Elevator control system

An elevator control system includes a power source which supplies AC power to an induction motor for driving an elevator car through a first thyristor gate circuit. Another induction motor provided for braking the elevator car is connected to the power source through a second thyristor gate circuit. A tachometer generator connected to the induction motors produces an speed signal indicative of the speed of the elevator car. The speed signal is compared with a reference signal and the difference therebetween is used to control the first and second thyristor gate circuits for controlling the elevator car speed.

BACKGROUND OF THE INVENTION 
The present invention relates to an elevator and, more particularly, to a 
control system for controlling the movement of an elevator car. 
In order to obtain a comfortable ride on the elevator car during the 
movement thereof, it is preferable to gradually increase the speed of the 
elevator car at the beginning of the movement of the car until it reaches 
a predetermined speed and, to gradually decrease the speed to stop the 
movement. More particularly, during the increase in speed of the elevator 
car, that is, during the acceleration thereof, it is preferable to 
gradually increase the acceleration. When starting the movement of the 
elevator car, it is accelerated gradually to reach a predetermined 
acceleration. Thereafter, the acceleration of the elevator car is 
gradually decreased to zero to run the elevator car at a predetermined 
speed. In a similar manner, during the decrease in speed of the elevator 
car, that is, during the deceleration, it is preferable to gradually 
increase the deceleration at the beginning thereof to reach a 
predetermined deceleration and to gradually decrease the deceleration at 
the ending thereof to stop the elevator car. 
In order to accomplish the above described movement of the elevator car, 
there have been proposed various methods and systems for controlling the 
driving means for driving the elevator. In FIG. 1, there is shown a 
circuit diagram of one conventional control system for controlling the 
movement of the elevator car. This control system includes two induction 
motors HM and LM whose rotating shafts are connected to each other and are 
further connected to a traction sheave (not shown) which moves the 
elevator car up and down upon rotation thereof. The induction motor HM or 
high speed motor is provided for starting and accelerating the elevator 
car while the other induction motor LM or low speed motor is provided for 
decelerating the elevator car. The high speed motor HM is connected to a 
three phase AC power source through three lead lines R, S and T each 
including a plurality of resistors connected in series. The movement of 
the elevator car is described hereinbelow with reference to the graph of 
FIG. 2 showing the relation between the speed of the elevator car and the 
time. 
When the three phase AC power is supplied to the induction motor HM through 
the resistors, the induction motor starts to rotate and, thus the elevator 
car starts moving (region A in FIG. 2). As the resistors in each line are 
shortcircuited one after another by a suitable switching means, the 
rotation of the induction motor HM increases to accelerate the elevator 
car and to cause the elevator car to move at a predetermined speed (region 
B in FIG. 2). When the elevator car reaches a point a predetermined 
distance away from the point where the car should stop, the induction 
motor HM is disconnected from the power source and the other induction 
motor LM is connected to the power source so as to decelerate the elevator 
car by the regenerative braking effect produced by the low speed induction 
motor LM (region C in FIG. 2). However, this regenerative braking does not 
completely stop the elevator car but only reduces the speed of the car to 
a very low speed determined by the rated revolution thereof. Then, when 
the elevator car reaches the point where the car should stop, the 
induction motor LM is disconnected from the power source and 
electromagnetic braking is applied to the elevator to completely stop the 
elevator car (region D in FIG. 2). 
Therefore, the control system described above is disadvantageous because 
the elevator car is accelerated to a greater degree each time one of the 
resistors is shortcircuited and because it takes a very long period of 
time before the car is completely stopped from the moment when the car is 
decelerated. Furthermore, the movement of the car changes abruptly at the 
moment when the induction motor HM starts to move the car or when the 
induction motor LM starts to decelerate the car. Therefore, this gives an 
uncomfortable ride to the passengers in the elevator car. 
SUMMARY OF THE INVENTION 
Accordingly, a primary object of the present invention is to provide an 
improved type of control system which smoothly changes the speed of the 
elevator car during the acceleration and deceleration for the elevator car 
to reach a destination in a very short period of time. 
Another object of the present invention is to provide an improved type of 
control system of the above described type which is effective to stop the 
movement of the elevator car at a predetermined position with high 
accuracy. 
A further object of the present invention is to provide an improved type of 
control system of the above described type which can be adjusted and 
maintained easily. 
In accordance with a preferred embodiment of the invention, the elevator 
car control system is constituted by a power supplying section producing 
AC power, driving and braking sections for driving and braking the 
elevator car, and a power control section which controls the power 
supplying section to control or adjust the speed of the elevator car. The 
power control section comprises means for generating an actual speed 
signal indicative of the instantaneous speed of the elevator car, a 
reference signal producing circuit producing a desired speed signal 
indicative of the desired speed of the elevator car, a comparator for 
comparing the voltage difference between the reference signal and actual 
speed signal and for selectively producing a positive signal when the 
voltage of the actual speed signal falls below that of the reference 
signal and a negative signal when the voltage of the actual speed signal 
exceeds that of the reference signal, and a control circuit which controls 
the power supplying section to increase the supply of power to the driving 
section upon receipt of a positive signal and to increase the dynamic 
braking effect from the braking section upon receipt of a negative signal. 
The control circuit comprising a first phase controller so connected as to 
receive the positive signal, and an inverter and a second phase controller 
so connected as to receive the negative signal.

DETAILED DESCRIPTION OF THE INVENTION 
Before the description of the present invention proceeds, note that like 
parts are designated by like reference numerals throughout the 
accompanying drawings. 
Referring to FIG. 3, there is shown one embodiment of an elevator control 
system of the present invention. The control system is divided mainly into 
three sections, i.e., a driving and braking section 2 for driving and 
braking an elevator car (not shown), a power supplying section 4 for 
supplying electric power to the driving and braking section 2 and a power 
control section 6 for controlling the power supplied to the driving and 
braking section 2. Each of the sections will now be described in detail. 
The driving and braking section 2 comprises two induction motors HM and LM. 
The induction motor HM is so designed as to rotate at comparatively high 
speed while the induction motor LM is so designed as to rotate at 
comparatively low speed. The induction motors HM and LM have their own 
rotating shafts connected to each other through a common shaft are further 
connected to a traction sheave (not shown) which moves the elevator car up 
and down during the rotation of the common shaft. 
The power supplying section 4 comprises a power source 8 which produces 
three phase AC power from output terminals 10, 12 and 14. The terminal 10 
is connected to one side of a switch S1 and also to one side of a switch 
S2. The other side of the switch S1 is connected to a lead line 16 and the 
other side of the switch S2 is connected to a lead line 20. In a similar 
manner, the terminal 14 is connected to one side of a switch S3 and also 
to one side of a switch S4. The other sides of the switches S3 and S4 are 
connected to the lead lines 16 and 20, respectively. The terminal 12 is 
connected directly to a lead line 18. Note that the switches S1, S2, S3 
and S4 are normally opened switches and that the switches S1 and S4 are 
closed simultaneously to supply the three phase AC power to the lead lines 
16, 18 and 20 in one sequential order while the switches S2 and S3 are 
closed simultaneously to supply the three phase AC power to the lead lines 
16, 18 and 20 in the other sequential order. The lead lines 16, 18 and 20 
are connected to a first gate means or a driving power control 22 
comprising power controlling elements such as thyristors TH1, TH2 and TH3, 
and diodes D1, D2 and D3. The thyristors TH1, TH2 and TH3 have their 
anodes connected to the lead lines 16, 18 and 20, respectively, while 
their cathodes are connected to three input terminals of the high speed 
induction motor HM. The diodes D1, D2 and D3 are connected in parallel to 
the respective thyristors TH1, TH2 and TH3 in a reverse polarity as to 
each of the thyristors. 
The power supplying section 4 further comprises a second gate means or a 
braking control 24 including power controlling elements such as thyristors 
TH4 and TH5 and diodes D4 and D5 which are connected in a mixed bridge 
rectification network. More specifically, the thyristors TH4 and TH5 are 
connected in series in the same polarity as to each other while the diodes 
D4 and D5 are connected in series in the same polarity as to each other. 
The series circuit of the thyristors TH4 and TH5 is connected in parallel 
to the series circuit of the diodes D4 and D5 in the same polarity and is 
further connected to the input terminals of the low speed induction motor 
LM. The junction J1 between the thyristors TH4 and TH5 is connected to the 
lead line 20, and the junction J2 between the diodes D4 and D4 is 
connected to the lead line 18. Note that the thyristors employed in the 
driving power control 22 and the braking control 24 can be replaced with 
other types of known power controlling elements such as mercury-arc 
rectifiers. 
The power control system 6 comprises a tachometer generator 26 having its 
shaft connected to the common shaft of the induction motor HM and LM. The 
tachometer generator 26 generates a voltage which is indicative of the 
speed of revolution of the common shaft. Since the speed of the rotation 
of the common shaft is related to the speed of the elevator car, this 
voltage produced from the tachometer generator 26 is also indicative of 
the instantaneous speed of the elevator car and, thus it is referred to as 
an actual speed signal, hereinbelow. A reference signal generating circuit 
28 generates a reference voltage which varies in relation to time. One 
waveform of the voltage produced from the reference signal generating 
circuit 28 is shown in a graph of FIG. 4 in which the abscissa represents 
time and the ordinate represents voltage. As it is apparent from the 
graph, the curve gradually increases at the beginning and gradually 
reaches a predetermined voltage level Ea and gradually decreases to zero 
voltage. When the ordinate is represented by the speed of the elevator 
car, the curve exhibits the ideal speed of the elevator car to be produced 
with respect to time. 
Noted here that the reference signal generating circuit 28 includes a 
number of switch buttons (not shown), each of which are pushed by an 
operator to command the elevator car to move from its present position to 
a desired position, and a voltage producing circuit (not shown) which is 
so programmed to produce a voltage waveform having the same waveform or a 
similar waveform to the waveform shown in FIG. 4 and which is 
automatically actuated corresponding to the one of the switch buttons 
pressed. When it is desired to move the elevator car a comparatively short 
distance, the reference signal generating circuit 28 produces one pattern 
of waveform in which the voltage level Ea is comparatively low while the 
time during which the voltage level Ea is maintained is comparatively 
short. On the other hand, when is desired to move the elevator a 
comparatively long distance, the reference signal generating circuit 28 
generates another pattern of waveform in which the voltage level Ea is 
comparatively high while the time during which the voltage level Ea is 
maintained is comparatively large. 
The voltage produced from the reference signal generating circuit 28 is 
applied to a comparator 30 which receives the actual speed signal from the 
tachometer generator 26 and produces a difference signal indicative of the 
difference in voltage between the reference signal and the actual speed 
signal. The difference signal produced from the comparator 30 is applied 
to an amplifier 32 which produces a positive signal when the voltage of 
the reference signal is higher than that of the actual speed signal and, a 
negative signal when the voltage of the reference signal is lower than the 
actual speed signal. No signal is produced from the amplifier 32 when the 
voltage of the reference signal is equal to that of the actual speed 
signal. Therefore, the amplitude of the positive and negative signals 
varies according to the difference between the reference signal and the 
actual speed signal. The positive signal is applied to a first phase 
controller 34 which produces a pulsating signal whose frequency is equal 
to the frequency of the AC voltage produced from the power source 8. The 
phase of the pulsating signal lags in accordance with the variation in 
amplitude of the positive signal. The pulsating signal produced from the 
first phase controller 34 is applied to the gates of the thyristors TH1, 
TH2 and TH3 contained in the driving power control 22 for firing the 
thyristors. A decrease in the phase lag of the pulsating signal results in 
an increase in the power supplied to the induction motor HM. Therefore, 
the less the phase lags, the larger the driving torque of the induction 
motor HM so that the speed of the induction motor HM becomes high. 
The power control system 6 further comprises an inverter 36 connected to 
the amplifier 32 to receive the negative signal and to produce an inverted 
and amplified signal. Thus, the signal produced from the inverter is a 
positive signal. To distinguish between the positive signal produced from 
the amplifier 32 and the positive signal produced from the inverter 36, 
the latter positive signal is referred to as the inverted positive signal, 
hereinbelow. The inverted positive signal is applied to a second phase 
controller 38 which also produces a pulsating signal in a manner similar 
to that of the first phase controller 34 described above. The phase of the 
pulsating signal produced from the second phase controller 38 lags in 
accordance with variation in amplitude of the inverted positive signal. 
The pulsating signal produced from the second phase controller 38 is 
applied to the gates of the thyristors TH4 and TH5 contained in the 
braking control 24 for firing the thyristors. A decrease in the phase lag 
of the pulsating signal produced from the second phase controller 38 
results in a reduction a rotation of the induction motor LM. Therefore, 
the less the phase of the pulsating signal produced from the second phase 
controller 38 lags, the larger the braking torque of the induction motor 
LM so that the speed of the induction motor LM becomes slow. Note that, 
according to a preferred embodiment, the second phase controller 38 has 
exactly the same structure as that of the first phase controller 34. 
Therefore, during the manufacture of the elevator control system, two 
phase controllers having the same structure and the same characteristic 
are prepared and they are employed as the first and second phase 
controllers 34 and 38. The operation of the elevator control system of the 
present invention is described hereinbelow. 
Initially, the switches S1, S2, S3 and S4 are opened to maintain the 
induction motors HM and LM in a suspended state while the reference signal 
generating circuit 28 generates no reference voltage therefrom. When the 
operator commands the elevator car to move a predetermined distance in one 
direction, such as the upward direction, by pressing one of the buttons 
(not shown), the switches S1 and S4 are closed to supply power to the 
driving power control 22 and, at the same time, the reference signal 
generating circuit 28 starts generating a reference signal having a 
waveform the same as or similar to the waveform shown in FIG. 4. 
Immediately after pressing the button, the voltage of the reference signal 
gradually increases. However, at this moment, the power supplied to the 
driving power control 22 is not applied to the motor HM because the 
pulsating signal produced from the first phase controller 34 prevents the 
thyristors TH1, TH2 and TH3 from transmitting power to the induction motor 
HM. Therefore, the voltage of the actual speed signal produced from the 
tachometer generator 26 is zero. This zero voltage of the actual speed 
signal produced from the tachometer generator 26 is compared with the 
voltage of the reference signal in the comparator 30. Accordingly, since 
the reference signal is higher than the actual speed signal, the amplifier 
32 produces a positive signal to the first phase controller 34. In 
response to the receipt of the positive signal, the first phase controller 
34 advances the pulsating signal produced therefrom. The degree of this 
phase lag depends upon the voltage level of the applied positive signal. 
Thereupon, the thyristors TH1, TH2 and TH3 transmit three phase AC power 
to the induction motor HM which is then rotated. The speed of revolution 
of the induction motor HM, i.e., the speed of the rotation of the common 
shaft increases correspondingly with the increase of the reference 
voltage. 
When the voltage of the actual speed signal exceeds that of the reference 
signal, particularly expected to occur when the voltage of the reference 
signal becomes low, a negative signal is produced from the comparator 30, 
which is in turn applied through the amplifier 32 to the inverter 36. The 
inverted positive signal produced from the inverter 36 is applied to the 
second phase controller 38 which delays the pulsating signal produced 
therefrom. Thereupon, the thyristors TH4 and TH5 allow the induction motor 
LM to excite DC power to brake the elevator car. Therefore, the speed of 
the rotation of the common shaft is reduced. Note that, during the braking 
of the induction motor LM, the other induction motor HM provides no 
driving force to the common shaft since the first phase controller 34 
prevents the thyristors from transmitting power to the induction motor HM. 
The speed of the rotation of the common shaft, that is, the speed of the 
elevator car is reduced in response to the decrease of the reference 
signal in voltage. 
As hereinabove fully described, the elevator control system of the present 
invention can control the elevator car to move at a desired speed 
established by a desired acceleration and reduced by a desired 
deceleration. Therefore, the elevator car does not make any abrupt change 
in its speed which often causes the passenger in the elevator car to feel 
uncomfortable. Since the speed of the elevator car is programmed by the 
reference signal generating circuit 28, an optimum speed can be obtained 
for each of the different distances of elevator car movement. Therefore, 
the elevator car moves from the place where it is located to a required 
place in the smallest possible time, and yet provides a comfortable ride. 
From this aspect, the elevator control system of the present invention is 
applicable to the elevators employed in high rise building where the 
elevator car is required to make a number of movements in different 
distances; from a comparatively short distance to a comparatively long 
distance. 
Furthermore, since the elevator control system of the present invention 
includes the inverter 36 inserted between the amplifier 32 and the second 
phase controller 38, the second controller 38 operates upon receipt of a 
positive signal in the same manner as the first phase controller 34 
operates. Therefore, the structure of the first and second phase 
controllers 34 and 38 can be arranged to have exactly the same 
constitution. Therefore, the manufacturing cost is reduced. Moreover, 
since the inverter 36 controls the amplitude of the inverted positive 
signal produced therefrom, it is simple to adjust the degree of phase 
shift in the second phase controller 38 in relation to the phase shift in 
the first phase controller 34. In other words, the gain of the positive 
signal applied to the first phase controller 34 controlled by the 
amplifier 32, while the gain of the inverted positive signal applied to 
the second phase controller 38 is controlled by the inverter 36. 
Therefore, the adjustment of the amplitude of the positive signal and the 
inverted positive signal can be simply effected. 
Although it is possible to arrange the second phase controller 38 in common 
with the first phase controller 34 by constituting only one phase control 
which is alternately connected to the driving power control 22 and braking 
control 24, it is preferable to arrange the first and second phase 
controllers 34 and 38 as independent phase controls so as to eliminate 
dead time during the switch-over. 
Referring to now to FIG. 5, there is shown an elevator control system 
according to another embodiment of the present invention. The elevator 
control system shown in FIG. 5 has the inverter 36 connected between the 
amplifier 32 and the first phase controller 34, instead of between the 
amplifier 32 and the second phase controller 38 such as in the foregoing 
embodiment, so that the first and second phase controllers 34 and 38 
operate upon receipt of negative signals. 
Furthermore, as shown in FIG. 5, the diodes D1, D2 and D3 which have been 
described as provided in the driving power control 22 can be replaced with 
thyristors TH6, TH7 and TH8 respectively. In a similar manner, the diodes 
D4 and D5 which have been described as provided in the braking control 24 
can be replaced with thyristors TH9 and TH10, respectively. 
Although the present invention has been fully described by way of examples 
with reference to the accompanying drawings, note that various changes and 
modifications are apparent to those skilled in the art. For example, the 
power supply section 4 can be replaced with any known power supplying 
system which controls AC power. Moreover, the induction motors HM and LM 
which have been described as being two separate induction motors can be 
one induction motor so designed as to serve as a high speed induction 
motor when it is connected in one way and as a low speed induction motor 
when it is connected in another way. Therefore, such changes and 
modifications, unless they depart from the true scope of the present 
invention, are to be understood as included therein.