Patent Application
20100037694
Inertial measurement units (IMUs) are used in a variety of applications. An IMU is the main component of inertial guidance systems used in air and space vehicles, watercraft vehicles, guided missiles and a variety of gun and artillery applications. IMUs work by detecting the current rate of acceleration, as well as changes in rotational attributes, including pitch, roll and yaw using a combination of accelerometers and gyroscopes. By way of example, the data collected from these sensors allows a computer to track a vehicle's position using a method known as dead reckoning. The term IMU commonly refers to a housing having an inertial sensor assembly, which may include three accelerometers and three gyroscopes comprising the assembly. The accelerometers and gyroscopes may be placed such that they can measure inertial acceleration, also known as G-forces. The accelerometers, for example, may be placed such that their measuring axes are orthogonal to each other. The performance of at least some IMUs may be dependent on the vibration and shock isolation of its inertial sensor(s) within the units.
Honeywell®, one of the leading producers of IMUs, makes IMUs that serve the unique and demanding requirements of precision guided tactical and strategic guidance and navigation platforms of all types including: missiles, guided projectiles, ballistic interceptors, unmanned vehicles, targets, and torpedoes. By way of example, Honeywell® is also pioneering super-miniaturized inertial navigation systems using Micro ElectroMechanical Systems (MEMS) technology that enables revolutionary gun-hard performance. In such applications, the IMUs should be both small and robust. These systems may be referred to as gun hard applications and some systems must meet shock requirements having at least a 10,000 G-force set back.
The present invention generally relates to a snubbing or damping system for reducing a shock impact on an isolated body within a shock sensitive device, which may take the form of an inertial measurement unit (IMU). The shock sensitive device includes a housing with an inertial body suspended in an isolated manner within the housing and engaged with the snubbing system. By way of example, the inertial body may take the form of an inertial sensor assembly. Further, the snubbing system may take the form of a plastically deformable snubbing mechanism positioned between the housing and the inertial body along a line of action of the inertial body during an acceleration (e.g. shock) event.
Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings:
In one embodiment of the invention, an inertial snubbing system includes a housing having a housing wall defining an internal cavity and a body located within the internal cavity. In one embodiment, the body may take the form of an inertial sensor assembly for sensing a navigational direction. The system further includes a suspension system configured to isolatingly support the body within the cavity and with respect to the housing wall. In addition, a deformable snubbing mechanism is positioned between the body and the housing wall. The deformable snubbing mechanism includes a first end proximate the body and a second end proximate the housing wall such that the snubbing mechanism is arranged to be compressed substantially in a first direction during acceleration of the body in the first direction.
In another embodiment of the invention, an inertial measurement unit includes sensing means for sensing a navigational direction; support means for isolating the sensing means within a cavity formed by a housing; and snubbing means for absorbing an amount of potential energy from the sensing means, wherein the snubbing means remains permanently deformed after being compressed by a predetermined amount due to movement of the sensing means, wherein the snubbing means includes a first end in contact with the inertial sensor assembly and a second end in contact with the housing before absorbing the amount of potential energy.
The inertial sensor assembly has a certain amount of potential energy because of the distance between it and the conventional snubber and because of the acceleration applied to the IMU. This is analogous to an object held some distance above the ground in the presence of gravity. The inertial sensor assembly gains kinetic energy and loses potential energy as it starts to move toward the conventional snubber. The snubber has to absorb the inertial sensor assembly's kinetic energy plus any remaining potential energy before it comes to rest against the snubber.
However, when the inertial sensor assembly is in contact with the deformable snubbing mechanism of the present invention as it begins to accelerate then the inertial sensor assembly gains little or even negligible kinetic energy. Most of the potential energy goes directly to the deforming the deformable snubbing mechanism.
In yet another embodiment of the invention, a method for decelerating an inertial sensor assembly within a housing of an inertial measurement unit includes the steps of (1) isolating the inertial sensor assembly within a cavity formed by the housing; (2) positioning a deformable snubbing mechanism with a first end in contact with the body and a second end in contact with the housing; (3) accelerating the inertial sensor assembly in a first direction; and (4) during acceleration in the first direction, compressing the deformable snubbing mechanism with the potential energy of the inertial sensor assembly, wherein the deformable snubbing mechanism remains permanently deformed after a predetermined amount of compression.
In one embodiment, the deformable snubbing mechanism 112 includes a first end portion 114 in contact with the inertial body 108 and a second end portion 116 in contact with the housing wall 104. Alternatively, the deformable snubbing mechanism 112 may include a small gap or space between the first end portion 114 and the inertial body 108 or between the second end portion 116 and the housing wall 104. The configuration of the snubbing mechanism 112 may be selected to have a desired cross-sectional profile and be made from a desired material such that the snubbing mechanism 112 substantially absorbs the work (e.g. potential energy) of the inertial body 108 during an acceleration event of the inertial body 108. By way of example, the deformable snubbing mechanism 112 may be made from a polymeric material, a metallic material, a fiber-reinforced composite material or some combination of the same. The deformable snubbing mechanism 112 operates such that it permanently deforms under a predetermined load or greater load from the inertial body 108.
While one embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of one embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.
