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Патент USA US3066549

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Dec. 4, 1962
3,066,540
R. H. SEVERANCE
ACCELERATION MEASURING DEVICE
Filed Sept. 23, 1960
_W
5. :
INVENTOR.
RALPH H. SEVERANCE
BY
1mm! ldm/m/ 911%{Web}
ATTORN EYS
free
3,95%,540
Patented Dec. 4, 1962
2
3,tl66,54tl
Ralph H. Severance, Urhana, llh, assignor to The Mag
ACCELERATION MEASURHNG DE‘VTQE
navox Company, Fort Wayne, llnd., a corporation of
Delaware
Filed §ept. 23, 1960, Ser. No. 58,641
12 Ciairns. (Cl. 73-4§€3>
balls around the shaft is closed by the ball return conduit
24.
A circular disk 26 is fastened to the ball nut ?ange 23
by means of the screws 27. The disk thereby can be car
ried freely up and down in the housing 11 with its pe
riphery 28 in closed proximtiy to the regular and usually
cylindrical inner surface 29 of the housing 11. The disk
26 normally has a plurality of magnetic poles disposed
This invention is related generally to accelerometers,
around its periphery and the housing 11 is normally made
and more particularly to means adapted to integrate 10 of an electrically conducting material so that as the disk
forces of acceleration so that a measure of the distance
traveled by an accelerated body is indicated by the de
vice.
moves in rotation about the shaft 14 and in translation
along the shaft, eddy currents are developed by the disk
in the housing to oppose the motion of the disk.
In work related to rockets and missiles and ordnance
In the embodiment shown, the disk would normally
generally, it is necessary to perform timing functions and 15 be positioned as close as possible to the uppermost point
initiate various effects during the course of ?ight. One
means of accomplishing this is to provide an accelerom
eter located within a rocket or missile itself and capable
of automatically initiating events in response to certain
conditions of motion or position. Of particular utility
in this respect is an accelerometer mounted in a rocket
or missile and capable of triggering events in response
to travel over a certain distance from the launching or ?r
ing site.
It is, therefore, an object of this invention to provide
a novel accelerometer adapted to incorporation in rockets,
missiles or the like.
It is another object of this invention to provide a means
for integration of forces of acceleration to produce a
measure of distance traveled by the accelerated body.
This invention includes in its scope a cylinder having
a?ixed thereto a post incorporating a screw thread there
on. A disk is threadedly engaged to the post by means
of the screw thread and the disk itself is of a dimension
in the housing so that as the housing is accelerated in the
direction shown by the arrow 31, the disk advances down
wardly, its motion being resisted by the eddy currents
developed by the disk in the housing.
A shaft 32 is shown mounted in the lower end cap 13
wherein it is guided by the walls of a hole 33 through
the end cap. A resilient member 34-, which may be an
O-ring, for example, is disposed in a groove 36 in the end
cap and permits positioning of the shaft 32. in any longi
r tudinal position desired in the housing. This shaft 32
can be associated with any appropriate type of mech
anism or circuitry in order to provide the initiation of
some desirable event upon actuation of the shaft 32 by
the disk 26 as it moves downwardly with respect to the
30
housing 11 in response to an acceleration of the housing
11 in the direction shown by the arrow 31.
FIG. 2, which is a section of the embodiment of FIG. 1
taken along the lines 2—2 of FIG. 1, illustrates a typical
disposition of the magnetic poles in the disk 26. The lines
which is such that a portion thereof is in close proximity 35 37 represent schematically ?ux lines linking the housing
to the cylindrical housing. Either the disk or the housing
11 to the disk 26 by a magnetic ?eld ‘between the mag
may carry magnetic poles disposed so that movement
netic poles of the disk 26.
of the disk in rotation about the threaded post and transla
In FIG. 3 the vertical coordinate represents the distance
tion therealong is inhibited to some extent by eddy cur
rents developed between the disk and the housing. At the 40 traveled by the disk with respect to the housing and the
horizontal coordinates represent the distance traveled by
?ring of the projectile the disk is positioned toward one
the housing in space. Curve A represents the relationship
end of the housing and advances in response to accelera
between the position of the disk and the distance traveled
tion of the projectile towards the other end of the hous
by the housing for the case where no eddy current loss is
ing. Some type of triggering means is employed in the
employed in the accelerometer. Curve B indicates the
housing so that when the disk engages the triggering means
elfect obtained when an eddy current loss proportional to
during its advance in the housing, certain events can be
the square of the angular velocity of the disk is obtained.
caused to take place.
Curve C indicates the relationship obtained by employing
The full nature of the invention will be understood from
the accompanying drawings and the following descrip
a slightly dicerent shape for the housing.
50
tion and claims:
It should be noted at this point that the invention has
FIG. 1 illustrates a typical embodiment of the present
been described in an embodiment where the mounting of
invention.
the disk to the housing is accomplished through a ball
FIG. 2 is a section of the embodiment of FIG. 1 taken
nut. Other low friction arrangements can be employed.
along the line 2--2 of FIG. 1.
55 For example, a more conventional screw thread could be
FIG. 3 illustrates the relationship between the distance
employed on the post 14. The inside diameter of the
traveled by the accelerometer and the disc present therein
disk 26 could be provided with a mating screw thread por
for several variations to this invention.
tion. To obtain particularly low friction operation these
Referring to the embodiment of FIG. 1, there is shown
parts could be treated or specially plated. One example
a cylindrical housing 11 having end caps 12 and 13 clos 60 of a satisfactory plating material is Te?on.
ing each end thereof. A post 14 is disposed between the
The embodiment described also employs magnetic
end caps 12 and 13 being fastened thereto by the nuts
poles. In some instances it is desirable for the accelerom
16 and 17. The post 14 is coaxial with the housing 11.
eter to respond in direct proportion to the distance it
The post 14 has a continuous groove 18 in its exterior
travels and in such instances the magnetic poles are elimi~
surface extending along the post in a spiral. The groove 65 nated.
‘
18 is of a generally curved section adapted to receive the
It was mentioned above in this description that the shaft
balls 19‘ of the recirculating ball nut 21.
32 could be positioned to initiate events upon actuation
The recirculating ball nut has a ?anged body portion
by the disk 26. This actuation is related to the distance
having the core 22 and a ?ange 23. The ball nut is
in space traveled by the housing inasmuch as the distance
shown with one and one-half rows of balls, but may be 70 traveled by the disk with respect to the housing is a
employed with more or less as desired. The circuit of
measure of the distance traveled in space by the housing.
3,066,540
3
Since
This effect is evident from the following mathematical der
ivations wherein:
m=mass of rotating magnetic disk
a=instantaneous acceleration applied to housing
by substitution:
y=distance traveled by rotating disk inside the housing in 01
time t
s=distance traveled by the projectile under acceleration
a applied to the housing in time t.
PE=Potential energy lost by mass m in time t
KE=Kinetic energy gained by the mass m in time t
2 2
4Klstt
10
Loss=Energy lost due to eddy currents
w=Angular velocity of disk
When a is constant:
s=1/2az‘2
15
where, as in the no loss case, the constants depend on
__2s
materials and con?guration of the accelerometer.
‘1-?
For
the no loss case, it was seen that y is related to s by
PE=may= 2mm;
,2
(l)
constants depending upon the mechanical constants of
the design. For the case with eddy current loss, i.e. loss
KE=1/2lw2
w=Koat
(2)
(3)
proportional to the ‘square of w, y increases at a rate
that decreases as .9 increases. This eifect is illustrated in
curve B of FIG. 3. In the case with losses it should be
Where K0 is an appropriate constant. Substituting (3)
in (2)
noted that by suitably shaping the cylinder, that the term
Kat in the last equation can be adjusted through fairly
wide limits to provide curves lying at various positions
For a no loss system; i.e. where magnets are omitted so
eddy currents are absent:
below the no loss curve, i.e. curve A of FIG. 3.
KEzKlazl‘z
PE=KE
One
example is curve C which can be obtained by providing
(5) 3O
Combining (1) and (4)
2sZLy=K1a2t2
2 my=K2s
As an alternative construction of the eddy current ver
sion of the accelerometer, the disk may be made a con
ductor and the cylinder a magnet with poles on its inner
surface.
The accelerometer described in the case where there
are no losses is .a true integrator, i.e. it integrates the ac
y=K3s or y is a measure of .9
celeration twice to provide a- true measure of distance,
independent of a.
i.e. y is directly proportional to s. It is small in size,
rugged and easy to make.
The unit described in the case with eddy current losses
does not perform only the double integration, and y is
not directly proportional to s but that to s+Kst. This
This relationship is represented in FIG. 3 by curve A.
In this instance the accelerometer is a true integrator, i.e.
it integrates acceleration twice to provide a true measure
of distance traveled by the housing. The value of con
stant K0 and therefore of K3 will, of course, depend on
means that the accelerometer may be so constructed as
to require the missile to reach a certain distance within a
certain time, i.e. with some minimum duration of ac
the actual materials and con?gurations of the accelerom
eter used.
For a system with eddy current losses
a cylinder with progressively smaller diameter.
45 celeration.
In addition it is small, rugged and easy to
make.
While'the invention has been disclosed and described
in some detail in the drawings and foregoing description,
they are to be considered as illustrative and not restric
50 tive in character, as other modi?cations may readily sug
Loss may be expressed as
gest themselves to persons skilled in' this art and within
the broad scope of the invention reference being had to
J'EZdt Ezt
or ——
7‘
the appended claims.
T
What is claimed is:
1. An accelerometer comprising: a housing member
having
a longitudinal axis; a translating member threaded
E=the voltage induced by the motion of the magnetic
ly coupled to said housing member, the threaded cou
?eld.
tation about said axis and in translation in said housing
r=the electrical resistance across which “E” is induced.
member for movement of said translating member in ro
60 tation about said axis and in translation in said housing
The expression
55
where :
E22
r
is the ohmic energy loss due to the eddy currents caused
by E ?owing in r.
member; magnetic means on one of said members and
an electrical conductor in the other of said members, said
magnetic means and said conductor being spaced to cre
ate a magnetic ?eld in said conductor, whereby accelera
65 tion of said housing member in a direction parallel to its
longitudinal axis causes said translating member to move
in rotation and translation in said housing member
through positions in said housing member with respect
to a normal initial position of said translating memben
70 which are representative of distance traveled by said
housing member in a direction parallel to said longitudinal
3X15.
2. An accelerometer comprising: a housing member
having an inner regular surface with an axis; a circular
75 disk member threadedly coupled to said housing member
3,066,540
5
and coaxial with said axis for movement in rotation and
translation in said housing member; magnetic means on
one of said members and an electrical conductor in the
other of said members, said magnetic means and said con
6
inner cylindrical surface of electrically conductive mate
rial; a post al?xed to said housing and extending inside
of said cylindrical surface, said post having an external
cylindrical surface coaxial with the inner cylindrical sur
face of said housing and having a continuous groove in
conductor, whereby acceleration of said housing mem
said external surface advancing in a spiral along said
ber in a direction parallel to the axis of its inner surface
post; a circular disk threadedly engaged with said post
causes said disk member to move in rotation and trans
by means of ‘said groove, said disk having a plurality
lation in said housing member inducing eddy currents
of magnetic poles in the outer periphery thereof in close
in said conductor to oppose said rotation and translation; 10 proximity with the inner cylindrical surface of said hous
and means responsive to motion of said disk member to
ing; means in operable association with and movable by
initiate an event upon attainment by said disk member
said disk, whereby acceleration of said housing in a di
of a position with respect to a normal initial position
rection parallel to the axis of its inner surface causes said
thereof, which is representative of a distance traveled
disk to move in rotation and translation in said housing
by said housing in a direction parallel to the axis of said 15 inducing eddy currents to oppose said motion and said
ductor being spaced to create a magnetic ?eld in said
inner surface.
.
3. An accelerometer comprising: a housing member
disk moves said means to initiate an event upon attain
ment by said disk of a position with respect to a normal
having an inner regular surface With an axis; a post
initial position thereof, which is representative of the
a?‘ixed to said housing and coaxial with said axis; a circu
distance traveled by said housing in a direction parallel
lar disk member threadedly engaged with said post; mag 20 to said inner surface.
netic means on one of said members and an electrical
8. An accelerometer comprising: a housing of electri
conductor in the other of said members, said magnetic
cally conducting material and having an inner cylindri
means and said conductor being spaced to create a mag
cal surface of a length substantially greater than its diam
netic ?eld in said conductor, whereby acceleration of
eter; a post a?ixed to said housing and extending inside
said housing member in a direction parallel to the axis 25 of said cylindrical surface, said post having an external
of its inner surface causes said disk member to move in
cylindrical surface coaxial with the inner cylindrical sur
rotation and translation in said housing member inducing
face of said housing and having a continuous groove in
eddy currents in said conductor to oppose said rotation
said external surface advancing in a spiral along said
and translation; and means operable by said disk member
post; a circular disk threadedly engaged with said post
to initiate an event upon attainment by said disk of a 30 by means of said groove, said disk having a plurality of
position with respect to a normal initial position thereof,
magnetic poles in the outer periphery thereof in close
which is representative of the distance traveled by said
proximity with the inner cylindrical surface of said
housing in a direction parallel to the axis of said inner
housing; means in operable association with and movable
surface.
by said disk, whereby acceleration of said housing in a
4. An accelerometer comprising: a housing having an 35 direction parallel to the axis of its inner surface causes
inner cylindrical surface of electrically conductive mate
said disk to move in rotation and translation in said
rial; a post affixed to said housing; a carrier threadedly
housing inducing eddy currents to oppose said motion
engaged with said post and having a plurality of mag
and said disk moves said means to initiate an event upon
netic poles disposed in close proximity with the inner
attainment by said disk of a position with respect to a
cylindrical surface of said housing; and means in oper 40 normal initial position thereof, which is representative
able association with and movable by said carrier whereby
of the distance traveled by said housing in a direction
acceleration of said housing in a direction parallel to the
parallel to said inner surface.
axis of its inner surface causes motion of said carrier
9. An accelerometer comprising: a housing of elec
and causes said magnetic poles to induce eddy currents
trically conducting material and having an inner cylin
to oppose said motion and said carrier moves said means 45 drical surface of a length substantially greater than its
to initiate an event upon attainment by said carrier of
diameter; a post a?ixed to said housing and extending in
a position with respect to a normal initial position there
side of said cylindrical surface, said post having an ex
of, which is representative of the distance traveled by
ternal cylindrical surface coaxial With the inner cylindrical
said housing in a direction parallel to said inner surface.
surface of said housing and having a continuous groove
5. An accelerometer comprising: a housing having an
in said external surface advancing in a spiral along said
inner cylindrical surface of electrically conductive mate
post; a circular disk threadedly engaged with said post by
rial; a post affixed to said housing and having an ex
means of said groove, said disk having a plurality of mag
ternal surface coaxial with the inner cylindrical surface
netic poles in the outer periphery thereof in close prox
of said housing and having means in said external sur
imity with the inner cylindrical surface of said housing;
face advancing in a spiral along said post; a circular disk
means in the annular space between the housing and the
threadedly engaged with said post through the means in
said external surface, said disk having a plurality of mag
netic poles in the outer periphery thereof in close prox
imity with the inner cylindrical surface of said housing;
and means in operable association with and movable by
said disk; whereby acceleration of said housing in a direc
tion parallel to the axis of its inner surface causes said
post and movable by said disk, whereby acceleration of
said housing in a direction parallel to the axis of its inner
surface causes said disk to move in rotation and transla~
tion in said housing inducing eddy currents to oppose said
motion and said disk moves said means to initiate an
event upon attainment by said disk of a position with re
spect to a normal initial position thereof, which is repre
sentative of the distance traveled by said housing in a
direction parallel to said inner surface.
disk moves said means to initiate an event upon attain 65
10. An accelerometer comprising: a housing of elec
ment by said disk of a position with respect to a normal
trically conducting material and having an inner cylin
initial position thereof, which is representative of the
drical surface of a length substantially greater than its
distance traveled by said housing in a direction parallel
diameter; a post a?ixed to said housing .and extending
to said inner surface.
inside of said cylindrical surface, said post having an
6. The accelerometer of claim 5 wherein said means 70 external cylindrical surface coaxial with the inner cylin
in the external surface is a screw thread of low friction
drical surface of said housing and having a continuous
material receiving a matching thread portion of said
groove in said external surface advancing in a spiral along
disk said matching thread portion being of low friction
said post; a circular disk threadedly engaged with said
material.
post by means of said groove, said disk having a plurality
7. An accelerometer comprising: a housing having an 75 of magnetic poles in the outer periphery thereof in close
disk to move in rotation and translation in said housing
inducing eddy currents to oppose said motion and said
3,066,540
27
proximity with the inner cylindrical surface of said
housing; a shaft extending into the annular space between
the housing and the post and parallel‘ to said post and
from an end opposite a normal initial position of said
disk, said shaft being positionable longitudinally in said
space and movable in a position in said space by said
8
an event upon attainment by said disk of a position with
respect to said normal initial position thereof, which is
representative of the distance traveled by said housing in
a direction parallel to said‘ inner surface.
12. A double integrating accelerometer comprising:
a housing of electrically conducting material and having
an inner cylindrical surface of a length substantially
disk whereby acceleration of said housing in a direc
greater than its diameter; a post af?xed to said housing
tion parallel to the axis of its inner surface causes said
and extending inside of said cylindrical surface the length
disk to move in rotation and translation in said housing
inducing eddy currents to oppose said motion and said 10 of said cylindrical surface, said post having an external
cylindrical surface coaxial with the inner cylindrical sur
disk moves said shaft to initiate an event upon attain
face of said housing and having'a continuous groove of
ment by said disk of a position with respect to said normal
semicircular cross section in said external surface advanc
initial position thereof, which is representative of the dis
ing in a spiral from one end of said post toward its other
tance traveled by said housing in a direction parallel to
15 end; a circular disk a?ixed to a recirculating ball nut
said inner surface.
threadedly engaged with said post through balls of said
11. A ‘accelerometer comprising: a housing of elec
nut movably disposed in said groove, said disk having a
trically conducting material and having an inner cylin
plurality of magnetic poles in the outer periphery there
drical surface of a length substantially greater than its
of in close proximity With the inner cylindrical surface
diameter; a post affixed to said housing and extending
inside of said cylindrical surface, said post having an ex 20 of‘ said housing; a shaft extending into the annular space
between the housing and the post and parallel to said
ternal cylindrical surface coaxial with the inner cylindri
post and from an end opposite a normal initial position
cal surface of said housing and having a continuous
groove of semicircular cross section in said external sur
face advancing in a spiral alonr7 said post; a circular disk
of said disk, said shaft being positionable longitudinally
in said space and movable in a’ position in said space by
threadedly engaged with said post through a recirculating 25 said disk whereby acceleration of said housing in a di
ball nut af?xed to said disk, balls of said nut being rnov
ably disposed in said groove, said disk having a plurality
of magnetic poles in the outer periphery thereof in close
proximity with the inner cylindrical surface of said hous
rection parallel to the axis of its inner surfacecauses said
disk to move in rotation and‘ translation in said housing
inducing eddy currents to oppose said motion and said
disk moves said shaft to initiate an event upon attain
ing; a shaft extending into the annular space between the 30 ment‘by said disk of a position with respect to said nor
mal initial position thereof, which is representative of
housing and the post and from an end opposite a nor
mal initial position of said disk, said shaft being posi~
tionable longitudinally in said space and movable in a
position in said space by said disk whereby acceleration
of said housing in a direction parallel to the axis of its 85
inner surface causes said disk to move in rotation and
translation in said housing inducing eddy currents to 0p
pose said motion and said disk moves said shaft to initiate
the distance traveled by said housing in a direction paral
lel to said inner surface.
References €ited in the ?le of this patent
UNITED STATES PATENTS
2,898,416
Clurman _____________ _- Aug. 4, 1959
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