FI70323C - FOERFARANDE OCH ANORDNING FOER TAENDNING AV EXPLOSIONER - Google Patents

Description

1 70323

Method and apparatus for igniting explosions

The present invention relates to an apparatus and method for igniting explosions. In particular, it relates to a method and apparatus utilizing ring-coiled lighters, such as those developed by ICI and marketed under the trademark "Magnadet".

Ring-coil igniters, as described above, are used in conjunction with ferrite rings.

Each igniter has its own ring, the inlet wire from each igniter is twisted several times (typically 4 turns) around the associated ring to form a secondary circuit. The length of the lead-in wires ensures the location of the rings at the mouth of each blast hole and the energy is supplied from the igniter to the system via a primary conductor which is wound only once through each ring.

A preferred feature of a system such as that described above is the frequency selective properties of ferrite rings. Thus, the rings have a bandpass feature that effectively attenuates low-frequency signals below about 10 kHz and high-frequency signals above about 100 kHz.

25 Because the inlet wire of each igniter consists of an insulated, closed loop, the igniters are substantially immune to stray currents and ground leakage.

The problem with such systems is that in the frequency range of 15-25 kHz (in which frequency range the 30 best energy transfers through ferrite rings are achieved), considerable losses of ignition energy occur due to the inductance of the system.

Applicant is aware that in order to overcome this problem, attempts have been made to take advantage of a series capacitor 35 in an attempt to use the system in series resonance mode.

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It is noted, however, that the inductance of the system varies with the number of ferrite rings and associated igniter units, the configuration of the primary conductor, and the like. Thus, when using an ignition machine that generates a fixed frequency-5 ignition signal, a series capacitor with a certain capacitance is required in each system, which provides a series resonance at a fixed frequency. Thus, it is necessary to measure the inductance of each system on site in the actuator, calculate the required capacitance, select a suitable capacitor from stock and place the capacitor in the circuit associated with the system. The method is time consuming, dangerous and requires a storage of capacitors and skilled personnel.

The invention provides an apparatus for igniting explosions, comprising a power oscillator device for generating a sufficiently powerful variable frequency oscillating electric ignition signal; 20 a frequency setting device to which the oscillator device is responsive, by means of which, in use, when the power oscillator device is connected to the load, it automatically generates a signal at the resonant frequency of the load.

25 The detonator may be an igniter.

The ignition machine may have an output switching device to which, as described above, the ends of the primary conductor forming part of the ignition system are connected. The series capacitor may be connected in series to the output switching device.

According to the invention, there is further provided a method of igniting detonations, comprising providing an ignition system that operates on an oscillating electrical signal and has an indeterminate impedance; 35 automatic generation of an oscillating ignition signal at the resonant frequency of the system.

3 70323

The invention extends to an ignition device as described in conjunction with and connected to an AC voltage ignition system.

One skilled in the art will recognize that the operating frequency of the oscillators will normally be determined by suitable elements or circuits. In the ignition machine according to the invention, the ignition system itself, in use, can form part of the oscillator device.

In one embodiment, the power oscillator device may include at least one controllable element and the frequency setting device may include a positive feedback loop to control the operation of the element according to the voltage or current supplied to the ignition system. The controllable element, or each of the controllable elements 15, may be of the switchable type and may be easily switched on or off, such as a transistor. This switchable element is connected to the phase with the ignition signal. Alternatively, the power oscillator device may include an amplifier.

One form of feedback loop may include a converter whose primary current is the ignition signal current and whose secondary current controls said switchable element or elements or an amplifier. An alternative form of feedback loop may be a direct loop by means of which the current of the ignition signal directly controls the element or elements to be switched. Still further, the feedback loop may include a detector that measures current in the output circuit and an amplifier in response to the detector to provide an output current in step to control an element or elements that can be switched on by the ignition signal 30. Transformer-coupled and straight-link are preferred when low powers are required. The detector and amplifier loop is preferred when higher powers are required.

The detonation igniter may also advantageously include a voltage setting device to provide a predetermined ignition current to any fixed load within the functional impedance range of the power oscillator.

Furthermore, additional inductance can be used to reduce the resonance range. This additional inductance may be in series with the switching device.

The power oscillator device may be direct current and the voltage setting device may thus include a controllable voltage source for providing the power oscillator with a variable voltage DC power source and a measuring device for measuring the amount of current supplied to the ignition system, the voltage source responsive to the measuring device.

The ignition machine may also include a timer device by means of which the ignition signal can be supplied for a predetermined period of time.

The ignition machine according to the invention makes it unnecessary first to determine the inductance of the ignition system and then to compensate it by means of a resonant capacitor in order to achieve a predetermined resonant frequency. Thus, the ignition system is energized by a signal that is automatically generated at the resonant frequency.

The invention will now be described by way of example with reference to the accompanying drawings, in which all similar components are referred to in the same way and in which: Figure 1 schematically shows an ignition system using an ignition machine according to the invention; Figure 2 shows an alternate ignition system connection; Figures 3 and 4 show two circuit diagrams of a power oscillator used in an ignition engine 30 utilizing a transformer-coupled feedback loop.

Figures 3 and 4 show two circuit diagrams of a power oscillator used in an ignition machine according to the invention, in which a transformer-connected feedback loop is utilized.

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Figure 5 shows a circuit diagram of an ignition machine according to the invention, including the circuit of Figure 4.

Figure 6 shows a circuit diagram of an alternative power oscillator utilizing a direct feedback-5 field loop.

Figure 7 further shows an alternative power oscillator utilizing a feedback loop including a current detector and an amplifier.

Figure 8 shows a circuit diagram further including 10 oscillators for use in conjunction with a power oscillator to provide a preset output voltage in the ignition engine.

Fig. 9 shows a circuit diagram of an ignition machine according to the invention, in which the circuits of Figs. 7 and 8 are included.

Reference is first made to Figure 1. The ignition arrangement is generally referred to therein 10. The ignition arrangement 10 comprises an ignition machine 12 connected to an ignition system 14. The ignition system 14 comprises a plurality of ignition modules 20 16. Each ignition module 16 comprises a standard electric igniter 22 connected to a ferrite ring through. As shown, each lead-in conductor 22 is wound a few times around its ferrite ring 20. The ignition system 14 further comprises an ignition conductor 24 and a primary conductor loop 26, the latter passing through the ferrite rings 20. Further, as shown, one end of the ignition conductor 24 is connected to the ignition machine 12 and the other end to the primary conductor loop 26.

Referring now to Figure 2, a substitution circuit diagram of the ignition arrangement 10 is shown. Ignition conductor 24 and primary conductor loop 26 are represented by inductance 28 and resistance 30, while ignition modules 16, referring back to primary loop 26, are represented by resistance 32 and inductance 34. Inductance 35 typically has a value of 60-600 yUH and resistance 32 has a value of N x 0.125 ohm, where N is the number of igniters 6 70323 and inductance 34 has a value of N x 2.5 ^ uH. As previously discussed, the ferrite rings 20 are frequency selective and have optimal energy transfer properties in the frequency range of 15-25 kHz. Thus, it can be appreciated that the inductive characteristics of the ignition system 14 are significant at these frequencies. To eliminate the inductive effect, a series capacitor 36 is included in the ignition machine 12, the value of which is suitable so that when used with certain types of ignition systems 10, the series resonant circuit thus formed has a resonant frequency between 15 and 25 kHz.

Referring to Figure 3, a power oscillator arrangement 38 connected to an ignition system 14 is shown. Figure 3 shows the inductances and resistors 15 shown in Figure 2 centered together to provide an inductance 40 and a resistance 42. The oscillator arrangement 38 further includes a control transformer 44 and a feedback transformer 46. The feedback transformer 44 is connected in series with the ignition system 14 via the resonant capacitors 36 of the primary winding 46.1 and 20 of the feedback transformer 46. In the center of the oscillator arrangement 38 is a transistor 48 which is controlled by a feedback loop from the secondary winding 46.2 of the feedback transformer 46. An open-pole "free-wheeling" diode 25 50 is used to protect the base-emitter connection of transistor 48. An energy storage capacitor 52 is also included.

It will be appreciated that the oscillator arrangement 38 is self-tuning in that it generates an oscillating signal at the resonant frequency of the circuit formed by the control transformer 44, the feedback transformer 46, the resonant capacitor 36 and the ignition system 14 30. In the operating condition, when the oscillator arrangement 38 is Touched (as indicated below with reference to Fig. 5), the transistor 48 turns on and current begins to flow through the primary winding 46.1. The polarity of the secondary winding 46.2 is selected to provide positive feedback to transistor 48. Thus, transistor 48 remains on for as long as the output current flows in the original direction.

When the current is turned on, the transformer 46 switches the transistor 4 8 to Jutila. The next time the polarity of the current is reversed, in its original direction, the transistor 48 switches back to the 5 on state and the process is repeated. The positive feedback signal applied to the switching transistor is proportional to the load current and always in phase with it. Accordingly, the oscillator arrangement 38 generates a signal at the resonant frequency of the load, provided that the inductance of the load circuit is within reasonable limits (e.g., 50 yUH to lmH).

Referring to Figure 4, an alternative oscillator arrangement 38.1 is shown. This arrangement 38.1 is similar to the arrangement 38 of Figure 3, except that 15 transistors 48 are used in phase switching. The various components shown in Figure 4 are referred to in the same manner as those shown in Figure 3. Since the operation of the circuit shown in Fig. 4 is self-evident to those skilled in the art with reference to Fig. 3, it will not be described further.

Although the control transformer 44 produces a rectangular waveform output voltage signal, the current in the ignition loop is sinusoidal, as is known from the theory of resonant circuits. The ignition current thus contains a small part of the harmonic frequencies. This is a very useful feature of the igniter - although harmonics consume the output power of the igniter, they are attenuated by ferrite rings and the inductance of the igniter input wires and are therefore only a very small part of the energy transfer to the igniters.

Referring now to Figure 5, there is shown a circuit diagram of an ignition machine 54 according to the invention. The ignition machine 54 has output terminals 56 to which an ignition system of the type previously described and referenced 14 can be connected. The igniter 56 also has a power oscillator arrangement 38.1, similar to that shown in Figure 4 and referred to in the same manner. However, the control transformer 44 is a voltage boost transformer that provides an output signal from a supply voltage of about 70323 35 volts with a peak value of about 115 volts. A control triac 58 is provided with the secondary winding in series. One skilled in the art will recognize that when the triac 58 is turned on, the transistor 48 must be triggered, thus initiating the oscillator arrangement 38.1. Further, while energizing the triac, the oscillator arrangement 38.1 enters the operating state. The ignition machine 54 has a pre-charged battery 60 and a manual switch 62. In the position shown in Fig. 5, the switch 62 is open and the ignition machine 54 10 is in an inoperative state.

When the switch 62 is closed, the charge capacitor 64 is charged. The voltage across capacitor 64 is monitored by a level detector 66 which provides an output signal across voltage capacitor 66 having a certain value (35 volts). The level detector 66 controls a timer 68 which supplies an output signal of about 4.5 milliseconds. The output signal of the timer 68 energizes the light emitting diode (LED) 70 and also the triac 58, which triggers the oscillator arrangement 38.1 and keeps it in operation for 20 milliseconds. With the ignition system connected across the output terminals 56, a resonant frequency oscillating signal is applied to the ignition system, which ignites the igniters in the system. It should be noted that the battery 60 can also be charged via the output terminals 56, with the diodes 72 and resistors 25 74 forming a one-way charging loop.

Referring to Figure 6, an embodiment of a power oscillator arrangement 38.2 using a direct feedback loop is further shown.

The arrangement 38.2 is similar to the arrangement 38.1 of Figure 4, except that the transformer 44.1 has an isolated secondary winding 44.2 and that the load current flows directly to the transistors 48.1 and 48.2 instead of passing through the feedback field transformer 46 of Figure 4.

The oscillator arrangement 38.2 is self-tuning to the resonant frequency of the series circuit formed by the transformer 44.1, the capacitance 36, the inductance 76, the ignition system 14 and the direct feedback loop leading to the transistors 48.1 and 48.2.

The operation of the arrangement 38.2 is similar to the operation of the circuit shown in Fig. 4, except that the load current controls the directly switchable elements 48.1 and 48.2, instead of the control via the feedback transformer 46 of Fig. 4. The polarity of the secondary winding 44.2 of the transformer 44.1 is selected so as to provide a positive feedback to the elements 48.1 and 48.2 to be switched.

The "Free Wheeling" diodes 75.3 and 75.4 allow the safe discharge of system energy by taking advantage of the ability to turn off the signal after a predetermined 15 time.

Referring now to Figure 7, which shows a power oscillator arrangement in which the detector and amplifier circuit 79 supplies the necessary positive feedback signal to the transistors 48. It is noted that when controlling the series tuning circuit 20 at its resonant frequency, the resulting current is in phase with the control voltage. With a control voltage in the form of a rectangular wave, the current thus bypasses the zero point at the moment when the polarity of the control voltage changes.

The voltage across the series resistor 78 is a measure of the current flowing in the series-25 tuning circuit.

By monitoring the voltage across the resistor and providing corresponding control signals to the transistors 48 for reversing the polarity at the moment when said voltage passes the zero point, the control signal oscillates at the resonant frequency.

The detection and amplification of the feedback voltage across the resistor 78 is performed by a zero point detector and amplifier circuit 79. To compensate for the propagation delays of the circuit 79, a small series coil 77 35 is used in the circuit 79 to advance the feedback voltage signal to the tuning circuit current. If the circuit 79 is polarity dependent, the polarity of the secondary winding 44.2 must be determined.

It is noted that the circuits of Figures 3-7 supply the ignition system 14 with an ignition current that varies depending on the load. In general, however, it is desirable for the ignition current to be above a certain specified minimum level to minimize the delay time scatter of the igniters.

The circuit of Figure 8 is designed to preset the output voltage of the circuits of Figures 3-7 according to the value of the load to provide a constant output current 10 above a certain minimum level.

In the circuits of Figures 3-7, the secondary voltage of the transformers 44 and 44.1 is obtained in the linear range (without losses) E = t V STG ............ (1> 15 where E is the secondary voltage, t is the ratio of the transformer revolutions, and VSTG is the voltage of capacitor 52.

Referring to Figure 7, a series circuit 84 to which voltage E is applied to ignite the ignition system 14 comprises a capacitance 36, an inductance 76, an ignition system 14, an inductance 77 and a resistance 78.

Since the series resonant circuit 84 operates in series resonant mode, the load impedance with respect to the supply voltage e is resistive and satisfies the equation 25 e = ir ................. (1) where e is the applied voltage, i is the resultant current, and r is the load impedance.

The total resistance RT (supply voltage-30 for e) of the series circuit 84 is the sum of the resistances included in said series circuit (42 and 78), the resistive losses (36, 76 and 77) at the control frequency of the reactive components of said series circuit and the resistive losses of the transformer 44.1. Thus, from Equation (2), the current produced by resistans-35 sin RT under the influence of voltage e is obtained i = 1 xe .................... (3) 11 70323

Equations (1) and (3) give, in particular, if the capacitor 52 is charged to V___, the power oscillator b I \ j

the output voltage of the market is the resulting load current I of tvSTG '

5 1 = RT X VSTG ........... (4)

The oscillator shown in Figure 8 generates a search current to the serial circuit 84 to distribute the ignition current required to determine the supply voltage required by the power oscillators of Figures 3-7. This oscillator self-tuning-10 works in the same way as the oscillator shown in Fig. 7.

If the output current of the search current generator is an integral part of the output voltage of the power oscillator, according to Equation (3), the resulting search current is the same fixed part of the expected ignition current. Denote this part by g: 11a, whereby 15 X from equation (4) gives 1 X S = RT X t VSTG X S ......

where tv_mr, x | is the output voltage of the oscillator and the resulting search current is I x to b. It is obvious that the value of S must be such that the current is insufficient to ignite the ignition system 14.

It can be seen from Equations (4) and (5) that when the search current reaches x g, where 1 is the desired ignition current to ignite the ignition system 14, the voltage value of the capacitance 52 is sufficient for any of the power oscillators of Figures 3-7 to ignite the ignition system.

In the circuit of Figure 8, the circuit 83 is a paging current generator which also measures the amplitude of the generated paging current.

Circuit 82 is a charge control circuit interposed between the energy source 81 and the energy storage capacitance 52. Circuit 82 includes a switchable element, such as a transistor, to terminate the charge current required for the VSTG in response to a signal from circuit 83.

Circuit 85 is an ignition control circuit that is also responsive to circuit 83 to provide a trigger signal for any of the power oscillators of Figures 3-7.

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Indicator 86 indicates when the igniter is ready to ignite and indicator 87 indicates if the load is outside the specified operating range of the igniter 12.

The operation of the circuit of Fig. 8 begins with the field of the circuit of the serial circuit 84 to the output of the paging current generator 83.

Resistance 80 is included in series with said output to simulate the resistive losses of the transformer 44.1 of Figure 7 and also to modify the relationship between the expected ignition current If and the total resistance 10 of the series circuit R 1. The modification is arranged to take into account the fact that when an approximately constant current is controlled from capacitance 52 upon ignition, resulting in an approximately constant rate voltage attenuation, the percentage rate of voltage attenuation is higher when the initial voltage is lower. The percentage rate of attenuation of the ignition current is thus higher when the load resistance is low. Low resistive loads thus result in a higher initial ignition current than high resistive loads with constant pulse energy.

The energy source 81 of the igniter is then connected to the energy storage capacitance 52 via the charge control circuit 82.

As the voltage across the capacitance 52 increases, the output voltage 25 of the search current generator 83 also increases, as shown in Equation (5) above.

When the amplitude of the search current reaches 1 ^ x | further charging of capacitance 52 is prevented by a switching signal from circuit 83 to circuit 82. Circuit 83 simultaneously signals to circuit 85 that the ignition engine is ready to ignite, and indicator 86 is energized.

In the circuit of Fig. 9, the switch 88 is a safety switch (shown in the normal or protective position) by means of which the capacitance 52 is discharged through the resistance 91. Ignition switches 89 and 90 operate together and are shown in the normal or 35 test positions.

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In the order of operation of the ignition system 14, the switch 88 is next used and a part of the ignition machine circuit, as shown in Fig. 8, is closed.

Capacitor 52 initiates charging from energy source 5 (which may be a hand crank generator) through charge control circuit 82. At the same time, the paging current generator 83 supplies a variable voltage, it is self-tuning to the resonant frequency of the series circuit 84 and having an amplitude proportional to the instantaneous voltage of the capacitor 52. When the amplitude of the resulting paging current is required, circuit 83 simultaneously communicates to circuit 82 to prevent further charging, to circuit 85 of the ignition engine's readiness to ignite, and energizes indicator 86.

15 Switch 88 must remain in the operating position and switches 89 and 90 in the rest position. The circuit of the igniter part of Figure 7 is now closed.

Circuit 85 triggers circuit 79 to begin the ignition operation as described in connection with the description of Figure 7, and may, if necessary, stop operation after a predetermined time.

Each igniter has certain limits on the load impedance within which it is capable of igniting the required ignition current. In the ignition machine according to the present invention, the values of the components of the circuit determine the maximum allowable voltage of the capacitance 52 and thus the maximum allowable load resistance.

Likewise, the maximum and minimum values of the frequency of the oscillating current to which the ignition system 14 responds effectively 30 and / or to which the ignition circuitry may respond determine the allowable minimum and maximum values of load inductance 40, giving capacitance 36 and inductances 76 and 77. The resonant frequency of the series circuit 84 is obtained from approximately Equation 35 f = -—— r = r-

2flyL x C

14 70323 where L is the total inductance of said series circuit, the sum of inductances 40, 76 and 77 and C is the capacitance 36.

In the ignition machine according to the invention, the circuit of Figure 9, including preliminary measurements of the search current, is used to ensure that the separate limits of load resistances and inductance are not exceeded. If any limit is exceeded, the circuit 83 signals that the load is out of the defined range and that the ignition engine is not ready to ignite and the indicator 87 is energized. The ignition machine is thus prevented from igniting even if switches 89 and 90 are used in the ignition attempt.

The ignition machine according to the circuit of Figure 9 thus provides a constant ignition current output to an ignition system with an undefined impedance. The components 15 of the ignition circuit are thus protected against overload and the ignition machine is efficient in using the energy from its energy source.

The circuit of the igniter of Figure 9 also provides a time delay self-discharge mechanism to prevent the partially or fully charged igniter from remaining in this state for longer than necessary.

Claims (10)

Device for initiating explosions, including a force oscillator means (48.1, 48.2, 79) for generating an oscillating electric ignition signal of sufficient power at a variable frequency, characterized by a frequency setting means (46, 38, 77, 78, 79) , to which the oscillator means reacts, by means of which the power oscillator means, when in use, is coupled to a ball load, automatically generates a signal at the resonant frequency of the load. Explosion initiating device according to claim 1, characterized in that the frequency tuning means (38, 46, 77, 78, 79) include a resonant capacitor, which is connected in series with a switching device (56) for the output power. Explosion initiating device according to claim 2, characterized in that the power oscillator means includes an amplifier (79) and that the frequency setting means (77, 78, 79) are connected to the amplifier (79) by positive feedback. Explosion-initiating device according to claim 2, characterized in that the power oscillator means includes a switchable element (48.1, 48.2) and that the frequency adjusting means (77, 78, 79) is controllably coupled to the switchable element so that, when used, it can be coupled to the same phase. ignition signal. Explosion initiating device according to claim 3 or 4, characterized in that the frequency setting means includes a transformer (46) with a primary winding (46.1) and a secondary winding (46.2), the primary winding being connected in series with the output device (56) for output. and the secondary winding is connected to the amplifier (79) or to the switchable element (38). Explosion initiating device according to claim 2, characterized in that the power oscillator means includes an output transformer (44). Explosion initiating device according to any of the preceding claims, characterized in that the