US 3127764 A
Abstract available in
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Description (OCR text may contain errors)
April .7, 1964 y E, B- HUDSON 3,127,764
CONCENTRIC DOUBLE APERTURE AIR NOZZLE 4Filed Sept. 18, 1961 4 Sheets-Shea?l 1 April- 7, 1964l E. B. HubsoN 3,127,764
` CONCENTRIC DOUBLE APERTURE AIR NOZZLE Filed Sept. 18, 1961 4 Sheets-Sheet 2 g BY www ATTORNEY April 7, 1964 Filed Sept. 18, 1961 E. B. HUDSON 3,127,764
CONCENTRIC DOUBLE APERTURE AIR NOZZLE 4 Sheets-Sheet 3 am E /Wfm/ l NVENTOR WA/M ATTORNEY April 7, 1964 E. B. HUpsN 3,127,764
CONCENTRIC DOUBLE APERTURE AIR NOZZLE ya .E //fm/ l NVENTOR BY www ATTORNEY United States Patent C) 3,127,764 CONCENTllC Dlillisl AFERTURE AIR NZZLE Earl lli. Hudson, Des Plaines, lill., assigner to GRE. Controls, lne., Chicago, lll., a corporation of Illinois Filed Sept. 1S, wel, Ser. No. 138,850 4 Claims. (tCl. I3-375) This invention relates to non-contacting sensing devices, and more particularly, to improved proximity nozzles capable of accurately measuring the distance to a nearby body over a greater range of distances. A variety of industrial processes, many of which involve winding and reeling, utilize proximity nozzles in order to sense the presence or absence of a material being processed for the purpose ot controlling servomechanisms or like devices to atlect some characteristic or condition ot the industrial process. For example, Patent No. 2,985,399 granted May 23, 1961 to David B. Digel and assigned to the same assignee as the present invention, illustrates the use of a proximity nozzle to follow the changing diameter of a roll of material being coiled without contacting the roll. Such a proximity nozzle is operative to develop a backpressure signal commensurate with the distance between the nozzle end and the roll of material, and the pressure signal may be used to control the speed, for example, Of the Wind-up reel via any one of a variety of servomechanisms. rl`he servomechanism is usually arranged to tend to maintain the nozzle at a given distance from the material surface. While the response of such servomechanisms allow the nozzle to follow roll diameter increase or decrease due to material build-up or payout, an eccentric roll provides rapid rises and dips in the surface to be followed, and unless servomechanism response is extremely rapid, a danger exists that the nozzle and the material may collide. lt a nozzle can be operated at a greater distance from the roll surface, greater roll eccentricities can be tolerated with a given servomechanism system. Ideally, proximity nozzles are capable of producing signal pressures high enough to operate conventional pressure transducers or other servomechanism input mechanisms, they ideally produce adequate signal pressures While maintaining their nozzle tips far enough away from the moving material surfaces that they never accidentally collide, they are conservative in the amount of air they consume, and they operate from a low pressure supply, so that pressure transducer diaphragms or equivalent devices will not be damaged even if the nozzle is accidentally clogged or closed ofi.
The resultant signal pressure developed by most prior art proximity nozzles is roughly proportional to the reciprocal of the distance between the nozzle end and the material surface, and for this reason most prior art proximity nozzles are operated very close to the material surface. While it is possible to increase the nozzle distance for a given pressure signal by increasing nozzle diameter, a small increase in nozzle diameter considerably increases air consumption, with little improvement in signal pressure. Thus it wili be seen that a need has existed for an improved proximity nozzle which may be operated at greater distances from material surf ce without loss of sensitivity.
The present invention contemplates, as a central concept, provision of a curtain of high velocity air around the usual signal air stream, thereby deterring or delaying dii-fusion of the exiting signal air stream until after the curtain of high velocity air has been expended. Beyond that distance the signal air stream eventually disperses as it reaches the material tace or eiiective surface. By preventing the diiiusion of the signal air stream for a distance after it has left the nozzle, the air curtain will be seen to act much like a continuation or extension of the nozzle 3,127,764 Patented Apr.. 7, 1964 ICC wall would act. While provision of the curtain of high velocity air does increase air consumption, the increase is quite modest and economical compared to the increase an equivalent increase in nozzle diameter would require.
Thus it is a primary object of the present invention to provide an improved proximity nozzle which is capable of operating economically and with good sensitivity at greater distances from a material surface. Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts, which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawing.
FIG. la is a View showing the cross-section oi a typical prior art proximity nozzle;
FIG. 1b is a graph of the performance characteristics of the prior art nozzle of FIG. la;
FIG. 2a is an end view of an exemplary embodiment of the present invention;
FIG. 2b is a section view taken along lines 2--2 of FIG. 2a;
FIGS. 3a, 3b and 3c are graphs illustrating the performance of a typical embodiment of the invention.
If a source of air at constant pressure is applied to the entry end 11 of the prior art nozzle of FlG. 1a, the air will ilow through restriction 13 and exit chamber 14,
eventually to impinge upon the surface ot a. material M whose presence or position is to be detected. The backpressure existing in signal pressure conduit 15 at any time depends upon the distance d between the nozzle exit end and the material surface. Curves in FlG. lb illustrate how signal pressure varies with nozzle distance for various representative constant supply pressures applied at 11. The signal pressure falls cti rapidly as distance d is increased. It will be seen that irrespective of the supply pressure, the slope of each curve, which is a measure of nozzle sensitivity, is very small for distance values in excess of 1li inch, thereby limiting use of the nozzle of FIG. la to systems where a nozzle distance of 1/4 inch or less may be tolerated.
Referring now to FIGS. 2a and 2b, the improved nozzle will be seen to comprise a rear block member 2l cylindrical in cross-section, with an axial bore 22 adapted to receive a constant pressure supply of air from a source (not shown). A reduced-diameter partially threaded passage 23 through member Z1 is provided with an externally-threaded hollow sleeve 25 which acts as an axially adjustable restriction. Slot 26 in the end of sleeve 25 allows screwdriver adjustment of sleeve restriction 2S to position the sleeve axially within passage 23. Tapped holes 44, 44 may be used to physically mount the nozzle.
Connecting with passage 23 forward from restriction 25 is signal pressure passageway Z6, which terminates at 27, at which place an air signal line (not shown) may be connected. Forward nozzle member 29 is tightly tted to the forward end of member 21 with an |D-ring 3i) of conventional type fitted therebetween. Member 29 may be aixed to member 21 by provision of threads (not shown) at mating surfaces 33 and 34, or alternatively, machine bolts such as 35, 3S passing through both members may be utilized. Fitted into and supported from the forward end of passage 23 is nozzle tube 36, a short length of hollow tubing adapted to extend through a high pressure chamber 38 concentrcally located Within member 29. Chamber 3S is connected by passage 39 to an external, constant high pressure source of air (not shown). Since exit throat 40 or" chamber 33 concentrically surrounds exit end 42 of nozzle tube 36, a tubular layer of high velocity air completely surrounds the circular pencil of low pressure air expelled from tube 35, substantially as diagrammatically indicated in FIG. 2a. The surrounding curtain of high velocity, low volume air prevents the low-pressure air stream from spreading or diffusing until the high velocity stream has spread, thereby allowing the improved proximity nozzle to operate at greater distances from material surfaces.
Some performance characteristics of a typical embodiment of the invention are illustrated in FIG. 3a, where the variation of signal back pressure with nozzle to surface distance is plotted for four different values of constant (low) pressure applied to entrance 22 of the improved nozzle, with the same value of high constant pressure air applied via passage 39 of the nozzle. The same nozzle characteristics but with an increase in the high pressure supply are shown in FIG. 3b. FIGS. 3a and 3b relate to characteristics of the nozzle when such a nozzle is directed toward a solid sheet, such as steel strip, while FIG. 3c shows comparable characteristics; for two different high pressures, when the improved nozzle is directed toward a partially open knitted or meshed material, such as tire cord. One will immediately notice that the curves of FIGS. 3cr-3c remain fairly steep at considerable distances in excess of 1/4 inch, indicating sufcient sensitivity to permit use of the nozzle at increased distances from material surfaces.
When the nozzle is quite close to the material surface the signal pressure approaches the high pressure supply value, and at very great distances to the material the signal pressure falls to a negative value. Thus, signal pressure varies over a much greater range with the invention than with the prior art device of FIG. 1a. When operating near M from the material, the sensitivity of the prior art nozzle is of the order of 1.5 inch wc per inch distance d, while the sensitivity of the invention at twice the nozzle distance (i.e., 1/2 inch) was approximately 11.5 inch wc per inch distance d, an improvement in sensitvity by a factor greater than 7, while air consumption increased by no more than a factor of 2.5 to 3.
While I have illustrated my invention in connection with a proximity nozzle of usual type, it should be recognized that the invention also may be applied to nozzles of' the type sometimes used for edge or side register control. For example, rather than a simple circular bore, the through low pressure passageway of the nozzle may be provided with an elongated slit cross-section. Provision of the curtain of high velocity air surrounding the resulting sheet-shaped signal airstream will serve to allow side register control by means of a nozzle mounted at a greater distance from the material whose presence is being sensed. The back-pressure signal wiil vary with height or distance from the material as well as edge position, however so that use of the invention for edge guiding will be limited principally to applications where the web of material does not vary appreciably in its distance from the nozzle.
Inspection of the performance characteristics also reveal that the use of the surrounding high velocity layer of air results in negative pressure at various distances. The use of negative rather than positive pressure provides desirable fail-safe features. If the high pressure air supply (or both the high pressure and the low pressure supply) is interrupted, the change in signal pressure resulting from the substitution of atmospheric pressure for the interrupted supply will be in the proper direction, in a servo-mechanism system adapted to maintain a given nozzle distance, to drive the nozzle away from the material, rather than toward the material. It solely the low pressure supply is interrupted, the nozzle back-pressure signal will, in such a follow-up system, maintain the nozzle at some xed distance from the material, rather than contacting the material.`
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are eciently attained, and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.
Having described my invention, what l claim as new and desired to secure by Letters Patent is:
1. An improved proximity nozzie for sensing the proximity of a material against which said nozzle directs an airstream, comprising in combination: first means defining a first passageway, said first passageway being connected at one end to a first air pressure supply, thereby to expel air toward said material; second means defining a chamber having an opening surrounding the exit end of said rst passageway; a second air pressure supply, said chamber being connected to said second air pressure supply to supply air to said chamber at a second pressure higher than the pressure of said first air pressure supply; pressure-detecting means; and a second passageway connected to said pressure-detecting means and to said first passageway between said one end and said exit end to sense back pressure in said first passageway resulting from the proximity of said material, the expulsion of air from said opening of said chamber serving to provide a curtain of air which surrounds, for a desired distance from said exit end, the air expelled from said first passageway, thereby allowing said nozzle to operate at an increased distance from said material.
2. A nozzle of the character claimed in claim 1 having an axially adjustable restriction mounted in said flrstpassageway between said one end of said first passageway and the point at which said second passageway is connected to said first passageway.
3. A nozzle of the type claimed in claim 1 in which said first means comprises a cylindrical metal block, said first passageway comprises an axial bore through said block, and in which said chamber is affixed to one end of said cylindrical block and located concentrically relative to said cylinder and said axial bore.
4. An improved proximity detection apparatus for sensing the proximity of a material against which said apparatus directs an airstream, comprising in combination: a first member having a through passageway, one end of said passageway being adapted to be connected to a first air source for supplying air at a rst pressure to said passageway; a chamber having an opening surrounding the other end of said passageway; a second air source connected to supply air to said chamber at a second pressure greater than said first pressure; pressure-detecting means; and a secondpassageway having one of its ends connected with said through passageway between the ends of said through passageway and its other end connected to said pressure-detecting means, thereby to enable said pressure-detecting means to detect variation in the back pressure in said through passageway as the distance between said material and said proximity detection apparatus varies.
References Cited in the le of this patent UNITED STATES PATENTS 2,813,750 Marantz Nov. 19, 1957 2,917,244 Gould Dec. 15, 1959 2985,399 Digel May 23, 1961