US3491332A - Sonic detector - Google Patents

Description

Haw 0R 3,491,332

Jan. 20, 1970 c, ca. LOMAS ET L 3,491,332

SONIC DETECTOR Filed June 28, 1968 I3 If (5 7.5

ENERGY NOR- 2 INVENTOR$ W cumwes G. LMAS mwm RQYMGND mowsm ATTORNEYS States ABSTRACT OF THE DISCLOSURE A sonic detector responds to interruption of an acoustic energy beam directed thereat. The beam is transmitted through an aperture in an enclosure wall behind which is a flowing fluid stream oriented to be impinged upon by portions of the beam transmitted througlflthe aperture. {The stream is sensitive to at least one frequency component of the beam whereby the stream remains laminar unless impinged upon by the beam in which case it is rendered turbulent. Means for discerning the laminar and turbulent states of the stream are provided. The edges of the aperture ditfract the beam energy such that the predetermined frequency components of'the beam converge at a focal point through which the fluid stream flofws. In addition, a reflector plate may be positioned behind the stream, with or without an apertu red enclosure, to reflect energy at said predetermined frequency back into impinging relation with thestream'.

BACKGROUND OF THE INVENTION The present invention relates to object detection based on interruptions of a beam of acoustic energy, and more particularly, to fluidic sonic detectors utilizing the phenomenon "of laminar-to-turbulent transition of a fluid stream in response to acoustic energy at a specified frequency impinging thereagainst.

It is known that laminar fluid streams may be rendered turbulent in response to impingement thereagainst of acoustic energy at a specified frequency. Su'ch fluid streams may be sensitive to one or more discrete frequencies or band of frequencies as determined by the distance between the nozzle and receiving aperture, and the stream Reynolds number. Thus, for a given set of parameters, a stream can have a greater sensitivity to one frequency or group of frequencies than to other frequencies. This phenomenon would appear to be readily applicable to object-detection applications whereby a stream would normally be rendered turbulent by a beam of acoustic energy impinging thereagainst and rendered laminar in response to the presence of an object appearing between the energy source and the fluid stream. However, there are a number of practical problems involved in utilizing the above described phenomenon for object-detection purposes, More particularly, due to the sensitivity of the fluid stream to various acoustic signals, the detector would have to be employed in an environment substan tially devoid of acoustic noise. In addition, in order for the acoustic beam to have a suflicient intensity at the point of impingement against the 'fluid stream to cause the stream to become turbulent, the acoustic energy source must either operate at extremely high power levels or must be located so close to the sensing stream as to render object detection impractical.

Further, it is desirable that the signal received by the sensing stream receiver tube be capable of utilization in driving a fluidic switching circuit such as a fluidic NOR gate which assumes a NOR state in response to a low pressure input signal below some threshold level, and an OR state in response to an input pressure signal above atent the threshold level. Since the fluid receiver tube for the sensing stream receives a pressure signal during both the turbulent and laminar states of the sensing stream, it. is important that the low pressure level, received when the sensing stream is in its turbulent state, is sufficiently low to permit the NOR gate to revert to its NOR state. This requires a highly turbulent state for the sensing stream when impinged upon by the acoustic beam, and this in turn requiresia relatively high-intensity acoustic signal in order to produce the required degree of turbulence. Again, this would appear to require either providing a high power acoustic energy source or, in the alternative, placing the source too close to the sensing stream to permit detection {if objects of any practical size.

Still another consideration limiting the practicability of utilizing the acoustic sensitivty of a laminar stream for. object-detecton applications is the sensitivity of the sensing stream to randomly occurring air drafts which may tend to either deflect the sensing stream from its receiver tube or, in some cases, induce turbulence in the stream.

It is therefore an object of the present invention to provide an acoustic-sensitive object-detection apparatus utilizing the laminar to turbulent transition of a fluid stream in response to impingement thereagainst of acoustic energy at a specified frequenry, wherein the abovedescribed problems are eliminated.

It is another object; of the present invention to utilize the laminar to turbulent transition of a fluid stream in response to acoustic signals impinging thereagainst to provide a practical and reliable device for detecting the passage of anobject between a source of acoustic energy and the fluid stream.

It is another object of the present invention .to utilize a fluid stream for detecting interruption of a beam of acoustic energy impinging thereagainst -by sensing whether the fluid stream is in its laminar or turbulent state.

SUMMARY OF THE INVENTION In accordance with the principles of the present invention a flowing fluid stream is located behind a wall of an enclosure toward which a beam of acoustic energy is directed. An aperture is defined in the wall for transmitting portions of the beam therethrough so as to impinge against the fluid stream. The fluid stream is laminar when undisturbed and becomes turbulent when impinged upon by acoustic energy at a predetermined frequency, a component of which frequency is present in the beam. The edges of the aperture diflract acoustic energy transmitted therethrough so that energy at the predetermined frequency converges toward a focal point behind the apertured wall. The fluid stream flows through the focal point and therefore the acoustic energy intensity at the point of impingement against the fluid stream is amplified.

Located behind the fluid stream is a reflector plate 1 which may be either flat or concave (the concave surface facing the fluid stream) for reflecting acoustic energy back toward the fluid stream. The reflector plate may be utilized with or without the apertured enclosure, depending upon the required degree of amplification of the acoustic beam intensity. I

The size of the aperture, the spacing of the fluid stream therefrom, and the spacing of the reflector plate from the fluid stream are all chosen for maximum amplification of the intensity of the acoustic beam at the point of impingement against the fluid stream. These dimensions de-v pend upon a particular frequency to which the fluid stream is sensitive, which in turn depends upon the distance between the supply tube issuing the stream and the stream receiver tube, and the stream Reynolds number.

The resulting configuration permits relatively large spacing between the acoustic beam source and the sensing stream without requiring a high power source because of the beam intensity amplification produced by the beam diffraction at the aperture edge and by the acoustic energy reflection from the reflector plate. In addition, external acoustic disturbances have minimal effect on the sensing stream due to the apertured enclosure, which also minimizes the effects of the random air drafts and other environmental disturbances. Further the reflector plate, when employed with the apertured wall configuration, produces a sufficient amplification of the acoustic energy beam intensity to render the pressure level of the turbulent stream received by the receiver tube substantially below the threshold of a conventional fluidic NOR gate.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects, features and advantages of the present invention; will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic representation of an object detection system in accordance with the principles of the present invention;

FIGURE 2 is a diagrammatic sketch illustrating the configuration of the sensor portion of the system of FIG- URE l;

FIGURE 3 is a diagrammatic sketch illustrating a modification of the sensor illustrated in FIGURE 2; and

FIGURE 4 is a schematic illustration of the sensor circuitry of the system illustrated in FIGURE 1.

DETAILED DESCRIPTION OF ;THE PREFERRED EMBODIMENT Referring now specifically to FIGURE 1 of the accompan'ying drawings, there .is diagrammatically illustrated a system for detecting objects in-accordance with the principles of the present invention. A source of acoustic energy 11 may take the form of a whistle mounted in a reflector, the latter beaming the acoustic energy across an open space. Preferably, the acoustic beam is at an ultrasonic frequency (that is, at a frequency above the range of frequencieswhich are normally audible to the human ear) in order to avoid annoyance of people in the surrounding area. The acoustic beam is directed generally toward an enclosure 13 within which is housed an acoustic-sensitive detector in accordance with the principles of the present invention. A front wall 15 (that is,

the wall facing source 11) of enclosure 13 has a circular aperture 17 defined therein. Aperture 17 .is in substantial alignment with the beam of energy transmitted from source 11 and of itself comprises part of the acoustic-sensitive detector of the present invention. An object 19 to be detected, when passed between source 11 and enclosure 13, intercepts the acoustic beam so that no more than a negligible level of acoustic energy is received at aperture 17. It is the function of the sensor unit Within enclosure 13 to provide a fluid output signal indicative of the passage of an object, such as object 19, between source 11 and enclosure 13.

Referring now to FIGURE 2 of the accompanying drawings, there is illustrated a sketch in partial section of the interior of enclosure 13 of FIGURE 1. Disposedbehind' wall 15 is a nozzle or supply tube 21 which is responsive to application of pressurized fluid thereto for issuing a laminar stream of fluid. A receiver tube 23 is disposed in coaxial alignment with supply tube 21 so as to receive the stream issued thereby, when undisturbed, in its laminar state. Supply tube 21 is disposed so that the fluid stream is directed generally perpendicular to the acoustic beam and so that acoustic energy transmitted through aperture 17 impinges against the stream. The perpendicular relationship between the stream and the beam is, not critical; however, in order to achieve the maximum 4 effect of the acoustic energy in converting the laminar stream to its turbulent state, it is desirable that the stream be directed as nearly perpendicular to the direction of the acoustic energy h 'earn as possible.

Acoustic energy transmitted through aperture 17 is diffracted by the edges of the aperture so that the transmitted acoustic energy converges toward a focal point some distance behind wall 15, the focal point position changing with :the frequency of the acoustic energy transmitted through the aperture. In addition, for any given frequency, variation in size of the aperture 17 produces concomitant Variations in focal point location. The supply tube 21 and receiver tube 23 are disposed so that the fluid stream flowing therebetween passes through the focal point for the frequency component of the acoustic energy to which the stream is highly sensitive. The frequency component to which the stream is highly sensitive, as discussed above, depends upon the stream Reynolds number (more specificallyfthe fluid supply pressure P+, the diameter of supply tube 21 and the kinematic viscosity of the stream) and the distance between the supply tube 21 and the receiver tube 23. These parameters are, of course, chosen so that the specified frequency to which the stream is sensitive is the same as the frequency of the acoustic energy beam, or at least the same as one frequency component of the acoustic energy beam. Since acoustic energy at the specifled frequency is focused to impinge against the stream, the intensity of the acoustic energy at that point of impingement is relatively high and therefore a relatively high degree of turbulence is induced in the stream thereby.

In addition to focusing the acoustic energy to provide intensity amplification, aperture 17 in wall 15 minimizes the effects of acoustic signals which are not axially directecl with respect to aperture 17. Such signals "may, in fact, be focused somewhat by the aperture but :at focal points other than that for which the axially directed acoustic beam is focused. Generally these signals will have too low an intensity after passage through aperture 17 to significantly affect the fluid stream.

The amplification of the acoustic beam intensity at the point of impingement against the fluid stream permits greater spacing between source 11 and enclosure'13 (of FIGURE 1) for a given power level of source 11. Practical object detection is therefore realizable by virtue of the arrangement thus far described.

Another means of amplifying the intensity of the acoustic signal impinging against the stream is to provide a reflector plate 25 behind the stream; that is, the plate is disposed on the side of the stream opposite aperture 17. Reflector plate 25 acts to reflect acoustic energy back toward the stream and thereby increase the turbulence of the stream in response to a given acoustic signal level. We have found that the optimum distance between plate 25 and the stream flowing between tubes 21 and 23 for inducing maximum stream turbulence varies with specified frequency component in the acoustic energy beam to which the stream responds by becoming turbulent. Further, it has been found that the provision of plate 25, spaced for maximum turbulence at the specified frequency, has the effect of rendering the stream sufficiently turbulent to lower the average pressure level in receiver tube 23 below that which is the threshold pressure in conventional fluidic NOR gates. That is to say, ,when a conventional fluidic NOR gate, such as the type illustrated and described in US. Patent No. 3,286,086 has its control port connected to receive the pressure signal procided by receiver tube 23, the NOR gate does, in fact, assume different states corresponding to the laminar and turbulent states of the fluid stream flowing between supply tube 21 and receiver tube 23.

It has been found that, in addition to utilizing acoustic beam frequencies above the range of audibility to humans, it is desirable to utilize ultrasonic frequencies above 30 kHz. This is because acoustic disturbances generated by frictional engagements between surfaces, such as might sonic source frequency:

Diameter of aperture 17 inch.' 1 Distance between wall and sensing stream flowing between tubes 21 and 23 inch Diameter of sensing stream do .023 Distance between supply tube 21 and receiver tube 23 inch .385 Supply pressure '(P+) p.s.i.g 2.91 Distance between sensing plate and sensing stream inch- .22

Referring now to FIGURE 3 of the accompanying drawings, there is illustrated an alternative embodiment to the sensor illustrated in FIGURE 2 wherein the flat reflector plate 25 of FIGURE 2 has been replaced by a concave reflector plate 27 in FIGURE 3. In all other respects, the apparatus illustrated in FIGURE 2 is identical to that illustrated in FIGURE 3 and like numerals are 7 employed in both figures to designate like components. Concave reflector plate 27 is disposed with its concave surface facing the sensing stream flowing between tubes 21 and 23. The apex of the concave surface is optimally spaced from the sensing stream to induce maximum turbulence therein in response to acoustic signals at the frequency to which the sensing stream is rendered turbulent.

Referring now to FIGURE 4 of the accompanying drawings, there is illustrated in schematic form a complete fluidic sensing circuit constructed in accordance with the principles 9f the present invention. The entire circuit is shown enclosed in enclosure 13 and the acoustic beam from source 11 is'illustrated as entering enclosure 13 via aperture 17. In all respects, the circuit illustrated in FIGURE 4 comprises elements which are the same as those illustrated in FIGURE 2 with the exception that NOR gate-29 is illustrated in FIGURE 4 as receiving the output pressure signal from receiver tube 23. NOR gate 29, as described above, may take the form of the NOR gate illustrated and described in US. Patent No. 3,286,- 086 and functions to provide an output signalonly in the absence of an input signal applied thereto and likewise provides no output signal when an input signal is applied thereto. When the beam of acoustic energy is received by aperture 17 and focused on the sensing stream from supply tube 21, the combined amplification effects of aperture 17 and the reflector plate 25 renders the sensing stream sufliciently turbulent so thatfiuid pressure below the switching threshold of NOR gate 29 is provided by receiver tube 23 and NOR gate 29 provides a NOR output signal. Upon interruption of the acoustic beam, such as by interposition of object 19 of FIGURE 1 between source 11 and enclosure 13, the fluid stream issuing from tube 21 becomes laminar and the receiver tube 23 receives a relatively large pressure. This relatively large pressure is sufficient to change the operational mode of NOR gate 29 to inhibit the NOR output signal therefrom.

Additional fluidic logic circuitry may be included within enclosure 13 to provide any one or a number of logic functions desired in response to object detection by the sensing stream.

While we have described and illustrated one specific embodiment of our invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be-resorted 'to without departing from the true spirit and scope of theinvention.

We claim:

1. A fluidic detec tor comprising:

awall member;

a source of acoustic energy disposed in front of said wall member for providing an acoustic energy beam directed generally toward said wall member and having at least one predetermined frequency component;

an aperture defined in said wall member and disposed for transmitting at least a portion of the acoustic energy in said beam when otherwise unimpeded through said aperture;

supply means disposed behind said wall member for issuing a fluid gstream which remains laminar when undisturbed and 'which becomes turbulent in response to impingement thereagainst by acoustic energy at said predetermined frequency;

wherein said aperture is configured such that acoustic energy at saidpredetermined frequency transmitted through said aperture is diffracted and converges toward a focal point through which said fluid stream flows;

means for sensing whether said fluid stream is laminar or turbulent.

2. The combination according to claim 1 wherein said aperture has edges which diflract acoustic energy transmitted through said aperture, the size of said aperture being such that aco'ilstic energy transmitted therethrough at said predetermined frequency converges toward a specified focal point behind said wall member, and wherein said supply means is positioned such that said fluid stream passes through said specified focal point.

3. The combination according to claim 2 wherein said wall member comprises one wall of an enclosure within which said supply means and said means for sensing are disposed.

4. The combination according to claim 3 wherein said supply means includes a supply tube responsive to application of fluid -"at a specified pressure thereto for issuing said fluid stream, and wherein said means for sensing includes a fluid receiver tube disposed substantiallyv coaxial with said supply tube and spaced therefrom to receive substantially all of said fluid stream in a laminar state when said fluid stream is undisturbed and to receive portions of said fluid stream in a turbulent state when acoustic energy at said predetermined frequency impinges against said fluid stream, and wherein the inside diameter of the supply tube, said specified pressure, and the distance between the supply tube and said receiver tube are interrelateclgsuch that the fluid stream is rendered turbulent in response to impingement thereagainst of acoustic energy at said predetermined frequency.

5. The combination according to claim 4 further comprising reflector means disposed within said enclosure on the opposite side of said fluid stream from said aperture for reflecting acoustic energy impinging against said reflector means into impingement against said fluid stream.

6. The combination according to claim 5 wherein the distance between said reflector means and said fluid stream is that which induces maximum turbulence in said fluid stream in response to reflection of acoustic energy at said predetermined frequency.

7. The combination according to claim 6 further comprising a fluidic NOR gate responsive to the fluid flow in said receiver tube for providing a fluid signal only when said fluid stream is turbulent.

8. The combination according to claim 6 where said reflector means comprises a flat plate having a reflecting surface disposed substantially perpendicular to said acoustic energy beam.

9. The combination according to claim 6 wherein said concave surface facing said fluid stream and wherein the apex of the concave surface is located a distance from said fluid stream such that maximum turbulence is induced in said fluid stream in response to reflection of acoustic energy at said predetermined frequency.

10. The combination according to claim 2 further comprising reflector means disposed on the opposite side of the fluid stream from said aperture for reflecting acoustic energy impinging against said reflector means into impingement against said fluid stream.

11. The combination according to claim 10 wherein the distance between said reflector means and said fluid stream provides maximum turbulence in said fluid stream in response to reflection of said predetermined frequency component of said acoustic energy beam.

12. The combination according to claim 11 wherein said predetermined frequency is ultrasonic and above 30 kHz.

13. The combination according to claim 11 wherein said source comprises a whistle for generating an ultrasonic signal and a reflector for beaming said signal toward said aperture in said wall member.

14. A fluidic detector comprising:

source means for providing a beam of acousticenergy having at least one predetermined frequency component;. means for issuing a fluid stream which is laminar when undisturbed and turbulent when impinged upon by acoustic energy at said predetermined frequency, said supply means being disposed such that said beam when otherwise unimpeded impinges against said fluid stream; reflector means disposed on the opposite side of said stream from said source for reflecting energy from said beam at said predetermined frequency into impinging relationship with said fluid stream; and

means for sensing whether said fluid stream is laminar or turbulent.

15. The combination according to claim 14 wherein said reflector means comprises a flat plate located at a distance from said stream for providing maximum reflection of said predetermined frequency component of said beam to induce maximum turbulencelin said stream.

16. The combination according to claim 14 wherein said reflector means comprises a concave plate having a concave surface facing the fluid stream with the apex of said concave surface located at a distance from said fluid stream for providing maximum reflection of the predetermined frequency component of said beam into impinging relation with said stream.

17. The combination according to claim 14 wherein the supply means includes a supply tube responsive to application of fluid at a specified pressure for issuing said fluid stream, and wherein said means for sensing includes a receiver tube disposed substantially coaxial with said supply tube and spaced therefrom to receive substantially all of said fluid stream when laminar and to receive portions of said fluid stream when rendered turbulent in response to impingement against said fluid stream by acoustic energy, andv wherein the inside diameter of said supply tube, said specified pressure, and the distance between said supply and receiver tubes are related such that said fluid stream is rendered turbulent in response to impingement thereagainst by acoustic energy at a predetermined frequency.

18. Affluidic detector responsive to interruption of a beam of acoustic energy directed thereat, said beam including at least one predetermined frequency component to which'said detector is sensitive, said detector comprisan enclosure including a wall member toward which said beam is directed from exteriorly of said enclosure, said wall member having an aperture defined therein for transmitting at least a portion of the said heard through said aperture; supply means disposed within said enclosure for issuing a fluid stream which is laminar when undisturbed and turbulent when impinged upon by acoustic energy at said predetermined frequency, said supply means being disposed in alignment with said aperture such that acoustic energy transmitted through said aperture impinges upon said fluid stream; and

means for sensing whether said fluid stream is laminar or turbulent.

19. The combination according to claim 18 further comprising reflector means disposed within said enclosure and in alignment with said aperture and said stream in the order stated for reflecting acoustic energy at said predetermined frequency back toward the fluid stream in impinging relationship thereto.

20. The combination according to claim 19 wherein the edges of said aperture difiract acoustic energy transmitted through said aperture such that acoustic energy at said predetermined frequency converges toward a specified focal'ipoint within said enclosure, wherein the supply means is located so that said fluid stream passes through said specified focal point and wherein the reflector means is spaced; from said fluid stream by a distance equal to one-quarter wavelength of said predetermined frequency component. i

21. The combination according to claim 20 further comprising a fluidic NOR gate responsive to said means for sensing for providing a fluid signal at one level when said stream is laminar and at a second level when said stream is turbulent, said fluidic NOR gate being disposed within said enclosure.

References Cited UNITED STATES PATENTS 3,271,755 9/1966 Bagno 34016 X RICHARD A. FARLEY, Primary Examiner US. 01. X.R.

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