US2793540A

US2793540A - Feed-back mechanism leaf spring clamp

Info

Publication number: US2793540A
Application number: US370589A
Authority: US
Inventors: John L Cronk
Original assignee: Worthington Corp
Current assignee: Worthington Corp
Priority date: 1953-07-27
Filing date: 1953-07-27
Publication date: 1957-05-28
Anticipated expiration: 1974-05-28

Description

yz 1957 J. CRONK 2,793,540

FEED-BACK MECHANISM LEAF SPRING CLAMP Filed July 27, 1953 2 Sheets-Sheet 1 IN vary-i 01R: JOHNLL'RO/VK y 1957 I J. L. CRONK 2,793,540

FEED-BACK MECHANISM LEAF SPRING CLAMP Filed July 27, 1953 2 Sheets-Sheet 2 Fig-7 d9 d7 /Z7 l I I I l I I I I I l I I II J' I I T gfi I INVENI'UR JOHN L CRoNK per increment of'force applied thereto.

Faun-BACK MECHANISM LEAF SPRING CLAMP John L. Crorilr, Milton, Mass, assignor, by mesne assignments, to Worthington Corporation, New York, N. Y., j v a corporationof Delaware Application July 27, 1953, Serial No. 370,539

remains. on. vi -522 i This invention relates to an improvement in controllers, transmitters and the like and particularly concerns a feed-back mechanism which is commonly employed in connection with a, primary response elementto vary a controlling pressure for the purpose of providing a propor- "tioning band width which issuited to the'process conditions. When so employed, the feed-back mechanism functions ina negative sense, since itmodifies the pressure change initiated'by the primary element. A controller of this type is disclosed" in the UnitedStates patent to C. E. Mason-No.'2,616,440, dated November 4, 1952, and includes-a primary response elementin combination with a pressure actuated leaf spring and clamping device there- 'for which isutilized for'this purpose.

between selected limits is actuated to reverse the direction of value change when either one of said limits is reached.

Whenthus-employed, the feed-back mechanism functions in a positive sense, since it amplifies the pressure change initiated by the primary element.

As'heretofore constructed, sofaras known to me, the feed-back mechanism includes a flat leaf springrigidly mounted at one endwith its free end subjected to the force of a bellows or the like responsive to an operating pressure. In its normal flat position the leaf spring is mounted in parallel witha track in the form of a pair of bars rigidly supported at each end and adapted to carry a clamping device by which the leaf spring can be rigidlyheld atany selected position within its'length for the purpose of varying the spring characteristic and therefore themovement of the free end of the leaf spring One objection to this arrangement is that a relatively intricate and expensive clamping device consisting of several special parts is required. Another objection relates to the adjustment of the clamping device, namely, to tighten orloosen 'the clamp by practicable means, two separate operationsare necessary, one to tighten or loosen that portion of the clamp that embraces the leaf spring, and the other to tighten or loosen that portion of the clamp which engages the track. And I have found that by reason of the clamp and leaf spring construction referred to, unless a definite clamping sequence is adhered to, improper clamping -results and the desired Width of proportioning band or gap action is not obtained.

T he mechanism embodying this invention overcomes the objections referred to and provides a cantilever spring member and clamping arrangement therefor which is inexpensive to, produce, is self-aligning, and may be quickly and accurately adjusted to meet the operating conditions. And it will be understood that while the device embodying this invention is, particularly suited for use as a feed back device in pneumatic controllers, transmitters and the United States Patent like, it may have other uses wherein itis desirable to actuate a drivenmember by the movement of the freeend of a cantile'verspring on abasis which has some required proportional relation to a change in force to whichthe spring is subjected.

It is an objectof this invention to provide a cantilever spring member combinedwith an, inexpensive yet positive, self-aligning clamp which may be tightened or looserred by asingle knob or equivalent member forfthe pujrposeof obtaining a selected-spring characteristic.

It isan object of this invention to provide atsimple form of cantilever springand clamp therefor for operation in conjunction with a pressure operated element and a driven member to be actuated thereby to provideany j desired proportional increment of movement to the driven member in relation tothe increment of movement of the pressure operated element.

And it is an object of this invention to provide a simple 'form of feed-back device which may beutilized with a primary element in a controller, transmitter, or the "like, for operating-a valve; governing the instrument pressure for the purpose ofmodifying a'change inpressure initiated by theprimary'element on any desiredproportional basis, j or for thepurpose of "amplifying the pressure change and reversing the directiono f said change when the pressure value has reached sclectedlimits.

These and otherobjectsof this invention willbe more fully understood from the following description when taken in connection with the accompanying drawings, in which,

Fig. 1 is a front elevationgparfly in diagram, of a controller or transmitter including a feed-back mechanism embodying this invention; j j, u

Pig. 2 is a detail iri'section of the clamp and associated spring member and guide member taken on line 22of Fig. 1 showing the parts enlarged and in clamped position;

' also be used as a transmitter, for themeasurement of liquid level. Forthis purpose anarc-shaped member 10 mounted ona-shaft 11 rotatedby'means responsive to changesin' liquid level, as by a'displacer, float or thelike, not shown, maybe employed. The memberllO is in operativeconnection with a valve in the form of a nozzle 12 and flapper13 by means of a flapper operating lever 14 and link l5, whereby rotary movements of the shaft 11 are communicated to the flapper. The member 10 is provided with arc-shaped slots 16 and 17 suitable to receive an adjustable fastening member 18 Withivhibh one endof the link is connected, as by a spring wire pivot 19, The other end of the link has a spring wire' pivotal connection-40 with a bracket 21. attached to the lever 14, and the lever has a leaf spring pivotalconnection-22 with the feed-back mechanism, to be described, and generally indicated at 23.

The nozzle 12. is mounted on the horizontal arm25 of. acontrolpointsetting angle lever"26 which is in turn pivotallymounted at 27 on a bracket 28. 'The fiapper'13 is pivotally mounted preferably on a depending portion 29 of thehorizontalarm30,-the parts being arranged so that the longitudinal aids of the flapper is normal to the axis of the nozzle when the parts are held in engagement,- as by asuitable; spiral spring 31 surroundingthe flapperpivotSZ and=connected withtheIflapperat one-end 33-and'wviththe arm portion-29 at theotheri ends34. 2 AI),

extension 35 at the free end of the flapper lever 14 serves to position the flapper in respect to'the nozzle.

It will be understood that by means of the slots 16 and 17 in the'arc-shaped-member 10 the movement of :the lever 14 per increment of rotation of the shaft 11 1 maybe varied to suit the operating conditions. And it will also be understood that thevalve action may be reversed by removing the fastening member 18 from the slot16 and connecting the member 18 with the slot 17 at the other side of the shaft 11. When the link 15 is disposed in the position shown in Fig. l, a clockwise rotation of the shaft 11 reduces the nozzle pressure, and when the fastening member 18 is in the slot 17 at the .opposite side of the shaft, the clockwise rotation of the ,shaft, increases the nozzle pressure. a a l Means for adjusting the control setting of the instrum ent may be in the form of a cam 37 which is rotatable on a fixed mounting, not shown, and cooperates with a screw 38 threaded through a cylindrical portion 39 of a vertical leg40 of the angle lever, the members being .held in engagement by an extension spring 41 secured vat one end to the arm 40 and at the other end to a fixed bracket 42. With the link positioned as shown in Fig. 1, I if it be assumed that the shaft 11 is rotated counterclockwise on a rise inliquid level,- adjustment of the angle lever 26 clockwise lowers the level setting and vice versa.

The nozzle 12 is connected with a supply of regulated fluid pressure from a source not shown by means of a pipe 45, a pilot 46 and a supply pipe 47. The pilot 46, herein diagrammatically illustrated, may be of any wellknown construction such, for example, as shown in the United States patent to Hubley No. 2,327,898, dated August 24, 1943. The pilot is provided with the usual restriction, not shown, having a capacity less than that of the nozzle 12, so that the nozzle pressure depends on the relative position of the flapper 13 in respect to the nozzle. The pilot is so arranged that an increase in nozzle pressure provides a proportional increase in pilot output pres- .sure and vice versa. The output pressure is connected by means of a pipe 48 with a device to be actuated, such as a valve 49, and is also connected by means of a pipe 50 with the feed-back mechanism 23, to be described. The mechanism hereinabove described constitutes a pri- .mary response device which is particularly adapted to measure changes in liquid level, it being understood that any well-known type of primary response suited to the process conditions may be employed.

' The feed-back mechanism 23 comprises a bellows 55 which is opposed by a compression spring 56, a cantilever spring member 57 which has associated therewith a guide member 58, and a clamping device, generally indicated at 59, having an index marking 60 which cooperates with a suitable scale 61. The bellows 55 and spring 56 are mounted at opposite ends of a frame 62 which may be secured to a fixed support 63 within the instrument case.

A laterally extending part 64 of the frame has a depending portion 65 to which the bellows is secured, a suitable passage 66 being provided for communicating the interior of the bellows with the output pressure pipe 50.

The other end of the frame has a laterally extending base part 67 having an upwardly extending portion 68 to which a spring plate 69 is secured. The plate 69 is in the form of a disk having an annular flange 70 and is adapted to receive the lower end of the spring 56. The other end of the spring 56 is received within a plate 71, similar in construction to the plate 69, which is secured to the lower 'end of a post 72, the upper end of the post being connected .to a disk 73 secured to the center of the free end of the bellows 55.' The post 72 carries a collar 74 to which one end of the leaf spring pivot 22 of the flapper lever is rigidly secured.

Referring to Figs. 1 to inclusive, the cantilever spring member 57 is in the form of a resilient solid rodas herein shown which is circular in cross section, but which may be in theform of a tubular member if desired. One end the output pressure drops below 9 p. s. i. .arc-shaped member 10 rotates clockwise as viewed in of the rod 57 is secured to a fixed member 75 which, as herein shown, is in the form of a clamp rigidly secured to a fixed support 76. The other end of the rod 57 is rigidly connected with a block 77, as by a set screw 78, which in turn may be secured to the post 72 by a set screw 79. The guide member 58 is of relatively rigid construction and is also preferably in the form of a reasonably heavy circular rod which may also be of tubular shape. One end of the guide rod 58 is rigidly held by means of the clamp 75 and the other end of the guide rod is connected, as by a screw 80, with an upwardly extending arm 81 which is preferably integral with the base member 67 of the frame. The parts are so arranged that when the output pressure is at the mid point of its range, for example, at 9 p. s. i. in a pressure range of 3 p. s. i. to 15 p. s. i., the force afforded by the compression spring 56 is just suflicient to counterbalance the force provided by the bellows 55. Under these conditions the spring rod 57 is in its normal unsprung position as shown in Fig. 1 with the guide rod 58 disposed in par allel therewith.

It will be understood that the bellows 55 deflects the free end of the spring rod 57 downwardly from its horizontal position when the output pressure increases above 9 p. s. i., and that the compression spring 56 deflects the spring rod upwardly from its horizontal position when Thus when the Fig. 1,- the flapper lever 14 is rotated clockwise about its pivot 22, thereby moving the flapper 13 away from the nozzle 12 and reducing the output pressure in the bellows 55. The decrease in output pressure in the bellows 55 permits the compression spring 56 to deflect the spring .rod 57 upwardly and contract the bellows 55 until the force exerted by the spring rod plus the force exerted by the bellows is equal to the force generated by the compression spring. The flapper lever 14 is thus. rotated counterclockwise about the link pivot 20, thereby returning the flapper 13 to a throttling relation with the nozzle and providing a reduction in output pressure, which reduction is proportional to the clockwise rotation of the arc-shaped member 10. Upon the counterclockwise rotation of the arc-shaped member 10, the output pressure is increased and the spring rod 57 is deflected downwardly by the bellows 55 from its normal mid position until the force generated by the compression spring 56 plus the force exerted by the spring rod is equal to the force generated by the bellows 55. Thus theflapper 13 is returned to a throttling relation with the nozzle 12 at an increased output pressure, which increase is proportional to the counterclockwise movement of the arcshaped member 10.

It will be seen from the above that unless the output pressure is at its mid value the spring rod 57 assumes a nonparallel relation with the guide rod 58, and it will be understood that the amount of movement afforded to the flapper lever pivot 22 per increment of output pressure change depends on the spring characteristic of the rod 57 which in turn depends on the free length of the spring rod, or in other words, on the position of the clamp 59.

The clamp herein disclosed in Figs. 1 to 5, inclusive, coacts with the spring rod and guide rod in a manner to enable the clamp to be readily positioned at any location .on the spring rod and guide rod required for thepurparallel relation with the guide rod between the clamp 59 and'the fixed'member 75. 7

Referring to Figs. 2 to 5, the clamp comprises two '

jaws

85 and 86, each jawbeing provided'with two V- shaped recesses or notches 87 and-88, the apex 89 of onenotchbeing spaced from the apex 90 of the other notch byan amount which is equalto the "distance be- 97 and are adapted to engage'lthe circular surface of the rods at points 98 and '9 9 asL-indicatedin sectional Fig. 2. It will benoted that the distance betweenthe points'98 on the rod'57 an between the,pointsf99 on the rod-58 is. less than theflwidthof the. entrancefportion 97 ofeach pair' of notches. It will beunderstood that angles other than the 9,0de gre'e angles shown may also be employed without departingfrom the scope of my invention.

Means'for drawirigthe jaws together is in the form of a screw 100 which passes. freely through an opening 101 in the jaw/86 and threa ds into. the opposite jaw 85 at a point midway between the

V notches

87 and 88. The screw 100 has aknob 102 provided with a collar 103 which is adapted to engagei'theouter surface 104 ofthe jaw 86.

"Thus when the jaws are clamped to the rods: 57 and 58 as: shown in Fig. 2, the notch surfaces 93 and 94 engage the circular surfaces of the rod57 at points 98 and the notch surfaces 95 and" 96 engage the circular surface of the rod 58 at the points 99 all as indicated in cross section. By this means the rod "'57 is rigidly secured to the rod 58 at the spacing desired.

Referring to Fig. 3, wherein the clamp has been loosenedand thelspring rod and guide rod are disposed in parallel, the output pressure being at its mid value, since the. guide rod andspring rod are centered in the V notches 87 arid '88, the clamp need only to be loosened slightly topermit it to be moved along therods to some selected position and thereafter tightened by one single operation. 3

Referring to Fig. 4,there is shown a clamp 59 which has been loosened'and the spring rod 57 and guide rod 58 are not in parallel since the instrument output pressure is less than its mid value. "Underthe'se conditions the clamp should be loosened slightly more than required when the rods are in parallel in order to readily slide it alongthe rods. However when the clampis drawn together by the screw 100, the notch faces 93 and 96 enfgagethe surface of the

rods

57 and 58, respectively, and afford a'wedging action by which the springrod 57 is drawn towards the guide rod 58 until the opposite faces 94 and 95 of the notches engage thesurface of the rods. Whenthis occurs, the rods are inparallel betweenthe clamp 59 and the fixed member-75. Furthermore as the screw is tightened, the-faces of the V notches align the clampingjaws with the rods so that the planes defined by the apexes '89 and 90 of each pair of oppositely disposed notches. are bisected by a plane defined by the

axes

91 and 92 of thespring rod and guiderod.

Referring to Fig. 5, there is shown a clamp which has beenloosened, the spring rod 57 and guide rod 58 being also in nonparallel relation since the instrument output pressure is higher than its mid value. When the clamp is suitably loosened for adjustment, it will be noted that the rods are closer together thanwhen the spring rod is in its normal undeflectedposition. Thus under these conditions, when the clamp is tightened, the faces 94 and 95 of the notches afford a wedging action by which the spring rod 57 is separated from the guide rod 58 until the opposite notch faces 93 and 96 engage the surface of the rods and the spring rod 57 isforced to its normal parallel relationwith the guide rod 58 between the clamp 59 and the fixed member 75.

In Figs. 6 and 7, modified constructions are illustrated. In Fig. 6 a spring rod 110 and a guide rod 111 are shown 6' r as square in cross section. In this arrangement the opposite sides 112 of-the spring rod 110 and the opposite sides 113 of the guide rod 111 define. a 90degree angular construction which is adapted to make a snug'fit within its associated V notch. It will be understood that when the-clamp is suitably loosened foradjustment, the ad justment may. bereadily made and thereafter thespring rod 110 may be drawninto. parallel relation with the guide rod lllbetweemtheclamp 59 and the fixed support75. And whilelhave shown the rods as square in cross section, they may have other cross sectional con- "figurations as long .astwo opposite sides define angles whichare adapted to .fit into theV notches of the jaws 85 in Fig.7, I have shown a flattened spring rod 115 and guide rod lld h a ving arc-shaped side portions 117 and l18,-respective1y.. The notches instead of being inthe form ofa V have

bed portions

120 and 121 each defining i an are which is preferably adapted to conform to the arcshaped side portions of the rods. Since the entrance portion 122 of the notchesis wider than the spacing between the clamp engaging points 98 on the

rod

57 and 99 on the rod'SS and thes'ides123 of each notch flare outwardly as shown, itfollowsfthabthe clamp may be loosened, adjusted, and tightened to. provide for adjustment and for the clamping action desired in the manner described above.

Referring to Fig. 8, there is shown a feed-back mechanism which is particularly suited for transmitters wherein an extremely accurate but relatively limited proportioning band adjustment is required. The feed-back mec -anism includes the clamp 59 and is generally similar to that shown inFig. l, with the exception that the device is providedwith a guide rod 125 which is associated with a vernier means for. accurately adjusting the clamp to provide theexact springflcharacteristic desired. For this .purpose the guide rod 125 is threaded as indicated at 125 preferably over a-major portion of its length. A suitably threaded knob1127 is mounted on the-guide rod 125 and'is provided with acollarportion 128 which is adapted to span the openingbetween the jaws of the clamp when the jaws are in their maximum open position, and engage the face130 of each jaw. The opposite face 131 of each jaw is suitably engaged by-a washer 132 which has a sliding fit with the guide rod 125, and a compression spring 133 surrounds the rod and is confined between the washer and the arm 81 of the frame 62 in which the bellows 55 andthe spring 56 are mounted. Thus the clamp is maintained in contactwith thecollar portion 128 of the knob 127 by thespring 133 and may be accurately positionedby the knob at any selected point along the rods 57 and 125, thereby permitting the exact spring characteristic required to be obtained.

Havingthus described my invention, what I claim a new and desire to secure by Letters Patent is:

1. In a feed-back mechanism for a pneumatic instrument which includes a pressure responsive element and a part to be actuatedthereby, in combination, a cantilever spring member having a rigidly supported portion and a free length defiectable from a normal, position, a single rigidly supported guide member spaced apart. from said spring member and having its longitudinal axis substantially in parallel with the longitudinal axis of the spring member when the latter is in its normal undeflected position, means connecting the free length of said spring member with said pressure responsive element and said part, a clamp spanning said spring member and guide member comprising clampingjaws disposed at opposite sides of said members and including a pair of oppositely disposed operating and clamping recesses in spaced parallel relation, the spacing'between the longitudinal axes of said recesses being equal to the spacing between the longitudinal axes of said members when the spring member is in its normal undeflected position, said recesses each having an entrance portion defined by outwardly flaring straight side portions and saidspring member and guide member each having at opposite sides thereof coacting portions for engagement with said side portions within said entrance portion when said members are both 'in parallel and in nonparallel relation, and means for varying the spacing between said clamping jaws to permit a part to be actuated thereby, in combination, a cantilever spring member having a rigidly supported portion and a free length deflectible from a'normal position, a single rigidly supported guide member spaced apart from said spring member and. having its longitudinal axis substan-' tially in parallel with the'longitudinal axis of the spring member when the latter is inits normal undeflected position, means connecting the free length of said spring member with said pressure responsive element and said part, a clamp spanning said spring member and guide member comprising clamping jaws disposed at opposite sides of said members and including a pair of oppositely disposed guiding and clamping recesses in spaced parallel relation, the spacing between the longitudinal axes of said recesses being equal to the spacing between the longitudinal axes of said members when the spring member is in its normal undeflected position, said recesses each having an entrance portion and a bed portion, said entrance portion being defined by outwardly flaring side portions and said spring member and guide member each having at opposite sides thereof coacting portions spaced apart at a width which is substantially less than the width of said entrance portion for engagement with said side portions between said entrance portion and said bed portion when said members are both in parallel and in substantial nonparallel relation, and means for varying the spacing between said clamping jaws to permit the free length of said spring member to be varied and to draw the remaining portion of said spring member into parallel relation with said guide member.

3. In a feed-back mechanism for a pneumatic instrument which includes a pressure responsive element and a part to be actuated thereby, in combination, a cantilever spring member having a rigidly supported portion and a free length deflectible from a normal position, a single rigidly supported guide member spaced apart from said spring member and having its longitudinal axis substantially in parallel with the longitudinal axis of the spring member when the latter is in its normal undeflected position, means connecting the free length of said spring member with said pressure responsive element and said part, a clamp spanning said spring member and guide member comprising clamping jaws disposed at opposite sides of said members and including a pair of oppositely disposed guiding and clamping recesses in spaced parallel relation, the spacing between the longitudinal axes of said recesses being equal to the spacing between the longitudinal axes of said members when the spring member is in its normal undeflected position, said recesses being V-shaped in cross section forming an entrance portion and a bed portion, and said spring member and guide member each havfor varying the spacing between said clamping jaws to permit the free length of said spring member to be varied and to draw the remaining portion of said spring member into parallel relation with said guide member.

4. In a feed-back mechanism for a pneumatic instrument which includes a pressure responsive element and a part to be actuated thereby, in combination, acantilever spring comprising a resilient member of curvilinear cross section having a rigidly supported portion and a free length deilectible from a normal position, a single rigidly supported "guide member spaced apart from said resilient member and having its longitudinal axis substantially in ber when the latteris in its normal undeflected position,

with said pressure responsive element and said part, a

,clamp spanning said resilient member and guide member comprising clamping jaws disposed at opposite sides of said members and including a pair of oppositely disposed guiding and clamping recesses in spaced parallel relation, the spacing between the longitudinal axes of said recesses being equal to the spacing between the longitudinal axes of'said'resilient member and guide member when the ,resilient member is in its normal undeflected position, f'said recesses having an entrance portion'an'da bed portion, said entrance portion being defined by outwardly flaring side portions and said resilient memberand guide member each having -at.opposite sides thereof coacting portions which are 'spaced at a width that is substantially less than the width of said entrance portion forengagement with said side portions between said entrance portion and said bed portionwhen said members are both in {parallel and in substantial nonparallel relation, and means for varying the spacing between said clamping jaws to permit the free length of said resilient member to be varied and to draw the remaining portion of said resilient .member into parallel relation with said guide member.

5. In a'feed-back mechanism for a pneumatic instru ment which includes a pressure responsive element and a part to be actuated thereby, in combination, a cantilever spring member having a rigidly supported portion and a free length deflectible from a normal position, a

single rigidly supported guide member spaced apart from .said spring member and having its longitudinal axis subin spaced parallel relation, the spacing between the longi- ,tudinal axes of said recesses being equal to the spacing between the longitudinal axes of said spring member and guide member when the spring member is in its normal undeflected position, said recesses having outwardly flaring side portions and at least two oppositely disposed recesses being V-shaped in cross section, one of said members having angular shaped portions at two opposite sides thereof which portions are adapted to make a snug fit within said V-shaped recesses, and the other of said members having recess engaging portions at two opposite sides thereof suitable for engagement with the outwardly flaring side portions of the other two oppositely disposed recesses, and means for varying the spacing between said clamping jaws to permit the free length of said spring member to be varied and to draw the remaining portion of said spring member into parallel relation with said guide member.

6. in a feed-back mechanism for a pneumatic instrument which includes a pressure responsive element and a part to be actuated thereby, in combination, a cantilever spring member having a rigidly supported portion and a free length deflectible from a normal position, a guide rod member of circular cross section supported against lateral and lengthwise movement spaced apart from said spring member and having its longitudinal axis substantially in parallel with the longitudinal axis of the spring member when the latter is in its normal undefiected position, means connecting the free length of said spring member with said pressure responsive element and said part to be actuated thereby, a clamp spanning said spring member and guide member comprising clamping members disposed at opposite sides of said members and including a pair of oppositely disposed guiding and clamping recesses in spaced parallel relation each having an entrance portion defined by outwardly flaring side portions which are adapted to engage said members at opposite sides thereof, the width of said entrance portion being substantially greater than the width of the loci of engagement of said members with said side portions to permit said side portions to engage said members within said entrance portion when the members are both in parallel and nonparallel relation, the spacing between the longitudinal axes of said recesses being equal to the spacing between the longitudinal axes of said members when the spring member is in its normal undeflected position, said guide rod member having a threaded portion, an adjustment member threaded on said portion and in operative connection with said clamp, at least one of said last mentioned members being rotatable in respect to the other, and means for varying the spacing between said clamping members to permit the free length of said spring member to be varied and to draw the remaining portion of said spring member into parallel relation with said guide member.

7. In a feed-back mechanism for a pneumatic instrument which includes a pressure responsive element and a part to be actuated thereby, in combination, a cantilever spring having a rigidly supported portion and a free length deflectible from a normal position, a rigidly supported guide rod member of circular cross section spaced apart from said spring member and having its longitudinal axis substantially in parallel with the longitudinal axis of the spring member when the latter is in its normal undeflected position, means connectingthe free length of said spring member with said pressure responsive element and said part to be actuated thereby, a clamp spanning said spring member and guide member comprising clamping jaws disposed at opposite sides of said members and including a pair of oppositely disposed guide and clamping recesses in spaced parallel relation, said recesses each having an entrance portion and a bed portion, the entrance portion being defined by outwardly flaring straight side portions, and said cantilever member and guide member each having at opposite sides thereof coacting portions spaced apart at a width which is substantially less than the width of the said entrance portion for engagement with said side portions between said entrance portion and said bed portion when said members are both in parallel and in substantial nonparallel relation, the spacing between the longitudinal axes of said recesses being equal to the spacing between the longitudinal axes of said members when the spring member is in its normal undefiected position, said guide member having a threaded portion, a rotatably mounted adjustment member threaded on said portion and adapted to engage one side of said clamp for moving said clamp along said guide member in one direction, resilient means in operative connection with said clamp tending to move it in the opposite direction, and means for varying the spacing between said clamping jaws to permit the free length of said spring member to be varied and to draw the remaining portion of said spring member into parallel relation with said guide member.

8. In mechanism of the character described wherein a driven member is actuated by the movement of the free portion of a cantilever spring on a basis which has some required proportional relation to a change in force to which the spring is subjected, in combination, a cantilever spring rod of circular cross section rigidly mounted at one end having its free portion in operative connection with a driven member and subjected to a forceapplying element, resilient means opposing the force of said element, a rigidly supported guide rod of circular cross section spaced apart from said spring rod and having its longitudinal axis substantially in parallel with the longitudinal axis of the guide rod when the latter is in its undeflected position, a clamp spanning said spring rod and guide member comprising clamping jaws disposed at opposite sides of said rods and including a pair of oppositely disposed guiding and clamping recesses in spaced parallel relation, each of said recesses having outwardly flaring straight side faces forming an entrance portion, one pair of said recesses being adapted to engage said spring rod within said entrance portion and the other pair of said recesses being adapted to engage said guide rod within said entrance portion when said members are both in parallel and in substantial nonparallel relation, and means for varying the spacing between said jaws to tighten or loosen said clamp.

9. In apparatus of the character described wherein a driven member is actuated by the movement of the free portion of a cantilever spring on a basis which has some required proportional relation to a change in force to Which the spring is subjected, in combination, a cantilever spring rod of circular cross section rigidly mounted at one end having its free end in operative connection with a driven member and subjected to a force-applying element, resilient means opposing the .force of said element, a rigidly supported guide rod of circular cross section spaced apart from said spring rod and disposed in parallel relation therewith when the spring rod is in an undeflected position, a clamp spanning said spring rod and guide rod comprising clamping jaws disposed at opposite sides of said rod and including a pair of oppositely disposed guiding and clamping recesses in spaced parallel relation, each of said recesses being generally V-shaped to form an entrance portion, one pair of said recesses being adapted to engage said spring rod within the entrance portion, and the other pair of said recesses being adapted to engage said guide rod within the entrance portion when said members are both in parallel and in substantial nonparallel relation, and means for varying the spacing between said jaws to tighten or loosen said clamp.

Smith Oct. 1, 1929 Mason Nov. 4, 1952