US2545921A - Control mechanism for fluid motors - Google Patents

Description

March 20, 1951 J. E. GOODWILLIE ET AL 2,545,921

CONTROL MECHANISM FOR FLUID MOTORS Filed July 2, 1947 3 Sheets-Sheet 1 pp y ZUJ EHZU E. Joy/v 6 aoarwn/e' I 41, a/vzo A EE'SE' March 20, 1951 J. E. GOODWILLIE ET AL 2,545,921

CONTROL MECHANISM FOR FLUID MOTORS Filed July 2, 1947 5 Sheets-Sheet 2 March 20, 1951 J. E. GOODWILLIE ETAL 2,545,921

CONTROLMECHANISM FOR FLUID MOTORS Filed 'July 2, 1947 5 Sheet-$heet s [DJ EHZ'DPE Jon/v E. GOOOW/LL/E v41. OM20 N 5 Patented Mar. 20, 1951 UNI TED STATES PATENT? OFFICE CONTROL MECHANISM FLUID MOTORS I John Ei-"Go'odwillie and Alonzo Neese Beloit,- Wis.,: assigno'rs to Beloit Iron Works, Beloit, Wis, a-corporation of Wisconsin ApplicationJul'y 2', 1947,Serial No. 758,568

This invention relates to a control mechanism for equalizing movements of-the'output members of fluid motors, and particularly to control mechanisms for roll positioningfluid motors for paper making machines which will insure thatthe'assoe ci'ated'roll is uniformly moved'lntoa nip defining position with respect'to-another roll to" provide simultaneous con-tact aIOn g-the- 'entire length of the nip defined by the two rolls. I

' In papermakin machines-, rolls of substantial size are commonly employed. and'it isfrequently desirable that such: massive rollsbe -m'oved into a nipdefining position with respect to a-nother' roll'while one orboth of such rolls arerotatin'gs To accomplish such'mowzementga plurality of fluid motors,'such asithe piston and. cylinder type,v are employed to" move one roll. in: contact with an-' other and 'then to apply pressure-to the nip thus defined. If, as frequently happens, the output member of one fluid motor moves" aheadiiof the output-member of the other motor; then one endof'the roll will come into contact withxthe operating roll bef'ore'the-"other"end; Since the rotating speeds Ofithe'tWD".1'01'1S"Wl1'1 not be ex-- actlyithe same. be'fore'contact; a felt or paper webrunning onieithe'r'of the rolls will be twisted'when a partial contact is made. This twistis often. powerful enough to tear the felt ofi'th'e machine and to damage' the'rubber cover on one: of' the rolls: In any case, 'an'uneven contact will twist the feltseam and make it tend'to move toward one side of the'machine during subsequent run n1ng..

Heretofore' thesolution of this. problem has been attemptedthrough the medium of mechanical ties between theroll'support-arms on which the individual fluid motors-"work in an attempt to force the fluid motors-to move equally. However, dueto the sizeof the rolls" and particularly the great axial length of such rolls, it is often difficult and quite expensive to obtain-a sufliciently stiff cross shaft to -insureequal movements of th roll positioning fluid motors.

- Accordingly, it is an object of this invention to provide animproved control mechanism fora plurality of fluid motors to insure simultaneous and equal movements of the-output members of such motors.

Another object of this invention isv'to provide an improved control mechanism for the roll'posi tioning fluid motors of a. paper-making machine" orthe like by which a roll moved by a plurality of fluid motors-may beunifiormly advanced. into?- a nip defining position with respect to another roll.

A particular object of this invention is to provide improvedcontrol'v arrangements for supplying: fluidv to a plurality'of fluid operated motorshavin output-members movable to-a-ndfroma predetermined position in sucha manner that 3 Claims. (01. BO -97) unequal movements of the output members to their respective predetermined positions produce unequal fluid flow to the fluid motors tending to equalize the-displacements of-th'e output-mem b'ers from. such predetermined positions.--

A particular object of this invention is td pro-" vide animproved-fluid supply control mechanismfor a pair of fluid motors respectively connected to independently movableroll support members" wherein a valve is associated with'each-"of the motors.for eontrolli'ng the supply of fluid thereto and the-shiftable member of suchfivalve is con nected by linkages to the respectivesupport-"arms so that movements-of such supportarms control:

' theflow of fluid through 'therespective valve member, and articularly, so that u-nequal movements of the support arms produce unequalfluid flow through' the valve members tending to'equal ize the movements of the supports.

The specific-nature of this invention; as weli as other o'bj ects and advantagesthereof, will become apparent to those skilled in the-art from the following detailed-descriptionof the annexed sheets of drawings which, by way ofpreferre'dexamples only, illustrate three specifieembodiments of thisinvention.-

On the drawings:

Figure 1 is a schematic perspectiv view of an assembly of elements embodying this invention illustrated in connectionwith a roll positioning mechanismfora papermaltirig machine? Figure 2 is a schematic perspectiveview of -a lector valves employed in the mechanism of 'Figure 4; and

Figure 6 is a partialsectional-view taken along" the plane VIVI of Figure'i'."

As shown on thedrawings:

While this inventionwill be particularly described and illustrated intconnecti'on with its application 'to a roll positioning mechanism of a paper making machine, it should be understood that the invention is not solimited but may be applied to any apparatus wherein equal move-- ments of the output members oi a plurality of fluid motors are required.

Referring to the drawings, the numerals I and 2 illustrate a pair of'rolls for a paper making machine or the like which are relatively movable so that they may be brought into juxtaposition to define a pressure nip therebetw-een. In the following description, it will be assumed that the roll I is fixed and the roll 2 is movable but it should be understood .that this is merely for purposes of example and both rolls could be movable with respect to each other without afiecting the operation or the desirable features of this invention.

The movement of movable roll 2 is accom plished by a pair of support arms l0, each of which is pivotally mounted on a fixed bracket I2 by a pin I4. A bearing block [6 is medially posi tioned on each support arm I!) and journals the shaft l8 for the movable roll 2. The free ends of the support arms ID are respectively connected to the output members 20 of a pair of fluid motors 5., While not limited thereto, fluid motors 5 are schematically illustrated as comprisin a cylinder casing 22 Within which a piston 24 is reciprocable and secured to output shaft 20. A fluid inlet port 25 is provided in cylinder casing 22 on one side of piston 24 and an exhaust port 28 is provided on the other side.

From the foregoing description, it is apparent that the support arms in are gravitationally biased to a position wherein the movable roll 2 isremoved from contact with fixed roll I. However, application of a suitable fluid under pressureto the cylinder casing 22 through inlet port 25' will produce an' upward movement of piston 24 and hence move roll 2 towards a nip defining position with respect to fixed roll I.

It will be understood by those skilled in the art that the support arms Ill ar substantially independently movable inasmuch as they are only coupled by the roll 2 journaled thereon. The roll 2 is generally of such construction as to not to provide a rigid tie between the support arms l and hence in accordance with this invention, the supply of fluid respectively to the fluid motors is controlled to insure substantially equal movement of the support arms [0 toward the nip definingposition of the movable roll 2 so that the movable roll 2 will contact the flxed roll I substantially concurrently along the full length of the roll;

Conduits-30 are provided respectively connecting with inlet 26 for the supply of fluid to the fluid motors 5. At an intermediate point in the conduits at there are provided pressure regulators 32 which are not illustrated in detail in as much as they comprise any conventional form of pressure regulating valves by which the maximum pressure transmitted to the fluid motors 5 may be manually adjusted.

Conduits 30 respectively communicate with output ports 34?) and 34d of a selector valve unit 34; Selector valve unit 34 also is provided with inlet ports 34a and 340 which are respectively connected by conduits 36' to two outlet ports 33a and 38b of a regulating valve 38.

Selector valve 34 may comprise any one of several well known constructions and includes a shiftable plug member 36 havin fluid flow passages 35a and 35b therein which may be respectively connected between one of the inlet ports and another one of the outlet ports of selector valve 34. Plug member 36 is manually shiftable 'by handle 31 and has at least two operative positions. In one such position, inlet port 34a is connected to outlet port 34?) while inlet port 340 is connected to outlet port 3401. In the other position of shiftable plug member 36, inlet port 34a 4 is in fluid communication with outlet port 34d, while inlet port 340 is in fluid communication with outlet port 34b. Hence, the operation of selector valve 34 effectively interchanges the connections of fluid motor inlets 26 with respect to the outlet ports 38a and 38b of regulating valve 38.

While regulating valve 38 has been illustrated as being of the sliding piston type, it will be recognized that other well known forms of valves may be substituted therefor. Regulating valve 38comprises a cylindrical casing within which a piston member 40 is reciprooable. An inlet port 380 is provided in the casing and a conduit 42 connects inlet port 380 with the outlet port of a .two position selector valve 44. The two inlet ports of selector valve 44 are respectively connected to a supply source of pressured fluid and to an exhaust conduit. Hence inlet port 38c of regulating valve 38 may be selectively connected to either a relatively high pressure fluid source or to a low pressure exhaust conduit by manual operation of the control hand 46 of selector valve 44.

The piston 40 of regulating valve 38 in reality comprises two axially spaced piston members 40a. and 4012 which cooperate with the two outlet ports 38a and 38b to selectively connect either one of such ports or both of the ports in fluid communication with inlet port 380, depending upon the axial position of piston 40. The normal position of piston4fl isas illustrated in Figure 1 wherein both of the outlet ports 38a and 38b are disposed in equal fluid communication with inlet port 38c. Hence, the fluid motors 5 will receive or discharge equal amounts of fluid. However, any movement of the piston 40 from such normal position will rapidly cut off the fluid supply or discharge from one of the fluid motors 5, the particular fluid motor 5 affected being determined by the direction of displacement of the piston 40.

The displacement of piston 40 of regulating valve 38 is controlled as a function of unequal movements of the support arms In by a linkage indicated generally by the numeral 50. Such linkage may obviously take a variety of well known forms. comprises an operating link 52 which is medially pivoted to the end of the rod 48 of piston 40.'

One end of operating link 52 is pivotally connected by a link 54 to an integral arm portion I I provided on one of the bearing support arms In. The other end of operating link 52 is connected to the other support arm [0 through a linkage including arm 55, cross shaft 56, arm 58, and adjustable link 60. Adjustable link 60 may conveniently comprise a pair of rods 60a and 501) having their adjacent ends threaded and adjustably connected by a nut member 600.

The eifective length of adjustable link 60 is selected so that equal movements of the bearing support arms I0 will produce equal but opposite pivotal movement of the ends of operating link 52 about its medial pivot on piston rod 48. Hence, so long as the bearing support arms I!) move equally and uniformly, no displacement of the piston 40 will be effected. However, when for any reason one support arm [0 moves faster than the other arm, the operating link 52 will produce a displacement of piston 40 which will be in the direction to modify the flow of fluid to The particular type illustrated.

gar en a movements of the output -shaft members- 2o of thefluid motorsi.

The control mechanism heretoforedescribed.

will uniformly-move the supportarm Hi both toward and away from the nip defining position of the movable roll'-2'. To move the roll 2 into engagement: with fixed roll l, the selector valve- 44 is manipulated to-connect-dnlet 380 of resulating valve 33 with the source of highpressure fluid. Selector valve 34 ismanipulatedtoconnect outlet ports 345 and 34d respectively with inletports 3'4a-and 34c; asillustratedin Figure 1. With suchadjustments, fluid will be supplied to: both ofthefluid'motors-E in such amanner asto uniformly move thevarying support arms H] to 5 is permitted to exhaust through selector valve 34, regulating valve 38 and selector valve M. Such fluid is of course forced'out of casings 22' by the gravitational bias produced by theweight of support arms H1 and-associated apparatus upon'the pistons 24. The piston 40 of regulating valve-38 will nevertheless control the rateof exhaust from each of the fluidmotors 5 to maintain uniform the retracting movements of the support arms Ill.

When the support arms I are moved to their nip defining positions, it is apparent that the nip pressure between therolls 2 and 'I may be conveniently adjusted by operation of pressure regulator valve 32 and that such adjustment of the-nip pressure is entirely independent of the control mechanism by which uniformity of move- I ment of the support arms H1 is obtained.

Referring to Figure 2, there is shown a fluid control mechanism constituting a modification-of this invention. In this modification, wherein similar numerals refer to elements corresponding to those'of Figure 1, a pair of independently movable support arms l0- are again provided to journal the movable roll 2 and position such roll with respect to the fixed-roll 'l. A pair of fluid motors are also .provided'for positioning the support arm II]. In this modification, the cylinder casings 22 of the fluid motors are provided with ports 62 and 64, respectively di'sposed be-' low and above the piston 24. unit Ill and an operatinglinkage Bills provided for "each of the fluid motors 5. Since such mechanisms are identical, only one will bedescribed in detail.

Each'con-trol valve unit may conveniently comprise'a selector valve having'four ports 10a, 105,100; and Hid, respectively (Fig; 3). The ports 10b and 10d are respectively connected by conduits 'I'2-to ports 62- and 64 in the associated fluid motor 5. Port Him is connected by conduit 13 through pressure regulating valve 32' to a source of high pressure fluidwhile the port'lllcis connected to an exhaust conduit 15.-

Each valve unit 10 is provided with a shiftable plug member 16 which has suitable passages 16a, 16b, 16c, and 16d, therein to selectively provide A control valvefluid communication between the various ports of the selector valve.- Preferably the passages'in the shiftable plug member are 'arrangedin-a manner similar to that illustrated in Figure 3;

each passage having openings 90P-displaoed from each other; Each of the openings-of the Various passagese lfia through 16d are, however, preferably equispaced from. each other-aroundthe periphery of the shiftable plug member 16. Hence, as shown in- Figure 3; the passage 'lfid -is aligned with theports Hie and 10d when" the passage-16b is aligned with ports 'mhandlflc.

closed at both ends. Hence, rotatio'nof the-shiftabIe plug member I 6' in either direction'fromthe-l position'shown in Figure 3 willeifect first a re- Y duction in fluidflow through ports 62 'and 64'of the fluid motor 5, then a complete interruption of fluid flow, and -finally,'-'upon still furthershiftirig of the plug member 16-,"the passage 16a will align with ports 10a andlilb and the passage ltcwill align with ports Hie-and 10d; and hence a reversalof direction of'fluidnew into the'casing of fluid motor 5 will result.

The control'linkage' '80 by which the valveunit Hlis operated comprises an arm 8 2 whichis suitably -secured to the shiftable plug member '15.-

arrangement indicated generally by the numeral 88a which may be adjusted by rotation of a pinion 88b associated therewith.

To produce concurrent adjustment ofadjustable link 88 of each of the control linkages 80, 21

cross. shaft 90 is provided having. a pair ofv worms 92 respectively engageable with the adjusting pinions-SSI). Crossshaft 9t isin. turn manually adjustable by hand wheel 94 The shiftable plug member ibisshown in Figure 3 in the position which it occupies when the bearing support arms III-are in their remote position with respect. to the fixed roll I To produce uniform. movement of the bearing support arms ID to their hip defining-positions with-re spect to the fixedroll I,. theadjustable links 88 are concurrently lengthened by rotationof hand 10c and 10d; Hence,v fluid will be supplied from" thelfluid source through'the ports 62in the casing of eachfluid moto fi beneath the piston and con.- currently, fluid will be exhausted through the ports 64- fromabovethe piston. Hence an upward movement of pistons 2 3 results and accordingly, the support armsi ii are moved toward their hip defining positions.

It shouldbe' noted thatsuch upward movement of support-arms H3 produces through controlling linkage a clockwise rotation of, the shiftable' plug member [6; Such clockwise shifting of the plug member 76 gradually decreases the flow of fluid to the fluid motors 5-and will completely cutoff such flow if the adjustablelinks 88" are notfurther lengthened. Hence, even though one support arm I ii is moved more rapidly by its fluid motor 5 than the other; the effect'of such movement will be to cutoff the-actuating fluid supe plied to such fluid motor sooner; whereupon all movement of the fast fluid motor ceases. Meanwhile, fluid is still being supplied to the slower fluid motor 5- and it catches up with thefaster In this same position; passages 16d and 'lfic are fluid motor 5 and automatically effects the cutofi of fluid supply to itself.

It is therefore apparent that so long as the hand wheel 94 is rotated to efiect a lengthening of the adjustable link 88, the fluid motors 5 will produce a substantially uniform and equal movement of the support arms I toward their nip defining position. Once the roll 2 arrives at its ni defining position, the hand wheel 94 need only be rotated sufiiciently to insure that the passages 16a and 16c are in alignment respectively between ports 10a and 10b and ports 10c and 10d. Thereafter, the effective force applied to the nip by the fluid motors is controlled by the fluid pressure regulators 32.

To retract the support arms I0 from their nip defining positions, the hand wheel 94 is rotated in the opposite direction which has the efiect of shortening the adjustable link 58. Such shortening of link 88 in turn produces a clockwise shifting of the shiftable plug members It and hence the fluid connections to the fluid motors 5 are reversed, high pressure fluid being supplied to port 64 and fluid being withdrawn to exhaust from port 62. Hence the pistons 24 will be urged downwardly and the sup-port arms III will be lowered. Such lowering movement of the support arms I0 will however occur uniformly for the same reasons as were heretofore described in connection with the raising movement. Any tendency of one fluid motor to operate ,faster than the other effects a more rapid cutofl or" the actuating fluid supplied to the faster motor, permitting the slower motor to catch up.

In the modifications of Figures 1 and 2 heretofore described, the movements of the output members of the pair of fluid motors was maintained substantially uniform throughout the entire stroke of such motors and in both directions. In the modification of this invention shown in Figures 4 through 6, the movementsof the fluid motors are equalized at only one point, which point may correspond to the support arms arriving at a certain minimum displacement from their nip defining positions.

The fixed roll I, movable roll 2, support arms I0, and fluid motors 5 for actuating the support arms are again provided in this modification in the same manner as was heretofore described. However, each fluid motor 5 has a cutofi valve I00 associated therewith. Cutoff valve I00 may conveniently comprise a cylindrical casing I02 within which a piston I04 is reciprocable. An adjustable link I06 connects each piston I04 to a fixed arm I08 provided on the corresponding support arm I0. Adjustable link :06 preferably comprises a pair of rods having their adjacent ends threaded, as indicated at I 060., and engaged by a nut member I061).

Each cutoff valve I00 has a pair of ports IIO (Fig. 6) provided therein, which are arranged to be concurrently cutoff by the movement of the piston I06 produced by the movement of the respective support arm I0 toward its nip defining position. The adjustable links I06 are adjusted so that such cutoff action occurs when each support arm I0 has obtained the same displacement from its nip defining position, preferably a short distance therefrom.

Actuating fluid for each fluid motor 5 is respectively supplied to the inlet port 25 in the casing of such motor through a selector valve II4. A conduit II6 connects inlet port 25 with port I I40 of selector valve II4 through pressure regulator 32. Port II4a of selector valve H4 is connected by conduit II8 to a suitable source of high pres sure fluid while port II4b is connected to a low pressure exhaust conduit II5. Selector valve port II4d is connected by conduit I20 to one of the ports IIO provided in cutofi valve I00. The other port H0 in each cutofi valve I00 is connected by conduit I22 to the supply source of high pressure fluid. The shiftable plug member I24 for each of the selector valves I I4 is provided with two passages I24a and I24b. Such passages are suitably arranged so that in one position, for example, the position illustrated in Figure 4,the passage I24a provides fluid communication between selector valve ports H411 and H40, while the passage I241) is closed. In another position of the shiftable plug I24, passage I24b provides fluid communication between selector valve ports I I4a and I I40 while the passage I24a is closed.

It is desirable that the shiftable plug members I24 of each selector valve II4 be operated simultaneously. Accordingly, the arrangement illustrated in Figure 5 will conveniently permit such condition to be obtained. The selector valves I I4 are disposed in superposed relationship and a common operating shaft I26 is suitably connected to both of the shiftable plug members I24 and is rotatable by a handle I28.

In the operation of this modification of this invention, the control handle I28 is manipulated to place the shiftable plug members I24 in the positions illustrated in Figure 4. In such positions, actuating fluid is supplied to both of the fluid motors 5 through their inlet ports 25, and the pistons 24 of such motors will be moved upwardly, thus moving the bearing support arms I0 toward their nip defining positions. When each bearing support arm reaches a certain predetermined minimum displacement from its nip defining position, the piston I04 of the respective cutoff valve I00 overrides the cutofi ports III! and thus completely interrupts the supply of actuating fluid to the associated fluid motor 5. Hence, irrespective of the speed of operation of the fluid motors 5, both motors are stopped when they arrive at the same predetermined displacement from their nip defining positions.

The movement of the roll 2 into engagement with roll I may then be completed b manipulation of handle I28 to position the shiftable plug members I24 in a second position wherein plug passage I24b is disposed in fluid communication between selector valve ports HM and H40. In this position, the cutout valves I00 are by-passed and the actuating fluid is supplied directly to both of the fluid motors 5. Since the support arms III are preferably stopped by operation of cutoif valves I00 at a very short distance from their nip defining positions, the remaining movement of the fluid motors 5, from the cutofi point to the nip defining point, is a sufiiciently short distance that difierences in speed of the fluid motors 5 are substantially negligible, and the movable roll 2 will be brought into substantially uniform engagement with the fixed roll I. In this position, the pressure on the nip may be conveniently varied by operation of pressure regulators 32.

To retract the movable roll 2 from its nip defining position, the shiftable plugs I 24 are moved to a third position wherein the passage I24a is disposed in fluid communication between selector valve ports I I41) and I I4c. This permits the fluid in fluid motors 5 to be forced out of the fluid motor easing into the exhaust conduit II5 by the gravitational bias exerted on such fluid motors by the support arms l and the weight of the mechanism associated therewith.

It is therefore apparent that each of the described modifications of this invention provides control mechanism for a plurality of fluid motors which insures that the output members of such motors will move uniformly and simultaneously to a predetermined position and hence, when applied to a roll positioning device for a paper making machine, insures that contact between a movable and fixed roll will occur substantially concurrently along the entire length of the rolls, thereby avoiding any possibility of damage to the rolls or to any felt or web trained on such rolls.

It will, of course, be understood that various details in construction may be varied over a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

We claim as our invention:

1. In combination, a pair of spaced, independently movable roll support members, a roll journaled on said support members and movable thereby to and from a nip defining position with respect to another roll, a fluid pressure motor for moving each of said support members, a control valve having an inlet connected with a source of fluid pressure and a pair of outlets respectively connected to said fluid pressure motors, a first selector valve arranged to selectively connect said inlet to a fluid pressure source or to a fluid exhaust conduit, a flow control member movable in said control valve to selectively connect either one or both of said outlets to said inlet, linkage means controlling the position of said flow control member as a function of unequal displacement of said roll support members from their nip defining positions to supply relat vely more fluid to the fluid pressure motor associated with the slower moving member, thereby insuring substantially concurrent movements of said support members, and a second selector valve connected between said outlets and said fluid motor means, said second selector valve being constructed and arranged to interchange connections between said outlets and said fluid motors, whereb the manipulation of said first and second selector valves between their two position respectively move said support members uniformly toward and away from their nip defining positions.

2. In combination. a pair of spaced, independently movable roll support members, a roll journaled on said supnort members and movable thereby into a nip defining position with respect to another roll, a fluid pressure motor for moving each of said support members, said support members being arranged with respect to said fluid pressure motors so as to gravitationally bias said motors toward positions remote from said nip defining position, a control valve having an inlet with a source of fluid pressure and a pair of outlets respectively connected to said fluid pressure motors, a first selector valve arranged to selectively connect said inlet to a fluid pressure source or to a fluid exhaust conduit. a second selector valve connected between said outlets and said fluid motors, said second selector valve being constructed and arranged to interchange connections between said outlets and fluid motors, whereby the manipulation of said first and second selector valves between their two positions respectively move said support members toward and away from their nip defining positions, a fiow control member movable in said control valveto selectively connect either one or both of said outlets to said inlet, and linkage means controlling the position of said flow control member as a function of unequal displacements of said rollsupport members from their nip defining positions to maintain relatively more fluid in the fluid pressure motor associated with the support member having the greater displacement, thereby insuring substantially concurrent movements of said support members to and from their nip defining positions.

3. In combination, a pair of spaced, independently movable roll support members, a roll journaled on said support members and movable thereby into a nip defining position with respect to another roll, a fluid pressure motor for moving each of said support members, a control valve having an inlet and a pair of outlets, a first selector valve arranged to selectively connect said inlet to a fluid pressure source or to an exhaust conduit, a second selector valve connected between said outlet and said fiuid motors, said second selector valve being constructed and arranged to interchange connection between said outlets and said fluid motors, a flow control member slidably movable in said control valve to selectively connect either one or both of said outlets to said inlet, an operating link, said flow control member being medially pivoted to said operating link, a first linkage connecting one end of said operating link to move as a function of the movement of one of said support members, a second linkage connecting the other end of said operating link to move as a function of the movement of said other support members, said first and second linkages being constructed and arranged to produce equal and opposite pivotal displacement of the ends of said operating link for equal movements of said support members, but to shift said control valve when said support members are unequally displaced from their nip defining positions, whereby the sliding movement of said control valve member supplies more fluid to that fluid motor associated with the support member having the greater displacement from said nip defining positions, and whereby the manipulation of said first and second selector valves between their two positions respectively moves said support members uniformly toward and away from their nip defining positions.

JOHN E. GOQDWILLIE. ALONZO A. NEESE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,051,434 Cavagnaro Aug. 18, 1936 2,225,515 Wood Dec. 17,1940 2,267,380 Tyler Dec. 23, 1941 2,310,100 Losey Feb. 2, 1943 2,350,795 Monier June 6, 1944 2,376,320 Butrovich et al May 22, 1945 2,380,973 Kopp -1 Aug. 7, 1945 2,410,603 Dubosclard Nov. 5, 1946 FOREIGN PATENTS Number Country Date 484,313 Germany Oct. 15, 1929

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