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Патент USA US2403605

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July 9, 1946.
Filed July 1, 1942
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Patented July 9, 1946
Robert N. Lesnick, Camden, N. 1., vass'lgnor to
Radio Corporation of America, a ‘corporation oi"
Application July 1, 1942, Serial No. 449,231
3 Claims.‘ (Cl. 172-239)
This invention relates to speed and accelera
tion responsive devices and more particularly to
systems for producing displacement or opera
tion of acontrcl device in response to-the speed
or acceleration, or both, of a rotating shaft. _
Speed and acceleration responsive devices of
' this type iind application in servo systems or vfol
low-up systems such as are used to move a rel
not exactly alike, or vary di?crently with tem
perature or age, the springs it and 20 maybe
arranged to bear against stops 22 on the support-,
ing member 2i. The spring arrangement illus
trated will accommodate angular displacements
oi the shalt it of approximately ten degrees in
either direction from the position or static equl- -
librium. If lawn-displacements are, required, a
modi?ed spring structure or suitable gearing may
atively massive object in accordance withthe
motion of a relatively small control device, In ‘til
The orbit sears 23 oi the differential 8 are ro
certain cases, it is desirable to add to the-elfect
tatably mounted on radially, extending shafts 25
of the control device an auxiliary factor which
is a function of the speed or acceleration of the . which are secured to a ring 21. The ring 21- may
be of relatively massive construction in order to
driven object, in order to compensate lag or hunt
ing of the driven object with respect to the con 15 function as a ?y wheel or inertia load, as here
inaiter described. Radlalvanes 29 may be pro
trol device.
vided on the surface of the ring l‘! to provide a
Accordingly it is an object of this invention to
frictional load on the system by air drag, orv
provide an improved method of and means for
by similar action in any suitable'?uld in which
deriving a displacement component related in
magnitude and direction vto the ‘angular. veloc 20 the device may be immersed. vThe vanes 28 may.
be omitted and sliding friction means substitut
ity or acceleration, or both, of a rotatable shaft.
ed, such as brake shoes 42 bearingin the ring
It is a. further object to provide an improved
21, as illustrated in Fig. 3. Another alternative means for correcting the errors inherent in cer
is to provide the ring 21 with a radial ?ange of
tain types of servo systems.
conductive material, and produce an eddy cur
These and other and incidental objects will
rent drug related to the speed by means of mag
become apparent to those skilled in the art upon
nets, as in the well known watt-hour meter con
consideration of the following description, with
reference to the accompanying drawing, in which
' The operation of the device is as follows; Ro
Fig. 1 is a side elevation, partly in section, of a
speed and acceleration responsive device con 30 tation of shaft l imparts to the gear ‘I an equal
motion which is divided by- well known di?eren
structedaccordinglto the invention, Fig. 2 is a
tlal action between the shaft l3 and the ring 21 view through the section 2-2 of Fig. 1, Fig. 3
inversely as they tend to. oppose' motion. The
shows a modi?ed speed-responsive means, and
motion of the shaft I2 is opposed by one of the
Fig. 4 is a schematic diagram of a servo system
embodying the invention.
35 springs Ii and 20, and that of the rind 21 is op
posed by the inertia force of the ring and the
Referring to Fig. l, a shaft I is driven at any
frictional force against the vanes 28. The spring
predetermined angular velocity and acceleration
‘force is a vfunction of the angular displacement
by a device 3, which may be an electric motor, in
of the shaft II, and the inertia and frictional
accordance with the operation of controlling
means associated with said device. The shaft 1 40 forces on the ring 21 are functions respectively
of the angular acceleration and angular velocity
may be connected with a mechanical load gen
of the ring. Thus the device functions as a yield-.
erally designated by the block ll in the draw
able coupling between the shaft; 1 and I3 with
ing. The shaft 1 is also connected to a gear ‘I
components responsive to the acceleration and to
of a differential 9. ' A corresponding gear H at
the other side of the diiferentlal i is connected 46 the velocity of the shaft] to rotate the shaft l2
against the spring restraining force.
‘through a shaft II to a control device (not
The shaft M will be rotated to an angular po
shown) which responds to movement of the shaft
sition in which the spring force balances the‘ in
l3 under the forces of springs l0 and inertia
ertia and frictional torces on the ring 21. Hence
forces of the means 2°! and 29 to control the 9.9- '
plicatlon of power to the motor I. A radial arm 50 the position of the shaft 13, and the control de
vice ls related'to the annular acceleration and
i7 is secured to the shaft 13 and extends between
the'angular velocity of the shaft l. The exact
two springs ll and 20 fastened on a fixed sup
relations are determined by the moment of ln-l
port 2| (Fig. 2). In order to determine posi
ertla of the ring 21, the area and arrangement
tively the equilibrium position of the arm l'l,
of the vanes 20 or other frictional means. and the
even if the characteristics of the two spring; are
constants of the springs I9 and :0. These fac
tors are all to be considered in the design of the
system for any specific application.
For example with the system initially at rest
Referring to Fig. 4, an electrical servo system
embodying the invention is illustrated. A pair
of Belsyn type transformers 30 and ii are me
chanically connected to a control shaft 31 and
a wntrolled shaft IM respectively. The shaft
:3 is arranged to be rotated by any desired means
such as a manually operable crank 35. The shaft
III is connected to a driving motor I03 and to
a device 31 like the mechanism illustrated in Figs.
1 and 2 of the drawing. The mechanical load
to be operated is represented by the block I05,
also connected to the driving motor W3.
A Selsyn transformer H5, similar to trans
formers l0 and 3|, is electrically connected be
tween corresponding windings of said transform
era; the rotor, for example, of the transformer
[l5 being connected to the stator of the trans
former I0 and the stator of the transformer i ii
being connected to the stator of the transformer
II. The stator of the transformer H5 is main~
tained stationary, and the rotor is connected
through a shaft llll, corresponding to the shaft
it of Fig. 1, to the device 31.
displacing the rotor of the transformer H5 by
means of the device of Fig. 1 described above.
The rotor winding of the transformer 3| is
‘ the crank 35 is rotated through some predeter
mined angle. Voltage applied to the transformer
II from the A.-C. lines 39 is converted to three
separate in-phase voltages which are applied to
the stator of the transformer H5. The ampli
tudes of these voltages with respect to each other
l0 depend upon the angular position of the rotor
of the transformer 3i. Corresponding voltages
are produced in the stator of the transformer I I5
and as long as the rotor remains in its initial
position with respect to the stator thereof, the
15 output of the transformer I I5 corresponds exactly
to the output of the transformer 31 . This output
is applied to the stator of the transformer 30,
providing a resultant field through the armature
thereof and inducing a voltage in the rotor wind
20 ing which corresponds in amplitude to the differ
ence in the angular positions of the crank 35 and
the output shaft IIH. This voltage is ampli?ed
by the amplifier ll, causing the motor I03 to
rotate toward a position corresponding to that
25 of the crank 35.
As' soon as the motor I03 starts to rotate, the
input shaft of the device 31 is rotated, causing
the output shaft to rotate in the opposite direc
lines 88. The rotor of the transformer 30 is con
tion due to inertia and friction loading on the
nected to the signal input circuit of an ampli?er 30 differential spider member. This causes the rotor
and motor control device designated by the
of the transformer H5 to move through an angle
block 4:. The device if is also energized from
which is a predetermined function of the accel
the lines 38, and is arranged to control the motor
eration and velocity of the driving motor I03,
in accordance with the amplitude of the control
altering the relationship between the three volt
input voltage and its polarity with respect to a 35 ages in the output circuit of the transformer and
voltage derived from the supply lines 89.
hence advancing the angular position of the field
The operation of the system of Fig. i is as fol
in the transformer 30 ina direction opposite to
lows. The output voltage of the transformer to
the direction of rotation of the crank 35. This
is amplified in the device 4!. If said voltage‘ is
increases the magnitude of the control signal
zero, the motor I0! is not energized. If the volt 40 applied to the ampli?er 4i, providing more ener
use is not zero, the motor His is caused to rotate
gization of the motor Hi3 and hence a greater
and turn the rotor of the transformer 3i, chang
torque than would normally be produced as a
ing the voltages applied to the transformer H5 .
result of the difference in angular position be
and through it the voltages at the primary of
tween the crank and the driving motor. Thus
the transformer 30. The voltage at the secondary 45 upon starting, the inertia of the load is overcome
of the transformer it depends on both the volt
by increasing the total control signal in response
ages impressed upon its primary, and the physical
to the acceleration of the output shaft. If rota
position of its rotor with respect to its stator.
tion of the crank 35 is continued, the output shaft
Thus the voltage at the input of the device 4|
will rapidly assume the velocity of rotation of
changes with the rotation of the motor I03 until
the crank and as soon as acceleration ceases the
it is again zero, whereupon the motor I03 stops
rotor of the transformer I [5 will tend‘ to assume
and the system remains at rest until unbalanced
its initial position under the action of the springs
energized with alternating current from supply
by some outside force such as rotr Z'Jh of the
l9 and 20.
crank 35.
In nearly all systems of this class, certain errors
device 31 will continue to provide its original
effect, maintaining an advance in the position
of the field in the transformer 30 proportional
to the velocity of the shaft IOI. Thus the mag_
nitude of the control signal is higher at the higher
velocities of operation, although not directly pro
are inherent.
For example, a consideration of
the ‘principles of operation shows that there must
be some difference in the angular positions of
the controlling and driven shafts in order to pro
vide a difference in the two voltages compared
in the device H and operate the motor. Hence
the two shafts normally do not remain .in posi
tional agreement while the system is in motion.
Another and often troublesome effect is that of
However the frictional load on the
portional to either the displacement or the ve
locity. Upon retardation of the crank 35 the
inertia of the device 31 acts in the opposite direc
tion from that during acceleration, reducing the
resultant control signal applied to the amplifier
"hunting,” oroverrunning and reversal of the
M to a value which is less than the normal dis
driven member about the point of positional
agreement with the control shaft. Servo systems
placement proportional signal, tending to reduce
the energization of the motor more rapidly than
the difference between the positions of the crank
subject to such difficulties.
35 and the output shaft Jill ‘is reduced. At the
It has been found that the above described 70 same time the frictional load on the device 31
defects may be partially or substantially elimi
tends to maintain the control signal at a higher
nated by adding to the control signal or equiva
level in response to the velocity of rotation of
lent force a quantity related in magnitude to the
the shaft ID]. This component retains its orig
velocity and acceleration of the driven member.
inal sense although the acceleration component
In the system illustrated in Fig. 3 this is done by 75 is reversed. Thus as the output shaft tends to
of many types, as well as electrical systems, are
sponse to the displacement of said restraining
overshoot, reversing the displacement signal, this
reversed signal is materially reduced by the ve
locity component, causing the shaft [ill to rotate
2. In a servo system comprising a control shaft.
’a driven shaft, means responsive to the differ»
to its correct angular position more slowly so as
to prevent overshooting in the opposite direction
and further reversal.
Thus the invention has been‘ described as an
ence in the angular positions of said shafts to
control a motor to drive said driven sliaf t toward
positional‘ agreement with said control shaft,
improved speed and/or acceleration responsive
means responsive to the angularvclocity and
acceleration of said driven shaft to produce an
device, comprising mass and drag or friction ele
ments driven through a differential having an 10 auxiliary control effect on said motor. including
a differential connected between said driven shaft
output shaft restrained by spring means. The
and an auxiliary control shaft resiliently re
spring force is balanced against the inertia and
strained against rotation, anda mechanical load‘
drag or frictionforces, resulting in a displace- -
connected to said differential to control the trans
ment of the output shaft which is a function of
the velocity and acceleration of the input shaft.
An illustrative application of this device in an
electrical servo system has also been described.
I claim as my invention:
mission of-torque from said driven shaft through
said differential to said auxiliary control shaft.
3. In a servo system including a driven shaft,
a motor coupled to said shaft, and means for
energizing said motor in response to a control
1. In a servo system including a, control shaft,
a controlled shaft, means for comparing the an 20 input signal, angular displacement responsive
means for producing an auxiliary signal in addi
tion to said control input signal, differential gear
ing including two shafts and a spider member,
said shafts being connected respectively to said
' so as to drive said controlled shaft toward a posi
tion corresponding to that of the control shaft, 25 driven shaft and to said displacement responsive
means for deriving auxiliary forces related in
means, and a mechanical load comprising fric
magnitude and direction to the velocity and to
tion and inertia elements coupled to said differ
the acceleration of said controlled shaft compris
ential spiderymember to cause rotation of said
gular positions of said shafts, means for deriving
a force related to the difference in said positions
and applying said force to said controlled shaft
displacement responsive means as the sum of
ing differential means connected to said con
trolled shaft and connected to drive a mechanical 30 predetermined functions of thepspeed and the
load comprising inertia and friction elements
against a resilient restraining member, and
means for deriving said auxiliary forces in re
acceleration of said driven shaft.
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