DETONATORS HAVING MULTIPLE-LINE INPUT LEADS

Abstract: A detonator (10) is equipped with an input lead (29) having multiple signal transmission lines (30, 31) which provide redundant initiation signals to the target charge (14) of a detonator (10, 10') thereby increasing the reliability of initiation. The multiple signal transmission lines (30, 31) may be made of shock tube and can be part of a long or short input lead (29, 129) and may be initiated by any suitable means, for example by being disposed in signal transmission relation to a detonating cord (60, 62) to improve the reliability with which a signal is transferred from the detonating cord (60, 62) to the detonator (10, 10').

Description: O 97 25298 PC17US96/20875 DETONATORS HAVING MULTIPLE-LINE INPUT LEADS BACKGROUND OF THE INVENTION Field Of The Invention The present invention relates to non-electric deton¬ ators for use in transmitting explosive initiation sig¬ nals and, in particular, to detonators having multiple- line input leads. Related Art Detonators are used as signal amplifiers to transfer initiation signals from one kind of line to another or to initiate various types of explosive charges, one specific example being to initiate boosters for downhole explosive charges in blasting operations. A conventional detonator comprises an elongated shell having one closed end and one open end. An explosive output charge is disposed in the closed end of the shell, and a delay element may also be disposed in the shell between the open end and the output charge. The output charge and the optional delay element may collectively be referred to as a target charge. A single input line, which may be a length of low energy detonating cord, low velocity signal tube, or shock tube, is passed through the open end of the shell and secured therewithin with the enclosed end of the input line dis¬ posed within the detonator adjacent to the target charge, so that when the line is fired the initiation signal is transferred from the enclosed end to the target charge. U.S. Patent 4,911,076 to Rowe, dated March 27, 1990, discloses a delay detonator having two shock tube lines having their ends disposed in signal transmission relation to the delay element of the detonator. Either of the lines can be used as a signal input line to initiate the delay element and then the explosive output charge of the detonator. After the designated delay, the detonator out¬ put charge is initiated, thereby initiating an output sig¬ nal in the other shock tube line. Because the ends of both shock tube lines are disposed in signal transmission relation to the delay element, an input signal emitted from either line will initiate the delay element and then the output charge. However, Rowe requires that the sig- nal-emitting ends of both lines are sealed so that when the one line selected as the input line ignites the delay element, the other line will not have a premature output signal initiated therein but the output signal will be in¬ itiated only by initiation of the output explosive charge after the delay period has expired. U.S. Patent 3,885,499, issued May 27, 1975 to Hurley, U.S. Patent 3,939,772, issued February 24, 1976 to Zebree, and U.S. Patent 4,073,235, issued February 14, 1978 to Hopler, Jr., each concerns non-electrically initiated blasting caps, i.e., detonators, which show two tubes en¬ tering the shell of the detonator. In each case, one tube transmits an explosive gas mixture into the detonator shell and the other provides a conduit exiting the detona¬ tor shell for transmitting the explosive gas mixture or a purge gas outwardly of the detonator shell. The detona¬ tors of these three patents are initiated by initiation of the explosive gas mixture and the paired tubes connected to each shell serve as conduits for passage of the explo¬ sive gas mixture through the detonators thence, e.g., to downstream detonators. U.S. Patent 4,485,741 to Moore et al, dated December 4, 1984, discloses a detonator and booster apparatus in which the detonator is initiated via a signal transmission tube that picks up an initiation signal from a detonating cord downline. In the embodiment of Figure 2C, the signal transmission tube is looped around a small section of the detonating cord where the two are tied in a knot. In the embodiment of Figure 2D, the end of the signal transmis¬ sion tube is looped around the detonating cord and a sig- nificant portion of the signal transmission tube is dis¬ posed in close parallel relation with the detonating cord. Moore et al is typical of the well-known expedient in the art of blasting to convey initiation signals from detonat- ing cords to signal transmission tubes such as shock tubes by disposing the detonating cord in signal transmission relation with the shock tube and firing the cord. SUMMARY OF THE INVENTION In accordance with the present invention there is pro¬ vided a detonator having an output section and comprising the following components. A shell defines an enclosure and has disposed within it at the output section thereof a target charge comprising at least an explosive output charge. An input lead, for example, one made of shock tube, extends into the detonator and is secured therewith- in, the input lead having at least two signal transmission input lines extending into the shell and terminating in signal-emitting ends disposed within the shell in signal transmission relation with the target charge. In one aspect of the present invention, the input lead comprises one or more, e.g., two, looped input line seg¬ ments, each comprising a bight portion connecting two legs extending into the shell and terminating in the signal- emitting ends. In another embodiment of the present invention, the input lead may comprise at least two separate signal transmission strand lines, each line having opposite first and second ends with the signal-emitting first end of each strand line being disposed within the shell in signal transmission relation with the target charge, and the second end of each strand line being disposed exteriorly of the shell. In one embodiment of the invention, the target charge further comprises a delay element connecting the input lead and the explosive output charge in initiation signal communication, e.g., the delay element is interposed be¬ tween the input lead and the explosive output charge. In a particular aspect of the present invention, the detonator has an input section and the shell has a closed end at the output section of the detonator and an open end which is sealed by a sealant means and is located at the input section of the detonator. In this embodiment, the signal transmission input lines extend into the shell through the open end thereof. Another aspect of the present invention provides a method of initiating a detonator having disposed therein a target charge comprising at least an explosive output charge dimensioned and configured to be initiated by an input signal transmitted thereto by a plurality of signal transmission lines having signal-emitting ends disposed in signal transmission communication with the target charge, the method comprising transmitting, e.g., substantially simultaneously transmitting, at least two initiation sig¬ nals to the target charge. In another method aspect of the invention, the method further comprises transmitting at least four initiation signals to the target charge. Yet another aspect of the present invention provides that the target charge further comprises a delay element having a selected delay period and interposed between the signal-emitting ends of the signal transmission input lines and the output charge, and the method comprises transmitting the initiation signals to the delay element and via the delay element to the output charge. In this way, travel of the initiation signals between the signal- emitting ends of the input lines and the output charge is delayed by the selected delay period. Other aspects of the invention are disclosed in the following description and drawings. As used herein and in the claims, the term "input line" as used in relation to a detonator refers to a length of signal transmission line that has an end secured in the detonator, for carrying an initiation signal to the detonator. The term "strand" as used in relation to a detonator input lead indicates an input line having two ends with only one end secured in the detonator. The terms "looped input line segment", "looped input lead" and "eyelet lead" refer to a segment of signal transmission line having two ends, both of which are se¬ cured in the detonator. A looped input line segment thus provides two input lines for the detonator. The term "input lead" refers collectively to all the input lines of a detonator. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side elevation view, with parts broken away, of a delay detonator, in accordance with one embod- iment of the present invention; Figures IA and IB are cross-sectional views, enlarged with respect to Figure 1, taken along, respectively, lines A-A and B-B of Figure 1; Figure IC is a view similar to that of Figure 1 of an instantaneous-acting detonator in accordance with another embodiment of the present invention; Figures 2A and 2B are side elevation views of alter¬ nate embodiments of a two-input line detonator in accor¬ dance with the present invention, showing in cross section a detonating cord disposed in signal transmission relation with the input lead; Figures 3A, 3B and 3C are side elevation views of three alternate embodiments of detonators according to the present invention and showing in Figures 3A and 3B cross- sectional views of detonating cord disposed in signal transmission relation with the input leads; Figure 4 is a schematic cross-sectional view of a booster charge within which a detonator according to one embodiment of the present invention is disposed; Figure 4A is a view identical to that of Figure 4 but reduced in size relative thereto and showing a detonator in accordance with another embodiment of the invention; Figure 5 is a perspective view of a slider unit useful for retaining a detonator, in accordance with the present invention, in place in a booster charge; Figure 5A is a plan view of the base plate of the slider unit of Figure 5; Figure 5B is a view similar to Figure 5A, showing the input lead of the detonator of Figure 2A in place on the base plate; and Figure 5C is a view similar to Figure 5B showing the input lead of the detonator of Figure 2B in place on the base plate. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF The present invention relates to detonators having im- proved initiation reliability. As indicated above, con¬ ventional detonators have an input lead comprising a sin¬ gle signal transmission input line that carries an initia¬ tion signal from a donor device to the detonator, specifi¬ cally, to a target charge contained within the detonator. The donor device may be any suitable device such as a spark igniter (in which case the input lead must be a shock tube), another detonator, detonating cord or the like. The target charge, in the case of an instantaneous- acting detonator, comprises the explosive output charge which conventionally includes a primary explosive such as lead azide and a secondary explosive such as PETN. In the case of delay detonators, the target charge comprises a delay element, either the well-known pyrotechnic delay el¬ ement or an electronic delay element such as briefly de- scribed below. In accordance with the present invention, a detonator is equipped with an input lead comprising at least two input lines by which a plurality of preferably simultaneous or substantially simultaneous initiation sig¬ nals are transmitted to the target charge of the deto- nator. The resulting redundancy in carrying an initiation signal to the detonator improves reliability because a failure of one of the lines to function properly is not fatal as only one of the plurality of initiation signals need reach the target charge. Therefore, reliance on a single input line to initiate the detonator is avoided. The present invention may be realized by providing a detonator with an input lead comprising a plurality of, i.e., at least two, signal transmission input lines which extend into the open end of the detonator shell and ter¬ minate in signal-emitting ends which are disposed in sig¬ nal transmission relation with the target charge within the detonator. For example, the input lead may comprise one or more looped input line segments each having a bight portion connecting two leg portions with the ends of both leg portions secured within the detonator, thus providing two input lines. Alternatively, the input lead may com¬ prise at least two separate strands of signal transmission line, each strand having opposite ends and having one end (the signal-emitting end) secured within the detonator and the other end sealed off at a point remote from the deto¬ nator. Preferably, the input lines comprise lengths of shock tube having an outside diameter (OD) not greater than about 2.380 mm (0.0937 inch), for example, a tube outside diameter (OD) of from about 0.397 to 2.380 mm (about 0.0156 to 0.0937 inch), and the ratio of the inside diameter of the tube to the radial thickness of the tube wall is from about 0.18 to 2.5. The inside diameter of the tube may be from about 0.198 to 1.321 mm (about 0.0078 to 0.0520 inch). The powder surface density of the reac¬ tive material contained within the bore of the tube may, but need not, be significantly less than that which the prior art considers to be minimum, acceptable powder sur- face density. Such shock tube is described in co-pending patent application Serial Number 08/380,839, filed January 30, 1995 in the name of E.L. Gladden et al for "Improved Signal Transmission Fuse" (Attorney Docket: P-1385). Referring now to Figure 1, an embodiment of a delay detonator in accordance with the present invention is gen¬ erally indicated at 10 and comprises an elongate tubular casing or shell 12 made of a suitable plastic or metal, such as a semi-conductive plastic material or, as in the illustrated embodiment, a metal such as aluminum or cop- per. Detonator 10 has an input section 11 and an output section 15 and shell 12 has a closed end 12a defining the end of the output section 15 and an opposite, open end 12b at the entry to the input section 11. At closed end 12a, shell 12 is configured as a continuous wall. The open end 12b is open to provide access of components to the inte¬ rior of shell 12 and is eventually sealed by bushing 28 and crimp 32 as described below. In the illustrated em- bodi ent, an input lead 29 is comprised of two signal transmission input lines 30, 31 each terminating in a respective signal-emitting end 30a, 31a. Input lead 29 is secured within shell 12 as more fully described below. A target charge generally indicated at 14 is disposed within shell 12 and is comprised of a pyrotechnic delay element comprising a sealer member 16 and a delay member 20 and an explosive output charge comprised of primary and secondary charges 22, 24, all connected in series and ter¬ minating at the closed end 12a of detonator 10. The ex- plosive output charge 22, 24 is disposed within, and in fact defines, the output section 15. Primary explosive charge 22 may comprise any suitable primary explosive, e.g., lead azide or DDNP (diazodinitrophenol) , and sec¬ ondary explosive charge 24 may comprise any suitable sec- ondary explosive, e.g., PETN. As those skilled in the art will appreciate, target charge 14 may include more or few¬ er elements than those illustrated in Figure 1. Thus, sealer member 16 and delay member 20 may be eliminated so that target charge 14 comprises only one or more explosive charges, such as primary and secondary charges 22, 24 to provide an instantaneous-acting detonator. Such an in¬ stantaneous-acting detonator 10' is illustrated in Figure IC wherein it is seen to be identical to delay detonator 10 except that the delay element (sealer member 16 and de- lay member 20) has been omitted and shell 12' consequently is shorter in length than shell 12 of the Figure 1 embodi¬ ment. The other components of instantaneous-acting deton¬ ator 10' are identical to those of delay detonator 10, are numbered identically thereto and therefore need not be de- scribed with respect to their structure. Generally, any known type of detonator construction may be used in con¬ nection with the invention, including those supplied with electronic delay elements. Such electronic delay elements may be used in conjunction with any suitable type of input lead, for example, one made of shock tube or deflagrating tube, which is used to transmit a non-electric, e.g., an impulse signal (which may be amplified or generated by a small amplifier explosive charge within the detonator shell) to generate an electrical signal by imposing the (optionally amplified) impulse signal upon a piezoelectric generator. The resulting electrical signal is transmitted to an electronic circuit which includes a counter to pro- vide a timed delay after which a capacitor circuit is triggered to initiate the output explosive charge. Such electronic delay elements and detonators including the same are disclosed and claimed in U.S. Patent 5,377,592, "Impulse Delay Unit", issued on January 3, 1995 to K.A. Rode et al, and U.S. Patent 5,435,248, "Extended Range Digital Delay Detonator", issued on July 25, 1995 to R.G. Pallanck et al. The disclosures of these patents are hereby incorporated by reference herein. Accordingly, target charge 14 may provide in delay detonators either a pyrotechnic or an electronic delay element as the immedi¬ ate target of the signal transmitted by input lead 29, or target charge 14 may provide, in instantaneous-acting det¬ onators, an explosive charge as the immediate target. As shown in Figures IA and IB, the sealer and delay members 16, 20 of target charge 14 each comprises respec¬ tive pyrotechnic cores 16a and 20a encased within suitable respective sheaths 16b and 20b. The sheaths 16b and 20b conventionally comprise a material that may readily be de¬ formed by pressure or crimping, such as lead or pewter or a suitable polymeric material ("plastic"). Thus, a crimp 26 may be formed in shell 12 to slightly deform sheath 16b, thereby securely sealing and retaining target charge 14 positioned within shell 12. Alternatively, the sheath 16b may be pressed longitudinally within the shell 12 to expand and seal the sheath against the inside wall of the shell or the sheath may be sized to provide an interfer¬ ence fit within shell 12. Target charge 14 occupies only a portion of the length of shell 12, and is disposed adjacent the closed end 12a thereof. The open end 12b of shell 12 is fitted with a sealant means which, in the illustrated embodiment, com¬ prises a retainer bushing 28. Open end 12b receives therein the end portions of signal transmission lines 30, 31 which terminate is signal-emitting ends 30a, 31a. The signal-emitting ends 30a, 31a are disposed within shell 12 and along with the associated end portions of lines 30, 31 are retained within shell 12 by a second crimp 32 formed at or in the vicinity of open end 12b of shell 12 about retainer bushing 28 to grip the latter and the end por¬ tions of lines 30, 31 in place, and to seal the interior of shell 12 against the environment. Accordingly, retain¬ er bushing 28 is usually made of a resilient material such as a suitable rubber or elastomeric polymer. As previous¬ ly noted, lines 30, 31 may be any suitable signal trans¬ mission lines such as low velocity (deflagrating) signal transmission tubes or low energy detonating cord or shock tube and, in the illustrated embodiment, comprise shock tubes. As is well known, shock tube comprises either a laminated tube or a monotube. A laminated tube typically has an outer tube which may be made of polyethylene, ex¬ truded over, or co-extruded with, a sub-tube which may be made of a polymer, such as a SURLYN™ ionomer, to which a coating of a reactive powder, e.g., a mixture of powdered aluminum and a pulverulent explosive such as HMX (cyclo- tetramethylene tetranitramine) adheres. A dusting of the reactive powder clings to the inner wall provided by the inside surface of the shock tube. Isolation member 34 is interposed between the signal- emitting ends 30a, 31a of input lines 30, 31 and the input end of the target charge 14 which, in the embodiment of Figure 1, is the end of sealer member 16 which faces the open end 12b of shell 12. As is well-known in the art, isolation member 34 is made from a semi-conductive mate¬ rial, so any static electricity that builds up in the shock tubes comprising lines 30, 31 is shunted to the shell 12 by isolation member 34, and is thus diverted away from the target charge 14 to prevent inadvertent detona¬ tions. It should be understood that although the input leads illustrated in Figures 2A-4 and Figures 5B and 5C are short input leads, input lead 29 may be quite long, as much as one hundred meters or so. Isolation member 34 has a generally cylindrical body that defines a central bore having an input end for engaging the signal-emitting ends 30a, 31a, and a discharge port 56 at its opposite end, the discharge port 56 being separated from the input end of isolation member 34 by a rupturable membrane 42. Initia¬ tion signals emitted by the signal-emitting ends 30a, 31a rupture membrane 42 and pass through discharge port 56 to initiate target charge 14. In the case of the illustrated embodiment, this occurs by initiating the sealer member 16 which in turn initiates delay member 20 then explosive charges 22, 24. In a conventional detonator, the signal-emitting end of but a single signal transmission line input lead is disposed at the input end of the central bore of isolation member 34. In contrast, in accordance with the present invention, the input end of isolation member 34 engages the signal-emitting ends of two or more signal transmis¬ sion input lines, any one of which suffices to initiate the target charge 14. Because none of the signal trans- mission input lines are used to carry an output signal from the detonator, it is not only not necessary to close the signal-emitting ends 30a, 31a of the input lines as in the above-mentioned Rowe U.S. Patent 4,911,076, but it would be counterproductive to the purposes of the present invention to do so. Leaving the signal-emitting ends 30a, 31a open provides a higher signal strength to impinge upon the target charge 14 as no signal strength need be ex¬ pended in breaking through a sealed end as is required in the Rowe Patent. Having two or more signal transmission input lines further increases the reliability of detonator 10 by providing redundant input signals. Figures 2A and 2B illustrate alternate embodiments of short input lead detonators in accordance with the present invention. In detonator 10a of Figure 2A, input lead 29a is comprised of signal transmission input lines 30 and 31, each comprising separate segments or strands of shock tube, each segment having two ends. One end of each shock tube strand is a signal-emitting end, not visible in Fig¬ ures 2A or 2B, but corresponding to signal-emitting ends 30a and 31a of Figures 1 and IC. The input lines 30, 31 extend outwardly from the open end 12b of shell 12 of det¬ onator 10a for a suitable distance and terminate in distal ends 30b, 31b, respectively. Distal ends 30b, 31b are sealed off by seals 33, 35 so that the hollow interior of the shock tube is not exposed to the environment. Since shock tube is conventionally made from thermoplastic pol¬ ymeric materials, sonic welding or any other suitable method may be used for sealing the distal ends 30b, 31b. Both input lines 30 and 31 are disposed in signal trans¬ mission relation to a signal donor line such as detonating cord 60, shown in cross section in Figures 2A and 2B. Thus, when the donor line initiates, initiation signals are ignited in both input lines 30 and 31, so that detona¬ tor 10a receives two substantially simultaneous initiation signals to ignite its target charge, not visible in Fig¬ ures 2A or 2B, but analogous to target charge 14 of Fig¬ ures 1 and IC. In the embodiment shown in Figure 2B, input lead (or "eyelet lead") 29b is comprised of signal transmission input lines 30 and 31 which comprise opposite legs or ends of a segment of line bent upon itself in a loop to provide a bight portion 29b' connecting the legs which provide input lines 30 and 31 in this embodiment. Alternatively, the looped input lead can be attained by sealing together the distal ends (30b, 31b of Figure 2A) of two separate signal transmission lines (such as 30, 31 of Figure 2A) so that the distal ends are secured together, e.g., within a sealant cap (not shown). The donor line, i.e., detonating cord 160, can be passed through the loop defined by input lead 29b and, as illustrated in Figure 2B, may be disposed inside the loop so that it has two points of contact with input lead 29b to initiate input signals on the inside of the loop of input lead 29b simultaneously at two points. This enhances the reliability of transferring a signal from detonating cord 60 or 160 to input lead 29a or 29b because even if signal transfer fails at one of the con¬ tact points it may well succeed at another. If the deto¬ nating cord is positioned against the inside curve of bight portion 29b' as illustrated by detonating cord 160 in Figure 2B, conforming contact is attained between about one-half the periphery of detonating cord 160 and input lead 29b. Providing such conforming contact is another way to improve signal transfer from the detonating cord to the input lead. Further, whether (a) the detonating cord is positioned outside the looped input lead (as shown in dash line at 160 in Figure 2B) so that it initiates a sig¬ nal at only one point in the loop, or (b) if only one of the contact points attained with detonating cord 160 in¬ side the loop is initiated by detonating cord 160, or (c) if conforming contact is established between the detonat- ing cord and the looped input line segment, detonator 10b will still receive two initiation signals because the sig¬ nal initiated in looped input lead 29b will travel in both directions from the point of initiation and then via sig¬ nal transmission lines 30, 31 to be emitted at both sig- nal-emitting ends thereof (not shown in Figure 2B) . Thus, the same input signal redundancy is achieved in the embod¬ iment of Figure 2B with one successful initiation as is achieved in the embodiment of Figure 2A with two success¬ ful initiations. For this reason, the looped embodiment of Figure 2B is preferred over the multiple strand embodi¬ ment of Figure 2A. Another reason for this preference is that since both ends of the legs of looped input lead 29b are secured in detonator 10b, there is no need for the extra step of sealing the distal ends of the shock tube signal transmission lines, as must be done for the embodi¬ ment of Figure 2A. In addition, securing the two ends of a shock tube segment in the input end of the detonator provides a better barrier against penetration of the tube by oil, water, and other environmental contaminants than sealing the distal end of a strand-type input line. In tests by the applicants, detonators having only looped input leads and detonators having strand input leads were immersed in oil for 16 hours at 175°F and about 12 hours at 160°F, respectively. The detonators were then tested, and the detonators having looped input leads detonated more reliably than the detonators having strand-type input leads. This shows that a detonator with a looped segment input lead may be preferred if the detonator will be ex¬ posed to external contaminants for extended periods of time, i.e., if the detonator will be required to "sleep" while being exposed to contaminants such as oil prior to initiation. It should also be noted that multiple contact points can be attained with detonating cord positioned outside the loop of input lead 29b as illustrated in Figure 2B by positioning the detonating cord as shown for detonating cord 260 which is maintained in contact with each of sig- nal transmission lines 30, 31. Alternatively, a detonat¬ ing cord 360 could be threaded through the eyelet loop to similarly maintain a contact area with each of signal transmission lines 30, 31. The relationship between the detonating cord and the input lead is maintained by any suitable means, a prefer¬ red version of which is described below in connection with Figures 5-5C which illustrates the use of the multiple- line input leads of the invention in conjunction with the slider unit of a booster charge. Figures 3A, 3B and 3C illustrate other embodiments of the invention comprising, respectively, detonators 10c, lOd and lOe, in each of which the input leads are com¬ prised of shock tube. In Figure 3A, input lead 29c is comprised of signal transmission input lines 30, 30', 31, 31' for a total of four separate signal transmission lines comprising four separate strands of shock tube, each hav¬ ing a signal-emitting end (not seen in Figures 3A-3C but analogous to signal-emitting ends 30a, 31a of Figures 1 and IC) secured in the detonator and a distal, sealed end 30b, 30b', 31b, 31b'. The embodiment of Figure 3B has an input lead 29d' which also has four signal transmission lines, but these are provided by two looped segments one of which provides signal transmission input lines 30'', 31''; the other of which provides signal transmission input lines 30''', 31'''. Figure 3C has an input lead 29e having three signal transmission lines provided in this case by a single strand input line 30 and a looped input line segment that provides input lines 30'' and 31''. The embodiment of Figure 3C accordingly illustrates that a strand-type input line and a looped input line segment may be used in the same detonator. The other portions of the embodiments of Figures 2A, 2B and 3A-3C are identical or similar to the embodiments of Figures 1 and IC and are identically numbered thereto and not further described herein. Figure 4 provides a schematic illustration of a typi¬ cal environment of use of a multiple input detonator in accordance with the present invention. Figure 4 shows a booster charge 36 resting upon a layer of stemming mate¬ rial 38 in a borehole (unnumbered). Booster charge 36 may have any suitable shape but is shown as a simple, constant circular cross-sectional cylindrical configuration, and has a downline well 37 and a detonator well 39 formed therein. A downhole line of detonating cord 62 passes through a borehole charge 40 which is typically an ANFO (ammonium nitrate-fuel oil) or other suitable (e.g., emulsion) charge, then through booster charge 36 via a downline well 37, then through stemming material 38 and, in the multiple deck arrangement illustrated, onward down the borehole to the next booster charge (not shown). The bottom portion of booster charge 36 is dimensioned and configured to receive a slider unit (omitted from Figure 4 for clarity of illustration but described below) that holds a detonator 110 which has an input lead 12a that comprises four signal transmission lines provided by two looped input line segments made of shock tube. Input lead 129 is disposed in signal transmission relation to deto¬ nating cord 62, which is passed through the inside of both loops of input lead 129. A suitable slider unit, such as that shown in Figure 5, may be used to retain detonator 110 within detonator well 39. As described below, the slider unit may also provide a shielding tube (e.g., shielding tube 46, Figure 5) to protect detonator 110, booster charge 36 and its downline well 37 from damage by the explosive force of detonating cord 62. If booster charge 36 or its downline well 37 are damaged by detona¬ tion of detonating cord 62, reliability of initiation by detonator 110 will be adversely effected. This and other benefits of slider unit 44 are described in detail in co- pending patent application Serial Number 08/548,813, filed on January 11, 1996, in the name of Daniel P. Sutula, Jr., et al for "Method and Apparatus For Transmission of Initi¬ ation Signals" (Attorney Docket P-1451). Figure 4A shows the same environment as Figure 4 with identical parts of Figure 4A identically numbered as in Figure 4 and not further described herein. In Figure 4A detonator 110' has an input lead 129' which comprises sig¬ nal transmission strand lines 130, 131 extending therefrom through downline well 37 parallel to and in contact with detonating cord 62. Although only two signal transmission strand lines are shown in Figure 4A, three or four could easily be used, e.g., by employing the detonator 10c of Figure 3A as detonator 110' of Figure 4A. It will be ap¬ preciated that a very large surface area of contact is at¬ tained between input lead 129' (or input lead 29a of Fig- ure 2A or input lead 29c of Figure 3A) and detonating cord 62 which greatly enhances reliability of signal transfer to the input lead by the detonating cord. Figure 5 shows a perspective view of the bottom of a slider unit useful for holding a detonator in place within a booster charge in the type of arrangement schematically illustrated in Figure 4, the slider unit of Figure 5 being greatly enlarged relative to Figure 4. Slider unit 44 is adapted for use with a booster charge of the type which is encased within an outer shell which has means thereon such as recesses located at the bottom of the booster charge which are engaged by protrusions 64 to mount slider unit 44 and a detonator carried thereon within a booster charge, as more fully disclosed in commonly owned co-pend¬ ing patent application Serial Number 08/575,244, filed on January 16, 1996 in the name of Daniel P. Sutula, Jr. et al for "Slider Member For Booster Explosive Charges" (At¬ torney Docket: P-1480-2). Slider unit 44 comprises a shielding tube 46 having an internal bore through which the downhole detonating cord passes. Shielding tube 46 not only facilitates sliding of the booster charge along the detonating cord 62, but also serves to protect the booster charge 36 from being damaged as discussed above or initiated directly from the downline detonating cord, which preferably is a low energy detonating cord. If booster charge 36 were to be initiated directly by deto¬ nating cord 62, it would disrupt the timing sequence pro¬ vided by the predetermined delay period provided when det- onator 110 is, as is usually the case, a delay detonator. Premature detonation of the booster charge 36 will, as will be appreciated by those skilled in the art, have an extremely adverse effect on the effectiveness of the blasting operation. A detonator retainer 48 is carried in parallel rela¬ tion with shielding tube 46, to hold a detonator such as any one of the detonators illustrated and/or described herein. Slider unit 44 also includes a base fixture com¬ prising a base plate 50, line-retaining means 52, and a hinged cover 54 attached to base plate 50 by a hinge 54a. Figure 5 shows hinged cover 54 in the open position; when the slider unit is closed by swinging cover 54 about hinge 54a, cover 54 and base plate 50 cooperate to define an en¬ closed base chamber 51 within which at least a portion of the input lead of the detonator is disposed. Base plate 50 and cover 54 each define an aperture 58a, 58b, respec¬ tively, and these apertures align with one another when cover 54 is closed over base plate 50, and together pro- vide a passage through which detonating cord 62 (Figure 4) may pass through the base fixture. Within the base cham¬ ber 51 formed when cover 54 is closed over base plate 50, the line-retaining means 52 keep the multiple input lines of the input lead of the retained detonator in signal transmission relation with the detonating cord, as will be described more fully below. As seen schematically in Figure 5A, line-retaining means 52 comprises flanges 66a, 66b, 66c and 66d which are dimensioned and configured to define retaining channels to receive the lines of an input lead from a detonator se¬ cured in slider unit 44. On opposite sides of aperture 58a, flanges 66a and 66b define "pinch" regions 68 where the input leads are disposed too close to one another to allow a typical detonating cord to pass between them. Be¬ tween the pinch regions 68, flanges 66a and 66b diverge slightly around aperture 58a in a deflection region to permit input lines to deflect around a detonating cord passing through aperture 58a. As seen in Figure 5B, when the detonator 10a of Figure 2A is in place and signal transmission input lines 30 and 31 are disposed in line-retaining means 52, pinch regions 68 constrain lines 30 and 31 to closely bend around a det¬ onating cord 62 passed through aperture 58a. By causing the input lines to closely conform to and bend around the detonating cord 62, the surface area of contact between the cord 62 and the lines 30, 31 of the input lead is in¬ creased, thus increasing the reliability with which an initiation signal is transmitted from detonating cord 62 to the input lead. Preferably, flanges 66a, 66b do not bear on lines 30, 31 in the deflection region even when lines 30, 31 are deflected about a detonating cord, i.e., they are disposed at a slight stand-off from the input lines in the deflection region. Such a stand-off helps the input lead engagement means to avoid imposing firm contact between the input lines and the detonating cord due to foreseeable variations in the diameters of the input lines and the detonating cord. The inherent resili- ence of the input lines and the slight stand-off of flanges 66a, 66b allows them to engage in casual abutting contact with the detonating cord in the deflection region. However, flanges 66a, 66b are configured to constrain lines 30, 31 from deflecting away from the detonating cord to a significant degree when the detonating cord initi¬ ated, since this could result in a failure to transfer the initiation signal to the input lines. Gussetts 70 rein¬ force flanges 66a, 66b against the lateral force of initi- ation of the detonating cord at the point of wherein lines 30, 31 contact detonating cord 62, and thus enhance the reliability of signal transfer to the input lead. Figure 5C shows detonator 10b of Figure 2B mounted within slider unit 44 with the bight portion 29b' circu - scribing aperture 58a to provide extended contact between input lead 29b and detonating cord 62. Despite the close, conforming contact of the input lead to the detonating cord 62, the arrangements shown in Figures 5B and 5C provide for a smooth sliding contact be- tween the input lead and detonating cord 62 so that slid¬ ing movement of booster charge 36 (Figure 4A) relative to detonating cord 62 is facilitated, the weight of booster charge 36 being more than ample to overcome the frictional resistance between detonating cord 62 and the input lead disposed in contact therewith. Other arrangements of the input lead about the line- retaining means 52 may be employed including a pretzel¬ like configuration which provides two passes of the signal transmission lines of the input lead adjacent to detonat- ing cord 62 as illustrated in Figure 5C plus a third pass crossing transversely to the first two passes adjacent de¬ tonating cord 62. Such arrangements are shown and de¬ scribed in detail in the aforesaid co-pending patent ap¬ plication Serial Number 08/548,813, filed on January 11, 1996, in the name of Daniel P. Sutula, Jr., et al for "Method And Apparatus For Transmission Of Initiation Sig¬ nals" (Attorney Docket P-1451). The bore of shielding tube bore 46 is preferably larg- er in diameter than aperture 58a in base fixture 48, and it preferably tapers down to the diameter of aperture 48 to facilitate threading a detonating cord through the slider device. Further, it is preferred that the detonat- ing cord have an oval cross-sectional configuration having a major flattened peripheral arc that extends along the major axis of the oval. The input lead for the detonator preferably bears against the major flattened peripheral arc of the detonating cord. Even more preferably, each input line may also have such a major flattened peripheral arc, for increased sensitivity, and the major flattened peripheral arc of the input line is in contact with the detonating cord. Preferred configurations for contact be¬ tween the input lead and the detonating cord are described in co-pending patent application Serial Number 08/548,813, filed on January 11, 1996, in the name of Daniel P. Sutula, Jr., et al for "Method And Apparatus For Transmis¬ sion of Initiation Signals" (Attorney Docket: P-1451). Those skilled in the art will, upon a reading and un- derstanding of the foregoing disclosure, appreciate that modifications may be made to slider unit 44 and line-re¬ taining means 52 to accommodate various embodiments of the input leads in accordance with the present invention, in¬ cluding those illustrated in the Figures. While the invention has been described in detail with reference to particular embodiments thereof, it will be apparent that upon a reading and understanding of the foregoing, numerous alterations to the describedd embodi¬ ments will occur to those skilled in the art and it is in- tended to include such alterations within the scope of the appended claims. For example, although the multiple-line input leads illustrated herein are short relative to the length of the detonator, the mulitple-line input leads may, as noted above, be quite long, up to many hundreds of meters in length, for connection of the input lead of a detonator to an initiator which is remote from, e.g., many hundreds of meters from, the detonator.

Claims: THE CLAIMS What is claimed is: 1. A detonator having an output section and com¬ prising: a shell defining an enclosure; a target charge comprising at least an explosive output charge disposed within the shell at the output sec¬ tion of the detonator; and an input lead extending into the detonator and secured therewithin, the input lead having at least two signal transmission input lines which extend into the shell and terminate in signal-emitting ends disposed with¬ in the shell in signal transmission relation with the tar¬ get charge. 2. The detonator of claim 1 wherein the input lead comprises one or more looped input line segments, each comprising a bight portion connecting two legs extending into the shell and terminating in the signal-emitting ends. 3. The detonator of claim 2 wherein the input lead comprises two looped input line segments. 4. The detonator of claim 1 wherein the input lead comprises at least two separate signal transmission strand lines, each line having opposite first and second ends with the signal-emitting first end of each strand line being disposed within the shell in signal transmission relation with the target charge and the second end of each strand line being disposed exteriorly of the shell. 5. The detonator of claim 4 wherein the input lead comprises shock tube and the second end of each strand line is sealed to seal the shock tube against the ele¬ ments. 6. The detonator of any one of claims 1 through 4 inclusively wherein the input lead is comprised of shock tube. 7. The detonator of any one of claims 1 through 4 inclusively wherein the target charge further comprises a delay element connecting the input lead and the explosive output charge in initiation signal communication. 8. The detonator of claim 1 further having an input section and wherein the shell has a closed end at the out¬ put section of the detonator and an open end sealed by the sealant means and located at the input section of the de¬ tonator, and the signal transmission input lines extend into the shell through the open end thereof. 9. A method of initiating a detonator having dis¬ posed therein a target charge comprising at least an ex¬ plosive output charge which is configured to be initiated by an input signal transmitted thereto by a plurality of signal transmission strand lines having signal-emitting ends disposed in signal transmission communication with the target charge, the method comprising transmitting at least two initiation signals to the target charge. 10. The method of claim 9 further comprising trans¬ mitting at least four initiation signals to the target charge. 11. The method of claim 9 or claim 10 wherein the target charge further comprises a delay element having a selected delay period and being interposed between the signal-emitting ends of signal transmission input lines and the output charge, and the method comprises transmit¬ ting the initiation signal to the delay element and via the delay element to the output charge, whereby travel of the initiation signals between the signal-emitting ends of the input lines and the output charge is delayed by the selected delay period. 12. The method of claim 9 or claim 10 comprising sub¬ stantially simultaneously transmitting the initiation sig¬ nals to the target charge. 13. The method of claim 12 wherein the target charge further comprises a delay element having a selected delay period and being interposed between the signal-emitting ends of the signal transmission input lines and the output charge, and the method comprises transmitting the initia¬ tion signals to the delay means and via the delay means to the output charge, whereby travel of the initiation sig¬ nals between the signal-emitting ends of the input lines and the output charge is delayed by the selected delay period.

Inventors: DUFRANE RONALD M, GLADDEN ERNEST L, DUFRANE, RONALD, M., GLADDEN, ERNEST, L.
Applicants: ENSIGN BICKFORD CO, THE ENSIGN-BICKFORD COMPANY
Application year: 1996
Main classification: C06C7
IPC codes: C06C5, C06C7, F42B3, F42C19