GB2381126A

GB2381126A - Switch

Info

Publication number: GB2381126A
Application number: GB0124980A
Authority: GB
Inventors: Keith Puddefoot
Original assignee: DEWHURST PLC
Current assignee: DEWHURST PLC
Priority date: 2001-10-17
Filing date: 2001-10-17
Publication date: 2003-04-23
Anticipated expiration: 2021-10-17
Also published as: GB0124980D0; GB2381126B

Abstract

A switch 30 has a switching device 210, an operating member 203 and a support 204. The operating member 203 is moveable relative to the support 204 to operate the switch. The first conductor of the switching device 202 moves relative to the second conductor to an operated position. The switching device 202 is mounted on p.c.b. 205 for pivotal movement with respect to the support 204. A resilient member 208 is provided between the switching device 202 and the support 204 to prevent damage to the device 202 in case of overtravel of the member 203.

Description

SWITCH The present invention relates to a switch and more particularly but not exclusively to a push-button switch.

Mechanically operated switches remain a fundamental component of modem electrical and electronic devices. Such switches normally consist of a switching device mounted with respect to a support, for instance, a casing, and an operating member acting on the switching device to cause contacts to open and close of the switching device.

One well-known type of mechanical switch is the so-called push-button switch.

Push-button switches are used in a wide variety of environments including the domestic environment but also including public spaces. Where a push-button switch is disposed in a public space it may be the subject of abuse, for example caused by people pressing the operating button (otherwise known as the"pressel") with undue force and with resulting overtravel.

Many mechanical switches are mounted on circuit boards for example, printed circuit boards, the circuit board carrying components associated with the switching device. Such components include indicator LEDs, resistors, protection diodes and the like.

Switching devices are of several types. One of these, the microswitch, has been used in many applications. Microswitches are unitary devices normally including a fixed contact and a moving contact together with a spring and operating lever for moving the contact between the open and closed positions. Typically some kind of lost motion arrangement is provided so that overtravel of the operating lever is possible without damage to the contacts. Another type of switching device is the membrane switch which is a type of snap-action switch that requires only a small movement of an operating surface to cause the switch to close (or open), thus making, or respectively breaking, contact between two conductors in the switching device.

Membrane switches used in push-button arrangements have specific problems which require the use of an overtravel protection modification. This is because the contact of the membrane switch may be damaged by high operating forces.

Microswitches may also be subject to damage by high operating forces, and this is true of other types of mechanical switching devices. The problem is at its most significant where there is a mismatch between the desired amount of movement of the operating member, for example the push-button and the amount of movement which the switching device can accept.

It is an object of the present invention to at least partially mitigate some of the known difficulties of the prior art.

According to a first aspect of the present invention there is provided a switch having a switching device, an operating member and a support, the switching device comprising a first conductor and a second conductor, the operating member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support.

By pivotally mounting the switching device with respect to the support and providing an operating member moveable with respect to the support, movement of the operating member is no longer directly coupled to the switching device. Whereas some prior art switches are known in which the switching device is disposed on a resilient pad which is mounted on a portion of the support, such arrangements are disadvantageous, for example in that the switching device can move unpredictably.

Furthermore, by mounting the switching device in a pivotal fashion with respect to the support and by providing a resilient member it is possible to provide embodiments which allow the operating force to be accurately set.

According to a second aspect of the present invention there is provided a switch having a switching device, an operating member and a support, the switching device

comprising a first conductor and a second conductor, the operating member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support, wherein overtravel of the operating member beyond an amount of movement necessary to operate the switch causes the switching device to pivot relative the support against the action of the resilient member.

According to a third aspect of the invention there is provided a switch having a switching device, an operating member and a support, the switching device comprising a first conductor and a second conductor, the operating member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support, wherein movement of the operating member causes the switching device to pivotally move relative to the support against the action of the resilient member until the switch is in the closed position and wherein overtravel of the operating member beyond an amount of movement necessary to operate the switch causes the switching device to further pivot relative the support against the action of the resilient member.

According to a fourth aspect of the invention there is provided a switch having a switching device, an operating member and a support, the switching device comprising a first conductor and a second conductor, the operating member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support, wherein the properties of the resilient member are selected such that no movement of the switching device, or substantially no movement of the switching device, takes place until the switching device has reached the closed position and wherein overtravel of the operating member beyond an amount of movement necessary to operate the switch causes the switching device to pivot relative the support against the action of the resilient member.

Preferably the operated position is the closed position in which the first and second conductors are in contact.

Advantageously the switching device is disposed on a circuit board having circuitry thereon associated with the switching device, and the circuit board has a proximal end region engaging the support and a distal end region supported spaced from a portion of the support via the resilient member.

By disposing the switching device on the circuit board and causing the circuit beard to move to operate the switching device of the switching device, it is possible to adopt any chosen position on the circuit board for the switching device. This is advantageous in that it is possible to leave particular areas of the circuit board free for other components. Such other components could for example be light emitting diodes or other illumination devices for providing illumination of the centre of the pressel or for illuminating the periphery of the pressel as required.

By providing the resilient member at a location remote from the pivot point, a lever is formed and the amount of force and movement can be correctly proportioned with respect to the resilient member.

In one embodiment the resilient member is disposed between the distal end region of the circuit board and the support, and an actuating portion of the switching device is disposed to engage the support upon pivotal movement of the circuit board.

In this arrangement it is possible to have the switching device disposed under the circuit board so that as the circuit board pivots downwardly upon depression of the operating member the actuating part of the switching device comes into abutment with the underlying support or base of the switch. By correctly locating the switching device along the circuit board the relative movement acceptable to the switching device can be proportioned to the amount of movement of the circuit board. The disposition of the switching device beneath the circuit board allows the top surface of the circuit board to be available for other components such as LEDs or other like, without hindrance.

In a preferred embodiment, the operating member includes a resilient member for allowing overtravel of a portion thereof.

Where the switch is a push button device the operating member may consist of an outer pressel separated from an inner operating wall via a spring so that pressing the outer pressel urges the operating wall under the action of the spring. Once the contact member has closed, continued movement of the outer pressel is possible due to the presence of the spring.

In an alternative embodiment overtravel of the operating member beyond a movement needed to cause the switching device IO reach the closed position causes the circuit board to move against the resilient member.

In one embodiment the properties of the resilient member are selected such that no movement of the circuit board, or substantially no movement of the circuit board, takes place until the switching device has reached the closed position. In other embodiments the resilient member is selected to have an increasing degree of resistance so that some movement of the circuit board occurs before the switching device has obtained the closed situation.

In one preferred embodiment the resilient member is disposed between an actuating portion of the switching device and the support.

In another embodiment the actuating member has a portion which engages an actuating portion of the switching device and the resilient member is disposed between the circuit board and the support.

Preferably the support has an engagement portion, and the actuating member abut the engagement portion to prevent damage caused by excessive travel.

In a typical arrangement, the support is a body and the actuating member is a pressel which is spring-biased away from the body. If the body has surfaces against which the actuating member engages, such an arrangement may allow for sufficient

movement to take place to ensure that the contact member reaches the closed position, together with additional movement needed to satisfy the specified amount of movement of the actuating member whilst preventing yet further movement from damaging the switching device itself.

Preferably the resilient member comprises a spring.

Although it is envisaged that the invention could be put into effect using resilient members other than springs, nevertheless springs are preferred. This is because of the predictability of performance of springs under a wide range of operating conditions.

In one embodiment, the switching device comprises a membrane switch. In an alternative embodiment, the switching device comprises a microswitch. Other switching structures are however envisaged.

By provision of the pivot it is possible to connect to the circuit board either on or immediately adjacent to the pivot. The provision of connection locations on the circuit board for wiring at such a disposition is advantageous since only minimal movement takes place at and immediately around the pivot. By comparison with the devices where the switching device is moved in translation, much smaller movement is provided when connections are made in the pivot region and this produces much smaller stresses on the wiring and as a result increases the durability of the switch.

Exemplary embodiments of the invention will now be described with reference to the accompanying drawings in which :- Figure 1 shows a partial cross-section through a first embodiment of a switch in accordance with the present invention; Figure 2 shows the switch of Figure 1 in an operated state; Figure 3 shows the switch of Figure 2 in an overtravel state; Figure 4 shows the switch of Figure 3 in a grounded state;

Figure 5 shows a partial cross-section through a second embodiment of a switch in accordance with the present invention ; Figure 6 shows the switch of Figure 5 in the operated state; Figure 7 shows the switch of Figure 6 in the overtravel state; Figure 8 shows a partial cross-section through a third embodiment of a switch in accordance with the present invention; Figure 9A shows a schematic diagram of a push-to-make switch; Figure 9B shows a schematic diagram of a push-to-break switch.

Figure 10 shows cross section through a spring plunger useable with the invention; and Figure 11 shows a partial perspective view of a circuit board for use with the invention, having a membrane switch.

In the various figures, like reference numerals indicate like parts; Referring to Figure 1, a first switch 30 in accordance with the present invention will be described.

The switch 30 has a switching device 202 shown as a membrane switch, an operating member 203 in the form of a push-button or pressel and a support 204 formed by the switch body. The switching device 202 is mounted on a circuit board 205 which carries circuitry associated with a switch shown here as LED 206. A LED may be used, for example, for providing confirmation that the switch has been activated. The switching device 202 is disposed on the upper surface of the circuit board 205 and is of the type shown in Figure 9A (described later herein). A spring 208 engages one end of the circuit board 205 whereas the other end of the circuit board is supported by a portion

207 of the switch body 204. The push-button or pressel 203 may be retained in the position shown in Figure 1 by springs, as known in the art, but not shown in Figure 1.

The pressel is in this embodiment generally circular and has a downwardly extending operating portion 209 so that in cross-section the pressel resembles a letter"T". The switching device has an operating surface 210 which projects upwardly towards the underside of the operating portion 209. Alternatively the pressel may be resting on the operating part 210 of the switching device 202.

Wiring 213 for the board 205 is connected at connection locations 212 at or immediately adjacent the pivot region 202. This gives a minimal stress impact on the wiring.

Referring now to Figure 2, the pressel is movable under hand or finger pressure inwardly of the body 204 so that the operating portion 209 contacts the operating surface 210 of the membrane switch 202. Figure 2 shows the situation after this contact has taken place and after the sufficient additional movement of the pressel has taken place to operate the membrane switch 202. This additional movement is typically around 1 millimetre. Figure 2 shows the situation where the spring 208 remains in its normal position, in other words the position before the circuit board 205 has moved from the rest position.

This is because the spring 208 is selected to have a restoring force which is greater than the operating force of the membrane switch 202. It would of course be possible to select a spring 208 having lesser force such that compression of the spring by an appreciable amount takes place while the operation of the membrane switch is taking place.

Referring to Figure 3 it will be seen that the pressel 203 has moved further inwardly of the switch body 204 in to an overtravel situation in which it is substantially beyond the position necessary to operate the switching device 202.

In this situation the circuit board 205 pivots against the force of spring 208, the reverse force of the spring 208 being selected to not allow damage to be caused to the switching device 202.

Referring to Figure 4 it will be seen that the edges of the pressel 202 engage with inwardly-directed projections 214 of the switch body 204 to prevent further inward motion taking place.

This switch therefore allows for a selected amount of overtravel of the pressel followed by a secure"grounding"of the pressel on the switch body thus preventing any possibility of damage to the switching device due to overforce or overtravel.

Referring now to Figure 5, a switch 1 has a switching device 2 shown as a membrane switch, an operating member 3 in the form of a push button and a support 4, in this embodiment the switch body.

Although the switching device is shown as a membrane switch other types of switch device are possible, for example a microswitch. In this embodiment the switch is of a type shown in Figure 9A.

Referring now to Figure 9A, a push-to-make switch 100 has a moving contact 101 which is maintained spaced from a normally open contact 102 by a spring 103. When a force shown figuratively by arrow 104 is exerted sufficient to overcome the force of the spring 103 moving contact or wiper 101 moves to contact the normally open contact 102 so closing the switch. Examples of switches which are suitable for push-to-make operation are membrane switches and microswitches.

Returning now to Figure 5, the switching device 2 is mounted on a circuit board 5 which in the embodiment also includes circuitry associated with the switch, for example an LED 6 disposed on an upper, as shown, surface of the circuit board 5. The switching device 2 is disposed on the lower surface, as shown, of the circuit board 5. A portion 7 of the switch body 4 engages the circuit board 5, at a proximal region of the board, allowing pivotal movement of the circuit board 5 with respect to the switch body 4. The operating button 3, otherwise known as a pressel has a downwardly-extending resilient member, here spring 9, which, as shown in Figure 5 is slightly spaced above the upper, as shown, surface of the circuit board 5. The pressel 3 may be retained in this position by springs, as known in the art, but not shown in Figure 5. A distal region of the board 5 contacts a

second resilient member 11 in the form of a coil spring, and the other end of the coil spring 11 abuts a part of the switch body 4. An operating surface 10 of the switching device 2 is spaced from a projecting part 8 of the switch body 4.

Referring now to Figure 6, the switch 1 of Figure 5 is shown being subject to a force 20 exerted downwardly, as shown, on the pressel 3. It will be seen that the pressel 3 has moved downwardly and the spring 9 has engaged the circuit board 5 causing it to pivot about the engagement region 7 against the upwards force of the second spring 11.

In this embodiment the resilience of the second spring 11 is selected to be greater than the force of the spring 103 (see Figure 9A) so that the movement of the circuit board 5 under the action of the pressel 3 causes the contact of the contact member to close by virtue of contact of the operating surface 10 with the projecting part 8.

Referring now to Figure 7, it will be seen that the pressel 3 has moved further down into the switch and that the outer extremity of the pressel 3 has engaged with the upper surface of ribs 15,16 of the switch body 4. No additional pivoting takes place due to the projection 8.

It will be understood by those skilled in the art that the switch 1 allows for normal operation of the switching device 2, where normal operation is that which is necessary to close the contacts of the switching device. This situation is shown in Figure 6. The switch 1 further allows for overtravel of the pressel 3 without any damage to the switching device 2 since the switching device 2 has its operating member 10 decoupled from the switch body via the second spring 11. Finally, if excessive force or movement is applied to the pressel 3 the pressel itself"grounds"on the ribs 15 of the switch body so that further movement of the circuit board is prevented thus obviating damage to the switching components.

In an alternative embodiment the pressel 3 is supported with respect to the switch body by the springs 11,15, there being no other pressel return springs. In another embodiment, the projecting part 8 and spring 11 are replaced by a spring disposed between the body and the operating surface 10.

The LED 6 is an exemplary component on the circuit board 5. Additional or other components are also envisaged. Where an LED is provided it may be actuated in response to closure of the switch. If the pressel is translucent the operation of the LED will be apparent to the switch user. Likewise, where a transparent region surrounds the pressel the actuation of the LED will be apparent to the user.

Referring now to Figure 8, a third switch 30 will now be described.

Referring to Figure 8 it will be seen that the switch 30 has a pivotable circuit board 5 engaging an engagement region 7 of a switch body 4 at a proximal region thereof.

A distal region of the circuit board is supported by a resilient member such as first spring 8. Pressel 13 engages the circuit board 5. In the switch 30 shown in Figure 8 a switching device 22 is disposed on the upper, as shown, surface of the circuit board 5. The switching device 22 comprises a switch of the type shown in Figure 9B.

Referring now to Figure 9B a switch 200 is of the push-to-break type. The switch 200 has a wiper or moving contact 201 which is connected to a normally closed contact 202. The contact is biased to the normally closed position via a spring 203 and the application of a force figuratively shown as 204 causes the wiper to move to the normally open position, thus opening the switch.

Referring again to Figure 8 the force exerted by the first spring 8 maintains the pressel 13 of the switching device 22 urged against a projecting portion 24 of the switch body 4 until the pressel moves the board 5 about its first pivot engagement region 7.

In this embodiment the force of the spring 8 is sufficient to overcome the force of spring 203 (Figure 9B) so that in the rest position of the switch the contacts are open.

It will be clear to those skilled in the art that downward movement causes the circuit board 5 to pivot about the engagement region 7 against the force of the spring 8 such that the internal spring 203 of the switch causes the contacts to close.

Also shown in Figure 8 are electrical wire connections 25 which in this case are made to the circuit board 5 in the region immediately adjacent to the engagement region

7. It would be clear to those skilled in the art that this is a position of near-minimum movement of the circuit board 5. This has the consequence that the amount of stress applied to the joint between the wires 25 and the circuit board is very low.

Although the embodiments of Figure 1 and Figure 8 have been described as having respectively push-to-make and push-to-break switches respectively it will of course be clear to those skilled in the art that other types of switches could be used. For example the embodiment of Figure 1 could use a push-to-break switch, or a changeover switch. Likewise, the embodiment of Figure 5 could use a push-to-make or changeover switch.

Referring now to Figure 10, a sprung operating member is shown. The sprung operating member 60 of Figure 10 consists of a first cup-shaped member 61 and a second cup-shaped member 62. Each of the cup members is a generally circular-cylindrical member having an end wall closing a side wall at one end thereof. The side wall of the second cup member 62, lower as shown in Figure 10, defines a space somewhat wider than that defined by the wall of the first cup member 61. The two cup members are disposed facing one another with the wall of the first cup member 61 partially housed within the wall of the second cup member 62 and a spring, for example a coil spring 63 extends between the base walls of the two cup members. The arrangement forms a telescopic plunger so that force on the base wall of one of the cup members is transmitted via the resilience of the spring 63 to the other cup member. Such an arrangement may be used with any of the switches of the invention.

Referring now to Figure 11, a perspective view of a circuit board assembly 70 is shown.

Referring to Figure 11 the circuit board assembly 70 has a circuit board 5 for example of plastics or glass fibre material. The circuit board 5 is generally planar and has a generally rectangular first portion 71. A tab portion 72 projects in the plane of the first portion 71 from one side thereof, the tab portion being of lesser extent than the wall and disposed symmetrically along it. Four contact pins 74 project from the plane of the circuit board 5 within the tab portion 72. A membrane switch 73 is disposed opposite the tab portion. The switch has an operating surface in the form of a projecting button 75

which may be formed as a plastics or metal dome or may be a projecting armature.

Alternatively a flat membrane device may be used, in which case a projection from the pressel may be provided. In a preferred embodiment the switch is of the magnetically retained armature type, an example of which is the switch manufactured by DuraSwitch and disclosed in US Patent Number 5523730.

Embodiments of the invention have now been described. It will be understood that these are not to included to be restrictive but instead to be descriptive. The invention is intended to extend to the full scope of the appended claims.

Claims

Claims

1. A switch having a switching device, an operating member and a support, the switching device comprising a first conductor and a second conductor, the operating member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support.

2. A switch having a switching device, an operating member and a support, the switching device comprising a first conductor and a second conductor, the operating member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support, wherein overtravel of the operating member beyond an amount of movement necessary to operate the switch causes the switching device to pivot relative the support against the action of the resilient member.

3 A switch having a switching device, an operating member and a support, the switching device comprising a first conductor and a second conductor, the operating member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support, wherein movement of the operating member causes the switching device to pivotally move relative to the support against the action of the resilient member until the switch is in the closed position and wherein overtravel of the operating member beyond an amount of movement necessary to operate the switch causes the switching device to further pivot relative the support against the action of the resilient member.

4. A switch having a switching device, an operating member and a support, the switching device comprising a first conductor and a second conductor, the operating

<Desc/Clms Page number 15>

member being movable relative to the support to operate the switch whereby the first conductor moves relative to the second conductor to an operated position, wherein the switching device is mounted pivotally for pivotal movement with respect to the support and a resilient member is provided between the switching device and the support, wherein the properties of the resilient member are selected such that no movement of the switching device, or substantially no movement of the switching device, takes place until the switching device has reached the closed position and wherein overtravel of the operating member beyond an amount of movement necessary to operate the switch causes the switching device to pivot relative the support against the action of the resilient member.

5. A switch as claimed in any of Claims 1 to 4, wherein the operated position is the closed position in which the first and second conductors are in contact.

6. A switch as claimed in any preceding claim, wherein the switching device is disposed on a circuit board having circuitry thereon associated with the switching device, and the circuit board has a proximal end region engaging the support and a distal end region supported spaced from a portion of the support via the resilient member.

7 A switch as claimed in any preceding claim, wherein the resilient member is disposed between the distal end region of the circuit board and the support, and an actuating portion of the switching device is disposed to engage the support upon pivotal movement of the circuit board.

8. A switch as claimed in any preceding claim, wherein the operating member includes a resilient member for allowing overtravel of a portion thereof.

9. A switch as claimed in Claim 8, wherein the switch is a push button device and operating member comprises an outer pressel separated from an inner operating wall via a spring so that pressing the outer pressel urges the operating wall under the action of the spring.

<Desc/Clms Page number 16>

10. A switch as claimed in Claim 9, wherein the properties of the resilient member are selected to have an increasing degree of resistance so that some movement of the circuit board occurs before the switching device has obtained the closed situation.

11. A switch as claimed in any preceding claim, wherein the resilient member is disposed between an actuating portion of the switching device and the support.

12. A switch as claimed in any of Claims 1 to 11, wherein the actuating member has a portion which engages an actuating portion of the switching device and the resilient member is disposed between the circuit board and the support.

13. A switch as claimed in any preceding claim, wherein the support has an engagement portion, and the actuating member abuts the engagement portion to prevent damage caused by excessive travel.

14. A switch as claimed in Claim 13, wherein the support is a body and the actuating member is a pressel which is spring-biased away from the body.

15. A switch as claimed in any preceding claim, wherein the resilient member comprises a spring.

16. A switch as claimed in any preceding claim, wherein the switching device comprises a membrane switch.

17. A switch as claimed in any of Claims 1 to 15, wherein the switching device comprises a microswitch.

19. A switch as claimed in Claim 6 or any claim dependent on Claim 6, and further comprising connection locations on the circuit board for securing wiring thereto, such locations being disposed in the proximal region of the circuit board.

20. A switch constructed and arranged substantially as herein described with reference to or as illustrated in Figures 1 to 4,5 to 7 or 8 of the accompanying drawings.