GB2151420A - Levelling apparatus for AC motor driven elevator - Google Patents

Abstract

A levelling apparatus for an AC elevator comprises a vector control unit (VC) for independently controlling a torque current component (It) and an exciting current component (Im) fed to an elevator drive induction motor (2). A difference between a level correction speed instruction, which increases in proportion to a level difference between an elevator car (10) and a target floor, and a rotation angular speed ( omega r) of the motor attributes to a torque current instruction (It). The torque current instruction is used as an instruction for the torque current component and corrected by a load on the elevator car, so that the level difference can be corrected at the level correction speed with high accuracy without being affected by passengers who get on or off the elevator car. <IMAGE>

Description

SPECIFICATION Levelling apparatus for AC elevator This invention relates to controlling of an AC elevator driven by an induction motor and more particularly to a levelling apparatus suitable for improving the stop position or landing level of the AC elevator at a target floor.

Generally, DC motors have hitherto been used widely as drive motors for elevators which are required to provide highly accurate controlling over a wide range and give a comfortable feeling to passengers in the elevator. However, the DC drive motor cooperative with a mechanical rectifying mechanism suffers from various restrictions thereby. In recent years, therefore, various types of elevators driven by robust and inexpensive induction motors of simplified structure have been developed and practiced.

Of such elevators with the induction motors, an elevator system disclosed in, for example, U.S. Patent No. 3,876,918 has been widely used in which speed controlling is effected by controlling the primary voltage.

The elevator in this system, because of its nature based on the primary voltage controlling, is implemented in the form of an elevator without gears or gearless elevator using, for example, the Ward-Leonard system or the thyristor-Leonard system and inevitably undergoes restrictions in performing the following types of controlling: (1) The gearless-drive induction motor, even when used for an elevator of a high speed of 360 m/min, has a rated revolution of 200 r.p.m. or less.Therefore, when an elevator of a lower rated speed than 360 m/min is desired to be controlled near a rated revolution of an induction motor on the basis of the primary voltage controlling, this induction motor must have a large number of poles; (2) The controlling of the induction motor contains a variety of non-linear factors and the induction motor is difficult to stably control over such a wide control range as attained by the DC motor; and (3) In DC gearless elevators, a so-called landing floor level correction operation is effected whereby a small difference between the floor level of the elevator car and the floor level of the target floor is detected and controlled to zero. Under the primary voltage control, however, such an operation is invalidated since accurate torque controlling is almost impossible near zero speed.

As described above, while the existing DC gearless elevator can realize very excellent operation characteristics, the AC elevator driven by the induction motor subject to the primary voltage controlling is almost impossible to realize various types of controlling mentioned above.

To achieve the level correction even under the primary voltage controlling, an elevator system as disclosed in U.S. Patent No. 4,094,385 has been proposed. An induction motor employed in this system has one type of winding having a small number of poles to which an AC voltage commensurate with a speed instruction is applied and the other having a large number of poles to which a DC voltage attributing to a breaking torque is applied. This permits the induction motor to generate a difference torque between the drive torque and the braking torque, so that the elevator car can be operated at a level correction speed.However, since delicate and continuous controlling of the relationship between the drive torque and the braking torque is difficult to achieve, it is inevitable that the elevator is operated when the level difference exceeds a predetermined value and stopped when this level difference becomes smaller. Consequently, the proposed system, though being successful in achieving a great improvement in controlling, fails to provide continuous level correction at a level correction speed commensurate with the level difference. In addition, the braking torque becomes zero at zero speed in the proposed system and as a result, a torque for correcting an amount of unbalance between the elevator car and the counterweight is difficult to be controlled.For these reasons, the proposed system is disadvantageous in that it can not actually control the level error and speed to zero even at the cost of the very complicated and expensive controlling scheme.

Incidentally, an induction motor control system based on the primary frequency controlling is available and considered to be superior to the primary voltage controlling described above. In this slip frequency controlling, the slip frequency is directly controlled to control the torque of the induction motor. This control scheme is well known in the art and details thereof will not be described here but features thereof will be itemized below.

(a) Precise speed controlling can be attained through the closed loop.

(b) Capability of the motor can be fully utilized to permit size-reduction of the motor.

(c) Speed controlling over a wide range is possible to thereby facilitate operations through four quadrants.

(d) Stability against variations in load and speed can be high.

(e) Mitigation of maintenance is possible to thereby improve adaptability to ambient conditions.

Therefore, the slip frequency controlling solves the problem of the rated speed described in item (1) and in addition, realizes stable control over a wide range described in item (2).

In the level correction speed range described in item (3), however, the slip frequency controlling faces difficulties as below.

During the level correction speed operation, for example, the door of the elevator car is usually kept opened and the induction motor is subjected to torque disturbance which occurs when passengers get on or off the elevator car. in the slip frequency controlling, however, only the slip frequency and primary current are changed in response to variations in torque but the phase of current is not controlled. Consequently, the exciting current component changes after the torque has changed, with the result that delay in torque response is increased to make it difficult to obtain smooth torque controlling during the level correction speed operation.

Accordingly, the slip frequency control scheme disadvantageously fails to give a confortable feeling to passengers in the elevator car and provide sufficient landing level control, during the level correction speed operation.

Meanwhile, in the field of induction motor control, the vector controlling has recently been highlighted. The vector controlling, first proposed in U.S. Patent No. 3,824,437 and subsequently announced in various articles and papers, has now become well known in the art. This vector controlling is featured by independent control of the torque current and exciting current components fed to the induction motor, thereby realizing stable speed control of the induction motor at a high response.

A principal object of this invention is to provide a levelling apparatus for an AC elevator which can give a comfortable feeling to passengers in the elevator car and provide highly accurate levelling in an AC elevator system driven by an induction motor.

According to a principal feature of this invention, a vector control unit is employed for controlling an elevator drive induction motor by making use of the high-response and highstability vector controlling, whereby a level correction speed instruction is generated in accordance with a level difference between the elevator car and a target floor, and a torque current instruction resulting from a difference between the level correction speed instruction and a rotation angular speed of the induction motor is used as an instruction for a torque current component fed to the induction motor, thereby correcting the level difference at the level correction speed commensurate therewith with high accuracy.

Other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Figure 1 is a block diagram showing a levelling apparatus for an AC elevator according to an embodiment of the invention; Figure 2 is a graphical representation useful in explaining the operational principle of the vector controlling; Figure 3 is a graphic representation showing a characteristic of a level correction speed instruction generator used in Fig. 1:: Figure 4 is a block diagram showing a levelling apparatus for an AC elevator according to another embodiment of the invention; Figures 5A and 5B are waveform diagrams useful in explaining the operation of the Fig. 4 embodiment; Figure 6 is a block diagram showing still another embodiment of the levelling apparatus according to the invention; and Figure 7 is a block diagram showing an embodiment of a level difference detector circuit used in Fig. 6.

The invention will now be described by way of examples.

Referring to Fig. 1, there is illustrated a levelling apparatus for an AC elevator embodying the invention. In the apparatus, a vector control unit VC as disclosed in the aforementioned U.S.

Patent No. 3,824,437 is well known and only its portion directly related to the invention will be described hereunder.

The levelling apparatus comprises a frequency converter 1 for controlling the instantaneous values of the primary currents fed to an elevator drive induction motor 2 and each consisting of a torque current component and an exciting current component, an angular speed detector 3 for detecting the rotation angular speed of the induction motor 2. power source buses 41 to 43, DC current transformers 5, 6 and 7 for detecting the instantaneous value of each of the primary currents, a current detector circuit 8 for converting the detection values of the DC current transformers 5, 6 and 7 into signal levels commensurate with those of a primary current calculation circuit to be described later, a sheave 9 coupled to a rotor of the induction motor 2, an elevator car 10, a counterweight 11, a main rope 1 2 trained around the sheave 9 to connect the elevator car 10 and the counterweight 11, an elevator speed instruction generator circuit 13, a level difference detector 14 for detecting the difference between the floor level of the elevator car 10 and the floor level of a target floor, a level correction speed instruction generator 15 for converting the level difference into a signal level of level correction speed, a flux instruction circuit 16, a speed control circuit 17 for control which makes the actual speed of the induction motor 2 equal to the instructed speed, a primary current calculation circuit 18 a torque current instruction. It from the speed control circuit 17, a flux instruction Im from the flux instruction circuit 16 and flux position signals from a flux position detector 19 to produce an instantaneous reference value i, of an a-axis (r-axis in the aforementioned U.S. Patent No.

3,824,437) component and instantaneous reference value ip of a p-axis (j-axis in the same U.S.

Patent) component of the primary current, a three phase converter circuit 20 receiving the instantaneous values of the a-axis and ssaxis components of the primary current to convert them into three-phase signals, and current controllers 21 U, 21V and 21W for controlling the primary current value of the induction motor 2 with reference to the three-phase signals. The flux position detector circuit 19 receives a rotation angular speed xr of the rotor and the torque instruction It to detect the flux position.

The operation of this embodiment will now be described.

Primary current i, is resolved, on the rotating field of the induction motor 2, into an exciting current vector component Im (used as the flux instruction) in a flux direction and a torque current vector component It (used as the torque current instruction) which is in a direction orthogonal to the flux direction and flows so as to cancel out a magnetomotive force due to the secondary current. This relation is indicated by a vector expression as follows: Ii = Im + It. (1) In order to control these orthogonal vectors Im and It independently, for a fixed Im, It is set to It2 within a region of larger torque and to It, within a region of smaller torque, as shown in Fig.

2, thereby attaining controlling equivalent to that obtained by the DC motor. This indicates the principle of the vector controlling as will be known from the aforementioned U.S. Patent No.

3,824,437.

The torque current instruction It from the speed control circuit 17 and the flux instruction Im from the flux instruction circuit 16 are defined by the coordinates on the rotating field pursuant to the above-described principle of the vector controlling. Thus, these instructions are required to be converted into variables defined by the coordinates on the stator having orthogonal a and ss axes by using rotating field position signals sin 1t and cos ,t from the flux position detector circuit 19, thus obtaining i,, and ifi as outputs from the primary current calculation circuit 18 which are:: sin = sin ,t Im + cos 1t It (2) ;/J = - cos art Im + sin so1t It (3) where , is an angular speed which is represented by the sum of rotation angular speed xr of the rotor and slip frequency os proportional to the torque instruction It.

These variables i" and i1 are converted into the three-phase primary current having phase currents which are out of phase from each other by 120 , thus obtaining three-phase primary currents iU, iV and iW as outputs from the three-phase converter circuit 20 which are: iU = i + iss (4) a 1 #3 iV = 2i&alpha; + 2 iss ............ (5) iw 1. li 1 = 21a 1 25 its (6) By supplying these three-phase primary currents serving as instantaneous reference values to the induction motor, the controlling performance equivalent to that of the DC motor can be obtained.

As will be appreciated from the foregoing description, when the speed control circuit 17 produces the torque instruction It in response to the output signal from the level correction speed instruction generator 15, the level correction speed operation characteristic equivalent to that of the DC motor can be obtained.

In this case, by setting the characteristic of the level correction speed instruction such that, as shown in Fig. 3, the more the level difference approaches zero, the smaller the speed instruction becomes, the difference between the floor level of the elevator car and the floor level of the target floor can be controlled to zero.

According to this embodiment, therefore, torque of the induction motor 2 developing during the very low speed operation inclusive of stopping of the induction motor can be controlled sufficiently smoothly and with high accuracy, to ensure that accuracy of correction for the difference between the floor level of the elevator car and the floor level of the target floor can be improved and comportable feeling can be given to passengers in the elevator car during the level difference correction operation.

Referring to Fig. 4, another embodiment of the levelling apparatus of the invention will be described which can give a comfortable feeling to passengers in the elevator car even under the condition that the load torque is externally disturbed during the level correction speed operation.

In the embodiment of Fig. 4, a load detector 30 for the elevator car 10 and a load correction torque instruction circuit 31 are added to the embodiment shown in Fig. 1.

According to this embodiment, therefore, a large change in the speed can be prevented even when the load torques changes as passengers get on or off the elevator car during the level correction speed operation, so that the floor level of the elevator car can coincide with the floor level of the target floor without giving an uncomfortable feeling to passengers in the elevator car.

More particularly, as shown in Fig. 5A, when the external disturbing torque develops in the Fig. 1 embodiment without ability to correct the external torque, a difference between the instructed speed and the actual speed develops and the difference attributes to a torque instruction. As a result, the actual speed undulates as shown in Fig. 5A, thus giving uncomfortable feeling to passengers in the elevator car.

In contrast, with the Fig. 4 embodiment added with the load detector 30 and load correction torque instruction circuit 31, as shown in Fig. 5B, the torque instruction can follow the change of torque without causing time difference and hence undulation of the actual speed disappears to permit a smooth level correction speed operation.

Fig. 6 shows still another embodiment of the invention which features in that a distance pulse generator 44 is provided which generates a distance pulse each time the elevator car 10 runs a unit of straight distance, and the level difference is detected by counting the distance pulse.

Referring to Fig. 6, a rope 43 connected with elevator car 10 is trained around upper and lower pulleys 41 and 42 disposed along the vertical movement paths, and a rotary disc 45 of the distance pulse generator 44 is connected to the upper pulley 41. Slits are formed in the rotary disc 45 concentrically therewith, and a pickup device 46 generates a pulse each time it detects the slit. Thus, the upper pulley 41 and rotary disc 45 rotate in synchronism with the running of the elevator car 10, and the pickup device 46 generates a pulse each time the elevator car 10 runs a unit of distance (1 to 2 mm).

A level difference detector circuit 47 receives the pulse from the distance pulse generator 44 and delivers a signal indicative of the level difference from the target floor to a level correction speed instruction generator 1 5.

Fig. 7 shows details of the level difference detector circuit 47 and the level correction speed instruction generator 1 5. Referring to Fig. 7, a car position detecting counter 48 counts the pulse from the distance pulse generator 44 and produces a car position signal. A floor level storage 49 stores the floor level of each target floor and produces a floor level signal corresponding to a landing floor. A comparator 50 compares the car position signal with the floor level signal to produce a level difference. Specifically, when the car position exceeds the floor level, the comparator 50 produces a positive value proportional to the difference, and when the car position is below the floor level, it produces a negative value proportional to the difference.The level correction speed instruction generator 1 5 receives the level difference to produce a descending level correction speed instruction proportional to a value of the level difference when the level difference is positive and an ascending level correction speed instruction proportional to a value of the level difference when the level difference is negative.

These descending and ascending instructions are illustrated in a block of the generator 1 5. The speed instruction becomes constant for the level difference exceeding a predetermined value, thereby preventing impartation of anxiety to passengers and occurrence of danger during the levelling operation at which the door is kept opened and passengers get on or off the elevator car.

As has been described, according to the present invention, the landing level of the AC elevator driven by the induction motor can be corrected accurately at the level correction speed commensurate with the level difference while giving a comfortable feeling to passengers in the elevator car.

Claims (6)

1. A levelling apparatus for an AC elevator wherein an elevator car is driven by an induction motor to run along a plurality of target floors, said apparatus comprising: a vector control unit for independently controlling a torque current component and an exciting current component fed to said induction motor; level detector means for detecting a level difference between the floor level of said target floor and the floor level of said elevator car; level correction speed instruction generator means for generating a level correction speed instruction in response to the level difference; angular speed detection means for detecting a rotation angular speed of said motor; and means for generating a torque current instruction on the basis of a difference between the output signal of said level correction speed instruction generator means and the output signal of said angular speed detector means, said torque current instruction being used as an instruction for the torque current component of said vector control unit.

2. The levelling apparatus according to Claim 1 wherein said level difference detector means comprises a distance pulse generator for generating a pulse each time said elevator car runs a unit of distance, a car position detecting counter for counting the pulse to detect the position of said elevator car, and comparator means for producing a difference between the car position and a predetermined floor level of the target floor.

3. The levelling apparatus according to Claim 1 or Claim 2 wherein said level correction speed instruction generator means generates a speed instruction which increases with the magnitude of said level difference and becomes constant for said level difference exceeding a predetermined value.

4. The levelling apparatus according to Claim 3 wherein said level correction speed instruction generator means generates the speed instruction which becomes positive or negative in accordance with the direction of said level difference.

5. The levelling apparatus according to Claim 1 further comprising means for detecting a load on said elevator car, said torque current component being corrected in accordance with the car load.

6. A levelling apparatus for an AC elevator substantially as herein described with reference to and as illustrated in any one of the accompanying drawings.