GB2369523A

GB2369523A - A sounder with a piezoelectric or rocking armature audio transducer

Info

Publication number: GB2369523A
Application number: GB0117503A
Authority: GB
Inventors: Christoper Anderson
Original assignee: Fulleon Ltd
Current assignee: Eaton Electrical Products Ltd
Priority date: 2000-08-03
Filing date: 2001-07-18
Publication date: 2002-05-29
Anticipated expiration: 2021-07-18
Also published as: GB0019078D0; DE10138210A1; GB0117503D0; GB2369523B

Abstract

A sounder has a casing 2 configured to receive either a rocking arm transducer 11 or a piezoelectric assembly (21 figure 3). The casing 2 has a central tube 3 which is received in an opening (13 fig 2) in the base (15 fig 2) of the transducer 11 or an opening (23 figure 4) in the base of the piezoelectric assembly (21 figure 3). The casing also has a raised ring 5 which interlocks with a groove (17 fig 2) in the transducer 11 or recesses 27A, 27B, 27C, 27D on the base of the piezoelectric assembly (21 fig 3).

Description

SOUNDER

The invention relates to sounders. In particular, it relates to sounders for use in fire alarms, smoke alarms, 5 intruder detection systems, or other such systems.

It is well known to provide sounders which use a rocking armature transducer. Rocking armature transducers produce sound with a broad range of frequencies. The transducer is held within a casing. Such casings 10 typically include a resonant portion and an internal structure for holding of the transducer inside the casing for the emission of sound. The casing must have an internal structure which holds the transducer in such a way that sound can be emitted.

15 Piezoelectric sounders are also known. These are generally easier to produce than rocking armature sounders and are cost effective. In such sounders a piezoelectric disc is connected to an electronic circuit for oscillation and coupled to a casing. It is important 20 that the piezoelectric disc be rigidly held and be precisely located to achieve the highest efficiency.

This occurs with a specific set of resonant conditions associated with a specific positioning of the piezoelectric disc. Assemblies or housings for 25 piezoelectric discs have been developed to provide for the correct positioning of the disc.

There are many differences between a rocking

armature transducer and a piezoelectric assembly. For example, piezoelectric assemblies are generally larger than rocking armature transducers and there are structural differences between the two. GB 2322502 5 describes a piezoelectric assembly, which includes a piezoelectric disc and a coupling means for receiving the piezoelectric disc and for coupling the sound emissions from the disc to a horn. The coupling means includes a cylindrical extension between the piezoelectric disc and 10 the horn. Such a coupling piece is not found in rocking armature transducers. The piezoelectric assembly of GB 2322502 attached to a horn is shown in Fig. 6. of the present application. For these, amongst other, reasons the casings designed for rocking armature transducers 15 cannot be used with piezoelectric assemblies.

Since the internal structure of the casing needs to fit precisely the particular transducer or piezoelectric assembly, known sounders contain either a piezoelectric assembly or a rocking armature transducer depending upon 20 the internal structure and dimensions of the casing.

In most general terms, the present invention provides a casing for a sounder, which casing is arranged to interchangeably receive a piezoelectric assembly and a rocking armature transducer. Such a casing gives 25 considerable flexibility in manufacturing and cost, in that a single casing can be manufactured and choice of rocking armature transducer or piezoelectric assembly can

be made according to the customers' preference.

The invention further provides a sounder comprising such a casing and either a piezoelectric assembly or a rocking armature transducer.

5 A preferred piezoelectric assembly comprises, a piezoelectric disc, an O-ring mounted upon the disc at its periphery, a floor to receive the piezoelectric disc, said floor including an opening and being attachable to a casing via said opening, and a cover means mounted upon 10 the disc and O-ring having a shoulder portion spaced radially inwards from its periphery such that the O-ring is held at the radial edge of the shoulder, between the cover means and the disc, when the cover plate is mounted thereon. 15 An embodiment of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1. is a perspective view showing a casing according to an embodiment of the invention, and showing 20 a rocking armature transducer. The position of insertion of the rocking armature transducer is indicated by arrow A / Fig.2. is a perspective view of the rocking armature transducer shown in Fig.1; 25 Fig 3. is a perspective view showing the casing of Fig.1., and showing a piezoelectric assembly. The position of insertion of the piezoelectric assembly is

indicated by arrow A; Fig 4. is a perspective view of the piezoelectric assembly shown in Fig.li Fig 5. is a plan view showing the internal structure 5 of the sounder of Figs. 1 to 4i Fig 6. is a cross-section through a prior art

piezoelectric assembly attached to a horn (as described in GB 2 322 502).

Referring first to Fig.1, a sounder comprises a 10 casing 1 which is shaped to receive either a rocking armature transducer 11 or, as shown in Fig. 2., a piezoelectric assembly 21. The casing comprises an outer shell 2, the interior of which is shaped to receive either a rocking armature transducer 11 or a 15 piezoelectric assembly 21. The interior of the shell 2 consists of raised ridges concentric with a central tube, as is better shown in Fig. 5.

The rocking armature transducer is fitted into the interior of shell 2 of the casing 1 so that the opening 20 13 in base 15 of the transducer fits over tube 3 at the centre of the sounder shell. Raised ring 5 of the shell interlocks with groove 17 of the transducer 11, when the transducer is in place it is cased by raised wall 7 of the sounder.

25 Fig 3. shows how a piezoelectric assembly 21 fits into the casing 1. The piezoelectric assembly fits into the shell 2 such that the opening 23 provided in the base

25 of the piezoelectric assembly fits over centre tube 3 of the sounder. Recesses 27A, B. C, D in base 25 receive raised ring 5 of the shell.

A known piezoelectric assembly is shown in Fig. 6, 5 and is described in more detail in GB 2 322 502. This piezoelectric assembly comprises a piezoelectric disc or plate 30 which operates in a known manner to vibrate when an electric field is applied across it. The

piezoelectric plate is mounted within a coupling piece 31 10 which includes a cylindrical extension 33 which extends from floor 37. In use, this cylindrical extension sits upon the open edge of the frustoconical portion of the horn 35.

In an embodiment of the present invention, the 15 piezoelectric assembly is based on that shown in Fig 6.

However, the cylindrical extension 33 is removed. This removal facilitates interchangeably with the rocking armature transducer, as rocking armature transducers lack such an extension. With the cylindrical extension 20 removed, the floor 37 defines the opening (23,38) which fits over the central tube 3 of the casing when it is attached as shown in Fig. 3.

The upper side of floor 37 is provided with an annular raised part 39 extending inwardly from 25 cylindrical wall 41. The piezoelectric disc 30 is mounted upon shoulder 39,43 and is of a diameter to fit within the diameter of wall 41. Since the disc 30 sits

directly upon shoulder 43, the central portion of disc 30 is spaced slightly above the floor 37 to enable correct operation of the sounder. An O-ring 45 is then placed on top of, and at the periphery of, the piezoelectric disc 5 30. A cover plate 47 is then mounted on top. The Oring 45 is made of an elastomeric, resiliently compressible material, e.g. , of rubber or plastic material.

A printed circuit board 42 is mounted within cylindrical wall 44 of cover plate 47. Additional 10 components 46 and 48 are located upon the circuit board, and the electrical assembly is encapsulated by an encapsulating material 50. This can be a resin or other suitable encapsulating material.

In this way the piezoelectric assembly, comprising a 15 piezoelectric disc 30, a floor 37, a cover plate and associated electronic circuitry can be assembled and transported as a single, complete unit, requiring only to be attached to a casing and to be connected to external cables to form an operative unit. In this way the 20 piezoelectric assembly can be easily transported, and can be interchanged with a rocking armature transducer into the casing. For example, this allows the customer to easily exchange a rocking armature transducer with the piezoelectric assembly in the sounder.

Claims

1. A method of assembling a sounder, comprising: providing a rocking arm transducer; 5 providing a piezoelectric assembly; providing a casing having internal surfaces for interchange ability receiving the rocking arm transducer and the piezoelectric assembly; and fitting a selected one of said transducer or said 10 assembly into the casing.

2. A method according to Claim 1, wherein the rocking

arm transducer has an opening therein, and the internal surfaces of the casing includes a tube, the tube engaging 15 the opening in the transducer when the rocking arm transducer is selected and fitted in the casing.

3. A method according to Claim 2, wherein a groove in the rocking arm transducer interlocks with a raised ring 20 in the casing when the rocking arm transducer is selected and fitted in the casing.

4. A method according to Claim 1, wherein the piezoelectric assembly has an opening therein, and the 25 internal surfaces of the casing includes a tube, the tube engaging the opening in the transducer when the

piezoelectric assembly is selected and fitted in the casing.

5. A method according to Claims 4, wherein the recesses 5 in the piezoelectric assembly interlock with a raised ring in the casing when the piezoelectric assembly is selected and fitted in the casing.

6. A method according to any one of the preceding 10 claims, wherein the piezoelectric assembly comprises a piezoelectric disc, an O-ring mounted upon the disc at its periphery, a floor to receive the piezoelectric disc, said floor including an opening and being attachable to the casing via said opening, and a cover means mounted 15 upon the disc and O-ring having a shoulder portion spaced radially inwards from its periphery such that the O-ring is held at the radial edge of the shoulder, between the cover means and the disc, when the cover plate is mounted thereon.

7. A kit of parts for assembling a sounder, comprising: at least one rocking arm transducer; at least on piezoelectric assembly; and a casing having internal surfaces for interchange 25 ability receiving the rocking arm transducer and the piezoelectric assembly;

whereby a selected transducer or assembly is fittable into the casing.

8. A method of modifying a sounder, comprising: 5 providing a sounder having a casing containing a rocking arm transducer; removing the transducer from the casing; and fitting a piezoelectric assembly into the casing; wherein the casing has internal surfaces for 10 interchange ability receiving the rocking arm transducer and the piezoelectric assembly.

9. A method of modifying a sounder comprising: providing a sounder having a casing containing a 15 piezoelectric assembly; removing the assembly from the casing; and fitting a rocking arm transducer into the casing; wherein the casing has internal surfaces for interchange ability receiving the rocking arm transducer 20 and the piezoelectric assembly.