WO2000004531A1

WO2000004531A1 - Sound generating reed

Info

Publication number: WO2000004531A1
Application number: PCT/ZA1999/000050
Authority: WO
Inventors: Pieter Rousseau Fourie; Etienne Rijkheer
Original assignee: Harwill Industries (Pty) Ltd.
Priority date: 1998-07-17
Filing date: 1999-07-19
Publication date: 2000-01-27
Also published as: AU5256099A

Abstract

This invention relates to a sound generating reed assembly (110) that includes a reed (112) made of a sheet material, preferably polycarbonate, of uniform thickness and a reed holder (114) including a reed bed (120) and a reed clamping mechanism constituted by a clamping wedge (116) and a complemental clamping socket (124) by means of which the reed (112) may be clamped to the reed bed (120). The reed assembly (110) is particularly suited for incorporation in a portable peak expiratory flow monitoring device.

Description

Sound Generating Reed

Background to the invention

This invention relates to a sound generating reed and reed assembly.

The reed assembly of the invention finds particular application in a portable peak expiratory flow monitoring device such as that described in PCT Patent Application No. PCT GB98/01253 -

Peak Flow Monitor - (Harwill Industries (Pty) Ltd). The invention will be described with reference to such an application, but it is not intended thereby to limit the invention to such an application.

Peak expiratory flow rate (PEFR) is a measure of lung function that can be easily and accurately determined by several devices. The monitoring of PEFR has gained acceptance as a means of monitoring asthma, since PEFR can be recorded reliably by a cooperative subject without the help of technically skilled personnel and with the use of simple, portable devices.

The monitoring devices disclosed in the abovementioned patent applications are not flow meters in the strict sense of the word, since they do not measure absolute flow through the device. Instead, the device serves as a threshold monitor of the PEFR of a subject in that it monitors achieved PEFR compared to a diagnostic threshold. The diagnostic threshold depends on the treatment protocol prescribed for the subject after measurement of the anticipated or predicted PEFR of the subject.

In these devices, the achievement of the predetermined threshold PEFR of the subject is determined by means of a sound generator constituted by a sound generating reed forming part of a reed assembly that is located within the fluid through flow passage of the device. A reed assembly that gives accurate, reliable and repeatable results will, understandably, have to be manufactured to close and accurate tolerances. The achievement of such fine tolerances during mass production of the devices requires costly equipment and extreme care in manufacture and assembly if the required tolerances are to be maintained within assembled batches and from batch to batch. This, it will be appreciated, is time consuming and costly. It is an object of this invention to provide a reed and reed assembly that comply with the accuracy, reliability and repeatability requirements of a monitoring device of this nature that address the problems inherent in their manufacture as described above.

Summary of the invention

According to this invention a sound generating reed assembly comprises a discrete reed of a sheet material of a substantially uniform thickness and a reed holder comprising a reed bed and means to clamp the reed to the reed bed.

The clamp means may be constituted by cooperating socket and spigot formations, the socket formation being defined by an arched cover extending at least partially over the end of the reed bed to which the reed is to be secured and the spigot formation being constituted by a clamping wedge that is shaped for insertion into the socket formation, between the surface of a reed located on the securement end of the reed bed and the arched cover, thereby to clamp the reed to the reed bed.

The reed holder may conveniently be injection moulded in plastics, in which event the parts of the reed holder adapted to secure the reed may be relatively bulky. In addition, the reed holder may be designed to have wails of a substantially uniform thickness, thereby to ensure better dimensional stability during the moulding and cooling process.

The reed itself may conveniently be of polycarbonate sheet material or sheet metal, such as stainless steel, provided, in either case, that the material conforms to predetermined structural and dimensional uniformity requirements.

The reed holder may be shaped externally to conform to a reed assembly mounting opening in a fluid flow passage such as the fluid flow passage of a peak expiratory flow rate monitor.

To this end, the reed holder may include an external mounting formation that is a friction fit in the reed assembly mounting opening in the fluid flow passage, which reed mounting formation may be located in an area of the reed holder apart from the reed clamping means. This is intended to minimise the translation, to the reed and reed clamping means, of possible strain or stress arising from press fitting of the reed holder to the mounting opening.

The invention includes a portable peak expiratory flow rate monitor including a sound generating reed assembly according to the invention summarised above. Brief description of the drawings

In the drawings:

Figure 1 is an exploded isometric view of a restricted reed assembly according to the invention;

Figure 2 is a similar isometric view of the restricted reed assembly of Figure 1 in its assembled form;

Figure 3 is a sectional side elevation on a line 3 - 3 in Figure 2;

Figure 4 is a plan view on the reed assembly of Figure 1 ;

Figure 5 is a detail on the area circled in Figure 3;

Figure 6 is an exploded isometric view of a free reed assembly according to the invention; and

Figure 7 is a similar isometric view of the free reed assembly of Figure 6 in its assembled form.

Description of embodiments of the invention

The reed assembly 10 illustrated in Figures 1 to 5 uses a so-called "restricted reed" while the reed assembly 110 illustrated in Figures 6 and 7 uses a so-called "free reed"

In the embodiment shown in Figures 1 to 5, the reed 12 is dimensioned to cover the aperture 22 and the reed 12 cannot vibrate or swing through the aperture 22. This type of reed is often referred to as a "restπcted reed". This type of reed 12 has the advantage that it provides an almost automatic compensation mechanism for possible manufacturing and assembly variations. since the reed assembly 10 can be manufactured to less demanding tolerances which therefore makes it less expensive to produce.

However it is possible to dimension the reed to fit within the aperture, allowing the reed to vibrate through the aperture without its movement being restricted by the reed bed. This type of reed is often referred to as a "free reed" which will be described in more detail below with reference to Figures 6 and 7

The restricted reed assembly 10 of Figures 1 to 5 might not be suitable for use in all situations since it tends, in use, to yield a lower signal to noise ratio than the free reed assembly of Figures 6 and 7. This aspect will also be described below.

The restricted reed assembly 10 illustrated in Figures 1 to 5 comprises a reed 12 and a reed holder made up of a reed holder body 14 and a reed clamping wedge 16.

The reed holder 14 is injection moulded in a relatively inert, tough plastics material, such as acrylonitrile-butadiene-styrene (ABS). In the moulding process it is not necessary to control the process parameters (and the plastics material heating and cooling parameters in particular) to any abnormally high standards. Normal, good injection moulding practice will be sufficient.

The reed 12 is cut from an accurately calibrated sheet material such as polycarbonate or stainless steel. The sheet material of the reed 12 must be structurally and dimensionally uniform. In addition, the material of the reed 12 is annealed or otherwise prepared prior to manufacture of the reed in order to stabilise the material and to remove stress internally of the material that could impact on the uniformity of the reeds 12 manufactured from the material.

During manufacture of the reeds 12, the reeds are stamped or cut from the material in a process that will minimise the imposition of localised stresses at the cut edges of the material. Such stresses tend to affect the physical and mechanical characteristics of the material that might yield non-uniform reeds 12, the intention being exactly the opposite, namely to produce reeds 12 that are as uniform as practically possible as regards size and physical characteristics.

The reed holder 14 is formed as a frusto-conical plug.

As can be seen from Figures 1 and 3, the plastics material wall thickness throughout the reed holder 14 is substantially uniform throughout. This is intended to minimise differential expansion and contraction during injection moulding as well as during cooling of the reed holder 14 after moulding.

The reed holder incorporates a reed bed 20 within which a through flow aperture 22 is formed. The intended fluid flow or airflow through the reed assembly 10 is in the direction of the arrow 31 (in Figure 2). Air flows under the reed 12, through the fluid flow aperture 22 and vents through the base 23. With airflow of sufficient magnitude, that is an airflow between the threshold values determined for the reed assembly, the reed 12 will vibrate to generate a characteristic sound.

The reed 12 is not moulded into the reed holder 14. Instead the reed 12 is clamped to the reed holder 14 in a post-moulding assembly step, in order to secure the reed 12.

This is done by means of cooperating socket and spigot formations constituted by a wedge socket 24 and a clamping wedge 16.

The wedge socket 24 is defined by an arched cover 24.1 extending over the securement end of the reed bed 20. The upper surface of the clamping wedge 16 is shaped complementally to the underside of the arched cover 24.1.

During assembly of the reed 12 to the reed holder 14, the insertion end 12.1 of the reed 12 is inserted into the wedge socket 24. The wedge 16 is then pressed into the socket 24 to wedge and clamp the insertion end 12.1 of the reed 12 against the floor 26 of the wedge socket 24. The clamping wedge 16 is formed with a short handle or grip (not shown) that is used to facilitate insertion of the clamping wedge 16 into the wedge socket 24. The grip is cut off after assembly leaving a circular remnant 18.

While the wedge socket floor 26 is essentially an extension of the reed bed 20, the wedge socket floor 26 is angled relatively to the reed bed 20. The reed 12 extends along the plane of the wedge socket floor 26, so that an acute angle 28 is formed between the reed and the reed bed 20.

A step 30 is formed at the junction of the reed bed 20 and the wedge socket floor 26. The junction step 30 provides a sharp edge or line of contact with the reed 12, thereby providing a more reliable and dimensionally accurate securement for the reed using current tool making and injection moulding techniques.

In the example illustrated, the reed holder 14 is shaped and dimensioned to be a friction fit within the monitoring device of which the reed assembly 10 is a part. In the peak flow monitoring device of PCT Patent Application No. PCT GB98/01253, for instance, the monitoring device is formed with a complementary frusto-conical socket that forms part of the airflow passage of the monitoring device.

The reed assembly 10 is dimensioned to be a friction fit within the socket in the peak flow monitor and when mounted for use, the base collar 32 provides an airtight seal with the socket of the device in which the reed assembly 10 is mounted.

To facilitate mounting of the reed assembly 10, the vent end of the reed holder 14 is externally stepped to provide an enlarged base collar 32. In the example illustrated, the external shape of the base collar 32 is complemental to the internal shape of the frusto-conical reed assembly mounting socket that forms part of the airflow passage of the peak flow monitoring device of PCT Patent Application No. PCT GB98/01253 - Peak Flow Monitor.

The plastics material from which the reed assembly 10 is moulded is inevitably deformed during mounting of the reed assembly due to the inherent deformability of the plastics material of the reed holder 14.

The base collar 32 serves to isolate the stress arising from press fitting of the reed holder to the mounting opening. The base collar 32 serves as the only point of contact with the surfaces of the mounting opening. Once mounted in the mounting opening, the remainder of the reed assembly 10 is, in essence, suspended within the mounting opening. In this manner, the translation of possible mounting strain or stress from the base collar to the remainder of the reed assembly 10, is minimised.

In addition, the reed clamping mechanism constituted by the wedge 16 and socket 24, are positioned inboard of the base collar 32. This serves further to minimise the possible translation of the insertion and mounting pressure externally imposed on the base collar 32 by the mounting opening, to the reed clamping mechanism and the reed 12.

Given air flow through the reed assembly 10 within the upper and lower threshold values determined for the reed assembly 10, the reed 12 will vibrate and generate sound. This will happen, for instance, when a monitored subject blows through the mouthpiece of a peak flow monitoring device within which the reed assembly 10 is fitted.

In a reed assembly for a peak flow monitor, such as the reed assembly 10 illustrated in the drawings, the length, shape and mass of the reed 12, the dimensions of the aperture 22 and the dimensions and mass of the components defining, resonance cavities surrounding the reed 12 and aperture 22, are chosen to optimise the sound produced by the reed assembly within the frequency range that human hearing is most sensitive. For instance the reed assembly 10 is - optimised to produce sound with a pitch in the range 2Hz to 20kHz.

The restricted reed 12 of the reed assembly 10 has the disadvantage that the reed bed 20 serves as a stop or barrier to unrestricted bending of the reed 12 to the limit of its elasticity, in one direction of bending of the reed 12.

This has two undesirable effects.

The reed bed 20 prevents the vibration of the reed 12 in a part of its vibrational cycle, thereby preventing the reed from producing sound in the entire frequency and harmonic range of the same reed unrestricted.

The physical interaction of the reed 12 with the reed bed 20 might also produce a buzzing noise in certain circumstances.

This would not normally be a problem, but it must be remembered that the reed assembly 10 is intended to provides clear and rapid onset of sound-when its flow threshold is exceeded. In essence it is intended to serve almost as an analogue-to-digital device which is either "on" or "off' with nothing in between. The possibility exists, however, that the buzzing sound of the reed 10 interacting with the reed bed 20 might occur outside one or both the upper and lower threshold values determined for the reed assembly 10, thereby detracting from the threshold indication capabilities of the reed assembly 10 in that the signal to noise ratio of the reed assembly 10 is adversely affected on two counts. The restriction of the reed 12 results in a reduction of the signal strength and an increase in the amount of noise produced.

To this end, the reed assembly of the invention can also be configured as the free reed assembly 110 illustrated in Figures 6 and 7. But for the differences described below, the free reed assembly 100 and its various components are the same as the reed assembly 10 described above with reference to Figures 1 to 5.

In the free reed assembly 110, the reed 112 is configured as a free reed in that the reed 112 and the fluid flow aperture 122 are dimensioned for the reed 112 to fit easily within the aperture 122 width- and lengthwise. This permits the reed 112 to vibrate freely through the reed bed 120 and the edges of the fluid flow aperture 122, thereby to produce its full range of frequencies and harmonics. This permits the output of the full potential sound of the reed 112 without the generation of excessive noise. In turn, this improves the signal to noise ratio of the free reed assembly 110 in that the signal strength is increased without a concomitant increase in noise production.

This benefit outweighs the extra expense occasioned by the need to produce the free reed assembly 110 to more precise manufacturing tolerances than are required for the restricted reed assembly 10 of Figures 1 to 5.

In Figure 7, the insertion end 112.1 of the reed 112 is shown as being bifurcated, with a notch 112.2 formed in the end intended for insertion into the wedge socket 124. The notch 112.2 is shaped complementally to a locating key formation 125 moulded into the floor 126 of the wedge socket 124. The key formation 125 assists in accurate location of the insertion end 112.1 of the reed 112 in the wedge socket 124 during assembly, thereby to ensure that the reed 112 is accurately centred with respect to the aperture 122.

The clamping wedge 116 is formed with a gap (not visible in drawings ) to enable insertion of the clamping wedge 116 into the wedge socket 124 without obstruction by the key formation 125.

Since the reed 112 is a free reed, accuracy in assembly of the reed 1 12 is important. In this regard, it is important that the reed is positioned accurately with respect to the wedge socket 124 and the fluid flow aperture 122 in particular. Because the reed 112 must not be fouled or obstructed by the edges of the aperture 122, the reed 112 must be properly centred with respect to the aperture 122. This feature could, however, also find application in the restricted reed assembly 10 of Figures 1 to 5.

Figures 7 and 8 illustrate the short handle or grip 119 that is used to facilitate insertion of the clamping wedge 116 into the wedge socket 24. As has been explained above, the grip 119 is cut off after assembly leaving a circular remnant (18 in Figures 1 and 2).

In the free reed assembly 110, with its enhanced signal to noise ratio, it is desirable to choose the length, shape and mass of the reed 112, the dimensions of the aperture 122 and the dimensions and mass of the components defining resonance cavities surrounding the reed 112 and aperture 122, in a manner that optimises the sound produced by the reed assembly at the low end of the audible human spectrum. This gives the free reed assembly 110 a relatively low hearing threshold thereby to obtain audible sensitivity.

To this end, the reed assembly 110 may be optimised to produce sound with a pitch in the range 5Hz to 1 kHz, the preferred pitch being 660Hz.

Claims

1. A sound generating reed assembly (10, 110) characterised by the provision of a discrete reed (12, 112) of a sheet material of a substantially uniform thickness and a reed holder (14) comprising a reed bed (20, 120) and means to clamp the reed (12, 112) to the reed bed (20, 120) at least partially to occlude a fluid flow aperture (22, 122).

2. A sound generating reed assembly according to claim 1 characterised in that the clamping means is constituted by cooperating socket (24, 124) and spigot formations (16, 116).

3. A sound generating reed assembly according to claim 2characterised in thatthe socket formation (24, 124) is defined by an arched cover (24.1) extending at least partially over the end of the reed bed (20, 120) to which the reed (12, 112) is to be secured.

A. A sound generating reed assembly according to either of claims 2 or ^characterised in thatthe spigot formation is constituted by a clamping wedge (16, 116) that is shaped for insertion into the socket formation (24, 124), between the surface of a reed (12, 112) located on the securement end of the reed bed (20, 120) and the arched cover (24.1).

5. A sound generating reed assembly according to any one of the preceding claims characterised in thatthe reed (12, 112) is of polycarbonate sheet material.

6. A sound generating reed assembly according to any one of claims 1 to A characterised in that the reed (12, 112) is of sheet steel.

7. A sound generating reed assembly according to any one of the preceding claims characterised in thatthe reed holder (14, 114) is injection moulded in plastics.

8. A sound generating reed assembly according to any one of the preceding claims characterised in that the reed holder (14, 114) has walls of a substantially uniform thickness.

9. A sound generating reed assembly according to any one of the preceding claims characterised in that the reed holder (14, 114) is shaped externally to conform to a reed assembly mounting opening in a fluid flow passage such as the fluid flow passage of a peak expiratory flow rate monitor.

10. A sound generating reed assembly according to claim 9 characterised in that the reed holder (14, 114) includes an external mounting formation (32) that is a friction fit in the reed assembly mounting opening in the fluid flow passage.

11. A sound generating reed assembly according to claim 10 characterised in that the reed mounting formation (32) is located in an area of the reed holder (14, 114) removed from the means (16, 116, 24, 124) to clamp the reed (12, 112) to the reed bed (20, 120).

12. A sound generating reed assembly according to any one of the preceding claims characterised in that at least one dimension of the reed (12) is greater than a corresponding dimension of the fluid flow aperture (22), the reed (12) being restricted from moving into the aperture (22) during vibration of the reed (12).

13. A sound generating reed assembly according to any one of claims 1 to 11 characterised in that the reed (112) is free to move into the aperture (22) during vibration of the reed (12).

14. A sound generating reed assembly according to claim 13 characterised in thatthe reed (112) and the reed holder (14, 114) include cooperating locating formations adapted to locate the reed (112) with respect to the fluid flow aperture (122).

15. A portable peak expiratory flow rate monitor including a sound generating reed assembly (10, 110) according to any one of claims 1 to 14.

16. A sound generating reed assembly substantially as described in this specification with reference to the accompanying drawings.