Abstract:
A mechanism is disclosed which can be used to selectively establish the amount of resistance to un-screwing associated with common fittings, especially those with high pitch-angle threads. Such a mechanism is useful in a variety of applications, including tamper-evident mechanical assemblies, child-proof medicine bottles and fittings under substantial axial loads.

Description:
This application is related to U.S. application Ser. No. 09/305,243, filed May 4, 1999, now pending. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention is a mechanical locking device for threaded connectors. 
     (2) Description of the Problems and the Prior Art 
     A number of connections utilize threaded components, including nuts and bolts, threaded pipes and couplings, soda bottles and caps, and medical connectors. Such connections are simple to mate and can be attached and disconnected many times. This simplicity comes with two side effects which are undesirable in certain applications. First, the presence of angled threads creates the possibility of the connection self-loosening under axial loading—a term referred to as “backdriving”. The greater the angle or “pitch” of the threads, the more likely that axial loading will cause backdriving. In some cases, users can add additional components such as lockwashers to prevent backdriving. In other cases, such additions are impractical or too expensive. Hence a need exists to provide backdriving resistance as an integral feature of the threaded connector. Secondly, very little torque is often required to disassemble the connections. This can be a problem when child-proofing is desired, or when one wants to discourage tampering with an assembly. The present invention may be used to overcome either of these shortcomings. An added advantage of the present invention is that it does not interfere with the ordinary function of threaded connections, and requires both mating sides to incorporate the described changes to operate. Components can be manufactured incorporating the feature, and only when assembled with a mating component also incorporating the feature would the user obtain the desired benefit. Hence a bolt with the features on the threads could still use a regular nut with no noticeable impact; a nut with the features on its threads could use a regular bolt with no noticeable impact; but a nut and bolt combined, with the mating features described herein, would demonstrate the desired characteristics. 
     SUMMARY OF THE INVENTION 
     The present invention provides features on both portions of a threaded connector to create an interference mechanism, leading to a “ratchet” effect. The extent of this interference can be determined by the designer to provide the degree of backdriving resistance desired for a given application. At modest levels of resistance the feature is not damaged by repeated assembly and disassembly. At high levels of resistance the features become permanently damaged and thereby may be used to indicate tampering. 
     The locations of these features can be selected so that they become engaged as assembly is started, only upon completion of assembly, or throughout the entire mating process. If the feature is engaged only at the start of assembly, one has, for instance, a nut which may be freely positioned anywhere along the length of a bolt, but resists having the nut fall all the way off the end of the bolt. If the feature is engaged only at the end of the assembly, it can be used to “lock” the nut in place, yet, once the strength of the “lock” is overcome, nut can be easily removed by hand. A bolt with the features along the length of the shaft would act like a ratchet, allowing the nut to be placed anywhere along its length and still require increased amounts of force to disassemble. 
     The amount of interference between the two components and the materials used in the interfering elements determines the amount of unscrewing resistance. It may range from being barely detectable, all the way through something which is nearly impossible to disassemble. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of the device of the present invention incorporated on a threaded bolt and nut. 
     FIG. 2A is a partial, sectional view of the device in FIG. 1, taken along the line A—A. It shows a close up of the features prior to assembly. 
     FIG. 2B is the same partial, sectional view of FIG. 2A except the connection is beginning to be tightened to bring the device of the present invention into operation. 
     FIG. 2C is the same partial, sectional view of FIG. 2B except the connection is now tight and will resist unscrewing. 
     FIG. 2D is the same partial, sectional view of FIG. 2C except that the feature is shown resisting unscrewing forces. 
     FIG. 2E is the same partial, sectional view of FIG. 2D except the strength of resistance is beginning to be overcome. 
     FIG. 2F is the same partial, sectional view of FIG. 2E except the feature of the present invention is continuing to be overcome. 
     FIG. 2G is the same partial, sectional view of FIG. 2F except the feature of the present invention has been entirely overcome and no further resistance to disassembly will be created. 
     FIG. 3 is a view of an alternate preferred embodiment of the device of the present invention, showing the feature deployed merely as a stop to prevent the nut from being fully removed from the bolt. 
     FIG. 4 is a sectional view of a device showing an alternate preferred embodiment of the device of the present invention. In this case, more than one set of interacting features is shown. 
     FIG. 5 is a sectional view of yet another preferred embodiment of the device of the present invention. In this case, the entire thread is replaced by locking features which now provide not only resistance to unscrewing but also all of the mechanical strength of the threads themselves. 
     FIG. 6 is a partial sectional view of an alternate preferred embodiment of the device of the present invention. Rather than requiring projections on one side of the mating connection to interfere with a projection emanating from the other side, this view depicts the same result being achieved with a recess on one side of the connection. 
     FIG. 7 illustrates an embodiment of the present invention utilized for attaching a syringe needle to a syringe chamber. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With first reference to FIG. 1, a preferred embodiment of the current invention is depicted using a male portion (in this case a bolt)  100 , and a female portion (in this case a nut  200 ). These items may be made of any material, but for the sake of the current discussion assume the components are injection molded of some form of fairly rigid plastic—nylon being commonly used for such components. The bolt is depicted with a head  110  and a shaft  120 . The threads may take any form, but the outer-most portion of the thread  101  is generally referred to as the “crest”, while the inner-most portion  102  is generally referred to as the “root”. In this embodiment, the thread is shown interrupted along the length of the shaft with a plurality of projections  103 . For the sake of this discussion, the projections will be referred to as “fingers”. 
     On a mating component  200  is shown threads compatible with those on component  100 , with a crest  201  and a root  202 . In this embodiment, interference with the fingers  103  will be provided by a plurality of ridges  203  located on the root segments. 
     While depicted as residing within the threads, it is important to note that the feature could just as easily have been incorporated in any area of the connection—say in an unthreaded extension to either the male  100  or female  200  portion of the connection. 
     Taking a partial sectional view along line A—A results in the depiction of the features in FIG.  2 A. Female portion  200  has a projection  203  on the root of a thread segment  202 . Male portion  100  has a finger  103  projecting from an interrupted portion of a thread whose crest is  101  and root is  102 . Arrow  301  shows the direction of relative movement for the female component during assembly, while arrow  302  shows the direction of relative movement for the male component during assembly. 
     FIG. 2A depicts an important feature of the lead-in portion of the screw threads. Note that the normal thread root  202  of female portion  200  is closer to male portion  100  than the root in the lead-in area. The lead-in area root radius  205  is greater than root radius  202  by an amount  304 . The function of this increased radius is to allow finger  103  to enter the thread form in its relaxed state, thereby having no impact on ease of initial assembly and preventing it from being inadvertently toggled forward during the process. Only when the threads are properly mated and threading begun will the projection  203  place the finger  103  into the correct orientation. 
     FIG. 2B shows the interaction of the fingers  103  and the projection  203  during assembly. Since the finger  103  is made of a relatively flexible material, and made thin enough to be quite flexible, finger  103  readily deflects to allow assembly. 
     FIG. 2C continues the assembly process as the two components are rotated into a tight connection. The feature has little or no impact on assembly at this stage. This figure also depicts another variable available to the designer. Angle  305  is the angle between the finger  103  when in the assembled position and a line drawn from the center of male component  100  and a point at the center of the base of finger  103 . This angle  305  determines a few critical operating parameters of the device. Too shallow an angle  305 —say, less than 5 degrees—allows finger  103  to toggle over at projection  203  with little interference. 
     Too steep an angle  305 , say 75 degrees—allows the finger  103  to continue deflecting and skip over the projection  203 . Hence the device fails to function at too steep an angle. At the operative range of angles, steeper angles correspond to longer fingers  103 , and thus increased distortion required of part  200 , as will be described below. Because distortion of part  200  is a primary determinant of unscrewing force, steeper angles of finger  103  also correspond to increased unscrewing force. 
     FIG. 2D depicts what happens at the start of disassembly, as arrow  301  shows the direction of relative rotation of the female part and arrow  302  shows the direction of relative rotation of the male part. Finger  103  comes into contact with projection  203 . The reverse angle of finger  103  imparted during assembly now becomes an impediment to disassembly, jamming against projection  203 . 
     FIG. 2E depicts what happens in the presence of sufficient force to begin to overcome the feature. As rotational force is applied in the direction of arrows  301  and  302 , the straightening of finger  103  forces female part  200  to deform outward in the direction of arrow  303 . This allows finger  103  to begin to “toggle over”. 
     FIG. 2F depicts the continued disassembly after overcoming the feature. Finger  103  now leans in a direction with will no longer prevent disassembly. Female component  200  may now recover to its original circular cross-section. 
     FIG. 2G depicts the feature after disassembly, with finger  103  no longer providing any material resistance to disassembly. 
     While depicted in a single material, two-component assembly, it is important to note that the feature can be incorporated using multiple materials in multiple components. Again with reference to FIG. 1, bolt  100  could be made of metal, and a slot could be machined into the side of the bolt. Fingers  103  could then be provided in the form of an inserted, flexible material such as plastic or spring steel. 
     Alternatively, if female component  200  is made of metal, it would likely resist the deformation required to allow non-destructive passage of fingers  103 . Hence disassembly would likely require forces sufficient to shear fingers  103  off projection  120 . In that case, if fingers  103  were thin and somewhat flexible, this might not require too much force—although the sheared remnants of fingers  103  would indicate that the connection had been disassembled. From such considerations as material, finger  103  sizing, engagement angle  305  and projection  203  sizing, the device of the present invention provides enormous flexibility to designers. 
     With reference to FIG. 3, the finger  103  is present only once, while projections  203  are present in plurality. In this embodiment, resistance to unscrewing is only present at the very end of the disassembly process. In this sense the feature provides a “nut retention” benefit—useful when complete disassembly and dropping the female component could be a problem (e.g. when a nut could fall into an engine or drop onto an operating electronic circuit board). Since it is possible that female component  200  may be threaded all the way down the shaft of male component  100 —past the point where the finger  103  is engaged within female component  200 —this embodiment requires some special consideration. Since finger  103  is “cocked” in the correct direction to resist disassembly as the projection  203  in the female component  200  passes it, it is important that finger  103  not re-straighten after it is completely out of the female component  200 . Hence finger  103  must be made of some deformable material, rather than the elastic fingers  103  in other embodiments. 
     Now with reference to the cross-sectional alternate preferred embodiment in FIG. 4, a multitude of fingers  103  are depicted along interrupted thread segments  104  with crests  101  and roots  102  on male component  100 . The female component  103  has two projections  203  emanating from the root section  202  of the threads. In the presence of rotational forces acting in the direction of arrow  302 , fingers  103  pass easily over projections  203 . In effect the fingers  103  “ratchet” over projections  203 . Disassembly now requires substantial and continued application of rotational force in the opposite direction of arrow  302 . Accordingly, the female component  200  could be readily placed anywhere along the threads of male part  100 , yet require higher force levels to disassemble. 
     Interestingly, the choice of tool used to disassemble the connection has additional impact on the force required to complete the disassembly. If a rigid, metal cylinder (say a metal socket) is placed over female component  200 , the metal cylinder would serve to reinforce the anti-rotation feature as it prevents part  200  from distorting to allow the finger  103  to pass. Conversely, if a segmented metal cylinder is used to grip female component  200 , disassembly might still be achieved at relatively low levels of force. 
     Now with reference to the alternative preferred embodiment shown in cross-sectional view FIG. 5, one can see what happens as the proportion of fingers is increased to its maximum. There are no thread segments left on male part  100 . The multitude of fingers  103  now provides the mechanical strength normally associated with the threads themselves. 
     Finally, with reference to the alternative preferred embodiment shown in partial cross-sectional view of FIG. 6, the obstructions to passage of finger  103  is provided not by projections but by recess  204 . This configuration may be easier to manufacture in metal, allowing standard threads to be cut and then a follow-on operation would create the recesses. 
     While all of the above embodiments depict the fingers on the male component and obstructions on the female, it may also be appreciated from FIG. 6 that there is no reason these two cannot be reversed and the same objectives achieved.