Patent Publication Number: US-2003221575-A1

Title: Detonator utilizing features of automotive airbag initiators

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to pyrotechnic detonators, and more particularly, to a detonator that incorporates features known in certain automotive airbag initiators.  
       [0002] The efficient use of explosives in mining operations and the demolition of structures often requires that many charges be placed in a predetermined pattern and detonated in a timed sequence. In general, timed detonation can be accomplished by detonators that use pyrotechnic delays, sequential-type blasting machines, and electronically programmable detonators. Some examples of time-delayed detonators are described in U.S. Pat. Nos. 6,173,651, 6,085,659, 6,079,332, 5,602,360, 5,460,093, 5,435,248, 4,869,170, 4,819,560, 4,730,558, and 4,712,477, the disclosures of which are hereby incorporated by reference herein.  
       [0003] Such detonators are subject to one or more drawbacks, however, such as the following: (1) the use of an ignition element that is difficult to manufacture to precise dimensions so as to ensure predictable performance, (2) the use of an ignition element that requires careful handling during manufacturing and thus impedes the beneficial incorporation of automated steps in the detonator assembly process, (3) the use of an ignition charge that contains lead, which presents an environmental and health hazard, (4) the use of a non-low energy ignition element, which reduces the ability to provide a compact design, (5) lack of reliability, and (6) costly manufacturing.  
       [0004] On the other hand, such problems are overcome or at least ameliorated in well-known automotive airbag initiators such as those currently manufactured and sold by the assignee of this patent application. Various patents also disclose other examples of initiators having features that address one or more of such problems, including U.S. Pat. Nos. 6,274,252, 5,709,724, 5,639,986, 5,602,359, 5,596,163, 5,404,263, 5,140,906, and 3,971,320, the disclosures of which are hereby incorporated by reference herein.  
       [0005] Despite the advances regarding these issues in the automotive airbag initiator field, it is believed that hitherto it has not been conceived or attempted to apply various features of such automotive initiators that overcome or ameliorate the aforementioned problems, to detonators that are used in mining, blasting, and demolition.  
       SUMMARY OF THE INVENTION  
       [0006] One object of the present invention is to provide a detonator that incorporates one or more features of automotive airbag initiators so as to overcome or ameliorate one or more of the problems enumerated above.  
       [0007] Another objective of the present invention is to provide a detonator utilizing an ignition element similar to those in automotive initiators, resulting in a reliable and economical detonator.  
       [0008] Another separate and alternative objective of the present invention is to provide a detonator utilizing an ignition element that is relatively easy to manufacture to precise dimensions with known and proven manufacturing processes, resulting in a detonator having predictable performance.  
       [0009] It is another separate and alternative objective of the present invention to provide a detonator utilizing an ignition element that is sufficiently durable to permit the incorporation of useful automation steps in the detonator assembly process.  
       [0010] It is a further separate and alternative objective of the present invention to provide a detonator utilizing an ignition charge that does not contain any lead, so as to reduce hazards to the environmental and health resulting from the use of the detonator.  
       [0011] It is yet another separate and alternative objective of the present invention to provide a detonator utilizing a low energy ignition element, resulting in a detonator that may be made more compact. 
     
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
     [0012]FIG. 1 is a side sectional view of an embodiment of the present invention, showing the ignition subassembly portion of the detonator.  
     [0013]FIG. 2 is a top sectional view of an alternate ignition subassembly embodiment to that of FIG. 1.  
     [0014]FIG. 3 is a partial exploded and sectional view showing how an ignition subassembly such as that of FIG. 1 fits into a loaded shell of a detonator according to the present invention.  
     [0015]FIG. 4 is partial top sectional view of the header and part of the circuit board of the ignition subassembly of FIG. 2.  
     [0016]FIG. 5 is a partial bottom view of the header and part of the circuit board shown in FIG. 4, illustrating the offset from centerline of the header&#39;s pins.  
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 1    
     [0017] Referring to FIGS. 1 and 2, an ignition subassembly  8  of an embodiment of the present invention, and an alternate embodiment  8 ′, are shown. As shown in FIG. 3, such a subassembly is placed inside of a shell  40  that may contain a primary charge  36  and a base charge  38  loaded into its closed end. (A detonator shell is typically a metal cylinder  6  to  8  mm. in diameter and from 60-100 mm. in length). Subassembly  8  can then be secured in place in the shell  40 , such as by placing an elastomeric plug or the like (not shown) in the open end of the shell and crimping the shell  40  to the plug, or other suitable method. Subassembly  8  may have a body portion  32  formed of an encapsulation  31  and may have ridges  57  protruding out from the outer surface of body portion  32 , so as to snugly hold subassembly  8  within the shell  40 . Such ridges  57  or other protuberances may preferably be formed to dampen vibrations to which the detonator may be subjected, generally in accordance with the teachings of U.S. Pat. No. 6,079,332.  
     [0018] Alternately, an ignition subassembly similar to that of FIGS. 1 and 2 (but preferably lacking encapsulation  31 ) can be directly incorporated into a shell, such as by molding it directly in the shell. Various other methods of incorporating an ignition element into a detonator in accordance with the present invention will be readily apparent, and it is noted that implementing various automotive airbag initiator features in a detonator according to the present invention does not require the use of a “standalone” ignition subassembly like the ones shown in FIGS.  1 - 3 .  
     [0019] Turning to the specifics of the automotive airbag initiator features incorporated in the depicted embodiments, it can be seen that an automotive airbag initiator-style ignition element  28  is provided at one end of the ignition subassembly  8 . Specifically, ignition element  28  includes a header assembly with a sealed electrical feedthrough, comprising an eyelet  10  (preferably stainless steel), insulator glass  14  (preferably a glass such as a sodasilicate, e.g., 9010, that is chosen to form a compression seal with the eyelet and center pin, or less preferably a matched seal), a center pin  18  (preferably an iron/nickel alloy), a ground pin  20 , and an igniter wire  12  (preferably a low energy igniter wire with a diameter of 10 to 20 microns). Ground pin  20  and center pin  18  are preferably selected of the same material. The ignition element  28  further preferably includes a charge can  26  that is preferably metallic and hermetically sealed to the eyelet at circumferential through-weld  16 , with an ignition charge  30  contained between the can  26  and upper surface of the header, in tight contact with igniter wire  12 . An insulator cup  27  may preferably be attached around the can  26  so that, except for female connectors  52  that protrude from the input end of the subassembly, the entire outer surface of ignition subassembly  8  consists of insulating material, thus providing electrical isolation and vibration and environmental protection to the components within.  
     [0020] In the depicted embodiment, a circuit board  24  and electronic components  25  may be provided within ignition subassembly  8 , to provide a means of triggering ignition of the ignition element based on the processing of an electrical ignition signal received by input leads  51 , which are electrically connected to a blasting machine or the like that powers the detonator. Such electronic components are well-known and preferably include means for imparting a programmable period of delay to the ignition, means for ESD and RF protection, et cetera. (Another preferred alternative is the use of an application-specific integrated circuit). Circuit board  24  and electronic components  25  are preferably encapsulated together in encapsulation  31 , and connected to pins  18  and  20  at contacts  22  through soldering or other suitable connection. Referring to FIGS. 2 and 4, as is well-known in encapsulated automotive airbag initiators, retention of the ignition element  28  to the encapsulation  31  may be enhanced by providing a lip  17  at the bottom of the eyelet  10 ′. The insulator cup  27 ′ may also be held within the encapsulation to facilitate its retention as well.  
     [0021]FIGS. 4 and 5 illustrate an alternate embodiment similar to that of FIG. 2, wherein the pins  18 ′ and  20 ′ are slightly offset from the centerline of the header, so that the circuit board  24  can occupy that centerline, which corresponds to the widest portion of the cylindrical body portion  32 .  
     [0022] By way of example, in an embodiment like that shown in FIGS. 1 and 2, it has been found that a nickel/chromium alloy, 13 micron diameter, 0.7 mm long igniter wire, a 50 mg ignition charge of zirconium potassium perchlorate having a height of 1.0 mm and a diameter of 4.8 mm is suitable. Preferably, a minimum suitable charge is approximately 30 mg for a configuration of this size, as a smaller charge may result in an insufficient charge thickness. A preferred all-fire voltage may be 6 volts, and may be delivered with a 100 microfarad capacitor included in the electronic components  25  in an embodiment like that depicted.  
     [0023] It should be noted that although the Figures depict embodiments including electronic components that receive, process, and deliver an ignition signal, such an ignition signal may alternately be received, processed, and delivered by a number of other well-known non-electronic or partly-electronic means, such as through the use of a shock tube to deliver an ignition signal to a piezoelectric device, column fuse delays, et cetera. It is noted that this detailed description of certain embodiments does not imply that such alternate embodiments are not within the scope of the invention.  
     [0024] A preferred embodiment of a detonator utilizing features known in certain automotive airbag initiators, and many of its attendant advantages, has thus been disclosed. It will be apparent, however, that various changes may be made in the form, construction, and arrangement of the parts without departing from the spirit and scope of the invention, the form hereinbefore described being merely a preferred or exemplary embodiment thereof. Therefore, the invention is not to be restricted or limited except in accordance with the following claims.