WO2004058618A1

WO2004058618A1 - Elevator machine with direct shaft torque sensing

Info

Publication number: WO2004058618A1
Application number: PCT/US2002/041690
Authority: WO
Inventors: Zbigniew Piech; James L. Hubbard; Nigel Morris; David J. Lanesey
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 2002-12-27
Filing date: 2002-12-27
Publication date: 2004-07-15
Anticipated expiration: 2005-06-27
Also published as: AU2002365061A1

Abstract

An apparatus for sensing the torque applied to a shaft (29) including a shaft (29) with a first end and a second end, a sheave (21) portion disposed between the first and the second end, a brake assembly (13) attached to the second end, at least one torque transducer (27) disposed about the shaft containing a magnetoelastic material (14) and a torque sensor (25).

Description

ELEVATOR MACHINE WITH DIRECT SHAFT TORQUE SENSING

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an apparatus, and method of using same, for sensing the torque applied to the brake and motor portions of an elevator machine system. More specifically, the present invention relates to applying agnetoelastic material about the shaft of an elevator system to continuously and accurately measure the torque applied to the shaft.

(2) Description of Related Art

Prior to releasing the brake on an elevator, the motor is engaged to provide a force of a magnitude sufficient to prevent a sudden downward movement of the elevator at the moment the brake is released. The motor applies a torque to its shaft that is equal and opposite to the torque experienced by the shaft as the result of the downward pull of the elevator and the force exerted by the brake.

Identification of the torque required in the elevator system is presently done by load weight sensors installed under the elevator cab floor. Signals for the sensors are introduced through the suspension cable to the drive mechanism. The drive mechanism calculates and supplies the required motor current to balance the suspended masses, and lifts the brake. Because of the unpredictable distribution of passengers on the cab floor, the load weight sensors typically experience errors of up to 20% in determining the actual load reading. As a consequence of this error, the drive mechanism continuously monitors the cab movement increasing or decreasing motor current until cab movement stops. This stage of the elevator motion cycle is called pre-torquing and can last up to 2 seconds.

The pre-torquing current imposes high thermal stress on the drive power devices and motor winding and therefore contributes to shortened motor and drive mechanism life time. Identification of the elevator brake state is presently done by additional limit or proximity switches on the brake. Signals from the switches are introduced by the suspension cables into the drive mechanism. What is needed is an apparatus and method for accurately measuring the load weight applied to an elevator cab that is not prone to errors and which eliminates the need to> compute the pre-torquing current required by the motor.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an apparatus, and method of using same, for sensing the torque applied to the brake and motor portions of an elevator machine system.

In accordance with the present invention, an apparatus for sensing the torque applied to a shaft comprises a shaft comprising a first end and a second end, a sheave portion disposed between the first and the second end, a motor disposed about the first end, a brake assembly attached to the second end, at least one torque transducer disposed about the shaft comprising a magnetoelastic material, and a torque sensor.

In accordance with the present invention, a method of pre- torquing a shaft prior to disengagement of a brake assembly comprising the steps of applying a torque generating load to a shaft, disposing a first torque transducer about a first end of a shaft comprising a sheave portion, the first torque transducer located between the sheave portion and a brake assembly attached to the first end, disposing a second torque transducer about a second end of the shaft between the sheave portion and a motor configured about the second end wherein each of the first and second torque transducers comprise a magnetoelastic material and a torque sensor, engaging a break assembly to stop the rotation of the shaft, measuring a brake torque experienced by the shaft at the first torque transducer, applying an electrical current to the motor to produce a motor torque on the shaft, measuring the motor torque with the second torque transducer, and disengaging the brake assembly when the measured brake torque is equal to the motor torque.

BRIEF DESCRIPTION OF THE DRAWING FIGURE A diagram of the direct shaft torque sensing apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (S) The present invention identifies the torque applied to a cylindrical elevator shaft by motor and/or by brake through the use of at least one torque transducer installed directly about the shaft. In a preferred embodiment, one torque transducer is located between the sheave and the motor's rotor, and/or another torque transducer is located between the brake and sheave.

With reference to the Figure, there is illustrated the direct torque sensing apparatus of the present invention. Shaft 29 is free to rotate on bearings 19. Bearings 19 are located, generally, on opposing ends of sheave 21 extending from the motor 11 to the brake assembly 13. Suspension cables 17 extend from the sheave 21 to the elevator cab 15. When the sheave 21 is rotated, suspension cables 17 wind and unwind about the sheave_.21 causing elevator cab 15 to move up and down. The shaft 29, and hence the sheave 21, rotates in response to an electrical current applied to motor 11 resulting in a torque applied to the shaft 29 and sheave 21 near the motor 11. Conversely, engaging brake assembly 13 results in a torque applied to the shaft 29 and sheave 21 near the brake assembly 13.

The torque transducers 27 enable measurements of the torque imposed by a loaded cab 15 on the brake assembly 13 and the motor 11. Each torque transducer 27 preferably should be a contact-less device consisting of (1) rotational part placed on the shaft surface, and (2) a stationary readout sensor (s).

In a preferred embodiment, two torque transducers 27 are placed directly on the shaft 29; one between the sheave 21 and rotational part of the brake assembly 13 (disk or drum) and the second between the sheave 21 and the motor 11. Each torque transducer 27 is comprised of a magnetoelastic (or magnetostrictive) material applied about the shaft 29. Preferred magnetoelastic materials include, but are not limited to, iron, nickel, and cobalt alloys. Magnetoelastic materials exhibit a change in their magnetic properties when placed under mechanical stress. Specifically, magnetoelastic materials experience in a change in their magnetic flux when placed under stress. In a preferred embodiment, magnetoelastic material 14 is applied to the exterior of the shaft 29. Magnetoelastic material 14 may alternatively be fabricated into shaft 29.

Each torque transducer 27 is additionally comprised of a torque sensor 25. Each torque sensor 25 is located near its corresponding magnetoelastic material 14 at a distance sufficient to facilitate measuring a change in the flux of the magnetoelastic material 14. The torque sensors 25 both measure the change in flux and generate an electronic signal indicative of the change in flux. Preferrably, neither torque sensor 25 is in physical contact with either magnetoelastic material 14.

The torque sensors 25 serve as devices for continuous monitoring of the torque imposed by cab 15 load on the motor 11 and brake assembly 13. The torque sensors 25 thereby eliminate the need for the load-weight devices in the cab 15 floor, as well as eliminate the calculation procedure for torque value based on current measurements. The elevator running cycle begins with a direct readout of the signal from the torque transducer 27 on the brake assembly 13 side. If the measured torque is not equal to zero, the the current supplied to the motor 11 is increased until a balance between brake torque and load torque is achieved (a zero .readout from the brake assembly 13 side transducer 27), and then the brake assembly 13 disengages to allow for rotation of the shaft 29.

The signal from the same torque transducer 25 (on the brake assembly 13 side) allows for the identification of a brake status. The scenario for determining if the brake status is engaged or not is as follows: (1) if, after the brake plates 3 forming the brake assembly 13 (or arms) are lifted, the signal from the torque transducer 27 installed on the brake assembly 13 side is higher than for the typical brake drag, the brake status is set to indicate a brake malfunction in which the brake plates did not disengage properly; (2) if, after brake plate 3 engagement, the signal from torque transducer 25 installed on the brake assembly 13 side is not equal to the signal from torque transducer 27 installed on the motor 11 side measured prior to brake plate 3 engagement the brake status is set to indicate a brake failure.

In this manner, the torque transducer 27 on motor 11 side enables direct torque control during the cab fly, thus enhancing ride quality by reducing torque ripple, and compensating for guide rail irregularity. In addition, the same torque transducer 25 allows after brake engagement for a gradual decrease of motor torque at the end of the cab 15 leveling period preventing brake backlash noise.

Because the torque transducer 27 near the brake assembly 13 continuously and accurately measures the torque experienced by the brake assembly 13, the present invention eliminates the need for typical brake sensors. The present invention further eliminates the need for load-weight devices in the system.

Direct torque observation by the torque transducers 27 further increase ride quality by allowing for torque ripple compensation, elimination of car motion during the pre-torquing, and better control of brake backlash noise during the brake engagements.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for sensing the torque applied to a shaft comprising a shaft comprising: a first end and a second end; a sheave portion disposed between said first and said second end; a motor disposed about said first end; a brake assembly attached to said second end; at least one torque transducer disposed about said shaft comprising: a magnetoelastic material; and a torque sensor.

2. The apparatus of claim 1 wherein said at least one torque transducer is located between said motor and said sheave.

3. The apparatus of claim 1 wherein said at least one torque transducer is located between said brake assembly and said sheave.

4. The apparatus of claim 1 wherein said magnetoelastic material is selected from the group consisting of iron alloys, nickel alloys, and cobalt alloys.

5. The apparatus of claim 1 wherein said shaft is cylindrical.

6. The apparatus of claim 1 wherein said magnetoelastic material is applied to a surface of said shaft.

7. The apparatus of claim 1 wherein said magnetoelastic material is fabricated into said shaft.

8. The apparatus of claim 1 wherein said at least one torque sensor is located at a distance from said at least one magnetoelastic material and said distance is sufficient to permit a measurement of a flux of said at least one magnetoelastic material.

9. The apparatus of claim 1 wherein said apparatus additionally comprises: a load; at least one suspension apparatus attached to said load and to said sheave.

10. The apparatus of claim 9 wherein said suspension apparatus comprises a cable.

11. The apparatus of claim 9 wherein said load comprises an elevator cab.

12. The apparatus of claim 1 wherein said shaft is supported by a plurality of bearings.

13. A method of pre-torquing a shaft prior to disengagement of a brake assembly comprising the steps of: disposing a first torque transducer about a first end of a shaft comprising a sheave portion, said first torque transducer located between said sheave portion and a brake assembly attached to said first end; disposing a second torque transducer about a second end of said shaft between said sheave portion and a motor configured about said second end wherein each of said first and second torque transducers comprise a magnetoelastic material and a torque sensor; applying a torque generating load to said shaft; engaging a brake assembly to stop a rotation of said shaft; measuring a brake torque experienced by said shaft at said first torque transducer; applying an electrical current to said motor to produce a motor torque on said shaft; measuring said motor torque with said second torque transducer; and disengaging said brake assembly when said measured brake torque is equal to said motor torque.

14. The method of claim 13 wherein measuring said brake torque comprises the steps of: measuring a first flux of said megnetoelastic material of said first torque transducer with said torque sensor of said first torque transducer; measuring a second flux of said megnetoelastic material of said first torque transducer with said torque sensor of said first torque transducer after engaging said brake assembly; and comparing said first and second flux to compute said brake torque.

15. The method of claim 13 wherein measuring said motor torque comprises the steps of: measuring a first flux of said megnetoelastic material of said second torque transducer with said torque sensor of said second torque transducer; measuring a second flux of said megnetoelastic material of said second torque transducer with said torque sensor of aid second torque transducer after applying said electrical current; and comparing said first and second flux to compute said motor torque.

16. The method of claim 13 comprising the additional steps of: measuring said motor torque with said second torque transducer prior to engaging said brake assembly to stop said rotation of said shaft; comparing said measured brake torque to said motor torque measured prior to engaging said brake assembly; and setting a brake status to indicate brake failure if said measured brake torque is not equal to said motor torque measured prior to engaging said brake assembly.