Measuring and testing – Vibration – Vibrator
Reexamination Certificate
1999-04-28
2001-07-10
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
Vibrator
C073S667000, C073S668000, C073S665000
Reexamination Certificate
active
06257067
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to systems and methods of environmental testing, and in particular to a method and system for subjecting a test object to vibrational energy.
2. Description of the Related Art
When in use, storage, or transport, many products are subjected to moderate to severe environmental factors that detrimentally impact their longevity and functionality. Such environmental factors include temperature variations, applied vibrational energy of a variety of different power spectral densities, shock, and exposure to corrosive materials.
During the development phase, products that are expected to be operated, transported, or stored in such environments are extensively tested to assure that the product design meets its design specifications in the expected environment. In addition to this development phase testing, some products are individually tested before delivery to further reduce the risk of failure in severe environments. This is especially important with products that cannot be easily or inexpensively repaired.
For example, commercial and military satellites are expensive to deploy and cannot be easily repaired when in orbit. At the same time, these satellites are exposed to a severe environment that includes wide temperature variations and strong vibrational energy when deployed by launch vehicles.
For these reasons, before deployment, satellites are usually exposed to substantial environmental testing before delivery. These tests verify the structural integrity of the spacecraft, and allow correlation of the spacecraft's structural dynamics with predictive models.
While extensive vibrational testing can effectively reduce the risk of a satellite failure during deployment or operation and can help verify spacecraft structural dynamics, one of the difficulties of such testing is that of simulating the vibrational environment induced by the launch event, particularly vibrations induced primarily along a thrust axis of the combined launch vehicle and assembly.
Current shaker systems rely on a force generator and its supports (flexures, trunions, seismic mass, etc.) to provide lateral and rotational restraint of the spacecraft. The dynamics of these additional masses and springs combine with the spacecraft dynamics in an undesirable manner. Other shaker systems place the satellite on a force generator and rigidly restrain all motion except in the direction of vibration from the force generator. Unfortunately, such systems require precision alignment and ambient temperature control of within plus or minus four degrees Fahrenheit (±4° F.) to prevent jamming between the movable portion of the shaker test device and the structure used to restrain motion.
Another solution is to use a “free” system that has a rigid connection between the vibration fixture coupled to the spacecraft and the force generator. Unfortunately, such “free” systems can induce several vibration modes that are attributed to the mass, stiffness, and inertia of the force generator and associated structures. The dynamics of the force generator and associated support structures therefore make it difficult for engineers to correlate math models with actual vibration test results.
What is needed is an apparatus and method for vibration testing that permits simulation of easily-definable and controllable boundary conditions, thereby providing a better approximation of the environment to be encountered during launch, and permitting more accurate comparisons with predicted results from mathematical models. The present invention satisfies that need.
SUMMARY OF THE INVENTION
To address the requirements described above, the present invention discloses an apparatus, and method for subjecting a test object to vibrational energy.
The apparatus comprises a rotatable joint such as a hydrostatic ball joint or flexure for transmitting energy from a force generator to the test object, and a support structure, coupled to the test object and the rotatable joint, for flexibly restraining the test object from rotating about the center of rotation of the rotatable joint. In one embodiment of the invention, the support structure comprises a support member and at least one suspension device disposed between the support member and a ground datum. In another embodiment, the suspension device applies a suspension force to the support member in a direction substantially perpendicular to a vector from the center of rotation to the suspending force. In this embodiment the suspension devices are subjected primarily to compression and tension forces. Also, a suspension system that applies forces acting directly through the center of rotation can be used to limit potentially damaging lateral forces applied to the force generator device. By acting through the center of rotation, these forces will not induce undesirable rotational excitations to the structure under test.
The method comprises the steps of coupling a test object to a rotatable joint having a center of rotation, flexibly restraining the test object from rotating about the center of rotation, and applying vibrational energy substantially along a first axis passing through the center of rotation to the rotatable joint.
The foregoing describes a de-coupled system in which the spacecraft boundary conditions can be easily defined as “free” with a known mass attached to the spacecraft interface. The foregoing system is also easier to manufacture, install, change axes, and maintain. Further, the foregoing system is insensitive to alignment and temperature changes.
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patent: 5594177 (1997-01-01), Hanse
Ankrom Mark E.
Pano Scott B.
Vicari Lawrence C.
Gudmestad T.
Hughes Electronics Corporation
Saint-Surin Jacques
Williams Hezron
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