Programmable Electronic Delay Fuse

This invention relates to a programmable electronic delay fuse.

The purpose of such a fuse is to provide a device which is capable of initiating a detonator or safety fuse after a preprogrammed and accurate delay time has been chosen.

It is already known to use links between projectiles and missiles, as shown for instance in U.S. Pat. No. 4,091,734, assigned to the United States of America as represented by the Secretary of the Navy, which uses an infrared digital beam to feed data to a missile, and U.S. Pat. No. 3,228,337, also assigned to the United States of America, which uses a laser communication system; and European Patent No. 0 082 445 of Brown, Boveri & Cie Aktiengesellschaft, which relates to a remote programming device for a projectile using a microwave signal which provides a energising signal and a return function-and-correct signal.

The unit comprises basically a fire control unit and a programming unit which are interconnected by an optical interface, the fire control unit having as its purpose the actuation of a non-electric (percussive) or an electric detonator, the purpose of the programming unit being to set the necessary time delays required in a unit of this type.

The device according to this invention can be arranged in many forms; a high reliability, single-fire device with a non-electric (percussive) output, fitted with a non replaceable pyrotechnic actuator; a reusable percussive output device suitable for training, in which the consumed actuator assembled is plug-fitted for easy replacement; or an electrical output device which is inherently a multi-fire device and which may be used for training or operational environments suited to the external connection of the electrical detonator.

According to this invention the fire control unit contains two independent delay timers and a safety timer. The timers supply initiating signals via a fire control circuit to the pyrotechnic actuator for the non-electric version or direct to the output terminals for the electric detonator version.

Operator control and observation of device function in a non-destructive test firing cycle are provided for the fire control unit.

The test firing cycle along with other checks inherent in the programmer unit-fire control unit interaction, may be used to establish the high degree of confidence in device safety and operability required of a product of this kind. Safety is also enhanced by the reversibility by delay programming, time counting and arming processes.

The invention consists of a programmable electronic delay fuse for initiating a firing after a programmed and accurate delay time has been chosen, characterised by a fire control unit with means to actuate firing means such as a non-electric (percussive) or an electric detonator, a programming unit separate therefrom having means to program and test the fire control unit, and optical coupling interface means on the fire control unit and the programming unit to link firing and status means on the fire control unit with command and test means on the programming unit.

According to one form the invention consists of a programmable electronic delay fuse for initiating a detonator or safety fuse after a programmed and accurate delay time has been chosen, and comprises a fire control unit and a programming unit interconnected by an optical interface, the fire control unit being arranged to actuate firing means such as a non-electric or an electric detonator and includes time delay means to allow testing and setting of the fire control unit, and multiposition switch means to select delay programming, test and arm activity and includes status indicators for "SAFE TO ARM" and "TIME UP", the programming unit comprising means such as a keyboard for entering instructions and includes a control processor and display, and a power source, the optical coupling interface means between the fire control unit and the programming unit allowing a single programming unit to be used to test and set a series of fire control units. If the actuator fuse is not continuous or if both TIME UP switches 18 and 19 are closed, the safe to arm indicator lamp 12 can not be energized.

To enable the invention to be fully appreciated but without in any way limiting the invention to the circuitry shown, a preferred form of the invention will be described with reference to the accompanying drawings in which

FIG. 1 shows a functional breakdown diagram of the fire control unit,

FIG. 2 shows a simplified representation of the fire circuitry, and

FIG. 3 is a block diagram of the programming unit.

Referring first to FIGS. 1 and 2 which show the fire control unit FCU, the numeral 1 indicates the interface, the numeral 2 the programmable timer which contains the first delay timer A and the second delay timer B, the numeral 3 shows the fire circuitry which also includes the status lamps, and the numeral 4 represents the primer assembly. The safety timer is designated by 5, and the control switch and power source by 6.

The safety timer 2 has a fixed delay time such as, for instance, forty seconds and provides protection against premature firing of a detonator due to either a single operator or single equipment failure. It inhibits the closure of the fire circuit switches for such time after arming, even if the programmable timer delays have expired.

The two programmable delay timers A and B of the fire control unit are independent delay timers each programmable in delay increments of say one minute over a range of one minute to twentyfour hours, but other time increments and length can be used.

The duplication of delay timers A and B provides a protection against a single fault condition producing a premature detonation in the period after the expiry of the safety delay, and both programmable timers, as well as the safety timer, produce a TIME UP condition for detonation to occur.

In addition to timing the programme delay, both delay timers A and B output a delay-related clock signal to the programming unit via the optical interface 1. These return signals allow the programming unit to verify correct delay programming, and the proper function of a substantial portion of the fire control units delay timing circuitry.

The optical interface 1 is only activated when the control switch is in the PROG position, and translates the optical input signal into an electrical delay programming signal used to programme the two delay timers in the programmable timer unit. Further it translates two electrical delay feedback signals into two optical output signals which provides the programming unit with confirmation of timer programming.

The control switch and power source 6 select five modes of operation for the fire control unit; PROG is the programming mode where the unit can be programmed, SET is the reset mode where the unit's timers are reset to their programmed delay time, RUN is the run mode where the unit's timers are allowed to operate, TEST is the test mode where the operation of the programmable timer, safety timer and fire circuitry and status lamps are checked, non destructively ARM is the arm mode in which the unit is fully activated and ready for firing.

All modes are reversible. Delay time may be changed by reprogramming, the delay count may be reset to the full programmed delay time at any time in the RUN mode by reselecting a SET mode, and a TEST or a full ARM firing cycle may be terminated at any time by switching to one of the modes where the firing circuit is non active.

The programmable timer 2, when the control switch is in the PROG position, is programmed from the delay programming signal and outputs two delay feedback signals one from delay timer A and the other from delay timer B indicating the programmed time of each. When in the SET mode both delay timers are set and held to programmed delay time. When in the RUN, TEST or ARM mode both delay timers are enabled to operate and will produce a time up A signal and a time up B signal when timed out.

The safety timer 5 is activated when the control switch selects the TEST or ARM modes upon which a fixed delay of approximately 40 seconds is started. Upon time out of this delay a safe time up signal is generated which then enables the fire circuit function. The safety delay is automatically restored to its full designated value as a result by both TEST-ARM and ARM-TEST switch drive transitions to fire.

The fire circuitry function is enabled only in the TEST and ARM modes, and will provide a fire signal only when the time up A, the time up B and the safe time up signals are true. When in the TEST mode the status lamps are enabled and the fire circuit current is limited below that required for firing, to enable the function of the fire control unit to be tested. The safe to arm signal is activated when the firing circuit is continuous and the fire condition is not true. The time up signal is activated when either the time up A of the time up B or the safe time up signal is active.

The programmable timers A and B are active in all modes except PROGRAM and SET, and timing activity is uninterrupted by control switching between RUN, TEST and ARM.

Firing of the pyrotechnic actuator or the electric detonator is achieved by connecting the actuator or the detonator via the main control switch and electronic switches which conveniently are two SCRs, across the battery power source. The firing circuitry is connected to the power source only in TEST and ARM modes and in the TEST mode the current available from the power source is limited to a level which will neither fire the actuator nor desensitise it.

The pyrotechnic actuator can contain a fuse wire and a small pyrotechnic charge contained behind a piston plunger. When supplied with a current above the firing threshold, the fuse wire ignites the pyrotechnic charge and drives a piston into a percussion primer, initiating the detonator. The electrical detonator can contain a fuse wire and a primer. When supplied with a current greater than the firing threshold the detonator will be initiated. The optical interface 1 between the fire control unit and the programming unit preferably comprises a phototransistor which converts the optical (infrared) pulses into electrical inputs to the programmable timers. Two infrared emitters also transmit the delay timer feedback signals to the programming unit.

It is preferred to use a five position rotary switch 6 to control the device functions, the switch positions corresponding to PROGRAM, SET, RUN, TEST, and ARM. A mechanical provision on the control switch assembly in conjunction with the device for arming and programming ensure that access to the programme position is only by deliberate action.

It will be seen from FIG. 2 that the test switches 10 and 11 are in circuit with the indicator lamps 12 and 13, the test switch 11 being series-connected with the TIME UP switches 14, 15 and 16 so that the indicator 13 can be energised only if one of the switches 14, 15 or 16 is closed together with switch 11.

The indicator 12 can be energised only if test switch 10 is closed and at least one of the TIME UP switches 18 or 19 is open. Switch 18 will close if the safe time up signal and the time up A signal are true. Similarly switch 19 will close if the safe time up signal and the time up B signal are true.

The current limiting device is indicated by 20 and the selector switch 6 is, as will be seen, in series with the battery 21 and booster capacitor 22.

The actuator being either an electric fire percussive actuator or an electric detonator, is indicated by the numeral 23 and is associated with the TIME UP switches 18 and 19 and the test switch 10.

The actuator will activate only as both switch 18 and switch 19 are closed, provided selector switch 6 is in the ARM position.

When switch 6 is in the TEST position, the actuator passes a limited current sufficient to energize SAFE TO ARM indicator 12 but insufficient to activate or desensitize the actuator itself. If the actuator fuse is not continuous or if both TIME UP switches 18 and 19 are closed, the SAFE TO ARM indicator lamp 12 cannot be energized.

Referring now to FIG. 3 which shows the programming unit PU, the keyboard is designated 30, the control processor 31, the display 32, the power source 33, the battery test 34 and the optical coupling unit 35.

The Keyboard 30 allows entry of the required time delay in hours and minutes in addition to clear and load commands. It also allows access to special test modes of operation.

The Control Processor 31 interprets the keyboard entries and controls the display function. It also provides a time delay signal to the optical coupling for transmission to the fire control unit, and then receives back from the fire control unit, via the optical coupling a time delay feedback signal, to verify that the correct delay time has been programmed into the fire control unit. The control processor also contains several test procedures which can be used for self testing the programming unit's circuitry including the optical coupling.

The Display 32 can be a four character alpha numeric display which is controlled by the control processor. It is used to display keyboard entries, operational and error messages and also to display the verified delay time of the fire control unit.

The optical Coupling 35 provides one part of the optical link between the programming unit and the fire control unit. It is used to transmit delay times to the fire control unit and to receive back programmed delay times from the two delay timers in the fire control unit.

The programming unit is a reusable hand-held device for programming the fire control unit with delay times. It serves also to act as a testing medium for the fire control unit to ensure a correct response to the programming action.

The keyboard 30 is preferably a twelve key keyboard which allows entry of time digits 0-9 with the remaining two keys used for special operator commands such as clearing the display, test sequencing, and loading the programme time into the fire control unit.

The control processor 31 can be a single chip micro-processor which responds to operator data and controls input via the keyboard, controls message and data read-outs on the display 32, and establishes the timing of programming signals to the fire control unit. It also measures the response of the fire control unit to the programming signals to verify the success of the programming action.

The display 32, which can be a four character alpha numeric display, provides visual feed-back of keyboard entries, message prompts for operational and test purposes, and a read-out of the fire control unit programmed time subsequent to programming.

The power source 33 may be supplied by any suitable battery such as an alkaline battery. A regulator circuit is used to ensure that the supply of voltages for the logic devices are held at proper level.

To programme a fire control unit with a delay time the programming unit and the fire control unit are first physically coupled to achieve an alignment of their optical interfaces. This maybe done by sliding the firing control unit into a guide channel incorporated in the body of the programming unit.

After the fire control unit is coupled to the programming unit the programming unit ON/OFF switch is turned to the ON position and the control switch is set on the fire control unit to PROGRAM. The device is now ready for delay time entry. Delay time is entered via the keyboard in hours and minutes with the tens of hours digits being entered first followed by hours, tens of minutes, then minutes. The delay time entered is displayed on the programmer display for confirmation of corrections.

Once satisfied that the correct time delay has been entered, the delay time may be loaded to the fire control unit by pressing a selected key such as by pressing the LOAD key twice, whereby on the first press the control processor checks for valid delay times.

If the programme time is valid a message on the display will prompt the second LOAD key action. If this occurs the time delay will be loaded into the fire control unit and a display blinking sequence will take place until time feed back signals are available from the fire control unit. If incorrect action occurs the loading will not take place.

On completion of the blinking sequence the control processor within the programming unit measures the feed-back signals from both intermediate delay channels from the fire control unit to verify the correct delay loading. The checking time is dependent upon the length of the programme delay and may be as long as eight seconds for the twentyfour hour delay time. Both delay channels are checked, and displayed messages confirm the checking process. The first message indicates that delay timer A is being measured, the second indicating that the delay timer B is being measured. When both channels are measured they are compared and the measured delay times, if identical, will be displayed, otherwise an error message is displayed.

The sequence can be varied substantially within the spirit of the invention.

The Power Source 33 supplies regulated 5 V power to the internal circuits of the programming unit from a 9 V battery source.

The Battery Test 34, when activated, tests the battery condition by applying a known battery load. A green indicator lamp will not dim during the test if a good battery is present.

From the foregoing it will be realised that the unit comprises firstly a fire control unit which is set to carry out the required action and is provided with the required safety mechanisms and delays, and secondly a programming unit which programs the fire control unit through an interface requiring no permanent connection to the fire control unit so that such a programming unit can be used to test and arm a number of fire control units.