Note: Descriptions are shown in the official language in which they were submitted.
1 Related Patent Applications
This application relates to U.S~ patent
No. 4,~45,376 to Merhav which issued May 1, 1984
and Canadian patent application Serial No. 462,247, filed
August 31, 1984 which are directed to apparatus
utilizing moving accelerometers to measure the specific
force and angular rate of a moving body.
Technical Field
The invention relates to the field of angular
rate determination utilizing movlng accelerometers and
more particularly to angular rate detectors using paired
accelerometers t
Background of the Invention
In the above cited U.S. patent No. 4,445,376
as well as the article by Shmuel J. Merhav entitled
"A Nongyroscopic Inertial Measurement Unit" published
May 1981 by Technion Israel Institute of Technology,
a method and apparatus for measuring the specific force
v~ctor and angular rate vector of a moving body by means
of a plurality of cyclically driven accelerometers is
disclosed. The Canadian patent application Serial No.462,247
cited above discloses similar techniques for measuring the
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specific force vector and angular rate vector of a moving
body utilizing either a single or a pair of accelerometers
vibrating at a constant frequency. In the embodiments of
the paired accelerometer rate and force sensors disclosed
05 in the above patent application, the masses of the
accelerometers are balanced with respect to rectolinear
translation. This means that the pairs of accelerometers
can be attached to a mountins frame work without causing
any vibrational translation of the center of mass.
~owever, the accelerometer configurations disclosed in the
above patent application will produce angular vibration of
any mass to which they are attached abou~ the center of
that mass.
As might be expected, it is important in many
systems such as in inertial navigation systems to reduce
to a minimum any vi~ration, be it linear or angular, that
could affect the system. For example, in inertial
navigation systems it is important to minimize the effects
of one sensor on the performance of other sensors in the
navigation system.
Summary of the Invention
It is therefore an object of the invention to
provide a force and angular rate sensing apparatus
utilizing a pair of vibrating accelerometers configured in
such a manner that torques resulting from the vibration of
the accelerometers are substantially eliminated.
It is an additional object of the invention to
provide an apparatus for generating a signal representing
the an~ular rate motion of a structure that includes:
first and second accelerometers; a structure for aligning
the accelerometers in a side by side relationship with the
force sensing axis of one accelerometer parallel to the
other; a vibrating mechanism for vibrating the
accelerometers individually in a substantially linear
05 direction along a vibration axis normal to the
accelerometers force sensing axis at a frequency ~, and a
signal processor for generating rate signals representing
the angular motion of the structure about an axis
perpendicular to the plane defined by the force sensing
axis and the vîbration axis.
It is a further object of the invention to provide
an angular rate sensing accelerometer structure that
includes a housing; a shaft mounted for rotation in the
housing; a first accelerometer secured to a first support
member; a first flexure for securing the first support
member to the hGusing such that the first accelerometer
can move in a substantially linear manner in a direction
generally normal to the axis of the shaft and in a
direction to and away from the shaft. The structure also
includes a second support member securing a second
accelerometer; a second flexure for securing the second
support member to the housing such that the second
accelerometer can move in a substantially linear manner in
a direction generally normal to the axis of the shaft in a
direction generally to and away from the shaft; a
mechanism for rotationally vibrating the shaft; and a
linkage arrangement connected to the shaft and the first
and ~econd support members effective to vibrate the
accelerometers in the directions permitted by the
flexures.
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Brief Description of the Drawings
Fig. 1 is a simplified perspective dia~ram of a pair
of accelerometers in a side by side arrangement with their
force sensing axes aligned in the same direction;
05 Fig. 2 is a front view of a mechanism for
implementing the paired accelerometer arrangement of
Fig. 1~
Fig. 3 is a side view of the accelerometer
arrangement of Fig. 2: and
Fig. 4 is a block diagram of an analog signal
separating circuit for use with a pair of accelerometers.
Detailed Description of the Invention
As shown in Fig. 1, a pair of accelerometers 10 and
12 are mounted in a side by side arrangement with their
force sensing axes Az and Az aligned in the same
direction. In order to minimize any mass imbalances as
well as torque imbalances that could be transmitted to a
support structure (not shown), the accelerometers 10 and
12 are vibrated in opposite directions to and away from
each other along the axes indicated by lines 14 and 16
which are normal to the sensitive axes Az and Az. As
described in detail in the Merhav U.S. patent,
the acceler~tion signals from the
accelerometers 1~ and 12 can be used to provide signals
representi~g translation of the structure containing the
accelerometers 10 and 12 along the axes Al and A2
along with signalo representing angular rotation of the
structure.
The preferred embodiment o:E an apparatus for
mechanizing the paired accelerometer structure of Figu 1
is illustrated in Figs. 2 and 3. In this apparatus,
substantially linear translation of the accelerometers 10
05 and 12 along the axes 14 and 16 as shown in Fig. 1 is
provided by a mechanism that includes a pair of support
members 18 and 20 that hold the accelerometers 10 and 12
respectively~ In turn, the support members 18 and 20 are
secured to a housing 22 by means of a pair of flexures 24
and ~6. A shaft 28 which is rotatably secured within the
housing 22 by a pair of bearings 30 and 32, has secured to
it a linkage member 34. Attached to the linkage member 34
are a pair of linkage pins 36 and 38 which are inserted
into slots 40 and 42 configured into support ~embers 18
and 20.
Also attached to the shaft 28 is a rotor 44 that,
when combined with a stator 46 attached to the housing 22,
will cause the shaft to vibrate back and forth through a
small angle at a frequency ~. As can be seen from Figs. 2
and 3, the vibration of the shaft 28 will result in the
linkage pins 36 and 38 forcing the support members 18 and
20 and hence the accelerometers 10 and 12 to move in a
direction perpendicular to the shaft and to and away from
each other. Since the accelerometers 10 and 12 will only
move a very mall distance, their direction of travel will
be substantially linear with respect to the axis of the
shaft 28. Signals representing the rotational motion of
the shaft 2B of accelerometers 10 and 12 can be obtained
by means of the capacitor pick-off arrangement shown at
48. The angular capacitive detector 48 provides a means
for angular motion feedback to be used in maintaining ~he
driven motion of the shaft 28 constant over time.
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A signal processor for separatin~ the force signals
F from the angular rate signals n and the output signals
of accelerometers 10 and 12 is provided in Fig. 4. A
control pulse generator 50 generates signals on a line 52
05 as a function of the frequency ~ that will cause a drive
signal generatGr 54 to vi~rate the accelerometers 10 and
12 at frequency ~ as previously desribed. The output
signals of the accelerometers 10 and 12 az and az are
transmitted over lines 56 and 58 to a preseparation
processor 60. The preseparation processor 60 shown in
Fig. 4 is appropriate for a paired accelerom~ter
mechanization of the type shown in ~ig. 1 where the force
sensing axes Az and Az are aligned in the same
direction. The accelerometer output signals at lines 56
and 58 are summed in a summing junction 62 and differenced
in a summing junction 64. A pair of scaling amplifiers 66
and 68 recieve the summed and differenced signals from
summing junctions 62 and 64 respectively over lines 70 and
72.
The principle force separation is the same as the
one disclosed in the previously cit~d patent application
Serial No. 462,247 wherein the combined signal from
amplifier 66 is provided over a line 74 to a force channel
76. The force channel 76 includes an integrating circuit
and a sample and hold circuit with signals from the
control pulse generator 50 being applied over lines 78 and
80 to the integrating and sample and hold circuits. The
combined acceleration signals on lines 74 are integrated
ovér the time period T of the frequency ~ to provide a
force ~ignal Fz on line 82 that represents the change in
velocity along the axis Z of the structure or housing 22
holding the accelerometers 10 and 12.
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Similarly, an angular rate channel processor 84
rec~ives the differenced signals over line 86 and
multiplies them by the zero mean periodic function
sgnc~t. As with the force channel, the resulting signal
05 is integrated over a time period T through a sample and
hold circuit to an output line 88. The signal Qi
representing angular rate information is transmitted
through a low pass filter 90 and output on a line 92.
In the above manner signals from the accelerometer
arrangement illustrated in Figs. 1-3 may be processed to
produce force signals and angular rate signals.
