WO2002002450A1

WO2002002450A1 - Elevator machine integrated load weighing system

Info

Publication number: WO2002002450A1
Application number: PCT/US2001/014454
Authority: WO
Inventors: Hartmut Engler; Michael Thomas Barten
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 2000-06-29
Filing date: 2001-05-03
Publication date: 2002-01-10
Anticipated expiration: 2002-12-29
Also published as: TW593114B

Abstract

A force sensor integrated into a main bearing of an elevator machine measures the force in the direction of the wire ropes or coated steel belts that support and move an elevator car. The resulting signal provides information on the car weight and on mechanical problems in the hoistway, motor, main bearing, or drive sheave. The signal amplitude is proportional to the weight of the elevator car. The amplitude is independent of the position of the load in the elevator car. In cooperation with the position decoder of the machine, it is possible to differentiate between hoistway and motor problems, or to determine the precise location of the problem if the problem is in the hoistway.

Description

ELEVATOR MACHINE INTEGRATED LOAD WEIGHING SYSTEM

FIELD OF THE INVENTION

This invention pertains to weighing the loading of an elevator car, and in particular to , weighing the loading of an elevator car at the machine.

BACKGROUND OF THE INVENTION

It is important to the function of an elevator car that its load be known at all times in order to achieve smooth and comfortable ride performance. Safety features need to know if the car is overloaded so that the elevator brake is not released while under that load, to determine which floor should be serviced based on the load in the car, or to allow anti- nuisance software to operate properly. Anti-nuisance software estimates the number of people in a car by assuming an average weight per person. It then determines the number of car calls and if the number of car calls exceeds the number of people estimated, it cancels those car calls.

Systems have been designed with the load weigher beneath the car. Some measure the deformation of resilient pads beneath the car platform. A disadvantage of the deformation systems is the inaccuracy introduced by hysteresis in the elastomeric material used in the pads. Another disadvantage with platform load weighing devices is that the resilient pads eventually harden through use and age. A further disadvantage is the need to install enough load cells to equally share the load under any loading condition. Other disadvantages include the expense, time, and difficulty involved in installation, low precision output, insufficient maintenance access, and the fact that the placement of the devices has to be adapted for each new design.

SUMMARY OF THE INVENTION

Briefly stated, a force sensor integrated into a main bearing of an elevator machine measures the force in the direction of the wire ropes or coated steel belts that support and move an elevator car. The resulting signal provides information on the car weight and on mechanical problems in the hoistway, motor, main bearing, or drive sheave. The signal amplitude is proportional to the weight of the elevator car. The amplitude is independent of the position of the load in the elevator car. In cooperation with the position decoder of the machine, it is possible to differentiate between hoistway and motor problems, or to determine the precise location of the problem if the problem is in the hoistway.

According to an embodiment of the invention, an integrated load weighing system for an elevator car includes a motor having a shaft; a drive sheave attached to the shaft via a main bearing; a tension member reeved over the drive sheave and supporting the elevator car; and a force sensor in the main bearing, wherein a force on the main bearing from the tension member detected by the force sensor is proportional to a weight of the elevator car.

According to an embodiment of the invention, an integrated load weighing system for an elevator car includes a drive sheave mounted on a first shaft via a first bearing; at least one additional sheave mounted on a second shaft via a second bearing; a tension member reeved over the drive sheave and the additional sheave, the tension member supporting the elevator car; and a force sensor in at least one of the first and second bearings, wherein a force on at least one of the first and second bearings from the tension member detected by the force sensor is proportional to a weight of the elevator car.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a machine for an elevator system.

Fig. 2 shows a schematic illustrating the principle of the invention.

Fig. 3 shows an integrated force sensor according to an embodiment of the invention.

Fig. 4 shows a schematic illustrating the damper spring equivalent of the elevator system of the present invention.

Fig. 5 A shows an output from the force sensor of the present invention under normal operating conditions.

Fig. 5B shows an output from the force sensor of the present invention due to a deformed sheave or motor.

Fig. 5C shows an output from the force sensor of the present invention due to a damaged bearing.

Fig. 5D shows an output from the force sensor of the present invention due to a damaged elevator car guide rail.

Fig. 5E shows an output from the force sensor of the present invention due to a damaged motor or closed loop controller. Fig. 6 shows a schematic illustrating an alternate suspension arrangement for an elevator car using an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figs. 1-2, a machine 10 includes a motor 12 which drives a shaft 20. A drive sheave 14 and a brake 16 are attached to shaft 20. Machine 10 is typically attached to a bed plate 18 which is in turn mounted in a machine room over an elevator hoistway. A tension member 15 such as a wire rope (cable) or coated steel belt (CSB) is reeved.over drive sheave 14 to an elevator car 22 and a counterweight 24.

Referring to Fig. 3, a bearing 26 connects drive sheave 14 to shaft 20. Bearing 26 preferably includes a force sensor 28 such as a resistance strain gauge or a piezoelectric force gauge which senses the load imposed on bearing 26 by tension member 15. Force sensor 28 outputs a signal whose magnitude is proportional to the load imposed by tension member 15, which includes the load from elevator car 22 and counterweight 24, and is independent of the location of the load in elevator car 22. The frequency of the signal is proportional to the speed of motor 12.

If the wave form differs from a regular sinusoidal curve, a change of some sort has occurred. The diagram of Fig. 4, which shows the damper-spring equivalent of the system of Fig. 2, is used to predict the signals output by force sensor 28 in the event of a change.

Referring to Fig. 5A, the signal output from force sensor 28 is shown changing as the car load changes. This signal is indicative of normal operation as people get on and off the elevator.

Referring to Fig. 5B, a deformed sheave 14, damaged motor 12, or damaged closed loop controller for motor 12 will excite the spring damper system of Fig. 4, resulting in the signal of Fig. 5B. The oscillation period equals the rotor speed of motor 12.

Referring to Fig. 5C, a damaged ball bearing 26 causes a spike in the signal with a periodic magnitude linked to the specific rotor position of motor 12.

Referring to Fig. 5D, a bad guiding rail adjustment for the rails in the elevator hoistway that guides elevator car 22 causes a signal that is linked to a specific position of elevator car 22 within the hoistway. Referring to Fig. 5E, the signal shown represents torque ripple caused by a damaged motor 12 or damaged close loop controller.

Referring to Fig. 6, elevator car 22 inside a hoistway 30 is shown suspended in an overslung arrangement. Tension member 15 is connected to a hitch 32, reeved over elevator sheaves 34 and 36 which are connected to a top of elevator car 22, over drive sheave 14, and connected to counterweight 24. The force sensor output is proportional to the weight of elevator car 22 whether it is installed in the bearing for drive sheave 14, sheave 34, or sheave 36. Although Fig. 6 shows an overslung arrangement, an underslung arrangement, where the elevator sheaves are connected to an underside of elevator car 22, also works with the present invention. Optionally, the machine (motor and drive sheave combination) can be located on or under the elevator car.

While the present invention has been described with reference to a particular preferred embodiment and the accompanying drawings, it will be understood by those skilled in the art that the invention is not limited to the preferred embodiment and that various modifications and the like could be made thereto without departing from the scope of the invention as defined in the following claims.

Claims

What is claimed is: 1. An integrated load weighing system for an elevator car, comprising: a motor having a shaft; a drive sheave attached to said shaft via a main bearing; a tension member reeved over said drive sheave and supporting said elevator car; and a force sensor in said main bearing, wherein a force on said main bearing from said tension member detected by said force sensor is proportional to a weight of said elevator car.

2. A system according to claim 1, wherein said force sensor outputs a signal; and wherein a frequency of said signal is proportional to a speed of said elevator car.

3. A system according to claim 2, wherein a characteristic of said signal represents a condition of at least one of said motor, said main bearing, said sheave, and said hoistway.

4. An integrated load weighing system for an elevator car, comprising: a drive sheave mounted on a first shaft via a first bearing; at least one additional sheave mounted on a second shaft via a second bearing; a tension member reeved over said drive sheave and said at least one additional sheave, said tension member supporting said elevator car; and a force sensor in at least one of said first and second bearings, wherein a force on at least one of said first and second bearings from said tension member detected by said force sensor is proportional to a weight of said elevator car.

5. A system according to claim 4, wherein said force sensor outputs a signal; and wherein a frequency of said signal is proportional to a speed of said elevator car.

6. A system according to claim 5, wherein a characteristic of said signal represents a condition of at least one of said motor, said main bearing, said sheave, and said hoistway.