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‘Oct. 29, 1946.
D. E.'G'ARR
2,410,233
SCREWDOWN CONTROL SYSTEM
Filed Aprii 24, 1945
I
3 Sheets-Sheet 1
Inventcr“: _
Donald E. Ga r‘,
b‘y
5%?
.
>
. is Attorney
Oct. 29, 1946.
D. E. GARR
2,410,283
SCREWDOWN CONTROL SYSTEM
"Filed April 24, 1945-
3 Sheets-Sheet 2
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l_________. __________-________|
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5 . MN
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Inventor‘: '
Donald E. Gaff;
. by ywazwéq
.His Attorney
- Oct. 29, 1946.
D. E. GARR
' '"SCREWDOWN
CONTROL
‘
SYSTEM '
_
Filed April 24,» 1945
.
2,410,283
s Sheets-Sheet a
Fig. 2.
.
{(lZ
FIE
Inventor":
Donald E. (Barr,
4348 '?éttovney.
Patented Oct. 29, 1946
2,410,283
UNITED STATES PATENT OFFICE
2,410,283
SCREW-DOWN CONTROL SYSTEM
Donald E. Garr, Schenectady, N. Y., assignor to
General Electric Company, a corporation of
New York
Application April 24, 1945, Serial No. 589,972
14 Claims.
1
This invention relates to control systems, more
(Cl. 80-56)
2
The exciter dynamo-electric machine is pro
particularly to control systems for rolling mill
vided with a control ?eld Winding which is excited
screwdown apparatus and it has for an object the
in response to the difference between a reference
provision of a simple, reliable and improved con
voltage and a control voltage derived from the
trol system of this character.
armature current of the screwdown drive motor.
More speci?cally, the invention relates to con
Means are provided for reducing the reference
trol systems in which means are provided for pre
voltage to a very low value when the movable roll
setting a plurality of consecutive roll openings,
is brought to rest in a position corresponding to
and a. further object of the invention is the pro
the preset position for which the roll opening se
vision of means for effecting a rapid and highly 10 lector unit is adjusted.
accurate positioning of the screws at the preset
An additional feature is the excitation of the
positions in response to simple, manual move
control ?eld winding in response to the difference
ments of a pilot device such as a pushbutton.
Another object of the invention is the provision
between a second reference voltage and a control
voltage derived from the ?eld excitation current
of a new and improved means for preventing 15 of the adjustable voltage generator together with
overshooting in moving one of the rolls to the cor
means for varying this second reference voltage
rect position for a selected roll opening.
in response to the difference between the preset
Another object is the provision of a control sys
position of the mill roll and its actual instan
tem of the character described in which the ?nal
taneous position.
movement of approach of the movable roll to the
For a better and more complete understanding
correct position for a roll opening is always in the
of the invention, reference should now be had to
same direction regardless of whether the opening
the following speci?cation and the accompanying
is being increased or decreased.
drawings of which Fig. 1 is a simple, diagrammati
Another object of the invention is the provision
cal illustration of the embodiment of the inven
of a system of this character in which provision 25 tion, and Fig. 2 is a simple, diagrammatical illus
is made for compensating for variations in the
tration of a detail.
diameters of the rolls such as are caused by grind
Referring now to the drawings, the lower roll I
ing the rolls.
of a rolling mill is journalled for rotation in up
Still another object of the invention is the pro
rights 2 and 3 of the housing (not shown) of a
vision of means for causing sufficient current to
rolling mill. An upper roll 4 is journalled in
circulate in the motor armature circuit after the
movable screw blocks 5 and 6 which are in
movable roll has come to rest in a correct position
to maintain pressure on the roll in the same di
rection as the ?nal movement of approach.
In carrying the invention into effect in one form
threaded engagement with screws 1 and 8 to pro
vide for moving the roll 4 with respect to the lower
roll I to vary‘ the opening between the rolls.
These screws 1 and 8 are driven by any suitable
thereof, the screwdown driving motor is supplied
driving means such, for example, as the direct
from an adjustable voltage generator. The sup
current electric motor 9 to the drive shaft of
ply of current to the motor is controlled by means
which the screws are connected through suitable
of an exciter dynamo-electric motor machine of
reduction Worm gearing l0 and H respectively.
which the excitation is controlled in response to 40 The upper roll 4 is to be moved to a plurality
the difference in position between a preselected
of preselected positions to provide a plurality of
position and the actual instantaneous position
roll openings. The movement of the roll 4 is under
of the movable roll. For presetting the roll open
the control of suitable roll opening selector means
ings, a roll opening selector means is provided.
I2 comprising a plurality of roll opening selector
This means is preferably a synchronous type of
units, one for each pass. These units are under
signal transmission system comprising a, plurality
the control of a pass selector l3 which has a plu
of units for presettinor a succession of roll open
rality of positions corresponding to the number
ings, and a unit connected with the screwdown
of roll opening selector units. In each position
mechanism for comparing the position of the roll
of the pass selector, a different roll opening se
with the preset positions for which the selector '
lector is brought into action.
Operatively associated with the screwdown
mechanism is a signal unit H which cooperates
units are adjusted. The di?erence in position of
the preset unit and the unit connected to the
screwdown mechanism is utilized to supply a sig
with the roll opening selector units to produce a
nal voltage which may be ampli?ed by suitable
amplifying means.
difference between the preselected position of the
signal voltage which serves as a detector of the
2,410,283
3
roll 4 and its actual position. This signal voltage
is ampli?ed by a suitable electric type valve am
pli?er I5. The output voltage of the ampli?er is
utilized to control the excitation of an exciter
dynamo-electric machine 16 which in turn con
trols the excitation of a generator I‘! from which
the screwdown drive motor 9 is supplied. The
generator supplies a voltage which causes the
4
accordance with the voltage drop across the re
sistors 21 and 26 respectively, which voltage drops
are proportional to the currents flowing in the
output circuits of the valves. The cathode grid
circuits of the valves 19 and 20 extend through
an adjustable self-biasing resistor 28 to the nega
tive bus 22 and thus the grids of these valves
are given a negative bias.
A twin triode electric valve 29 constitutes the
motor to move the movable roll to the position
10 ?rst stage of the ampli?er 15. It has a pair of
preselected on the roll Opening selector unit.
conducting paths for controlling the grid voltage
The motor 9 is provided with a ?eld winding
of the valves is and 2D. The anode-cathode or
9a which is supplied from any suitable source
output circuit of the valve 29 is connected across
of direct voltage. As shown, the armature of
the secondary winding 30a of a transformer 30
the motor 9 is connected in a loop circuit with
the armature of the supply generator l1. This 15 of which the primary winding 30b is supplied
from a suitable source of alternating voltage
generator is driven at a speed which is preferably
which may be and preferably is the source 23.
substantially constant by any suitable driving
As shown, the anodes ‘29a and 291) are connected
means such as the induction motor 18. The gen
through resistors 3| and 32 respectively and
erator is provided with a ?eld winding Ila which
through the opposite halves of an adjustable
is connected to the load circuit brushes [6a of
equalizing resistor 33 to one terminal of the
the exciter dynamo-electric machine [6. Since
secondary winding 30a and the common cathode
the generator I‘! is driven at a substantially con
we is connected through an adjustable biasing
stant speed, its voltage varies in accordance with
resistor 34 to the opposite terminal of the sec
the excitation of its ?eld winding.
The exciter I6 is a special cross-armature ex 25 ondary winding 3611. Since the valve 29 has
two anodes, it has two conducting paths and the
cited dynamo-electric machine. In addition to
currents in these paths are controllable by con
its load brushes I6a it has a pair of short-cir
trolling the voltages applied to the two control
cuited armature brushes lBb which are arranged
grids 2% and 29e. The grid 29d controls the
on an axis at right angles to the axis of the
load brushes. The exciter I6 is driven at a 30 flow of current in the path between the anode
‘29a and the cathode, and the grid 296 controls
speed which is preferably constant by any suit
the conductivity in the path between the anode
able driving means (not shown). The axis of
29b and the cathode. The cathode grid circuit
the ?ux which is produced by the short-circuited
for the left-hand conducting path of the valve
armature brushes l6b is referred to as the “short
extends from the cathode through the biasing
circuit axis” and the axis which is displaced 9!]
resistor 35%, the upper half 35a of a resistor, and
electrical degrees from the short-circuit axis is
the secondary winding 36a of a transformer 36
referred to as the “control axis.” The net ?ux
and resistors 31 and 38 to the grid 29d. Similar
along the control axis is produced by two oppos~
ly, the cathode grid circuit for the right-hand
ing directional reference ?eld windings I60 and
Mid, a series compensating ?eld winding lite, and 40 conducting path of the valve extends from the
cathode through the biasing resistor 34 and the
a control ?eld winding IS)‘. The flux along the
lower half 35b of a resistor and a secondary
short-circuit axis on the machine is produced
winding 38?) of transformer 36, and resistors 39
by the armature reaction of the short-circuit
and lit} to the grid 296. The voltages of the grids
current. This short-circuit axis ?ux generates
the voltage which appears across the load axis .1, 29d and 29c with respect to the voltage of the
cathode 290, as a result of the inclusion of the
l6a, and the control axis ?ux produces the volt
biasing resistor 34 in the anode-cathode circuit,
age which appears across the short-circuit
are such that both paths of the valve normally
brushes [6b and causes short-circuit current to
conduct equal amounts of current. This con
?ow. Two important characteristics of the ma
chine l6 are its extremely high speed of response in) dition of equal conduction in both paths of the
valve 29 occurs when the active roll opening
and its high ampli?cation factor, i. e., the ratio
selector unit is in correspondence with the mill
between the watts input to the directional ?eld
roll signalling unit it, i. e., when the movable
windings I60 and 16d to the watts of the load
roll ll is in the selected position to which the
circuit. This ampli?cation factor may be as
When equal
' active selector unit is adjusted.
high as 25,000z1.
amounts of current are ?owing through both
The directional ?eld windings 16c and ltd are
paths of the valve 29, the voltage drops across
connected in the output circuits of the electric
the resistors 3| and 32‘. are equal and these volt
valves l9 and 20 which constitute the second
age drops combined, with the voltage drop across
stage of the ampli?er l5. The output circuits of
these valves l9 and 20 are connected across a Gil the resistor 28 bias the voltages of the grids of
valves #9 and 20 with respect to their cathodes so
suitable source of direct voltage such as repre
that these valves also conduct equal amounts of
sented by the positive and negative buses 2| and
current. The equal currents conducted by the
22. This direct voltage may be obtained from a
valves l9 and .29 produce voltage drops across the
source of alternating voltage 23 by means of an
resistors 26 and 21 which excite the control ?eld
electric type valve recti?er 24. The ripple is
windings I60 and Hid of the exciter dynamo
removed from the recti?ed voltage by means of
electric machine l6. However, since the control
a suitable ?lter illustrated as comprising a series
?eld windings Hid and IE6 act in opposition to
reactor 25 and a shunt capacitor 25a. A voltage
each other, the net exciting flux along the control
drop resistor 26 is included in the output circuit
axis of the machine I6 is zero. It will thus be
of the valve l9 and a similar resistor 21 is in
clear from the foregoing that when the movable
cluded in the output circuit of the valve 20. The
roll it is in a position corresponding to the posi
directional ?eld winding [6c is connected across
tion to which the active selector unit is adjusted,
the resistor 21 and the directional ?eld winding
equal amounts of current ?ow through both
l6d is connected across the resistor‘ 26. Thus
the ?eld windings [6c and IM are excited. in
paths of the valve 29 and, likewise, equal amounts
5
2,410,283 a
of current ?ow in valves l9 and 20 with the result
that the terminal output voltage of the exciter
I6 is zero.
The signal voltages are supplied to the grids
29d and 29e of the valve 29 from the active roll
opening selector units |2 through the transformer
36 of which the secondary windings 36a and 36b
are connected in the cathode grid circuits of the
valve 29, as explained in the foregoing, and whose ,
primary winding is connected to the active roll
opening selector unit.
Each roll opening selector unit comprises two
6
member 4|a is said to be in correspondence with
the rotor member 45a of the Selsyn 45. _ When
the axis of the rotor Winding of the Selsyn 4| is
parallel to the axis of the alternating magnetic
?eld produced by the currents in the stator wind
ing, the voltage induced in .the rotor winding is a
maximum. For intermediate positions of the axis
of the rotor winding with respect to the axis of
the alternating magnetic ?eld, the induced volt
age has corresponding intermediate values.
The axis of the magnetic ?eld of the Selsyn 4|
can be shifted by rotating the rotor member 49a
rotary induction devices of which one provides a
of the differential Selsyn 49 with respect to the
coarse control and the other provides a ?ne or
stator member 49b, thereby to vary the angle be
Vernier control. The unit for the ?rst pass com 15 tween the axis of the magnetic ?eld produced by
prises the two rotary induction devices 4| and 42
currents ?owing in the stator winding of the
and the unit for the last pass comprises the in
Selsyns 49b with respect to the axes of the wind
duction devices 43 and 44. Since the selector
ing elements on the rotor member 49a.
'
units for all passes are identical, only the units
The Selsyns 42 and 46 are in all respects iden
for the ?rst and last passes are illustrated and
tical with the Selsyns 4| and 45, and the di?eren
only the unit for the ?rst pass is described in
tial Selsyn 50 is in all respects identical with the
detail.
differential Selsyn 49. The rotor member of the
The device 4| of the ?rst selector unit furnishes
Selsyn 42 is connected to the rotor member of the
the coarse control and the device 42 furnishes the
Selsyn 4| through gearing 5| which may have any
?ne control. Similarly the device 43 of the ?nal
suitable ratio such, for example, as 35:1. Simi
pass selector unit furnishes the coarse control
larly, the rotor members of the Selsyns 45 and 46
and the device 44 furnishes the ?ne control. The
and the rotor members of the differential Selsyns
rotary induction device 4| comprises a rotor
49 and 50 are connected together by means of
member 4| a which is provided with a single phase
gearings 52 and 53 having the same ratio of 35:1.
winding (not shown) and a stator member 4| 1)
The rotor members of the Selsyns 45 and 46 are
provided with a distributed 3~element winding
connected to the screws 1 and 8 through gearing
(not shown) which is physically similar to the
54 of which the ratio is such that the rotor mem
3-phase winding of an ordinary wound rotor in
ber 45 rotates through an angle which is some
duction motor. The stator and rotor windings
what less than 360 degrees, e. g., 267 degrees when
are arranged in inductive relationship with each 35 the roll 4 is moved from its zero position to its
other. This device is known to the art as a Selsyn.
The device 42 is in all respects identical with the
maximum opening position.
single-phase winding on the rotor member of the
45 the rotor member 46a of the Selsyn 46 is ro
tated a full 360 degrees. However, since the axes
of the rotor winding of the Selsyn 42 and the
magnetic ?eld of the stator winding are parallel
at two points in each. complete revolution of the
rotor 46a of the Selsyn 45, i. e., at zero degrees
rotation and at 180 degrees rotation, it will be
clear that the rotors 46a and 42a must not be
allowed to become more than 180 degrees out of
The high ratio of the gearing, i. e. 35: 1, between
device 4|.
the Vernier control Selsyns and the coarse con
The signal unit M which is connected with the
trol Selsyns produces an extremely high degree
screwdown mechanism comprises two Selsyns 45 40 of accuracy and sensitivity of the control. If
and 46 of which the Selsyn 45 cooperates with the
the ratio is 35:1 as assumed, then for each move_
coarse control Selsyn 4| and the Selsyn 46 co
ment of the roll 4 which produces 102/1 degrees
operates with the Vernier control Selsyn 42. The
of rotation of the rotor member 4511 of the Selsyn
Selsyn 45 is supplied with alternating voltage
from a suitable source which is preferably the
source 23 from which the ?rst stage valve 29 of
the ampli?er I5 is supplied. The corresponding
terminals of the 3-phase stator windings of the
Selsyns 4| and 45 are connected together by elec
trical connections 41 and, similarly, the corre
sponding terminals of the stator windings of the
Selsyns 42 and 46, are connected together by
correspondence with each other, because when
means of electrical connections 48.
this amount of positional disagreement occurs,
For the ‘purpose of compensating for variations 55 the same electrical relationship exists between
in the diameters of the mill rolls resulting from
the rotor windings as exists when the rotors are
grinding, differential electrical devices 49 and 50
in correspondence with each other. Before this
are included in the connections 41 and 48 respec
amount of positional disagreement is exceeded
tively. The device 49 has a rotor member 49a
the control is taken over by the coarse control
which is provided with a distributed 3-element 60 systems comprising the Selsyns 45 and 4|,
winding (not shown) and the stator member 491)
From the foregoing it is seen that when the
is provided with a similar distributed 3-element
rotor member 42a of the Selsyn 42 is not in cor
winding (not shown).
respondence with the rotor member 46a of the
The excitation of the single-phase winding on
Selsyn 46, a voltage is supplied to the grid cir
the rotor of the Selsyn 45 produces an alternat 65 cuit of the ampli?er I5 which in turn results in
ing magnetic ?eld which induces voltages in the
a variation. in the relationship of the currents
elements of the stator winding. These induced
flowing in the conducting paths of the valve 29.
voltages cause currents to ?ow in the stator wind
The grid connections to the electric valve 29 are
ing of the Selsyn 4|, thereby producing an alter
so made, that when the voltage applied to one of
nating magnetic ?eld similar to the magnetic ?eld
the
grids is increased, the voltage applied to the
produced by current flowing in the rotor winding
other grid is simultaneously decreased and, con
of the Selsyn 45. When the axis of the rotor
sequently, when the current through one of the
winding of the Selsyn 4| is at right anglesto the
conducting
paths is increased, the current
axis of the alternating magnetic ?eld, zero voltage
through the other conducting path is simulta
is induced in the rotor winding and the rotor 75 neously decreased.
I
2,410,288
7
In order that the coarse control Selsyns may
take over the control from the Vernier Selsyns
before the positional disagreement of the rotors
of the Selsyns 42 and 46 exceeds 180 degrees, the
single-phase rotor winding of the coarse Selsyn
4| is connected to the terminals of the primary
winding 55a of a transformer 55 of which the
terminals of the secondary winding 551) are con
8
each of the operating coils is connected to a cor
responding stationary contact of the pass selector
switch, e. g., that of the coil 590 is connected to
the first contact in the counterclockwise direction
and that of the coil 590 is connected to the 13th
contact.
As pointed out in the foregoing, a roll open
ing selector unit similar to the unit 4 i, 42 is pro
vided for each pass. These additional selector
nected to the grids 29d and 29a through electric
units are connected in parallel with the unit 4|,
10
valves 55 and 51. The midpoint of the secondary
42 as indicated by the open-ended parallel con
winding 55!) is connected to the midpoint of the
nections shown in the drawings and designated
resistor 35a, 3573. Thus, it will be seen that the
“other units.” For each of these additional units
Selsyns 4| and 45 constitute a low speed system
there is provided an electromagnetic switch simi—
and provide the desired coarse control.
lar to the switch 58 having normally open con
The electric valves 55 and 51 may be of any 15 tacts in the connections from its associated roll
suitable type but are preferably of the two elec
opening selector unit to the input of the am—
trode type into the envelopes of which a small
pli?er l5 and having an operating coil of which
quantity of inert gas such, for example, as neon
one terminal is connected to one terminal of the
is introduced after exhaust. A characteristic of
recti?er 64 and the other terminal is connected
20
a valve of this character is that when a voltage
to a corresponding stationary contact of the pass
of less than a predetermined critical value is ap~
selector switch.
plied to its terminals, the valve does not conduct
The current limit control ?eld winding 15]‘ of
current and when this critical voltage is exceeded,
the exciter dynamo~e1ectric machine It is ex
the neon gas becomes ionized and the valve be
cited in response to the difference between a ref25
comes conducting.
erence voltage and a voltage derived from the
The transformer 55 is so designed that when
current which ?ows in the armature circuit of
the positional disagreement of the Selsyns 4i and
the drive motor 9. This reference voltage is pro
45 is less than a predetermined amount, e. g. 5
vided by means of a resistor 65 which is con
degrees or less, the voltage applied to valves 56
nected across a source of substantially constant
and '51 is less than the critical ionization or
direct voltage such as the recti?er B6. The re
breakdown voltage of these valves, but equals or
sistor 65 has a center tap 65a which is connected
exceeds the critical voltage when the positional
to one terminal of the current limit control ?eld
disagreement equals or exceeds this predeter
winding IS)‘. The opposite terminals of the ref
mined amount. Thus, when the positional dis
erence voltage resistor 65 are connected through
35
agreement is less than the predetermined
reversely connected recti?ers E1 and 68 to one
amount, the control connections between the
terminal of a voltage dropping resistor 59 which
coarse control system and the grids of valve 29
are interrupted and the coarse control system is
ineffective, and when the disagreement equals
is connected in the armature circuit of the drive
motor 9. The opposite terminal of the ?eld
winding I6)‘ is connected to the opposite terminal
or exceeds this amount, the valves 56 and 51 be 40 of the resistor 69 by means of a conductor 10.
come conducting and the voltage induced in the
As a result of the inclusion of the recti?ers 61
secondary winding of the transformer 55 is ap
and 68 in the connections, one half of the re
plied to the grids of the valve 29 and is therefore
sistor 65 provides the reference voltage when the
effective in controlling the valve. The resistors
current flow in the armature circuit is in one
31 and 39 have very high ohmic values and there
direction and the other half provides the refer
fore assist the valves 56 and 51 in transferring
ence voltage for current ?ow in the opposite di
the control from the ?ne control Selsyns to the
rection. The voltage drop across the resistor 59
coarse control Selsyns when the positional dis
is a measure of the current ?owing in the arma
agreement equals or exceeds the predetermined
ture circuit of the motor. When the voltage drop
amounts mentioned in the foregoing description.
across the resistor 69 is less than the voltage drop
For the purpose of transferring the control of
across the active half of the resistor 65, no cur
the screwdown motor from one roll opening se
rent flows in the ?eld winding I61‘ and no cur
lector unit to another, a plurality of switching
rent-limiting action takes place. On the other
devices such as the electromagnetic switches 58
hand,
when the voltage drop across the resistor
and 59 are provided. These switching devices are 55 69 exceeds the reference voltage across the active
under the control of the pass selector switch 13.
half of the resistor 65, current flows in the ?eld
The switching device 58 has normally open con
winding I67‘. The magnitude of this current de
tacts 58a and 58b in the connections 69 and BI
pends upon the difference between the voltage
respectively between the input to the ampli?er
drop across the resistor 69 and the reference volt
l5 and the rotor windings of the Selsyns 4| and 60 age of the active half of the resistor 65. The
42 which constitute the roll opening selector unit
current in the field winding 15]‘ ?ows in such a
for the ?rst pass. Similarly, the switch 59 has
direction that the ?ux of the ?eld winding l?f
normally open contacts 59a and 59b in the con
opposes the ?ux of whichever of the directional
nections 62 and 53 respectively between the input
control ?eld windings [Be or Hid is predominate
to the ampli?er and the rotor windings of the
ly energized. As a result of this differential ac
Selsyns 43 and 44 which constitute the roll open
tion of the ?eld winding 16]‘, the current flowing
ing selector unit for the last pass, which in the
in the armature of the motor 9 is limited to a pre
apparatus illustrated is the 13th pass.
determined value of which the magnitude corre
These switches 58 and 59 have operating coils
58c and 59c respectively. One terminal of each 70 sponds to the magnitude of the reference volt
age of the resistor 55.
of these operating coils is connected to one ter
When the drive motor 9 is at rest with the
minal of a source of direct Voltage such as the
mill roll 4 in a position corresponding to a se
recti?er 64 of which the other terminal is con
lected roll opening, a small amount of current
nected to the movable contact arm I3a of the
is caused to circulate in the armature circuit of
pass selector switch [3. The other terminal or
2,410,283
the motor in such a direction as to maintain a
downward force on the roll 4. In order that this
circulating current may not overheat the motor,
it is limited to a very low value.
For this purpose
a relay ‘H is provided which has normally closed
contracts 1 la in the connection between the mid
point 65a of the reference voltage resistor and
the terminal of the voltage dropping resistor 69
to which the resistor 65 is connected through rec
ti?ers 61 and 68. The relay H is provided with l0
an operating coil ‘llb which is supplied from a
tachometer generator 12 to' the terminals of
10
cuit the voltage drop across the resistor 18 is com
pared with the voltage drop across the opposite
half of the reference voltage resistor and the dif
ference is applied to the current limit ?eld Wind
ing I61‘.
'
For the purpose of varying the reference volt
ages the reactance winding 8Ia of a saturable
core reactor is connected in circuit between the
source 16 and the recti?er 15 from which the
reference voltage resistor 14 is supplied. As
shown,'it is connected in circuit with the primary
winding of the transformer 11. The direct cur
rent which is proportional to the positional dis
ti?er 13. The tachometer generator 12 is driven
agreement between the active roll opening selec
by the motor 9 to the drive shaft of which it is 15 tor unit and the position of the mill roll 4 is sup
connected through the gearing 54. Thus, the
plied to the saturating winding Nb of the reac
tachometer generator 12 generates a voltage
tor from an electric valve type ampli?er B2 of
which is proportional to the speed of the motor
which the input circuit is connected by means of
9‘. Whenever the motor 9 is rotating, the gener
conductors 83 to the rotor winding circuit of the
ated voltage of the tachometer generator en 20 coarse control Selsyn oi the active roll opening
ergizes the operating coil of the relay ‘H su?i
selector unit. This ampli?er has two stages of
ciently to maintain the contacts 1 la open. How
which the valve 84 constitutes the ?rst stage and
ever, when the motor 9 is at rest, the voltage of
the valve 85 constitutes the second stage. As
the tachometer generator is zero thereby deen
shown, the valve 84 is connected in series with a
ergizing the operating coil ‘H b and allowing the
voltage dropping resistor 86 across the direct volt
contacts ‘Ha tovclose. In ‘the closed position of
age source 81. A voltage divider comprising re
the contacts ‘Ha. both halves of the reference
sistors 88 and 89 connected in parallel with each
which it is connected through a full wave rec
voltage potentiometer are short-circuited so that
the effective reference voltage is very close to
zero. As a result, the circulating current in the
armature motor 9 is limited to a very low value.
For the purpose of preventing “overshooting,”
i. e., driving the mill roll 4 past a selected position
in the downward position, means are provided for
stabilizing the position. These stabilizing means
comprise a control circuit for reducing the voltage
supplied by the generator I'I to the motor 9 in
accordance with the positional disagreement be
tween the mill roll and the selected position to
which it is being driven and also in accordance
with the speed at which the roll is being driven.
This is accomplished by exciting the current limit
?eld winding [6]‘ of the exciter in response to the
di?erence between a control voltage which is pro
portional to the current supplied to the ?eld
winding l‘la of the supply generator and a ref
erence voltage which is varied in accordance with
the positional disagreement between the active
roll selector unit and the position of the mill roll
4. The reference voltage is provided by means
of a center tap resistor 74 to which a direct volt
age is supplied from a full wave recti?er 15. An
other and in series with a resistor 90 is connected
from the anode of the ?rst stage valve 84 to the
negative side of the source 81. The second stage
valve 81 is connected in series with the saturating
winding 8lb across the source. Its control grid
5a is connected to the slider 88a of the volt
age divider 89, 90.
‘
The alternating voltage of the coarse Selsyn of
the active roll opening selector unit is recti?ed by
the left-hand conducting valve of a twin triode
valve 9| and the recti?ed voltage appears across
the series adjustable resistor 92 of which the ter
minal which is remote from the anode is con
nected to the negative side of the source 81. The
control grid of the ?rst stage valve 84 is connected
to the slider 92a of the resistor 92. As a result of
these connections, a current which is propor
tional to the positional disagreement of the active
selector unit and the mill roll 4 is caused to flow
through the resistor 92. This current produces a
corresponding voltage drop across the resistor 92,
thereby decreasingv the grid voltage of the ?rst
stage valve 84. The decreased grid voltage pro
duces a corresponding decrease in the voltage
drop across the resistor 86 and a corresponding
alternating voltage is .supplied to the recti?er
increase in the voltage supplied to the voltage
from a suitable alternating voltage source 16
divider 88, 90. This increases the grid voltage of
through a transformer 11 of which the primary 55 the second stage valve and correspondingly in
winding is connected to the source, and the sec
creases the current supplied to the saturating
ondary winding is connected to the input of the
winding-of the reactor 8|. The increased satu
recti?er, The control voltage is derived from the
ration of the reactor correspondingly reduces its
generator "?eld current by means of a voltage
reactance and thereby increases the voltage sup
dropping resistor 18 which is connected in the 60 plied to the valve 84. ’
.
circuit of the generator ?eld winding Ila. One
Thus, the magnitude of the reference voltage is
terminal of this resistor is connected to one ter
adjusted in proportion to the distance of the mill
minal of the current limit ?eld winding l6)‘ of
roll 4 from the selected position to which it is
the exciter and the other terminal is connected
moving. For the purpose of reducing the refer
through reversely connected half wave recti?ers 65 ence voltage substantially to zero when the mill
19 and 80 to the opposite terminals of the refer
roll is very close to the preselected position, a re
ence voltage resistor 14 of which the center tap
lay 93 is provided for substantially short-circuit
is connected to the other terminal of the current
ing the reference voltage resistor. The operating
limit ?eld winding. ' Thus,,for one direction of
vcoil 93a of the relay is connected in circuit with
current flow in the generator ?eld circuit, the 70 the right-hand‘ conducting path of the valve 9|
voltage drop across resistor 18, is compared with ‘ of which the control grid 9la is connected to the
the voltage drop across one-half of the reference
slider 89a of the ‘voltage divider 89, 90. The net
voltage resistor and the difference is applied to
effect of the connections‘ described in the forego
the control ?eld winding “if. v For the reversev di
ing is to control the excitation of the control ?eld
rection of current flow in the generator ?eld cir 75 winding “if so that the voltage which is supplied
2,410,283
11
to the drive motor 9 and consequently the speed
of the motor 9 is caused to be proportional to the
distance the roll must move to its preselected po
sition. The movement of the roll is therefore
made in a minimum time. Further to aid in sta
bilizing the system, the reduction in the reference
voltage is correlated with the speed with which
the mill roll approaches a preselected position.
12,
in which the movable contact |3a engages the
stationary contact at the ?rst pass position. In
response to the closing of these contacts, the op
erating coil 580 of the switch 58 is energized and
closes its normally open contacts 58a and 58b
thereby to complete the connections from the
rotor windings of the coarse Selsyn 4| and the
Vernier Selsyn 42 of the ?rst pass selector unit
to the input circuit of the ampli?er l5. It is
This is accomplished by supplying to the grid
circuit of the ?rst stage valve 84 a reverse po lo assumed that the distance of the roll 4 from the
larity voltage which varies with the speed of the
motor 9. This voltage is obtained from the tach
ometer generator 12 through the recti?er '13 to
which the resistor 84b in the grid circuit of the
preselected position for the ?rst pass is greater
than the distance which corresponds to 5 de
grees of positional disagreement between the
?rst stage valve 84 is connected by means of con
ductors 94. Owing to the presence of the recti?er
quently, the voltage from the Selsyn 4| is suffi
cient to ionize the valves 56 and 51 so that the
signal voltage from the Selsyn is applied to the
grids 29d and 29a of the ?rst stage valve ‘29. As
13 in the connections, the polarity of the voltage
supplied in the input circuit of the valve 34 is al
rotors of the coarse Selsyns 4| and 45.
Conse
a result, an exciting current is supplied to the
ways the same irrespective of the direction of ro
tation of the tachometer generator‘.
20 ?eld winding Ila of the supply generator l1 so
that a voltage is supplied to the motor 9 which
The main anti-hunt effect is produced by sup
causes the motor to drive the mill roll 4 toward
plying to the input circuit of the ampli?er IS a
the preselected position for the ?rst pass at a
reverse polarity voltage which varies with the
speed proportional to the positional disagreement
speed of the drive motor 9. This voltage is ob
of the rotors of the Selsyns 4| and 45.
tained from a potentiometer 95 which is sup
The signal voltage supplied from the Selsyn 4|
plied from a tachometer generator 96 of which
to the input of the ampli?er 82 causes a sufficient
the drive shaft is connected to the drive shaft of
Voltage to be supplied to the operating coil 93a of
the motor 9. The voltage derived from the po
relay 93 to cause the relay to pick up and open
tentiometer 95 is supplied through conductors 91
to the resistor 35a, 35b which is connected in the 30 its normally closed contacts, thereby to remove
the short circuit from the reference voltage re
grid circuit of the ?rst stage valve 29. The
sistor "M. The operating coil ‘Nb of the relay ‘II
polarity of this voltage is such as to oppose the
is energized ‘by the voltage supplied from the
voltage which is supplied from the Selsyns to the
tachometer generator 72. In response to ener
input circuit. To this anti-hunt voltage is added
gization the relay 1| picks up and opens its nor
a component voltage which is proportional to
mally closed contacts ‘Ha to remove the short
the rate of change of the voltage that is supplied
circuit from the reference voltage resistor 65.
to the motor 9. This voltage is added to the
Following the removing of the short circuits
voltage derived from the potentiometer 95 by
from the reference voltage resistors 65 and 14,
means of a transformer 98 of which the primary
the control ?eld winding I5)‘ is controlled to limit
winding is connected across the terminals of the
the current which flows in the armature circuit
motor 9 and the secondary winding is connected
of the motor 9 and also to limit the voltage of
in circuit with the potentiometer 95.
the supply generator ll to predetermined values.
A recti?er 99 is included in circuit with the
At the beginning of the movement of the roll 4
tachometer generator 96 and the potentiometer
when its distance to the preselected position for
95. The polarity of this recti?er is such that no
the ?rst pass is large, the signal voltage supplied
anti-hunt voltage is supplied from the tachometer
from the Selsyn 4| to the ampli?er 82 produces
generator 96 to the ampli?er l5 when the rotation
of the motor 9 is in a direction to move the upper
a large reference voltage across the reference
voltage 14. Consequently, the voltage of the sup
mill roll 4 in the upward direction.
To further the stabilization of the system, two 50 ply generator and the speed of the motor 9 are
permitted to rise to a high value which corre
reversely connected selenium cell recti?ers I00
sponds to the magnitude of the reference voltage.
and |0| are connected in circuit ‘between the
As the mill roll 4 approaches its preselected
Vernier Selsyn of the active roll opening selector
position, the signal voltages supplied from the
and the input circuit of the ampli?er l5. These
selenium cell recti?ers have a non-linear char 55 Selsyn 4| to the ampli?ers I5 and 82 decrease
correspondingly. The decrease in the voltage
acteristic so that very little current is conducted
supplied to the ampli?er l5 produces a decrease
in the rectifying direction until the voltage per
in the voltage supplied from the ampli?er l5 to
plate reach approximately .3. With the recti?er
the control ?eld windings [6c and “id of the ex
so connected, no signal voltage is applied to the
input circuit of the ampli?er [5 until there is a 60 citer Hi. This in turn produces a decrease in the
voltage of the generator and a corresponding
few degrees of positional disagreement between
decrease in the speed of the motor. The decrease
the Vernier Selsyn 45 connected to the mill roll
in the signal voltage supplied to the ampli?er
and the Vernier Selsyn of the active selector unit.
82 reduces the reference voltage across the re
With the above understanding of the elements
and their organization the operation of the sys 65 sistor 14 so that the voltage of the generator I‘!
and the resulting speed of the motor 9 are pro
tem itself will be readily understood from the
following detailed description: The dials for each
gressively decreased by the decreasing reference
voltage across the resistor ‘I4 as the mill roll 4
selector unit are set to their correct positions for
approaches a preselected position.
the rolling schedule of the billet which is to be
When the distance‘ of the mill roll 4 from the
reduced. It is assumed that the mill roll 4 is at 70
preselected position is less than the distance
its upper limiting position, i. e., the rolls are at
their maximum opening.
The roll 4 is caused to move to the correct posi
tion for the ?rst pass by movement of the arm
|3a of the dial switch to the number one position
which corresponds to 5 degrees positional disa
greement of the Selsyns 4| and 45, the signal
voltage supplied from the Selsyn 4| to the ampli
?er I5 is no longer su?icient to maintain conduc
13
2,410,283
tion through the valves 56’ and 51. These valves
therefore become non-conducting and the ampli
?er I5 is controlled by the signal voltage supplied
from the Vernier Selsyn‘ 42.
As the mill roll 4 more closely approaches the
preselected position, the progressive decrease in
the reference voltage across the resistor ‘I4 causes
the voltage of the generator I’! and the motor 9
14
versedand the roll 4 is levelled to the correct po
sition at low speed. During this levelling opera
tion in the downward direction the anti-hunt
circuits are again effective and the roll 4 is
brought to its correct position without over
shooting in the downward direction. Thus, ir
respective of the position of the roll from which
it is moved to a selected position, its ?nal ap
to be progressively decreased. Simultaneously,
proach to the selected position is always in the
the voltage supplied from the potentiometer 95 10 same direction. This feature eliminates the er
to the input circuit of the ampli?er I5 in oppo
ratic e?ects which would otherwise result from
sition to the signal voltage from the Selsyn 42
back lash in the gearing. Consequently, the dials
further reduces the excitation of the generator
always read the correct roll opening when the
I‘I, thereby reducing the tendency to hunt to a
mill roll comes to rest.
minimum.
15
The movable contact arm I 3a may be moved
When the mill roll is within a few thousandths
by means of an electric motor instead of manu
of an inch of the preselected position, the signal
ally by means of the knob I3b. For this purpose,
voltage supplied from the Selsyn 4I to the am
an electric motor I02 is provided which is under
pli?er 82 decreases to such a low value that the
the control of a manually operated down.push
voltage supplied from the ampli?er to the oper 20 button switch I03, a manually operated up push
ating coil 93a is no longer sufficient to maintain
button switch I04, a detent type limit switch I 05,
the relay contacts open. Responsively to'deen
ergization, the relay drops out to open its nor
and limit switches I06 and I01.
mally closed contacts, thereby substantially to
tor I02 to return the pass selector arm to the
zero position after a number of passes which is
short circuit the reference voltage resistor ‘I4
and to reduce the reference voltage substan
tially to zero. As a result of the reduction of the
reference voltage to this low value, the voltage
of the generator I‘! is reduced to such a low value
that the motor 9 comes to rest. Since the voltage
of the generator is not reduced to zero, a cur
rent is caused to circulate in the armature of
the motor 9 which maintains a pressure on the
mill roll 4 in the downward direction. The mo
tor being at rest, it has no countervoltage and
this circulating current may rise to a value which
would overheat the motor. However, this is pre
vented by the operation of the relay '1 I, which in
response to zero voltage of the tachometer gen
erator 12 drops out to close its contacts ‘Ha. In
closing, contacts 1 la effectively short circuit the
reference voltage resistor 65. Thus, the reference
voltage proportional to armature current which
appears across the resistor 69 is compared with
a very low reference voltage. If the voltage drop
across the resistor 69 exceeds the reference volt
age which is approximately zero, the difference
between the two voltages excites the current lim
it voltage winding I6f of the exciter I6 in such
a direction that the exciting current supplied to
the ?eld winding I'Ia of the generator I‘! is still
further reduced.
-
The limit switch I06 serves to control the mo
determined by the position to which the pointer
I08 is moved on an indicating dial I09.
Assuming that a total of seven passes is desired
in a rolling program, the pointer I 08 is moved by
its knob until it coincides with the numeral '1
on the dial I09. In response to this movement,
the limit switch I06 is rotated through gearing
I I0 to a corresponding position.
,
The operation is as follows: The operating coil
of a relay II I is connected across the source H2,
H3 through the normally closed contacts I 03a
and I04a and the normally closed contacts I 05a
of the detent limit switch I05.
In response to
energization, the relay III picks up to close its
normally open contacts IIIa and “lb. Relay
I II seals itself in through contacts lIla. With
the movable roll 4 in its uppermost position for
the widest roll opening, the down pushbutton
switch I03 is depressed to open its normally closed
contacts I03a and H331) and to close its normally
open contacts I030 and IBM. Contacts “1311 In
closing complete an energizing circuit for the
operating coil II 4a of a control relay H4. The
circuit extends from the lower side II3 of the
50 source through the coil II4a, contacts I03d, nor
mally closed contacts I041), normally closed con
tacts I06a of the preset limit switch, normally
closed contacts II5a of relay II5 to the positive
The movement of the mill roll 4 to the suc
cessive selected positions for which the roll open
side II2 of the source. In response to energizaing selector units are adjusted is accomplished by 55 tion, the relay II4 closes its normally open con
movement of the contact arm I3a of the pass se
tacts I MD and I I40 and opens its normally closed
lector to its corresponding successive positions.
contacts II4d. Contacts II4b in closing complete
If for any reason the operator should move the
a sealing-in circuit in parallel with the contacts
contact arm I3a farther than intended so that
I03d of the pushbutton switch. Contacts I030
the mill roll 4 is moved beyond the desired posi 60 in closing complete an energizing circuit for the
tion it may be brought back to the desired posi
operating coil IIBa of the down contactor II6.
tion by returning the arm I3a of the pass selector
This circuit is traced from the lower side of the
to the correct position. In this case the opera
source II3 through the ope-rating coil IIBa, con
tion is the same as that described in the fore
tacts
I030 in the closed position thereof, contacts
going with the exception that the voltages sup 65 IIIb, normally
closed contacts II5e of relay II5
plied from the Selsyns M and 42 to the ampli
to the upper side II2 of the source. In response
?er I5 are of reverse phase. This causes the
to energization, the down contactor H6 closes
motor 9 to rotate in the reverse or up direction.
its contacts to effect energization of the motor
Owing to the polarity of the recti?er 99 no anti
I02 for rotation in a direction to move the con
hunt voltage is supplied from the anti-hunt 70 tact arm I3a of the pass selector and the pointer
tachometer generator 96 to the input of the am
I3b toward the number one pass position.
pli?er I 5 and consequently the roll overshoots the
As the motor rotates, the detent disk II‘! is
correct position in the up direction. In over
driven in a clockwise direction and the detent
shooting, the polarities of the signal voltages sup
follower I050 is moved by the ?rst tooth of the
plied; from the Selsyns to the ampli?er are re 75 disk to open the normally closed contacts I05a
2,410,283
15
and to close the normally open contacts I051).
The closing of contacts I05b provides a maintain
ing circuit for the operating coil I IBa of the down
contactor. This maintaining circuit is traced
from the lower side of the source II3 through
16
direction to return the movable contact arm I3a
and the pointer I31) to the zero position. When
the arm I30. and the pointer I319 reach the zero
position, the arm H0 opens the contacts I01
thereby to interrupt the energizing circuit for
the operating coils of the relay H5 and the up
contactor I I8, which is in response to deenergiza
tion drop out. The contactor IIB in dropping
I03 may now be released. The opening of con
out stops the motor I02 and the control is thus
tacts I05a of the detent limit switch interrupts
the energizing circuit for the operating coil of 10 left in a reset condition for subsequent operations.
Although in accordance with the provisions of
the relay IiI which thereupon drops out and
the patent statutes this invention is described
opens its normally open contacts.
as embodied in concrete form and the principle
As the movement of the detent disk continues,
thereof has been explained together with the
the detent follower I050 drops into the detent
for the ?rst position thereby reclosing the con 15 best mode in which it is now contemplated ap
plying that principle, it will be understood that
tacts I05a and opening the contacts I051) of the
the apparatus shown and described are merely
detent limit switch. Contacts [05b in opening
illustrative and that the invention is not limited
interrupt the energizing circuit for the operating
thereto since alterations and modi?cations will
coil of the down contactor which thereupon drops
out and stops the motor I02 with the contact 20 readily suggest themselves to persons skilled in
the art without departing from the true spirit
arm I3a of the selector in engagement with the
of this invention and the scope of the annexed
number one stationary contact and the pointer
I3b in the number one pass position. In response
claims.
What I claim as new and desire to secure by
to the engagement of the contact I3a with the
?rst stationary contact, the motor 9 is started 25 Letters Patent of the United States is:
1. A control system for a mill having a pair oi
to move the mill roll 4 to the ?rst pass position.
rolls and movable supporting means for one of
The operation is identical with that described in
said rolls comprising a motor for driving said
the foregoing in connection with the manual
supporting means to vary the pass opening be
movement of the contact arm I3a into engage
ment with the ?rst stationary contact. The
tween said rolls, means for supplying a voltage
to said motor comprising an adjustable voltage
down pushbutton switch I03 must be depressed
again to initiate a movement of the contact arm
generator provided with a ?eld winding, a pass
I3a to the second pass position.
opening selector device, means responsive to p0
sitional disagreement of said selector device and
If it is desired to move the selector switch in
said supporting means for controlling the ener
the counterclockwise direction, the up pushbut
gization of said generator ?eld winding to cause
ton switch I04 is depressed. This completes an
energizing circuit for the operating coil II8a of
said motor to drive said supporting means toward
the up contactor II8 which picks up to close its
a position of correspondence with said selector
contacts and complete the energization of the
device, means for limiting the current in said
motor I 02 for rotation in a direction to move the
?eld winding to a predetermined value, and
contact arm I3a and the pointer I3b in a counter
means for varying the magnitude of said prede
clockwise direction to the next lower number pass
termined value in accordance with said positional
the coil lI'o‘a, contacts lI4c, contacts I051) to the
positive side of the source. Pushbutton switch
opening position.
disagreement.
If the clockwise rotation of the contact arm
I31: and the pointer I3b is to be continued, the
2. A control system for a mill having a pair of
rolls and movable supporting means for one of
down pushbutton switch I03 is depressed follow
said rolls comprising a motor for driving said
ing the completion of each pass of the strip
supporting means to vary the pass opening be
through the mill rolls thereby to advance the
tween the rolls, means for supplying a voltage
contact arm l3a and the pointer I312 to successive
to said motor comprising an adjustable voltage
pass positions in which successive roll opening 50 generator provided with a ?eld winding, means
selector units are connected to the ampli?er I5.
for supplying excitation current to said ?eld
In the ?nal pass position set upon the selector
Winding comprising an exciter provided with a
I09, the movable arm II9 which is driven by the
main control ?eld winding and an auxiliary op
motor I02 closes the normally open contacts IElBa
posing ?eld winding, a roll opening selector de—
of the preset limit switch and opens the normally 55 vice, electric valve means responsive to positional
closed contacts I05b. Contacts IOEa in opening
disagreement of said selector device and support
interrupt the energizing circuit for the operating
ing means for controlling the energization of said
coil II4a of relay H4 which thereupon closes its
control ?eld winding to control said motor to
normally closed contact HM and opens its nor
drive said supporting means toward a position of
mally open contacts IMb and H40. Contacts 60 correspondence with said selector device, means
IOIib in closing complete an energizing circuit for
for controlling the excitation of said exciter to
the operating coil II5b of relay H5 which picks
limit the current supplied to said generator ?eld
up and closes its normally open contacts H50
winding to a predetermined value, and means re
and II5d and opens its normally closed contacts
sponsive to said positional disagreement for vary
I Mia and “Se. The contacts I i5c in closing com 05 ing the magnitude of said predetermined value
plete a sealing-in circuit for the relay. When
of generator ?eld current.
3. A control system for a mill having a pair of
the pushbutton switch I03 is released, an ener
gizing circuit is completed for the operating coil
rolls and movable supporting means for one of
of the up contactor I I8 which is traced from the
said rolls comprising a motor for driving said
lower side of the source I I3 through the normally 70 supporting means to vary the pass opening be
tween the rolls, means for supplying a voltage to
closed contacts I01, operating coil IIBa, contacts
said motor comprising an adjustable voltage gen
I03b, conductor I20, contacts II5d to the upper
side of the source. In response to energization,
the up contactor closes its contacts to complete
erator provided with a ?eld winding, a pass open
ing selector device, means responsive to posi
energization of the motor I02 for rotation in a 70 tional disagreement of said selector device and
2,410,288
17
said supporting means for controlling the excita
tion of said ?eld winding to cause said motor to
drive said supporting means toward a position
of correspondence with said selector device, and
means for varying said position of correspondence
to compensate for variations in the diameter of
the rolls.
‘
18
for controlling the energization of said control
?eld winding to cause said motor to drive said
supporting means toward correspondence with
said selector device, means for limiting the cur
rent supplied to said motor to a predetermined
value comprising a source of reference voltage,
means for deriving from the armature circuit of
said motor a signal voltage proportional to cur
4. A control system for a mill having a pair
of rolls and movable supporting means for one
rent and a differential ?eld Winding on said
of said rolls comprising a motor for driving said 10 dynamo electric machine excited by the differ
supporting means to vary the pass opening be
ence of said reference and derived voltages, and
tween the rolls, means for supplying a voltage to
means responsive to a predetermined low value of
said motor comprising an adjustable voltage gen
speed of said motor for reducing said reference
erator provided with a ?eld winding, a pass open
voltage substantially to zero thereby to limit the
ing selector device, means responsive to positional 15 stalled armature current of said motor to a pre
disagreement of said selector device and said sup
determined low value.
porting means for controlling the excitation of
8. A control system for a mill having a pair
said ?eld winding to cause said motor to drive
of rolls and a movable supporting means for one
said supporting means toward a position of cor
of the rolls comprising a motor for driving the
respondence with said selector device comprising 20 supporting means to vary the pass opening be
a rotary induction device connected to said
tween the rolls, means for supplying a voltage to
selector device, a second rotary induction device
said motor comprising an adjustable voltage gen
connected to said supporting means and elec
erator provided with a ?eld winding, means for
trical connections between said induction de
supplying excitation current to said ?eld wind
vices, and means for varying said position of cor
ing comprising an exciter dynamo electric ma
respondence to compensate for variations in the
chine provided with a control ?eld winding, a
diameter of the rolls comprising an electrical dif
pass opening selector device, means responsive to
ferential device included in said connections.
positional disagreement of said selector device
5. A control system for a mill having a pair
and supporting means for controlling the en'
of rolls and movable supporting means for one of 30 ergization of said control ?eld winding to cause
said rolls comprising a motor for driving said
said motor to drive said supporting means toward
supporting means, a pass opening selector device,
correspondence with said selector device, means
means responsive to positional disagreement of
for limiting the current of said generator ?eld
said selector device and supporting means for
winding to a predetermined value comprising a
producing a control voltage, electric valve means
source of reference voltage, means for deriving a
responsive to said control voltage for controlling
voltage proportional to said generator ?eld cur
the energization of said motor ‘to drive said sup
rent and a differential ?eld winding on said ex
porting means toward correspondence with said
citer machine energized by the difference of said
selector device, and means for modifying the op
reference and derived voltages, and means for
eration of said control voltage producing means 40 varying said generator ?eld current in accord
to compensate for variations in the diameter of
ance with said positional disagreement compris
the mill rolls.
ing means responsive to said positional disagree
6. A control system for a mill having a pair
ment for varying said reference voltage.
‘
of rolls and movable supporting means for one
9. [A control system for a mill having a pair of
of said rolls comprising a motor for driving said
rolls and a movable supporting means for one of
supporting means to vary the pass opening be
the rolls comprising a motor for driving the sup
tween said rolls, means for supplying a voltage
porting means to vary the pass opening between
to said motor comprising an adjustable voltage
the rolls, means for supplying a voltage to said
generator provided with a ?eld winding, means
motor comprising an adjustable voltage generator
for controlling the energization of said ?eld 50 provided with a ?eld winding, means for supply
winding comprising an exciter dynamo electric
ing excitation current to‘said ?eld winding com
machine provided with a main control ?eld wind
prising an exciter dynamo electric machine pro
ing, a pass opening selector device, means respon
vided with a control ?eld winding, a pass opening
sive to positional disagreement of said selector
selector device, means responsive to positional
device and said supporting means for controlling , disagreement of said selector device and support
the excitation of said main control ?eld winding
ing means for controlling the energization of said
to cause said motor to drive said supporting
control ?eld winding to cause said motor to drive
means toward correspondence with said selector
said supporting means toward correspondence
device_ and means limiting the armature current
with said selector device, means for limiting the
' of said motor and the ?eld current of said gen 60 current of said generator ?eld'winding to a pre
erator to predetermined values comprising a dif
determined value comprising a source of alternat
ferential ?eld on said exciter having connections
ing voltage, a recti?er for deriving a direct ref
to the armature circuit of said motor and addi
erence voltage from said source, means for de
tional connections to the ?eld circuit of said gen
riving a signal voltage proportional to said gen
erator.
erator ?eld current and a di?erential‘?eld wind
7. A control system for a mill having a pair
ing on said exciter machine energized by the dif
of rolls and movable supporting means for one of
ference of said reference voltage and said signal
said rolls comprising a motor for driving said
voltage, and means for varying said generator
supporting means to vary the pass opening be
?eld current comprising a saturable core reactor
tween the rolls, means for controlling the supply
having its reactance winding connected between
of voltage to said motor comprising a dynamo
said source and said recti?er and having the ex
electric machine provided with a main control
citation of its saturating winding controlled by
?eld winding, a pass opening selector device,
said positional disagreement responsive means for
means responsive to positional disagreement of
varying said reference voltage.
said selector device and said supporting means 75 I 10. A control system for a mill having a pair
2,410,283
19
20
of rollsand a movable supportingmeans for one of
the rolls comprising a motor for driving the sup
porting means to vary the pass opening between
the rolls, means for supplying a voltage to said
to said grid to cause said motor to drive said sup
porting means toward correspondence with said
motor comprising an adjustable voltage generator
provided with a ?eld winding, means for supply
ing excitation current to said ?eld winding com
prising an exciter dynamo electric machine pro
from overshooting said position of correspondence
comprising a tachometer generator driven by said
tween the rolls, means for controlling the supply
of ‘voltage to said motor comprising electric valve
bilizing means ineffective for one direction‘ of ro
apparatus provided with a control grid, a pass
respondence so that said supporting means is al
ways moved in the same direction to rest in said
selector device, stabilizing means for controlling
said valve means to prevent said supporting means
motor for supplying an antihunt voltage to said
control grid, and means for limiting the operation
of said stabilizing means to one direction of rota
vided with a contro1 ?eld winding, a pass opening
selector device, means responsive to positional 10 tion of said motor comprising a unidirectional
conducting device included in circuit between said
disagreement of said selector device and support
tachometer generator and said control grid.
ing means for controlling the energization of said
13. A control system for a mill having a pair
control ?eld winding to cause said motor to drive
of rolls and a movable supporting means for one
said supporting means toward correspondence
of the rolls comprising a motor for driving the
with said selector device, means for limiting the
supporting means to vary the pass opening be
armature current of said motor to a predeter
tween the rolls, means for controlling the supply
mined value comprising a ?rst source of referof voltage to saidmotor comprising electric valve
ence voltage, means for deriving a, voltage pro
apparatus provided with a control grid, a pass
portional to armature current and a di?erential
?eld winding on said exciter machine energized 20 opening selector device, means responsive to po
sitional disagreement of said selector device and
by the difference of said reference and derived
voltages, and means for varying the generator
supporting means for supplying a contro1 voltage
to said grid to cause said motor to drive said sup
?eld current in accordance with said positional
porting means toward correspondence with said
disagreement comprising a source of a second ref
erence voltage, means for deriving a signal volt
selector device, stabilizing means for controlling
age from said generator ?eld current and connec
said valve means to prevent said supporting means
from overshooting said position of correspondence
tions for supplying the difference of said second
reference voltage and said signal voltage to said
and a transformer having its primary winding
differential ?eld winding.
connected across the terminals of said motor and
its secondary-winding connected in circuit be
11. A control system for a mill having a pair
tween said tachometer generator and said grid,
of rolls and a movable supporting means for one
and means for limiting the operation of said sta
of the rolls comprising a motor for driving the
supporting means to vary the pass opening be
bilizing means to one direction of rotation of said
motor comprising a unidirectional conducting de
tween the rolls, means for controlling the supply
of voltage tosaid motor comprising electric valve
vice included in circuit between said tachometer
apparatus provided with a control grid, 9,. pass
generator and said control grid. '
opening selector device, means responsive to pc
14. A control system for a mill'having a pair
sitional disagreement of said‘selector device and
of rolls and a movable supporting means for one
supporting means for‘supplying a control voltage
of the rolls comprising a motor for driving the
to said grid to cause said motor to drive said sup‘ 40 supporting means to vary the pass opening be
porting means toward correspondence with said
tween the rolls, means for controlling the supply
selector device, stabilizing means for controlling
of voltage to said motor comprising electric valve
said valve means to prevent said supporting means
apparatus provided with a control grid, a pass
from overshooting said position of correspondence,
opening selector-device, means responsive to po~
and means for rendering said stabilizing means
sitional disagreement of said selector device-and
ineffective for one direction of rotation to permit
supporting means for supplying a control voltage
overshooting said position of correspondence so
to said grid to cause said motor to drive said
that said supporting means is always moved in
supporting means toward correspondence with
the same direction to rest in said position of cor
said selector device, a nonlinear resistance device
respondence.
included in circuit with said grid to provide a
12. A control system for a mill having a pair
narrow dead‘ zone, stabilizing means for control
of rolls and a movable supporting means for one
ling said valve means to prevent said supporting
of the rolls comprising a motor for driving the
means from overshooting said position of cor
supporting means to vary-the pass opening be—
respondence, and means for rendering said sta
tation to permit overshooting said position of cor
opening selector device, means responsive to po
position of correspondence.
sitional disagreement of said selector device and
supporting means for supplying a control voltage 60
DONALD E. GARR.
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