Spring devices – Resilient shock or vibration absorber
Reexamination Certificate
2000-03-02
2004-10-19
Siconolfi, Robert A. (Department: 3683)
Spring devices
Resilient shock or vibration absorber
C267S153000
Reexamination Certificate
active
06805337
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of art to which this invention relates is an apparatus for semi-active isolation of payloads with low transmissibility, and more particularly to an apparatus having semi-active means for isolating vibration of a payload from a base structure.
2. Description of the Related Art
Traditionally, one of two approaches have been used to isolate a payload from the vibrations of a base structure. Either the payload is very rigidly connected, to the base structure such that it could withstand the effects of the vibrations or the payload is connected to the base structure by vibration damping elements such that the payload is free to move relative to the base structure.
In certain applications, the former approach is impractical because of the extra material and weight needed to make the very rigid connection between the payload and base structure. Launch vehicles are one such application. The heavier a launch vehicle is, the more thrust is needed to lift it to its predetermined destination. Added thrust means bigger, heavier, and more expensive engines which transmit even more vibrations to the payload.
The latter approach also has its disadvantages in certain applications, such as launch vehicles. Referring to
FIG. 19
, there is illustrated a schematical representation of a conventional launch vehicle
400
having a payload
101
, a base structure
102
, engines
403
fixed to the base structure
102
, damping elements
404
disposed between the base structure
102
and the payload
101
, and a fairing
405
covering the payload
101
and base structure
102
. The payload
101
generally houses sensitive electronics and other sensitive equipment that is prone to failure due to vibrations that can be transmitted to the payload
101
through the base structure
102
by the engines
403
. As the launch vehicle
400
travels, the effective weight of the payload
101
varies due to the acceleration of the launch vehicle
400
as well as changing mass of the launch vehicle
400
(due to the consumption of fuel which powers the engines
403
).
The damping elements
404
generally require a relative movement between payload
101
and the base structure
102
in the vertical (axial) and horizontal (lateral) directions. Unfortunately, these damping elements also allow some rotation of the payload
101
with respect to the base structure
102
. Since the height of the launch vehicle payload is typically great, even a slight rotation of the payload results in a large displacement near the top of the payload
101
. However, the fairing
405
of the launch vehicle
400
typically only has approximately one inch of clearance between its inner surface and the outer surface of the payload
101
. Thus, to avoid contact between the fairing
405
and the payload
101
even the slightest rotation cannot be tolerated.
To counter this problem, heavy, active rotational restraint systems are necessary, typically comprising at least three voice coil motors which direct a restoring force to the payload to keep it from rotating. A feedback system senses the rotation of the payload
101
and signals the motors to direct force accordingly. Such an active system is heavy, complicated, and prone to failure. Furthermore, such an active system requires electrical power to drive the motors which is either siphoned from the engines or stored in heavy batteries. Neither of which is very desirable in a launch vehicle.
For the above reasons, there is a need in the art for a payload isolation system which is low weight, uncomplicated, does not permit rotation of the payload relative to the base structure, and preferably mechanical which operates in a passive or semi-active mode so as not to be prone to failure or require an undesirable energy drain.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an apparatus for isolating a payload from a base structure upon which it is supported so as to suppress the transmission of vertical (axial) and/or horizontal (lateral) vibration between the payload and base structure.
It is a further object of the present invention to provide an apparatus for maintaining effective isolation in the presence of varying effective payload weight, which may be due to either variation of the vertical acceleration field or of the payload mass, or both.
It is yet a further object of the present invention to provide an apparatus for maintaining the natural frequency of vertical isolation means substantially constant and low while accommodating the variations in the effective weight with substantially no variations in the deflection.
It is yet a further object of the present invention to provide an apparatus for providing an automatic or convenient manual means to adjust the isolation for variations in the effective payload weight and optimize for lowest practical natural frequency.
It is yet a further object of the present invention to provide an apparatus for providing the desired isolation entirely passively, i.e., with no expenditure of energy, during periods when the payload is substantially fixed and when the payload varies, by using active means solely to adjust the parameters of the passive system to compensate for payload variation, i.e., by constructing a semi-active means of control.
It is yet a further object of the present invention to provide an apparatus for preventing the transmission of vertical and lateral vibration forces, prevent any relative rotational motion between the base and the payload.
It is still yet-a further object of the present invention to provide an apparatus for preventing excessive buildup of destructive resonant oscillations if the natural frequency of the isolation system should overlap with the spectrum of vibrational excitation to which it is exposed.
The present invention provides a novel means for passively isolating a payload from a base structure, upon which it is supported, to prevent transmission of both vertical (axial) and lateral vibration between. the payload and base structure, while providing for active parameter adjustment to compensate for changes in the payload mass or effective weight or the required isolation spectrum with very low cost in terms of power consumption, weight and volume. Here, lateral is defined for the purposes of the invention as being orthogonal to the quasi-static acceleration field, i.e., the vertical (axial) direction. The quasi-static acceleration in this context may be, for example, gravity or the average gross acceleration of a vehicle carrying the payload. The acceleration is considered to be quasi-static when its variation is slow compared with the frequency of structural vibrations being isolated.
With the present invention, vertical and lateral transmissibility of vibration is substantially reduced above a relatively low system natural frequency, such as above about 5-10 Hz, which requires a relatively low effective isolation system spring rate for a given payload mass, while the static or quasi-static spring deflections are simultaneously small. With this invention, such a capability is achieved with a nonlinear elastic element that is relatively rigid at low and at high levels of displacement, but is very compliant at intermediate levels of displacement.
The present invention also provides an improved means for making the system rigid to rotational deflections while simultaneously providing the extreme flexibility to vertical and lateral displacement that is necessary to achieve the low system natural frequency that is required for the desired low vertical and lateral vibration force transmissibility. This is achieved by mechanically constraining the rotational motion of the payload relative to the base structure, with variations of properly placed one or more parallelogram linkages.
Moreover, the present invention also provides improved means for preventing buildup of resonant oscillations when the system is subject to vibrational excitation at frequency near its natural frequency. The improved means utilizes nonline
Khorrami Farshad
Rastegar Jahangir S.
Rothchild Ronald
OmniTek Research & Development, Inc.
Scully Scott Murphy & Presser
Siconolfi Robert A.
LandOfFree
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