US2814121A - Pneumatic gage - Google Patents

Description

Nov. 26, 1957v c. A. WHITNEY ETAL 2,814,121

PNEUMATI'C GAGE Filed Jan. 4. 195e 2 sheets-sheet 1 INVENTORS CHARLES A- WHITNEY WAYNE E-. TINKER v M//TTO ,J

Nov. 26, 1957 c. A. WHITNEY x-:T A1. 2,814,121

PNEUMATIC GAGE Filed Jan. 4, 1956 2 Sheets-Sheet 2 I ,f/ l a' a ATTORNEY United States Paten-t PNEUMATIC GAGE Charles A. Whitney, Bloomfield, and Wayne E. Tinker, Granby, Conn., assignors to Pratt & Whitney Company, Incorporated, West Hartford, Conn., a corporation of Delaware Application January 4, 1956, Serial No. 557,311

Claims. (Cl. 33f147) is essentially non-linear, and only a relatively small portion of the resulting pressure vs. clearance curve is sufficiently linear to permit its adaption for gaging purposes.

The pneumatic circuit of an air operated dimensional gage is relatively simple. In o ne type of circuit, air from a source of supply is passed through a pressure regulator and a restriction valve arranged in tandem.v From this valve, the air is conveyed to the inlet end of the air cartridge, a pressure indicating gage being serially connected between the inlet of the cartridge and the restriction valve. The cartridge is. provided with a longitudinal bore and a plurality of passages providing pneumatic communication between the bore interior and the atmosphere. A piston member is arranged for sliding axial displacement within the bore, and adapted to variably uncover or close these passages, the amount of air permitted to escapefrom the cartridge through the passages being a function ,ofthe axial displacement `of the piston memben The airpressureto the cartridge inlet` forces the outer end Aof the piston`4 member into Vcontact with the piece being gaged.

The resulting pressure drop appearing inthe pressure indicatingV gage provides the dimensional intelligence which is sought.`

t As previously mentioned,'since` the relationship between pressure drop and clearance is linear only over a small portion of its, plotted curve, it becomes a problem for the operator vto first calibratel the pneumatic comparator and cartridge before putting the gage to use.

The prior artrhas not solved `this problem` of calibration satisfactorily and in currentV practice it is entirely fortuitous that an operator will locatethe linear portion f of operation after a reasonable number of tries. The problem of adjustment is complicated by Vthe fact that essentially three factors are involved; the pressure of the air in the' intake of the cartridge as shown on thel indicating meter, theV amount ofopening in the restriction valve, and the initial clearance point (the point selected for zero on the indicating-` meter as determined by a predetermined displacement of the piston member). Thesethree factors are interrelated, and"selectionof any two of them determines' rthe third. For any given magnitude of` pressure supply, there is onlyl onecurve which will satisfy the re'- quirementsforlinear gaging. Further, for each selected crnbination of factors there arewhole families of curves, so that the number. of possible choices is extremely wide. v Moreover, it should be borne inmind that the operator does not have these families of curves before him so that his choice of factors to be manipulated must be based on an intelligent appraisal of what is taking place as he manipulates these various factors. i t A j v111 itspreferred form theaircartridge for; useiwith a pneumatic comparator gage in accordance with the present invention comprises a barrel member having a longitudinal bore therein and a plurality of passages provtdlng pneumatic communication between the bore and the at mosphere. The barrel includes an intake end serially connected to a source of air under pressure and to a gaging meter on the comparator. Piston means are mounted for axial displacement within the bore, and are adapted to variably uncover or close these passages as a function of its axial displacement. Calibrated means mounted on the barrel enable precise determination of specic displacements of the piston means, so that the pneumatic comparator gage may be quickly calibrated to provide a linear relationship between the pressure in the barrel intake and the displacement of the piston means over a pre# selected range of movement thereof.

Accordingly, it is an object of this invention to provide an improved air cartridge which enables the operator to quickly calibrate the associated pneumatic comparator gaging circuit.

A further object is to provide a novel air cartridge havingA reliable calibration means of simple and inexpensive construction.

The novel features which are believed to be characterf istic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

Figure l is a pictorial showing of the general role played by the air cartridge in pneumatic gaging;

Fig. 2 is a schematic of the pneumatic circuit including the air cartridge in accordance with one illustrative embodiment of the present invention;

Fig. 3A is a diagram showing the pressure-nozzle clearance curve for a typical air gage;

Fig. 3B is a diagram showing the pressure-nozzle clearance family of curves of a typical air gage with only the opening of the air restriction valve being Varied;

Fig. 3C is a diagram showing a similar family of curves when the supply pressure is varied, all `other factors being held constant;

Fig. 4 is a sectional view of the air cartridge unit in accordance with one illustrative embodiment of the invention;

Fig. 5 is a view taken along the line 5-5 of Fig. 4;

Fig. 6 is a sectional view showing the barrel member proper; and

Figs. 7 and 8 are pictorial views showing how the calibration means are adjusted in accordance with the present invention.

Before proceeding with a detailed description of the air cartridge unit according to this invention, it will be helpful to consider the following brief account of the role played by the air cartridge in the overall problem of pneumatic comparator gaging.

Referring now to Fig. l, let us assume that Aa work piece 10 is to be checked for accuracy in its height dimension. The operator first checks the magnification ofthe air cartridge comparator combination by any convenient standards, such as Holte blocks 12 for example. These blocks are placed on a stand or base 14, and assembled in numbers sufficient to equal the desired dimension as well as the maximum and minimum deviations therefrom respectively. The base 14 may be a granite slab ,or a piece of steel carefully treated or lapped to provide a perfectly planar support. The cartridge unit indicated generally at 16 is coupled to a hose line 18 by means `of a fitting 20 screwed to the threaded end (Fig. 4: 64) -thereof.` The cartridge unit is held in xed position by means of a suitable clamping means 22.

Air under pressure is fed via conduit 24 to an Air- O-Limit comparator indicated generally at 26. The pneumatic comparator internally houses a number of components (filter, amplifier, etc.) not important to our present discussion. It will suice for present purposes to observe that its function is to supply air at a predetermined constant pressure to the cartridge 16 and to indicate on a gage shown generally at 3) the pressure at the inlet kend ,of the cartridge 16 as a function of the clearance area of the nozzle openings 3S (Figs. 2 and 4) which have been exposed or voided to the atmosphere. The pressure Vsupplied to the pneumatic circuit is adjusted by means of pressure regulator 28.

In'the process of checking the magnification, the air cartridge 16 is brought successively over the gage blocks so'tlia't the plunger 62 (Fig. 2) is in contact with the uppermost block. The cartridge is carefully adjusted in the clamping means 22 so as to displace the plunger outwardly or inwardly as the case may be, until the meter needle 34 gives the correct indication, i. e., maximum, minimum and zero. As will be made clear presently the correct calibration requires the careful adjustment of three factors. (The additional set of hands 32 are positioned in a plane above the plane of the needle hand 34, and they Vare manually adjustable so as to provide a means for quick visual indication of the permissible maximum and minimum dimensional excursions which may `be tolerated.)

When the operator is certain that the correct magnification has been obtained, he is then ready to begin gaging the work pieces. The plunger 62 (Fig. 2) is now placed in contact with the top of work piece 10. The amount by which the plunger is displaced inwardly or outwardly will be represented by a needle reading in the positive (oversize) or the negative (undersize) direction respectively. If the dimensional indications of the work pieces Vso gaged fall within theangular displacement defined by the hands 32 they are within dimensional tolerance; conversely, if they fall without this permissible area the pieces must be discarded or reworked as the case may be.

The operation of checking the pressure vs. clearance curve or checking the magnification as it is known in the art, is a rather painstaking process because the actual correct setting is a function of three variables: pressure in the cartridge intake, the amount of restriction. permitted, and the initial clearance. The discussion tofollow'will reveal that an almost infinite number of combinations are possible. In order to make these facts more lucid, reference will now be had to Figs. 2, 3A, 3B and 3C.

The principles of operation of the air gage are quite simple. Referring now particularly to Fig. 2, the air fromy the supply passes through the pressure regulator 28 (Figs. l, 2) where it is adjusted approximately to the pressure recommended by the manufacturer. This pressure is indicated by gage 37, and in the actual physical embodiment illustrated in Fig. l, the gage is positioned on the rear portion (not shown) of the comparator 26 (Fig. 1). After leaving the regulator 28, the air is fed to a restriction 36 which is also positioned conveniently in the practical embodiment on the far or rear side of the comparator 26. The restriction 36 is connected by any suitable conduit or hose 18 to the air cartridge 16. The indicating gage 30 is arranged so as to read the pressure in the passageway between the restriction 36 and the nozzles 38.

Since the opening in the restriction 36 is rather small, there is a pressure drop across it when air is flowing. This pressure drop is directly proportional to the amount of air owing through the system. The mass ow of air depends upon the nozzle clearance area uncovered by the plunger 62. The plunger 62 is urged toward contact with the work piece being gaged, so that the area of the nozzles open to the atmosphere is a function of plunger displacement, and hence, of the dimension being gaged.

Assume that the manufacturer has specified a pressure of 42 lbs. With the plunger held inward with the fingers, the nozzles 38 will be completely closed and the pressure on each side of the restriction 36 will read 42 lbs. (This is point 44 on the pressure vs. clearance curve shown in Fig. 3A.) With the nozzle completely open to the atmosphere, the air pressure will approach the so-called open nozzle pressure (Fig. 3A: 42). In this case the pressure across the restriction is about 38 p. s. i. so that the back pressure (i. e., the reading of gage 30) is 42-38=4 p. s. i.

As will be seen from Fig. 3A, as the nozzle clearance (area opened to the atmosphere) increases, the back pressure falls oif, and nally asymptotically approaches the open nozzle pressure 42 of about 4 p. s. i. For the most part this relationship between pressure and clearance is substantially non-linear, so that only a small portion of the curve (A to C) is sufficiently linear to be useful for the kind of measurements so necessary for accurate gaging. However, more than being merely linear, the manufacturer has carefully selected the operr ating curve so that as the nozzle clearance increases in equal increments, the pressure falls off in equal increments. Thus in Fig. 3A:

ADl: AD2 AP1= APa In the `art, the mid-point B (Fig. 3A) is called the initial clearance, and the end points A and C are related toV the calibration on the dial of meter 30.

The problem for the customer who wishes to use this gage is to find this exact curve, and in prior art practice this has been strictly a hit-and-miss affair as will presently be made clear.

The prior art operator in setting up his equipment adjusts the pressure regulator 28, so as to approximately approach the pressure recommended by the manufacturer. Then the plunger 62 is placed in contiguous relation with the three settingsof gage blocks or similar standards previously referred to and the cartridge is physically adjusted until the meter 30 gives the correct deection. The gage should have a maximum usable range from A to C. However, the process of finding this exact position on the first, or atlbestna few tries, is strictly a fortuitous matter. Note that three variables are involved, the pressure 30, the amount of opening in the restriction 36 and the initial clearance. For example if the operator notices that his maximum reading coincides with point A, but that his minimum falls short of C, he does not know whether to adjust yhis lpressure regulator 28, or the restriction 36, or to locatea new initial clearance point since it is possible that his initial clearance point may be far down enough on the straight line portion (A-C) so that his minimum deflection means that he is operating on the lower, and hence'non-linear portion of the pressure vs. clearance curve.

These difficulties may be more clearly explained by reference to Figs. 3B and 3C. First, referring to the family of curves shown in Fig. 3B, if the pressure 37 is held constant, and the restriction 36 made smaller, the backk pressure 30 falls off more rapidly, and there is a greater magnification. Assume that the operator has selected 4B1H as hisuinitial clearance, and that his pressure regulator 28. is held'at a fixed value. As the restriction 36 is closed more and more, the back pressure falls o more rapidly and we obtain the family of curves shown. If the operator makes no `adjustment: in his initial clearance, it wouldfall along the intersection of the line 46 with the selected curve, and he would be operating more and more in the non-linear portion. Hence, after adjusting thewrestriction 36, the operator must locate a new initial clearance point which will be along the line 48. When he has-located such a point he is not finished, because he must check the magnification to see that: (a) equall'increments of clearance produce equal increments of pressure, and (b) that he is making full use of the dial, i. e., the movement is from A to C (120 of needle displacement). The result (a) will not obtain unless the slope of the lstraight line AC (Fig. 3A) is correct, and even if (a) is obtained the operator will not be able to use the manufacturers calibrated scale unless he also satisfies (b).

` Referring now to Fig. 3C, assume that the restriction 36 is held at a constant setting, and that an initial clearance B2 is selected. If the operator selects pressure 37 to be varied, the family of curves obtained will be that depicted in Fig. 3C. If the initial clearance is unchanged, the zero point will be along the line 50, while the true zero should be along the line 52. Again the operator must check the magnification for equal increments and the total needle displacement. i

l The air cartridge in accordance with the present invention i-s sho-wn in Fig. 4. The cartridge 16 comprises five main parts: a barrel portion 54, a plunger 56, a step ring 58, a thimble 60, and a contact member 62. i

Referring now to Figs. 4, and 6, the barrel 54 is threaded at 64 to receive fitting 20 (Fig. 1), and is centrally bored at 68 to receive the piston means or plunger 56. The barrel is further provided with two longitudinal slots '70 (Fig. 6) cut on diametrically opposite sides of the barrel, so as to communicate lthe bore 68 with nozzles 38.

A sleeve 66 (Fig. 4) having a plurality of nozzles 38 is pressed over the barrel 54, the nozzles communicating with slots 70 so as to provide direct passage from the bore 68 to the atmosphere.

The plunger 56 (Fig. 4) includes two bearing portions 56a and S6b, which are in sliding contact with bore 68, and a stem portion 56a` of reduced diameter. As will be readily yseen at this point, as the plunger is reciprocated within the bore 68, the slots or ports 70 are more or less vented to the atmosphere so that more or less air is a1- lowed to escape to atmosphere. Bearing portion 56a of the plunger 56 is internally threaded to receive the threaded portion 62a of the contact member 62. With the contact member 62 screwed into plunger 56 by means of threads 62a there is defined a shoulder portion 62b as indicated in the drawing.

The barrel 54 (Fig. 6) is reamed to two diiferent diameters at the threaded end 64 to provide the reamed holes 72 and '74, the hole 72 and the bore 68 defining shoulder 72a. The hole 72 is slotted at 75 (Figs. 4, 5, 6) to receive the tail end of a pin 78.

A washer 76 having four notches 76a (Fig. 5), and an outside diameter less than that of bore 72, is mounted on the stem portion 56e of the plunger, and is arrested against displacement in one direction by means of a pin 78 passing through the stem portion 56C. The function of the notches 76a is to permit the free passage of air into the chamber provided by reamed hole 72 in cooperation with the piston member 56. As may be seen from a study of Figs. 4 and 5, the tail or longer end of pin 78 is fitted into the slot 75 'so as to prevent rotational displacement while permitting limited displacement axially of the bore 68. A spring 80 (Fig. 4) is mounted between the shoulder 72a and the washer 76, so that the plunger is resiliently urged to the left or intake end of the barrel.

The barrel 54 at the opposite end includes a reduced diameter portion 82, upon which are mounted the step ring 58 and the thimble 60. The reduced diameter portion 82 is slotted at 84 (Figs. 4, 6) to receive a rubber O-ring or any similar packing. The function of the rubber ring or packing is toprovide `some friction so that the thimble 60 will not be accidentally rotated or displaced by small forces over which the thimble is passed.

As may be seen from Figs. 7 and 8, the step ring 58 is provided with steps or projections 58a, 58b, 58C, and in this particular embodiment, the step from 58a to 58b is .001 in. The thimble 60 has a projection 60a which by rotation may be brought into successive 58band 58e.

In operation of the device, the air cartridge is connected to the air comparator 26 as shownin Fig. 1. For this particular illustrative embodiment, the pressure regulator 28 is set for 42 lbs. Thegage 30 (Fig. 2) provided with this comparator is calibrated to correspond to .002" movement of the plunger 62 when the needle hand 34 moves through the complete of arc (Fig. 3A: ABC). The marks 40a and 40b are half-way between AB and BC and therefore they represent -l-.0005 and .0005 respectively.

Next the thimble 60 is rotated so as to contact the high step 58a as shown in Fig. 8. The contact member 62 is pressed back by hand against the face 60b of the thimble 60. The air restriction 36 is then opened slowly until the needle 34 points to the -.0005 division (Fig. 3A: 40b). Next, the thimble 60 is rotated to the lowerstep 58b (Fig. 7) and the contact member 62 is again depressed by hand as far as it will travel. The needle 34 will now swing to the -l-.OOOS divisin (Fig. 3A: 40a). The reason why this will always be so arises from the fact that the exact position of the steps has 'been determined empirically for each piece by themanufacturer (by accurately preparing face 6011). The operator is now on the linear portion of the pressure vs. clearance curve, and the magnilication is correct. In other words, the linear portion YAC (Fig. 3A) has been definitely located so that:

The only task remaining for the operatoris to locate the initial clearance point B. This can readily be accomplished because any initial clearance point selected will be along line AC, the only problem being for the operator to correctly locate the mid-point by physically adjusting the cartridge unit 16 in the clamping means 22.

While a specific embodiment has been shown and described, it will, of course, be understood that various other modifications may yet be devised by those skilled in the art which will embody the principles of the invention and found in the true spirit and scope thereof.

We claim as our invention:

l. An air cartridge of the type described for use with a pneumatic gaging arrangement including a variable source of air under pressure and an adjustable restriction means connected in series relation comprising a barrel member having a longitudinal bore therein and passages providing communication between said bore and the atmosphere, said barrel member having an intake end and a remote end, said intake end being serially connected to said source of air under pressure and to said adjustable restriction means, a plunger mounted for axial displacement within said bore and adapted to uncover said passages to the atmosphere as a function of said axial displacement, and Calibrating means mounted on vsaid barrel member for determining the settings of said variable source of air under pressure and said adjustable restriction means as a function of specific displacements of said piston, whereby the air cartridge may be quickly calicontact with58a,

` brated to provide a linear relationship between the pressure in the intake end of said barrel member and said axial displacement over a preselected pneumatic range.

2. An air cartridge according to claim 1 including spring means for resiliently urging the plunger toward the intake end of said barrel member, and a contact member secured to the plunger and having an end for contiguously engaging a work piece being gaged, the contact member being secured to the end of the plunger in proximity to said remote end.

3. An air cartridge according to claim 1 including a contact member secured to the plunger, said contact member having an end for contiguously engaging a work piece being gaged, said contact member including a shoulder portion adapted toY arrest plunger displacement when pressed into engagement with said calibrating means.

4'.` Anair `cartridge Vof the type described for use with a pneumatic compaiator gage, comprising a barrel member: having a longitudinal bore therein, and a plurality of passages 'providing communication between said bore and the atmosphere, said barrel member having an intake at oneend and a remote end, the intake of said barrel member being, serially connected to a source of air pressure and to a gaging meter on said comparator, -a plunger mounted-for axial displacement within said bore, and adapted to variably permit egress of air through said passages to the atmosphere, the degree of egress permitted beinga function of said axialr displacement, a ring member having two Calibrating peripheral steps of :predeterminedidimensions, said :ring member being mounted coaxiallynori the said remote end of the barrel member, a thimblehaving-ra,peripheral projection, `said thimble being rotatably mounted coaxially on said remote end of the barrel member, the projection being in juxtaposition to said peripheral steps and adapted to engage each step successively to precisely dene the magnitude of plunger displacement during calibration, whereby the pneumatic -comparator gage may be quickly adjusted in two steps to provide a pressure in the intake of the barrel member i' which is a linear function of the axial displacement of the plunger over the'range of said gaging meter.

5. An air lcartridge of the type described for use with a pneumatic comparator gage, comprising a barrel member having a longitudinal bore therein and a plurality of slots positioned around a circumference of said bore, a sleeve member having a plurality of nozzles, said sleeve member vbeing mounted on the barrel member and arranged so that said slots and nozzles provide a plurality of ,passages t'o the atmosphere, said barrel member having anintakeat one 'end and a remoteV end, the intake of said barrel member being adapted for serially connecting to a source ofrair pressure and to a gaging meter on said comparator, a plunger member mounted for axial displacement within said bore and adapted to variably uncover said slots to the atmosphere as a function of said axial displacement, said plunger member comprising spring means resiliently urging said plunger member toward the intake of said barrel member and a contact piece secured to the plunger member and having an end for contiguously engaging a work piece, a ring member having two calibrating peripheral steps of predetermined dimensions, said ring member being mounted coaxially on the remote end of said barrel member, a thimble having a peripheral projection, said thimble being rotatably mounted coaxially on the remote end of the barrel member, the projection being in juxtaposition to said steps and adapted to engage each lstep successively to precisely define the magnitude of plunger member displacement during calibration, whereby the pneumatic comparator gage may be quickly adjusted in two steps to provide a pressure within the intake of said barrel member which is a linear function of the axial displacement of the plunger member over a selected range,

References Cited in the le of this patent UNITED STATES PATENTS 2.504,212 Mennesson Apr. 18, 1950

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