Note: Descriptions are shown in the official language in which they were submitted.
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SINGLE AXIS M~LTISENSOR
BACKGROUND OF THE DISCLOSURE:
FIELD OF TAO INVENTION
I've present invention relates to inertial guidance
instrumentation. Gore particularly this invention pertains Jo
multisensory for measuring both the linear acceleration and rate
of rotation of a moving body.
DESCRIPTION OF THE PRIOR ART
A number of attempts have been made to utilize an
inertial Nazi to detect the rate of rotation of a body.
Generally such attempts have been based upon the Charles
acceleration experienced by a vibrating or rotating body fixed to
a second body whose rotation is to be sensed. Charles
acceleration is described by the following equation:
A = 2 x v;
where: A = Charles acceleration;
= angular rate of rotating coordinate
system second body) to be measured, and
v = velocity component perpendicular to
the axis of rotation.
As referenced above, the foregoing expresses the basic
principle on which all vibratory gyros as well as spinning wheel
gyros are based; namely, a Charles acceleration force is expert
fenced when a moving mass has a velocity component perpendicular
to the axis of rotation of a associated rotating coordinate
system. In application this principle allows the sensing of
angular rate with an oscillating pendulum as was first demonstra-
ted by Leon Faculty in the early 1850's. Since then a number of
attempts have been made to apply Charles acceleration principles
to to design I rate and rate integrating gyros.
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Prominent among the automats to develop a rate sensing
gyro in accordance with the foregoing principles have been the
following inertial sensors Hall referred to by trademark name):
"Gyrotron" of the Sperry Gyroscope Corporation ~194G); "A Gyro"
of Royal Aircraft Establishment; "Vibrating String Gyro" of North
American Rockwell Corporation ~Autonetics Division, Anaheim,
California), "Vitro" of the General Electric Corporation and
"Sonic Bell Gyro" of General Motors Corporation Delco Division).
All of the above-mentioned, with the exception of ~yrotron, began
development in the early 1960's.
In general, the above named systems rely upon either a
rotating body or an unconstrained vibrating Cody to supply the
velocity component v perpendicular to the axis of rotation of the
second body The acceleration force experienced by such rotating
or vibrating body is then measured in some manner to provide the
Charles acceleration A. Knowing the Charles acceleration and
thy velocity of a force-sensing element, Snow can then simply
determine the rate of rotation of the body.
Vibrating bodies offer obvious advantages over rotating
assemblages in terms of mechanical simplicity. In order to
arrange a rotatable inertial instrument having sensitivity to
Charles acceleration, such as an accelerometer, ball bearings,
slip rings, spin motors and the like must be provider further,
a rotational arrangement must be referenced in phase with the
case in which it is mounted to resolve the input angular rate
into the orthogonal sensitive axes, additionally complicating
such arrangements.
A potential problem inherent in any mllltisensor
comprised of one or more vibrated sensors of the inertial mass
type results from the fact that acceleration information along
the input axis of the sensor is included in the swooners
output. While, err many applications and environments, the
frequency of acceleration is predictable and lies outside the
bandwidth of concern, confusion will arise when the frequency of
linear acceleration along the input axis is close to the
frequency of ~ibrakion of the sensor.
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SUMMARY OF THE INVENTION
The preceding and other problems of the prior art are
addressed and solved by the present invention which provides an
improved multisensory Such ~ultisensor includes means responsive
to acceleration along a first axis and means responsive Jo axle-
oration along a second axis. Means are provided or mounting
such last named means 50 what the first axis is collinear with
the second axis. In addition, means are provided for vibrating
each Of such acceleration responsive means out of phase along
parallel axes, each of such axis being orthogonal to the first
and second axes.
The foregoing and additional features of the invention
will become further apparent from the retailed description that
follows. This description is Accompanied by a jet of illustra-
live drawing figures. Numeral are utilized within the detailed
description and the drawing figure to printout various features
of the illustrated embodiment of the invention. Such numerals
refer to like features of the invention throughout,
RELIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a top view of a single axis multisensory with
certain portions removed for purposes of clarity;
Figure 2 is, in part, a-cross section of the single axis
mul~isensor taken along section line 2-2 of Figure 1 and add-
tonally including certain of the components thereof what were
omitted from the prior figure;
Figure 3 is an enlarged partial cross section taken
along the line 3-3 of Figure I for the purpose of illustrating
the manner by which vibration of the right and left acceder-
oln~-ters is effected in accordant with the invention; and
Figure 4 is a functional block diagram of rate and
acceleration extraction circuitry for use in the present
invention.
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DETAILED DESCRIPTION
Turning now to the drawings, Figure 1 presents a top
view of a multisensory in accordance with the present invention.
A number of features of the embodiment have been removed from
Figure 1 to enhance the clarity of illustration. Such features
will be shown and pointed out in subsequent views and accompany-
in discussion.
The multisensory of the invention includes a right
accelerometer 10 and a left accelerometer 12 arranged within a
case 14, the top of which is removed in Figure 1 Jo allow visual
access. At least one accelerometer may be of a type in which an
inertial mass therein is arranged Jo react to and thereby provide
an indication of acceleration forces along a predetermined dire
Sheehan It might further be of he constrained mass type.
Alternatively, accelerometers of the open loop type or a
combination of open and closed loop type sensors may be employed
in the multisensory Additionally, the present invention may be
practiced by means of accelerometers including elements whose
optical properties are altered during acceleration.
The accelerometers are situated within a cavity 16
formed interior to the case 14. Each accelerometer is fixed to a
three part bracket, the right accelerometer being fixed to the
bracket that includes the finger 18 and beam 19 and the left
accelerometer 12 being mixed to the bracket that includes finger
20 end beam 21, Side beams are not shown in figure 1 to permit a
clear view of each accelerometer and bracket assembly. however,
as will be shown in succeeding illustrations, each combined
bracket-and-accelerometer assembly is sandwiched between a pair
of spaced-apart flexible sodomize thaw include piezoelectric
elements bonded thereto for effecting predetermined vibratory
sensor motion.
The accelerometers 10 and 12 are arranged within the
cavity 16 in such a way that, at rest, their input axes 22 and
I respectively, are substantially collinear. This nay be seen
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more clearly in Figure 2, a crocus sectional view generally taken
along line 2-2 of Figure 1 end folding some elements removed
from the prize figure for purposes of clarity. In Figure 2 one
can view the right and left parallel beam suspensions comprising
spaced apart side beams in pairs 25, 26~ and 27, 28~ respectively
that sandwich the right and loft accelerometer~and-b~acket
assemblies. (It is to be noted that the right bracket assembly
is completed by means of a lower firlger 30 and the left bracket
is completed by a lower finger 32.~
The masses of the eight and left assemblages of
accelerometer, bracket and side beam pairs are substantially the
same to minimize loading at the case mountings 34, 36, 38 and 40.
Such pairing of masses tends to a first order, to compensate
linear (pure translational) vibration fortes. Identical holes 42
and 44 are provided in the beams lug and 21, the hole 42 Essex-
tidally serving only to equalize mass while the hole 44 accommo-
dates a magnet 46 that corresponds to the magnet 48 fixed to the
right accelerometer 10.
Each of the magnets 46 and 48 interacts with a case-
fixed pair of coils that, taken together, act as the multisensory
velocity kickoff. In the instance of the magnet 48, its
vibration with the right accelerometer 10 induces current in
velocity kickoff coils 50 and 52 what are secured to a case fixed
bracket 54. (The bracket 54 additionally provides the location
of the right acceleration restoring amplifier 56.) The vibration
of the left accelerometer 12 arid magnet 46 induces current in
velocity kickoff coils 58 and 60 that are associated with the
bracket 62. Thy left acceleration. restoring amplifier 64 is
secured to the case fixed bracket 62.
Figure 3 is an enlarged partial cross sectional view
taken along the line 3-3 of Figure 1 for the purpose of
illustrating the means employed Jo effect vibration of the
accelerometers 10 and 12. As can be seen in this view, the right
accelerometer 10 is maintained in secure relation between
sidewalls 25 and 26 of the right parallel bar suspension by means
of the spaced apart fingers 18 and 30 of the retaining bracket.
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the side beams 25 and I extend the length of the cavity 16 and
are fixed at their ends to the opposed beam support flexors 66
and 68. The side beams are each of generally W-shaped cross
section with outwardly-facing reinforced portions integral with
thin, web-like members.
Piezoelectric elements to 72, 74, 76 are bonded to the
web-like portion of the side beams by adhesive means such as
epoxy or the like. Metallized contacts as shown are plated Jo
the piezoelectric elements in pairs. As is well known ugh
piezoelectric material is subject to predictable and reproducible
deformation in response to positive and negative electrical
potentials. For example, by application of negative and positive
electrical potentials to properly polarized elements in
accordance with the combination indicated in Figure 3/ new forces
will applied to the side beam tending to force each upward at
its midpoint Conversely, by the reversal of sign of the
indicated potentials, the combinations of sidewall, bracket and
accelerometer will be forced downward Thus by appropriate
sequencing of polarities of the electrical signals applied to the
sidewalls, the accelerometer 10 Rand the accelerometer 12) can be
caused to vibrate up and down at a preselected frequency and
amplitude.
Referring back to Figure 2, the vibrations of the
accelerometers 10 and 12 are induced with a 180 degree phase
difference, to occur along the parallel axes 78 and 30. us a
result of the above-described Charles acceleration forces that
are induced in a vibrating system, the vibrations of the
accelerometers 10 and 12 along the indicated axes will induce
measurable acceleration forces proportional to the rate of
rotation of the multisensory in the direction of the input axis of
each accelerometer. Thus, the output of the accelerometers lo
and 12 will contain a measure of the rate of rotation of the
system about axis 82, shown in Figure 1.
Figure 4 is a schematic diagram of electrical circuitry
foe determining both linear acceleration along the input axes of
thy accelerometers 10 and 12 end rotation about axis I with
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great accuracy by utilizing the output generated by a multisensory
in accordance with the preceding discussion By processing the
signals as shown, one attains accuracy of measurement thaw would
otherwise be jeopardized in a Charles type mul~isensor when
accelerations along the accelerometer input axis are experienced
a regencies approXimatincJ the modulation frequency of
vibration of the accelerometer.
The signals that create the vibrations of the
accelerometers are provided along conductors 88 and 90 by a
driver circuit 86. Currents induced in the right and left
kickoff coil pairs actuate the driver 86 in a self-resonant
circuit arrangement. For example, the sensed vibration of the
left accelerometer 12, converted into a corresponding sinusoidal
current proportional to velocity through interaction of the
magnet 46 with left kickoff coils 58, 60 is shown in the Figure
to be applied as an input to the driver circuit 86~ In addition,
the signal induced in the kickoff coils serves as a demodulation
reference signal by application to a demodulator 92. [As should
be apparent, the Charles acceleration signal, a cross product,
is oscillatory with frequency equal to thaw of the frequency of
vibration of the sensing accelerometer and amplitude proportional
to the input angular rate. Thus/ the extraction of angular rate
or velocity information requires demodulation of a sinusoidal
signal.)
The outputs of the right and left accelerometers are
fed, in parallel, to both a differential amplifier 94 and a
summing amplifier 96. Pus the i3ccelerometers ace vibrated 180
degrees out-of-phase, the component portions of their signal
outputs that relate to the measurement of Coors acceleration
are of opposite sign while the portions relating to linear
acceleration are not so effecter and are of like sign Thus the
Outlet of the differential amplifier 94, a measure of the
difference between the accelerometer outputs, is solely a measure
of Charles acceleration and, hence, rotation, since the portions
of the outputs responsive Jo linear acceleration are canceled
regardless of the relationship between the frequencies of these
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two individual component portiolls of accelerometer output. As a
further consequence of the equal and opposite senses of the
Charles or rate components of the sensor outputs, the OlJtput of
the differential amplifier I provides twice as sensitive a
measure of rotation as the output of a single component
accelerometer of the multisense.
The rate output is then applied to the demodulator 92
which, as discussed above, utilizes the induced sinusoidal
current of the velocity kickoff coils as its demodulation
rc~erence. The demodulated rate output is then applied to a
filter 98 for final extraction of the rate signal.
As a further consequence of the opposite senses of the
Charles components of the outputs of the right and left
accelerometers the output of the summing amplifier 96, to which
the accelerometer outputs Grew applied, contains no rate
information and is twice as sensitive a measure of linear
acceleration along the coincident accelerometer input axes as is
the output of a single one of the accelerometers lug or 12. This
output signal is not demodulated (unlike the rate signal) since
it is a direct measure of acceleration whether or not such
acceleration is vibratory in nature. The signal is then applied
to filter 100 for extraction of acceleration information
therefrom.
Thus it is seen that there has been provided an improved
multisensory of the vibratory yo-yo thaw achieves enhanced sense-
tivity to both acceleration and rotation and is not susceptible
to errors that might otherwise be induced when the frequency of
acceleration coincides with or is very close to the modulated
frequency of the vibrated sensor. While this invention has been
described with respect to its presently preferred embodiment its
scope is by no means thereby so. loomed Rather, this invention
is intended to embody all variations falling within the language
of the set of claims what follows and their equivalents.
worry IS CLAIMED IS:
