Load Change Responsive Elevator Speed Control Apparatus

This invention relates to an improved elevator speed control apparatus for regulating the running speed of an elevator cage to accommodate load changes when passengers exit before the cage comes to a complete halt at an accessed floor.

A conventional elevator speed control system is shown in FIG. 1, wherein an electric power converter 2 which comprises a plurality of thyristors connected in a 3-phase bridge configuration, is coupled to a 3-phase AC power source 1 and generates DC power that is supplied to an armature 3 of a DC elevator drive motor through a line 2a. The field winding for the motor is not shown in the drawing.

A tachometer generator 4 driven by the armature 3 produces a speed signal on line 4a proportional to the rotation speed of the armature. A traction sheave 5 also driven by the armature 3 drives an elevator cage 7 and a counterweight 8 through a main cable 6 as is well known. A speed arithmetic circuit 10 receives the speed signal on line 4a from the tachometer generator 4 and a speed instruction signal on line 9a from a speed instruction signal generator 9 as inputs, and generates a current instruction signal on output line 10a. The speed arithmetic circuit 10 along with the speed instruction signal generator 9 and the tachometer 4 constitute a speed control system.

A current arithmetic circuit 12 receives as inputs the current instruction signal on line 10a from the speed arithmetic circuit 10 and a current signal on line 11a from a current detector 11 proportional to the current supplied to the converter 2. A phase shifter 13 receives the output signal on line 12a from the current arithmetic circuit 12 as an input, and outputs a firing control signal on line 13a for the converter 2. The current arithmetic circuit 12 along with the current detector 11 constitute a current control system.

By controlling the firing angle or phase of the thyristor converter 2 by means of both the speed control and current control systems, the voltage applied to the armature 3 is correspondingly controlled and thus the running speed of the elevator cage 7 is controlled through the traction sheave 5. In other words, the elevator cage 7 is speed controlled in accordance with the difference between the speed instruction signal on line 9a and the actual speed signal on line 4a with a high degree of accuracy.

In the aforementioned speed control system, in order to compensate for the non-linearity of the converter 2, the response time of the minor loop constituted by the current control system is set at an extremely short value, generally in the range of 0.01 to 0.03 second. On the other hand, the response time of the main loop constituted by the overall speed control system must be set at a higher value in order to avoid resonances in the suspension and traction cables. Consequently, the speed control system is generally designed so as to have a response time in the range of 0.2 to 0.33 second.

With such a conventional elevator system, in order to improve the transport efficiency and speed up the overall operation both the internal cage door and the external door on the accessed floor are sometimes controlled to be simultaneously opened just before the cage reaches the floor. A brake system (not shown) is also provided to engage the traction sheave 5, but such engagement does not occur until the cage comes to a complete stop. Passengers may thus step out of the cage before the brake system acts upon the traction sheave, and as a result an abrupt variation in torque is exerted on the sheave due to the change in the cage load or weight, as shown in FIG. 2(a).

Upon the occurrence of a torque variation, the current flowing through the armature 3 correspondingly varies in response to the output of the speed arithmetic circuit 10 due to the functioning of the current control system, as described above. In this case, however, based on the relatively slow response time characteristics of the speed control system the current flowing through the armature 3 varies or adjusts relatively slowly as shown in FIG. 2 (b). The running speed of the cage 7 therefore varies as shown in FIG. 2 (c), as a result of which the cage may overshoot or undershoot the exact position of the accessed floor, which constitutes a potentially dangerous situation. Even in the best case where the cage ultimately stops at the exact position of the floor sill, the passengers will experience a discomforting "acceleration-deceleration bump".

It will be understood that the curves of FIG. 2 have been simplified by removing or subtracting therefrom the normal transient values, to leave just the "abnormal"variants caused by a premature passenger exit (or entry).

It is thus an object of this invention to provide an elevator speed control apparatus which is capable of eliminating or at least minimizing any undesired undershoot or overshoot between an accessed floor sill where the cage is to be stopped and the position where the cage is actually stopped, as well as any acceleration-deceleration bump, even though one or more passengers may have exited the cage before the brake system acts upon the traction sheave.

It is another object of the invention to provide an elevator speed control apparatus which exhibits excellent control and performance characteristics without causing the passengers to feel uncomfortable or endangered.

The aforementioned objects are attained by providing a load detecting device for detecting the load in the elevator cage, and means for applying the output of the load detecting device to the current control system when the load in the cage abruptly changes.

FIG. 1 shows a schematic diagram of a conventional elevator speed control apparatus,

FIGS. 2(a), 2(b) and 2(c) are simplified time plots of operating parameters for the apparatus shown in FIG. 1,

FIG. 3 shows a schematic diagram of an elevator speed control apparatus according to a preferred embodiment of this invention,

FIG. 4 shows a detailed circuit configuration of the speed and current arithmetic circuits shown in FIG. 3, and

FIGS. 5(a), 5(b), 5(c) and 5(d) are simplified time plots of operating parameters for the apparatus shown in FIG. 3.

With reference to FIGS. 3 through 5, a preferred embodiment of the present invention will now be described. In FIG. 3, reference numeral 14 designates a load detecting device provided for the cage 7 which produces an output corresponding to the load in the cage, and which may take any one of a number of conventional forms. The device 14 may, for example, comprise a vibration absorbing rubber element mounted between the cage floor and an underlying support beam, and a differential transformer affixed to such element which detects its compression in response to the number of passengers and converts it to an electrical signal. A floor relay contact 15 is connected to the output of the load detecting device 14, and is held open during the running of the cage 7. The relay contact is closed just before the cage reaches a desired floor by any suitable means (not shown), and reopened again just before the cage is restarted. A memory circuit 16 is provided between the relay contact 15 and the current arithmetic circuit 12'. The remaining circuit components correspond to those shown in FIG. 1 and are designed by the same reference numerals.

FIG. 4 shows an embodiment of the speed and current arithmetic circuits 10, 12' shown in FIG. 3. The speed arithmetic circuit comprises resistors 10b through 10e, a variable resistor 10f, a capacitor 10g, and an operational amplifier 10h; the current arithmetic circuit comprises resistors 12b through 12e, a variable resistor 12f, a capacitor 12g, and an operational amplifier 12h.

The speed signal on line 4a from the tachometer generator 4 and the speed instruction signal on line 9a from the speed instruction signal generator 9 are different in polarity. When the cage 7 is moving up the speed instruction signal on line 9a is positive and the speed signal on line 4a is negative, and vice versa when the cage is moving down. The amplifier 10h along with the feedback resistor 10d and capacitor 10g integrates the difference signal between the two inputs to generate the current instruction signal on output line 10a.

Furthermore, the current signal on line 11a from the current detector 11 is different in polarity from the other two signals on lines 10a and 16a. The amplifier 12h along with the feedback capacitor 12g integrates the difference signal between the three inputs to generate the voltage instruction signal on output line 12a.

In operation, AC power produced by the power supply 1 is converted to DC by the converter 2 and supplied to the armature 3. At the same time, the speed arithmetic circuit 10 calculates the deviation between the speed instruction value on line 9a and the tachometer generator speed signal on line 4a, and applies the current instruction signal on line 10a to the current arithmetic circuit 12'. The latter then calculates the deviation between the current instruction signal 10a, the detected current signal on line 11a and the output signal on line 16a from the memory circuit 16, and applies an output signal on line 12a to the phase shifter 13. The phase shifter then operates to control the firing angle of the thyristors in the converter 2 in response to the output of the current arithmetic circuit 12'.

The floor relay contact 15, as mentioned above, is maintained closed while the cage 7 is stopped, and is opened immediately before the cage is started up, upon door closure for example. During the running operation of the cage the memory circuit 16 thus stores the last output of the load detecting device 14, which was produced just before the cage was restarted. The floor relay contact 15 prevents the memory circuit 16 from being affected by the changing output from the load detecting device 14 in response to the acceleration and deceleration of the cage.

As the cage 7 approaches a desired floor, the relay contact 15 is closed to cause the value stored in the memory circuit 16 to vary in accordance with the output of the load detecting device 14. At the same time, and as described above, the cage and floor doors are opened just before reaching the accessed floor sill; the door opening signal may also be used to close the relay contact 15.

If any passengers now exit the cage 7 before the brake system acts upon the traction sheave 5, an abrupt variation in torque as shown in FIG. 5(a) is exerted not only on the traction sheave but also on the armature 3. The output of the load detecting device 14 thus changes in response to the decreased cage load, as does the value stored in the memory circuit 16 through the closed relay contact 15. The variation of the output of the memory circuit 16 is shown in FIG. 5(b).

Due to the quick response of the current arithmetic circuit 12', the current flowing through the armature 3 varies abruptly as shown in FIG. 5(c), closely following the output of the memory circuit 16. As a result, the running speed of the cage 7 is more smoothly controlled as shown in FIG. 5(d) and the "disruption bump" is minimized, whereby any undesired distance between the accessed floor sill and the cage stop position is substantially eliminated.

Consequently, excellent cage control is maintained even when an abrupt variation in torque due to passengers exiting before the brake system engages the traction sheave is exerted on the armature 3.