Abstract:
The present invention is directed to a radial snubber for use with a vibration isolator. The radial snubber cushions any impact of the aluminum insert of the isolator against the remainder of the isolator, thereby reducing the strain experienced by the isolator.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to snubber devices and more particularly to a snubber device for an elastomeric vibration isolator. 
     BACKGROUND OF THE INVENTION 
     The guidance system for a missile program requires an inertial sensor assembly that can survive a severe shock input, such as one of 400 Gs (1 G equals the force of gravity). The inertial sensor assembly comprises sensors, such as accelerometers and gyroscopes, mounted to a rigid aluminum structure. Because the accelerometers and gyroscopes are relatively fragile instruments, they are isolated from external vibration and shock inputs by means of vibration isolators. It is the function of the vibration isolators to absorb the high energy of the shock input, thereby protecting the sensors. The shock input that must be absorbed by this particular inertial sensor assembly greatly exceeds the requirements of other current programs utilizing the same hardware. 
     Under high radial shock loads, the internal metal insert of an isolator deflects and can impact the outer element of the isolator, thereby creating excessive G forces. This places a great amount of strain on the isolator, which reduces the survivability of the system in the shock environment. This deflection of the isolators can also damage the sensors mounted thereon. 
     One option would be to stiffen the isolators by constructing them of different, stiffer material. Although this would lead to reduced deflection of the isolator, the isolator would not absorb the energy of the shock input and, as a result, the sensors would be damaged. Thus, this option is not feasible. 
     Another option would be to greatly increase the size of the isolator such that the inner element could not impact the outer element. Due to the size constraints of the guidance system, however, this option is not practical. 
     Thus, there is a need in the art for a way to reduce the strain experienced by a vibration isolator under high G loading. 
     There is a further need in the art for a cost-effective way to increase the survivability of a vibration isolator in a shock environment. 
     SUMMARY OF THE INVENTION 
     The present invention meets the needs of the prior art by providing a radial snubber that reduces the strain experienced by a vibration isolator. The radial snubber is placed about the inner element of the isolator. Under high G loading, the snubber cushions the impact of the inner element against the remainder of the isolator. Thus, the deflection of the inner element is avoided, thereby reducing strain on the isolator and damage to the inertial sensors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of an isolator used with the present invention. 
     FIG. 2 is a side view of the isolator of FIG.  1 . 
     FIG. 3 is a cross-sectional view of the radial snubber of the present invention in use with an isolator. 
     FIG. 4 is a cross-sectional view of an alternate embodiment of the radial snubber of the present invention in use with an isolator. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is depicted in FIGS. 3 and 4 and is intended for use with a vibration isolator  10 , shown in FIGS. 1-4. Such a vibration isolator is available from Lord Corporation, Erie, Pa. The vibration isolator  10  generally includes an outer element  12  and an inner element  14 . The outer element  12  has a central opening  13  through which the inner element  14  extends. As can be seen best in FIGS. 2 and 3, the inner element  14  is attached to the outer element  12  by means of an elastomeric member  15 , preferably constructed of a silicon elastomer, such as Broad Temperature Range (BTR) type, available from Lord Corporation, Erie, Pa. This elastomeric member  15  absorbs the energy from external vibration and shock loading such that the energy level is reduced on the inertial sensor assembly. 
     The outer element  12  of the isolator  10  further includes two flanges  16  for attaching to the chassis of the guidance system. As can be seen in FIGS. 1 and 3, each flange  16  defines an aperture  18  for mating with an appropriate fastener (not shown). 
     The inner element  14  is comprised of a threaded metal insert. As can be seen in FIG. 3, the insert  14  is provided with a central aperture  20  for mounting an inertial sensor assembly to the isolator. The insert  14  is preferably constructed of aluminum. 
     The present invention is directed to a radial washer or snubber  30  for use with isolator  10 . The snubber  30  is constructed of rubber, preferably die-cut from a sheet of elastomeric material similar to that used in the isolator construction. The snubber  30  is provided with a central opening  32  to accommodate the outer diameter of the aluminum insert  14 . As shown by the arrows in FIG. 3, the snubber  30  is mounted to the aluminum insert  14  of the vibration isolator  10 . The washer or snubber  30  can be molded onto the insert  14  or bonded to the insert  14  with a silicon glue such as Dow Corning 3145RTV. 
     Referring to FIG. 4, an alternate embodiment of the radial snubber is depicted. Since the isolator of FIG. 4 is similar to the isolator of FIG. 3, the same reference numerals are used to denote common elements. The isolator of FIG. 4 differs from the isolator of FIG. 3 in the placement of the radial snubber  130 . As can be seen from FIG. 4, the radial snubber  130  is mounted to the outer element  12  of the isolator  10 . The snubber  130  may be molded onto the outer element  12  or bonded thereto. 
     In the preferred embodiment, the radial snubber has a 0.45 inch outer diameter and a 0.25 inch inner diameter. These dimensions allow clearance during normal usage such that the frequency characteristics of the isolator are not altered. It should be understood that the dimensions of the radial snubber may change, depending upon the type of vibration isolator with which the snubber is used. 
     When the isolator undergoes a high G radial load (for example, &gt;400 G), the inner element tends to move against the outer element. With the radial snubber in place, the impact of the aluminum insert against the outer element is cushioned. The radial snubber absorbs the energy of the impact in a controlled fashion. Thus, the inner element does not directly impact the outer element and the creation of excessive Gs is avoided. 
     It should be understood that the present invention is not limited to use with only a single type of isolator or a single type of application. Rather, it may be used with any number of vibration or shock isolators in various applications. 
     While the invention has been described in connection with certain embodiments, it should be understood that it is not intended to limit the invention to these particular embodiments. To the contrary, it is intended to cover all alternatives, modifications and equivalents falling within the spirit and scope of the invention.