U.S. patent number 3,746,954 [Application Number 05/181,515] was granted by the patent office on 1973-07-17 for adjustable voltage thyristor-controlled hoist control for a dc motor.
This patent grant is currently assigned to Square D Company. Invention is credited to Fred Erb, Asa H. Myles.
United States Patent |
3,746,954 |
Myles , et al. |
July 17, 1973 |
ADJUSTABLE VOLTAGE THYRISTOR-CONTROLLED HOIST CONTROL FOR A DC
MOTOR
Abstract
A direct current series motor is powered by adjustable voltage
from an alternating current source. The motor is series connected
during hoisting and powered by a single AC-DC converter, and shunt
connected during lowering with a second AC-DC converter supplying
the field. An isolation resistor permits dynamic lowering and
provides emergency dynamic braking even with the independently
energized armature and field. A teaser field resistor which
prevents overspeeding when the motor is hoisting a light load is
automatically disconnected while the motor is hoisting a
sufficiently heavy load and is reconnected if the load becomes too
small. During lowering, a dynamic braking resistor may be removed
from across the armature without any material change in motor
speed.
Inventors: |
Myles; Asa H. (Solon, OH),
Erb; Fred (Northfield, OH) |
Assignee: |
Square D Company (Park Ridge,
IL)
|
Family
ID: |
22664597 |
Appl.
No.: |
05/181,515 |
Filed: |
September 17, 1971 |
Current U.S.
Class: |
318/247;
174/DIG.16; 318/258 |
Current CPC
Class: |
H02P
7/298 (20130101); B66C 13/24 (20130101); H02P
7/281 (20130101); Y10S 174/16 (20130101) |
Current International
Class: |
B66C
13/22 (20060101); B66C 13/24 (20060101); H02P
7/298 (20060101); H02P 7/28 (20060101); H02P
7/18 (20060101); H02p 005/06 () |
Field of
Search: |
;318/258,261,269,274,341,342,344,375,247,248 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Duncanson, Jr.; W. E.
Claims
We claim:
1. A control system for operating a direct current motor having an
armature and a series-wound field from an alternating current
source, said system comprising a motor having an armature and a
series-wound field, first and second AC-DC converter means each
having control and power input terminals and output terminals, said
source being electrically connected to the power input terminals of
the first and second converter means, master switch means
selectively operable in a first range for controlling operation of
the motor in one direction of rotation and a second range for
controlling operation of the motor in an other direction of
rotation, signal means producing a voltage of a first polarity when
the master switch means is in its first range and producing a
voltage of a second polarity when the master switch is in its
second range, reference control means electrically connected to the
signal means and to the control input terminals of the first and
second converter means and responsive to a voltage of the first
polarity from the signal means to produce a direct current output
from only the first converter means and responsive to a voltage of
the second polarity from the signal means to produce direct current
outputs from both the first and the second converter means, means
serially connecting the armature and the field across the output
terminals of the first converter means when the master switch means
is in its first range, means connecting the armature across the
output terminals of the first converter means and connecting the
field across the output terminals of the second converter means
when the master switch means is in its second range, and an
isolation resistor serially connected between the armature and the
field so that excitation of the field is related to the voltage
across the armature when the master switch means is in its second
range.
2. A control system as in claim 1 wherein said means serially
connecting the armature and the field across the output terminals
of a first converter means and said means connecting the armature
across the output terminals of the first converter means and
connecting the field across the output terminals of the second
converter means maintains the polarity of the voltage impressed on
the field the same for both ranges of the master switch and causes
the voltage impressed on the armature to be of one polarity in the
first range of the master switch and of a different polarity in the
second range of the master switch.
3. A control system as in claim 1 wherein said first range of said
master switch means is a non-overhauling range in which a load on
the motor is normally non-overhauling and said second range of said
master switch means is an overhauling range in which the load on
the motor is normally overhauling.
4. A control system as in claim 1 wherein said system is for
driving a crane hoist, said first range of said master switch means
is a hoisting range, and said second range of said master switch
means is a lowering range.
5. A control system as in claim 4 including an overhoist limit
switch having normally closed limit switch contacts and wherein
said means serially connecting the armature and the field across
the output terminals of the first converter means when the master
switch mean is in its hoisting range includes the limit switch
contacts and wherein said means connecting the armature across the
output terminals of the first converter means and connecting the
field across the output terminals of the second converter means
when the master switch means is in its lowering range is
independent of the limit switch contacts.
6. A control system as in claim 1 and including an
electromagnetically-released brake means having a release winding
connected serially with said armature and field and energized by
the direct current output of only said first AC-DC converter means
when said master switch means is in its first range and by the
direct current outputs of both said first and second AC-DC
converter means when said master switch means is in its second
range.
7. A control system as in claim 1 wherein said master switch means
includes means for changing the voltage of said signal means, and
wherein said reference control means includes means responsive to a
change in the voltage of the first polarity from the signal means
to produce a change in the direct current output of said first
AC-DC converter means and means responsive to a change in the
voltage of the second polarity from said signal means to produce a
change in the direct current outputs of both said first and second
AC-DC converter means.
8. A control system as in claim 1 and including a teaser field
resistor, switching means for connecting the teaser field resistor
across the armature, and current sensitive means for operating the
switching means at a predetermined magnitude of the direct current
output of the first converter means while the master switch is in
the first range, the teaser field resistor being connected across
the armature at low magnitudes of the direct current output and
being disconnected from the armature at high magnitudes of the
direct current output.
9. A control system for operating a direct current motor having an
armature and a series-wound field from an alternating current
source, said system comprising a motor having an armature and a
series-wound field, AC-DC converter means having control and power
input terminals and output terminals, said source being
electrically connected to the power input terminals of the
converter means, master switch means having an operating range for
controlling operation of the motor, signal means for producing a
voltage of a selected polarity and of a magnitude controlled by
said master switch means, reference control means electrically
connected to said signal means and to the control input terminal on
the converter means and responsive to the magnitude of the voltage
from said signal means to control a direct current output from the
converter means at said output terminals, means serially connecting
the armature and the field across said output terminals, a teaser
field resistor connected across the armature, and current sensitive
means for disconnecting the teaser field resistor at a
predetermined magnitude of the direct current output of the
converter means; said current sensitive means comprising
current-indicating means interposed in the motor circuit for
producing a current-magnitude signal indicating the magnitude of
direct current output of said AC-DC converter means, and load
sensing means connected to said current-indicating means and
responsive to a first predetermined magnitude of said
current-magnitude signal to disconnect said teaser field resistor
and responsive to a second predetermined magnitude of said
current-magnitude signal to connect said teaser field resistor;
said load sensing means comprising biasing means providing a
biasing signal, comparison means connected to said
current-indicating means for comparing said current-magnitude
signal to said biasing signal and producing a voltage of one
polarity if said current-magnitude signal is of greater magnitude
than the biasing signal and of an other polarity if said
current-magnitude signal is of smaller magnitude than the biasing
signal, time delay means connected to said comparison means and
providing an output after a time delay, and relay means responsive
to the output of the time delay means for selectively connecting
and disconnecting said teaser field resistor.
10. A control system as in claim 9 wherein said time delay means
comprises amplifier means having an input terminal and an output
terminal, a first capacitor connected between the input terminal
and the output terminal, a first input resistor providing a time
delay of a first predetermined duration, a second input resistor
providing a time delay of a second predetermined duration, and
rectifier means applying voltage of said one polarity from said
comparison means to the first input resistor and applying voltage
of said other polarity from said comparison means to the second
input resistor.
11. A control system as in claim 10 wherein said time delay means
includes switching means connected to the output terminal of said
amplifier means for conducting current when a voltage of said one
polarity is applied to said time delay means and blocking current
when a voltage of said other polarity is applied to said time delay
means, said switching means being connected to a source of voltage
of said other polarity, a second capacitor connected between the
source of voltage and the input terminal of said amplifier means
for discharging through said amplifier means when said switching
means begins to conduct.
12. A control system as in claim 9 wherein said biasing means
includes means connected between said relay means and said
comparison means providing a first predetermined magnitude of said
biasing signal and when said teaser field resistor is connected
across said armature and a second predetermined magnitude of said
biasing signal when said teaser field resistor is disconnected.
13. A control system as in claim 9 wherein said reference control
means includes amplifier means having an input terminal, a first
input resistor connected to the amplifier input terminal for
receiving voltage of said selected polarity from said signal means,
a second input resistor connected between the amplifier input
terminal and a source of voltage of said selected polarity, and
voltage divider means connected between the first and second input
resistors and having a wiper connected at a voltage of
predetermined magnitude.
14. A control system for operating a direct current motor
comprising an armature and a series-wound field from an alternating
current source, said system comprising a motor having an armature
and a field, first and second AC-DC converter means each having
control and power input terminals and output terminals, said source
being electrically connected to the power input terminals of the
first and second converter means, master switch means having an
operating range for controlling operation of the motor when the
motor is subject to an overhauling load, signal means for producing
a voltage of a first polarity and of a magnitude controlled by said
master switch means, reference control means electrically connected
to said signal means and to the control input terminals of both the
first and second converter means and responsive to the magnitude of
the voltage from the signal means to control direct current output
from both the first and second converter means, means connecting
the armature across the output terminals of the first converter
means and connecting the field across the output terminals of the
second converter means, a dynamic braking resistor connected across
the armature, and current sensitive means for disconnecting the
dynamic braking resistor at a predetermined magnitude of direct
current output from both the first and second converter means.
15. A control system as in claim 14 wherein said current sensitive
means comprises current-indicating means for producing a
current-magnitude signal indicating the magnitude of the direct
current output from both said first and second AC-DC converter
means, and load sensing means connected to said current-indicating
means and responsive to said current-magnitude signal produced at
said predetermined magnitude of direct current output to disconnect
said dynamic braking resistor.
16. A control system as in claim 15 wherein said load sensing means
comprises comparison means connected to said current-indicating
means comparing said current-magnitude signal to a biasing signal
of predetermined magnitude and producing a voltage of one polarity
if said current-magnitude signal is greater than the biasing signal
and of an other polarity if said current-magnitude signal is less
than the biasing signal, time delay means connected to said
comparison means and providing an output after a time delay, and
relay means responsive to the output of the time delay means for
disconnecting said dynamic braking resistor.
17. A control system as in claim 16 wherein said time delay means
comprises amplifier means having an input terminal, a first input
resistor providing a time delay of a first predetermined duration,
a second input resistor providing a time delay of a second
predetermined duration, and rectifier means applying voltage of
said one polarity from said comparison means to the first input
resistor and applying voltage of said other polarity from said
comparison means to the second input resistor.
18. A control system as in claim 14 wherein said reference control
means includes matching means preventing material change in speed
of said motor when said dynamic braking resistor is
disconnected.
19. A control system as in claim 18 wherein said reference control
means includes first amplifier means having an output terminal
connected to said first AC-DC converter means and an input
terminal, second amplifier means having an output terminal from
which an output voltage is transmitted to the first amplifier means
in response to an input voltage from said signal means, and third
amplifier means having an output terminal and from which an output
voltage is transmitted to the first amplifier means in response to
an input voltage from said signal means, and said matching means
includes switching means limiting the output voltage of the second
amplifier means when said dynamic braking resistor is connected
across said armature and limiting the output voltage of the third
amplifier means when the dynamic braking resistor is disconnected,
and means connected between the input terminal of the first
amplifier means and the output terminals of the second and third
amplifier means permitting the output voltage of greater magnitude
to be applied to the first amplifier means.
20. A control system as in claim 19 wherein said reference control
means includes fourth amplifier means having an output terminal
connected to the control input terminal of said second AC-DC
converter means and inverting a non-inverting input terminals, the
inverting input terminal being connected to receive said voltage of
said first polarity from said signal means, a source of voltage of
a second polarity, opposite from said first polarity, connected to
the inverting input terminal of the fourth amplifier means, and
resistance means providing a portion of said signal means voltage
to the non-inverting input terminal of the fourth amplifier means,
and wherein said switching means includes means diverting said
signal means voltage from the non-inverting input terminal when
said dynamic braking resistor is connected across said
armature.
21. A control system as in claim 20 including an additional
current-indicating means serially connected with the output
terminal of said second AC-DC converter means and wherein said
reference control means includes means connected between said
additional current-indicating means and the non-inverting input
terminal of said fourth amplifier means for applying a voltage of
said first polarity indicating the magnitude of direct current
output of said second converter means to the non-inverting
terminal.
Description
This invention relates to hoist control systems for DC motors, and
more particularly to a hoist control system for operating a direct
current series motor from a single-phase or three-phase alternating
current source.
It is an object of this invention to provide an improved hoist
control for a DC series motor.
It is a further object to provide an improved adjustable voltage
speed control for operating a DC series motor from an AC
source.
A still further object is to provide a hoist control in which,
during hoisting operation, the armature and field of a DC series
motor are connected as a series motor, and in which, during
lowering operation, the armature and field are shunt connected and
generally independently powered.
Another object is to provide an improved adjustable voltage hoist
control system for a DC series motor in which dynamic braking,
dynamic lowering, and emergency dynamic braking are provided for
the motor during lowering operation.
Another object is to provide a DC hoist control system in which
improved automatic control for selective application and removal of
a teaser field resistor during hoisting operation of the motor is
provided.
Another object is to provide a DC hoist control system in which
automatic removal of the dynamic braking resistor during lowering
operation of the motor is accomplished without any material change
in motor speed.
Other objects and advantages of the invention will be apparent from
the following description wherein reference is made to the
drawings, in which:
FIG. 1 is a schematic wiring diagram, partly in block form, of a
hoist control system in accordance with this invention;
FIG. 2 is a schematic wiring diagram of a reference control circuit
for use in the hoist control system of FIG. 1;
FIG. 3 is a schematic wiring diagram of a load sensing module for
use in the hoist control system of FIG. 1;
FIGS. 4-9 are graphs illustrating relationships between output
voltage of a signal converter of the hoist control system of FIG. 1
and various amplifier voltages appearing in the reference control
circuit of FIG. 2.
A preferred embodiment of the thyristor hoist control system of the
present invention is illustrated in FIG. 1 wherein a direct current
motor comprising an armature 11A and a series-wound field 11F is
powered by a three-phase alternating current source L1-L2-L3 and
used to selectively hoist and lower a load 14. An overhoist limit
switch 15 of the power circuit type is preferably arranged to be
operated by the load 14, as is well known in the art. The limit
switch 15 has two sets of normally open contacts 15a and 15b and
two sets of normally closed contacts 15c and 15d. A spring-applied
electromagnetically-released friction brake 16 having an operating
winding 16w is preferably provided for armature 11A.
A conductor 17 extends between a junction 19 and a junction 20 and
forms a series connection comprising the junction 19, normally open
contacts 21a of a first electromagnetic hoisting contactor 21, the
limit switch contacts 15c, the armature 11A, the limit switch
contacts 15d, an isolation resistor 22, the motor field 11F, the
operating winding 16w of the brake 16, normally open contacts 24a
of a main contactor 24, a winding 25w of an overload relay 25, a
resistor serving as a first current-indicating means or current
measuring shunt 26, and the junction 20. The circuit is preferably
grounded at the junction 20.
A conductor 27 forms a series connection from the junction 19
through normally open contacts 28a of an electromagnetic lowering
contactor 28, the limit switch contacts 15b, a limit switch
resistor 29 to the side of the field 11F adjacent the operating
winding 16w of the brake 16. The conductor 27, between the contacts
28a and the contacts 15b, is connected by a winding 3w of a limit
switch relay 30 to the conductor 17 between the contacts 21a and
the contacts 15c, by the series combination of a dynamic braking
resistor 31 and normally closed contacts 32a of an electromagnetic
dynamic braking contactor 32 to one side of the armature 11A
adjacent the limit switch contacts 15c, and by a conductor 34 to
the other side of the armature 11A adjacent the limit switch
contacts 15d.
A conductor 35 is connected from the one side of the armature 11A
through a pair of normally closed contacts 36a of an
electromagnetic teaser field contactor 36, a teaser field resistor
37, and a pair of normally open contacts 39a of a second
electromagnetic hoisting contactor 39 to the side of the field 11F
adjacent the isolation resistor 22. A conductor 40 connects a pair
of normally closed contacts 41a of an electromagnetic dynamic
lowering contactor 41 between the one side of the armature 11A and
the other side of the field 11F. A conductor 42 connects the
normally open limit switch contacts 15a between the conductor 40,
adjacent the armature 11A, and the conductor 17, between the limit
switch contacts 15d and the isolation resistor 22. The conductor 42
is also connected to the conductor 35 between the teaser field
resistor 37 and the hoisting contacts 39a.
A first controlled rectifier means, preferably in the form of an
AC-DC converter 44, has its DC output connected by a conductor 45
through a winding 46w of an overload relay 46 to the junction 19
and by a conductor 47 to the junction 20. The AC-DC converter 44
may be either single phase or three phase in accordance with the
requirements of the motor, and may be either a semi-converter of a
full converter, the circuits of which are well known to those
skilled in the art. A second controlled rectifier means, preferably
in the form of an AC-DC converter 49, has one side of its DC output
connected by a conductor 50 to one side of the field 11F adjacent
the isolation resistor 22. The other side of the DC output of the
AC-DC converter 49 is connected by a conductor 51 through a
resistor serving as a second current measuring shunt 52 to the
junction 20. The AC-DC converter 49 may also be either single phase
or three phase, but this converter cannot include a free wheeling
diode if a limit switch is to be used. If desired, the AC-DC
converter 49 may comprise three thyristors, each connected to one
leg of the secondary winding 53b. The neutral of the secondary 53b
would then be an output terminal of the converter 49 for connection
of the conductor 51.
The AC-DC converters 44 and 49 are powered by the secondary
windings 53a and 53b, respectively, of a transformer 53. The
transformer 53 has a primary winding 53p, which may be either delta
or wye-connected, connected to the source of alternating current
L1-L2-L3. The secondary winding 53a is connected by conductors 54
to the AC-DC converter 44 and the secondary winding 53b is
connected by conductors 55 to the AC-DC converter 49. Although a
three-phase transformer 53 has been illustrated, it will be readily
apparent to those skilled in the art that the motor control
circuitry of the present invention may be utilized, when
appropriate, with a single phase power supply and that the
secondary windings 53a and 53b could be energized by separate
primaries.
A pair of conductors 56 supply single phase alternating current
from the source of alternating current L1-L2 to a primary winding
57p of a transformer 57 having a secondary winding 57s. The
secondary winding 57s of the transformer 57 supplies power for the
control circuitry which will now be described in detail.
The motor is controlled by a multi-position, reversing master
switch 58, which may be of the type described in U. S. Pat. No.
3,221,246, issued on Nov. 30, 1965, to Calvin B. Sanborn, Jr., and
assigned to the assignee of the present invention. A pair of
conductors 59 carry operating power from the secondary winding 57s
to a rectifier 60 and a pair of conductors 61 carry operating power
from the secondary winding 57s through normally open auxiliary
contacts 24b of the main contactor 24 to the serially connected
primary windings 62p and 64p of a pair of differential transformers
62 and 64, as is fully disclosed in the aforementioned patent.
The rectifier 60 changes alternating current from the secondary
winding 57s of the transformer 57 to direct current and may be in
the form of a standard diode bridge rectifier having its output fed
through a positive conductor 65 and a negative conductor 66. The
master switch 58 has normally closed contacts 67 and six normally
open contacts 69 through 74. The closed or open condition of the
contacts 67 and 69 through 74 in the hoisting and lowering position
is indicated by the presence or absence of substantially
rectangular blocks aligned with the contacts. For example, the
contacts 69 are closed in the hoisting range of the master switch
58 and open in the lowering range. The contacts 67 and 69 through
74 control the energization of operating windings of various
contactors and relays, power for which is obtained through the
conductors 65 and 66.
An operating winding 75w of an undervoltage relay 75 is energized
through the contact 67 when the master switch is in an OFF position
and is maintained in its energized state in other positions of the
master switch through normally open contacts 75a of the relay 75,
the contacts 75a being interposed in the conductor 65. Normally
closed contacts 25a of the overload relay 25 and normally closed
contacts 46a of the overload relay 46 are connected in series with
the winding 75w of the undervoltage relay 75. The operation,
interconnection, and function of the overload relays 25 and 46 and
the undervoltage relay 75 are well known in the art.
A winding 41w of the dynamic lowering contactor 41 is energized
through the contact 69, and normally closed auxiliary contacts 28b
of the lowering contactor 28 in the hoisting range of the master
switch 58. Connected in parallel with the winding 41w for operation
through the contacts 69 and 28b are a winding 21w of the first
hoisting contactor 21, connected through normally open auxiliary
contacts 41b of the dynamic lowering contactor 41, a winding 39w of
the second hoisting contactor 39, connected through normally open
auxiliary contacts 32b of the dynamic braking contactor 32, and a
winding 36w of the teaser field contactor 36, connected through
normally open contacts 76a of a first load sensing relay 76 (FIG.
3).
A winding 28w of a lowering contactor 28 is energized through the
contact 70 and normally closed auxiliary contacts 39b of the second
hoisting contactor 39 whenever the master switch 58 is operating in
its lowering range.
A winding 32w of the dynamic braking contactor 32 is energized
through the contact 71 in the hoisting range of the master switch
58, through the contact 72 and normally open contacts 30a of the
limit switch relay 30 in the high speed lowering range of the
master switch 58, and through the contacts 73, a pair of normally
open contacts 77a of a second load sensing relay 77 (FIG. 3) and
the contacts 30a in the intermediate and high speed lowering ranges
of the master switch 58.
A winding 24w of the main contactor 24 is energized through the
contact 74 throughout the hoisting and lowering ranges of the
master switch 58.
The differential transformers 62 and 64 have secondary windings 62s
and 64s, respectively, connected to a signal converter 79 which
converts its alternating current input to a direct current output
preferably having a negative voltage output during hoisting
operation and a positive voltage output during lowering operation
as is described in the above-mentioned Sanborn patent. It should be
noted, however, that any source of adjustable voltage direct
current adapted for output of one polarity during hoisting
operation and another polarity during lowering operation may be
used as a signal means. This direct current output is transmitted
through a conductor 80 to a reference control circuit 81, which
will be described in detail with reference to FIG. 2. A load
sensing module 82 is electrically connected to the first shunt 26
by a conductor 83 and to the reference control circuit 81 by a
conductor 84 and operates in a manner to be described in detail
with reference to FIG. 3.
The reference control circuit 81 is connected by a conductor 85 to
the second shunt 52 and provides a control output through a pair of
conductors 86 and 87 to a first firing circuit 88 which in turn
controls operation of the first AC-DC converter 44. The reference
control circuit 81 also provides a control output through
conductors 89 and 90 to a second firing circuit 91 which in turn
controls operation of the second AC-DC converter 49.
The reference control circuit 81 is best described with reference
to FIG. 2 and obtains a direct current input voltage through the
conductor 80 from the signal converter 79 as is also shown in FIG.
1. Some of the other circuitry of FIG. 1 is also repeated in FIG. 2
for a clarity. The output of the reference control circuit 81 is
transmitted through conductors 86 and 87 to the first firing
circuit 88 and through conductors 89 and 90 to the second firing
circuit 91.
A conductor 92 connects the conductor 80 through a diode 94 to an
input resistor 95 of an inverting amplifier 96 having a feedback
resistor 97. A conductor 99 connects the diode 94 to a hoisting
permissive circuit 100. The hoisting permissive circuit 100
produces a fixed negative output voltage in response to a variable
negative input voltage transmitted through the conductor 99 in a
manner well known to those skilled in the art. This output signal
is applied to an input resistor 101 of the amplifier 96 and is
applied to the first firing circuit 88 through the conductor 87.
The conductor 84 transmits this output voltage also to the load
sensing module 82 (see also FIG. 1). A minimum hoisting speed
adjustment potentiometer 102 is connected between the input
resistor 95 and the input resistor 101 and has a wiper 102w which
is connected to ground. The output of the amplifier 96 is
transmitted to the first firing circuit 88 through the conductor
86.
A conductor 104 connects the conductor 80 through a diode 105 to a
lowering permissive circuit 106, an input resistor 107 of a
non-inverting amplifier 108, an input resistor 109 of an inverting
amplifier 110, and to a conductor 111 which is connected to an
input resistor 112 at the inverting input of an amplifier 113.
The lowering permissive circuit 106 responds to a positive variable
input voltage to produce a fixed negative output voltage. This
output voltage is transmitted to the first firing circuit 88
through the conductor 87 and to the second firing circuit 91
through the conductor 89. The output of the lowering permissive
circuit 106 is also applied to an input resistor 114 at the
inverting input of the amplifier 113.
The amplifier 108 has a feedback resistor 115 and has an input
resistor 116 connected to a source of negative voltage 117. The
output of the amplifier 108 is applied to an input resistor 119 of
an inverting amplifier 120 having a feedback resistor 121. A second
input resistor 122 of the amplifier 120 is connected to a source of
positive voltage 124 and a third input resistor 125 is connected by
a conductor 126 to the collector of a transistor 129. A conductor
130 transmits the output of the amplifier 120 through a diode 131
and a conductor 132 to an input resistor 133 of the amplifier
96.
The amplifier 110 has a feedback resistor 134. The input resistor
109 of the amplifier 110 is connected by a conductor 135 through a
diode 136 to the emitter of a transistor 137 which is connected to
ground through a resistor 139. The collector of transistor 137 is
connected to a source of positive voltage 140, and the base of the
transistor 137 is connected to the wiper of a potentiometer 141 one
side of which is connected to a source of positive voltage 142. The
other side of the potentiometer 141 is connected by a conductor 144
to a junction 145 joining a diode 146 and a diode 147. The diode
146 is connected to a source of positive voltage 148 and, by a
conductor 149, through normally closed contacts 30b of the limit
switch relay 30 to a source of negative voltage 150. The diode 147
is connected by a conductor 151 through normally open auxiliary
contacts 32c of the dynamic braking contactor 32 and normally open
auxiliary contacts 28c of the lowering contactor 28 to the source
of negative voltage 150. The diode 147 is also connected to a
source of positive voltage 152 and by a conductor 153 to the base
of the transistor 129. The emitter of the transistor 129 is
connected to ground and the collector of the transistor 129 is
connected through a resistor 156 to a source of negative voltage
157.
The output voltage of amplifier 110 is transmitted through a
conductor 159, a diode 160, and the conductor 132 to the input
resistor 133. As has been shown, the outputs of amplifiers 120 and
110 are applied through diodes 131 and 160, respectively, to the
input resistor 133 of amplifier 96.
The output voltage of the second shunt 52 is transmitted through
the conductor 85 to an input resistor 161 of an inverting amplifier
162 having a feedback resistor 163. The output of amplifier 163 is
transmitted to an input resistor 164 of the amplifier 113 which has
a feedback resistor 165. The conductor 111, at the input resistor
112, is connected to ground through a potentiometer 166 having its
wiper connected to the non-inverting input of amplifier 113 and to
the collector of a transistor 167. The emitter of the transistor
167 is connected to ground and the base of the transistor 167 is
connected to the junction 145.
The load sensing module 82 is best described with reference to FIG.
3 which also includes some of the circuitry shown in FIG. 1. Input
to the load sensing module 82 is provided by the first shunt 26
through the conductor 83 (see also FIG. 1) and from the reference
control circuit 81 through the conductor 84 (see also FIG. 2).
The conductor 83 feeds the input voltage from the first shunt 26 to
an input resistor 168 of an inverting amplifier 169 having a
feedback resistor 170. The output voltage of the amplifier 169 is
transmitted to an input resistor 171 of an inverting amplifier 172
having a feedback resistor 174. A potentiometer 175 is connected by
a conductor 176 between a source of positive voltage 177 and a
grounding conductor 179 and has its wiper 175w connected to an
input resistor 180 of the amplifier 172.
A conductor 181 connects the input terminal of the amplifier 172 to
a combination of resistors comprising a resistor 182 which is
connected in parallel with serially connected resistors 184 and
185. A junction 186 between the resistor 184 and the resistor 185
is connected to the collector of a transistor 187 the emitter of
which is connected to a grounding conductor 189.
A conductor 190 connects the junction of the resistor 182 and the
resistor 185 to a wiper 191w of a potentiometer 191. The
potentiometer 191 is connected between the grounding conductor 189
and a diode 192. The diode 192 is connected by a conductor 194 to
the base of a transistor 195. The conductor 84, providing input
from the reference control circuit 81, is connected to the
conductor 194.
The output voltage of the amplifier 172 is transmitted through a
conductor 196 to an input resistor 197 of an inverting amplifier
199 having a feedback resistor 200.
The output of the amplifier 199 is transmitted by a conductor 201
to a voltage divider comprising series-connected resistors 202,
204, and 205 and connected at its opposite end to the grounding
conductor 179. A conductor 206 connects the collector of the
transistor 195 to the grounding conductor 179, and the emitter of
the transistor 195 is connected to the voltage divider at a point
between the resistors 204 and 205.
The voltage divider, at a point between the resistors 202 and 204,
is connected by a conductor 207 through a diode 209 to an input
resistor 210 of an integrating amplifier 211 and by a conductor 212
through a diode 214 to an input resistor 215 of the amplifier 211.
The amplifier 211 has a feedback capacitor 216. A conductor 217
transmits the output of the amplifier 211 to the base of a
transistor 219 which has its emitter connected to the grounding
conductor 179 and its collector connected by a conductor 220 to a
junction 221.
The junction 221 is connected by a conductor 222 through a
capacitor 224 to an input resistor 225 of the amplifier 211, by a
conductor 226 through a resistor 227 to a source of positive
voltage 229, and by a conductor 230 to the base of a transistor
231. The emitter of the transistor 231 is connected by a conductor
232 to a source of positive voltage 233 and the collector of the
transistor 231 is connected by a conductor 234 through a diode 235
and a resistor 236 to a source of negative voltage 237. A conductor
238 is connected from the conductor 234 between the diode 235 and
the resistor 236 through a diode 239 to the base of the transistor
187. A conductor 240 connects the collector of the transistor 231
to the base of a transistor 241 and, through a conductor 242, to
the base of a transistor 243. The collector of the transistor 241
is connected through a winding 76w of the first load sensing relay
76 to a source of positive voltage 244 and the emitter of the
transistor 242 is connected to a source of negative voltage 245.
The emitter of the transistor 243 is connected to a source of
negative voltage 246 and the collector of the transistor 241 is
connected through a winding 77w of the second load sensing relay 77
to a source of positive voltage 247. A conductor 249 connects the
collector of the transistor 241 through normally open auxiliary
contacts 32d of the dynamic braking contactor 32 to a source of
negative voltage 250.
Referring now to FIGS. 1-3, operation of the thyristor hoist
control of the present invention will be described assuming that
the motor, comprising the armature 11A and the field 11F, is being
used to selectively hoist and lower a load 14 in response to
operation of the master switch 58.
When the master switch 58 is in its OFF position, master switch
contacts 67 are closed and master switch contacts 69-74 are open.
Therefore, voltage is applied by the rectifier 60 to the winding
75w of the undervoltage relay 75 which closes its contacts 75a to
form a holding circuit through a conductor 251 in a manner well
known in the art.
When an operating handle of the master switch 58 is moved in a
direction calling for hoisting operation of the motor, the normally
closed master switch contacts 67 open and the normally open master
switch contacts 69, 71 and 74 close. Energization of the winding
24w of the main contactor 24 through master switch contacts 74
closes the contacts 24a and 24b. The winding 32w of the dynamic
braking contactor 32 is energized through the master switch
contacts 71 and opens its normally closed contacts 32a and closes
its normally open contacts 32b, 32c (FIG. 2), and 32d (FIG. 3).
The energization of the winding 41w of the dynamic lowering
contactor 41 through the master switch contacts 69 opens the
contacts 41a and closes the contacts 41b. Closure of the contacts
41b enables the winding 21w of the first hoisting contactor 21 to
be energized and close its contacts 21a. Because the contacts 32b
have been closed, the winding 39w of the second hoisting contactor
39 is also energized and the contacts 39a close. The contacts 39b
are opened to prevent operation of the lowering contactor 28. Until
the winding 76w of the first load sensing relay 76 (FIG. 3) is
energized, the teaser field contactor 36 will not operate.
In this manner, a hoisting circuit is provided for energizing the
armature 11A and the field 11F as a series-connected motor through
a circuit comprising the first AC-DC converter 44, the conductor
45, the overload relay winding 46w, the junction 19, the conductor
17, the first hoisting contacts 21a, the limit switch contacts 15c,
the armature 11A, the limit switch contacts 15d, the second
hoisting contacts 39a, the field 11F, the brake winding 16w, the
main contacts 24a, the overload relay winding 25w, the first shunt
26, the junction 20, and the conductor 47. The teaser field
resistor 37 is connected in parallel with the armature 11A through
the still closed contacts 36a.
During hoisting operation, the motor is energized solely by the
first AC-DC converter 44; the second AC-DC converter 49 does not
operate. Since, as is clear from the diagram of the master switch
58, hoisting operation is stepless, the speed of the motor is
controlled by varying the output voltage of the first AC-DC
converter 44.
When the operating handle of the master switch 58 is moved in a
hoisting direction, a negative output voltage is produced in the
signal converter 79 and transmitted to the reference control
circuit 81 through the conductor 80.
Referring now to FIG. 2, the negative output voltage of the signal
converter 79 is transmitted by the diode 94 and blocked by the
diode 105 so that a negative voltage is applied only to the input
resistor 95 of amplifier 96 and to the hoisting permissive circuit
100. The hoisting permissive circuit 100, in response to the
negative input voltage, transmits fixed negative output voltages to
the input resistor 101 of amplifier 96, to the first firing circuit
88 through the conductor 87, and to the load sensing module 82
through the conductor 84 (see also FIG. 1). The voltage applied to
the first firing circuit 88 by the hoisting permissive circuit 100
acts as a permissive input which unclamps the first firing circuit
88 and permits it to respond to operating input voltage transmitted
through the conductor 86. Since the lowering permissive circuit 106
is not activated during hoisting operation, the second firing
circuit 91 is clamped by the lack of a permissive input so that the
second AC-DC converter 49 remains inactive.
The amplifier 96 produces a positive output voltage which is
proportional to the sum of the input voltages applied to the input
resistors 95 and 101. This output voltage is transmitted through
the conductor 86 to the first firing circuit 88 which, in a manner
well known to those skilled in the art, produces a corresponding
voltage output from the first AC-DC converter 44.
The constant negative biasing input voltage applied to amplifier 96
by the hoisting permissive circuit 100, through the input resistor
101, fixes the minimum output voltage of amplifier 96 and,
accordingly, the minimum output voltage applied to the motor by the
first AC-DC converter 44. Therefore, the input voltage to the
resistor 101 determines the slowest speed at which the motor will
operate and, also, the lightest load 14 which may be floated, i.e.
held motionless by the motor with the brake disengaged. If it is
desired to change the minimum available speed of the motor, or to
float a lighter load 14, the wiper 102w of the minimum hoist
adjusting potentiometer 102 may be adjusted to move the ground
connection either closer to, or further from, the input resistor
101 to alter the biasing voltage applied to the input resistor 101.
Moving the wiper 102w closer to the input resistor 101 lowers its
input voltage and, accordingly, the minimum speed setting of the
motor. Moving the wiper 102w away from the input resistor 101
increases its input voltage.
Although it is desirable to be able to adjust the minimum speed
setting of the motor, this adjustment should not affect the motor
speed obtained at the maximum speed setting of the master switch
58. Therefore, the input resistor 95 is connected to the other side
of the potentiometer 102. When the wiper 102w is moved in a
direction to increase the voltage through the input resistor 101,
it causes a corresponding decrease in the voltage through the input
resistor 95. Conversely, when the wiper 102w is moved in a
direction to decrease the voltage through input resistor 101, it
causes a corresponding increase in voltage through input resistor
95. In this manner, the voltage input through the resistor 95 is
adjusted to compensate, at the maximum speed setting, for the
change in input voltage at the resistor 101. At the minimum speed
setting of the master switch 58, the voltage input through the
resistor 95 is small so there is minimal compensation. However,
when the output voltage of the signal converter 79 calls for full
hoisting speed, the input voltage through the resistor 95 is of
sufficient magnitude to fully compensate for the change in input
voltage through the resistor 101 so that, regardless of the minimum
hoisting speed setting, the maximum hoisting speed remains
substantially the same.
The teaser field resistor 37, as is well known to those skilled in
the art, is a relatively high resistance armature shunt which
prevents a lightly loaded series motor from overspeeding. The
teaser field resistor 37 should be removed from across the armature
11A to reduce heating of the field 11F whenever the load being
hoisted is sufficient to, by itself, prevent overspeeding of the
motor.
Application and removal of the teaser field resistor 37 is
controlled by the load sensing module 82 (FIG. 3). When the motor
is operated in the hoisting mode of operation, the magnitude of the
motor current is dependent upon the torque required to hoist the
load and thus upon the size of the load. Therefore, the load
sensing module 82 can accurately determine the size of the load
being hoisted by the motor by sensing motor current. Motor current
is measured by the first shunt 26 the output of which is fed to the
input resistor 168 of the amplifier 169. This positive voltage
signal is amplified and inverted by the amplifier 169 so that a
negative voltage signal is transmitted by the amplifier 169 to the
input resistor 171 of the amplifier 172.
A positive biasing voltage from the voltage source 177 is applied
to the input resistor 180 of amplifier 172 through the
potentiometer 175. The negative voltage from the reference control
circuit 81 is transmitted through the conductor 84, the conductor
194, the diode 192 and across the potentiometer 191. The transistor
187 has its base connected through the conductor 238, the diode
239, the conductor 234 and the resistor 236 to a source of negative
voltage 237, the transistor 231 being in a non-conducting
condition. The resulting negative biasing of the transistor 187
causes it to conduct and ground the junction 186 so that, of the
resistors 182, 184 and 185, only the resistor 182 functions as an
input resistor for the amplifier 172. The negative voltage across
the potentiometer 191 is transmitted through the conductor 190 to
the input resistor 182.
The negative voltage thus applied to the input resistor 182 is less
than the positive voltage applied to the input resistor 180 so that
a net positive biasing voltage is applied to amplifier 172. As long
as the negative output voltage of amplifier 169 is less than this
net positive biasing voltage, the amplifier 172 will produce a
negative output voltage.
The amplifier 199 is a high gain switching inverting amplifier. If
a positive voltage is applied to the input resistor 197, a negative
output voltage of fixed magnitude is produced, regardless of the
magnitude of the input voltage. Conversely, a negative input
voltage produces a positive output voltage of fixed magnitude.
If the load being hoisted by the motor is too small to cause the
input voltage through resistor 171 to exceed the net positive bias
of the amplifier 172, the negative voltage to the input resistor
197 will cause the amplifier 199 to produce a positive voltage
output signal.
The negative voltage transmitted from the reference control circuit
81 through the conductor 84 is carried by the conductor 194 to the
base of the transistor 195 which is thereby biased into conduction.
This by-passes the resistor 205 so that the output voltage of the
amplifier 199 is applied across a voltage divider comprising only
the resistors 202 and 204.
The amplifier 211 is an integrating amplifier and provides a time
delay for the application of voltage to the base of the transistor
219. The duration of this time delay is dependent upon the
magnitude of the input voltage to the amplifier and the resistance
of the input resistor, the resistor 210 for a positive input
voltage and the resistor 215 for the negative input voltage. The
resistors 210 and 215 are preferably chosen so that the input
resistor 210 provides a time delay which is short in comparison
with that provided by the input resistor 215.
Since the output voltage from amplifier 199 is positive, it is
transmitted through the diode 209 to the input resistor 210. After
a time delay, the amplifier 211 applies a negative output voltage
to the base of the transistor 219. This biasing voltage will not
enable the transistor 219 to turn on. Therefore, its collector, and
accordingly the junction 221, is positively biased by the source of
positive voltage 229 through the resistor 227. The base of the
transistor 231 is also positively biased so that it remains turned
off with its collector maintained at negative voltage as previously
described. Transistors 241 and 243, their bases negatively biased,
will not conduct so that neither the winding 76w of the first load
sensing relay 76 nor the winding 77w of the second load sensing
relay 77 is energized.
Since the contacts 76a (FIG. 1) of the first load sensing relay 76
remain open, the teaser field contactor winding 36w cannot be
energized. Thus, when the motor is hoisting a small load, the
teaser field resistor 37 remains connected across the armature
11A.
If a load greater than a predetermined size is being hoisted by the
motor, the current through the first shunt 26 is of a magnitude
such that the negative output of the amplifier 169 (FIG. 3) exceeds
the net positive biasing voltage input to amplifier 172 and
amplifier 172 produces a positive output voltage. This positive
output voltage, when applied to the input resistor 197 of amplifier
199, switches the output of amplifier 199 to its fixed negative
voltage output. This is applied across the voltage divider, still
comprising only the resistors 202 and 204. The input of the
integrating amplifier 211 is now tapped off the voltage divider
through diode 214 to the input resistor 215.
After the time delay, which is of sufficient duration to prevent
relay activation by current transients, the output of amplifier 211
becomes sufficiently positive to bias transistor 219 into
conduction. The collector of transistor 219, and accordingly the
junction 221, is now grounded thus causing the transistor 231 to
conduct. The collector of the transistor 231 achieves a positive
voltage and turns on transistors 241 and 243. Conduction of
transistor 243 activates the second load sensing relay 77 which has
no effect upon the motor control circuit during hoisting operation.
Conduction of transistor 241 activates the first load sensing relay
76. This causes the winding 36w (FIG. 1) of the teaser field
contactor 36 to be energized resulting in opening of the contacts
36a removing the teaser field resistor 37 from across the armature
11A.
To provide positive, chatter-free operation of the first load
sensing relay 76, a regenerative pulse feedback network comprising
the resistor 227, the capacitor 224 and the input resistor 225 is
utilized in conjunction with the integrating amplifier 211. The
capacitor 224 is connected between the input resistor 225 and the
junction 221. At the moment that the transistor 219 is biased into
conduction so that the junction 221 attains ground potential, a
negative voltage pulse is applied by the capacitor 224 to the input
resistor 225. This provides additional input of short duration to
enhance the output voltage of amplifier 211 and maintain the
conducting condition of the transistor 219 until the unenhanced
output of amplifier 211 has increased to its maximum value.
When the teaser field resistor 37 is removed from across the
armature 11A, there is a decrease in motor current and, as a result
thereof, in the voltage signal amplified and inverted by amplifier
169 and presented to the input resistor 171 of the amplifier 172.
This decrease in negative voltage would cause the circuit to drop
out the first load sensing relay 76 and result in relay
"chattering." Therefore, it is necessary to decrease the
sensitivity of the circuitry after the relay 76 is activated to
prevent reconnection of the teaser field resistor 37.
When the transistor 231 is turned on, its collector becomes
positively biased, as has been previously shown. This positive
voltage is not applied to the base of the transistor 187 because of
the blocking action of the diode 239. This removes the biasing
voltage to the transistor 187 which is thereby turned off. Now, the
series combination of resistors 184 and 185 is functionally
connected in parallel with the resistor 182 and decreases the input
resistance, and accordingly the gain, for the negative voltage
provided by the potentiometer 191. The net positive bias of the
amplifier 172 is thus further reduced and the sensitivity level of
the circuit is lowered. Proper adjustment of the potentiometers 175
and 191 will produce a change in sensitivity which provides proper
compensation for the removal of the teaser field resistor 37 and
permits the circuit to reconnect the teaser field resistor 37 in
response to a decrease in current through the first shunt 26 to a
level below that required for operation without the teaser field
resistor 37.
If the load is decreased during operation of the motor, as when a
load is released or a cable breaks, it is necessary to rapidly
reconnect the teaser field resistor 37 across the armature 11A to
prevent overspeeding of the motor. The decrease in current through
the first shunt 26 corresponding to the decrease in motor load acts
through amplifiers 169 and 172, as previously indicated, to switch
the output of amplifier 199 to full positive voltage. This voltage
is transmitted by the diode 209 to the input resistor 210 which
causes the amplifier 211 to have a time delay of very short
duration (sufficiently short to provide rapid recycling after
transients), after which the output of amplifier 211 decreases to a
level which turns the transistor 219 and, in turn, the transistors
231, 241 and 243 off. The winding 76w is deenergized and the
contacts 76a open (FIG. 1) de-energizing the teaser field contactor
winding 36w causing the contacts 36a to close the reconnect the
teaser field resistor 37 across the armature 11A.
Motion of the operating handle of the master switch 58 (FIG. 1) in
a direction toward the OFF position decreases the output voltage of
the signal converter 79 and, correspondingly, of the reference
control circuit 81 to reduce the direct current output of the AC-DC
converter 44 and decrease the speed of the motor. When the
operating handle reaches the OFF position, master switch contacts
69, 71 and 74 open to de-energize the contactors controlled
thereby. The AC-DC converter 44 is turned off and operating power
is, therefore, removed from the armature 11A and field 11F. No
current now flows through the brake winding 16w and the brake 16 is
thereby set and the motor stops.
When the operating handle of the master switch 58 (FIG. 1) is moved
from the OFF position in a direction calling for lowering operation
of the motor, the master switch contacts 67 open and the master
switch contacts 70 and 74 close to energize the windings 28w and
24w, respectively. Energization of the main contactor winding 24w
closes the contacts 24a and 24b. Energization of the lowering
contactor winding 28w through the now closed hoisting contacts 39b
close the contacts 28a and 28c (FIG. 2) and opens the contacts 28b
to lock out the hoisting circuitry.
For lowering, the motor is shunt connected with the armature 11A
being powered by the first AC-DC converter 44 through a circuit
comprising the first AC-DC converter 44, the overload relay winding
46w, the conductor 45, the junction 19, the conductor 27, the
lowering contacts 28a, the conductor 34, the armature 11A, the
conductor 40, the dynamic lowering contacts 41a, the brake winding
16w, the main contacts 24a, the overload relay winding 25w, the
first shunt 26, the junction 20, and the conductor 47. The dynamic
braking resistor 31 is connected by the dynamic braking contacts
32a across the armature 11A. The limit switch relay winding 30w is
connected in parallel with the armature 11A, as during hoisting
operation, to be energized by the first AC-DC converter 44 and
close contacts 30a and open contacts 30b (see FIG. 2). The relay 30
becomes activated after the speed of the armature 11A has increased
sufficiently to increase the counter emf and permit an adequate
voltage to be applied across the winding 30w to energize it.
The field 11F is energized by the second AC-DC converter 49 through
a circuit comprising the second AC-DC converter 49, the conductor
50, the field 11F, the brake winding 16w, the main contacts 24w,
the overload relay winding 25w, the first shunt 26, the junction
20, the conductor 51 and the second shunt 52. The speed of the now
shunt-connected motor is determined by the voltage applied to the
armature 11A from the first AC-DC converter 44 and the voltage
applied to the field 11F by the second AC-DC converter 49.
When the operating handle of the master switch 58 is moved in a
lowering direction, a positive output voltage is produced by the
signal converter 79 and transmitted to the reference control
circuit 81 through the conductor 80. This positive voltage is
transmitted by the diode 105 (FIG. 2) and blocked by the diode 94
so that it is only applied through the conductor 104 to the
lowering permissive circuit 106, the input resistor 107 of
amplifier 108, the input resistor 109 of amplifier 110, and,
through the conductor 111, to the inputs of amplifier 113.
The lowering permissive circuit 106, in response to the positive
input voltage, transmits a fixed negative voltage output signal to
the first firing circuit 88 through the conductor 87, to the second
firing circuit 91 through the conductor 89, and to the input
resistor 114 of amplifier 113.
Amplifier 108 sums the positive input voltage with a negative
biasing voltage applied to the input resistor 116 from the source
117 and produces a negative output voltage which diminishes in
magnitude as the voltage output of the signal converter 79
increases. This negative voltage is applied to the input resistor
119 of amplifier 120 and summed with a positive biasing voltage
applied to the input resistor 122 from the source 124. Since the
dynamic braking contacts 32c are open, the transistor 129 is turned
off and a biasing voltage from the negative voltage source 157 is
applied to the input resistor 125 of the amplifier 120. This
biasing voltage is sufficient in magnitude to cause the amplifier
120 to produce a positive voltage regardless of the output of
amplifier 108. This positive voltage from amplifier 120 is blocked
by the diode 131 so that, until the dynamic braking contacts 32c
close, the effective output of amplifier 120 is zero.
Amplifier 110 produces a negative output voltage proportional to
its positive input voltage. However, the input to amplifier 110,
and hence its output, is limited because it is connected through
the diode 136 to the voltage limiting circuit comprising the
transistor 137 and the resistor 139. When both the contacts 30b and
32c are open, the potentiometer 141 is connected between a source
of positive voltage 142 and ground through the base-emitter circuit
of the transistor 167. The base of the transistor 137 is thus
maintained at positive voltage which is of a value determined by
the setting of the potentiometer 141 and is in turn applied,
through the base-emitter circuit of the transistor 137, to
reverse-bias the diode 136. Output voltage of the signal converter
79 not exceeding this reverse-biasing voltage, preferably
sufficiently high as not to interfere with motor speed, is applied
to the input resistor 109 of amplifier 110.
If either the contacts 30b or 32c close, the contacts 28c being
closed throughout lowering operation, the negative voltage source
150 is connected, through the diode 146 or the diode 147,
respectively, to the junction 145 and increases the voltage drop
across the potentiometer 141. The voltage at the base and emitter
of the transistor 137 is reduced to a value also determined by the
setting of the potentiometer 141, and the voltage to the input
resistor 109 of amplifier 110 is limited to a value substantially
equal to the emitter voltage of the transistor 137. Thus, when
either the limit switch relay contacts 30b or the dynamic braking
contacts 32c are closed, the negative voltage output of the
amplifier 110 is limited to a value determined by the setting of
the potentiometer 141.
The negative output voltage of amplifier 110 is applied through the
conductor 159, the diode 160 and the conductor 132 to the input
resistor 133 of amplifier 96. Since there are no other voltage
inputs to amplifier 96 during lowering operation, its output
voltage is proportional to this input signal and is applied to the
first firing circuit 88 so that the first AC-DC converter 44
increases the voltage applied to the armature 11A as the operating
handle of the master switch 58 is moved further in the lowering
direction.
Energization of the field 11F is controlled by the output of
amplifier 113. Input voltage to amplifier 113 is supplied by three
sources. A constant negative voltage input is provided by the
lowering permissive circuit 106 to the input resistor 114. A
negative signal, proportional to current through the field 11F, is
transmitted from the second shunt 52 through the conductor 85 to
the inverting amplifier 162 from which a positive voltage is
applied to the input resistor 164 of amplifier 113. This voltage is
a feedback input to help ensure proper energization of the field
11F. The output voltage of the signal converter 79 is transmitted
through the conductor 111 and applied to the input resistor 112 at
the inverting input of amplifier 113 and, through the potentiometer
166, to the non-inverting input of amplifier 113.
When both the dynamic braking contacts 32c and the limit switch
contacts 30b are open, the base of the transistor 167, connected to
the junction 145, is positively biased and the transistor 167 turns
on so that the non-inverting input of amplifier 113 is connected to
ground and the voltage transmitted from the signal converter 79
through the conductor 111 is applied solely to the inverting input.
The fixed negative voltage from the lowering permissive circuit 106
is of sufficient magnitude so that the output voltage of amplifier
113 results in maximum output of the second AC-DC converter 49. In
this manner, maximum energization of the field 11F results to
provide the minimum lowering speed of the motor. As the operating
handle of the master switch 58 is moved further in the lowering
direction, the positive output voltage of the signal converter 79
increases and is combined with the fixed negative voltage of the
lowering permissive circuit 106 to form an output which decreases
the voltage across the field 11F. The input voltage provided by the
second shunt 52 serves as a feedback signal to aid in the
stabilization of the energization of the field 11F. Thus, when the
operating handle of the master switch 58 is moved further in the
lowering direction, the voltage across the armature 11A is
increased while the field 11F is weakened to produce an increase in
motor speed.
The relatively high resistance of the isolation resistor 22 (FIG.
1) permits the armature 11A and the field 11F to be generally
separately energized and controlled while, at the same time, it
maintains an electrical connection between the armature 11A and
field 11F so that a dynamic lowering loop, which also functions to
provide emergency dynamic braking upon power failure, may be
provided. The dynamic lowering loop comprises the armature 11A, the
limit switch contacts 15d, the isolation resistor 22, the field
11F, the conductor 40 and the dynamic lowering contacts 41a.
The dynamic braking resistor 31 (FIG. 1) must be connected across
the armature 11A to maintain slow lowering speeds under heavy load
conditions. However, the dynamic braking resistor 31 is speed
limiting and must, therefore, be disconnected to obtain high speed
operation, leaving only the dynamic lowering loop effective in the
circuit. However, the significant change in speed which may occur
when the dynamic braking resistor 31 is removed from across the
armature 11A is undesirable in many applications of the hoist
control. Therefore, the control circuit of the present invention
provides for the removal of the dynamic braking resistor 31 from
across the armature 11A with no material change in speed,
regardless of the size of the load being lowered. This is
accomplished by selecting a dynamic braking resistor 31 and an
isolation resistor 22 which are of proper ohmic value, removing the
dynamic braking resistor 31 at a predetermined value of motor
current, and adjusting the outputs of the AC-DC converters 44 and
49 to compensate for the change in speed which otherwise would
occur at the moment the dynamic braking resistor 31 is removed.
If the operating handle of the master switch 58 is moved to the
intermediate speed lowering range, the master switch contacts 73
close so that the dynamic braking contactor winding 32w may be
energized through the second load sensing relay contacts 77a and
the limit switch relay contacts 30a. If the limit switch has not
been tripped, the contacts 30a will be closed so that energization
of the winding 32w will be controlled by the condition of the
contacts 77a. In this manner, the disconnecting of the dynamic
braking resistor 31 may be controlled by the load sensing module
82.
The load sensing module 82 removes the dynamic braking resistor 31
from across the armature 11A when a predetermined value of motor
current is detected through the first shunt 26. Because the first
shunt 26 is connected in that portion of the power circuit between
the brake winding 16w and the junction 20, both the armature
current and the field current pass through the first shunt 26 so
that the sum of the currents of the AC-DC converters 44 and 49 are
measured.
As during hoisting, the positive voltage signal from the first
shunt 26 is transmitted through the conductor 83 to the input
resistor 168 of amplifier 169 (FIG. 3) which transmits a negative
voltage signal to the input resistor 171 of amplifier 172.
Amplifier 172 combines this signal with the positive input voltage
from the potentiometer 175. During lowering, input to the hoisting
permissive circuit 100 (FIG. 2) is blocked by the diode 94 so that
there is no voltage signal transmitted along the conductor 84 and
thus no voltage input to amplifier 172 from the potentiometer
191.
As during hoisting operation, until the negative output of
amplifier 169 exceeds the positive biasing voltage, amplifier 172
has a negative output which causes amplifier 199 to produce a fixed
positive output voltage. This voltage, when inverted by amplifier
211, negatively biases the transistor 219 so that the load sensing
relays 76 and 77 are not activated. However, when the negative
output of amplifier 169 exceeds the positive biasing voltage of the
potentiometer 175, the output of amplifier 172 becomes positive and
switches amplifier 199 to its fixed negative output voltage.
Since there is no voltage input from the reference control circuit
81 through the conductor 84, the transistor 195 is not conducting
and, accordingly, the voltage divider across which the output of
amplifier 199 is placed comprises the three resistors 202, 204, and
205 so that a greater voltage is presented to amplifier 211 than
was present during hoisting operation. The increased voltage input
reduces the time delay provided by the integrating amplifier 211 to
an interval which is appropriate for lowering operation. The input
voltage to amplifier 211 is transmitted through the diode 214 to
the input resistor 215 which provides the suitable time delay after
which a sufficient positive biasing voltage is applied to the base
of the transistor 219 to ground its collector which in turn biases
the transistor 231 into conduction and produces a short duration
negative input pulse in the regenerative pulse feedback network, as
previously described.
The conduction of the transistor 231 causes its collector to attain
a positive voltage which biases the transistor 243 into conduction
and energizes the second load sensing relay winding 77w. Transistor
241 is also biased into conduction and energizes the first load
sensing relay winding 76w. However, since the contacts 76a are in
the hoisting portion of the control circuit, operation of this
relay has no effect upon circuit operation during lowering.
When the contacts 77a close (FIG. 1), the dynamic braking contactor
winding 32w is energized opening contacts 32a to remove the dynamic
braking resistor 31 from across the armature 11A and to close the
auxiliary dynamic braking contacts, including the contacts 32d in
the load sensing module 82 (FIG. 3). Because there is a significant
reduction in motor current when the dynamic braking resistor 31 is
removed from across the armature 11A, the contacts 32d complete a
holding circuit for the winding 77w comprising the positive voltage
source 247, the winding 77w, the conductor 249, the contacts 32d
and the negative voltage source 250. This holding circuit maintains
the energized state of the winding 77w regardless of the current
through the first shunt 26 until the dynamic braking contactor
winding 32w is de-energized by manually moving the operating handle
of the master switch 58 to the low speed lowering range thereby
opening the master switch contacts 73.
When the dynamic braking resistor 31 is removed, the output of the
reference control circuit 81 fed to the firing circuits 88 and 91
must be compensated to prevent any material change in lowering
speed.
If the values of the dynamic braking resistor 31 and the isolation
resistor 22 are properly chosen, the speed range of the motor when
lowering with the dynamic braking resistor 31 connected will
overlap the lowering speed range without the dynamic braking
resistor regardless of the load on the motor. Thus, at speeds
within this overlap range, if motor speed is adjusted
simultaneously with the change of operating mode, the dynamic
braking resistor 31 may be disconnected from the circuit without
causing a material change in motor speed. As the motor load is
increased, the corresponding increase in speed resulting when the
dynamic braking resistor 31 is disconnected increases
proportionally with the load. Therefore provision must be made for
decreasing the voltage across the armature 11A by dropping the
output of the reference control circuit 81 to the first firing
circuit 88 and strengthening the field 11F by increasing the output
of the reference control circuit 81 to the second firing circuit 91
in a manner which will prevent the material change in speed which
would otherwise occur.
As has been previously indicated with reference to FIG. 2, for slow
speed positions of the master switch 58, with the dynamic braking
contacts 32c open, the effective output of amplifier 120 is zero so
that only the negative output voltage provided by amplifier 110 is
transmitted to amplifier 96. As the output voltage from the signal
converter 79 increases, the output of amplifier 110 increases
causing a corresponding increase in lowering speed and in motor
current. At a predetermined value of current through the first
shunt 26, the load sensing module 82 activates the second load
sensing relay 77 to disconnect the dynamic braking resistor 31.
Activation of the dynamic braking contactor 32 closes contacts 32c
and increases the voltage drop across the potentiometer 141 which
clamps the voltage applied to the input resistor 109 of amplifier
110. The corresponding decrease in output of amplifier 110, applied
through amplifier 96 to the first firing circuit 88, decreases the
voltage across the armature 11A. The closing of the contacts 32c
also turns off transistor 167 allowing the output voltage from the
signal converter 79 to be applied through the potentiometer 166 to
the non-inverting input of amplifier 113. This partially negates
the effect of the signal applied to the input resistor 112, to an
extent determined by the setting of the potentiometer 166, and
increases the output of amplifier 113 to the second firing circuit
91 to increase the voltage across the field 11F. Without any other
change in the motor circuit, these voltage changes would cause the
speed of the motor to decrease. However, if the potentiometers 141
and 166 are properly adjusted, the changes in the voltages of the
armature 11A and field 11F will just compensate for the increase in
speed which would have otherwise resulted from the removal of the
dynamic braking resistor 31 from across the armature 11A.
If the motor is operating with a load on the hook, there will be an
increase in counter emf of the motor so that the current through
the first shunt 26 will not reach the value necessary to operate
the load sensing module 82 until the motor has attained a greater
speed than with an empty hook. This requires an increased output of
the signal converter 79. Thus, the output voltage of amplifier 110
will have increased and the output voltage of amplifier 113 will
have decreased beyond their empty hook values before the contacts
32c close to adjust their outputs. The increase in effect on the
output of the AC-DC converters 44 and 49 as the load 14 is
increased just compensates for the increase in effect on motor
speed with load 14 caused by removal of the dynamic braking
resistor 31.
Operation of the reference control circuit 81 during automatic
transfer from dynamic braking to dynamic lowering mode may be more
clearly understood with reference to the graphs of FIGS. 4-9.
Operation of amplifier 110 is illustrated by the graphs of FIGS. 4
and 5, each of which is a graph of the output of amplifier 110
(A-110 on the graph) versus the output of the signal converter 79
(S/C on the graph). Points a and b indicate, respectively, the
minimum and maximum outputs of the signal converter 79 for which
automatic mode transfer can be provided. Point c represents maximum
output of the signal converter 79 during lowering operation. Point
d represents the clamped value of output voltage of amplifier 110
after the dynamic braking contacts 32c close. As can be seen in
FIG. 4, which illustrates empty hook operation, when the output of
the signal converter 79 reaches the minimum transfer point a, the
output of amplifier 110 is decreased by a small amount to the
clamped level d at which it remains for all higher values of signal
converter 79 output.
FIG. 5 illustrates operation of amplifier 110 during lowering
operation with a load on the hook. When the output of the signal
converter 79 reaches the value indicated at a, the current through
the first shunt 26, due to increased counter emf in the motor, is
not sufficient to trigger operation of the load sensing module 82.
Therefore, the output of the signal converter 79 must be increased
beyond the point a, correspondingly increasing the output of
amplifier 110. When the current through the first shunt 26 is
sufficient to trigger the load sensing module 82, the output of
amplifier 110 is diminished to the value indicated at d and held at
that value for all greater outputs of the signal converter 79.
Although in certain applications of the crane control circuit of
the present invention, it would be possible to match the speeds
during automatic mode transfer solely through an adjustment of the
voltage across the armature 11A, generally the voltage across the
field 11F must be increased to properly match the dynamic lowering
and dynamic braking mode speeds. FIGS. 8 and 9 are graphs of output
of amplifier 113 (A-113 on the graph) versus signal converter 79
output. FIG. 8 illustrates empty hook operation corresponding to
that illustrated in FIG. 4 for amplifier 110. As signal converter
79 output increases, the output of amplifier 113 decreases along
the curve 252 weakening the field 11F. At the minimum transfer
point a, upon operation of the load sensing module 82, the signal
converter 79 output applied to the non-inverting input of amplifier
113 boosts the output of amplifier 113 to the field weakening curve
254 and thereby increases the voltage across the field 11F to a
magnitude which will provide no material change in speed during
mode transfer.
FIG. 9 illustrates operation of amplifier 113 during lowering
operation with a load on the hook and corresponds to the operation
of amplifier 110 illustrated in FIG. 5. When the current through
the first shunt 26 reaches the value necessary for transfer, the
output of amplifier 113 has decreased to less than that illustrated
in FIG. 8 due to the increase in output voltage of the signal
converter 79. At transfer, this increased signal converter voltage
is applied, through the potentiometer 166, to the non-inverting
input of amplifier 113 so that the field is strengthened by a
proportional amount to a corresponding point on the field weakening
curve 254.
When the dynamic braking contacts 32c close, the transistor 129 is
biased into conduction so that the negative biasing input is
connected to ground and not applied to amplifier 120. Now the only
inputs to amplifier 120 are the fixed biasing voltage from the
positive voltage source 124 and the negative output voltage of
amplifier 108. Since the negative output voltage of amplifier 108
decreases in magnitude as signal converter 79 output increases, the
combined input voltage causes amplifier 120 to produce a negative
voltage output which increases in magnitude with increasing output
of the signal converter 79.
The outputs of amplifiers 110 and 120 are transmitted, through
diodes 160 and 131, respectively, so that only the negative output
signal having the greatest magnitude is transmitted to amplifier
96. FIG. 6 illustrates the output of amplifier 120 (A-120 on the
graph) plotted against the output of the signal converter 79. Until
contacts 32c close, amplifier 120 has a positive output which may
be of any magnitude and which is blocked by the diode 131 yielding
an effective zero output. When the contacts 32c close, a negative
output voltage is produced by amplifier 120 but cannot be
transmitted through the diode 131 because this output voltage does
not exceed that of amplifier 110, which is clamped at the indicated
point d, until the output voltage of the signal converter 79
exceeds the value indicated at b. Thus, the output voltage provided
by the combined outputs of amplifier 110 and amplifier 120 through
diode 160 and diode 131, respectively, and transmitted to the
amplifier 96 generally follows the curve indicated in FIG. 7, a
plot of the input to amplifier 96 (A-96) versus the output of the
signal converter 79. The voltage applied to the armature 11A during
lowering operation of the motor is generally proportional to the
input to the amplifier 96 and therefore, also follows the curve of
FIG. 7.
Excitation of the field 11F, as has been previously indicated, is
controlled by the output of amplifier 113. Before the contacts 32c
close, the output of amplifier 113 is diminished at a rate
illustrated by the curve 252 in FIG. 9. However, after the dynamic
braking resistor 131 has been disconnected and the transistor 167
has been turned off, signal converter 79 output voltage applied to
the non-inverting input of amplifier 113 shifts its output to the
curve 254 in FIG. 9. In this manner, proper field weakening is
provided throughout the lowering range of the motor.
If it is desired to rapidly obtain high speed lowering for the
motor wherein the change in speed resulting from removal of the
dynamic braking resistor 31 is not important, the operating handle
of the master switch 58 may be moved in the lowering direction
until the master switch contacts 72 close. This completes an
energizing circuit for the winding 32w which bypasses the second
load sensing relay contacts 77a so that the dynamic braking
resistor 31 is instantly removed from across the armature 11A, as
long as the limit switch relay contacts 31a are closed.
As the operating handle of the master switch 58 is moved in a
direction toward the OFF position, the output of the signal
converter 79 decreases. This decreases the voltage across the
armature 11A and strengthens the field 11F. When the operating
handle reaches the low speed lowering range, the contacts 73 open
and the dynamic braking resistor 31 is reconnected across the
armature 11A. The dynamic braking contacts 32c (FIG. 2) now open so
that the voltage across the armature 11A is now controlled by the
output of amplifier 110 and the energization of the field 11F now
follows the curve 252 in FIG. 8. When the master switch is placed
in the OFF position, the contacts 70 and 74 open and the AC-DC
converters 44 and 49 are turned off so that the armature 11A and
field 11F are de-energized. No current flows now through the brake
winding 16w and the brake 16 is set. In this manner, the motor is
stopped.
If, during hoisting operation of the motor, the load 14 is hoisted
a sufficient distance to trip the power limit switch 15, contacts
15a and 15b close and contacts 15c and 15d open. Contacts 15c and
15d, located in the hoisting power circuit, disconnect operating
voltage from the armature 11A and field 11F. At the same time a
dynamic braking loop for stopping the armature is formed comprising
the armature 11A, the conductor 40, the conductor 42, the limit
switch contacts 15a, the second hoisting contacts 39a, the field
11F, the conductor 27, the limit switch resistor 29, the limit
switch contacts 15b and the conductor 34. Tripping of the limit
switch 15 removes energizing voltage from the limit switch relay
winding 30w so that the contacts 30a are open and the auxiliary
contacts 30b (FIG. 2) are closed until the limit switch 15 is
reset.
During lowering operation with the limit switch 15 tripped, the
armature 11A and field 11F are energized through the same circuit
as without the limit switch 15 tripped since the energizing
circuits do not include the limit switch contacts 15c and 15d. The
dynamic braking resistor 31 is connected across the armature 11A.
Since the limit switch relay contacts 30a in the master switch 58
are open, the dynamic braking relay winding 32w cannot be energized
while lowering with the limit switch 15 tripped so that the dynamic
braking resistor 31 cannot be removed from across the armature 11A
until the limit switch has reset.
The closing of the limit switch relay contacts 30b (FIG. 2) clamps
the output of amplifier 110 without unclamping the output of
amplifier 120. Since the dynamic braking contacts 32c cannot be
closed until the limit switch has reset, the output of amplifier
120 remains clamped and the motor can only be lowered in its low
speed range, regardless of the output of the signal converter
79.
When the limit switch 15 resets, the limit switch relay 30 is
activated and normal operation of the reference control circuit 81
is restored.
It should be understood that for certain applications of the
circuits of the present invention it may be possible to match
speeds during automatic mode transfer without strengthening the
field 11F at the transfer point. The reference control circuit is
readily adaptable for operation in this manner by adjusting the
potentiometer 161 to connect the non-inverting input of amplifier
113 to ground.
If it is desired, the reference control circuit 81 may be provided
with a current limiting circuit, as is well known in the art, to
limit current from the first AC-DC converter 44. A control signal
may be provided by a shunt connected between the junction 20 and
the first AC-DC converter 44, in which case the first shunt 26 may
be eliminated. The signal for operating the load sensing module 82
may then be obtained by combining the outputs of the two
shunts.
Although the control system of this invention has been disclosed
for use as a hoist control, it is useable in any motor control
system wherein the force of the load opposes armature rotation in
one direction of rotation of the armature 11A (non-overhauling
load) and assists armature rotation in the other direction of
rotation of the armature 11A (generally an overhauling load).
* * * * *