WO1996006793A1

WO1996006793A1 - Angle measuring apparatus in a synchronous motor comprised in an elevator machinery and procedure for detecting the position of a motor pole

Info

Publication number: WO1996006793A1
Application number: PCT/FI1995/000454
Authority: WO
Inventors: Harri Hakala; Jorma Mustalahti; Esko Aulanko
Original assignee: Kone Corp
Current assignee: Kone Corp
Priority date: 1994-08-26
Filing date: 1995-08-25
Publication date: 1996-03-07
Anticipated expiration: 1997-02-26
Also published as: FI943916A7; FI943916A0; AU3259395A; FI943916L

Abstract

In a permanent magnet synchronous motor (21) comprised in an elevator machinery (6), angle measurement is implemented by detecting the position of a rotor pole by means of a detector (1) measuring the magnetic field. The magnetic field generated by the permanent magnets of the rotor (113) is measured at a point close to the rotor circle (113).

Description

ANGLE MEASURING APPARATUS IN A SYNCHRONOUS MOTOR COMPRISED IN AN ELEVATOR MACHINERY AND PROCEDURE FOR DETECTING THE POSITION OF A MOTOR POLE

The present invention relates to an angle measurement appa- ratus as defined in the preamble of claim 1 and to a procedure for detecting the position of a rotor pole as defined in the preamble of claim 5.

In recent times, elevator drive machinery solutions based on the use of a flat axial motor have been developed. They are technically efficient and their manufacturing costs are reasonable, among other things because the motor is largely integrated with the rest of the machinery. An advantageous solution in respect of efficiency and in other respects as well in the case of this type of elevator machinery is to construct the motor as a permanent magnet synchronous motor. However, for the regulation of a synchronous motor in an elevator drive to function properly, accurate position data is required. The position data for motor regulation could be obtained e.g. by using an absolute angle detector based on an optical decoder, but the problem with such a solution is its very high price, especially if a high resolution is required.

To meet the need to achieve a cheap and reliable system for angle measurement in an elevator motor, an angle measuring apparatus and a procedure for detecting the position of a rotor pole are presented as an invention. The angle measuring apparatus of the invention is characterized by what is presented in the characterization part of claim 1. The pro¬ cedure of the invention for detecting the position of a rotor pole is characterized by what is presented in the char- acterization part of claim 5. Other embodiments of the invention are characterized by the features presented in the other claims. The invention allows various advantages to be achieved, including the following:

- The manufacturing costs of the solution of the invention are moderate. - The position of the rotor in relation to the frame and the stator is measured by a direct method, giving an excellent frequency response.

- The solution of the invention allows a good measurement accuracy to be achieved. - The solution of the invention involves no wearing parts, and once the apparatus has been installed, the measuring function remains constant.

- The invention can be applied both for the regulation of motor operation and to provide position data for use in elevator control.

- Flux sensors can be used to monitor the state of the magnets.

In the following, the invention is described in detail by the aid of one of its embodiments and by referring to the attached drawings, in which

Fig. 1 presents a diagrammatic side view of an elevator machinery employing the invention, Fig. 2 presents an elevator machinery employing the invention as seen from the side of the traction sheave,

Fig. 3 presents a portion of a detector signal proportional to the flux, and Fig. 4 signals obtained by modifying the detector signals.

Fig. 1 shows a diagram representing an elevator machinery 6 employing the invention. The elevator machinery 6 is fixed to a beam 16. Fig. 1 presents the elevator machinery in a form sectioned along a plane starting radially upwards from the axis 11 of rotation. The machinery 6 consists of a motor 21, a disc brake and a traction sheave 7. The motor is an axial-motor type synchronous motor. Fig. 1 presents the machinery magnified in the axial direction of the motor to render the figure more legible. In reality, the machinery is flat in the direction of the axis 11.

The motor 12 has a rotor 113 mounted on a rotor disc 112 and a stator 109 mounted on a stator disc 118. In this motor, the rotor is composed of permanent magnets. The rotor and stator are separated by an air gap 114, the plane of which is substantially perpendicular to the shaft 115 of the motor 21. The stator with the stator winding 117 forms an annular structure placed in an annular cavity 119 in the rotor disc 118, said cavity being open on one side. The stator is fixed to the cavity wall perpendicular to the motor shaft by means of fixing elements 120, preferably screws. In principle, the stator can be fixed to any one of the walls of the cavity 119. The cavity 119 is formed by a ringlike trough in the stator disc whose open side faces towards the rotor disc 112, leaving an annular cavity between the stator disc and the rotor disc. The rotor disc 112 is provided with an annular brake disc 116 forming an extension of the rotor disc in its radial direction. The annular brake disc may be integrated with the rotor disc to form a single part. The brake (not shown in the figures) is floatably mounted in the axial direction of the shaft 115, allowing the brake to engage the brake disc 116.

Attached to the rotor disc 112 is a cylindrical traction sheave 7 provided with rope grooves 121. The diameter of the traction sheave is smaller than the diameter of the circle formed by the rotor bars 113 on the rotor disc and of the outer circle of the stator 109 in the stator disc. The rotor disc 112, the traction sheave 7 and the brake disc 116 are integrated into a single part. The brake disc thus substan¬ tially forms an immediate extension of the rotor disc, yet with a narrow annular area for a sealing between the rotor bars and the brake disc.

The stator disc 118 and the shaft 115 are likewise integrated into a single part which also functions as the frame of the elevator machinery. Mounted on the frame or on a holder 2 immovable with respect to the frame and stator is a detector 1. One or more detectors can be used. The detector measures the magnetic field. Particularly suitable is a detector which gives a signal proportional to the density of the magnetic flux. The signal is passed via a signal conductor 3 to a signal processing device (not shown in the figure) , which processes the signal to give it a more usable form or even to produce a final position signal. In the case of a single detector, a signal is produced whose phase angle can be used to determine the positions of the detector and the pole pair generating the signal with respect to each other. An advantageous solution is achieved by using two detectors 1. When there are more than one detector, it is possible to choose portions of the detector signals that are best suited for use in the formation of a position signal. The assembly consisting of the stator disc 118 and the shaft 115 is preferably made of a casting which is also provided with a mounting bracket 123. Bearings 122 are provided between the rotor disc and the stator disc. An annular sealing 126 is placed between the rotor and stator discs. The stop face for the sealing on the rotor disc lies between the rotor bars and the brake disc. The sealing 126 seals the cavity 119 so as to form a closed space, thus preventing dust from entering into the cavity. The area of adhesion 127 required to fix the sealing is implemented as a groove in the axially oriented wall 128 of the stator disc cavity. The sealing may be e.g. a felt seal. In this example, the detector 1 is located in a place where it can be easily accessed for various operations. It is possible to place the detector 1 in the cavity 119, in which case it can be fixed to the stator disc 118 or even to the stator 109. A suitable distance between the detector and the rotor magnets is about 15 mm, which is of the same order of magnitude as the magnets. In this way, the detector produces a relatively disturbance- free signal of a good form, in an ideal case a triangular wave or a nearly triangular wave.

Fig. 2 shows the elevator machinery of Fig. 1 as seen from the side of the traction sheave. The rotor disc 112 is presented partly sectioned around the rotor 113 to bring the permanent magnets of the rotor to view. Two detectors 1 are mounted on a holder 2, on the side of the holder facing towards the rotor. The signal conductors 3 are passed from the detectors through the holder and, attached to the holder, further to a signal processing device 5. The signal processing device can be placed in a different location from that shown in the figure. It may be implemented e.g. as part of the elevator's motor control or elevator control equipment.

Fig. 3 presents a sample portion of a signal 4 proportional to the density of the magnetic flux, obtained from a detector. The sample consists of about three and a half cycles of the signal, i.e. about 3.5 times 360 electric degrees. One cycle or 360 electric degrees corresponds to a motor angle change equalling 360° divided by the number of pole pairs in the motor. The detector signal 4 proportional to the magnetic flux density can also be used for monitoring the state of the permanent magnets. A fall in the overall signal amplitude or in the amplitude produced by some of the pole pairs indicates an extenuation of the overall magnetic flux generated by the permanent magnets or of the flux of some of the rotor magnets. The signal processing equipment can be provided with a monitoring function which produces a separate indication of the occurrence of a signal amplitude lower than a preset limit. The effect of the stator field is eliminated from the detector signal by computational means when the flux to be measured is influenced by the stator field. For instance, in a so-called sector motor the detector is so placed that the stator field has no effect on the measurement.

Fig. 4 presents normalized signals A and B with a 90° phase shift between them, which are obtained by processing the signals produced by two detectors 1 placed at a distance of 90 electric degrees from each other. In this context, a distance of 90 electric degrees may also mean that the second detector measures another pole pair of the motor at a position on this second pole pair which is removed by 90 electric degrees from the position corresponding to the measurement position on the pole pair measured by the first detector. Fig. 4 also shows a position data signal C. As to their form, signals A and B are essentially triangular waves. The phase shift of 90° between signals A and B follows from the placement of the detectors 1 at a distance of 90 electric degrees from each other. The placement of the detectors 1 at 90 electric degrees from each other is based on a knowledge of the distance between the pole pairs of the rotor 113, which is directly determined by the placement on the rotor disc 112 of the permanent magnets forming the rotor. Besides being normalized in amplitude to value 1, signals A and B are usually processed in other ways, too. From these signals, a position signal is produced as explained below. To generate position data, signals A and B need not necessarily be specially processed or even normalized, but the signals obtained from the detectors 1 can be multiplied by a suitable constant or they can be amplified to achieve normalization. In the following, however, the generation of position data C from triangular wave signals A and B normalized in amplitude to unity will be described. For the formation of a position signal, at each instant one of the signals A,B supplied by the detectors 1 is selected to be used as part of the position signal. The decision as to which one of the signals A,B is to be selected is made on the basis of the prevailing value of the signals. In a preferable solution, signals A,B normalized in amplitude to unity and having a form essentially resembling a triangular wave are produced from the signals provided by the detectors 1 and a position signal C is generated from the normalized signals A,B on the basis of their prevailing value as follows:

if 0<A< and B<- then C=A , if 3s<A<l and -%<B<0 then C=B+1 if <A<1 and 0<B< then C=B+1 , if 0<A< and H<B<1 then C=-A+2 , if 0>A>- and <B<1 then C=-A+2 if A<-% and 0<B<% then C=-B+3 if A<-^5 and 0>B>-3j then C=-B+3 , if - <A<0 and B<h then C=A+4

Generated in this way, the value of the position signal C varies between zero and four within the range of each pole pair. The scaling of the position signal C can be performed in other ways, too. For instance, if A and B are so normalized that their values lie between k...+k, then the value of the position signal C varies between 0...4k, k being a selected constant or a constant set during signal processing. The essential point is that one interval between the varying values of the position signal C corresponds to the movement of the pole pair. During one revolution of the motor, the position signal C reaches its maximum and minumum values a number of times equalling the number of poles in the motor. Thus, the position of the motor can be roughly determined by counting the position signal cycles and more accurately by adding the value of the position signal to the number of cycles. The position signal C is formed using only the more linear parts of the curve of the original signal obtained from the detector, whereas the signal portion at the 'corners of the triangle' is only used as a criterion for the selection of a calculation rule for generating the momenetary value of the position signal C. In the angle measuring apparatus, the detectors are usually separate components, whereas the signal processing devices can be integrated with the motor controller or other equipment.

It is obvious to a person skilled in the art that different embodiments of the invention are not restricted to the ex¬ amples described above, but that they may instead be varied within the scope of the following claims.

Claims

1. Angle measuring apparatus in an axial-motor type permanent magnet synchronous motor (21) comprised in an elevator machinery (6), characterized in that, to detect the position of a rotor pole in the synchronous motor (21) , the elevator machinery (6) is provided with at least one magnetic field measuring detector (1) and that the detector (1) is so placed that it primarily measures the magnetic field produced by the permanent magnets of the rotor (113) of the synchronous motor (21) .

2. Angle measuring apparatus as defined in claim 1, characterized in that it comprises two magnetic field measuring detectors (1) .

3. Angle measuring apparatus as defined in claim 1, characterized in that the detectors (1) are placed at a distance of 90 electric degrees from each other.

4. Angle measuring apparatus as defined in any one of the preceding claims, characterized in that the magnetic field measuring detector (1) is of a type that produces a signal (4) proportional to the density of the magnetic flux.

5. Procedure for detecting the position of a rotor pole in an axial-motor type permanent magnet synchronous motor, characterized in that, to detect the position of a rotor pole in the synchronous motor (21) , the magnetic field generated by the permanent magnets of the rotor (113) is measured by means of at least one detector (1) placed near the rotor circle (113).

6. Procedure as defined in claim 5, characterized in that the magnetic field is measured by means of two detectors (1) producing a signal (4) proportional to the density of the magnetic flux, said detectors (1) being placed at a distance of 90 electric degrees from each other.

7. Procedure as defined in claim 6, characterized in that, from the signals (4) obtained from the two detectors (1) producing a signal (4) proportional to the density of the magnetic flux, a position signal (C) is generated

- by forming from the signals (4) obtained from the detectors (1) signals (A,B) substantially resembling a triangular wave and normalized to the same amplitude value, and - by using at each instant in the formation of a position signal only one of the normalized signals (A,B) as part of the position signal, and

- by making the decision as to which one of the normalized signals (A,B) is to be used at the instant for the genera- tion of a position signal on the basis of the prevailing value of the normalized signals.

8. Procedure as defined in claim 6 or 7, characterized in that, from the signals (4) obtained from the two detectors (1) producing a signal (4) proportional to the density of the magnetic flux, a position signal (C) is generated

- by forming from the signals (4) obtained from the detectors (1) signals (A,B) substantially resembling a triangular wave and normalized in amplitude to a constant value, preferably unity, and - by using at each instant in the formation of a position signal only one of the normalized signals (A,B) as part of the position signal, and

- by making the decision as to which one of the normalized signals (A,B) is to be used for the generation of a posi- tion signal on the basis of the prevailing value of the normalized signals as follows: if 0<A<^k and B<~h- then C=A , if k<A<k and -3jk<B<0 then C=B+k , if ^k<A<k and 0<B< k then C=B+k , if 0<A<3sk and k<B<k then C=-A+2k , if 0>A>- k and k<B<k then C=-A+2k if A<- k and 0<B<%k then C=-B+3k if A<-3sk and 0>B>- k then C=-B+3k if - k<A<0 and B<^k then C=A+4k

9. Procedure as defined in any one of claims 5-8, charac¬ terized in that the signal (4) obtained from the detector (1) is linearized in its rising and falling portions to form a triangular signal (A,B).

10. Procedure as defined in claim 6, characterized in that an extenuation of the overall flux produced by the permanent magnets or the flux produced by some of the magnets of the rotor (113) is indicated separately when a signal amplitude lower than a preset limit occurs in the detector signal (4).