GB2200515A

GB2200515A - Method of and apparatus for producing a transducer diaphragm assembly

Info

Publication number: GB2200515A
Application number: GB08801872A
Authority: GB
Inventors: John Thurston Taylor
Original assignee: T H D MANUFACTURING Ltd
Current assignee: T H D MANUFACTURING Ltd
Priority date: 1987-01-28
Filing date: 1988-01-28
Publication date: 1988-08-03
Anticipated expiration: 2008-01-28
Also published as: GB2200515B; GB8801872D0

Abstract

A heated upper forming tool cooperates with cooler lower tool 4 and a support ring 9 of ABS to seal a diaphragm 2 of polycarbonate to the ring 9 prior to shaping, due to plastic deformation under pressure, between mating tools 50 and 4. Sealing is achieved by spring-biassed cylindrical tool 40 through which shaping portion 50 is slidable. Shaping portions 50, 6 are a close sliding fit in the ring 1 which therefore self-centres relative to the tools, which are also arranged to abut on the ring to determine the spacing between the tools during shaping. The temperature of the upper tool is controlled by means of thermostatic heating while that of the tool 4 is controlled by means of a water circuit subject to heating/cooling in dependence on the return flow temperature. <IMAGE>

Description

METHOD OF AND APPARATUS FOR PRODUCING A TRANSDUCER DIAPHRAGM ASSEMBLY -The present invention relates to a method of and apparatus for producing a transducer diaphragm assembly and to diaphragm assemblies produced by such a method.

In the field of electrodynamic transducers and particularly those intended for use in the telephone engineering field, it is often necessary to provide a diaphragm assembly intended for the conversion between electrical and sound energy. Nowadays, generally speaking, the diaphragms are made of a resiliently-deformable plastics material and are disc-shaped. The diaphragm must be shaped to provide an annular groove on one side and a corresponding rib on the other side around a central portion of the diaphragm, the rib being intended for attachment to a coil used in the production or detection of sound energy in the diaphragm.

Problems arise in trying- to ensure that the annular groove/rib is concentric in order to optimise the characteristics of the diaphragm (see European patent specification No 0 040 948 B1). At the same time, it is highly desirable to try to provide as simple and economical a method of production as possible.

According to this invention there is provided a method of producing a diaphragm assembly for an electrical transducer, said method including the steps of securing a diaphragm to an inner peripheral portion of a support ring, and shaping the diaphragm by means of two forming tools applied from respective sides of the diaphragm, at least one of the tools having a portion of a diameter corresponding to an inner peripheral portion of the support ring, and each of the tools having abutment shoulders such that when the tools are applied to the respective -sides of the diaphragm held in the support ring, the centering of the diaphragm relative to the tools and the final spacing of the tools during the shaping operation is determined by means of the close fit between at least one of the tools and the inner peripheral portion of the support ring and the abutment of said shoulders on the support ring.

Preferably, the diaphragm before or after cutting may be secured to the support ring prior to, but at the same work-station, as the shaping operation.

In another method a continuous strip of diaphragm material has support rings secured to it along the length of the strip and in a subsequent operation, the strip is severed around the outer periphery of the diaphragm before or after the forming operation is carried out.

Advantageously, it may be arranged that one of the two forming tools serves to cut the diaphragm from a plain sheet or strip placed across the support ring immediately before or after the diaphragm has been secured to the support ring so that the securing and cutting operations are carried out in the same work-station as the forming operation.

An embodiment of this invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram of the operation of shaping the diaphragm in accordance with a first embodiment of this invention; Fig. 2 is a schematic cross-sectional diagram of a modified form of the apparatus shown in Fig. 1; Fig. 3 is a cross-sectional diagram of a diaphragm assembly formed by the apparatus shown in Fig. 2; and Fig. 4 is a schematic plan view of a production arrangement in yet a further embodiment of the invention.

Referring to the drawing, a support ring 1 of a substantially rigid plasticsmaterial (in particular ABS) has secured to it (by means of glutination, ultra-sound welding, thermal welding or R.F.

[radio frequency] welding) a central disc-shaped diaphragm 2 made of a resiliently-deformable plastics material (in particular polycarbonate).

Mating tools 3 and 4 have respective shaping portions 5 and 6 which are arranged formatting with each other, the outer diameters of the shaping portion 6 corresponding to the diameter of the inner periphery 7 of the support ring 1. Thus, the shaping portion 6 has a cylindrical face 8, arranged for smooth sliding contact with the inner periphery 7 of the support ring.

The diameter of the shaping portion 5 substantially corresponds with the diameter of the diaphragm so as to clamp the latter to the support ring during the forming operation. The depth of the shaping portion 5 corresponds with the height of the top surface 9 of the support ring above the diaphragm.

Each tool 3,4 also has a carrier portion 10,11 arranged to project radially outwardly relative to the shaping portion and thus provide a shoulder 12,13 for abutting the top or bottom surface respectively of the support ring when the tools are brought together.

The tools and support ring are dimensioned relative to each other such that when the tools are brought together to shape the diaphragm, the support ring provides self-guidance relative to the tools to ensure optimum centering of the groove/rib 14 formed in the completed diaphragm. Also the abutment of the shoulders on the top and bottom surfaces of the support ring serve to determine the displacement of, and hence the pressure applied by, the tools to control the deformation of the various portions of the diaphragm during shaping.

During shaping the tool 3 is heated sufficiently (by means of a thermostatically-controlled electrical heating arrangement) to soften the diaphragm material and is brought into contact with the latter before the tool 4 to allow shaping to take place in the optimum manner by plastic deformation when the tool 4, at a lower temperature (below the softening temperature of the diaphragm material) than the tool 3, is brought into mating relationship with the tool 3 to exert controlled pressure on the diaphragm to determine the thickness and form of the resulting diaphragm.

The tool 4 is preferably kept at the desired temperature by means of a pumped water circuit (not shown) whose return flow temperature is used to control heating or cooling of the circulated water.

For the materials Abc and polycarbonate mentioned above it has been found that the temperature of the tool 3 must be kept in the range 1500Cj10%, preferably substantially 1500C, and the temperature of the tool 4 must be kept in the range 500Cii0%, preferably substantially sooc.

In a modified embodiment the diaphragm before or after cutting may be secured- t-o the support ring prior to, but at the same work-station as, the shaping operation.

Referring to Fig. 2, the arrangement shown differs from the arrangement shown in Fig. 1 to-the extent that the upper forming tool 3 has been modified to include a cylindrical sealing tool 40 slidable between a modified shaping portion 50 and an outer cylindrical end stop 60. A backplate 70 and springs 80 provide a spring bias urging the sealing tool to project slightly in advance of the shaping portion 50 so as to make contact with the diaphragm 2 before the shaping portion makes contact with the diaphragm. In this way, the diaphragm can be sealed to the support ring before the application of the shaping-portions apply forces to the diaphragm which would tend to move the outer periphery of the diaphragm relative to the support ring.

In an alternative method, a continuous strip of diaphragm material has support rings secured to it along the length of the strip and in a subsequent operation, the strip is severed around the outer periphery of the diaphragm before the forming operation is carried out, possibly at the same work-station as the severing operation.

Referring to Fig. 4, a production line for the diaphragm assemblies comprises a sealing station 100 having an input channel 110 for support rings 1. The support rings are delivered to a sealing position 120 by means of a feeder wheel 130 having arcuate recesses in its outer periphery arranged to receive the support rings and to deliver them to the sealing position 120 to which a continuous strip 140 of diaphram material is delivered.

At the sealing position 120, apparatus (not shown in Fig. 4) as shown in Fig. 2 seals the support ring (preferably by means of ultrasonic welding) to the continuous strip of diaphragm material by means of the sealing tool and immediately thereafter forms the diaphragm 2 by means of the forming tools.

The support rings 1 are then carried by means of the strip 140 to which the support rings are sealed to a cutting station 200 where a cutting tool 210 severs the diaphragm around its outer periphery to release the diaphragm assembly into an output channel 220 arranged to convey the diaphragm assemblies out of the production line.

In an alternative arrangement to that shown in Fig. 4, the forming of the diaphragm 2 may be carried out in a separate station located between the sealing station and the cutting station.

In a further alternative embodiment, the upper of the two forming tools serves to cut the diaphragm from a plain sheet or strip placed across the support ring immediately before or after the diaphragm has been secured to the support ring so that the securing and cutting operations are carried out in the same work-station as the forming operation.

In a further embodiment of the invention (not shown) the upper tool 3 is provided with means for cutting and securing the diaphragm to the support ring immediately prior to shaping so that the entire operation can be carried out using a plain sheet of the diaphragm material placed over the support ring in a single station.

Further details of the support ring relating to the various provisions for receiving the coil for operating the diaphragm and for the installation of the support ring and diaphragm in a particular application are not given here since these are not directly relevant to the invention. The precise materials used may differ from the preferred materials mentioned above, for example, polyester sheet can be used instead pf polycarbonate. This would however require different operating temperatures to be used.

The method of forming the diaphragm described above provides a simple and economical method of producing a diaphragm which is accurately located on the support ring and whose groove/rib is accurately concentric with the support ring and hence with a coil fitted to the diaphragm and arranged to make smooth sliding contact with the inner periphery of the support ring as for example disclosed in European Patent Specification No. 0 040 948.

Claims

CLAIMS:

1. - A method of producing a diaphragm assembly for an electrical transducer, said method including the steps of securing a diaphragm to an inner peripheral portion of a support ring, and shaping the diaphragm by means of two forming tools applied from respective sides of the diaphragm, at least one of the tools having a portion of a diameter corresponding to an inner peripheral portion of the support ring, and each of the tools having abutment shoulders such that when the tools are applied to the respective sides of the diaphragm held in the support ring, the centering of the diaphragm relative to the tools and the final spacing of the tools during the shaping operation is determined by means of the close fit between at least one of the tools and the inner peripheral portion of the support ring and the abutment of said shoulders on the support ring.

2. A method according to claim 1, wherein the diaphragm, before or after cutting, is secured to the support ring prior to, but at the same work-station as, the shaping operation.

3. A method according to claim 1 or claim 2, wherein one of the tools is kept at a higher temperature than, and is arranged to contact the diaphragm before, the other tool, such that the diaphragm is softened sufficiently for plastic deformation to occur when the tools clamp the diaphragm between them.

4. A method according to any one of the preceding claims, wherein the support ring is made of ABS and the diaphragm is made of polycarbonate.

5. A method according to claim 4 as appendent to claim 3, wherein said one tool is kept at a temperature in the range 150or110% and the other tool in the range 50 C+108.

6. A method according to claim 5, wherein said one tool is kept at substantially 150 C and the other tool substantially at 50 C.

7. A method according to any one of the preceding claims1 wherein a continuous strip of diaphragm material has support rings secured to it along the length of the strip and in a subsequent operation, the strip is severed around the outer periphery of the diaphragm before or after the forming operation is carried out.

8. A method according to any one of the preceding claims, wherein one of the two forming tools serves to cut the diaphragm from a plain sheet or strip placed across the support ring immediately before or after the diaphragm has been secured to the support ring so that the securing and cutting operations are carried out in the same work-station as the forming operation.

9. A method of producing a diaphragm assembly for an electrical transducer, said method being substantially as described herein with reference to Fig. 1 or Fig. 2, each in combination with Fig. 3 and Fig. 4 of the accompanying drawings.

10. Apparatus for producing a diaphragm assembly for an electrical transducer and including two forming tools arranged for carrying out a method according to any one of the preceding claims.

11. Apparatus according to claim 10, wherein electrical heating means are provided for keeping one of the tools at a desired temperature and a temperature-controlled water circuit is provided for keeping the other tool at a lower temperature than said one tool.

12. Apparatus for producing a diaphragm assembly for an electrical transducer, said apparatus being substantially as described herein with reference to Fig. 1 or Fig. 2 alone or in combination with Fig. 4 of the accompanying drawings.

13. A diaphragm assembly produced by a method in accordance with any one of claims 1 to 9.

14. An electrical transducer including a diaphragm assembly according to claim 13.