U.S. patent number 3,584,706 [Application Number 04/758,776] was granted by the patent office on 1971-06-15 for safties for elevator hoist motor control having high gain negative feedback loop.
This patent grant is currently assigned to Reliance Electric Company. Invention is credited to Donivan L. Hall, Richard C. Loshbough.
United States Patent |
3,584,706 |
Hall , et al. |
June 15, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
SAFTIES FOR ELEVATOR HOIST MOTOR CONTROL HAVING HIGH GAIN NEGATIVE
FEEDBACK LOOP
Abstract
A variable voltage hoist motor control wherein a pattern signal
is compared with a feedback signal in a high gain closed loop and
the signals at critical points in the control are monitored to
ascertain unsafe operating conditions. Indicated unsafe conditions
alter the control to either a safe operating mode or shut down the
system. Monitored signals include the error signal at the summing
point for the pattern and feedback signals, rate of change of the
feedback signal, signal level at the high power levels for the
motor control during the period the elevator car is to be
stationary and to be driven at leveling speeds.
Inventors: |
Hall; Donivan L. (Toledo,
OH), Loshbough; Richard C. (Toledo, OH) |
Assignee: |
Reliance Electric Company
(Euclid, OH)
|
Family
ID: |
25053071 |
Appl.
No.: |
04/758,776 |
Filed: |
October 10, 1968 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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373136 |
Jun 4, 1964 |
3435916 |
Apr 1, 1969 |
|
|
Current U.S.
Class: |
187/289 |
Current CPC
Class: |
B66B
1/285 (20130101); B66B 1/30 (20130101) |
Current International
Class: |
B66B
1/28 (20060101); B66B 1/30 (20060101); B66b
005/02 () |
Field of
Search: |
;187/29 ;317/13
;318/20.070,20.085,141--143,309--311,329--331,436,445,449,450 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rader; Oris L.
Assistant Examiner: Duncanson, Jr.; W. E.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a divisional continuation-in-part of application, Ser. No.
373,136 filed June 4, 1964 in the names of Robert E. Bell, Donivan
L. Hall and Richard C. Loshbough now U.S. Pat. No. 3,435,916
entitles "Elevator Motor Speed Control Including a High Gain
Forward Loop and Lag-Lead Compensation" which issued Apr. 1, 1969.
Claims
We claim:
1. A hoist motor control for an elevator having a guided path of
travel comprising a hoist motor; means for generating a signal
proportional over said performance parameter signal for disabling a
performance parameter of said hoist motor as it drives the elevator
along its path of travel; means for generating a performance
parameter command signal to command said hoist motor to accelerate
the elevator, to decelerate the elevator and to move the elevator
at constant velocity along its path of travel; means for comparing
said performance parameter signal and said command signal to
develop an error signal; means for controlling the operation of
said hoist motor in accordance with said error signal; and means
responsive to an error signal representing a predetermined excess
of said performance parameter signal over said command signal and
responsive to an error signal representing a predetermined excess
of command signal over said performance parameter signal for
disabling the response of said motor to said error signal whereby
said performance parameter signal is confined within predetermined
magnitudes of said command signal during acceleration, deceleration
and constant velocity operation of the elevator along its path of
travel.
2. A hoist motor control for an elevator having a guided path of
travel comprising a hoist motor; means for generating a signal
proportional to a performance parameter of said hoist motor as it
drives the elevator along its path of travel; means for generating
a performance parameter command signal to command said hoist motor
to accelerate the elevator, to decelerate the elevator, and to move
the elevator at a constant velocity along its path of travel; means
for comparing said performance parameter signal and said command
signal to develop an error signal; means to amplify said error
signal to control the operation of said hoist motor; and means
responsive to an amplified signal representing a predetermined
excess of said command signal over said performance parameter
signal for disabling the response of said motor to said amplified
signal, whereby said performance parameter signal is confined
within predetermined magnitudes of said command signal during
acceleration, deceleration and constant velocity operation of the
elevator along its path of travel.
3. A hoist motor control for an elevator having a guided path of
travel comprising a hoist motor; means for generating a signal
proportional to a performance parameter of said hoist motor as it
drives the elevator along its path of travel; means for generating
a performance parameter command signal to command said hoist motor
to accelerate the elevator, to decelerate the elevator, and to move
the elevator at a constant velocity along its path of travel; means
for comparing said performance parameter signal and said command
signal to develop an error signal; means for controlling the
operation of said hoist motor in accordance with said error signal;
and means responsive to an error signal representing a
predetermined excess of said performance parameter signal over said
command signal and responsive to an amplified signal representing a
predetermined excess of said command signal over said performance
parameter signal for actuating an indicator.
4. A hoist motor control for an elevator having a guided path of
travel comprising a hoist motor; means for generating a signal
proportional to a performance parameter of said hoist motor as it
drives the elevator along its path of travel; means for generating
a performance parameter command signal to command said hoist motor
to accelerate the elevator, to decelerate the elevator, and to move
the elevator at a constant velocity along its path of travel; means
for comparing said performance parameter signal and said command
signal to develop an error signal; means to amplify said error
signal to control the operation of said hoist motor; and means
responsive to an amplified signal representing a predetermined
excess of said performance parameter signal over said command
signal and responsive to an amplified signal representing a
predetermined excess of said command signal over said performance
parameter signal for actuating an indicator.
5. A combination in accordance with claim 1 including means
responsive while said elevator is stopped to enable said disabling
means and responsive while said elevator is moving to render said
disabling means ineffective.
6. A hoist motor control for an elevator including a car serving a
plurality of landings comprising a hoist motor; means for stopping
said car at one of said landings; means for sensing a misalignment
of said car with said landing at which it is stopped; means for
generating an elevator performance parameter signal proportional to
a performance parameter of the elevator; means for generating a
performance parameter command signal; means for comparing said
performance parameter signal and said command signal to develop a
performance parameter error signal for controlling said hoist
motor, means for actuating said command signal generator in
response to a misalignment of said car with said landing at which
it is stopped to generate a signal tending to correct said
misalignment; and means responsive to an error signal exceeding a
predetermined level during the operation of said misalignment
responsive control of said hoist motor for disabling the response
of said motor to said error signal. &. A combination in
accordance with claim 1 wherein said performance parameter is hoist
motor speed; and including means amplifying said error signal;
and means applying said amplified signal to control said hoist
motor. 8. A combination in accordance with claim 2 wherein said
performance parameter
is hoist motor speed. 9. A hoist motor control for an elevator
including a car serving a plurality of landings, said control
comprising a hoist motor; means to stop said car at said landings;
means to sense misalignment of said car with a landing at which it
is stopped; means for generating a signal proportional to an
operating parameter of said elevator; means for generating an
operating parameter command signal; means for comparing said
operating parameter signal with said command signal for producing
an error signal; means to amplify said error signal; means to apply
said amplified signal to said hoist motor to control said motor,
first check means responsive to an error signal exceeding a first
level; second check means responsive when said elevator is stopped
at a landing to an amplified signal in excess of a second level;
means to actuate said command signal means to issue a signal
tending to align said car with a landing at which it is stopped in
response to said sensing means, third check means effective while
said actuating means is responsive, said third check means being
responsive to an amplified signal in excess of a third level; and
means responsive to the response to an excessive level of any of
said check means for disabling the response of
said motor to said amplified signal. 10. A combination in
accordance with claim 1 including an alternate motor control
effective upon the disabling of the response of said motor to said
error signal to continue operation
of said motor in response to said alternate motor control. 11. A
combination in accordance with claim 1 including an alternate motor
control responsive to said command signal upon the disabling of the
response of said motor to said error signal to continue operation
of said
motor in response to said alternate motor control. 12. A
combination in accordance with claim 2 including an alternate motor
control effective upon the disabling of the response of said motor
to said amplified signal to continue operation of said motor in
response to said alternate motor
control. 13. A combination in accordance with claim 2 including an
alternate motor control responsive to said command signal upon
the
disabling of the response of said motor to said amplified signal.
14. A combination according to claim 1 wherein said hoist motor is
a direct current motor, said combination including a direct current
generator supplying a variable voltage to the armature of said
hoist motor; said generator having a shunt field divided into at
least two portions; a first portion of said shunt field of said
generator being connected to receive said command signal; a second
portion of the shunt field of said generator being connected to
receive said error signal and said disabling means interrupting the
application of said error signal to said second portion
of said shunt field. 15. A combination according to claim 2 wherein
said hoist motor is a direct current motor, said combination
including a direct current generator supplying a variable voltage
to the armature of said hoist motor; a shunt field for said
generator divided into at least two portions; a first portion of
said shunt field of said generator being connected to receive said
command signal; a second portion of said shunt field of said
generator being connected to receive said amplified signal; said
disabling means interrupting the application of said amplified
signal
to said second portion of said shunt field. 16. A combination
according to claim 2 including means responsive while said elevator
is stopped to
enable said disabling means. 17. A combination according to claim 2
including an elevator car driven by said hoist motor, closure means
for said car, means sensing the opening of said closure means, and
means responsive while said closure means is open to enable said
disabling
means. 18. A combination according to claim 1 including means
amplifying said error signal; means applying said amplified signal
to control said hoist motor; and means responsive to an amplified
signal in excess of a predetermined level for disabling the
response of said motor to said error
signal. 19. A combination according to claim 1 including a
generator supplying power to said motor; a shunt field for said
generator; said means for controlling said hoist motor supplying
power to said generator shunt field; and said disabling means
disconnecting said controlling means
from said generator shunt field. 20. A hoist motor control for an
elevator comprising a hoist motor; means for generating a signal
proportional to an actual performance parameter of said elevator;
means for generating a performance parameter command signal; means
for comparing said performance parameter signal and said command
signal to develop an error signal; means for controlling the
operation of said hoist motor in accordance with said error signal;
and means responsive to a rate of change of one of said signals at
a rate in excess of a predetermined level for disabling the
response of said motor to said error signal. 21. A combination
according to claim 20 wherein said one signal is that proportional
to said actual
performance parameter. 22. A combination according to claim 21
wherein said performance parameter is velocity and said rate of
change of said
performance parameter is acceleration. 54 23. A combination
according to claim 22 including manually operable emergency stop
means for said hoist motor, whereby excessive rates of change of
motor velocity are imposed and means responsive to the reset of
said emergency stop means for resetting said disabling means
whereby said motor is rendered responsive to said error signal.
Description
Related motor controls particularly applicable to elevator hoist
motors are disclosed in U.S. Pat. application, Ser. No. 380,385
filed July 6, 1964 in the names of Donivan L. Hall, Richard C.
Loshbough and Gerald D. Robasziewicz entitled "Elevator Control,"
and U.S. Pat. application, Ser. No. 757,929 filed Sept. 6, 1968 in
the name of Richard C. Loshbough entitled "Motor Control Having a
Feedback Stabilized Generator."
SUMMARY OF THE INVENTION
This invention relates to motor controls and more particularly to
controls for the hoist motor of an elevator.
Elevator hoist motors, particularly those employed for relatively
high-speed operation of the elevator car, e.g., 800 feet per minute
and above, are subject to rather critical control requirements due
to the large inertial masses which are to be driven under a wide
range of loadings, the precision with which the elevator car must
be positioned when brought to a landing, and the smooth and
comfortable accelerations and rates of change of acceleration which
must be satisfied. It is common practice to counterbalance the
elevator car and a portion of its load capacity, usually 40 percent
of rated load. Thus, five conditions of loading are encountered on
an elevator counterbalanced at 40 percent of rated load. When the
car is loaded at 40 percent of capacity, only the inertia of the
load must be overcome. For any other loading a variable,
uncontrolled, unbalanced load is superimposed upon this inertia.
When it is loaded less than 40 percent of rated load, the car when
descending must be driven downward or retarded when ascending. When
the load is greater, the car when ascending must be driven and when
descending must be retarded.
Since floor to floor time is a major criteria of high caliber
elevator service maximum comfortable smooth acceleration is sought
under all of these conditions. Slowdown and stopping of the car
should follow similar maximum decelerations for all loadings.
Precise control of the elevator speed throughout its travel is
therefore highly desirable in order that accurate initiation of
slowdown and stopping of the car level with the landing is obtained
at all loadings.
Heretofore the preferred elevator motor control has been a DC motor
having a variable voltage source for its armature and a shunt field
winding that can be energized at a constant level or with some
limited range of variation to provide speed control. This type of
control has been subjected to much refinement and to the
superposition of auxiliary equipment in an effort to achieve the
characteristics noted above. These have included numerous
compensation means for variations in load, speed signal developing
means which are fed back to the motor control, variable braking
means dependent upon load or speed, supplemental motors to absorb
some of the load torque particularly as the car is brought to a
landing, and regulating generators responding to the factors noted
including speed, loading and direction of travel.
Frequently, such variable voltage controls have been adjusted to
incipient instability in an effort to achieve the maximum
characteristics wherein adjustment has been critical, requiring the
efforts of highly skilled personnel to adjust and frequently
readjust the system. Further apparently identical lifting motors
and lifting motor controls often required different adjustments and
provide different operating characteristics under identical
conditions. These systems have been sensitive to temperature
variations, brush and commutator condition, brush position and to
aging.
As set forth in the aforenoted related applications, these
variations in operating parameters and their effects on the ride
afforded by a hoist motor can be swamped out by closing a feedback
loop on the control and introducing gain into the loop sufficient
to force the error in control to acceptable levels. In elevator
applications this usually involves a closed negative feedback loop
having a loop gain in the order of 10 and the inclusion of suitable
compensation to attenuate the closed loop gain as a function of
increasing frequency sufficiently to reduce the closed loop gain to
a value less than unity at and above the natural resonant frequency
of the resonant circuit comprising the total inductance and
resistance in the hoist motor armature circuit and capacitive
effect of the total driven mass, including the elevator car, the
driving means for the car and the counterweight, coupled into said
armature circuit through the hoist motor. Elevators are suitably
compensated by a lag-lead network having a lead break frequency in
the range of 2.5 to 5 radians per second.
With a loop gain of 10, controls of the nature under consideration
can respond to excursions of the signals which may be experienced
in a manner resulting in unsafe operation of the elevator car. For
example, where a controlled source feeds the shunt field of a
generator supplying the motor armature, gains of 15 or more can be
present in the source and the generator may have a gain of 4. Where
a direct controlled drive for the motor is employed it may have a
gain of 60. Excessive error signals to such controlled source or
excessive outputs therefrom can be dangerous to both passengers and
equipment.
It is an object of the present invention to obviate the above
difficulties in a motor control system having the operating
characteristics sought for high-speed elevators.
Another object is to apply a high level of gain to a signal
representative of a performance parameter of an elevator hoist
motor while avoiding instability of the system.
A further object is to avoid unsafe operating conditions in an
elevator and its hoist motor, particularly with regard to high gain
elements which upon certain malfunctions might operate the hoist
motor at excessive speeds.
A fourth object is to monitor the feedback signal of a motor
control system for transients indicative of a malfunction.
A fifth object is to monitor the error signal from the summing
point of a closed negative feedback loop for excessive error signal
levels.
A sixth object is to detect excessive signals in the feedback loop
of a motor control occurring at times when only limited signal
levels should be present.
In accordance with the above objects one feature of this invention
resides in the provision of safety interlocks which are utilized to
limit the energization of the motor in a high gain negative
feedback closed loop elevator hoist motor control in the event of
an excessive error signal, an excessive releveling signal or an
appreciable speed signal prior to the start of the motor. More
particularly, the interlocks may either reduce the response of
which the motor is capable to acceptable levels or they may shut
down the motor to avoid further operation under the potentially
unsafe conditions.
Another feature involves an auxiliary control available to operate
the motor to advance the elevator to the next landing at a reduced
speed when an unsafe operating condition or an excessive signal is
sensed. In one embodiment utilizing a Ward Leonard type system, the
amplifier and its associated error signal circuitry is supplanted
by a direct pattern control of the current in the generator shunt
field.
DESCRIPTION OF THE DRAWINGS
The above and additional objects and features of this invention
will be appreciated more fully from the following detailed
description when read with reference to the accompanying drawings
in which:
FIG. 1 is a functional block diagram of the system illustrating
many of the salient features of the invention;
FIG. 2 is a schematic diagram of the system of FIG. 1 showing a
velocity signal control of an elevator hoist motor;
FIG. 2a is a spindle diagram arranged to be aligned with FIG. 2 to
locate the relay contacts shown in FIG. 2;
FIGS. 3 through 11 are waveforms of the signals appearing at
various points in the firing circuit and output of the phase
controlled, controlled rectifier source supplying the shunt field
of the generator supplying the hoist motor in FIG. 2, the signals
representing those present when a zero input signal is applied to
the circuit;
FIGS. 3a through 11a are waveforms of the signals appearing at the
same points as for FIGS. 3 through 11 respectively when a positive
signal is applied to the input of the circuit;
FIG. 12 is a schematic diagram of a monitoring circuit suitable for
providing the velocity error signal check, the zero signal check
and the leveling signal check for the system of FIG. 2 as
functionally represented in FIG. 1;
FIGS. 13 and 14 are across the line diagrams of certain of the
elevator system controls which enter into the control of the hoist
motor operation, particularly with respect to stopping the
elevator, leveling it at landings and enabling it to apply its
unbalanced load to the hoist motor, together with certain safety
and bandwidth control functions;
FIG. 15 is a composite diagram partially in block form and
partially in schematic form showing another embodiment of this
invention wherein the entire generator shunt field is controlled
through a closed negative feedback loop having high gain and
showing particularly certain details of the safety monitors;
and
FIG. 16 is an across the line diagram of fragments of the controls
for the system of FIG. 15 showing the relay logic of the safeties
for the system.
Before proceeding with a detailed description of one embodiment of
the invention, certain aspects of the drawings will be discussed. A
number of relay contacts are shown in FIGS. 2 and 13 through 16.
These contacts are all depicted in the condition they assume with
their actuating coils deenergized and their armatures released. Two
forms of diagram have been employed. In the schematics of FIGS. 2
and 15 the contacts of relays, the actuating coils and energizing
circuits for which are shown in FIGS. 13, 14 and 16, are disclosed.
The spindle diagram of FIG. 2a is provided to facilitate the
location of these contacts. When FIGS. 2a and 2 are placed side by
side in alignment the contacts on FIG. 2 are horizontally aligned
with their vertical position along the spindles of FIG. 2a.
The across the line diagrams of FIGS. 13, 14 and 16 are arranged
with the contacts physically separated from their operating coils.
In order to provide a correlating means these diagrams are provided
with a marginal index on the right side. Line or zone numbers are
assigned to horizontal bands extending across the diagrams and are
set forth in the index in the first column to the right of the
diagrams. Each zone containing an operating coil has that coil
listed in the index next to the zone number and all contact
depicted in the diagrams are listed by their zone number next to
the reference character for the coil. Those contacts which are
normally closed and are opened when the coil is energized or the
armature pulled in, back contacts, have their zone numbers
underlined to distinguish them from front contacts which are also
listed by their zone numbers. Certain of the contacts on FIGS. 14
and 16 are mechanically operated as by the position of a cam shaft
employed in generating the pattern command for the hoist motor or
by the position of the doors. The cam shaft contacts are provided
with the prefix V, the door contacts are numbers.
In order to further facilitate an understanding of the circuits a
list of the relay symbols set forth in alphabetical order with
their functional designations and, where shown, the zone location
of their actuating coils follows: ##SPC1## ##SPC2##
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A block diagram of the system of this invention is shown in FIG. 1.
In the illustrative embodiment a speed pattern or speed command
generator which comprised a group of resistors selectively
connected and disconnected in a combination of series and parallel
circuits is supplied from a direct current power source. The
resistor interconnections can be controlled by a group of inductor
switches mounted on the elevator car so as to be actuated as the
car moves along the hatchway and they are carried into proximity
with ferromagnetic vanes secured in the hatchway at critical
positions spaced from the landings. Other resistor connections are
made by means of cam actuated switches which are driven through
suitable motion reduction devices in accordance with the car
position with respect to its starting or stopping position. Such a
system is set forth in detail in U.S. Pat. application, Ser. No.
343,301 filed Feb. 7, 1964 for Elevator Control in the names of
Robert O. Bradley and Paul F. DeLamater.
During the running of the elevator from a landing and until it
enters the final portion of its stopping region, the speed pattern
is fed to a first section of the shunt field of the generator
supplying the variable voltage to the armature of the hoist motor.
In addition to supplying a portion of the generator field flux the
first section tends to smooth the steplike pattern developed from
the closure of switches in the pattern generator.
The smoothed pattern signal is combined with a hoist motor speed
error signal as that representing the difference between the
pattern speed commanded and the current elevator or hoist motor
speed. This error signal is then fed through a compensating network
which adjusts both the phase and magnitude of the signal to permit
an increase in both the gain and the bandwidth of the system within
which it will operate without instability.
A high gain buffer amplifier, one having a gain of from 50 to 100,
applies the amplified and compensated speed error signal to a
second portion of the generator shunt field to determine the
voltage level applied by the generator to the armature of the hoist
motor. It should be noted that with this arrangement, a car can be
driven by the first portion of the generator shunt field once it
has attained full speed and the speed signal will supply a
correcting flux to overcome only such losses as those due to
unbalanced load, generator saturation, and windage. Further,
excessive speed error signals indicative of a malfunction can be
readily sensed and made to actuate controls which control the speed
of the hoist motor and car only through the first portion of the
generator shunt field and the speed pattern generator, effectively
eliminating the amplified error signal from control until
corrective action or inspection and reset of the system has been
completed.
Returning to the first portion of the generator shunt field, during
the final approach of the elevator to the landing at which it is to
stop, this portion of the field is rendered ineffective and the
pattern and speed signals are compared to effect control of the car
entirely through the second portion of the field. Under these
conditions the system exhibits broad bandwidth characteristics
which are advantageous for picking up the load, stopping
accurately, and releveling, if required.
In the illustrative example the amplified and compensated velocity
error signal controls the phase of a firing circuit for a pair of
controlled rectifiers connected with like polarity electrodes each
connected to one of the two terminals of a single phase alternating
current source. These rectifiers are triggered, for zero signal
input to their firing circuit, by an alternating current shifted
1350.degree. from the line phase so that they are each conductive a
like period and the net DC derived therefrom is zero. Changes in
this supply to the load are achieved by raising or lowering the
base of the firing signal to increase the conduction interval in
one rectifier over that in the other for a first polarity of
pulsating unidirectional current and to reverse that relationship
for the opposite polarity when the base of the signal is shifted to
the other side of the zero signal level.
The rectifiers are illustrated as supplying a portion of the shunt
field of a direct current generator having an armature connected to
the armature of the hoist motor. The high gain amplifier and
compensator can effectively be applied to control the hoist motor
by other techniques in accordance with this invention. For example
controlled rectifiers can be employed to supply the hoist motor
armature directly, advantageously in a polyphase arrangement.
Accordingly, this invention contemplates an amplifier which can be
considered a composite of a buffer amplifier, a controlled
rectifier or magnetic amplifier power stage and control circuits
for the power stage applied directly to the hoist motor or the
amplifier can be considered to include the controlled rectifier and
the direct current generator in the present example.
Since the primary concepts of elevator hoist motor control involved
in the present system include the utilization of a high gain
amplifier with suitable compensation to avoid instability and
responsive to a principal operating parameter to swamp out the
effect of the numerous variables inherent in hoist motor controls,
it is to be appreciated that these concepts can be applied to other
than a velocity based system. While the exemplary embodiment
utilizes a hoist motor speed signal as derived from the counter
e.m.f. of the motor corrected for armature current and brush drop
effects or from a tachometer, it is to be appreciated that other
operating parameters of the system might be employed as the basis
of control. Monitoring the motor armature current to measure the
required torque can be related to acceleration in a manner to
provide effective control. Where signal proportional to an
operating parameter other than speed is employed, a suitable
modification of the command signal to produce the desired operating
parameter is made so that the command signal and the operating
parameter signal can be compared to produce a suitable error
signal. However, the compensation and amplification of this error
signal will involve the same considerations presented here.
In any such system where amplification of the signal to the hoist
motor can result in excessive speeds, acceleration, or rate of
change of acceleration, the check and interlock functions of the
present example are advantageously incorporated. Thus the velocity
error check is made at the summing point of the command signal and
hoist motor speed signal. This check occurs prior to amplification
of the signal but effectively checks the amplifier since any
tendency of the amplifier to run away will result in an excessive
error signal at the summing point. The check of the zero signal
when the elevator is stopped and the leveling signal check when it
is leveling is made on the amplified signal. Thus in the example
this check is made at the input to the generator shunt field. If
any of these checks indicate an excessive signal the alternating
supply is disconnected from the controlled rectifiers thereby
disabling the supply to the shunt field or, in the case of a zero
check, starting is prevented.
The schematic diagram of FIG. 2 shows the principal elements of the
system as represented in the block diagram of FIG. 1. A three-phase
supply 11 feeds a suitable rectifying circuit including filters to
provide a smooth output from the block 12. This output is fed to a
speed pattern generator of the type discussed above or an
equivalent thereof, represented by a rheostat 13 having
sequentially operated contacts 14, and through brake relay and main
switch contact BK-3 and M to a reversing circuit.
The reversing circuit applies the pattern signal to a portion of
the generator shunt field PF hereinafter termed the pattern field.
This circuit is controlled by conventional generator field relays
of the elevator circuit as by up generator field relay UF or by
down generator field relay DF to reverse the polarity. The
inductance of the pattern field tends to smooth the current through
resistance 16 and parallel potentiometer 17 in which the difference
between the smoothed pattern voltage and a speed voltage derived
from the hoist motor 18 is developed as a speed error signal. This
summing point thus constitutes means for comparing the speed or
other performance parameter signal with the pattern or command
signal to produce an error signal. Since the speed pattern lags the
command from rheostat 13, when the elevator car approaches the
landing at which it is to stop, this lag becomes detrimental and
precise positional control is sought. Accordingly, it is
advantageous to eliminate the pattern field at this time. This is
done by opening the back contact R14 in series with the pattern
field and by closing contact R14 around the field whereby the
pattern is fed directly to the resistances 16 and 17. At this time
the circulating current in the field is dissipated through
resistance 19 which can be of the order of 500 ohms whereby the
pattern field will decay in about 0.2 seconds. In the event the
rapid decay produces an undesired response in the generator 21
supplying hoist motor 18, the pattern can be adjusted to overcome
this effect at the time it occurs.
Hoist motor 18 is provided with a shunt field 24 energized from a
suitable source of direct current, as shown at 231 of FIG. 14,
which may include some control of the current therein as a speed
control supplementing the primary control afforded by the voltage
impressed across the motor armature. Generator 21 provides a
controlled motor armature voltage. Its armature is driven at a
constant speed by a suitable prime mover (not shown) and its output
voltage is controlled by control of the current in its shunt field
made up of pattern field PF and error field EF. Error field EF is
supplied with current from rectifiers controlled by the amplifier
25 and in turn the error signal from potentiometer tap 22.
The speed signal is fed to potentiometer 17 on lead 26. It is
derived from a bridge arrangement as disclosed in Robert O. Bradley
U.S. Pat. application, Ser. No. 368,623 which was filed May 19,
1964 and is entitled Motor Speed Control, now U.S. Pat. No.
3,358,204 which issued Dec. 12, 1967. This arrangement provides a
voltage proportional to the e.m.f. generated in the motor, and thus
the motor speed, while eliminating the effects of brush drop and
armature current on that voltage. It involves providing pilot
brushes 27 and 28 on motor armature 18. A potentiometer 29 is
connected across the generator interpole winding GIP, one main
brush 30 of the motor and the motor armature 18 to pilor brush 28.
A second potentiometer 31 is connected from pilot brush 27 across
main brush 30. With the taps 32 and 33 of potentiometers 29 and 31
set so that the resistance of their upper portions is related to
the resistance of their lower portions in the same proportion as
the external resistance provided by the generator interpole
windings GIP is related to the motor armature resistance, the
voltage developed between taps 32 and 33 is proportional to the
speed voltage of the motor. In the example tap 33 is grounded and
tap 32 is connected through lead 34 to the voltage divider provided
by series resistance 35 and resistance 36 connected to ground so
that a signal also proportional to the speed voltage of the motor
is fed on lead 26 to potentiometer 17.
The error signal taken as a voltage at tap 22 of potentiometer 17
is applied through loop gain adjustment potentiometer 37 to the
compensating filter 38. This filter adjusts the magnitude of the
signal applied to the input of amplifier 25 as it results from an
error signal in accordance with the rate of change of that error
signal whereby the effective signal is attenuated when its
effective frequency is in the range where the system is unstable.
This filter passes constant signals effectively without attenuation
through the serially connected resistances 39 and 41 since its
insertion loss is made up in the amplification around the loop. It
also passes very high frequencies without significant attenuation
through the bridging capacitance 42. At intermediate frequencies,
attenuation is caused by the passing of a portion of the signal to
ground as through resistance 43 and capacitance 44 and in the
following section through resistance 45 and capacitance 46. The
effect of this compensating network will be discussed in more
detail below. However, it can be characterized as attentuating the
closed loop gain as a function of increasing frequency sufficient
to reduce that closed loop gain to a value less than unity at and
above the natural resonant frequency of the resonant circuit
comprising the total inductance and resistance in the hoist motor
armature circuit and the capacitive effect of the total driven mass
coupled into the armature circuit through the hoist motor.
From compensating network 38 the error signal is passed over lead
47 to notch filter 48 which is tuned to reject 60 cycle per second
signals which might be picked up through spurious coupling to the
line supplying the system. This filter is made up of a parallel-T
network including resistances 49 and 51 with capacitance 52 to
ground and capacitances 53 and 54 with resistance 55 to ground.
Capacitance 56 connects the output of the network to ground.
The output of the filter 48 is connected by lead 57 to the input of
direct current amplifier 25 at the base of transistor Q1. This
amplifier is stabilized by negative feedback to provide the desired
amplifier gain. It comprises a plurality of transistor amplifier
sections biased from a bus 58 held at positive 12 volts and a bus
59 held at negative 12 volts. Terminal 60 is also connected to a
positive 12 volt supply to produce a voltage divider for zero
adjustment potentiometer 61. This potentiometer is accurately
regulated by forward biased diodes 62 to ground so that it can be
adjusted for zero voltage at the emitter of transistor Q9 with zero
input on lead 57.
Operation of the amplifier 25 to control the firing point of the
controlled rectifiers supplying field EF will best be appreciated
from a consideration of its operation. Application of a positive
input on lead 57 will raise the emitter voltage of Q1 through the
increase in the current flowing in resistance 63. The resultant
increase in base voltage of transistor Q2 causes an increase in
current in resistance 64 to raise the emitter of Q2 and Q3.
The base of Q3 is held at a constant voltage so that the increase
of Q3 emitter voltage reduces the collector current and causes a
rise in the potential at junction 65. Transistor Q4 is a constant
current source in the collector circuit of transistor Q3 and causes
this stage to have extremely high gain.
In order to ensure stability transistors Q1 and Q5 are mounted to
maintain uniform temperatures. Q5 offsets any base-to-emitter
voltage of Q1 by establishing the base voltage of Q3.
When the voltage at junction 65 and the base of transistor Q1
rises, the emitter of Q6 increases its voltage be decreased current
flow in resistance 66. This increases the base voltage on
transistor Q7 causing the emitter of Q7 to increase its voltage
with the reduced drop in resistance 67. The emitter voltage of
transistor Q8 is increased thereby causing an increase of Q8
collector current since the base of Q8 is held at a constant level
by Zener diode 68. The increased collector current through
collector resistor 69 raises the voltage on lead 71 to the base of
transistor Q9 forcing the emitter of Q9 to raise the voltage at
junction 72.
Amplifier stability is ensured by feeding a portion of the Q9
emitter voltage back to the base of Q5 through resistor 73.
Resistor 73 is shunted by a condenser 74 which imparts stability to
the feedback loop by introducing some lead into that loop. The
magnitude of resistor 73 determines the amount of negative feedback
in accordance with well-known principles and if desired can be
adjustable. The amount of signal fed back is also determined by
ground resistor 75. This arrangement is such that the increase in
Q9 emitter voltage in response to an increase in input or Q1 base
voltage (e.g., by a factor of 500) causes the Q.sub.5 base voltage
to be increased by the same amount as the input. Such an increase
at Q5 base voltage results in a current change in resistor 77
increasing Q.sub.5 emitter by the same voltage and thus Q.sub.3
base by that voltage. It will be recalled that Q.sub.3 emitter
voltage increased by the amount of input voltage change. Therefore
the base-to-emitter voltage of Q3 is the same at this new signal
level as when zero input was present. The system is thus stabilized
since a tendency of Q.sub.9 emitter voltage to drop causes a
corresponding rise in Q.sub.3 collector voltage which forces the
Q.sub.9 emitter voltage to rise.
Condenser 78 passes high frequency components of the signal at Q4
collector to ground to stabilize the amplifier and condenser 79
from the base of Q.sub.9 is also included for stabilization.
The firing circuit of the controlled rectifiers is based upon a
displacement of the firing wave from the applied line wave so that
a pair of back-to-back rectifiers are fired symmetrically to
produce no net current at zero signal and are fired assymmetrically
to apply either a positive or negative net current on the generator
shunt field EF depending upon the direction of the shift in firing
angle.
Transformers T.sub.1 and T.sub.2 are each driven from the same line
voltage so that their inputs are in phase. The output of
transformer T.sub.1 is phase shifted 135.degree. by the three,
cascaded, phase shifting networks each comprising a condenser 81
and a resistor 82. Exact adjustment of this shift is obtained by
means of potentiometer 83. This voltage is summed with the output
of the amplifier 25 in the summing network of resistors 84 and 85.
Resistor 86 connected from a highly regulated positive source of
direct current (not shown) to lead 87 and the base of transistor
Q10 offsets any threshold voltage of Q.sub.10.
In considering the firing circuit two sets of waveforms will be
considered. The first set represents the signals at various points
in the circuit when zero input is applied at lead 57. The second
represents the signals at corresponding points when a positive
input or error signal exists. The second set will be distinguished
by a lower case a.
The waveform across the resistor 85, which is applied on lead 87 in
a form modified by the clamping action of diode 88 and the
base-emitter diode of transistor Q10 to the base of Q10 with no
output from amplifier 25, is shown in a sine wave A shifted
135.degree. from line sine wave B and having its origin shifted as
shown in FIG. 3. The waveform at the collector of Q10 is shown in
FIG. 4. Excessive reverse bias on Q10 from the AC signal on 87 is
avoided by the diode 88 which passes negative signals above its
threshold to ground. When applied voltage reaches the threshold
voltage of Q10, the transistor begins conducting current and the
drop in resistor 89 causes the collector voltage to drop at
junction 91. The collector waveform corresponds to the input until
the transistor becomes saturated and the curve flats.
Transistor Q11 is an emitter-follower whose emitter voltage would
correspond to the signal at junction 91 but for the clamping action
of the base-emitter diode of transistor Q12. The dashed line in
FIG. 4 is the emitter waveform of Q11.
The collector wave of Q12 is shown in FIG. 6, and the waveform of
Q13 is shown in FIG. 5. Transistors Q12 and Q13 and their
associated circuitry constitute a Schmitt trigger wherein the
triggering signal is developed at junction 91. When zero signal is
present at 91, transistor Q13 is conductive and transistor Q12 is
held off.
As the base of Q12 goes positive with the emitter of Q11, collector
Q12 draws current through resistors 92 and 93 reducing the voltage
on base Q13 below its sustaining level and terminating conduction
in Q13 whereby its collector voltage rises at junction 94. The
increased voltage on the control electrode of silicon-controlled
rectifier SCRA causes that rectifier to conduct when its applied
anode-cathode voltage from transformer T2 is in the forward
direction. At this time the voltage at junction 95 is the forward
drop of diode 96 above ground and, in view of the forward drop of
diodes 97, the voltage on the control electrode of SCRB is brought
to ground through resistor 98 to enable its conduction to be
terminated.
When the base of Q12 returns to ground, it is cut off and the
voltage at the collector of Q12 rises. This voltage is applied
through the voltage divider of resistors 99 and 101, and diode 102
to the base of Q13 so that it initiates conduction. The voltage at
junction 94 falls below the threshold of diodes 103 so that the
control electrode of SCRA is grounded through resistor 104. At this
time the potential at junction 95 has risen so that when it exceeds
the threshold of diodes 97 the control electrode of SCRB is driven
positive beyond its threshold of conduction to enable SCRB to
fire.
The collector signals of Q13 and Q12 as shown in FIGS. 5 and 6 are
at levels V2 and V1 determined by the conduction drop of the gates
of SCRA and SCRB and the threshold voltages of the diodes 103 and
97 in the collector circuits. The voltage in series with the SCR's
and load is in phase with the line supplying the primary of T2. If
the load were resistive, the voltage across SCRB is shown in FIG. 7
while that across SCRA would be similar for the other half cycle.
The resulting waveform across a resistive load would appear as in
FIG. 8.
The circuit for SCRA would extend from grounded junction 105
through rectifier 106, junction 107, brake relay contact BK-5,
resistor 108, contact BK-4, junction 109, closed "power" switch
111, contact SCR-2, the secondary of transformer T2, fuses 112,
switch 111, contact SCR-1, SCRA and junction 105. The corresponding
circuit for SCRB is traced through rectifier 113. It should be
noted that pilot lamp 114 is connected across the secondary of
transformer T2 to indicate power is applied to the firing circuit
at terminals 115 and 116 connected to T1 and to the SCR circuit.
When the generator field power is on, pilot lamp 117 is
illuminated.
The true load on the SCR's is the highly inductive generator field
EF and the resistor 108 is significant only when the generator
suicide connections are made to permit the decay of the field. This
inductive load imposes limits upon pulsating current so that
virtually no DC flux could be developed in the field winding alone.
However, circulating currents are permitted without any direct
current loss by shunting field winding EF with a large capacitance
118, e.g., 1,500 mf. This arrangement is further enhanced in its
operating characteristics, particularly with respect to the surge
currents through SCRA and SCRB, by including a relatively low
inductance 119 in series with the capacitance as a limiting means,
e.g., 0.01 henry and 0.16 ohm. This LC series circuit has
substantial advantage over a shunting resistor of low value in that
no DC power loss is incurred and the efficiency of the circuit is
enhanced. Resistor 120 is of a relatively high value, e.g., 1,000
ohms, and therefore passes negligible current to the applied
signal. Its function is to provide a discharge path for the LC
circuit when the power is disconnected.
As a result of the high inductive load presented by field EF to the
SCR's the current reaches its peak when the input voltage is zero.
The SCR's do not turn off until the current goes to zero even if
the impressed voltage has reversed sign. Therefore, the voltage
across the inductive load of field EF is shown in FIG. 9. The
voltage across SCRB for this load is shown in FIG. 10. A
corresponding voltage is developed across SCRA for the other half
cycle under this load.
The filter composed of capacitance 118 and inductance 119 employed
to overcome the high impedance presented to pulsating voltages by
field EF and to smooth the SCR outputs has a current form as shown
in FIG. 11.
Since the areas under the curves of FIG. 11 representing flow in
each direction for SCRA and SCRB and in the filters are equal the
net of DC value is zero and the generator shunt error field EF
receives zero input where the signal from amplifier 25 is zero.
A positive or negative signal from amplifier 25, indicating a
velocity error signal, as it appears at junction 72 will alter the
firing circuit and produce a net DC input to the shunt error field
by shifting the phase of the firing signal. A positive signal
indicative of a hoist motor speed less than the speed commanded
when the commanded speed is plus, increases the conduction interval
of SCRB while decreasing the conduction interval of SCRA. This
change tends to change the generator voltage in a manner to
increase the motor speed and decrease the error. Conversely, a
negative signal at junction 72 for the same command signal will
decrease the conduction interval of SCRB while increasing that of
SCRA. This will tend to retard the motor speed by reducing the
current in the field EF to reduce or reverse the impressed voltage
on the armature thereby decreasing the motor speed to tend to
decrease the error.
If a positive voltage is present at junction 72 the waveforms are
as shown in FIGS. 3a through 11a. The firing circuit voltage
waveform Aa is shifted positively as shown in FIG. 3a with the
result that it achieves the threshold of Q10 earlier and sustains
that threshold later to lengthen the interval of conduction for
SCRB as shown in FIG. 6a and shorten the interval for SCRA as shown
in FIG. 5a. The resulting change in the voltage applied to the
field EF is shown in FIG. 9a. It will be noted that the flow in
SCRB is substantially greater than in SCRA and a net current
results causing a generator armature voltage which drives the motor
18. When the motor approaches the desired speed, so that the speed
voltage on lead 26 balances the pattern voltage on potentiometer
17, the error signal approaches zero, the voltage at output
junction 72 of the amplifier 25 is zero and the net DC into the
fields is zero. Any change in motor speed results in a speed error
signal which forces the motor back to its proper speed.
In view of the consequences of a malfunction in this system for an
elevator hoist motor, particularly in the event the amplifier
issues a large signal within the limits of the capacity of the
element supplying power so that the power applied to the motor
tends to cause excessive speed change, the present system has been
provided with means for monitoring the signals and barring
operation of the amplifier system when those signals exceed levels
which are reasonable for the prevailing conditions. The monitoring
is accomplished by completing enabling circuits for the amplifier
system so that any failure of a monitoring element causes a "fail
safe" operation and the amplifier system will not operate.
The armature of the generator is connected to the shunt field in
the usual "suicide circuit" when the elevator car is stopped and
the brake set as shown in FIG. 2. In this circuit a brake relay
which is deenergized upon the setting of the brake closes its back
contacts BK-1 and BK-2 to connect the generator armature to field
EF, opens its contact BK-3 to field PF and opens both leads from
SCRA and SCRB to EF at contacts BK-4 and BK-5. The suicide circuit
causes armature current to flow in a manner to produce a flux
opposing any buildup in the generator. The circuits of FIGS. 13 and
14 are shown across leads 158 and 159 which are supplied from a
suitable source of direct current (not shown) connected across
these leads.
While the elevator car is stopped, the elevator hoist motor shunt
field 24, FIGS. 2 and 14 at line 231, has resistances 121 and 122
in series and is passing minimum current, the pattern signal source
13 is disconnected at main switch contact M and brake relay contact
BK-3, the pattern field PF is isolated by open contacts of the up
and down generator field relay UF-1, UF-2, DF-1 and DF-2, and the
compensating network is discharged to ground through lead 26,
potentiometer 17 and back contact BK-6 of the brake relay. A start
signal is ineffective at this time unless the direct current output
voltage is to be applied to the generator field EF is at the
prescribed level. A zero check circuit as shown in FIG. 12 monitors
this voltage and enables a start signal only if it is below a
limiting level. The circuit of FIG. 12 is duplicated for monitoring
the output from the amplifier when the elevator is releveling and
for continuously monitoring the velocity error signal during a run.
In the case of the zero check and leveling check the monitoring
circuits corresponding to FIG. 12 are connected to FIG. 2 just
ahead of the brake relay contacts between the source and generator
field EF at terminals 107 and 109. The velocity error signal check
is taken from a high input impedance amplifier 138 at terminals 130
and 130a. This amplifier derives its input as the difference
between the speed signal feedback voltage and the input speed
pattern voltage obtained from the high side of the gain
potentiometer 37 of FIG. 2.
The voltage detector circuit employed for each of these monitoring
functions, as shown in FIG. 12, comprises input leads 124 and 125
for connection respectively to the terminals 109 and 107 for zero
and leveling monitors and terminals 130 and 130a for the velocity
error monitor. A rectifier bridge 126 is provided to ensure that
input signals of either polarity will result in a positive signal
at resistor 127 and the upper end of potentiometer 128. Capacitance
129 avoids the effect of transients. The threshold signal places
the 6-volt Zener diode 131 in conduction. Accordingly, the setting
of potentiometer 128 establishes the desired threshold for each of
the utilizations of this circuit.
An alternating voltage, e.g., 20 volts, is applied to leads 132 and
133. If the Zener diode 131 is subject to less than its threshold
voltage, the base of transistor Q14 is at ground and the transistor
is shut off. Under these conditions the half-wave current through
the silicon-controlled rectifier SCRC energizes relay coil R since
during the positive half cycle of the power supply Q14 collector
voltage is high and turns on SCRC. The voltage across the relay
coil R pulls in the relay while the diode 134 provides a conductive
path for the current of the relay coil during the negative half
cycles of the power supply.
When the voltage monitored across leads 124 and 125 is sufficient
to raise the cathode voltage of the Zener diode 131 to its
threshold for conduction, the voltage developed in resistors 135
and 136 raise the base voltage of transistor Q14 and turns it on.
The collector current of Q14 causes sufficient drop at junction 137
to reduce the control electrode of SCRC below its trigger voltage.
The absence of conduction in SCRC drops the relay having coil
R.
Three relays ZCF, LCF and VCF respectively signifying safe signal
levels when energized for the "zero check," the "leveling check"
and the "velocity error signal check" have coils (none of which are
shown) located in circuits as the coil R in FIG. 12. In the case of
relay VCF the circuits of FIG. 12 is fed from a high impedance
amplifier 138 as shown at the bottom of FIG. 2.
The error voltage amplifier 138 comprises an input 139 from gain
potentiometer 37 to the base of transistor Q15 which is adjusted to
a suitable potential by zero adjustment potentiometer 141 connected
through resistors 142 and 143 to buses 144 and 145 respectively
connected to suitable sources of direct current at negative 18
volts and positive 18 volts. When the brake relay is energized to
open back contact BK-6, this circuit is effective. The emitter of
Q15 is grounded. A positive error voltage applied to Q15 base
reduces the collector voltage since the current in resistor 146 is
reduced. This reduces the voltage applied through resistor 147 to
the base of transistor Q16 thereby reducing the collector current
of Q16 through resistor 148 to raise the voltage applied through
resistor 149 to base of transistor Q17. Capacitance 151 between Q16
collector and ground prevents high frequency oscillation to
stabilize the amplifier at high frequencies. The increase of
voltage at base Q17 increases the collector current of Q17 thereby
increasing the voltage drop across resistor 152 and reducing the
voltage at terminal 130. A feedback path through lead 153 and
resistor 154 stabilizes the amplifier by tending to decrease the
effect of the increased error voltage. As in the preceding check
circuits an increase in the absolute value of the signal between
terminals 130 and 130a applied to the monitor of FIG. 12 causes
velocity error check relay VCF having a coil as at R in FIG. 12 to
drop.
As will be noted from FIG. 2, relay SCR must be energized to
connect the alternating current to controlled rectifiers SCRA and
SCRB through contacts SCR-1 and SCR-2. Relay SCR at 206 of FIG. 13
remains energized in normal operation. However, the check circuits
are each effective to deenergize that relay or otherwise disable
the amplifier feed to error field EF. Under these circumstances the
pattern field PF, controlled by the command signal from rheostat 13
provides control for the elevator to bring it to a landing. Note
that the deenergization of relay SCR also deenergizes the retard
stop approach relay R14 at 238 by opening contact SCR at 238
whereby pattern field PF remains effective even when the elevator
approaches a landing for a stop. An indicator "SCR OFF" is actuated
by the drop of relay SCR to close its back contact at 210 and if
the car was running or leveling during the drop of relay SCR, the
relay is locked out by failure relay FE at 212 energized at back
contact SCR at 212 and start relay contact ST and 212 to open back
contact FE at 206 until FE is reset.
With the car stopped, the monitoring circuit for zero signal is
effective, and if the threshold level is not exceeded relay ZCF is
energized. With the doors open, as when stopped at a landing, and a
start signal imposed, as during a normal starting sequence or
during a releveling as might be required by a load change changing
the stretch of the supporting cables, leveling signal monitoring is
effective and if the signal is excessive relay LCF is deenergized
to disconnect the amplifier. A car starting operation is initiated
by energizing car starting relay CS (not shown) to close its
contacts at 203 in the circuit of want to run relay WTR as shown in
FIG. 13 at line 202. Pull in of WTR closes its contact at 214. If
no velocity error has been sensed which is of a magnitude to drop
relay VCF during the previous run of the elevator, relay SCR is
energized through contacts FE and VCF at 206 and ST at 208 until
the start signal is effective. With SCR energized contact SCR at
214 is closed. If the zero check relay is energized, indicating the
zero signal below the threshold considered the lower limit of a
malfunction, start relay ST is energized at line 214. Back contacts
ST at 208 and 209 open while front contacts at 212, 215 and 220
close.
Contact ST at 208 enters in a leveling function and will be
discussed below.
Contact ST at 209 opens the "off zero" indicator circuit so that
the increased voltages applied to the generator field EF which
result in the dropping of relay ZCF while the car runs, will have
no effect. If during the stop ZCF had dropped at any time, the
circuit at 209 would have been completed to actuate "off zero"
indicator.
Failure relay FE at 212 locks out the system once it is energized
by its seal contact FE at 213 and retains that state through its
manually actuated reset switch at 213 until the switch is operated.
Relay FE is energized by a coincidence of a start signal, which may
be issued either as a conventional starting or by a releveling
operation, to close contact ST at 212 and the drop of normally
energized relay SCR to close back contact SCR at 212. As will be
discussed relay SCR can be dropped by an excessive velocity error
signal through the opening of contact VCF at 206 or during
leveling, when contacts LG at 207 and ST at 208 are open by an
excessive leveling signal which opens contact LCF. Thus, any
leveling signal or velocity error signal exceeding the
predetermined limits set for the two monitor circuits of relays LCF
and VCF will drop SCR to pull in relay FE thereby locking out relay
SCR by opening back contact FE at 206 and actuating the "reset"
indicator by closing contact FE at 210. The drop of SCR will close
back contact SCR at 210 to actuate the "SCR OFF" indicator, prevent
energization of start relay ST by opening contact SCR at 214 and
open the supply to SCRA and SCRB in FIG. 2.
Start relay ST can also be prevented from operation by an excessive
zero check signal to deenergize relay ZCF and open contact ZCF at
214. In the event the zero check signal is within limits and the ST
relay is pulled in, it seals itself at contact ST in line 215. This
seal is required since, as the signal magnitudes are increased
during the normal running of the car, contact ZCF at 214 will
open.
The start sequence involves other functions. As indicated above,
the hoist motor is arranged to pick up the load rapidly by
arranging the system to function with a broad bandwidth in its
response to signals during the initiation of starting. The broad
bandwidth is achieved by effectively eliminating the pattern field
as the motor developes a load sustaining torque. Relay R14 at line
238 of FIG. 14 provides this function while energized. It opens
back contact R14 and closes front contact R14 in FIG. 2 so that
pattern field PF is bypassed by the pattern signal and the field
decays by circulating current in resistor 19. R14 remains energized
during the final portion of the door closing interval and
incidental thereto the brake is lifted after the car is
sufficiently closed to prevent further load exchanges whereby the
system senses the unbalanced load prior to any significant motion
of the car. When the hatchway and car doors are completely closed,
the speed signal then initiates car motion.
The start signal issued by relay CS closes contacts to energize
door control relay DT (not shown) and at 216 to energize door close
relay CLA in conjunction with closed contacts of door open control
relay OPS (not shown) open while the door is opening, minimum start
time relay TR (not shown) open until the door open interval has
expired, door open control relay DO (not shown), open upon a
command for a door opening operation, and door control relay DT all
at line 216. CLA seals itself around start signal relay contacts CS
at 217, energizes the brake relay BK at contact CLA at 220 if the
safety switches are all closed and the start relay ST is energized
to close its contact at 220 and partially completes circuits for
the up and down generator field relays UF and DF and the landing
and gate relay LG.
Relay CS also opens the leveling controls for relays UF, DF and BK
at back contact CS at 221. The motor field is increased by the
start signal through closure of contact CS at 228 to energize motor
field normal relay MFN and close its contact around resistance 121
in series with motor shunt field 24 at line 231. Relay MFN also
closes at 221 to afford a partial path for relays UF, DF and BK
which will be retained after relay CLA is dropped by the opening of
contact DT.
The motor field thus builds up as the car and hatchway doors are
driven toward their closed position. Pull in of relay BK causes the
energization of main switch M at 218 by the closure of contact BK
at 217. Contacts BK-3 and M connect command signal to the reversing
circuit by the closure of contacts BK-4 and BK-5 and the opening of
BK-1 and BK-2 connects error field EF of the generator to the
amplifier. Main switch energizes motor full field relay MFL by
closing contact M at 230 to short resistor 122 in the motor field
circuit by closed contact MFL at 233.
With both M and BK energized to close their contacts in the brake
solenoid circuit at 235 a partial energization of the brake is
effected. This is insufficient to lift the brake in view of
resistors 161 and 162 and hence the elevator is held by the brake.
As the doors advance toward their closed condition and after they
are sufficiently closed to prevent further load transfers, door
limit switch 163a at 232 is closed. This pulls partial brake relay
PBK at 234 to close contact PBK at 235 and complete the brake
solenoid circuit to lift the brake.
Upon the energization of the car start relay the path for
energizing the generator field relays UF and DF is opened by back
contacts CS at 221. Landing and gate interlock contacts 164 and 165
which are open until the interlocks make up with the doors fully
closed are also open at this time. Coincident with the lifting of
the brake the generator field relays are enabled through the
leveling circuit so that any movement of the car due to unbalanced
load will actuate leveling switches and cause a correcting command
signal from rheostat 13 to be applied to the error signal means,
potentiometer 17 and lead 26. Contact 163b closes around open car
starting contact CS at 222 to enable leveling relay contacts LU and
LD to energize generator field relay UF or DF. This circuit can be
traced from closed MFN contact at 221, through closed 22-inch
leveling relay contact L22 (closed while the car is within 22
inches of level with the landing at which it is stopped), and door
limit contact 163b at 222. If the car sags downward, contact LD at
222 is closed to complete a circuit for up generator field relay UF
through LD AND LU at 221. If it sags upward, contact LU at 222 is
closed to energize DF through LU and LD at 222. Thus, a command
signal is generated by the leveling relays through the closure of
contacts 14 to change the command from sheostat 13 and the
generator field relays connect the command at DF-1 and DF-2 and
UF-2 to the amplifier. With the pattern connected and the field EF
of the generator connected a signal is developed to sustain the
load while the system is in its rapid response, broad bandwidth
mode of operation.
Once the doors are fully closed and the interlocks made up, landing
gate relay LG at 227 is energized through closure of interlock
contacts 164 and 165 at 224. These contacts remain closed so long
as the doors are fully closed.
While the car is in the leveling zone back contact LDO at 225 of
leveling door open relay is open. This contact closes when the car
is outside the zone in which door operation is normally permitted,
e.g., 8 inches from the landing. It closes to maintain the
generator field and brake relays after the car has stopped
accelerating. During acceleration contact ACR at 223 provides an
energizing path for these relays. The makeup of the landing and
gate interlocks causes the energization of acceleration relays ACR
and ACC to initiate the generation of a speed pattern in rheostat
string 13 tending to move the car away from the landing. If the
rheostat is not subject to a correcting operation at this time,
contact V1 at 224 is closed and the generator field relays are
energized from interlocks 164 and 165 through contact V1 at 224,
acceleration relay contact ACR at 223 either direction determining
relay U or D the overtravel limits 167 or 168, interlocked back
contacts DF or UF all at 223 or 226 and relays UF or DF. Also at
the time acceleration away from the landing is initiated back
contact ACC at 238 is opened to deenergize relay R14 and insert
pattern field PF across the command signal, thereby reducing the
bandwidth of the system. The car then proceeds to develop speed
steps as by the operation of hatchway inductor switches while
closely adjacent its starting landing followed by operation of
rheostat cams controlling contacts 14 by car motion as described in
the aforenoted Bradley-DeLamater patent application, or by the
operation of time based acceleration steps followed by operation of
said rheostat contacts 14.
The drop of relay R14 closes back contact R14 and opens front
contact R14 in FIG. 2 to reconnect the pattern field PF of the
generator to the pattern signal and to reduce the bandwidth of the
system whereby the accelerating steps of the hatchway inductor
switches and the rheostat switch contacts is smoothed as it is
combined with the speed signal from the hoist motor to produce a
smooth error signal at potentiometer 37.
Door time control relay drops a brief timed interval following the
pull in of relay LG to drop relay CLA. At this time alternate
circuits are available for those controlled by CLA earlier in the
sequence. Brake relay BK is now controlled through the circuits
controlling generator field relays UF and DF. The motor field
relays and main switch are also controlled by either BK or UF or
DF.
If at any time during the run of the elevator an excessive velocity
error signal is issued, velocity error check relay VCF will drop
out opening contact VCF at 206 of FIG. 13.
Failure relay FE responds to a drop of SCR either during a run or a
releveling operation since start relay ST is energized at such
times to close its contact S.sup.T at 212. When FE pulls in, it
seals itself at contact FE in line 213 until the manual reset
switch is opened at 213.
As the car continues to accelerate on a normal run and as it
approaches full speed, a further speed step is achieved by
weakening the shunt field of the hoist motor. This is accomplished
by opening normally closed contact V12 at 230 to drop motor full
field relay MFL and open its contact at 233. Resistor 122 is placed
in series with motor shunt field 24 in this manner to reduce its
current. Contact V12 can be controlled by the cam device which
actuates rheostat switches 14 of FIG. 2 when that device has
advanced to the final speed step. Similarly, when the command to
the car is to reduce speed, the contact closes to strengthen the
field by removing resistor 122 from the circuit.
Upon approaching a landing at which the elevator is to be stopped
the rheostat 13 is increased in effective resistance by the opening
of does switches 14 to produce a speed pattern calling for a lower
speed. Since the actual speed signal indicated on lead 26 will
exceed the lower speed a retarding error signal will be transmitted
to compensator 38 from potentiometer 37. Start relay ST of FIG. 13
remains energized until the car is stopped level with the landing
as does main switch M, brake relay BK, generator field relays UF
and DF, the motor field relays MFN and MFL, partial brake relay PBK
and the brake solenoid.
While the car is running and more than a certain distance, e.g., 14
inches, from level with the landing at which it is to stop, the
narrower bandwidth system is effective in which the speed pattern
steps are smoothed by the presence of pattern field PF in the
circuit. The stopping of the elevator involves inserting the
resistance of rheostat 13 in the pattern signal source by opening
contacts 14. When the controller for contacts 14 has returned to a
condition in which it has no speed pattern control, it permits
contact V2 at 238 to close. At this time the speed pattern of the
elevator is a function of its position as ascertained by inductor
switches which are carried past vane secured in the hatchway to
actuate those switches when they are in proximity.
Inductor switch control is provided for a number of contacts shown
in FIGS. 13 and 14. Contacts L22 at 221 and L14 at 238 open as the
car approaches the landing for a stop and close when the car is
within a given distance of its level position, e.g., 22 inches and
14 inches respectively. Landing door zone relay LDO (not shown) is
energized by inductor switches when the car is within a zone in
which the doors can be opened, e.g., 8 inches from level. A dead
zone comprising a range of positions centered around absolute level
and ordinarily extending between a half inch and an inch is defined
as its upper limit by a leveling up relay LU (not shown) and at its
lower limit by a leveling down relay LD (not shown) each responsive
to inductor switches so that LU is energized if the car is at or
above the level limit and in the leveling zone and LD is energized
when it is at or below that limit and in the leveling zone. Either
of relays LD or LU deenergize a dead zone relay DZ (not shown) if
they are energized.
Advance of the elevator to within the range of proximity of level
defined by relay L14 closes back contact L14 at line 238. Since the
car is not set to accelerate relay ACC is deenergized and back
contact ACC is closed at 238. If the amplifier is controlling the
error field EF, relay SCR is energized to close contact SCR at 238.
Hence during the stopping sequence, 14-inch regulation relay R14
pulls in at 238 and transfers the system to its broad bandwidth
operating condition by bypassing pattern field PF in FIG. 2. The
controls thereafter respond more rapidly to pattern steps as
generated by the operation of the inductor relays and smoothness of
the elevator motion is achieved by employing relatively small
signal steps. This operation of R14 can also be considered as
occuring in response to a given command signal since the closure of
contact L14 is also indicative of a command signal step from
rheostat 13.
While the elevator is running outside of the leveling zone for the
landing at which it is to stop and is not accelerating, the brake
relay and the generator field relays are energized through safety
switches at 218, start contact ST at 220, motor field normal
contact MFN at 221, landing and gate interlocks 164 and 165 and
pattern generator corrector contact V1 all at 224, contact LR1 and
landing door zone contact LDO to junction 166. An ascending car
having relay UF in maintains a circuit from 166 through contact UF
at 224, upper overtravel limit switch 167 and back contact DF at
223 and relays UF and BK to lead 159. A descending car has a
circuit for DF and BK from junction 166 through contact DF at 225,
lower overtravel limit switch 168 and back contact UF at 226.
When the car is advancing in the leveling zone contacts L22 and CS
at 221 are closed so that a leveling circuit for relays UF, DF and
BK is available when the door zone is entered and back contact LDO
at 225 is opened to interrupt the running circuit for those
relays.
A car is stopped level when both of relays LU and LD are
deenergized and the car is in the dead zone. This is accomplished
since relays UF, DF and BK are all dropped to disconnect the
generator and motor from the amplifier and set the brake. Front
contacts LD at 221 and LU at 222 open to interrupt the circuit for
relays UF, DF and BK and front contacts LD at 201 and LU at 202
open with generator field relay contacts UF at 204 and DF at 205 to
drop want to run relay WTR and through the opening of contact WTR
at 214 start relay ST.
A releveling operation as occasioned by changes in effective cable
length due to changes in load, commonly termed "sag," functions
through this system by operation of one of the leveling relays LU
or LD. An upward sag energizes relay LU to cause releveling
downward. A downward sag energizes relay LD to relevel upward.
If LD is energized a circuit is completed to pull in relay WTR at
202 through contacts LD and LU at 201. This completes a circuit for
start relay ST at contact WTR at 214. If the zero check is within
limits, contacts ZCF at 214 is closed and the closing of contact
WTR energizes relay ST. If the leveling check indicates a signal
from the amplifier within limits, contact LCF at 206 is closed and
relay SCR remains energized, provided failure contact FE at 206 is
not open and the velocity error check is within limits so that
contact VCF at 206 is closed. The only circuit available to relay
SCR at this stage in the releveling operation is through contact
LCF at 206 since the car doors are open to deenergize landing gate
relay LG and open contact LG at 207 and the energized start relay
opened back contact ST at 208. Thus, if an excessive releveling
signal is sensed during a releveling operation, relay SCR is
dropped to disconnect the supply from the silicon-controlled
rectifiers.
The sag of the elevator out of the dead zone also energizes the
motor field 24 by closing dead zone relay back contact DZ at 229 to
energize motor full field relay MFL. Contact MFL at 226 is closed
to energize motor normal field relay MFN at 228 while full current
is applied to field 24 through contact MFL at 233. Contact MFN at
221 is closed to complete a circuit for the generator field and
brake relays, as in the case of a sag downward, through relay UF
from lead 158, safety switches at 218, contact ST at 220, contact
MFN at 221, leveling contact L22 at 221, back car start contact CS
at 221, contact LD at 221, back contact LU at 221, back contact DF
at 223, coils UF and BK and lead 159. The motor then drives the car
upward with the brake relieved by the energization of leveling
brake relay LBK (not shown) to parallel resistor 161 with lesser
resistor 169 in the brake solenoid circuit through the closure of
contact LBK at 237. Thus, upon energization of brake relay BK to
close its contacts at 235 and in main switch M circuit at 217 to
close contact M at 235 the brake is partially lifted to permit the
hoist motor to move the elevator.
Another embodiment of the elevator safety circuits of this
invention is disclosed in FIGS. 15 and 16. In this embodiment the
generator shunt field is supplied from a single-controlled source
and a more direct approach to the control of the hoist motor by the
high gain negative feedback loop is employed. The safety
considerations parallel those described above and illustrate that
these considerations are in large part universally applicable to
elevator hoist motor controls where a closed negative feedback loop
having high gain is employed. Thus while the second embodiment
employs a velocity based pattern, it is to be appreciated that a
position based pattern or an acceleration based pattern could be
employed. Both embodiments employ silicon-controlled rectifiers in
the controlled power sources for which other controlled valves can
be substituted and both employ as a motor armature feed a
dynamoelectric generator which can be supplanted by other feed
systems such as controlled rectifiers arranged to feed the motor
armature directly, advantageously such controlled rectifier feeds
are in a polyphase arrangement.
As shown in FIG. 15, a velocity pattern generator 171 is arranged
to produce a voltage scale to velocity on a time base of the
general form shown at 172 in which there is a gradual increase from
zero velocity to a maximum acceleration, a period of constant
maximum acceleration, a gradual transition from constant
acceleration to maximum constant velocity, and then a slowdown
including a gradual transition to maximum deceleration, an interval
of constant maximum deceleration, and as the stop is approached a
gradual transition from maximum deceleration to zero velocity. The
hoist motor 173 is forced to closely follow the commanded velocity
of this pattern by feeding a signal scaled to actual motor
velocity, as derived from tachometer 174, over lead 175 and summing
resistor 176 to summing point 177. Motor 173 drives hoist sheave
178 over which cables 179 supporting the car 181 and its
counterweight 182 are trained. Tachometer 174 is coupled to be
driven by the motor 173.
The pattern signal is differentially related to the actual speed
signal at summing point 177 through summing resistor 183 by means
of the directionally controlled switching matrix 184. The matrix is
arranged to close a circuit across the pattern generator output
terminals through back contacts UF and DF of the up and down
generator field relays (not shown) when the elevator is not set to
run. At this time the pattern input is also grounded through series
back contacts of UF and DF. Tachometer 174 develops a negative
signal at 177 for up travel of elevator 181 and a positive signal
for down travel. The pattern signal is coupled to summing point 177
with a polarity opposing that of the tachometer signal by the
connections through front contacts UF and DF in matrix 184.
The signal from 177 to lag-lead compensator 185 represents the
velocity error between the commanded velocity and actual velocity.
Compensator 185 enables the error signal to be amplified to a level
forcing the error, the deviation of hoist motor speed from
commanded speed, to a negligibly small value through the gain of
the negative feedback loop without introducing instability in the
system. A total loop gain is selected which is at least equal to
the ratio of the unregulated open loop hoist motor speed error to
the allowable closed loop hoist motor speed error. Gain may be set
from about 5 to about 60. The compensator 185 attenuates the closed
loop gain as a function of increasing frequency sufficiently to
reduce the closed loop gain to a value less than unity at and above
the natural resonant frequency of the resonant circuit comprising
the total inductance and resistance, in the hoist motor armature
circuit and the capacitive effect of the total driven mass,
including the car, the driving means for the car and the
counterweight, coupled into the armature circuit through the hoist
motor. A lag-lead network of resistance and capacitance having a
lead-break frequency of from 2.5 to 5 radians per second
accommodates elevator hoisting systems as shown.
The compensated velocity error signal is amplified by an
operational amplifier 186 and then fed to summing point 187.
Generator linearization is achieved in accordance with the
aforenoted Loshbough patent application by an inner closed negative
feedback loop from the generator armature terminals. This generator
loop can have a gain of the order of 10. It comprises generator
armature 188, lead 189, resistance 191, main switch contact M and
resistance 192 to summing point 187. The generator armature voltage
error signal, resulting from the difference between the commanded
generator armature voltage signal from amplifier 186 and the signal
scaled to actual generator armature voltage, issues from summing
point 187 to amplifier 193 where it is applied to gate control 194
which can be a phase control firing circuit, corresponding
generally to that of FIG. 2, controlling the controlled rectifiers
195 and 196 through their gates.
Alternating current source 197 is coupled across the controlled
rectifiers and their diodes 198 and 199 by the secondary S.sub.1 of
transformer 201. Choke 202 and capacitance 203 are connected across
the controlled rectifiers and the highly inductive load of the
generator shunt field 204. Surge suppressing Thyrector 205 and
resistance 206 are also connected across the output of the
controlled rectifiers to accommodate circulating currents when main
switch contacts M are open.
The main switch M is pulled in when the car is set to run and is
dropped after the car is stopped. When dropped, a suicide circuit
is established through resistance 207 and normally closed contacts
M to the generator armature 188. Resistance 208 limits inductive
surges during switching. The drop of switch M also inserts
resistance 209 in the circuit between the armatures of the motor
173 and generator 188.
Two relays responsive to excess signal levels are arranged to shut
down the hoist motor if the signals to which either responds exceed
levels which are chosen to be within those acceptable for safe
operation. As in the embodiment of FIGS. 1, 2, 12, 13 and 14
signals are sensed at the output of the controlled supply to the
generator shunt field. This supply can be considered an amplifier
and with appropriate modification could be employed to supply the
hoist motor directly as when controlled rectifiers are connected to
the motor armature. Accordingly, the monitoring circuit is termed
the EXCESS AMPLIFIER OUTPUT safety and its relay is designated
EAO.
The amplifier output is sensed through leads 211 and 212 across the
capacitance 203 in order to take advantage of the smoothing action
of inductance 202 and the capacitance 203. Surge protection is
afforded the safety circuit by Thyrector 213 and resistance 214.
The parallel-T network is a notch filter 215 for attenuating 60
cycle components in the amplifier output. Positive and negative
signal levels are passed to leads 216 and 217 by rectifier bridge
218 and are further smoothed by capacitance 219. Negative
excursions of signal at 217 are effective to drop relay EAO at a
threshold level set by potentiometer 221. Sensitivity adjustment
potentiometer has its wiper connected to the base of transistor Q21
such that a negative going signal at 217 reduces the base potential
to cut off conduction in the collector of Q21 to reduce the drop in
resistance 222 and raise the base potential of transistor Q22. This
increases the drop in resistance 223 to provide feedback on lead
220 to the base of Q21 and further reduce its base potential while
reducing the base potential on transistor Q23 to reduce its
collector current and drop relay EAO.
Regulated bias is supplied the EAO safety circuit from secondary
S.sub.2 of the transformer 201 through rectifier 224 and across
smoothing capacitance 225 and regulating Zener diode 226. Rectifier
227 is across relay EAO to damp transients due to the inductance of
its coil and resistor 228 limits current in the event the diode 227
is shorted. As will be discussed more fully, the drop of relay EAO
under certain conditions, where greater than the preset threshold
signal is present to indicate an unsafe condition, actuates
emergency circuits which shut down the hoist motor.
This system is also shut down by the dropout of excess error signal
relay EE. Relay EE is controlled through two channels, both of
which must indicate signals within the threshold levels to maintain
EE energized. One channel responds to an excessive error signal
derived from summing point 228 and the other responds to an
excessive rate of change of feedback signal as from tachometer 174
as derived from lead 175.
Each channel includes an operational amplifier and an absolute
value circuit which responds to a signal of either polarity of
greater than a preset value. They differ from each other only in
the setting of the threshold level for dropping relay EE. Hence,
but one channel will be described in detail.
The velocity error signal sensing channel is represented as a block
229 labeled EXCESS ERROR SENSOR. Block 229 includes an operational
amplifier and an absolute value circuit set to respond to a
deviation in velocity error of either polarity from a preset level.
The input to block 229 is from summing resistors 231 and 232
respectively connected to pattern generator 171 and tachometer 174.
The output from block 229 is a signal maintaining transistor Q24
conductive while acceptable error signals are produced whereby the
coil of relay EE remains energized from the positive bus 230. That
output places transistor Q24 in nonconductive condition to open the
circuit to ground for the coil of relay EE and drop the relay when
the error signal is excessive.
The rate of change of the feedback signal, a rate of change of
velocity signal in the present system, is sensed through a
differentiation circuit comprising a series resistance 233 and
capacitance 234 in the lead from tachometer 174 to operational
amplifier 235. Amplifier 235 passes excessive transient signal on
lead 236 to absolute value circuit 237 which transfers transistor
Q24 from a conductive to a cutoff condition by reducing the
potential on the base of Q24. In the absence of a rate of change of
the feedback signal exceeding the tolerable rate of change, base
drive is maintained for transistor Q24.
When an excessive rate of change of feedback signal is imposed
through amplifier 235 to the absolute value circuit, it tends to
reduce the potential on the base of Q24 whereby the circuit
supplying the coil of relay EE is effectively opened to drop the
relay. When no excessive rate of change of feedback signal is
present the signal on lead 236 is at a level to cause transistor
Q26 to be cut off, transistors Q25 and Q27 to be conducting in
saturation, and transistor Q28 to be cut off whereby the potential
at the base of transistor Q24 is positive by virtue of the
restricted current from positive bus 230 through resistor 238 of
the voltage divider to negative bus 239. The conductive state of
Q25 and the nonconductive state of Q26 is established by the base
potentials derived from the voltage divider comprising resistances
241, 242, 243 and 244 between buses 230 and 239.
A positive going signal on lead 236 in excess of the threshold,
e.g., +5 volts, causes transistor Q26 to become conductive thereby
removing base drive from transistor Q27 by the voltage drop in
resistance 245. The resultant opening of the path to ground for
resistance 246 provides base drive for transistor Q28 effectively
grounding resistance 238 to cut off transistor Q24 and open the
coil circuit for relay EE.
A transient resulting in a negative going signal on lead 236 in
excess of the threshold, e.g., -5 volts, causes transistor Q25 to
become nonconductive by removing its base drive . This opens the
path to ground for resistance 246 applying base drive from
transistor Q28 to place it in conduction to ground resistance 238
and remove base drive from Q24. Thus for a positive excursion of
the amplified signal indicative of an excessive rate of change of
velocity, transistor Q27 is cut off to open the path from
resistance 246 to ground through the collector-emitter circuits of
Q25 and Q27, while a negative excursion indicative of an excessive
rate of change of velocity in the opposite direction cuts off
transistor Q25 to open that path. In each instance the application
of base drive to Q28 causes relay EE to drop by terminating
conduction through Q24 to ground.
Diode 247 is for surge protection in the circuit including the
relay coil and resistance 248 to limit inducted current.
FIG. 16 shows the relay logic of the safety circuits of FIG. 15 in
across the line form. When safe conditions exist to run the car,
the conventional safety interlock contacts represented by cam
actuated, normally closed switches 251 and 252 are closed and the
manually actuated safety switches represented by normally closed
pushbutton switch 253 are closed to complete a circuit energizing
emergency relay EM at 278. The main switch coil M at 279 is also
behind these safety switches and can be energized only when the
safe conditions prevail. Main switch M also requires the system to
be conditioned for operation with its electronic emergency relay
EME at 275 energized to close its contact EME at 279, its field
protective relay FP at 272 to be energized to close contact FP at
279 indicating there is current in the motor shunt field, its
motor-generator set to run relay LR (not shown) energized to close
contact LR at 279 indicating the motor driving the generator
armature 188 is running, and a direction of running established by
the energization of its up or down generator field relay UF or DF
(not shown) to close contacts UF at 279 or DF at 280.
M switch is energized to start the elevator in motion. As noted
above, it connects the generator armature to the motor armature,
disconnects the suicide circuit, connects the controlled rectifiers
to the generator shunt field, closes the generator linearizing
negative feedback loop, and removes the ground connection to the
velocity error signal summing point 177, all as shown in FIG. 15.
In FIG. 16, the M switch when energized increases the current in
the hoist motor shunt field by closing contact M at 271, and
enables the brake solenoid circuit at contact M at 273 so the brake
can be lifted when contacts of brake relay BK (not shown) are
closed at 273.
Under normal conditions of stopping the drop of the M switch is
delayed in operating sequence to permit a gradual stopping of the
car. Delay is afforded by the resistance and capacitance in series
with the leveling door open relay contact LDO all at 280. When the
car is making a normal stop, relay LDO (not shown) is energized to
connect the delay circuit across the coil of the M switch. On an
emergency stop the LDO contact at 280 remains open and rapid drop
of the M switch results.
The electronic emergency relay EME at 275 responds to the safety
relays EE and EAO discussed above and to an interlock relay ITL
such that the drop of any of these relays opens a contact at 276 to
drop relay EME and thereby open the circuit for main switch M at
contact EME at 279. This stops the elevator by setting its brake,
disconnecting the feed to the generator shunt field and suiciding
the generator. Interlock relay ITL (not shown) is energized when
all connections to the units making up the system are completed.
These connections include plug and socket connections and printed
circuit board connections to the chassis. Each of the safety relays
has a neon lamp indicator 254 at 275 which is illuminated when the
respective safety relay contact is open.
In operation, the proper assembly of the system energized relay ITL
to close contact ITL at 276. If at any drop of relay EE at any time
is during the operation of the system an excess error signal is
developed from the pattern signal and the feedback signal at
summing point 228, this signal, which corresponds to the error
signal at summing point 177 establishing the control signal, will
cause relay EE to drop by placing the transistor corresponding to
Q28 of circuit 237 in its absolute value circuit in conduction to
remove over lead 249, base drive from transistor Q24. If the
feedback signal is increased or decreased at an excessive rate any
time during operation it will cause EE to drop. The drop of relay
EE at any time is effective to drop relay EME by opening contact EE
at 276. Thus, the threshold for the excess error signal should be
set to permit error signals within the range encountered at summing
point 177 when the system is operating in a satisfactory manner and
the threshold for the excess rate of feedback signal (excess
acceleration for a velocity feedback signal) should be beyond the
range of suitable operation, that range normally being dictated by
passenger comfort.
The excess amplifier output safety monitors the output at all
times. However, it is effective only while the shunting circuit
around contact EAO at 276 is open. This shunt is opened when the
car doors are open beyond a point about two inches from closed to
energize door close relay DCL (not shown) and open its back contact
DCL at 277, or when the car brake is set and brake relay BK is
dropped to open contact BK at 277. Thus, when the car is
stationary, leveling in its final approach to a landing, or
releveling when at a landing, the shunt at 277 is open and the
opening of contact EAO at 276 is effective to light the excess
amplifier output indicator lamp and drop relay EME. Under these
conditions, the threshold for the drop of relay EAO is set for a
signal level suitable for leveling the car. This threshold
therefore may be below the peak levels encountered in running the
car under normal circumstances and during normal runs contact EAO
may be opened without effect in view of the shunt.
The safety circuits controlling relays EE and EAO restore
themselves to the normal operating condition when their tripping
condition is removed. Hence, contacts EE and EAO at 276 may be
opened only briefly. Relay EME is arranged to respond to the brief
interruptions of its energizing circuit by maintaining its
deenergized state through open seal contact EME at 276.
Seal contact EME is paralleled by a back contact LR at 275 of the
m-b run relay. When the system is conditioned for the car to run,
relay LR is energized to open back contact LR at 275. Therefore,
back contact LR is open when the EE and EAO safeties are effective.
Contact LR enables the reset of relay EME by the stopping of the
m-g set to close the contact. Thus reset is affected after an EE or
EAO failure by stopping and restarting the m-g set.
Seal contact EME is also paralleled by a back contact EM at 277.
When the elevator is subjected to an emergency stop as by the
opening of the emergency stop switch 253 on the operating panel
(not shown) in the car, the deceleration to which the car is
subjected produces a rate of change of velocity exceeding the
threshold of feedback rate responsive circuit 237 to drop excess
error relay EE and drop EME at open contact EE. Under these
circumstances the passenger can manually reset the emergency stop
button from within the car. Such a reset is effective to run the
car since the EME relay can be restored automatically while relay
EM is deenergized and after the rate of change of velocity has been
reduced below the threshold dropping relay EE, since a circuit will
be available through contacts ITL, EE and EAO at 276 and back
contact EM at 277. When relay EM is manually reset from within the
car the system will continue to operate since EME will also be
energized.
It is evident from the above embodiments that variations in the
monitoring of the signals of a closed loop, high gain, negative
feedback, elevator hoist motor control system, where a malfunction
resulting in an excessive signal level can result in damaging
forces being imposed by the motor, can be accomplished in a variety
of ways, by monitoring various combinations of signals, by
rendering certain of the signals effective at selected times in the
operation of the system, and by enabling certain indicated failures
to be corrected by passengers while others require a manual
resetting under conditions dictating the presence of a skilled
elevator technician. Further, the failed state of these controls
can be employed to shut down the system by stopping the car as
rapidly as is reasonable at any position or can be arranged to set
the system for running at a reduced speed through auxiliary control
means. These variations indicate that the system lends itself to
many combinations of the safety mechanisms and functions.
Accordingly, it is to be appreciated that the above embodiments are
to be read as illustrative and not in a limiting sense.
* * * * *