Electrically driven alarm bell

Abstract

 This invention relates to an electrically driven bell and provides an improved rotary bell whereby selecting the position of the striker assembly within the gong off-set from the centre thereof in accordance with a particular geometrical relationship, the impact of the striker assembly can be much reduced having regard to the size of the impact associated with a similar size gong and a striker assembly as centrally mounted as hitherto proposed.

Description

[0001] The present invention relates to an electrically driven alarm bell.

[0002] Electrically driven alarm bells are well known and have been known in the art for well over 50 years.

[0003] An early example of an electrically driven alarm bell is to be seen in British Patent Specification No. 109,889 which discloses a bell having a gong, a motor having a central armature generally concentric with said gong and adapted to rotate a striker bar carrying strikers which are enabled to float on their mountings. On activation of the alarm bell, the armature is caused to rotate and the strikers swing outwardly under their centrifical force to the limit of their ability to impact upon a projection on the gong thus sounding the alarm.

[0004] Bells of this type are generally very well known and have been used for many years.

[0005] With the advant, however, of modern micro processor control systems, it has become important not only to have a rotary bell that simply rings, but to have a rotary bell that has a minimum performance specification, i.e. that there is a minimum number of strikes per second or per minute for the bell. It will be appreciated, therefore, that with the construction of British Patent Specification No. 109,889, a minimum requirement of say 3,000 strikes per minute will require a rate of rotation of the armature of 1,500 rpm to allow two strikes each to strike once during one revolution. While this is technically possible it will be appreciated that with a gong of acceptable size the centrifugal force due to the radial extent of the strikers, and the kinetic energy due to the circumferential velocity will both be high and in consequence the impact of each striker on the gong itself will be large with a consequential reaction on the armature of the motor. This results in the need for a motor of a construction heavy enough to withstand these operating loads.

[0006] Reducing the size of the gong will tend to result in an increase in the pitch of the note when the gong is truck, but at the same time, it will be accompanied by a reduction in the loads acting upon the motor during operation.

[0007] However, to reduce the impact of the strikers on the gong to an acceptable level, the pitch of the gong must be increased to an unacceptably high level.

[0008] To overcome this problem, therefore, bell manufacturers have sought to deal with the problem by resorting to a plunger striker for the gong.

[0009] British Patent Specification No. 1,600,808 describes and claims an electric bell comprising a bell body, a driving electric motor having a rotor, a piston plate fitted to oscilate between first and second end positions, said piston plate being drivingly connected to said motor whereby rotation of the motor is directly and continuously converted to oscilation of the plate, a reciprocally mounted hammer adapted to strike the bell body, at least one spring serving to drivingly couple the piston plate to the hammer whereby the hammer is driven in at least one direction under the resilience of the spring.

[0010] The mechanism whereby rotary motion is converted to reciprocating motion for a striker clearly results in some loss of efficiency.

[0011] It is desirable therefore to provide a light weight, electrically driven, bell; having a rotary striker assembly whereby force of the impact of the striker on the bell is reduced to an acceptable loading level on the bearing assembly on the motor employed.

[0012] According to the present invention, there is provided an alarm bell comprising a gong shaped to provide a housing portion, motor means having a rotary output shaft and disposed within said gong with its output shaft extending towards the periphery thereof,

a striker assembly rotatable about an axis in a plane transverse to the axis of said output shaft, and disposed towards the periphery of said gong and adapted to be driven by said motor means,

and a plurality of strikers associated with said assembly adapted sequentially to strike the gong when the assembly is driven, characterised in that being such that the radius of the circle defined by the strikers during rotation is less than two thirds of the minimum dimension of the gong when measured from its centre to its periphery.

[0013] In a preferred embodiment of the invention, the gong is preferably circular and is adapted to be secured by means of a central fastening. The motor is preferably mounted with its rearward end at or towards the centre line of the gong and its output shaft at the forward end, substantially perpendicular thereto, i.e. disposed along the gong radius.

[0014] The motor may be supported by means of a support assembly and associated motor clamp which locates the motor securely in position, said support assembly including means for attachment of the bell gong thereto. The support assembly may include a pair of opposed blind bores adapted to receive a lay shaft accommodating a striker assembly, said lay shaft being in substantially spaced parallel relationship with the centre line of the gong.

[0015] The output shaft of the motor may be provided with a pinion which meshes with the teeth of an angled gear whereby rotation of the upward shaft to the motor is transmitted to the corresponding sub-assembly of the striker sub-assembly.

[0016] Following is a description by way of example only and with reference to the accompanying drawing of one method of carrying the invention into effect.

[0017] The alarm bell 10 comprises a base 11 having a peripheral edge wall 12 defining the circular , extremity of base 11, edge wall 12 being configured to provide an upstanding annular rim portion 13 and a frustoconical intermediate portion 14. As viewed in cross-section in the accompanying drawing, the base 11 has an upstanding gong support 15 defined by an upstanding wall 16 and a substantially planar portion 17 having a central threaded bore 18 and a peripheral rubber cushion 19. The extremity of planar portion 17 remote from wall 16 is provided with a downwardly inclined portion 20 which terminates in an extremity portion 21 extending in substantially spaced parallel relationship with the base line 22 of the bell assembly. The extremity portion is provided with a blind bore 23 directed towards said base line 22.

[0018] The base 11 co-operates with a motor clamp assembly 25 comprising a base plate 26 which latter is disposed generally contiguous the base 11 whereby the base 11 and the base plate 26 together define the base line 22 of the bell assembly. The base plate 26 extends generally beneath the planar portion 17 in a direction away from the wall 16 and is provided in register with blind bore 23 with an upwardly directed blind bore 27 which together with blind bore 23 define journals for a shaft 28. Base plate 25 terminates inwardly of the line defined by wall 16 and serves to provide a base opening 29.

[0019] The motor clamp assembly 25 serves to secure locate and clamp a motor 30 with its output shaft 31 disposed radially of the centre line 32 of the bell. The output shaft 31 carries a pinion 33; shaft 28 carries a pair of spaced discs 34 mounted concentrically on shaft 28, each disc having on its face remote from the other, a ring of gear teeth 35, one set of which are adapted to engaged with pinion 33 whereby rotation of the output shaft 31 of motor 30 drives via pinion 33 and gear teeth 35 disc 34 for rotation about the axis of shaft 28.

[0020] Each of discs 34 carries towards the periphery thereof a spigot (not shown) in spaced parallel relationship with shaft 28 and adapted to engage with the adjacent disc, said spigots being diametrically disposed one with respect to the other. Each spigot carries a striker member 36 which is substantially cylindrical and has a central bore of approximately twice the diameter of the spigot on which it is mounted, the arrangement being such that each striker member 36 is capable of rotation about its associated spigot and is carried in floating relationship therewith.

[0021] Central threaded bore 18 is adapted to receive a captive screw 40 for securing a gong 41 to planar portion 17 of gong support 15 so that the gong is retained by screw 40 against cushion 19. The gong has a central planar portion 42 and an annular convex portion 43 which terminates in inwardly extending frustoconical side wall 44. Side wall 44 has, juxtaposed strikers 36, an inwardly directed impact blister 45.

[0022] The gong 41 is preferably a one-piece pressing from sheet steel and each of the base 11 and the motor clamp assembly are preferably formed from glass fibre reinforced polypropylene or glass fibre reinforced polyethylene.

[0023] In operation, the electric motor 30 is connected via the terminal block assembly mounted in juxtaposition with gong support 15 with the current supply wires which enter the alarm bell by means of the base opening 29. Energisation of the motor 30 results in rotation of the shaft 31 which drives the discs 34 at a predetermined rate of rotation so that the strikers 36 swing outwardly to the limit of their "float" and serve to strike the impact blister 45 at the periphery of the gong 41 thereby sounding the alarm bell.

[0024] The relatively short radius between the axis of shaft 28 and the periphery of each of strikers 36 at the extremity of their float serves to limit the centrifugal force and hence the circumferential velocity of each striker and therefore reduces the actual impact of the striker upon the impact blister 45 without reducing to any significant extent the volume of the alarm bell in operation. The pitch of the note of the alarm bell is, of course, determined by the dimensions of the gong 41. This arrangement means that a motor 30 of much less heavy construction than hitherto can be employed and does not suffer from the disadvantage of relative loss of efficiency through conversion of rotary motion to reciprocating motion as set out in much of the prior art.

Claims

1. An alarm bell comprising a gong shaped to provide a housing portion, motor means disposed within said gong housing portion and a striker assembly rotatable about an axis and drivable by said motor means, characterised in that the motor means has a rotary output shaft extending towards the periphery thereof, the striker assembly is rotatable about an axis in a plane transverse to the axis of said output shaft and disposed towards the periphery of said gong, a plurality of the strikers associated with said assembly adapted sequentially to strike the gong when the assembly is driven, the radius of the circle defined by the striker during rotation being less than two thirds of the minimum dimension of the gong when measured from its centre to its periphery.

2. A bell as claimed in claim 1 characterised in that the gong is circular and is secured by a central fastening.

3. A gong as claimed in claim 1 or claim 2 characterised in that the motor is mounted with its rearward end at or towards the centre line of the gong and its rotary output shaft is disposed substantially radially with the gong.

4. A bell as claimed in any preceding claim characterised in that the motor is supported by means of a support assembly in associated motor clamp which locates the motor assembly securely with respect to the gong.

' 5. A bell as claimed in claim 4 wherein the support assembly includes a pair of opposed blind bores adapted to receive a lay shaft accommodating a striker assembly, said lay shaft being in substantially spaced relationship with the centre line of the gong.

6. A bell as claimed in claim 5 wherein the output shaft of the motor is provided with a pinion which meshes with teeth and angled gear whereby rotation of the motor shaft is transmitted to the corresponding sub-assembly of the striker.

Drawing