US3576131A

US3576131A - Pneumatic snap acting mechanism

Info

Publication number: US3576131A
Authority: US
Inventors: Franklin J Calderazzo
Original assignee: Northeast Fluidics Inc
Current assignee: Northeast Fluidics Inc
Priority date: 1969-02-19
Filing date: 1969-02-19
Publication date: 1971-04-27
Anticipated expiration: 1988-04-27

Abstract

The disclosure includes an object proximity sensing device of the type ejecting a fluid jet towards the object. This jet is ejected through a chamber having a wall in which an opening is positioned so that the jet passes through this opening going towards the object and the wall is reciprocative in the direction of the jet. The jet passing through the opening acts as an aspirator so that normally the chamber is at subatmospheric pressure and the wall is pulled backwardly, but when the jet leaving the opening senses the proximity of the object the pressure in the chamber begins to rise, the wall begins to move forwardly with a consequent increase in the back pressure on the jet, and this action continues with great rapidity so that the wall snaps forwardly. The reverse occurs when the object moves away. In this fashion the pressure in the chamber changes rapidly from subatmospheric to superatmospheric pressure, thus providing a positive on or off, or digital, signal.

Description

United States Patent [72] lnventor FranklinJ.Calderazzo Branford,Conn. [21] AppLNo. 800,633 [22] Filed Feb.19, 1969 [45] Patented Apr. 27, 1971 [73] Assignee Northeast Fluidics, Inc.

Bethany,C0nn.

[54] PNEUMATIC SNAP ACTING MECHANISM 8 Claims, 2 Drawing Figs.

[52] U.S.Cl 73/37.5, 137/815 [51] 1nt.Cl FlSc 1/20, GOlbl3/12 [50] FieldoiSearch 73/376, 37.7, 37.8, 37.5; 137/815 [56] References Cited UNITED STATES PATENTS 2,618,288 11/1952 Catheron 73/37.6UX 2,665,579 1/1954 Fortier 73/376 2,669,246 2/1954 Segerstad... 73/37.7X 2,884,495 4/1959 Frankel 73/37.7UX

2,985,399 5/1961 Digel 73/37 .7X 3,213,670 10/1965 MacGeorge... 73/37.6 3,341,673 9/1967 Arnold 73/37.6X

Primary Examiner-Samuel Scott Attorney-Kenyon & Kenyon Reilly Carr & Chapin proximity of the object the pressure in the chamber begins to rise, the wall begins to move forwardly with a consequent increase in the back pressure on the jet, and this action continues with great rapidity so that the wall snaps forwardly. The reverse occurs when the object moves away. In this fashion the pressure in the chamber changes rapidly from subatmospheric to superatmospheric pressure, thus providing a positive on or off, or digital, signal.

PNEUMATEQ fiNAlP ACTWG MECHANHSM This invention is in the field of automatic controls requiring the sensing of various types of varying physical quantities such as pressure, temperature and position. Pressure and temperature are commonly transduced to mechanical motion through the use of bourdon tubes, bellows, diaphragms, etc. in the case of pressure, and by metallic or bulb elements for temperatures. Therefore, the sensing problems for all of such quantities becomes one of sensing position.

Air gauging systems have been in use for many years wherein the proximity of the object, being sensed, to a nozzle arrangement produces a back pressure in the nozzle as a function of the position of the object. This back pressure is commonly read out on pressure gauges, or set points are monitored by pressure switches or by expensive stackeddiaphragm type pressure controllers. it is the intent of this invention to provide a pneumatic device which senses the position of an object and provides a snap-acting" signal in response to that position.

According to the present invention, an object proximity sensing device includes means, such as a nozzle, for ejecting a fluid jet or stream towards the object for sensing the latters proximity by determining the back pressure on this fluid caused by impingement of the jet or stream on the object. Without more than this, this introduces the problem that when the object has a very small motion, and therefore provides a marginal control signal, the usual devices operated by this signal, such as fluidic amplifiers, diaphragm operated and pneumatically piloted devices, operate instably because they do not have snap-acting capability.

However, in the case of the present invention such instabilities are avoided by providing a digital or step function control wherein the control switches rapidly from fulloff to full-on. This action is obtained by means forming a chamber into which the jet or stream is ejected, this chamber having a wall in which there is an opening positioned so that the fluid jet or stream passes through this opening going towards the object, this wall being reciprocative in the direction of the jet or stream.

in operation the jet or stream has an aspirating action which normally renders the pressure in the chamber subatmospheric so that the wall is held at a backward position by the outside atmospheric pressure. As an object approaches and is impinged by the jet or stream, the resulting back pressure raises the chamber pressure above atmospheric and the wall moves towards the object effecting an increase in the back pressure regardless of motion of the object, the wall therefore moving to its full forward position rapidly and with a snap action and without any tendency for instability. The chamber pressure provides the output signal.

The accompanying drawings illustrate a specific example of the invention:

H6. 1 being a long'tudinal section, and

FIG. 2 being a front view.

In this example the jet 1 is supplied with compressed air at a suitable pressure, as for example a very low pressure of around one p.s.i. up to 100 p.s.i. The exact pressure depends upon the application of the device. This nozzle ejects a jet of air towards the object, which in this case is a diaphragm 2 having on its outside a connection 3 for connection with fluid pressure to be sensed. As this pressure varies, the diaphragm 2 moves towards or away from the sensing jet. The chamber l is formed by a body 5 having a hole 6 in which the nozzle 1 is screwed in a forward position, the left-hand portion of this e being adapted for screw-threaded connection to the supply of air under pressure. The reciprocative wall is formed by a diaphragm 7 made of easily flexed material such as relatively soft rubber.

The opening through which the jet from the nozzle 11 passes for effecting the aspirating action is fon'ned by a nozzle 8 mounted in the diaphragm 7. The passage to through the nozzle 1 and passage 8a through the nozzle b are in axial alignment with each other and the passage ha is of larger diameter than the diameter of the passage Ila.

In operation the air jet from the passage 1a goes through the passage ha and impinges on the diaphragm 2 forming the object whose proximity to the nozzle 1 is to be determined. The body 5 in this example consists of two'parts screwed together and the right-hand portion forms a chamber 9 protecting the diaphragm 2 against mechanical damage. The

.air freely exhausts from this chamber 9' through holes 10.

With the diaphragm 2 in the position shown by FIG. 1, the aspirating action of the jet going through the passage 8a causes the pressure in the chamber A to be at a subatmospheric or relatively low pressure. The body 5 has a passage ll communicating with the chamber 4 to permit its pressure to be sensed as, in other words, to obtain a signal. As the diaphragm 2, which in this instance forms the object, moves towards the nozzle 8 a condition is reached where the back pressure on the air jet from the passage causes the pressure in the chamber 4 to increase to atmospheric pressure or a pressure that is relatively high as compared to the previously existing pressure. The diaphragm 7 forming the reciprocative wall begins to move forwardly or to the right, this resulting in a rapid buildup of the back pressure on the jet and causing the diaphragm 7 to move forward rapidly.

Thus, a snap action is achieved causing the pressure in the chamber 4 to go very rapidly from the previous lower pressure to the higher pressure. This almost instantaneous change is, of course, detected or read out via the passage 11.

Note that this snap action occurs no matter how slowly the diaphragm 2 moves to the left or towards the nozzle 8. Undesired instability is eliminated.

if instead of the diaphragm 2, the object whose proximity is to be sensed is capable of resisting impact by the nozzle 8, the latter may be permitted to strike against the object itself to limit the forward or right-hand or outward reciprocation of the diaphragm 7. Also, it is to be understood that the latter can be substituted by a freely movable: piston, for example, although this is not illustrated. Also, the left-hand, backward or inward reciprocation of the wall, formed in this instance by the diaphragm 7, should be limited to maintain a space between the outlet of the means ejecting the fluid jet, such as the nozzle passage lla and the inlet to the opening through the reciprocative wall of the chamber formed in this instance by the inlet of the passage 8a of the nozzle 8. In other words, the construction must be such as to permit the described aspiration of the chamber 4.

In the illustrated example, excessive forward or outward reciprocation of the diaphragm 7 is prevented by a relatively rigid abutment plate 12 having a hole or opening in which the nozzle 8 reciprocates freely. The diaphragm 7 has a conical shoulder 7a which strikes against a correspondingly conical surface 12a of the plate 12 when the diaphragm snaps forwardly thus limiting its displacement. The nozzle 8 has a circumferential flange db which engages the outer face of the plate 12 to limit backward or left-hand motion of the diaphragm 7.

It should be noted that the body 5 may have its left-hand portion unscrewed from its right-hand portion and used alone with the nozzle b ejecting against any movable object whose proximity relative to the nozzle 8 is to be sensed with the desired snap action being fully effective. Also, that the device may be made very small such as having a diameter and length in the area of 1 inch. Depending upon the ease with which the diaphragm 7 or other reciprocative wall used, the device may be made extremely sensitive. However, in all cases the snap action is obtained.

The relative diameters of the two nozzles may be varied as required to set the pressure of the chamber 4 to a wide range of values. The switching differential or position at which the snap action is obtained can be set by the diaphragm travel allowed by the means limiting its limits of reciprocation.

lclaim:

1. An object proximity sensing device including means for ejecting a fluid jet or stream towards the object for sensing the latter's proximity by determining the back pressure on this fluid caused by impingement of the jet or stream on the object; wherein the improvement comprises means for forming a chamber having a wall in which there is an opening positioned so that said jet or stream passes through this opening going toward said object, said wall being reciprocative in the direction of the jet or stream.

2. The device of claim I in which there is a means for limiting the movement of said wall.

3. The device of claim 1 in which said chamber has a port through which the fluid pressure in said chamber may be determined.

4. The device of claim 1 in which said wall is a flexible diaphragm.

5. The device of claim 1 including an object displaceable by a quantity external of the device and means for connecting the just named object movably to said chamber in front of said opening.

6. The device of claim 1 in which said fluid ejecting means is a nozzle and a nozzle is mounted in said opening, said nozzle being mutually aligned and the nozzle in said opening having a greater flow capacity than the other one.

7. The device of claim 6 in which there is a means for limiting the movement of said wall, said wall being a flexible diaphragm.

8. The device of claim 7 in which said chamber has a port through which the fluid pressure in said chamber may be determined.

Claims

1. An object proximity sensing device including means for ejecting a fluid jet or stream towards the object for sensing the latter''s proximity by determining the back pressure on this fluid caused by impingement of the jet or stream on the object; wherein the improvement comprises means for forming a chamber having a wall in which there is an opening positioned so that said jet or stream passes through this opening going toward said object, said wall being reciprocative in the direction of the jet or stream.

2. The device of claim 1 in which there is a means for limiting the movement of said wall.

4. The device of claim 1 in which said wall is a flexible diaphragm.