Brakes – Inertia of damping mass dissipates motion
Reexamination Certificate
2001-04-26
2003-06-17
Butler, Douglas C. (Department: 3613)
Brakes
Inertia of damping mass dissipates motion
C267S136000, C267S140130
Reexamination Certificate
active
06578682
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to compact vibration isolation systems for limiting the transmission of externally generated vibrational, shock, and acoustic energy to mechanically sensitive components.
In certain environments, it is necessary to isolate mechanically sensitive assemblies from shock, vibrational, and acoustic energy. In many applications, this is accomplished by placing the sensitive components within some form of container or housing. Resilient, shock and vibration absorbing mounts are frequently used to limit transmission of externally generated vibrational and shock energy into the housing containing the sensitive assemblies.
The need to isolate a device from shock, vibrational, and acoustic energy is particularly acute when the device is an inertial sensor assembly (ISA), which is the sensor suite for an inertial measurement unit (IMU). An ISA typically includes inertial sensors that detect acceleration and rotation in three planes. Usually there are three accelerometers and three rotational rate sensors arranged with their input axes in a perpendicular relationship. The sensors are generally rigidly and precisely mounted within a housing along with related electronics and hardware. Commonly, the housing is in turn mounted to a support or chassis through suspension mounts or vibration isolators. In turn, the chassis is rigidly and precisely mounted to a frame of a vehicle, such as an aircraft.
In operation, the sensors provide inertial data, such as linear and angular acceleration information to a navigational computer on board the aircraft. The navigational computer processes the data for flight control and/or navigation of the aircraft. For optimum performance, the sensors of the ISA must provide precise inertial data to the navigational computer. Aircraft maneuvers (i.e., acceleration; changes in roll, pitch, and yaw; takeoff and landing), turbulence and engine operation all generate shock, vibration, and acoustic energy that is conveyed through the aircraft frame to the support for the ISA. This energy may manifest itself as linear or angular errors in the inertial data provided by the sensors to the navigational computer. Hence, there is a need for a vibration isolator which provides shock and vibration isolation of the ISA. Before discussing the present invention, it will be beneficial to discuss the prior art for purposes of comparison.
One such known vibration isolator system
10
for an ISA
12
is illustrated in
FIGS. 1 and 2
.
FIG. 1
is an exploded perspective view of a multiple mount vibration isolator system for an inertial sensor assembly known to those skilled in the art.
FIG. 2
is an assembled perspective view of the known vibration isolator system shown in FIG.
1
.
As shown in
FIG. 1
, ISA
12
includes inertial sensors
14
mounted within housing
16
, defined by base member
18
and cover member
20
. Inertial sensors
14
are defined by three accelerometers and three ring laser gyroscopes and their associated electronics and hardware.
Base member
18
of housing
16
includes three mounting lugs
22
(only two of which can be seen in
FIG. 1
) equally spaced about the circumference of base member
18
. Each mounting lug
22
includes an aperture
24
adapted to receive a threaded fastener
26
. Fasteners
26
engage cooperating, threaded openings
28
of inertia ring
30
to rigidly secure the ISA
12
to inertia ring
30
.
Vibration isolator system
10
includes three isolator mounts
32
. Each isolator mount
32
includes an outer frame
34
adapted to hold an elastomeric element
36
that provides isolator mount
32
with its shock and vibration isolation functionality. Elastomeric element
36
is a donut-shaped member with inner aperture element
38
. Elastomeric element
36
is injection molded onto outer frame
34
. Inner aperture element
38
of each elastomeric element
36
is adapted to receive a threaded fastener
40
. Each threaded fastener
40
engages a cooperating threaded hole
42
in inertia ring
30
to secure the elastomeric element
36
of the respective isolator mount
32
to inertia ring
30
secured to the ISA
12
. Isolator mounts
32
are equally spaced about inertia ring
30
.
As seen best in
FIG. 2
, outer frames
34
of isolator mounts
32
are secured to support
44
(shown in dashed lines in
FIG. 2
, and only partially shown relative to one of the isolator mounts
32
for clarity) via threaded fasteners. The fasteners pass through apertures
48
of support
44
to engage threaded openings
50
of outer frames
34
of isolator mounts
32
.
Though isolator mounts
32
of the vibration isolator system
10
adequately isolate ISA
12
from shock and vibration energy conveyed through support
44
, there are some difficulties encountered with the use of multiple, discrete isolator mounts. For example, when using multiple discrete isolator mounts, it is necessary to match the natural frequencies of each of the isolator mounts to be used on a selected ISA. In other words, because natural frequency matching is commonly required at the ISA integration level, each individual isolator mount must be tested, segregated, and marked according to its specific natural frequency and amplification factor. The segregated isolator mounts are then packaged as matched sets for installation to a selected ISA. If one isolator mount of the matched set is damaged or lost during the assembly process, the entire matched set must be scrapped since unmatched mounts may allow uncompensatable motion of the ISA which will result in inertial data errors.
Another difficulty encountered with the use of multiple discrete isolator mounts results because the discrete mounts are attached at various locations about the ISA. Care must be taken to accurately mount and align the center of gravity (CG) of the ISA on the elastic centers of the isolator mounts. Otherwise CG and elastic center offsets may result in uncompensated rocking and coning motions in the ISA which will manifest themselves in inertial data errors. Therefore, multiple discrete isolator mount systems are expensive and difficult to manufacture and use.
A second such known vibration isolation system
60
for a ring laser gyroscope ISA
62
is disclosed in U.S. Pat. No. 5,890,569 to Goepfert and illustrated in
FIGS. 3-4
.
FIG. 3
is an exploded perspective view of a vibration isolator system for an inertial sensor assembly known to those skilled in the art.
FIG. 4
is an assembled perspective view of the known vibration isolator system shown in FIG.
3
.
As seen in
FIG. 3
, vibration isolator system
60
includes isolator mount
64
defined by annular elastomeric member
66
, rigid annular outer member
68
, and rigid annular inner member
70
. Outer member
68
encircles and is concentric with elastomeric member
66
. Inner member
70
is encircled by and is concentric with elastomeric member
66
. Outer member
68
also includes three apertures
72
equally spaced (i.e., 120 degrees apart) about the periphery of outer member
68
.
Coupling apparatus
80
attaches inner ring
70
of vibration isolator system
60
to housing
82
of ISA
62
. Housing
82
is defined by base member
84
and cover member
86
. Housing
82
contains and protects inertial sensors
88
of ISA
62
.
Coupling apparatus
80
includes an adjustment mechanism defined by threaded region
90
on inner side wall
92
of inner member
70
. Threaded region
90
mates with cooperating threaded portion
94
on outer side wall
96
of base member
84
of housing
82
. Threaded interengagement of threaded region
90
with threaded portion
94
attaches ISA
62
to vibration isolator system
60
and permits limited linear movement of housing
82
of ISA
62
along longitudinal axis
98
of ISA
62
, which is perpendicular to a plane defined by elastomeric member
66
. The limited linear movement permitted by the threaded interengagement referred above allows alignment of a lateral center of gravity of ISA
62
(i.e., housing
82
) with an elastic center of elastomeric member
66
of vibration
Braman Todd L.
Hagenson Dale J.
Riesgraf Mark J.
Butler Douglas C.
Honeywell International , Inc.
Siconolfi Robert A.
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