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Oct. 1, 1946.
J. J. MÓYNIHAN
2,408,472
ELECTRICAL SYSTEM FOR THE CONTROL OF MECHANICAL DEVICES
Filed Aug. 28, 1941
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2 Sheets-Sheet l
Oct. 1, 1946.r
J. J. MoYNlHAN
2,408,472
ELECTRICAL SYSTEM FOR THE CONTROL OF MECHANICAL DEVICES
Filed Aug. 28, 1941
2 Sheets-Sheet 2
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2,408,472
Patented Oct. 1, 1946
`UNITED STATES PATENT. OFFICE
2,408,472
ELECTRICAL SYSTEM FOR THE CONTROL
OF DIECHANICAL DEVICES
John J. Moynihan, Boston, Mass., assigner of
one-half to Joseph B. Brennan, Cleveland,
Ohio
Application August 28, 1941, Serial No. 408,658
19 Claims.
(Cl. Z50-_2)
1
2
This invention relates as indicated to control
devices, and more especially to a novel method
and apparatus for the comparison of com
mensurable properties of a plurality of entities,
reached, until the correction has been achieved
within the desired limits.
Other objects of my invention will appear as
such comparison being accomplished by cyclically
varying a parameter of one such, and determin
ing whether the parameter of the other lies with
in the range of such variation. Not only does
this invention relate to such method and appa
ratus for making the comparison, but it also pro
vides an improved method and apparatus for so
changing one of the variables, when upon com
the description proceeds.
To the accomplishment of the foregoing and
related ends, said invention then comprises the
features hereinafter fully described and partic
ularly pointed out in the claims, the following
description and the annexed drawings setting
-iorth in detail certain illustrative embodiments
of the invention, these being indicative, however,
of but a few of the various ways in which the
principle oi the invention may be employed.
parison in the mode stated it is found to lie out
In said annexed drawings:
side of said range of variation, as to bring it
Fig. 1 is a schematic diagram of a remote con
within such range.
trol system for airplanes, such system compris
This invention has a wide ñeld of application
ing one embodiment of my invention which will
may be observed from the foregoing statement
be illustrative of its wider field of application as
oi its general principles. The invention can best
will be presently described.
be illustrated by having reference to one specific
embodiment thereof. This specific embodiment, 20 Fig. 2 is a schematic diagram similar to Fig, 1
showing the incorporation in the system of Fig. l
which is only one of its many possible adaptations
of a protective expedient preventing accidental
will be hereinafter more particularly pointed
or intentional outside interference;
out, pertains to the remote control of devices,
Fig. 3 is a representation of the type of emission
such as aircraft and the like, from a control sta
tion, such a problem giving rise, not only to the 25 from the local airplane oscillator.
Referring now more specifically to the draw
need for a comparison of a commensurable prop
ings, and more especially to Fig. 1, the system
erty or condition in both the control station and
illustrated in this figure may be divided into
the airplane, but also giving rise to the need for
two parts, A and B.
maintaining within limits at all times such prop
That part designated by the ordinal A is a
erties or conditions even though one such property 30
schematic representation of the equipment at the
or condition, as for example at the control sta
ground or control station from which the air
tion, may be varied with the intent that a corre
plane, carrying system B, is to be controlled. I
sponding variation will occur at the controlled
shall first indicate the nature of the apparatus
station.
which is thus shown assembled in Fig. 1, and
It is a principal object of my invention to pro
then follow such description with a detailed ex
vide a method and apparatus of the character
planation of its mode of operation by having
above described which is characterized by a high
reference to several selected sets of conditions.
sensitivity without, however, requiring the em
The control station A includes a control stick
ployment of extremely sensitive instruments and
40 I which, for convenience, may correspond in its
the like.
By having reference to the specific embodi
ment of the invention, which is to be presently
described, it is a further object of this invention
to provide method and apparatus of the char
construction and general mode of manipulation
to the control stick l' in the airplane. It will
be kept in mind that it is one of the objects of
this invention to provide control mechanism
actor described which will make possible not only 45 whereby the operator on the ground may manipu
late the stick I at his station, and have the stick
the desired sensitive control, but also the accom
I’ in the airplane follow precisely, and within
plishment of such control by apparatus which is
deiinite and known limits, the same manipula
not only readily available, but which, not being of
tions.
extreme sensitivity, may be used practically under
Mechanically connected with the stick I is a
conditions where rough usage is encountered.
50
conventional audio frequency oscillator 2.
It is a îurther object of this invention to pro
Throughout the following description, reference
vide a method and apparatus of the character
will Vbe had to certain standard radio equipment.
described in which the corrective force, applied
I have not attempted to illustrate the precise
when the system determines the necessity there
of, is such that it does not decrease in intensity 55 construction of such pieces of equipment. At a
later point in this specification, and after all of
as the neutral point ofthe control'system is
2,408,472
4
such conventional pieces of radio equipment have
been identified by reference characters, I shall set
forth a table in which such pieces of equipment
are cross-referenced to a standard treatise on
The effect of the periodic connection of con
denser Il into the resonant circuit of the fixed
frequency section of the beat-frequency oscil
lator is to modify the audio frequency output of
radio engineering in which the precise construc
tion and particular mode of operation of such
individual pieces of equipment is fully explained.
the oscillator which now emits a signal for any
The oscillator 2 is mechanically connected to
on the size of the condenser I‘I. The output of
the fixed frequency section I6 is fed through a
the stick I by means of a link 3. When the stick
I, or, as is now common practice, the control
wheel of the airplane, is moved in one direction
or other, the link 3 will cause an adjustment of
the oscillator 2 so that the latter is caused to
send out audio waves of different frequencies.
Generally, and in particular where apparatus
such as an airplane is to be controlled, it will be
necessary that the output of the oscillator be a
continuous frequency spectrum. from one end of
its range to the other. The audio frequency out
put of the oscillator 2 is applied to a modulator
stage 4 which modulates the output of a conven
tional radio frequency transmitter 5. The out
put of the transmitter is fed to a suitable an
tenna 6.
Referring to the apparatus, B, the modulated
one position of the control stick I', periodically
varying in frequency by an amount dependent
radio frequency filter 2U, in the conventional
manner, to a mixer stage 2|, and the low fre
quency heterodyne output of the mixer stage is
fed to an audio frequency amplifier 22 and a
band pass filter 23, all in a manner well-known
in the art.
The output of the airplane beat-frequency os
cillator I3 is now fed by suitable connections C to
the heterodyne mixer stage I2 simultaneously
with the incoming signal as heretofore described.
The heterodyne signal from mixer stage I2 is
fed through a low pass filter 24 and a high pass
filter 25 to an audio frequency amplifier 25, The
numerical value of the cut-off point of the low
pass filter 24 will be approximately equal to the
difference between the lowest frequency emitted
radio wave emitted by the ground station an~
by the ground station oscillator 2, and the highest
tenna 6 is received at the airplane antenna 'I,
frequency emitted by the airplane oscillator I3.
and fed, if necessary, through a current limiting
The numerical value of the cut-off point of the
network 8, the purpose of which is to prevent a
high pass filter 25 will be approximately equal to
destructive amount of energy being applied to 30 the difference between the signals emitted by the
the radio receiver 9 when the aircraft is in the
ground station oscillator 2, and the airplane os
immediate vicinity of the ground station.
cillator I3, for corresponding positions of the
After passing through the current limiting net
control stick. The audio frequency amplifier 26
work 8, a signal is impressed on a standard radio
must be capable of amplifying linearly any sig
receiver 9 and, after detection, is amplified by a
nals which pass through both the low pass filter
standard audio frequency amplifier I3. The
24 and the high pass filter 25. After the hetero
characteristics of the current limiting network
dyne signal has been ampliñed, it is applied to a
8, radio receiver 9, and the audio frequency am
rectiñer stage 21, the output of which is fed to
plifier IIJ, should be such that audio signals over
the coil 28 of a single-pole, dcuble-throw relay
the entire spectrum used by the ground control 40 29.
stations should be amplified substantially linear
Referring again to the motor driven switch I9,
ly; that is, the system should comprise a high f1
there is provided an auxiliary switch 3D connect~
delity receiver system over the range of audio fre
ed in synchronism with switch I9, and so ar
quencies used.
ranged that when switch I9 is closed, switch 30
After amplification, the signal is passed to the » is closed onto contact 3|, and when switch I9 is
band pass filter II, the cut-off points of which
open, switch 39 is closed on contact 32. Relay
correspond to the extreme frequencies emitted
29 is arranged so that when the coil 23 is ener
by the ground station oscillator with the control
gized, the switch element is closed on contacts
stick in either extreme position. The incoming
33, and when the coil 28 is not energized, the
audio frequency signal is now passed to the het- 50 switch element is closed on contacts 34.
erodyne mixer stage I2 where a locally generated
A local source of current such as a storage bat
signal is also applied.
tery 35 is provided. The terminal I 90 of the stor
The locally generated signal is produced as
age battery 35 is connected by means of the lead
follows: Connected to the control stick I’ of the
airplane is a beat-frequency oscillator I3 by
means of a link I4. One section of the beat-fre
quency oscillator I3 consists of an oscillator I5,
the output frequency of which is capable of being
varied. The other section of the beat frequency
IIII to the arm of switch 39. The other terminal
|02 of the battery 35 is connected by means of a
lead IIJ3 to one pair of contacts 33 and 34 of the
relay 29. A lead IM connects the other contact
34 to the contact 32 of the switch 30. A lead
IU5 connects the other Contact 33 to the contact
3I of the switch 39. It will be observed that
put frequency of which is substantially constant
the coil of relay 3l is connected in series in line
except when periodically varied as described
|04 and the coil of relay 36 is connected in series
later.
in the line Illl‘». It will be observed that when
The resonant circuit of oscillator I6 has con
contacts 33 of relay 29 are closed, and contact
nected therein a small condenser I'I in series with
3! of switch 30 is closed, solenoid valve coil 35 is
a single pole switch I9, and so arranged that it
energized; and when contacts 34 of relay 29 are
may be connected in shunt with the main tun
closed, and contact 32 of switch 33 is closed,
ing condenser IB for one position of the switch
solenoid valve coil 3l is energized; and under
I9.
all other combinations of switch and relay posin
The switch I9 is actuated by a motor driven 70 tions, solenoids 33 and 3l are deenergized.
mechanism. A motor I9a is coupled thereto by
Solenoid coils 36 and 3l operate to open sole
means of an eccentric arm or pitman C whereby
noid valves 38 and 39 respectively when ener
rotation of the motor continuously in one direc
gized, and a double acting compressed air cylin
tion will cause the switch to be alternately
der 40 is provided, so arranged that when valve
opened and closed.
75 38 is opened by the energizing of coil 35, the
oscillator I3 consists of an oscillator I6 the out
2,408,472
5
oiîset from the ground station oscillator as shown
in the table. It will also be apparent that it is
undesirable for the highest frequency emitted
by the ground station oscillator to exceed twice
the lowest frequency, if the control frequencies
airplane stick I’ is pushed forward, and when
valve 39 is operated by the energizing of coil 3l,
the airplane stick l’ is pushed backward by means
of the cable assembly generally indicated at 4I.
A line for the admission of compressed air to
are selected according to the above considera
the cylinder 40 is shown at 42, and will be con
tions. The exact values of the frequency allo
nected to some suitable source of compressed air
cations are not critical and do not constitute a
supply, not shown.
part of the invention.
The system shown in Fig. 1 is complete as to
The band pass filter II will, in all cases` have
the control of any one function of the airplane. 10
cut-ods at the extreme limits of the frequency
In this case, I have chosen to illustrate the con
values of the oscillator 2. The purpose of the oí
trol of the stick fore-and-aft. For complete con
setting of the local oscillator by a constant num
trol of the airplane, provision must be made for
ber of cycles from the corresponding positions
control of the motion of the stick right-and-left,
of the ground station oscillators is to provide
and control of the rudder bar position, in ac
a directive characteristic to the control system;
cordance with the established principles of con
that is, the function of the onset is to cause a
trolling the motion of> an airplane in pitch, roll
discrimination between the signal produced (be
and yaw. Auxiliary controls are also necessary.
yond the heterodyne mixer stage I2) by the mo
For example, the engine speed should preferably
be controlled. Similarly, such auxiliaries as 20 tion of the ground control stick to a position, say,
flaps, brakes, landing gear manipulating devices,
and >armament may require to be controlled. In
such cases, additional control channels will be re
quired, said channels being tied in after the audio
frequency amplifier I0.
Two such additional control channels |06 and
200 cycles higher than neutral, land a similar
motion to a position, say, 20D cycles lower than
neutral.
The control frequency channels should prefer
ably be separated from one another by dead spots
25
in the audio spectrum so that the band pass
filters II do not have to discriminate sharply
|01 are shown in Fig. l in skeleton form for the
between received signals.
control of the motion of the stick left-and-right
For the study of the operation of the device,
and for the rudder bar control. For purposes
certain
instantaneous positions of some of the
of establishing an illustrative design, the follow 30
elements thereof will be assumed. First, we will
ing numerical values have been assigned to the
assume that the ground control stick is neutral,
frequency of the oscillators and filters in the sys
the airplane control stick is neutral, switch I9
tem shown in Fig. 1.
is open, and switch 30 is on contact 32. This
35 will be, for purposes of convenience, referred to
Stick
Stick
Stick
Local osc.
forward
neutral
back
offset by
Ground BFO ________ __
1, 250
1,600
1, 950 }
Airplane BF O _______ _ _
1, 750
2, l0()
2, 450
hereinafter as “Condition A.”
Condition A
500~
Stick
Stick
Stick
Local csc.
left
neutral
right
offset by--
Ground BFO ________ __
2, 500
3, 200
3, 900 }
Airplane BF O ____ _ _'. _ _
3, 500
4, 200
4, 900
Rudder
Rudder
Rudder
left
neutral
right
1 OOON L
’
Local osc.
offset by
The first thing we will show is that under
these circumstances, the mechanism in the air
plane does not tend to throw the airplane con
trol off the neutral position. The same thing ap
plies Veven if the two sticks are not in neutral,
provided their positions relative to their respec
tive neutral positions are the same. That is, if
the ground control stick is in a dive position,
and the airplane control stick is in the corre»
sponding dive position, the mechanism of the
airplane will not tend to change the position of
the airplane stick.
Ground BFO ________ __
5, 000
6, 500
8, 00() }
Airplane BFO _______ __
6, 000
7, 500
9.000
1 OOON
’
For purposes of description, we will assume that
the ground control oscillator delivers a note of
1600 cycles when the ground stick is in neutral,
and that the output of the airplane beat fre
ous table headed “Local osc. Oiïset by” are in n quency oscillator is 2100 cycles for the neutral
each instance the difference between the fre
position of the airplane control stick. This 2‘100
quency of the signal emitted by the ground beat
cycles is the basic note delivered by the airplane
frequency oscillator and the airplane beat fre
beat frequency oscillator. The mechanism in the
airplane is arranged to change this basic note
quency oscillator.
Certain practical considerations are responsi 60 periodically by any of several means, the most
convenient of which is probably to shunt a small
ble for the choice of the frequencies. Since it
condenser Il, similar to an ordinary radio trim
is desired that the corrective control frequency
mer condenser, across the tuning condenser I8
and any possible positions of ground stick and
of either section of the beat frequency oscillator,
airplane stick be unique, it is necessary that the
but preferably across the fixed frequency tuning
range of difference frequency produced by the
condenser. The reason for this preference is that
heterodyne mixer stage I2 should not include
under these circumstances, the addition of a fixed
either the radio control signal frequency or the
condenser to the tuning section will detune the
locally generated signal frequency. Therefore,
fixed frequency section a constant amount, and
the low pass filter, after the mixer stage I2, will
have a cut-off for each channel equal to the .dii 70 will change the note delivered by the entire beat
frequency oscillator by a constant amount, say
ference between the lowest frequency generated
100 cycles, for all positions of the beat frequency
by the oscillator 2, and the highest frequency
oscillator.
generated by the oscillator I3.
, This is not necessarily true if thevariaible fre
The high pass ñlter 25 will have a cut-off ,equal
to the frequency by which the ‘local oscillator is 75 quency section of the beat frequency oscillator
The figures given in the last column of the previ
2,408,472
7
is shunted by this condenser, that is, under these
latter circumstances, the note might vary, say
100 cycles, at the low frequency end of the set
8
a value not exceeding about 21/2% of the value
of signals which are not attenuated.
A high-pass ñlter is, of course, one which
ting, and 150 cycles at the high frequency end.
Driven in synchronism with the switch I9 which
passes frequencies above its cut-off point, and
which attenuates frequencies below the cut-off
cuts the modifying condenser in and out, is an
other single-pole, double-throw switch 30 whose
function will appear later. In operation, the
1600 cycle note emitted by the ground station
oscillator is used to modulate a standard radio
transmitter. The standard radio transmitter car
rier is received at the aircraft antenna, and if
the airplane and the transmitter are to be oper
ated close to one another, a current-limiting net
work is inserted after the antenna, as the high
power field in the vicinity of the transmitter
might cause damage in the first stages of the
radio receiver.
point. The design of the filter must be such that
it will attenuate the frequencies below the cut
off point so that they will be incapable of oper
The signal having passed through the current
ating any device beyond the filter, and I have
assigned an arbitrary figure of 21?¿% because it is
easy to make the relays to be operated compara
tively insensitive.
The 500 cycle signal having been passed by the
high-pass filter 25 is amplified by a conventional
audio frequency amplifier 26 and rectified or de
tected by a power rectifier 21. The function of
the power rectifier is to enable the use of the
energy contained in the control signal for oper
ating a direct current relay 29 by energizing its
limiting network 8 is impressed on a standard
radio receiver, probably a good high-grade ama
coil 28. If the energy in the 500 cycle signal
were not rectified, the signal being alternating
teur communication receiver 9, and, having been
detected in the radio receiver, is amplified, pref
erably with automatic volume control operated
from the audio signal. This arrangement is dif
lay 29. An arbitrary figure of 10 milliamperes
ferent from the automatic volume control ordi
narily employed in radio receivers in that the
conventional control operates on the carrier in
order to maintain a constant radio signal in the
radio receiver prior to detection.
After amplification, the received signal is split
up by means of band pass filters into the control
signals required for controlling the flight path of
the airplane along its three axes, and for such
other controls as may be desired.
We are con
current would not be able to operate the D. C. re
of D. C. current has been assigned as the value of
the current output of the rectifier. The only
reason for assigning this value is that it is with
in the range of ordinary operating currents, and
it allows us to discriminate in this discussion
between conditions where no current is flowing,
30 and where current sufiicient to operate the re
lay is flowing.
Since under the assumed conditions current is
flowing in the relay coil 2‘8, the contacts 33 of
relay 29 are closed. Now referring back to the
35 synchronously driven switch 3D, associated with
the switch I 9, we find that during the interval
sidering only the control of the stick fore-and
aft. The band pass ñlter II for this control
under consideration, the modifying condenser I1
channel will correspond to the oscillator control
is not cut into the circuit, switch I9 being on an
limits of the ground stick oscillator. That is, only
open contact, and switch 30 being on contact 32.
those frequencies will be effective in this channel if) Since contacts 33 of relay 29 are in series with
beyond the band pass filter II which lie within
contact 3I of switch 30, there is no current flow
the limits of the oscillator at the ground station
ing at the instant under consideration in any
corresponding to the stick fore-and-aft control,
part of the network comprising contacts 33 and
in this case assumed to be 1250 to 1950 cycles.
34 of relay 29, contacts 3I and 32 of switch 30,
Since the control frequency' 1600 cycles lies
and the two solenoid operating valve coils 35 and
within the pass iband of the iilter II, it is passed
31 which comprise the network. There is thus
unattenuated to the heterodyne mixed stage I2.
at the instant under consideration no tendency
The output of the airplane beat-frequency oscil
for the compressed air cylinder to be energized
lator, in this case 2100 cycles, is also passed to
to change the position of the control stick which
the heterodyne mixer stage. When the two sig
is assumed to be in neutral position.
nals are mixed there will appear in the output
The foregoing description has been given for
four signals, viz.1 the two signals which are ap
the instantaneous condition which maintains
plied to the input, a signal frequency equal to
when the ground control stick and the airplane
their sum, and another signal frequency equal
control stick are both in neutral position, and
to their difference. This is the case in all heter- ; the switch I 9 is open. With both ground and
odyne systems. The applied signals and the sig
airplane control sticks still in the neutral posi
nal frequency equal to the sum of the applied
tion and with motor I9a operating continuously,
signals are of no value in the control of the air
during the next instant (approximately one-half
plane. They are, therefore, rejected by means
second later for example) the motor I9a will
of a low-pass filter 24 which rejects all frequen 60 have closed the switch I9, and simultaneously
cies above 1200 cycles for this particular channel.
the switch 30 will be on contact 3|. This will
The reason for the choice of 1200 cycles is that
be referred to for convenience hereinafter as
it represents the difference-frequency corre
“Condition B.”
sponding to a heterodyne between a 1250 cycle
Condition B
note and a 2450 cycle note, the former represent
The
ground
signal
is the same as that out
ing the low limit of the ground oscillator, and the
lined
in
Condition
A,
that is, the stick is in
latter the high limit of the airplane oscillator.
neutral and the ground oscillator is emitting a
Since the difference-frequency under the as
1600 cycle note. The synchronously driven
sumed conditions of both sticks being in the same
switches I9 and 30 in the airplane, however, are
relative position is 500 cycles, for this channel, 70 in the position shown in Fig. 1, that is, the modi
this is passed through the low-pass filter unat
fying condenser I1 has been cut into the beat
tenuated. This 500 cycle signal is applied to a
frequency oscillator tuning circuit. The beat fre
high-pass filter, which passes all frequencies
quency oscillator, therefore, is delivering a signal
greater than 500 cycles unattenuated, and which
equal to 2000 cycles instead of the 2100 cycles as
attenuates all frequencies less than 500 cycles to 75 sumed previously.
9
2,408,472v
The exact value of the difference between that
delivered by the airplane frequency oscillator
the ground stick has been moved forward sulfi
cient to Vcause a change of A200 cycles in the fre
quency emitted by the ground station oscillator
under Condition A and under Condition B is not
important, the only function of this difference
in frequency being to provide a tolerance for the
operation of the device.
2, and with the airplane stick in the neutral posi
tion, and at the instant in the cycle when switch
I9 is open and switch 30 is on contact 32 (the
I have assumed a 100 cycle difference in fre
quency when the switch I9 is cut in. This fre
quency may be different for the three control
same as in Condition A above).
Condition C
In the case assumed, the signal emitted by the
ground station is 1400 cycles, and we are assum
ing that the stick in the- airplane is in neutral.
We will consider the situation under the same
channels without affecting the operation of the
device. The condenser Il may change in value,
and the frequency emitted by the control oscil
lator in the airplane may change in value, with
out affecting the operation of the device. The
only important thing is that the note delivered
by the airplane oscillator should change, when
the switch I9 is closed, sufficiently to enable
ordinary cheap, conventional, rugged filters to
time circumstances as the first discussion, that is,
cycles instead of 500 cycles as before.
are the same as outlined previously.
with switch I9 open and switch 30 on contact 32.
Under these circumstances, a signal of 2100 cycles
is fed into the mixer together with a 1400 cycle
signal from the receiver. The output of the mixer
discriminate with respect to the two notes
includes the difference-frequency, 700 cycles,
emitted.
20 which is passed through the low-pass filter un
Switch 30 synchronously driven with switch
attenuated, and through the high-pass filter un
I9 is now in the 31 position. The incoming sig
attenuated since the signal lies vbetween the cut
nal as before is received at the aircraft antenna,
off points of each filter. The signal is amplified
passed through 9 and I0 as a 1600 cycle signal,
and rectified as before. A D. C. current of l0
and following the same reasoning as before, is 25 milliamperes assumed is applied to the relay 29,
passed unattenuated through the band pass
and the switch bar of relay 29 is on contacts 33.
filter II. However, when the 1600 cycle signal
However, no current will flow in the circuit, and
from the receiver and the 2000 cycle signal from
accordingly relay 36 will not be energized be
the airplane beat frequency oscillator are ap
cause switch 30 is on contact 32. As before, no
plied to the mixer stage, the difference-frequency 30 operation of the solenoids 36 and 3l occurs, since
in the output of the mixer is observed to be 400
the switch conditions of relay 29 and switch 30
The 400
cycle note is passed through the low-pass filter
unattenuated.
Condition D is assumed to be approximately
The high-pass filter, however,
one-half second after Condition C just described,
attenuates the 400 cycle signal so that although 35 with the switch I9 in the closed position, switch
it has some value, the audio frequency amplifier
30 on contact 3! and the ground stick in the posi
is unable to build up the energy in the signal to
tion described in Condition C and the airplane
a point where, after rectification, sufficient D. C.
stick still in the neutral position.
can be derived to operate the relay 29.
We will assume that a half milliampere of D. C. 40
is applied to the closing coil of relay 29, and that
the sensitivity of the relay has been adjusted by
Condition D
In the succeeding half second, the switches I9
conventional methods so that a half milliarnpere
and 3i) being in the same respective positions as
assumed in our second discussion, the oscillator
will not lift the armature, and, therefore, the
output of the airplane oscillator being 2000 cycles
switch bar of relay 29 will not be lifted from the 45 and the incoming signal 1400 cycles, a difference
contacts 3d. For any current to flow in the cir
frequency of 600 cycles is produced in the mixer
cuit of the battery, it would be necessary, for this
stage. The 600 cycle signal is' passed unattenu
instant of operation, for the switch bar 30 to be
ated through the lowépass and high-pass filter,
closed on contact 32. However, since the switch
amplified and rectified as before, and the current
bar 30 is closed on contact 3 I, no current will flow 50 of 10V milliamperes D. C. derived from the rectifier
in the relay coil 31.
used to operate the relay 29.- Since the relay 29
The above description has shown, therefore,
is energized, contacts 33 are closed, and since
that under the conditions outlined with both
contact 3| of switch 30 is also closed, the circuit
sticks neutral, no tendency exists for a change
is closed, energizing te solenoid operating valve
in the position of the stick in the airplane. By
a similar process of reasoning in which only the
values of the frequencies emitted by the ground
and airplane oscillators are changed, it can be
shown that at any time when the two are in coin
cident positions no tendency exists to change the
position of the stick in the airplane.
At this- point we might summarize the reasons
for the difference by 500 cycles of the signals re
spectively emitted by the ground station oscillator
and the airplane station oscillator. The differ
ence 015500 cycles is to provide a discriminating
indication between a change of, for example, 100
cycles due to moving the ground stick forward,
and the change of 100 cycles due to moving the
ground stick backward; this will become evident
in the description of what happens when the
ground stick is moved forward by an amount suf
ficient to cause a change’ of 200 cycles in the fre
quency of the ground station oscillator.
For Condition C, we willl assume the case where
coil 30, allowing compressed air to be applied to
one end of the air cylinder which, through me
chanical linkages, moves the stick forward.
AsY soon as the position of the stick in the air
plane has reached a point where, when the switch
60 30 is on contact 3I a signal of less than 500 cycles
is delivered by the mixer stage, the relay 29 will
no longer lift the armature in closed circuit 33,
and under these circumstances, the energizing
circuit will no longer be closed, andthe stick will
65 tend to remain in the position it has adopted,
which is the same relative toits neutral position
as the position of the ground stick is to its neu
tral position, until either the ground stick is
moved or the airplane stick moves or drifts out
70 of such relative position.
Condition E
For Condition E, the ground stick is assumed
to be moved backward to a pointv where a signal
75 of 1800 cycles is emitted from the ground sta
2,408,472
1l
12
tion, the airplane stick is assumed to be in neu
the previous portion of this description relating' td
tral, switch I9 is open, and switch 30 is on con
tact 32.
Under these circumstances, the output of the
mixer stage is a 200 cycle note, which is at
tenuated on passage through the high-pass filter,
such apparatus.
A single beat frequency oscillator is provided
aboard the airplane, the output of which is ap
plied to the heterodyne mixer stages I2 and I2a
as described in connection with Figure l, and
the operation of the entire duplicate set of con
trol channels up to and includingr relays 29 and
29a through their connections c’ and c" is as
previously described. In the wiring of the relays,
and which on rectification delivers a D. C. cur
rent insufficient to operate the relay 29. Con
tacts 34 of relay 29 are, therefore, closed, and a
circuit comprising contacts 34, contact 32 of switch
solenoids, and switch 3B, however, the contacts
SB, and solenoid 31, is closed.
In each of the foregoing conditions, it has been
assumed that the airplane control stick is in the
neutral position and the ground control stick
of the two relays 29 and 29a are connected in se
ries so that simultaneous operation of the two
either in a coincident or different position. It will .
be obvious that the conditions of operation which
have been described will be the same for all rela
tive positions of the plane and ground stick,
whether one or both are in neutral or off-neutral
positions.
relays is required to permit the energizing of the
solenoids 36 and 3l. Thus, it will be seen that
the legitimate control signal, being transmitted
by both the control transmitters 5I and 5Ia, will
operate the relays 29 and 29a simultaneously, and
thus effect the control of solenoids 3B and 31.
20 A single interfering signal, however, even if on
the frequency of one of the control transmitter
carriers, will operate only one of the relays 29
or 29a, and unless the operation happens to co
incide with the desired control, no effect will
the plane stick into correspondence with the posi
be had on solencids 3S and 31. It will, there
tion of the ground stick.
fore, lbe impossible for accidental or willful inter
In the description of conditions B and D, it
ference to produce miscontrol of the airplane
has been stated that the airplane stick is in a
unless such interference comprises two transmit
neutral position, when in the case of condition
ters operating on the same frequency as those of
D, particularly, a corrective force may have been
applied. The description of the conditions has 30 the control station, and modulated by identical
signals different from those required for control.
not taken into account the possible movement of
It is obvious too, as an evidence of this inven
the airplane stick in response tc- the corrective
tion, that a plurality of transmitters and control
force applied during the previous instant. It is
channels greater than two may be employed, the
obvious that the device will operate properly re
When the two sticks are not in corresponding
position, there is a corrective tendency on the
part of the mechanism in the airplane to bring
relay contacts being connected in series to pre
vent operation unless three or more carriers are
during the period when switch I9 is open, or dur
received simultaneously.
ing the period when switch I9 is closed, and it
As previously indicated, the equipment illus
will also be obvious, from a study of the descrip
trated diagrammatically and referred to in gen
tion, that corrective changes of the position of
the airplane stick occur during opposite relative 4.0 eral terms in the foregoing description is all more
or less standard radio equipment, and for a full
halves of the cycle of switch I9, depending on
understanding of the precise construction and
whether the airplane stick is forward or aft, rela
mode of operation of these various items refer
tive to the position occupied by the ground stick.
gardless of whether the ground signal changes
Figure 2 is a disclosure of a modification of this
system, the purpose of which is the prevention
of accidental or willful interference with the op
eration of the device when, as may happen, a
modulated carrier is received on the same fre
quency as the ground control transmitter, but
emanating from some other transmitter in the
vicinity. In particular, when the control is used
for military purposes, the enemy may, by listening
in on the lband in which the control transmitter
is operating, determine the carrier frequency, and
adjust his own transmitter to emit a carrier of
the same frequency on which he may modulate
a random frequency, different from that em
ence may be had to the work on “Radio Engineer'
ing” by Frederick Emmons Terman, second edi
tion, McGraw-Hill Book Company, Inc., New
York (1937). In the following table are given,
first, a list of the reference characters employed
in the foregoing description and in the drawings
in the identification of particular equipment
units; second, the figure number, if any, of the
Terman book illustrating such unit in greater de
tail; and third, the page of such book where such
figure number occurs, and in certain instances, a
description of the apparatus.
Reference character
Termen Fig. No.
Tcrmau page No.
2
200
371
ployed by the original station, thus eliminating
the original station as the controller. The meth
od by which this interference may be circum
vented comprises simultaneously modulating two
radio transmitters having different carrier fre
quencies with identical signals from oscillator 2.
In Figure 2, the modulators and transmitters
are shown as 50, 50a, 5I, and 5Ia. The control 65
equipment aboard the airplane has the same nu
merals assigned to it as in Figure l for one chan
nel, and the same numerals with the switch, a,
for the other channel. For convenience in de
scription, items 8, 9, I0 and II have been grouped
into a block, and similarly, items 24, 25, 25 and
21 have been grouped into a block.
For an illustration and for identification of the
apparatus used between the antenna and relays
(Various other types of audio-frequency oscilator are also suitable)
4 5
l
227
l
411
t (see rig. 5)
9 (Conventional amateur communications receiver)
~
n
101A
42
189
88 t0 92
25o, 251, 252
45o to 452
15 (Similar to Ref. 2)
16 (Similar to Ref. l5, with modifications shown on
2
drawinff)
2l
22
23
~
a
24
114
250, 251, 252
101A
450 to 452
189
42
es to 92
24 (Similar to Fig. 268i)
25 (No illustration iu this text)
483
26
27
18€)
433
101A`
239
The design of the various components adapted
from Terman’s text is intended to be merely illus
29 and 29a, reference may be had to Figure 1 and 75 trative as an aid in tracing the operation of the
2,408,472'
'
13
system, and it is not intended that the citation
of these ñgures from this text are restrictive of
the methods which may be employed to obtain my
results; nor is it intended as a statement that
the methods shown by Terman may be employed
exactly as shown. Rather, it may be necessary to
modify them to adapt them to use in this inven
tion, but such modifications are apparent to those
skilled in the art.
In Figure 3, I have illustrated the character
istics of the signal emitted by the airplane oscil
lator. From the following description of Figure 3,
the wider application of my invention than its
restricted application on remote control airplanes,
will become apparent to those familiar with the
art.
In Figure 3, the horizontal axisv of the graph
is a time axis, and the graduations along the
14
tion of the stick in the airplane. For example, a
wheel may be used on the ground to affect motion
of a stick in the airplane.
It is obvious that the cyclically varied signal
may originate at either the control station or the
station to be controlled provided there are means
for synchronizing the signal varying mechanism
with the relay 29.
As readily seen, analogous conditions may be
controlled similarly where there is in general a
variable factor' at one point which is to be corre
lated to and controlled by suitably varied con
trolling means at another point, with transmission
of signals between.
Other modes of applying the principle of the
invention may be employed, change being made
as regards the details described, provided the fea
tures stated in any of the following claims or the
equivalent of such be employed.
horizontal axis are marked according as the switch
I, therefore, particularly point out and dis
I9 is opened or closed at the time under con 20
sideration. When the switch I9 is open, the fre
quency emitted by oscillator I3 which is dotted
along the vertical ordinate of the graph will be
higher than the frequency emitted when switch
tinctly claim as my invention: ~
l. In apparatus for the comparison. of two com
mensurable properties, within a predetermined
range of variation of a parameter thereof, the
Thus, for any one setting of the 25 combination of means for selecting from one a
stand-ard of value and means for simultaneously
control stick I', a periodically varying frequency
comparing together values indicated by the two
will be emitted by oscillator I3. The variation in
respectively while cyclically varying the value of
the emitted frequency will be of the order of
the parameter of one of said properties and means
100 cycles when the switch is closed. This 100
cycle Variation in frequency is constant approxi 30 for determining whether the parameter of the
other property lies within such range.
mately at all positions of the control stick I". The
2. In apparatus for the comparison of two’ com
basic frequency, that is, the frequency of the
mensurable properties, within a predetermined
oscillator I3 when condenser Iï'I is out of the
range of variation of a parameter thereof, they
circuit, will Vary according to the position of the
~ combination of means for selecting from one a
control stick. The modified frequency, that is,
standard of value and means for simultaneously
the frequency emitted by the oscillator I3 when
comparing together values indicated by the two
condenser I1 is connected into the circuit, will
respectively while cyclically varying the valueI of
likewise vary as the position of the control stick
the parameter of one of said properties over said
I is varied; and the modified frequency will, for
predetermined range and means for determining
all positions of the control stick, be approxi
whether the parameter of the other property lies
mately 100 cycles lower than the basic fre
within such range.
quency.
3. In apparatus for the comparison of two
I have indicated on the drawings, and elsewhere
I9 is closed.
in the specification, that the approximate period
commensurable properties, the combination of
of the motor driven switch is one second. It will
means for selecting from one a standard> of value
be appreciated that the exact value of this period
is a matter for the judgment; of the designer. 'I‘he
period should not be so short that switching dini
culties will be encountered due to the mechan
ical inertia or difliculty inl keeping switch 30 in .
synchronism with switch I9; and ' the period
should not be so long that the aircraft flies for an
appreciable length of time in an undesired direc
tion without a corrective tendency on the-part of
the mechanism.
In an analysis of the control system, it will be
seen that we have here two variables, the position
and means for simultaneously comparing together
values indicated by a common characteristic of
the two respectively while cyclically varying a
characteristic of one of said' properties over a
predetermined range, and means for determining
whether a characteristic of the other property
bears a particular relationship to such range.
4. In apparatus for the correlation of two com
mensurable properties, within a predetermined
range of variation of a parameter thereof, the
combination of means for selecting from one a
standard of value and means for simultaneously
comparing together values indicated by the two
of the ground stick, and the position of the air
respectively while cyclically varying, from a nor
plane stick; that each of these variables has a
common parameter, for example the frequency 60 mal, the value of the parameter of one of said
properties and means for adjusting the normal
of the audio frequency signals emitted by the
value of the parameter of one of said properties
ground and aircraft oscillators respectively; that
so that the said range of cyclic variation of the
this parameter is a function of the respective
magnitude of the parameter of one of said proper
positions of the sticks; that these two functions
are being constantly compared as to magnitude 65 ties includes the magnitude of the parameter of
the other of said properties.
by the cyclic variation of the parameter of one
5. In apparatus forthe correlation of two com
of them, that is, the airplane control stick oscil
mensurable properties, within a predetermined
lator; and that the comparison of the two func
range of variation of a parameter thereof, the
tions of the parameter is utilized to obtain a
corrective force for changing the position of the 70 combination of means for selecting from one a
standard of value and means for simultaneously
airplane control stick. It is obvious that the
comparing together values indicated by the two
principle here enunciated is of wide application.
respectively while cyclically varying, from anor
Retaining the airplane control system as a basis,
mal, thevalue of the parameter of one of said
it is obvious that the method of varying the ground
stationV oscillator need not be similar to the Ino 75 properties, and means for adjusting the' said nor
15
2,408,472
mal and accordingly the said range of cyclic
variation so that'l such range includes the param
eter of the other of said properties.
6. In apparatus for the correlation of two com
mensurable properties, within a predetermined
range of variation of a parameter thereof, the
combination of means for selecting from one a
standard of value and means for simultaneously
16
signal bears’ a predetermined relationship to the
signal of the other device.
12. In apparatus for the correlation of two
remote mechanical devices actuating electrical
devices respectively adapted to emit electrical
signals having variable frequencies indicative of
different states of physical adjustment of each
said mechanical device, the combination of means
comparing together values indicated by the two
for selecting frequencies from one as control
respectively while cyclically varying the value 10 and means for mixing together frequencies simul
of the parameter of one of said properties and
taneously from the two systems while cyclically
means for adjusting the value of the parameter
varying the frequency of the signal of one of said
of the other of said properties so as to bring the
devices over a predetermined range, and means
same within the said range of cyclic variation.
for adjusting the physical condition of said last
'7. In apparatus for the correlation of two com 15 named device so that the range of cyclic varia
mensurable properties, within a predetermined
tion of the frequency of its signal bears a prede
range of variation of a parameter thereof, the
termined relationship to the signal of the other
combination of means for selecting from one a
device.
standard of value and means for simultaneously
13. In apparatus for the correlation of two
comparing together values indicated by the two 20 remote mechanical devices actuating electrical
respectively while cyclically varying the value
devices respectively adapted to emit electrical
of the parameter of one of said properties and
signals having variable frequencies indicative of
means for adjusting the value of the parameter
different states of physical adjustment of each
thus cyclically varied so as to bring the range
said mechanical device, the combination of means
of such variation into predetermined relationship 25 for selecting frequencies from one as control and
to the parameter of other of said properties.
means for mixing together frequencies simultane
8. In apparatus for the comparison of two
ously from the two systems while cyclically vary
systems respectively adapted to emit electrical sig
ing the frequency of the signal of one of said
nals having commensurable characteristics, the
devices over a predetermined range and means
combination of means for selecting from one a 30 for adjusting the physical condition of said last
standard of value and means for simultaneously
named device so that the range of cyclic variation
comparing together signals of the two systems
of the frequency of its signal includes the signal
While cyclically varying the said characteristic
of the other device.
of one of said signals and means for determining
14. In apparatus for correlating the physical
the relationship of the said characteristic of the 35 condition .of an apparatus at a remote station
other signal with respect to such range of cyclic
with the physical condition of apparatus at a
variation.
control station, with each such station adapted
9. In apparatus for the correlation of two
to emit a variable frequency electrical signal
systems respectively adapted to emit electrical
indicative of the physical condition sought to be
signals having commensurable characteristics, 40 correlated, the combination of means for select
the combination of means for selecting from
ing frequencies from one as control and means for
one a standard of value and means for simul
mixing together frequencies simultaneously from
taneously comparing together signals of the two
systems while cyclically varying the said char
the two systems while cyclically varying the fre
acteristic of one of said signals and means for
stations, and means for adjusting the physical
adjusting the said characteristic of the said
cycllcally varied signal so as to bear a prede
termined relationship to the said characteristic
quency of the signal emitted from one of said
condition of the apparatus at the last named sta
tion so that the range of cyclic variation of the
frequency of its emitted signal bears a prede
of the other system.
termined relationship to the frequency of the
10. In apparatus for the correlation of two 50 signal emitted from the other of said stations.
systems respectively adapted to emit commensur
l5. The process of correlating the physical con
able electrical signals indicative of a state of
dition of apparatus at a remote station with appa
physical adjustment of the system, the combina
ratus at a control station which comprises the
tion of means for selecting from one a standard
steps of simultaneously emitting from the con
of value and means for simultaneously comparing 55 trol station a plurality of significantly different
together signals of the two systems While cyclically
electrical signals each indicative of the physical
varying the signal of one of such systems over a
condition of the apparatus at the control station,
predetermined range, and means for adjusting
receiving such signals at the remote station and
the physical condition of said system so that the
generating at least one signal at the remote sta
range of cyclic variation of its signal bears a pre 60 tion variable in accordance with variations in the
determined relationship tothe signal of the other
physical condition of the apparatus at the remote
system.
station, mixing the respective signals together,
11. In apparatus for the correlation of two
and adjusting the physical condition of the appa
remote mechanical devices actuating electrical
ratus at the remote station so that its signal bears
devices respectively adapted to emit alternating 65 a respective predetermined relation to each of
current signals having commensurable character
said control station signals.
istics indicative of a state of physical adjustment
1G. In a remote control device, the combina
of each said mechanical device, the combination
tion with a controller at a control station and a
of means for selecting from one a standard of
controlled element at a remote station, of means
value and means for simultaneously comparing 70 functionally responsive to different positions of
together signals of the two systems while cyclically
varying the commensurable characteristic of the
signal of one of said devices and means for adjust
ing the physical condition of said last named
the controller for
ent signals, means
tionally responsive
controlled element,
emitting significantly differ
at the remote station, func
to different positions of the
for emitting cyclically varied
device so that the range of cyclic variation of its 75 signiñcantly different signals, and mixing them
2,408,472
17
together with the signals received from the con
trol station and means at said remote station
functionally responsive to move said controlled
element when a parameter of the signal emitted at
the control station lies outside of the range of
cyclic variation of the parameter of the signal
emitted at the remote station.
17. In apparatus for correlating the position
18
signals and effective to adjustably maintain the
said element at said remote station at such a posi
tion that a parameter of the signal from the con
trol station lies within the cyclic variation of the
parameter of said signal generated at said remote
station.
19. In a device for correlating the position of
a movable arm at a remote station with the posi
tion of a movable arm at a control station, the
manually controlled lever at a ground station, 10 combination of a radio transmitter including a
the combination of means at the ground station
beat frequency oscillator at the control station
and movements o-f a lever in an airplane and a
for emitting radio signals signiñcantly different
for each position of the lever at said ground sta
tion, means actuated by the lever in the air
plane for emitting cyclically varying signals sig
nificantly different for each setting of such lever,
means in the airplane for receiving the radio
signals emitted by the ground station and mix
ing them together with those generated on the
airplane, and means functionally responsive to
both sets of signals for moving the lever on the
airplane so that a parameter of the ground sta
tion signal will lie within the range of cyclic
variation of the parameter of the signal emitted
on the airplane.
18. In a remote control device for correlating
movable elements respectively located at a control
station and a remote station, the combination of
means at the control station functionally re
sponsive to different positions of the said element
at the control station for emitting radio signals
adapted, for various adjustments of said beat
frequency oscillator, to send out radio signals in
cluding significantly different frequencies, means
connecting said arm at said control station with
the said beat frequency oscillator so that move
ment of said arm to different positions results
in significantly different settings respectively of
said beat frequency oscillator, means at said re
mote station including an adjustable beat fre
quency oscillator adapted upon various adjust
ments of the latter to generate cyclically varying
radio signals of significantly different reference
frequencies respectively, means connecting said
arm at said remote station with said last named
beat frequency oscillator whereby movement of
said last named arm to different positions will
adjust to different settings said last named beat
frequency oscillator, means at the remote station
frequencies,
for combining the said signal from said control
station with the said signal generated at said
remote station, and for setting up a signal which
means at the remote station functionally respon
sive to different positions of said element at said
is a function of said combined signals, a relay
energized by said latter signal, and power means
including signiñcantly different
remote station for emitting significantly different 35 controlled by said relay for moving the arm at
cyclically varied radiosignals, and means at said
remote station combining the aforesaid sets of
said remote station.
JOHN J. MOYNIHAN.
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