IE53117B1 - Improvements relating to focussing apparatus - Google Patents

Abstract

A focussing apparatus essentially comprises a truncated outer cone (10) and a coaxial inner cone (11) which between them define a narrow annular passageway through which signals can be transmitted from and to a transducer (30). The arrangement tends to create a substantially parallel beam of radiation and the focussing apparatus has very good directional characteristics. The transducer (30) is mounted on a pillar (32) within a transducer housing collar (12) resulting in a very compact design. The inner cone (11) is held in place by a number of radiating ribs (13) so that the apex of the cone lies on the plane of truncation A-A of the truncated cone (10).

Description

This invention relates to cones and concave reflectors which are used for focussing acoustic signals. Examples of these are the speakers in radios.

Such a reflector can be used as part of a distance 5 sensing apparatus wherein an ultrasonic transducer situated in a recess is excited by an exciter means within 1 a case to emit pulses of ultrasonic radiation, the conical or concave sides of the recess serving to define the field of view of the transducer. A problem with this 10 design is that the moment the signal exits from the recess it is free to begin to diverge. Xn diverging, a lot of the energy in the transmission signal is wasted as the distance to be measured is almost always directly in the forward direction of the transmitting beam. Spurious reflected signals can be received from obstacles outside the direct line to the target but in the field of view which can lead to erroneous readings of the distance to be measured. The reception of the reflected signals may well be very poor due to the size of the transducer and the inefficiency of the recess in collecting the reflected signals.

It is an object of the present invention to overcome some of the problems described above and to provide a focussing apparatus which will radiate a narrow beam and collect reflected signals from target objects directly in front of the cone and which will prevent spurious reflected signals from being collected.

According to the invention there is provided a focussing apparatus comprising a truncated cone as hereinafter defined, a cone having a closed apex and mounted coaxially within the truncated cone such that the apex of the cone lies at or near the plane of truncation of the narrower end of the truncated cone and such that the wider ends of the cone and the truncated cone both face in the same direction, and a transducer housing mounted adjacent the truncated end of the truncated cone and incorporating an electroacoustic transducer, the transducer housing comprising a collar extending back from the narrower end of the truncated cone, with the transducer mounted on a support pillar within the collar.

The term truncated cone is used herein to define a geometrical shape having substantially the configuration of a cone with its apex removed.

The cone and the truncated cone may have substantially identical angles of divergence, or if desired, the truncated cone could have a larger angle of divergence than the cone.

Ideally the transducer will be of the type which is capable of radiating and receiving ultrasonic signals.

A resilient buffer is preferably included between the support and the transducer. Also the transducer may have a signal collecting plate mounted centrally thereon. Advantageously the cone may be replaceably mounted within the truncated cone.

The invention also extends to a distance measuring 3 117 device comprising focussing apparatus according to the invention as hereinbefore defined, and including control circuitry for energising the transducer and processing signals received by the transducer and a display device for indicating results of a calculation of distance measured made by the control circuitry.

Preferably means for projecting a light beam is mounted on or in the device to act as a direction finder.

The invention may be performed in various ways and preferred embodiments thereof will now be described with reference to the accompanying drawings, in which:Figure 1 is a diagrammatic perspective view of one form of apparatus of this invention; Figure 2 is a further diagrammatic perspective view of the apparatus of Figure 1; Figure 3 is a diagrammatic perspective view of the central part of the apparatus in Figure 1; Figure 4 is a longitudinal sectional view of the apparatus shown in Figures 1 and 2, indicating the path of transmitted and received signals; Figure 5 is a view similar to that of Figure 4 illustrating a modified form of apparatus of this invention; and Figure 6 is a drawing of a distance sensing and measuring apparatus incorporating a focussing device and as shown in the previous Figures.

Referring firstly to Figures 1, 2 and 3 the apparatus comprises a truncated cone member 10, a cone 11, a transducer housing collar 12 and four ribs 13 projecting outwardly from the outer surface of the cone 11. The transducer housing 12 is open at both ends 14, 15 and the end 15 is attached to the truncated open end 16 of the truncated cone member 10. The cone 11 is attached to the inside surface 20 of the truncated cone member 10 by means of the fixing ribs 13 in such a manner that the apex 17 of the cone 11 is situated in the centre of the plane of truncation, indicated by the dashed line A-A in Figure 4, of the truncated cone member 10 so that the mouth 18 of the cone 11 is facing in the same direction as mouth 19 of the truncated cone member 10.

The cone 11 in this case has a preferred inclusive acute solid angle of 54°, but this angle may be varied. Referring now more particularly to Figure 4, the truncated cone member 10 is shown having a larger acute solid angle than the cone 11. In this example the inner surface 20 of the truncated cone member 10 diverges relative to the inner surface 21 of the cone 11. However the inner surfaces 20 and 21 of the cone 11 and of the truncated cone member 10, respectively, may converge relative to each other or they may be substantially parallel.

Figure 5 illustrates a focussing device of slightly modified form from that shown in Figure 4 and in particular illustrates how a transducer 30 will desirably be mounted within the collar 12. Thus the end of the collar 12 is enclosed by a plate 31 and carries a central 5 mounting pillar 32 on which a plate-like ceramic transducer 30 is mounted via a resilient buffer 33. A collecting plate 34 is positioned on top of the transducer plate. A pair of wires 35 is connected to the transducer plate 30 by means of which an electric current may be supplied to excite the transducer plate.

A signal 22 from the transducer 30 housed within the transducer housing 12 will be transmitted in the direction of the cone 11. Most signals from the transducer 30 will strike the outer surface 23 of the cone 11 at an angle to the horizontal of approximately 27° and thereafter will be reflected outwards towards the inner surface 20 of the truncated cone member 10 substantially in a plane parallel to the plane of truncation A-A of the truncated cone member . On striking the inner surface 20 of the truncated cone member 10 the signal 22 will be reflected towards the mouth 19 of the truncated cone member 10 and in a plane substantially perpendicular to the plane of truncation A-A. In this way a substantially parallel beam of radiation can be made to travel in a specific direction, although the beam will tend to diverge as the distance it traverses increases. 3117 If the signal 22 is reflected from an obstacle then it may return to the transducer along a substantially similar path to that followed when being transmitted as described above. Ideally a major part of any signal transmitted from the transducer (not shown) situated in the transducer housing 12 will be reflected by obstacles and follow a path similar to but in the opposite direction to that of the signal 22 as described above, and will be received in the transducer again. Reflections such as these which follow the same path on reflection as followed on transmission shall be called direct reflections.

Indirect reflections are also received and these are signals which are reflected back to the transducer but which do not follow the same path as on transmission. Signals such as that following the path 24 shown in Figure 5 shall be called indirect reflections. An example of an indirect reflaction will now be described. A signal 24 is transmitted from the apparatus as described above and . because of the shape and/or direction of an object from which it is reflected a signal is deviated slightly. On reflection back to the apparatus the signal 25 will not travel along the same path as on its transmission journey, but may be received by the apparatus and then undergo a multiplicity of reflections between the inner surface of the truncated cone member 10 and the outer surface 23 of the cone 11 before finally entering the transducer again.

It will be appreciated that the focussing device shown in Figure 4 will operate in much the same manner as that shown in Figure 5 and sample signals 22, 24 and 25 are illustrated in the same manner.

The narrowness of the angle of the beam produced by the focussing device will depend upon the angles formed by the inner surface of the inner cone member 10 and the outer surface of the cone 11. Requirements may vary for different purposes and the desired beam angle can be achieved for any particular purpose by incorporating a cone 11 of a shape sufficient to produce the desired beam angle. For most purposes it is envisaged that a projection angle of between 2° and 5° will be desirable. The shape of the inner surface of the truncated outer cone 10 determines the beam intensification and the changes in size will naturally modify the overall collection area for reflected signals.

The apparatus may be used with equipment and signals for measuring the dimensions of a room, the height of a ceiling, or height of a vehicle and as a focussing and/or distance finder in cameras and rifles, for use by reversing vehicles, and for direction finding in foggy conditions.

Such equipment is illustrated diagrammatically in Figure 6 and comprises a hand-held box 36 which incorporates a built-in power supply and electronic circuit unit 37 which feeds signals to the transducer 30 through the wires 35 and processes reflected signals which are received by the transducer 30. The unit 36 controls a display device 38 Which indicates a distance measure as calculated by the unit 37. A button 39 is provided for switching on the device when in use. The box 36 may also carry a direction finding device comprising a halogen bulb 40 powered from the power supply unit 37 which can produce a narrow beam of light over a relatively long distance even if a low voltage power source is used, by passing the light through a series of prisms 41. The light beam can be aimed at a target object so that the beam of sonic or ultrasonic signals will also be targetted onto that object.

The apparatus may be constructed in various ways other than those as shown. For example the apparatus may be constructed in one piece, such as in a moulding process or it may be constructed by fixing together the cone 11, the truncated cone member 30, the ribs 13 and the transducer housing 12. In a further embodiment the truncated cone member 10 may be constructed from a plurality of detachable sections which for instance would facilitate storing of the apparatus.

The major advantages of this apparatus over prior knovm focussing systems are 1. The apparatus has strong directional focussing properties. 2. The apparatus can focus a more powerful signal. 3. The apparatus will minimise false readings by keeping the signal beam as narrow as possible and the apparatus will also be able to pick up much weaker signals which are reflected from objects a greater distance away.

The truncated cone 10 acts as an ear to collect the reflected signals but it will only collect substantially signals from a direction in which they were transmitted and will thus tend to eliminate false readings.

Claims (11)

1. A focussing apparatus comprising a truncated cone as hereinbefore defined, a cone having a closed apex and mounted coaxially within the truncated cone such that the apex of the cone lies at or near the plane 5 of truncation of the narrower end of the truncated cone and such that the wider ends of the cone and the truncated cone both face in the same direction, and a transducer housing mounted adjacent the truncated end of the truncated cone and incorporating an electroacoustic 10 transducer, the transducer housing comprising a collar extending back from the narrower end of the truncated cone, with the transducer mounted on a support pillar within the collar.

2. A focussing apparatus according to claim 1, 15 wherein the cone and the truncated cone have substantially identical angles of divergence.

3. A focussing apparatus according to claim 1, wherein the truncated cone has a larger angle of divergence than the cone. 20

4. A focussing apparatus according to any one of claims 1 to 3, wherein the transducer is of the type which is capable of radiating and receiving ultrasonic signals.

5. A focussing apparatus according to any one 25 of claims 1 to 4, including a resilient buffer between the support and the transducer.

6. A focussing apparatus according to any one of claims 1 to 5, wherein the transducer has a signal collecting plate mounted centrally thereon. 5 -

7. A focussing apparatus according to any one of claims 1 to 6, wherein the cone is replaceably mounted within the truncated cone.

8. A focussing apparatus according to claim 1, substantially as herein described with reference to the accompanying drawings.

9. 10 9. A distance measuring device comprising focussing apparatus according to any one of claims 1 to 8, including control circuitry for energising the transducer and processing signals received by the transducer and a display device for indicating the 15 results of a calculation of distance measured made by the control circuitry. 10. A distance measuring device according to claim 9, wherein means for projecting a light beam is mounted on or in the device to act as a direction 20 finder.

10.

11. A distanco measuring device according to claim 1, substantially as herein described with reference to the accompanying drawings.