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Патент USA US2411401

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42,411,401 _
SrTEs PATENT
Fisici:
2,411,401
ACCELEROMETEB
William r. welch, Arlington, va., ssngnor'» to
Westinghouse Electric Corporation, East Pitts
burgh, Pa., a corporation of Pennsylvania
_ Application July 28, 1942, Serial No. 452,576
4 claims. (on. 1v1-209)
l
,
This invention relates to a device for use in
determining ’ the characteristics of motion im
Referring to the drawing, the numeral I desig
nates as a Whole a device for producing a measur
parted to a body upon being subjected to a shock
able impulse ln response‘to movement of a body
2 as caused by the application thereto of a shock
The possibility of failure of apparatus when it ci ing force. The device l comprises a housing 3
ing force.
`
y
_ is subjected to an instantaneous or rapidly ap
' adapted to be rigidly attached to the body 2 and
pliediorce in the nature of a shock is well known.
-to this end the housing 3 is provided with a
Apparatus which is apt to be subjected to shock
threaded opening t for engagement with a
ing forces in this manner is frequently tested for
threaded end 5 of a member 6. The member lìy
its ability to stand up under shock prior to being 10 preferably is formed ‘from a single piece of ma
placed in actual use. To the best of my knowl
terial having a hexagonal middle section and`
edge, no device has been heretofore devised which
will indicate or measure the motion whichv is im
threaded ends band l.
The other end 'l of the '
member S is threaded into a nut 5 welded to the
parted' to a body upon being subjected to a shock
body 2 for the purpose of securing the housing 3
ing force. Obviously, an instrument that will 15 to the body 2.
y
I
measure the motion of a body subjected to shock
A pair of quartz crystals 9 and l@ are mounted
is desirable in that it will provide an aid in den
within the housing l for generating a charge or
' termining the nature of a shock and explaining
electrical impulse in response to smovement'. of
why apparatus breaks when shocked.
One of the principal objects ot this invention
the casing 3 and body 2 by a shocking force ap
plied to the body 2. -`'I'he crystals 8 and l0 are
_. cylindrical in shape and are cut with their elec
trical axis parallel to their cylindrical axis. A
is to provide a device for producing a. measurable
impulse proportional to the movement of a body
subjected to a shocking force.
copper electrode Il is positioned ,` 'between the
A further object of this invention is to provide
facing end surfaces of the crystals 9 and lll. The
a device whichmay be readily attached to a. 25 other end surface of the crystal 9 is adapted to
body to be subjected to a shocking force, and
seat on a surface l2 formed in the housing 3. .
which will generate an electrical impulse proper-_
The other end surface'of the crystal l@ is adapted
tional to the movement of the body in response
_to seat on surface ill provided by a member l5.
to a shock from which the frequency and ac
The member l5 is provided with a bias for
celeration. of movement of the body may be de 30 maintaining the crystals 9 and l0 in position be- _
termined.
_
tween the surfaces l2 and it. To this end the
A further object is to provide a device for de
_ member l5 is resiliently mounted within the
Éecting the movement of a’body under a shock
housing ßvby annular disk springs l 8 and I'l. The
outer edges of the springs l@ and il' are anchored
A further object is> to provide a device for rigid 35 to the housing t by an annular element I3 adapt
attachment to a. body to be subjected to shock
ed to seat against the housing 3 as at i9, an an
orce.
with charge generating means comprising a
piezo-electric quartz crystal which will generate
an impulse in response to movement of the body
under shock from` which the acceleration and .40
frequency of movement imparted to the body
_may be readily determined.
‘
‘
nular spacer element 2b, and an annular adjust
ing member 2l having threaded engagement with
the housing 3. Upon positioning the spring I6
between the members it and 20 and the spring
ll between the members 2@ and 2l as shown, the
outer ends of the springs 'it and il will be
Other objects and advantages of the invention '
anchored with respect to the casing 3. .
will become apparent from a study of the follow» _
The inner ends of the springs I6 and Il are
ing description, _taken in connection with the ac 45 anchored to the 'member i5 by an annular spacing
companying drawing in which:
Figure 1 is a-sectional view of a charge gen
erating device constructed in accordance with the
principles of this invention;
-
member 22- and an internally threaded member
23 adapted to have threaded engagement with ‘
the _member l5. Upon positioning the inner edge
,_ '
_ of the spring l5 between the annular surface 24
Fig. 2 is a schematic view showing the device 50 and the member 22 and the inner end of the `
oi' Fig. 1, with apparatus for measuring the ex
_ tent and nature ofthe impulse produced by move
ment in response to a. shocking force; and;
Fig. 3 is a modification for use in connection
with the device shown in Fig. 1.
_
.
spring I1 between the members 22 and 23, such
inner `edges will be anchored in position with re
spect to the member l5.
‘
Thr-:__ anchoring parts :for the springs I6 and Il «
65 are so designed that upon assembly of the parts
2,411,401
4
as viewed in Fig. 1, a compression of the crystals
9 and I0 will be had due to the mass of the mem
ber I5 tending to remain at rest by reason of its
inertia. The piezo-electric property of the crys
tals 9 and I9 causes a charge to be produced pro
portional to the force exerted by the accelerated
as shown in_Flg. 1, the springs I6 and I1 will be
flexed in a direction to provide a resilient bias
maintaining the member i5 in engagement with
the `crystal I 9. To adjust the deñection of the
springs IE and I'I and thus the resilient bias on
the member I5, removable shims 25 are provided
between the outer edges of the springs I6 and the
seating member I8. If the bias is to be increased,
mass thereon.
The crystals 9 and I9 are so ar
ranged that their inner facing surfaces will be of
it is merely necessary to remove one or more of
like polarity. The charge produced by the crys
mounted on armor-plated structure when it is
struck by a projectile. The measurement of the
faces of theucrystals 9 and I0. It frequently hap
the shims 25 and thereafter operate the member 10 tals 9 and I0 is taken 01T as an electric impulse
through the terminal 28 which is electrically con
2I to move the outer edges of the springs I6 and
nected to the electrode II. The impulse flowing
I1 inwardly with respect to the inner edges there
through the electrode 28 is employed in a manner
, of, the position of the inner edges being ñxed by
to be described to indicate or measure the char
the 4‘position of the member I5 as determined by
acteristics of the motion imparted to the casing
the crystals 9 and I0.
3 by the shocked body 2.
When a body is struck a shocking force, it is
The end surfaces of the crystals 9 and III, to
subjected to large and rapidly applied accelera
gether with the seating surfaces I2 and I4, are
tions and consequently vlbrates at extremely high
so formed that pressure applied to the crystals 9
frequencies. Such vibrations and accelerations
are encountered, for example, by apparatus 20 and l0 will be distributed uniformly over the sur
pens that adjacent surfaces will be formed withl
high spots which may cause a concentration of
the force applied thereto in a manner likely to
bration, as made possible by the device I, pro
vides knowledge which is helpful in theldesign of 25 cause crystal breakage. Such concentration of
force may likewisevbe cau-sed by a particle of dirt
apparatus to be used on an armor-plated struc- .
4being lodged between the surfaces I2 and I4 and
ture such as a naval vessel which apparatus must
the end surfaces of the crystals. In order to
function even though the vessel be struck by a
amount of acceleration andthe frequency of vi- ,
projectile.
_
`
prevent such concentration of force due to high
'
spots or dirt particles, a thin strip of relatively
In order to prevent movement of the surface
soft conducting material 21 such yas tin-foil, the
thickness thereof being exaggerated in the draw
I4 out of engagement with the crystal IIJ,A the bias
on the member I5 must be suiiicient to withstand
ing for the purpose of illustration, is inserted
between the crystals and their seating surfaces
By keeping down the mass of the member i5 and 35 on the casing 3 and the member I5. Thesoftness
of the >conducting material enables the high spots '
Aemploying stiff springs i6 and I'I a bias may
or deposited dirt‘particles to embed in the con
readily be provided for maintaining the crystals
extremely large accelerations tending to move `
the member I5 to the right a-s viewed in Fig. i.
_9 and I0 in position suñlcient for accelerations
ducting material andthe force is thereby dis--
tributed uniformly over the surfaces of the crys
However, in this respect, -it »is necessary
that the conducting material or tin-foil be thin
tremely high frequencies and such `frequencies
in order that a cushioning effect which would
will be found to have a range up to 5,000 cycles
otherwise interfere with the natural frequency
per second or greater. For an indicatorto have
will not be had.
a response proportional to acceleration, its nat
In the schematic showing of Fig. 2, the essen
ural frequency must be greater than twice the 45
tial parts shown in~ Fig. 1 are indicated by like
-frequency of the acceleration being measured.
numerals. In this showing, it will be noted that
The natural frequency of a device is a function
the element 29 `is substituted for the springs I6
of its spring constant and its mass. In the case.
and I‘I. The electrical impulse or chargek gen
' of the device I, the spring constant is approxi
mately the elastic stiffness of the crystals 9 and 50 erated by the crystals 9 and I0 is taken of!
through a conduit 30' which is connected to one
I0 in an axial direction. By maintaining the
side of a condenser 3l, the other side of the con
mas-s of the member I5 small, the natural fre- f
denser 3I being grounded tothelcasing 3. The
quency of the device I will be found to, be very
l charge which goes into the condenser 3l pro
high and in the nature of from about 10,000 to
duces a voltage which is proportional to the
about 20,000 cycles per second. By increasing
force supplied to the crystals 9 and I0 and is
the weight of the mass I5, the sensitivity -of the
measurable. A resistance 32 is shunted across
. device I will ibe increased at the expense of a
the condenser 3| and it is necessary ythat this
'decrease in the natural frequency thereof. Such
resistance be sufñciently high to allow .the volt
increase in sensitivity accordingly lowers the fre
quency of vibration whichthe device I is capable 00 age across the condenser 3l to be proportional
to the charge for the lowest frequency to be
of measuring. However, the increase in sensi
measured. The voltage across the condenser '3l
tivity i-s frequently desirable for measuring
is fed into an amplifier 33 of a type having a
smaller accelerations. In this' respect, it will be
y high input impedance. The output of the am
noted that crystals 9 and I9 function> in the dual
capacity of a piezo-electric generator and a ine-_ 65 pliñer 33 is fed into a cathode ray type oscillo
up to about 8,000 times gravity.
‘
_
Bodies subjected to shock will vibrate at ex
40 tals.
scope 35 capable of following frequencies of the
type encountered. A tuned fllter 34 is located
in the output circuit and is tuned to correspond
on the body subjected to the shocking force in
with the natural frequency of the device I. By
the manner explained above. Upon a shock being
applied to the body 2, the device I will be vibrated 70 this means transient impulses due to the natural
frequency vibrations of the member I5 on the
back and forth with the body 2 and a similar
elastic stiffness of the crystals 9 and I9 are sup
acceleration will be imparted to the casing 3 and
is imparted to the body 2 by the shocking force. I pressed.
chanical spring of high stillness.
In operation, the detector device I isfmounted
The electron beam of the oscilloscope is thus
housing 3 is assumed in a direction to the richt 75 deflected by an amount proportional to the ac
_ If the instantaneous acceleration imparted to the
v2,4.1 1,401
5
6
,
celeration of the casing 3. Thefbeam is at the
in response to shock comprising a piezo-electric ì
same time moved with a constant velocity in a
crystal seated within said housing, a mass having
a surface engageable with said crystal, resilient
means for biasing said mass into engagement with
direction perpendicular to the aforementioned
deflection by means of a suitable sweep circuit
(not shown).
The trace of the beam is pho
said crystal and forming therewith a vibratory
tographed by the camera to produce arecord of _
system of 'a natural frequency higher than that
of the shock movements to be detected, and re
ternative to the use of a sweep circuit, the camera
silient means disposed between said mass and
ñlm may be moved with a constant velocity in a
said housing for permitting said mass to remain
direction transverse _to the beam ~deflection. 10 substantially at rest when the device is subï'ected
From the photographic record -the acceleration
to shock.
and the frequency of vibration imparted to the
2. A device for detecting the movement of a i
casing 3 may be readily determined. _
_
body under a shock force comprising a housing
From the foregoing, it will be apparent vthat
for rigid attachment to said body, charge gen
the piezo-electric properties of the crystals 9` and
erating means for producing an electric impulse
the motion imparted to the casing 3. As fan al
ill,` together with their mounting withinv the
in response to movement of said body comprising
a pair of piezo-electrical elements arranged for
opposite polarity, Asaid housing having a surface
engaging an end surface of one of said elements.'
housing 3 provide a novel _and efñcient detector
device for producing a measurable impulse from
which the characteristics of the motion imparted
to a body in response to the application thereto
of a force of shock proportions may be deter
mined. l The device I has the’advantage of being
light in weight and small in size. It will thus
a mass having a surface engaging an end surface
of said other element, an electrode positioned be
tween said elements and engaged by the other
‘end surfaces of said elements, and means'resil
be apparent that its size and weight limitations
`ientlilv
mounting said mass within said housing
do not interfere with its attachment to the body 25 and providing
a biasing force applied axially of
to be studied. Moreover, the apparatus for
said elements.
`
_
measuring the impulse generated in response to
3. A device for detecting the movement of a
shock may be located'at a distance from the de- .
body under a shock force comprising a housing
vice, the impulse from the terminal 28 being
for rigid attachment to said body, charge gener
transmittable by cable to such apparatus.
ating means for producing an electric impulse
Referring to Fig. 3, there is shown a modified 30 in
response to movement of said body comprising
form of the member ISa for use in the device I
a pair of piezo-electrical elements arranged for
to enable such device to be employed as a force y
opposite polarity, said housing having a surface
meter. _In this showing, the numeral 38 desig
natesthe threaded portion adapted to have en 35 engaging an Yend-surface of one of said elements.
a mass having a surface engaging an end surface
gagement with the element 23 as shown in Fig. 1.
_ of said other element, an electrode positioned be
The difference in_theconstruction of the- mem
tween said elements and engaged byfthe other Y
ber I5a lies in the provision' of the -additional
end surfaces of said elements, and resilient means
threaded portion 31. The portion 31 is adapted
f_or engagement with anotherv part of a struc 40 vdisposed between said mass and .said housing for
permitting said mass to remain substantially at
ture (not shown) similar to the part 2. Relative
’ rest when the device is subjected lto shock so that
‘movement between such vDarts will vthus cause
said generating means andv mass,- when under
relative' movement between the part lia and the
housing 3. vthelatter movement being representa
. shock, form a vibratory system whose elastic de
tive of :a force due to loading causing a deflec-- 45 terminant is substantially given by the axial elas- _
ticity of> said crystals.
.
tion of the structure being`> examined. This
4. A device for detecting the movement of a
movement will cause a compression or change in
body under a shock force comprising a `housing
pressure onthe crystals 9 and I0 and a corre
- for rigid attachment to said body, charge gener
spondingchange in the charge or electric im
ating means for producing an electric impulse in .
pulse therefrom. -In using the device I as a force
meter, it will be noted that the crystals 9 and 50 response to‘ movement of said body comprising a
pair 'of piezo-electrical elements arranged for op- \
I0 are mounted between the- relatively movable ’
posite polarity, said housing having a surface en
housing'3 and member I5a and that crystals 9
and I0 will indicate the amount of relative move
gaging an end surface of one lof said elements,
a mass having a surfaceengaging an end _sur
ment as a measure of the force applied.
Since certain changes may be made in thev 55 face oi!1 said` >other element, an electrode posi-`
, tioned between said elements and engaged by the
_above described construction> Í'andl diii'erent em
other‘end surfaces of said elements. and means
bodiments of the invention' may be made without
departing from the scope thereof, it is intended ' resiliently mounting said mass within ~said hous
ing and providing a biasing force applied axially
that all matter contained in the above descrip
tion or shown in the accompanying drawing shall ‘ 60 of said elements, said mass and said crystals
be interpreted as illustrative and not in a limit
ing
sense.
-
`
I claim as my invention: _
Y
_
i
,
_
.
.
1. A device for detecting the movement of a
'forming together a vibratory system oi' a natural j
frequency higher than that of the shock move
ment to be detected and. said resilient biasing.
means havinga stiffness relative to said mass‘so
'body under a shock‘ force comprising a housing 65 as to permit said mass to remain substantiallyat
rest when shock is applied to said housing.
to saidbody, charge gen
Y for rigid attachment
erating meansfor producing an electric impulse
,
-
».
-
WIIZLIAM P. WELCH.
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