GB2074418A

GB2074418A - Electro acoustic transducers

Info

Publication number: GB2074418A
Application number: GB8012362A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1980-04-15
Filing date: 1980-04-15
Publication date: 1981-10-28
Also published as: GB2074418B

Abstract

Electro-acoustic transducers, e.g. armature receivers used as the ear-pieces of standard British Post Office telephones, have hitherto been assembled by thread-rolling screws between the drive unit (yoke, magnet system and armature) and the frame. This has disadvantages, and to overcome these the assembly uses plain rivets. In one form, Fig. 5, the rivet is a separate item with a flange (10) between its ends to locate when its lower end is fitted to a hole in the frame. This lower end is ironed over (11) to lock the rivet to the frame, and the upper end is fitted through a hole in the end (12) of one arm of the armature and a hole in the yoke (13). The upper end is then ironed over (14) to lock the assembly together. To facilitate assembly the drive unit plus rivets are fixed together as a sub-assembly for attachment to the frame. In a further form, Fig. 7, each rivet is formed by an upstanding pillar (20) integral with the frame which, when the device is assembled, fits through a hole in the end (22) of the armature arm and a hole in the yoke (21) after which the upper end is ironed over (23) to hold the assembly together. <IMAGE>

Description

SPECIFICATION Electro acoustic transducers This invention relates to electro-acoustic transducers and especially to such transducers of the rocking armature type, as now used in the ear-pieces of the standard British Post Office telephone subscribers' instruments.

Rocking armature transducers such as referred to above follow the principles of the transducers described in out British Patent No.

606,012 (J.S.P. Robertson-18). Such transducers have a drive unit which consists basically of an E shaped magnetic structure, the central leg of which is a permanent magnet and the outer legs of which carry the operating coils. The armature is a plate-like structure pivotted about the central leg, and which as it vibrates due to the speech currents in the coils drives the diaphragm via a drive rod.

Various methods have been used to fix the yoke and magnet assembly, wound coil spools, terminai assembly and armature, which combination is referred to herein as the drive unit, to the frame of the transducer assembly. The method currently employed involves the use of two steel tritobular threadrolling screws. These project through two plain holes in the aluminium frame, wherein they are rotated and driven by twin automatic screwdrivers, during which they roll-form threads in the frame to secure the drive unit thereto. Unfortunately this operation tends to generate magnetic swarf which can find its way into one or other of the air gaps of the drive unit, causing it to malfunction.

An object of the invention is to provide a transducer in which the above indicated disadvantage is overcome, and which is cheaper and simpler than the arrangements hitherto used.

According to the present invention there is provided an electro-acoustic transducer, which includes a diaphragm, an electro-magnetic drive unit for driving the diaphragm and a frame to which the drive unit is assembled at a plurality of spaced-apart points, wherein at each said spaced-apart point the frame is provided with a hole in the drive unit, and wherein the end of a said rivet which extends through a said hole is ironed over the drive unit to retain the drive unit to the frame.

According to the invention there is also provided an electro-acoustic transducer, which includes a diaphragm, an electro-magnetic drive unit which includes a yoke, a magnet assembly on said yoke and a rockable armature associated with the magnet assembly, and a frame to which the drive unit is assembled at two spaced-apart points, wherein the frame has two rivets each formed by an upstanding pillar formed integral with the frame, and wherein the assembly is completed by fitting the drive unit to the frame with each said pillar extending through a hole in the end of one of the arms of the armature and a hole in the yoke, whereafter the end of the rivet is ironed over the yoke.

Although the invention is hereinafter described as applied to a rocking armature transducer, as referred to in the preceding paragraph, it will be appreciated it is not so limited, and may be applied to other forms of transducer.

Embodiments of the invention will now be described with reference to the accompanying drawing, in which: Figure 1 is a simplified part-sectioned view of a rocking armature transducer to which the invention is applicable, the region of the transducer to which the invention is relevant being ringed.

Figure 2 is a rivet used in a first embodiment of the invention.

Figure 3 shows in section the ringed region (Fig. 1) of the frame of the transducer as used in the first embodiment of the invention.

Figure 4 shows in section how the rivet of Fig. 2 is fixed to the frame.

Figure 5 shows in section how the drive unit is assembled to the frame.

Figure 6 also in section, relates to an alternative method of assembly using the rivet of Fig. 2.

Figure 7 is a view, also in section, of a second embodiment of the invention.

The rocking armature transducer is shown end-on and partly in section in Fig. 1. Here we have the yoke 1, which carries the magnet structure with its magnet (not visible in Fig.

1), which carries two coil spools one of which is shown at 2. The armature 3, which is platelike as mentioned above, has sideways extending arms via which it rocks and which extend out to the side of the yoke. The yoke with the magnet, coils, and armature are assembled to the frame 4 by the two trilobular thread-rolling screws such as 5, each of which extends through holes in the yoke and armature arm into a boss 6 on the frame.

To overcome the disadvantage referred to above, in the new arrangement the screws are replaced by plain rivets, in one case the rivets being separate items while in the other case they are each formed integral with the frame.

The first embodiment to be described uses rivets which, as already mentioned, are separate items, to secure the drive unit to the frame. One such rivet is shown in Fig. 2: this has a flange 10 part-way along its length, and as can be seen from Fig. 2 the two portions of the rivet, one on each side of the flange are of different diameter.

Fig. 3 is a cross-section of the portion of the frame to which the drive unit is to be rivetted, and Fig. 4 shows a rivet in position on the frame. The flange 10 provides the seating and location for the rivet in its position. After the rivet is fitted in, its lower end is ironed over the frame to secure it in place.

Then, see Fig. 5, the drive unit is fitted over the upstanding ends of the rivets where we see the end 1 2 of one armature arm and an eyelet 1 3 on the yoke 1 (see Fig. 1). Then the upper end of the rivet is ironed over, as shown at 14.

With this arrangement, no magnetic swarf is-produced, and if the assembly is defective it is possible to remove the rivets and use the frame again. This would not apply in the case of the method of assembly referred to which was trilobular screws. Note that these rivets can be of non-ferrous metal.

Another aspect of the use of rivets such as that shown in Fig. 2 is shown in Fig. 6. Here we see that the drive unit can be assembled as a separate sub-assembly which can later be assembled to the frame. An advantage here is that the sub-assembly allows improved access to the armature, which usually has to be adjusted torsionally to ensure that the two airgaps formed by the main body of the armature and the pole-pieces of the yoke are equal in-length. Such equality is desirable to ensure optimised performance of the transducer.

Again the assembly does not generate magnetic swarf, and again if the drive unit is faulty the frame can be salvaged.

In the arrangement shown in Fig. 7, each rivet such as 20 is formed integral with the frame, and the drive unit, including the yoke.

21 and armature end 22 are fitted over the rivets, as shown. Then the end of the rivet is ironed over, as shown at 23.

Claims

1. An electro-acoustic transducer, which includes a diaphragm, an electro-magnetic drive unit fdr driving the diaphragm and a frame to which the drive unit is assembled at a plurality of spaced-apart points, wherein at each said spaced-apart point the frame is provided with a plain-shanked rivet which extends through a hole in the drive unit, and wherein the end of a said rivet which extends through a said hole is ironed over the drive unit to retain the drive unit to the frame.

2. A transducer as claimed in claim 1, wherein each said rivet is a separate item with flange intermediate its ends, wherein one end of said rivet extends through a hole in the frame, being located therein by the flange, wherein the said one end is ironed over the frame to retain the rivet to the frame, and wherein the other end of the rivet is the portion thereof which extends through a said hole in the drive unit.

3. A transducer as claimed in claim 1, and wherein each said rivet is formed by an upstanding pillar on said frame, which is integral with said frame.

4. A transducer as claimed in claim 1, and wherein each said rivet is formed by an upstanding pillar on the drive unit which is integral with said drive unit.

5. A transducer as claimed in claim 1, 2, 3 or 4, and wherein said drive unit is of the rocking armature type, each said rivet extends ing through a yoke which forms part of the drive unit, the end of one of the arms of the rocking armature and the frame.

6. An electro-acoustic transducer, which includes a diaphragm, an electro-magnetic drive unit which includes a yoke, a magnet assembly on said yoke and a rockable armature associated with the magnet assembly, and a frame to which the drive unit is assembled at two spaced-apart points, wherein the frame has two rivets each formed by an upstanding pillar formed integral with the frame, and wherein the assembly is completed by fitting the drive unit to the frame with each said pillar extending through a hole in the end of one of the arms of the armature and a hole in the yoke, whereafter the end of the rivet is ironed over the yoke.

7. An electro-accoustic transducer substantially as described with reference to Figs.

2 to 5, Fig. 6 or Fig. 7 of the accompanying drawings.

CLAIMS (8 Jan 1981)

8. An electro-acoustic transducer, which includes a diaphragm, an electro-magnetic drive unit which includes a yoke, a magnet assembly on said yoke and a rockable armature associated with the magnet assembly, a frame to which the drive unit is assembled at two spaced-apart points, and two solid plain rivets, wherein each said rivet is a separate item and has a flange intermediate its ends, wherein one end of a said rivet extends through a hole in the frame, being located therein by its said flange, wherein the one end of a said rivet is ironed over the frame to retain the rivet to the frame, wherein the other end of each said rivet extends through a hole in the drive unit, and wherein the said end of a rivet which extends through a said hole in the drive unit is ironed over the drive unit to retain the drive unit to the frame.