Joints and connections – Interconnected flanges or shoulders – Axially bolted or riveted
Reexamination Certificate
2001-01-30
2003-03-11
Novosad, Christopher J. (Department: 3671)
Joints and connections
Interconnected flanges or shoulders
Axially bolted or riveted
Reexamination Certificate
active
06530718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of fasteners and, in particular, to a non-pyrotechnic fastener that automatically separates a nut from a bolt upon actuation.
2. Description of Related Art
Reliable fasteners that separate upon actuation have many applications. One critical application is on launch vehicles designed to place spacecraft into orbit. Not only must the fasteners reliably secure booster stages together under high loads, they must rapidly separate upon actuation in order to achieve proper timing of stage separation. This is particularly true when several fasteners must be simultaneously separated. Thus pyrotechnically actuated devices are typically used. One example can be found in U.S. Pat. No. 3,926,090 “Separation Nut” by J. W. Bunker. An extreme example is an explosive actuated system that uses a metal coupling to join the segments of the fairing together. A tubular member is positioned next to or within the coupling. Upon ignition, the explosive expands the tubular member, which in turn fractures the coupling. Such a system is disclosed in U.S. Pat. No. 5,443,492 “Payload Housing And Assembly Joint For A Launch Vehicle” by A. L. Chan, et al.
However, pyrotechnic fasteners and the like, while well proven, can not be tested prior to use, thus must be assembled with great care. This makes them generally expensive to manufacture. Special storage areas must be set aside for any device containing explosives. They are always subject to inadvertent actuation, and, therefore, handled with great care. Additionally, they are particularly subject to ignition by electromagnetic interference (EMI) and thus must be protected by EMI shielding devices, which also raises the cost. One of the most important disadvantages is that upon actuation, most generate significant shock loads, which can damage nearby equipment.
One approach to eliminate such problems is to use shape memory alloys to actuate the fasteners. Shape memory alloys offer a solution to the problem. There are basically two types of shape memory alloys:
1. Simple memory alloys where a deformation undergone in an austenitic state is definitively cancelled out during the passage to the austenitic state.
2. Reversible memory alloys where a deformation undergone in the martensitic state is cancelled out during the passage into the austenitic state, but is reassumed during a subsequent passage to the martensitic state. However, the transformation takes place with a certain hysteresis.
There are numerous alloys having shape memory characteristics such as Ti—Ni, Au—Cd, In—Zn, Ti—Ni—Cu, Cu—Zn—Al and Cu—Al—Ni and many are commercially available. The theory of shape memory alloys is well established and, therefore, need not be discussed in further detail.
There are many examples of fasteners making use of a shape memory alloy (SMA). For example, U.S. Pat. No 5,312,152 “Shape Memory Metal Actuated Separation Device” by W. H. Woebkenberg, Jr., et al. uses a segmented nut that is kept in engagement with a threaded bolt by a retainer.
The retainer is held in place by a SMA element. Upon heating of the SMA element, it returns to its un-deformed state and releases the retainer, which in turn releases the nut. U.S. Pat. No 5,722,709 “Separation Device Using A Shape Memory Alloy Retainer” by B. K. Lortz also uses a segmented nut. However, in this case the nut is retained in contact with the threaded bolt by a SMA collar. Upon heating, it expands to its original shape releasing the segmented nut. Other examples of fasteners using shape memory alloys can be found in U.S. Pat. No. 5,060,888 Temporary Linking Device Especially For An Artificial Satellite Lengthening Piece, And Method To Free Such A Link” by G. Vezain, et al., U.S. Pat. No. 5,129,753 “Shape Memory Wire Latch Mechanism” by K. S. Wesley, et al., U.S. No. 5,150,770 “Recharge Device, Particularly For Drive Mechanisms For Extending And Withdrawing Operative Members Of A Space Vehicle” by G. Secci and U.S. Pat. No. 5,718,531 “Low Shock Release Device” by E. C. Mutschleer, Jr. All use SMA materials as the primary actuating force. However, when using SMA material as the primary actuating device, precise timing of the release can prove difficult to achieve. In addition, shape memory alloys are sensitive to high temperature environments.
Another approach is to use of ball latches. U.S. Pat. 3,887,150 “Internal Ejector Mechanism” by T. Jakubowski, Jr. U.S. Pat. No. 4,132,147 “Store Retention And Release Mechanism” by A. Contaldo, U.S. Pat. No. 4,350,074 “Mechanical And Electrical Coupling Device Fore Charges, Particularly Military Charges” by J. P. Rouget, et al., U.S. Pat. No. 4,520,711 Loop Retention Device For Hook Operated Bomb Arming Solenoids” by P. R. Robinson, U.S. Pat. No. 5,364,046 “Automatic Compliant Capture And Docking Mechanism for Spacecraft” by M. E. Dobbs, et al., U.S. Pat. No. 5,520,476 “Tie-Down And Release Mechanism For Spacecraft” by G. W. Marks, et al. all disclose the use of ball detent mechanisms to secure components of one type or another together. The main problem with such ball latch fasteners is limited trigger force reduction, which is required for activation with SMA systems. In launch vehicle and spacecraft, which are subjected to very large vibration loads, the satellite must be secured using very high pre-loaded joints. Ball latch systems typically don't allow for the application of type of pre-loads that can be obtained with a threaded fastener. However, they are very good locking devices.
In U.S. Pat. No. 5,603,595 “Flywheel Nut Separable Connector And Method” by W. D. Nygren an attempt was made to take advantage of SMA technology to provide actuation initiation for a conventional nut and bolt and to use the high pre-load forces therebetween to provide the primary separation forces, i.e. to rotate the nut to the point of separation. The nut having a high helix angle or lead is essentially a flywheel. It is torqued until the desired pre-load is achieved. Thereafter, the flywheel is latched. The latch is secured by a SMA spring. Upon heating the spring, the latch releases the flywheel and the stored energy in will cause the flywheel to initially rotate at high speed. The strain energy due to the pre-load is dissipated as the nut unwinds, the stored energy in the flywheel continues to cause the nut to rotate until separation occurs. The advantages are numerous; high pre-loaded joints are possible and the need to only heat a small wire spring greatly reduces actuation time. However, this design had problems in that it had a greater parts count than equivalent explosive actuated separation nuts and was somewhat more massive and occupied more volume.
U.S. patent application Ser. No. 09/610,594 “Connector Assembly” by W. Nygren discloses an improved fastener using a wrap spring. In detail, this invention includes a connecting member including a threaded end with a specific pitch diameter, thread lead angle, and helix angle. A hollow housing having a cylindrical wall with a specific thickness contains a body rotatably mounted therewithin. The body is threadably engagable with the threaded end of the connecting member. A first mechanism releasably restrains the rotatably supported body from rotating until released. The first mechanism includes the cylindrical wall having a plurality of rectangular slots. A plurality of cylindrical rollers are movably mounted in the slots. The body includes a plurality of cylindrical grooves alignable with the slots in the body. A wrap spring is wound about the cylindrical wall of the housing movable from a first position such that the it engages the rollers forcing the rollers into the grooves locking the body to the cylindrical wall of the housing, when the grooves are aligned with the slots to the a second position allowing the rollers to move out of the slots in the body. A second mechanism is included for winding the spring about the cylindrical wall of the housing such that spring is moved from the second relaxed position to the first position. This second mec
Fix Jeremy
Nygren William D.
Lockheed Martin Corporation
Marsh & Fischmann & Breyfogle LLP
Novosad Christopher J.
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