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Dec‘, 3, 19460
E. F. w. ALEXANDERSON'
2,412,027
-CONTROL SYSTEM.
Filed May 25, 1936
Inveritcir: ‘
Ernst. F. W. Alexanderson.
2,412,027
coN'ritoL svs'raM'
Ernst F. W. Alexanderson, Schenectady, N. Y.,
assignor toGeneral Electric Company, a cor
poration of New York
Application May‘23, 1936, Serial No. 81,426
12 Claims. (Cl. 60-58)
This invention relates to control systems, more
control means to cause the motor to drive the
particularly to control systems for controlling an -
driven object toward correspondence with the
hydraulic motor to drive an object in positional
‘agreement with a pilot device, and an object of
pilot device. In order to prevent hunting, means
responsive to the rate of change of the torque of
the invention is the provision of a simple reliable
the driving means are provided for effecting an
and improved system of this character.
actuation of the control means in the opposite
direction from that produced by the means re
Such systems are commonly referred to as
“follow-up” systems or torque ampli?ers. An ex-'
ample of a system of this character is one in which
a heavy object possessing large inertia is .to be
sponsive to positional disagreement. Since the
torque of the hydraulic motor is a function of the
pressure of the ?uid supplied thereto, the rate of
change of torque responsive means may take the
form of a device'responsive to the rate of change
' . driven in correspondence with alight, easily mov
able device- such as a telescope.
2
and driven object are provided for actuating the.
The large in- '
ertias of the driven object and driving means,
and the high accuracies required lead to insta-l
bility and to a condition of violent accumulative
oscillations, usually referred to as “haunting.".
of pressure of the system.
_
In illustrating the invention in one form there
of, it is shown as embodied in a system for con
trolling the driving of a gun in positional agree
ment with a telescope. It will be understood,
In any synchronous system, the problem is- to
however, that the invention has other applica
drive a shaft with considerable power in accurate
correspondence with a master device. One way 20 tions.
For a better and more complete understanding
7 to accomplish this electrically is to couple the
of the invention. reference should now be had to
output shaft to a, synchronous motor and the mas
the following speci?cation and to the accompany
.ter shaft to a synchronous generator. The syn
ing drawing, the single figure of which is a simple
chronous motor drive has a point of correspond
This, of course, is most undesirable.
ence, and a departure from this point of corre
25
- ,
diagrammatical representation of an embodiment
‘spondence causes energy to flow in the electric
Referring now to the drawing, an object such
circuit that produces a torque proportional to
as the gun Ill is to be driven in accurate corre
the displacement from correspondence. In elec
spondence with a pilot device, such as the tele
trical terms this is known as “phase displace
ment," but in order to avoid confusion this dis 30 scope l I.
The gun i0 is- driven by suitable hydraulic
placement is hereinatfer referred to as "angular
‘driving means such as the fluid motor l2 whose
displacement.” because this concept is more com‘
output shaft is connected to gun ill. Any suitable
parable with the mechanical angle of the hy
?uid, such as oil, is supplied under pressure to
draulic system.
7
I
‘
the motor from a pump it that is‘driven. at a
One aspect of the hydraulic problem in follow
speed that is preferably substantially constant,‘
up ‘systems is to cause an hydraulic motor to de—
by suitable driving means illustrated as an elec
velop a torque that is proportional to angular dis
tric motor. Iii. Although motor Hi may be of any
placement. In either the electrical system or the
suitable type. it is illustrated as a direct current
hydraulic system the action is the same as though
of the invention.
the output shaft and the master shaft were con
,
p
'
'
'
-
40 tyne motor and is supplied with power from a -
suitable direct current source represented by the
nected together with a spring that delivers the
same torque at the same angular displacement.
supply lines it.
Such an arrangement. whether it be a spring, an
electric motor or an hydraulic motor has a tend
its structure forms no part of the invention. This
'
The pump it is shown conventionally because '
45 pump is‘ preferably a positive displacement tvoe
pump and it may be either a constant stroke
pending upon the synchronizing torque and the
pump or a variable stroke pump. 'In either case,
mass connected to the output shaft.
means actuated by the’ connecting rod l8 are
In carrying the invention into effect in one form
ency to be oscillatory with a natural period de
provided for controlling the supply of fluid to the
thereof. the driven object is driven by suitable
hydraulic driving means comprising a ?uid motor 50 motor. If the pump is a constant stroke type of
pump, it is provided with a pressure relief valve
connected to the driven obiect and a pump for
to prevent building up destructive pressure. If
supplying fluid under pressure to the motor.
the pump is a variable stroke pump, the control
Means are provided for controlling the supply
‘means actuated by the connecting rod it may be
of ?uid to the motor, and means responsive .to
the positional disagreement between a pilot device 55 any suitable device ""or varying the ‘stroke such as
2,412,027
4
.
a pivoted, tilting box carrying either the pump
pistons or the cylinders. Suitable Dumps of each
the latter rotates, the rod i6 is moved to actuate
that the control means actuated by connecting rod
ll varies the‘ volume of ?uid supplied to the
motor.
The connecting rod I3 is connected through 10
movement of the telescope ||. The output shaft
32 of ?uid motor | 2 is connected through bevel
gearing 33, shaft 34, bevel gearing 35 and shaft
35 to the input spider 20a of differential device
20, and through gearing 31, 38 to the gun. The
the control mechanism to cause the pump l3 to
of the types mentioned are available on the
supply ?uid to the ?uid motor l2, in a direction
market. For the purposes of the present inven
corresponding to the direction of movement of
tion, it is su?lcient to understand that the pump 5 rod l6. As a result, motor l2 drives the gun ill
l3 supplies a volume of ?uid to the motor | 2 and
in a direction corresponding to the direction of
suitable means, illustrated as a lever II, a rack
and pinion l8, l9, and a mechanical di?erential
device 20, to a pilot motor 2|. This motor is
illustrated as a direct current type of motor sup
plied from suitable electric valve apparatus 22
which in turn is supplied through a supply trans
former from a suitable source of alternating volt
age represented by the supply lines 24. The valve
ratio of this gearing is such that when the gun
ID has rotated through an angle equal to the angle
through which the output shaft 2h of motor 2|
has been rotated, the control rod l6 will have been
returned to its off position and the gun It brought
to rest in substantial correspondence with the
motor shaft 2h. As pointed out in the forego
apparatus 22 comprises two pairs of valves 25, 26.
ing, shaft 2| 5. is driven in synchronism with tele
Each pair of valves is connected for full wave 20 scope i | and therefore the gun in is brought to
rest in correspondence with the telescope H.
recti?cation, and has its output circuit connected '
to the armature of motor-2|. The pair of valves
In order to prevent oscillations or hunting,
25 when energized supplies current to motor 2|
means 39 are provided for introducing a correc
in one direction and the other pair when ener
tion‘in the control responsive to the rate of change
gized supplies current in the reverse direction,
of torque of the driving means. In .a closed hy
and thus when either pair of valves is energized
the motor 2| is energized for rotation in‘a corre
sponding direction.
draulic system comprising a ?uid motor supplied
from a pump, the torque of the ?uid motor is a
function of the ?uid pressure of the system. Ac
For the purpose of controlling the energization
cordingly, the anti-hunting means 39 is made re
of the electric valve apparatus, suitable rotary 30 sponsive to the rate of change of the pressure of
induction apparatus is provided. This apparatus
the ?uid supplied from pump l3 to motor l2.
which is similarto electrical motion transmitting‘
It comprises a pair of cylinders 40 and ‘I, each
apparatus comprises an electrical transmitting
having a movable piston, and each having ?uid
device 21 and an electrical receiving device 28.
connections from the spaces on opposite'sides of
The transmitter 21 has a rotor member 21a pro 35 the pistons to the ?uid supply connections 42,
vided with a single phase winding (not shown)
43 to motor l2. Thus, the cylinder 4|! contains a
and a stator member 211) having a three element
movable piston 44 which is maintained by springs
winding (not shown) that is physically similar to
45, 46 in a central position when no difference
a three-phase winding. The receiver 28 is identi
' in ?uid pressure exists across motor l2. Sim
cal with the transmitter. As shown, the rotor 40 ilarly, the cylinder 4| has a piston I‘! which is
winding of the transmitter is connected to the
maintained in central position by springs 48,- and
upper and middle supply lines 2|, the stator wind
49 when the pressure drop across ?uid motor |2v
ings of the two devices are connected together
is zero. The space above piston 44 and the space
by means of conductors 29, and the rotor wind
beneath piston 41 are connected by pipes 50 and
ing of receiver 28 is connected to the grid or input . 5| to the lower supply connection 53, and the
circuit of the electric valve apparatus. The rotor
space beneath piston “and the space above pis
member 21. of the transmitter is connected
ton 41 are connected by means of pipes 52 and
through gearing 30 to the pilot device, 1. e., tele- '
53 with upper supply connection 42. Valves 54
scope II, and the rotor member of the receiver
and 55 are respectively connected in pipes 52 and
28 is connected through gearing 3| to the shaft 50 53 for restricting the ?ow in pipes 52 and 53 a
of motor 2|.
,
desired amount. One of these valves is opened a
When telescope | | and the shaft of motor 2|
greater amount than the other so that the rate
are in positions 01’ correspondence no ‘voltage is
of ?ow through the valves is different. It is as
supplied through transmitter 21 and receiver 28
sumed that valve 55 has the greater opening.
to the grid or input circuit of the electric valve
The 'two pistons 44 and 41 are connected to a
apparatus 22. As a result, the valve apparatus is
mechanical differentiating system which responds
deenergized and the motor 2| is at rest. When
only to the difference in position of the two pis
the telescope H is rotated in either direction, a‘
tons. Thus, when the steady state has been
voltage is supplied to the grid circuit of the valve
reached the two pistons come to rest at positions
apparatus, which energizes one or the other of 60 of equal displacement, both representing the ?uid
the pairs of valves, depending on the direction of
pressure of the system. However, one piston
rotation. This causes the motor to rotate in a
arrives at its steady state position faster than
corresponding direction, thereby rotating the
the other because of the di?'erence in the restric
rotor member of receiver 28 toward a position of
tions of valves 54 and 55. The di?'erential me
correspondence with telescope | I. When this po
sition of correspondence is reached the valve ap
aparatus becomes deenergized- and motor 2|
comes to rest. The load on motor 2| is so small
05 chanical system will therefore respond only when
there is a state of change of pressure.
The mechanical differentiating system ls'illus
trated as comprising a lever 56 pivotally attached
that the velocity lag between the'motor 2| and . at each end to one of the pistons 44, 41 and piv
the telescope is negligible. In other words, the 70 otally attached at its center to end of lever l'l
shaft of motor 2| .is always in substantial cor
remote ‘from control rod It.
respondence with telescope || both when the
With the foregoing understanding of the appa
tele :ope is moving and when it is at rest.
ratus and its organization in the system, the oper
As pointed ‘out in the foregoing, the connecting
ation of the system itself will readily be under
rod I5 is connected to the motor 2|, so that when 75 stood from the'following detailed description.
aeiaioa'i
?uid motor it, it begins to catch up with the
Assuming the‘sy'stem to be at rest with ‘the sun
shaft 2“, thereby rotating the output gear 201,
Ill in a position of correspondence with the tele
in the reverse direction, raising the control rod is
scope ii, the control will be deenergized and the
and decelerating the motor i2'and load ill. This
various parts in the positions in which they are
will again bring about changes in the pressure and
illustrated. Rotation of telescope H energizes in torque to which the anti~hunting ‘means will re
one or the other of the pair of electric valves 25,
spond to introduce the necessaryfcorrection. _
28 depending on the direction of rotation and
The movements of the pistons M and 61 in
causes the motor 2i to rotate the shaft 2i; in
‘response to pressure and torque changesgunder - '
substantial synchronism with the telescope.
varying conditions of speed, acceleration and de
Since the input spider 20a of the di?erential de
vice 20 is, for the instant, held against rotation
by the gun ill, the output elementg??s of the
differential is rotated causing the rack i8 to
celeration are sometimes extremely complex. ‘The
action described .in the foregoing is merely one
example of many possible. In general, when the
control functions and brings about a change in
move and actuate the control rod IS in a direc
tion, for example downwardly, such as to cause
?uid motor I? to drive gun in toward correspond
ence with telescope ll. As the control rod is
moved, the pressure of the ?uid in the system
rises very abruptly. almost instantaneously to
a high value. This means that a very high torque
is being applied to accelerate the mass of the
gun. Now, if this high torque continues to be _
. applied the gun l0 would be accelerated so rapidly
that it would over-shoot the position of corre
spondencewand thus give rise to a condition of
hunting. However, as the pressure starts to rise,
and assuming the upper connection at to be the
high pressure side, the piston 46 starts to move
upwardly and the piston l1 starts to move down
wardly. Since the valve 85 is opened much wider
than valve Sl' piston 41 moves downwardly at a
the pressure and torque conditions, the anti
hunting mechanism acts after a time interval to
introduce a correction responsively to the rate of
change ‘of torque opposing the action of the con~
trol and subsequently subtracts the correction so
introduced.
_
'
Although in accordance with the provision of
the patent statutes, this invention is described as
embodied in concrete form, it will be understood
that the apparatus and connections shown are
merely illustrative and that the inuvention is not
‘ limited thereto since alterations and modi?cations
will readily suggest themselves to persons skilled
in the art without departing from the spirit of
this invention or from the scope of the annexed
claims.
much greater rate than piston 64 moves upwardly.
The effect of this difference in the rates of move
ment of the pistons is to displace the fulcrum
point 585 downwardly and thereby to move the
control rod l6 upwardly or in~a direction oppo
\ site to that in which it was moved by motor 2!.
. This of course reduces the volume of ?uid sup
J What I claim as new and desire'to secure by
Letters Patent of the United States is:
1. In combination with a pilot device and driv
en object, hydraulic driving means for said object
comprising a ?uid motor connected to said object,
means for supplying ?uid under pressure to said
'motor, means responsive to positional disagree
ment of said device and object for controlling the
supply of ?uid to said motor, and anti-hunting
plied to motor l2 and thereby reduces the ?uid
means responsive to rate of change of torque of
pressure or torqueloi motor l2, and thereby pre 40 said "driving means for controlling the supply, of
vents over-shooting.
?uid 'to said motor.
At this point, it will be noted that immediately
2. In a follow-up system for driving an object
upon positional disagreement of the telescopeand
in positional agreement with a, pilot device, driv
gun, the ?uid pressure Or motor torque rises
ing means for said object comprising a ?uid
quickly to a high value, and a time interval after 45 motor connected to said object, a pump for sup
ward the anti-hunting means 39 operates to I
plying ?uid under pressure to said motor, means
oppose or reduce this rapid increase in torque.
responsive to positional disagreement of said de
As the ?uid pressure approaches a steady value, . vice and object for controlling the supply of ?uid
the piston 51 is displaced from its central position
to said motor to cause said motor to drive said
an amount proportional to the pressure drop 50_ object toward correspondence with said device,
across the ?uid motor I 2. Since the piston 41
and anti-hunting‘ means responsive to rate of
moves faster than piston M, it arrives at its ?nal
change of the pressure of said ?uid for control
displacement before piston 55. Thereafter, the ' ling the supply of ?uid to said motor.
piston 45 continues to move upwardly toward its
3. In a follow-up’ system for'driving an object
?nal displacement, and the effect of this move Cr in in positional agreement with a pilot device, driv
ment of piston 44 after piston it‘? has ceased to
ing means for said object comprising a ?uid mo
move is to move the control rod l6 downwardly
again thereby tending again to increase the ?uid
pressure and motor torque until the piston 44
has been displaced anv amount equal to the dis
placement of piston 41. After the ?uid pressure
of the system has become steady both pistons M
and 51 will be displaced equal amounts in oppo
site directions from their normal positions and
the correction introduced in the control by the
faster moving piston will have been completely
subtracted by the slower moving piston. Thus, it
will be seen that the anti-hunting mechanism
does not introduce corrections under steady state
conditions of ?uid pressure or motor torque, but
only introduces corrections when the pressure or
torque is changing. These corrections are also
proportional to the rate of change of pressure or
motor torque.
'
tor connected to said object, a pump for supply
ing ?uid under pressure to said motor, means for
controlling the supply of ?uid to said motor,
on means responsive to positional disagreement of
said device and object for actuating said control
means to cause said motor to‘ .drive said object
toward correspondence with said device, and .
.- anti-hunting means responsive to rate of ‘change
of torque of said driving means for effecting a
reverse operation of said control means a, time in
terval after actuation thereof by said positional
disagreement responsive means.
.
4. A follow-up control system comprising in
combination a pilot device, a driven object, driv
ing means for said object comprising a ?uid mo‘
tor connected to said object and a pump for sup
plying ?uid under pressure to said motor, a device
for controlling the supply of ?uid to said motor,
As the gun It is accelerated by the torque of 75
2,412,021?
means responsive to 'posltionaldisagreement of
said pilot device and driven object for actuating
said control device to cause said motor to drive
said object ‘toward correspondence with said pilot
device and means responsive to rate 0! change 01'
the pressure of said ?uid for producing a. reverse
actuation of said control device an interval of
time after actuation thereof by said positional
I
. 8
8; A follow-up system ‘for driving an object in
positional agreement with, a pilot device com- '
prisinga ?uid motor connected to said object, a
pump and ?uid supply connections from said
pump to said motor, a device for controlling the
supply of ?uid to said motor, means responsive to
positional disagreement of said ‘pilot device and
driven object for actuating said control device
disagreement responsive means.
7
to cause said motor to drive said object toward
5. ‘A follow-up system comprising in combina 10 correspondence with said pilot device, and anti
tion a pilot device, a driven object, driving means
hunting means for actuating said control device
for said object comprising a, ?uid, motor con
comprising a pair of cylinders, each‘ having a
nected to said object and a pump for supplying
piston movable therein in response to the pres
?uid to said motor, a device for controlling the
sure of said ?uid, means for causing said pistons
supply oi ?uid to said motor, means responsive 15 to move at di?’erent rates, and a mechanical dit
to'positional disagreement of said pilot device
ierentiating connection between said pistons and
and driven object for actuating said ‘control de
said control device for effecting actuation of said
vice to cause said motor to drive said object
control device in response to ‘the difference in
vtoward positional agreement with said pilot de
position of said pistons.
vice, and anti-hunting means comprising-a cyl
9. A follow-up control system for driving an
inder and a piston movable therein in response
object in positional agreement with a pilot device
to‘ the pressure of said ?uid for producing a re
verse actuation of said control device a time in—
comprising a ?uid motor connected to drive said
object, a pump for supplying ?uid to said motor,
terval after actuation thereof by said positional
a device for controlling the supply of ?uid to said
disagreement responsive means.
,
25 motor, means responsive to positional disagree
{6. Means for reproducing position comprising
a pilot device, a driven object, driving means for
said object comprising a ?uid motor connected to
ment of said pilot device and object for actuating
said control device to cause said motor to drive
said object toward correspondence with said pilot
said object and a pump for supplying ?uid to said
device, and anti-hunting means for producing an
motor, a device for controlling said pump to con 30 opposite actuation of said control device an in
trol the rate of supply of ?uid to said motor,
terval of time after actuation thereof by said dis
means responsive topositional disagreement of
agreement responsive means comprising a pair‘oi
said object and pilot device for actuating said
control device to cause said motor to drive said
object toward correspondence with said pilot de
vice and anti-hunting means for effecting a're
verse actuation 01' said control device a time in
terval after actuation thereof by said disagree
cylinders having connections to said ?uid system
and having pistons movable in response to pressure
35 of said liquid, ?ow-restricting means in said con
nections to provide for movement oi’ said pistons
at different rates and a mechanical di?'erentiating '
' connection between said pistons and said control
ment responsive means comprising a cylinder
device thereby to introduce an anti-hunting cor
having communication with said ?uid supply, a 40 rection substantially solely. in response to rate of
piston movable in said cylinder in response to the
change of ?uid pressure.‘
pressure of said‘?uid and means for restricting
10. A hydraulic power system, comprising a _
the ?ow of ?uid to said cylinder to control the
?uid motor, a pump to supply ?uid under pres
rate of movement of said piston.
sure to said motor, a device for controlling the
7. A follow-up control system comprising in 45 output of said pump, and means responsive to
combination a pilot device, a driven object. hy
rate of change of the pressure of said ?uid for
draulic driving means for said object comprising
producing reverse actuation of said control de- ‘
‘a ?uid motor connected to said object and a pump
vice an interval of time after actuation thereof.
for supplying ?uid to said motor, a device for
1.1. A hydraulic power system, comprising a‘
controlling the rate of supply of ?uid to said m0 50 ?uid motor, a pump to supply ?uid under pres
tor, ‘means responsive to positional disagreement
of said device and object for actuating said con
trol device to cause said motor to'drive said ob
sure to said motor. a pair of cylinders, a resil
iently balanced piston in each cylinder, means
connecting said cylinders to the ?uid supply be-.
ject toward correspondence with said pilot device,
tween said pump and said motor to move said pis
and anti-hunting means comprising a cylinder 55 tons differentially in response to rate of change of
and a piston movable therein in response to the
pressure of said ?uid for effecting a reverse actu
ation of said control device a time interval after
actuation, thereof by said positional disagreement
pressure in said ?uid supply, and means actuated
in common by said pistons to control the supply
of ?uid to said motor by said pump.
12. ‘A hydraulic power system, comprising a
responsive means and a‘ second cylinder having a. 60 ?uid motor, a pump to supply ?uid under pres~
piston movable therein in response to pressure of
sure to said motor, and anti-hunting means 11e
said ?uid and connected to said control device
for subsequently counteracting the e?ect of said
?rst piston.
sponsive to rate oi! change of torque of said motor
for controlling the supply of ?uid to said motor,
ERNST F. W; ALEXANDERSON.
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