disposition of the flags 20,22 in the hoistway in relation to the landing door 48. The flags are fixed on bands 50,52 which are carried by stretched vertical cables 54,56 extending throughout the height of the hoistway. The upper flag 20 serves to measure the speed of displacement of the car when descending and is fixed slightly above the stopping zone of the car whilst the flag 22 serves to measure the speed of displacement when ascending and is fixed slightly below the stopping zone of the car. As for the optical fork, it is fixed on a wall of the car, at a height such that it is positioned between the flags 20,22 at the stop. This positioning is advantageous because it permits the electronic control card to calculate the speeds sufficiently in advance of the car arriving at the stopping zone and that enables the precision of the stop to be improved. The diagram of Fig. 5 shows the variation of the speed of displacement of a car as a function of time, in the particular case where the car is driven by a motor-reducer with two coils, for example of 16 poles and 4 poles respectively, and has a drum brake. When, starting from the stopped state at a floor, one supplies the 16 pole coil, the car accelerates to achieve its normal speed of displacement V 0 which it maintains over practically all of its path. Shortly before the car arrives at the landing where it must stop, the supply is switched to the 4 pole coil so that cabin moves at the low constant speed V 1 . The stop is achieved by cutting the supply to the motor and by releasing the jaws of the brake. The speed decelerates progressively until the car stops. Of course the measuring of the speed must be carried out at a time when it is constant and preferably during the course of the low speed movement, because the precision of the measurement will be better in this phase. We will now explain by the use of a particular example how to choose the height of the flag as a function of the precision which one seeks for the speed. We suppose that the low speed is of the order of 250mm/s, that a precision of 0.5% is required and that a circuit is used having a time base of 4 ms to measure the time and to calculate the speed. In 4 ms the car travels a distance of 4.10 -3 x 250 = lmm. This distance represents the required precision of 0.5%. It follows that the flag must have a height h such that h x 0.5/100 = lmm from which one obtains h = 200mm. With a circuit having a lower time base, one can use shorter flags.

Claims: A device for measuring the speed of an elevator car, comprising: an optical fork (10) fixed on the elevator car (24), the said fork comprising two hollow arms (12,14) disposed in a horizontal plane and housing respectively an emitter and a receiver of infra-red radiation, such that the infra-red beam (16) crosses horizontally the space between the said arms, a plurality of vertical flags, (20,22) opaque with respect to infra-red rays, having a predetermined height h, fixed in the elevator hoistway (26) at positions where one wishes to know the speed of displacement of the car (24) and disposed in such a manner that they cut the infra-red beam (16) each time the fork (10) passes their level, the receiver giving out electrical signals which have a first logical state when the infra-red beam (16) passes and a second logical state when the beam is cut, and a calculating unit (30) which receives from the receiver when positioned at each level information on the duration Δt during which the infra-red beam (16) is interrupted by the flag (20,22) mounted at that level, and which calculates the speed of the car (24) by means of the formula V=h/Δt. A speed measuring device according to claim 1 wherein the calculating unit (30) comprises the electronic control card with which the elevator installation is normally provided. A speed measuring device according to claim 1 wherein the calculating unit (30) comprises a specific electronic card based on a microcontroller. A speed measuring device according to claim 1 wherein the optical fork (10) is fixed on an exterior wall of the car (24) and it is oriented in such a manner that the branches (12,14) are in the same horizontal plane, and that in the hoistway (26) are fixed a plurality of flags (20,22) disposed in a vertical plane, at the different levels where one wishes to measure the speed of displacement of the car (24) and in such a manner that they pass between the branches (12,14) of the fork (10), when the latter arrives at their level. A speed measuring device according to claim 4 wherein at each floor served by the car (24) a first flag (20) is fixed above the stopping zone of the car (24) for measuring the speed of displacement when descending and a second flag (22) is .fixed below the stopping zone of the car (24) for measuring the displacement speed when ascending and in that the optical fork (10) is fixed on the wall of the car (24) at a height such that it is positioned between the flags (20,22) when the car (24) is at the stop. A speed measuring device according to claim 4 wherein the flags (20,22) are fixed on supports (50,52) carried by stretched vertical cables (54,56) extending the whole height of the hoistway (26). A speed measuring device according to claim 1 wherein the measure of the duration of interruption Δt of the infra-red beam (16) is carried out during a portion of She travel where the speed of displacement of the car (24) is constant. A speed measuring device according to any preceding claim for an elevator car (24) driven at a high constant speed over practically all of its path and at a low constant speed for a short distance before stopping at a landing, wherein the measurement of the duration of interruption of the infra-red beam (16) is carried out when the car (24) is moving at said low constant speed.

Inventors: BONGIBAULT THIERRY, DURAND CHRISTOPHE, BONGIBAULT, THIERRY, DURAND, CHRISTOPHE
Applicants: OTIS ELEVATOR CO, OTIS ELEVATOR COMPANY
Application year: 1996
Main classification: G01P3
IPC codes: G01P3, G01P11