TAMPER-RESISTANT THREADED FASTENER FIELD OF THE INVENTION [0001] The present invention relates to a fastener and more particular to a threaded which may be readily installed and adjusted in a workpiece, but once installed cannot be readily removed therefrom.

BACKGROUND OF THE INVENTION [0002] Certain fastener applications specify that a fastener should be readily adjustable within the threaded hole, while at the same time resistant to complete removal from the threaded hole. Such applications can encounter a problem when the fastener is loosened sufficiently such that it falls out and is lost, or if inadvertently loosened to a point where it is no longer retained in the threaded aperture. Accordingly, there is a need for a screw or other similar threaded fastener that may be driven into a workpiece easily, which can be adjusted readily therein but which cannot be removed easily therefrom. There is a further need for a self-threading fastener having these characteristics.

SUMMARY OF THE INVENTION [0003] The present invention is directed to a tamper-resistant fastener having an enlarged head portion and a shank portion extending from the enlarged head portion. A threaded region is formed at a first end of the shank adjacent the head portion. A retaining element is formed at a second end of the fastener opposite the threaded region and has a radial dimension which is not greater than a major diameter of the threaded region. A dwell region is interposed between the threaded region and the retaining element. The dwell region has a diameter which is less than the radial dimension of the retaining element.

[0004] In one preferred aspect of the present invention, the threaded region is defined by thread rolling screw design such as a Swageform0 screw that forms a thread using thread rolling technology in which material is reformed

by rolling it towards the root of the screw as opposed to removing material in a more conventional thread tapping process.

[0005] In another aspect of the present invention, the retaining element is defined by a flattened area at the tip of the fastener.

[0006] In another aspect of the present invention, a threaded assembly is formed whereby the threaded portion releasably secures the fastener within an aperture while the retaining element prevents complete withdrawal of the fastener from the aperture, and a dwell region provides a free spinning area in which both the threaded and the retaining element are disengaged from the aperture.

[0007] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: [0009] Figure 1 illustrates a tamper-resistant threaded fastener in accordance with the present invention; [0010] Figure 2 is a detailed side view of the retaining element formed at the end of the threaded fastener; [0011] Figure 3 is a detailed plan view of the enlarged head portion; [0012] Figure 4 illustrates the tamper-resistant fastener of the present invention prior to insertion within a workpiece; [0013] Figure 5 illustrates the tamper-resistant fastener of the present invention partially inserted into the workpiece; [0014] Figure 6 illustrates the tamper-resistant fastener as it forms threads through the workpiece;

[0015] Figure 7 illustrates the tamper-resistant fastener in an installed configuration; [0016] Figure 8 illustrates the tamper-resistant fastener in a retained configuration; and [0017] Figure 9 is a detailed illustration of the retaining element cooperating with the workpiece to retain the threaded fastener within the aperture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0018] The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0019] With reference now to Figures 1-3, a tamper-resistant threaded fastener 10 in accordance with the present invention is illustrated. Fastener 10 includes an enlarged head portion 12 and a shank portion 14 extending from the enlarged head portion 12. The shank portion 14 includes a threaded region 16, a dwell region 18 and a retainer element 20 formed therein. The enlarged head portion 12 has a tool interface 22 formed therein. While the tool interface takes the form of a Philips recess in the preferred embodiment, one skilled in the art will recognize that other suitable tool interface recesses may be utilized.

[0020] As presently preferred, the threaded region 16 is configured as a self-threading design in which a thread rolling process is used to form complementary threads in an aperture of the workpiece. Specifically the threaded portion does not remove material in the thread forming process like a conventional tap but rather reforms the material, rolling it towards the root of the screw, thereby closing up the hole in the workpiece. The threaded region 16 has a lead-in region 24 and a threaded region 26. The threaded region 26 defines a major diameter D measured from crest-to-crest and a minor diameter d measured from root-to-root. The dwell region 18 is preferably a generally cylindrical segment having a diameter less than the minor diameter d which

extends for a length at least equal to the thickness of the workpiece. The retaining element 20 includes a flared end region 28 which is preferably formed by a crimping or swadging process during fastener forming. A blind bore 30 may be formed in the end of the fastener to facilitate flaring of the retaining element 20. The shank portion 14 of fastener 10 may also include a shoulder portion 32 interposed between the enlarged head portion 12 and the threaded portion 16.

The shoulder portion 32 may be adapted to be received within an aperture formed through a washer, a thumbwheel, an adjacent workpiece or other similar element shown in broken lines.

[0021] The relative diameters of the various regions 16, 18, 20 formed in the shank portion 12 provide mechanical features that afford the tamper resistant function of the present invention. Specifically, the radial dimension rd of the retaining element is greater than the minor diameter d of the threaded region 16 but less than or equal to the major diameter D of the threaded region 16. The dwell region 18 has a diameter which is less than the radial dimension rd of the retaining element 20. In this manner, once the tamper resistant fastener 10 is installed, the retaining element 20 retains the threaded fastener 10 within the aperture while providing a free spinning area at dwell region 18.

[0022] Turning now to Figures 4-9, installation of the tamper-resistant fastener will be further described. Specifically, fastener 10 is adapted to be inserted into workpiece 40 through an aperture 42. As presently preferred aperture 42 is a drilled but not threaded aperture. The diameter of aperture 42 is approximately equal (within a suitable tolerance) to the radial diameter rd of retainer element 20. Threaded fastener 10 is inserted into aperture 42 such that retaining element 20 extends therethrough proximate an inner surface 44 of workpiece 40. In this location, as shown in Figure 5, the dwell region permits fastener 10 to be free spinning with aperture 42. Further advancement of threaded fastener 10 into aperture 42 causes lead-in portion 24 to engage aperture 42 of workpiece 40. As fastener 10 is further advanced into workpiece

40, as shown in Figure 6 a series of threads 42'are formed in aperture 42 by a thread rolling process. In this regard, the material of workpiece 40 adjacent aperture 42 is rolled towards the root of the threaded portion 16, thereby effectively reducing the diameter and closing up aperture 42 in workpiece 40.

[0023] As the threaded fastener 10 is further advanced into aperture 42 as shown in Figure 7, the threaded portion 26 engages threaded aperture 42'to provide a threaded interface therebetween. As the threaded fastener 10 is withdrawn out of the workpiece 40 as best seen in Figure 8, the threaded portion disengages threaded aperture 42'. At this point, the threaded fastener 10 is allowed to free spin on the dwell region 18. If an attempt is made to further extract the threaded fastener 10 from the aperture 42, the retaining element 20 engages the inner surface 44 of the workpiece 40 to limit withdrawal thereof.

Specifically, the thread forming processes has reduced the effective diameter of the aperture such that the radial dimension rd of the retaining element 20 is greater than the effective diameter of aperture 42. As such, the threaded fastener 10 is now held captive within the workpiece 40 and further extraction would require excessive force causing damage to the threaded aperture 42.

[0024] With an understanding of the detailed description of the preferred embodiment provide above, one skilled in the art will recognize that the present invention is directed to a tamper-resistant threaded fastener having an extended unthreaded dwell region terminating at a retaining element which is dimensionally equal to the diameter of the hole in the workpiece. The retaining element just fits into the hole, while the dwell region allows the retaining element to pass therethrough. A threaded region formed in the shank engages the workpiece to machine a thread in the aperture by a thread rolling process which reduces the effective diameter of the workpiece aperture. With the workpiece aperture now closed up, the retaining element which previously passed through the aperture is held captive such that the threaded fastener may not be readily withdrawn from the workpiece.

[0025] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.