EP4617617A1

EP4617617A1 - Switch, electronic safe and arm unit, fuze system, munition and method

Info

Publication number: EP4617617A1
Application number: EP24275026.3A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: BAE Systems PLC
Current assignee: BAE Systems PLC
Priority date: 2024-03-15
Filing date: 2024-03-15
Publication date: 2025-09-17

Abstract

According to the present disclosure there is provided a switch for controlling provision of an electrical signal to control electronics of a munition, the switch comprising: a flexure member in the form of a flexible circuit board, the flexure member configured to deflect due to acceleration of the switch, wherein, in use, deflection of the flexure member is used to change a switch state of the switch.

Description

FIELD

The present invention relates to a switch, in particular to a switch for controlling provision of an electrical signal to control electronics of a munition. The present invention further relates to an electronic safe and arm unit (ESAU), a fuze system, a munition, and a method.

BACKGROUND

Munitions are provided in a number of different forms, for a number of different applications. Typically, a particular munition will be used for a particular application or intention. For the purposes of this patent application, munitions are taken to include but are not limited to artillery shells and charges, missiles, rockets, and mortar rounds, as well as small arms munitions such as bullets.
Munitions comprise electronic control devices for controlling and/or monitoring operation of the munition. An electronic safe and arm unit (ESAU) is an electronic control device utilised in munitions to prevent inadvertent or accidental detonation of explosive material within the munitions during routine handling or in the launcher, as well as during the initial flight. The ESAU is typically part of a munition fuze system and prevents arming of the fuze until certain conditions are met, such as a determination of launch of the munition.
The munition fuze system includes a switch to provide an electrical signal for control of munition operation. The switch may be incorporated in the ESAU, to provide an electrical signal to activate power supply to the ESAU when the condition is met. In this way, the ESAU is not provided with electrical power to allow arming thereof until the condition is met. In this way, the risk of inadvertent or accidental detonation can be mitigated. Conventional fuzes use mechanical acceleration switches, which are typically bespoke (i.e., designed for a particular munition or type thereof), require manual assembly, and are complex in their construction. Furthermore, such switches may be expensive to manufacture.

SUMMARY

According to a first aspect of the present invention, there is provided a switch for controlling provision of an electrical signal to control electronics of a munition, the switch comprising: a flexure member in the form of a flexible circuit board, the flexure member configured to deflect due to acceleration of the switch, wherein, in use, deflection of the flexure member is used to change a switch state of the switch.
In one example, the flexure member is connected to, or is mounted on, a substrate circuit board.
In one example, the flexure member is connected to, or is mounted on, the substrate circuit board by one or more spacers, optionally wherein the one or more spacers are one or more circuit boards.
In one example, the one or more spacers are connected to the substrate circuit board by electrically conductive elements.
In one example, a mass member arrangement is provided on or in the flexure member, wherein the mass member arrangement comprises one or more mass members formed of electrically conductive material and arranged to contact a corresponding conductive pad of a conductive pad arrangement during deflection of the flexure member.
In one example, the mass member arrangement comprises a plurality of mass members, wherein a first mass member is arranged to contact the corresponding conductive pad during deflection of the flexure member above a first threshold acceleration of the switch, and a second mass member is arranged to contact the corresponding conductive pad during deflection of the flexure member above a second threshold acceleration of the switch, wherein the first threshold acceleration and second threshold acceleration are different.
In one example, the flexure member comprises one or more curved arms.
In one example, the flexure member has the form of a flat spiral or has a helical form.
In one example, the flexure member comprises one or more breakable elements configured to break above a threshold acceleration.
In one example, one or more of the one or more breakable elements comprises a conducting part.
In one example, the switch comprises a cover. The cover may be configured to cover a part or all of the flexure member.
According to a second aspect of the invention, there is provided an electronic safe and arm unit, ESAU, comprising the switch according to the first aspect.
According to a third aspect of the invention, there is provided a fuze system comprising the switch according to the first aspect or the ESAU according to the second aspect.
In one example, the fuze system comprises a power source in the form of a battery.
According to a fourth aspect of the present invention, there is provided a munition comprising the switch according to the first aspect, the ESAU according to the second aspect, or the fuze system according to the third aspect.
According to a fifth aspect of the present invention, there is provided a method of assembling a switch for controlling provision of an electrical signal to control electronics of a munition, comprising: providing a flexure member in the form of a flexible circuit board, the flexure member configured to deflect due to acceleration of the switch, wherein, in use, deflection of the flexure member is used to change a switch state of the switch.
In one example, the method comprises providing a mass member arrangement on or in the flexure member by wave soldering one or more mass members.
According to a further aspect of the present invention, there is provided a method of a switch for controlling provision of an electrical signal to control electronics of a munition, comprising: providing a flexure member in the form of a flexible circuit board, the flexure member configured to deflect due to acceleration of the switch; subjecting the flexure member to an acceleration to cause deflection of the flexure member; and using the deflection of the flexure member to change a switch state of the switch.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will now be described by way of example only with reference to the figures, in which:

Figure 1 shows a side cross sectional view of a switch
Figure 2 shows a side cross sectional view of a part of a switch; and
Figure 3 shows a perspective view of a flexure member comprising one or more curved arms;
Figure 4 shows a plan view of a part of a flexure member comprising a breakable element;
Figure 5 shows a schematic electronic safe and arm unit;
Figure 6 shows a schematic fuze system;
Figure 7 shows a schematic munition; and
Figure 8 shows general methodology principles.

DETAILED DESCRIPTION

In overview, a switch is described for controlling provision of an electrical signal to control electronics of a munition. In this way, the provision of an electrical signal to control electronics can be controlled to prevent arming of the munition prior to launch of the munition. Thus, the risk of inadvertent or accidental detonation can be mitigated. The described switch is simple in construction (at least compared with prior art approaches). Furthermore, the described switch can be formed having a small profile, enabling incorporation in small munitions or those having limited internal space. Furthermore, the described switch makes use of a simple switching mechanism and does not require electrical power to operate.
Referring to Figure 1, a switch 100 is shown. The switch 100 is for controlling provision of an electrical signal to control electronics of a munition 700 (shown in Figure 7).
The switch 100 comprises a flexure member 110. The flexure member 110 is in the form of a flexible member, medium, element or substrate on which one or more electrical component are mountable, to form an electrical connection therewith. Preferably, the flexure member 110 is in the form of a flexible circuit board.
In some examples, the flexure member 110 may form at least a part (e.g., an integral part) of a primary circuit board, and the flexure member 110 may be a flexible region or member integrally formed from the primary circuit board. The primary circuit board from which the flexure member 110 is formed may also comprise a non-flexible (i.e., rigid) region or portion.
The flexible circuit board (i.e., the flexure member 110, or, in the example mentioned above, the part of the primary circuit board which provides the flexure member 110) may be a flexible printed circuit (FPC), or other flexible circuit board. For example, the flexure member may be formed of copper conducting tracks set within a suitable substrate, such as polyimide. The suitable substrate may be a flexible substrate, e.g., configured to flex to provide the functionality as described herein. The flexible circuit board may be formed from a glass-reinforced epoxy laminate material, such as flexible FR-4 glass epoxy. A further example may be a flexible aluminium circuit board.
The flexure member 110 is configured to deflect due to acceleration of the switch 100. In other words, acceleration of the switch 100 causes deflection, or a displacement, of the or a part of the flexure member 110.
In use, deflection of the flexure member 110 is used to change a switch state of the switch 100. The switch state of the switch 100 may change from an open state to a closed state due to deflection of the flexure member 110.
By this construction, a switch 100 is provided in which electronic components can be installed or mounted directly on the flexure member 110, or as part of the same circuit board from which the flexure member 110 is formed, thereby providing a switch 100 having a reduced number of parts compared with conventional switches. The supply chain for components of the switch 100 is thereby considerably simplified with respect to conventional electromechanical switches. Furthermore, the switch 100 can be built into (i.e., integral in) electronic circuitry of an electronic safe and arm unit (ESAU) or fuze system. Electronic components are mountable on the circuit board, providing a more compact arrangement. Additionally, by this construction, the switch 100 is more readily suitable for automated manufacture using existing large scale assembly techniques, in particular using surface-mount techniques (including pick-and-place and reflow techniques), as will be appreciated from the description herein. High precision manufacture is facilitated, with wider availability.
It will be appreciated that acceleration of the switch 100 which causes deflection of the flexure member 110 will depend on the orientation in which the switch 100 is provided in the munition. A longitudinal axis of the munition 700 may correspond with an intended travel direction of the munition 700, and in some examples, the munition may spin or rotate about the longitudinal axis. The switch 100, and in particular the flexure member 110, may be mounted perpendicular to the longitudinal axis - in this way, the switch 100 may be employed to detect longitudinal acceleration of the munition. That is, the flexure member 110 may be caused to deflect in a direction parallel to the longitudinal axis of the munition due to launch of the munition (which may be known as a "set-back" force, or "gun-launch set back force") or due to impact at a target. In another example, the switch 100, in particular the flexure member 110, may be mounted parallel to the longitudinal axis - in this way, the switch 100 may be employed to detect centrifugal acceleration or force caused by rotation of the switch 100. That is, the flexure member 110 may be caused to deflect outwardly in a direction orthogonal to the longitudinal axis of the munition due to rotation thereof.
Components of the switch 100 will now be described in greater detail.
The switch 100 comprises a supporting member 120 to which the flexure member 110 is to be connected to or mounted on. The supporting member 120 may be known as a substrate. The supporting member, or substrate, may be rigid, or relatively more rigid in contrast with the flexibility of the flexure member 110. In a preferred example, the supporting member 120 is a substrate circuit board 120. Most preferably, the substrate circuit board 120 is a substrate PCB, although it will be appreciated that other circuit board types may be employed. The flexure member 110 is connected to, or is mounted on, the substrate circuit board 120. The substrate circuit board 120 may be a rigid circuit board.
In an example, the flexure member 110 may be directly connected to, or mounted on, the substrate circuit board 120, for example by virtue of integral protrusions from the flexure member 110 or the substrate circuit board 120. In another example, the flexure member 110 may be indirectly connected to, or mounted on the substrate circuit board 120, for example by virtue of spacers.
In the illustrated example, the flexure member 110 is connected to the substrate circuit board 120 by being mounted on the substrate circuit board 120 by one or more spacers 130. The spacers 130 provide for spacing between the flexure member 110 and substrate circuit board 120 in which deflection of the flexure member 110 into the spacing can occur. In an example, spacer 130 may have the form of an annular ring (for example, as illustrated in Figure 3).
Advantageously, mounting the flexure member 110 to the substrate circuit board 120 provides for ease of handling.
The one or more spacers 130 may be, or may be formed of, one or more circuit boards or circuit board material. For example, the spacers 130 may be formed from the same material as the substrate circuit board 120. In this way, electrical connection can be formed between flexure member 110 and substrate circuit board 120.
The one or more spacers 130 are connected, at a first end, to the flexure member 110. An adhesive may be used to connect each spacer 130 to the flexure member 110 at the first end.
The one or more spacers 130 are connected, at a second end opposite the first end, to the substrate circuit board 120 by electrically conductive elements 140. The electrically conductive elements 140 may be Surface Mount Device (SMD) pads. An SMD pad is an area of electrical conductor used to attach electrical components to a circuit board. The electrically conductive elements 140 facilitate mounting of the flexure member 110 and spacers 130 to the substrate circuit board 120. Further advantageously, the elements 140 may prevent ingress of potting compound into the switch 100 or components thereof.
The switch 100 may comprise one or more electrical vias 142. The one or more electrical vias 142 provide electrical connection between the flexure member 110 and the supporting member 120, particularly where the supporting member 120 is a substrate circuit board 120.
The switch 100 further comprises a mass member arrangement 150. The mass member arrangement 150 may be provided on or in the flexure member 110. The mass member arrangement 150 being provided on the flexure member 110 may mean that mass members thereof are deposited, disposed on a surface of the flexure member - in some examples, may be separately formed and subsequently provided. The mass member arrangement 150 being provided in the flexure member 110 may mean that mass members thereof are formed integrally with the flexure member 110, or may be embedded therein.
The mass member arrangement 150 comprises one or more mass members 152. The one or more mass members 152 may otherwise be known as one or more "seismic masses" or "reaction masses". The one or more mass members 152 are formed of electrically conductive material. In one example, the one or mass members 152 are swaged mass members, and are embedded in the flexure member 152. In another example, one or more mass members 152 may be installed on the flexure member 110 by Surface Mounting Device circuit assembly techniques. The one or more mass members 152 may be formed from solder applied to the flexure member 110. In an advantageous manufacturing technique, wave soldering may be used, which is a time efficient process.
The one or more mass members 152 are arranged to contact one or more conductive pads of a conductive pad arrangement 160 during deflection of the flexure member 110. That is, during deflection of the flexure member 110 for example due to longitudinal acceleration of the switch 100 the flexure member 110 will deflect resulting in contact of the one or more mass members 152 with one or more conductive pads of the conductive pad arrangement 160. The mass members 152 and conductive pads may be provided in a corresponding arrangement, such that a first mass member is arranged to contact a first conductive pad, a second mass member is arranged to contact a second conductive pad, and so on.
The switch 100 may comprise the conductive pad arrangement 160 and one or more conductive pads 162. In Figure 1, an example is illustrated wherein the switch 100 comprises one mass member 152 and one conductive pad 162. In Figure 2, an alternative example of the switch 100 is illustrated wherein the switch 100 comprises a plurality of mass members 152, specifically a first mass member 152a and a second mass member 152b, and a plurality of conductive pads 162, specifically a first conductive pad 162a and a second conductive pad 162b. In the example illustrated in Figure 2, the first mass member 152a is arranged to contact the first conductive pad 162a during, or due to, deflection of the flexure member 110 above a first threshold acceleration of the switch 100, and the second mass member 152b is arranged to contact the second conductive pad 162b during, or due to, deflection of the flexure member 110 above a second threshold acceleration of the switch 100. The first threshold acceleration and second threshold acceleration are different, in particular, the second threshold acceleration is greater than the first threshold acceleration. In this way, the switch 100 may enable the level of acceleration to be determined, possibly for provision of such data to a control system, such as that of the ESAU or fuze system.
In general, contact of the one or more mass members 152 with the one or more conductive pads 162 results in, or enables determination of, a change in the switch state. That is, contact of the mass member 152 with conductive pad 162 (and/or contact of member 152a with pad 162a and/or contact of member 152b with pad 162b) forms a closed circuit thereby providing an indication of a change in switch state. In this way, it may be determined that an acceleration event at or greater than a threshold level required to cause the necessary deflection of the flexure member 110 has occurred or is occurring.
Whilst in the illustrated example a contact arrangement is shown (comprising a mass member arrangement 150 and conductive pad arrangement 160 configured to come into contact), alternative mechanisms for changing the switch state may be employed. For example, an accelerometer provided on the flexure member 110 may provide an output signal to change the switch state, where the acceleration detected by the accelerometer exceeds a threshold level. In a further alternative example, a second order lever may be employed for changing the switch state due to deflection of the flexure member 110.
Referring to Figure 3, a perspective view of the flexure member 110 of the switch 100 is shown. As shown, the flexure member 110 comprises one or more curved arms 111. In the illustrated example, a curved arm 111 is curved from a point of connection with spacer 130 (in this example, an annular spacer 130) to a point of connection with the mass member 152. The flexure member 110 may comprise a plurality of curved arms 111, together providing a flexure member 110 having a spiral form. Curved arms are highly advantageous in resisting rotational spin forces, which is particularly beneficial where the switch 100 is mounted such that the flexure member 110 is perpendicular to the longitudinal axis of the munition, or to the munition travel direction, and the switch 100 is configured to detect longitudinal forces such as setback force or force on impact.
In an example, as shown in Figure 3, the flexure member 110 has the form of a flat spiral, which may be referred to as a flat spiral spring or planar spiral spring. A spiral or form is highly advantageous in resisting rotational spin forces, which is particularly beneficial where the switch 100 is mounted such that the flexure member 110 is perpendicular to the longitudinal axis of the munition, or to the munition travel direction, and the switch 100 is configured to detect longitudinal forces such as setback force or force on impact. In other examples, the flexure member 110 may have the form of a helical spring. Such a construction may facilitate variation in level of acceleration required to change a switch state of the switch 100. One of the mass members 152 may be provided at the centre of the flat spiral or helical spring. This is advantageous as the centre is configured to undergo maximal deflection due to acceleration forces.
Referring to Figure 4, the flexure member 110 comprises one or more breakable elements configured to break above a threshold acceleration. A breakable element 112 is illustrated in Figure 4 as a region of the flexure member 110. A breakable element 112 may be a region of a spiral or helical flexure member. The breakable element 112 may be a thinning or narrowing of a part of the flexure member 110, or an otherwise weakened part or region of the flexure member 110. For example, in Figure 3, the breakable element 112 may be provided by the narrower part of the flexure member 110 proximal to the mass member 152. Above a threshold acceleration, force on the breakable element may cause it to permanently break or separate, thereby resulting in complete or partial termination of function of the flexure member 110. Advantageously, non-linear or "one-time" behaviour is provided for, thereby ensuring safety criticality. The flexure member 110 may comprise a plurality of breakable elements 112 each configured to break above a different threshold acceleration. Further advantageously, by the present construction, the threshold level of acceleration is highly controllable.
One or more of the one or more breakable elements 112 may comprise a conducting part 114. The conducting part 114 may be a layer of conducting material, for example copper, provided in the region of the breakable element 112 which is intended to break. Advantageously, in this way, the conducting part 114 can be connected to control circuitry and by monitoring or interrogation thereof, acceleration above a threshold level can be established based on a determination that the circuit is broken due to breaking of the breakable element 112 and conducting part 114 provided thereon. Further advantageously, additional data channels are provided for monitoring operating parameters of the munition, for example multiple acceleration levels thereof. Additionally, and also advantageously, the breakable elements 112 may be interrogated at a suitable time following an acceleration event and still provide an indication that an acceleration above a threshold level has occurred, which is beneficial where electrical power is not available at the time of sensing but is subsequently available, for example following launch (e.g., after setback acceleration) of the munition 700.
Referring back to Figure 1, the switch 100 may further comprise a cover 170. The cover 170 may otherwise be known as a cap, or capping layer. The cover 170 overlays the flexure member 110. The cover 170 may be in the form of a circuit board, such as a PCB. Nevertheless, it will be appreciated that the cover 170 may be formed from any suitable material. Advantageously, the cover 170 prevents ingress of contaminants into the switch 100.
Referring to Figure 5, an electronic safe and arm unit 500 (ESAU) is schematically shown. The ESAU 500 comprises the switch 100. The ESAU 500 may comprise any or all of the features of the above-described switch 100.
Referring to Figure 6, a fuze system 600 is schematically shown. The fuze system 600 comprises the switch 100 or the ESAU 500. The fuze system 600 may comprise any or all of the features of the above-described switch 100 or ESAU 500. The fuze system 600 may further comprise a power source 610. In this example, the power source 610 is a battery. This is highly advantageous, as the battery (such as a Li-Ion battery) can replace conventional energisers.
Referring to Figure 7, a munition 700 is schematically shown. The munition 700 comprises the switch 100 or the ESAU 500 or the fuze system 600. The munition 700 may comprise any or all of the features of the above-described switch 100 or ESAU 500 or fuze system 600.
Referring to Figure 8, method of assembling a switch for controlling provision of an electrical signal to control electronics of a munition is schematically shown. Step S810 comprises providing a flexure member in the form of a flexible circuit board, the flexure member configured to deflect due to acceleration of the switch, wherein, in use, deflection of the flexure member is used to change a switch state of the switch. Optional step S820 comprises providing a mass member arrangement on or in the flexure member by wave soldering one or more mass members. Wave soldering is a highly time efficient process for providing mass members.

Claims

A switch for controlling provision of an electrical signal to control electronics of a munition, the switch comprising:
a flexure member in the form of a flexible circuit board, the flexure member configured to deflect due to acceleration of the switch,

wherein, in use, deflection of the flexure member is used to change a switch state of the switch.
The switch according to claim 1, wherein the flexure member is connected to, or is mounted on, a substrate circuit board.
The switch according to claim 2, wherein the flexure member is connected to, or is mounted on, the substrate circuit board by one or more spacers.
The switch according to claim 3, wherein the one or more spacers are connected to the substrate circuit board by electrically conductive elements.
The switch according to any one of the preceding claims, wherein a mass member arrangement is provided on or in the flexure member, wherein the mass member arrangement comprises one or more mass members formed of electrically conductive material and arranged to contact a corresponding conductive pad of a conductive pad arrangement during deflection of the flexure member.
The switch according to claim 5, wherein the mass member arrangement comprises a plurality of mass members, wherein a first mass member is arranged to contact the corresponding conductive pad during deflection of the flexure member above a first threshold acceleration of the switch, and a second mass member is arranged to contact the corresponding conductive pad during deflection of the flexure member above a second threshold acceleration of the switch, wherein the first threshold acceleration and second threshold acceleration are different.
The switch according to any one of the preceding claims, wherein the flexure member comprises one or more curved arms, optionally wherein the flexure member has the form of a flat spiral or has a helical form.
The switch according to any one of the preceding claims, wherein the flexure member comprises one or more breakable elements configured to break above a threshold acceleration.
The switch according to claim 8, wherein one or more of the one or more breakable elements comprises a conducting part.
The switch according to any one of the preceding claims, comprising a cover.
An electronic safe and arm unit, ESAU, comprising the switch according to any one of the preceding claims.
A fuze system comprising the switch according to any one of claims 1 to 10 or the ESAU according to claim 11.
A munition comprising the switch according to any one of claims 1 to 10 or the ESAU according to claim 11 or the fuze system according to claim 12.
A method of assembling a switch for controlling provision of an electrical signal to control electronics of a munition, comprising:
providing a flexure member in the form of a flexible circuit board, the flexure member configured to deflect due to acceleration of the switch,

wherein, in use, deflection of the flexure member is used to change a switch state of the switch.
The method according to claim 14, comprising:
providing a mass member arrangement on or in the flexure member by wave soldering one or more mass members.