US2599899A - Servomotor - Google Patents

Description

June 10, 1952 J. A. DENTON 2,599,899

SERVOMOTOR Filed June 15, 1949 2 swans-awn 1 5? u a INVENTOR. ii I JOSEPH A.DENTON J Q J. A. DENTON June 10, 1952 SERVOMOTOR 2 SHEETS-SHEET 2 Filed June 15, 1949 INVENTOR. JOSEPH A. DENTON Patented June 10, 1952 SERVOMOTOR Joseph A. Denton, Milwaukee, Wis., assignor to The Filer & Stowell Qo., Milwaukee, Wis., a

corporation of Wisconsin Application June 15, 1949, Serial No. 99,137

This invention relates to. improvements in servomotors for the control of mechanism in which a work-gripping member is moved into variably positioned work-gripping stations and thereafter caused to continuously assert workgripping pressure.

Servo-motors embodying a cylinder and a piston with a manually controlled exhaust valve therein have been used, for example, to control the valves for the steam feeds of sawmill carriages. In these motors gas, such as steam or air, under pressure was constantly supplied to both ends of the cylinder and the exhaust valve selectively connected either one of the ends of the piston to atmosphere or exhaust to cause the piston to be forced toward the desired end of the cylinder. One disadvantage, however, of suchmotors was the loss of the gas when the piston was continuously forced in one direction to supply a continuing pressure. Another disadvantage was the sudden manner in which the piston slammed forward when attempting to advance to a selected position.

It is an object of this invention, therefore, to provide a servo-motor which will supply a continuing work-gripping pressure without undue loss of the power-supplying gas.

Another object of the invention is to provide a servo-motor which will control the positioning of a work-gripping member so as to prevent the slamming of the work thereby as such member is advanced and which will also supply a continuing pressure to such member when it has engaged the work.

The first of these objects is obtained by inserting a biased to open control valve between the piston retracting end of the servo-motor cylinder and the source of gas under pressure, mounting such control valve so that it bodily moves with the piston of the motor, and operatively connecting such control valve with the exhaust valve so that such valve is automatically closed after the exhaust valve has been partly opened. Withthis arrangement the exhaust valve controls the placement of the piston within its range of travel until its movement is resisted by the contact between the work and the workgripping member. When this occurs the exhaust valve upon being further opened closes the control valve thus shutting off the retracting end of the cylinder from the source of gas under pressure. Thereafter the gas is supplied only to the advancing end of the cylinder. Thus the work-holding force of the motor is accomplished without continual loss. of gas.

5 Claims. (Cl. 121-41) The second object is obtained by inserting a' restricted opening between the piston advancing end of the cylinder and the source of gas under pressure. When the exhaust valve is moved to- .ward piston advancing position, even though the size of the opening for escape of gas to atmosphere is larger than the restricted opening, the restricted inflow of such gas will advance the piston slowly and in small increments. This step like stop and start advance of the piston prevents the accumulation of momentum which would cause the work-gripping member to slam against and damage the work. However, the rate of retraction is not so retarded by such re-.

tion and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which:

Fig. 1 is a view in cross section of a servo-motor embodying the present invention with the control valve thereof shown in plan; 7

Fig. 2 is an enlarged fragmentary cross sectional view of the control valve of Fig. 1;

' Fig. 3 is a cross sectional view of the piston and. cylinder of the servo-motor of Fig.1 in piston advancing position; and

Fig. 4 is a fragmentary enlarged cross sectional view of the control valve shown in Fig. 2 when said valve is moved to closed position.

Referring to the drawings by reference numerals, the servo-motor I0 is of conventional construction and has a fixed cylinder 12 in which gripping member (not shown) such as the feed rolls of a band saw. The advancing end 20 of the piston is connected with a false hollow piston rod 22. Both piston rods extend outwardly from the cylinder l2 through conventional stufling boxes. In the interior of the piston Hi there is slidably mounted an exhaust valve 24 which when moved toward the retracting end [6 connects such end through passageway 26 to the cylinder exhaust opening 28. When the exhaust valve 24 is moved toward the advancing end 29 such end is connected to the exhaust opening 28 by passageway 30. Subsidiary passageways 32 connect the ends of the exhaust valve chamber with the exhaust to eliminate development of back pressure during the shifting of valve 24. In order to move the exhaust valve 24 relative to the piston I4 an exhaust valve stem 34 extends outwardly through the hollow piston rod 22; a customary packing gland 2| sealing the end of the hollow piston rod 22 and the-exhaust'valve stem 34.

The cylinder 12 has a piston-advancing inlet 36 and a piston-retracting inlet 31?. A sou'rceofgas under pressure, such as steam or compressed air, is supplied through the main pipe 40 to the advancing inlet 36. This same source is normally co'nnected to the retracting inlet 38*by sections offlexible piping 42" and 44 connected with'a normally open control valve 46. When the-valve stem' 34is moved to the left by manually operatede ntror levers or the like the retracting end I6 is'jconnected to the exhaust" opening. 28 and the piston M will advance until'it meets with re- When thevalve stern34 is moved to the until-it meets with resistance to' movement or u'n'tilit retracts relative to the exhaust valve 24" toclose the passageway 30.

Iniman'y instances it is desirablenot'only to move the work-gripping member to a desired pomember. In the normal position of the control valve 46, gas under pressure passes out through the openings 58 into the space within operating member 60 and inwardly through openings 59. However, as the operating member 60 is moved to the left against the compression in spring 64, the right-hand end of such member will close the openings 59 (see Fig. 4)? thusi-shuttingzoff the communication between'thesourc'eof gas under pressure and the retracting inlet 38. With the exhaust valve 24 in a neutral position (Fig. i), the second crosshead 52 is adjusted in its position onthe stem 34 so that it is spaced approximately a quarter of a'n inch from ,the operating member 6p". Such spacingpermits the valve stem 34 to be moved to the left a sufficient amount to con nect'the retracting end ltwith the exhaust open-- ing.28 without operating the normally open consition'but 2.180 130" continue it to" supply gripping forcetos'uch member after it has reached'the desiredposition in contact'with' the work. With thej s'ervomo'tor" constructed as heretofore described,- to supply such continuous force there will tea steadyjlo's's ofgas under pressure through the retracting end l6; passageway 26; and exhaust opening. 28. igsagtrie normally open control valve 4515' closed after the'advancingmotion' or the piston has been arrested by engagement betweena'workegripping member operated by thepisto'n rod [8' andthe work. To effect such opening and control of'the control valve 46, a" crosshead'48, isi secured to utnow pis'ton'rod 22 and supports ajpair of guide rods50 and the control valve"4i.f v A'second'crossnead izis fixedly secured on'".tne1va1ve stem 34 afidis guided by the guide rods 50; extending through openings therein. The second cross- HadEZ also has an opening which loosely'encirclesfthe body of'the control valve 46 so that such crosshead isin alinement with and may engage-the operating member 69 of suchvalve. Thewalve 46 consists of amain body' 54 which theleft-handside of such wall there'are.a.plu-

rality'ofopening's 58 extending from the interior tetne' exterior of the body 5-4; 'Adj'acent'. the

right hand' side of such wall' are a plurality of openingsiewhich also extend from the interior toftheexteriorof such body. An operating memboth sets of openings 58 and 59. The operating member 60 is continually urged into normalvalve. 0 5 position by a coil spring 64 reactin between ai'w'asher' 651m the body Hand-such operatin In order to prevent such has an internal wall or partition 56; 'Adjac'ent 'end l6'to theexhaust opening 28:

, the exhaust valve 24 normally openspassag jway 26 and the piston I4 is automatically'ad trol valve 46.

The operation of the"servo-motor is manually controlled by the usual levers (not shown); As the valve stem 34 is moved t'oward' th'e-left, the-- piston I4 and piston rod" l8-wil1"also cont;inue= to move toward theleft until the work-gripping member operated by such piston"r0d contacts' the work. At such time the advance-of thepiston is stopped and advancing*pressurefwill-be maintained on the piston by reason of thees cape of gas under pressure from" the-retracting- V If-'-1nore'-force-' is desired; the valve stem '3'4-ismoved farther -to the left'so that the'crosshead EZEenga-ges the: operating member 68' closing the contro1-'valve-4$- (see Fig. 4) and further'opening theconnection-- between the retracting end l6 and the" exhaust opening 28. The effect of this is to substantially eliminate all pressure on the retracting end: I6 and place the full unbalanced force of the gas under pressure against the'advancingj'end 20-of the'piston. While in this position only'such gas will be lost as might escape through imperfect fits between the various glands,;connections, and valve seats. When it isdesired to" remove the grippingwandth'e" advancing pressure; the va lve stem" 34 is moved to therightwith respect-to the hollow piston rod 22 to 'letthecontrol valve" 46-. move to normally open iposition :(Fig: 2' auditomove the exhaust" valve"24 to neutral' position (Fig; 1). Such, neutral. positionfis': determined" by the engagementjbetween thecrossl' ead52 and a pair of adjustable springsBBpbsitioned-ohthe; guide, rods 50 between 'thesecond crosshe'ad 52* and adjusting nuts 68 on'the outer 'ends' ofsuch' rods. Thereafter further movement of'thevalve stem 34 to the1right1will be; accomplished by, slightly'compressing'fthe springs 66. which givesa feel to the operator while actuating the valve stem. This further movement to the right'opensthe passageway 30 between the advancing end' 205 and the exhaust opening Z'athus causing the piston 14 to retract towardtheright end of-the" cylinder I2. H

In some ,uses ofjthe' servo-motor it might be desirable. to have the. pistonautomatically-ad Vance whenever it is not being manually retracted. To accomplish this, the nuts- 68'"- are tightened so as tO move; the springs-B6} towards the left thus puttingthosespringgunden sufficient tension to always movethe valvestem- 34" a small distance to the leftof centeri In'mak ing such adjustment the gap between V theoperf ating member fill and ;the second fcrossheadiliz; is eliminated. With the servof-mo'torfso'adjusted:

vanc'd to the leftso that a work-carrying inemi" ber actuated thereby would be automatically moved to work-gripping position. Whenever it is desirable to supply work-gripping pressure, the valve steni 34 is manually advanced farther to the left relative to the piston [4, thus closing the control valve ifi with the resulting action heretofore explained.

By utilizing an. operating lever and linkage arrangement for the valve stem 34, and incorporating with such lever a quadrant with positioning notches or with a friction drag, the relative positioning of the piston l4 within the cylinder [2 may be regulatedj and controlled. The exhaust valve [4 always seeks neutral position unless it is influenced by some outside force. Hence by moving such operatinglever to a selected position where it is held by the action of the quadrant or friction drag, the piston M will advance to the desired position and when such; position is reached the exhaust valve 24 being fixed will be in neutral position as the result of movement of the piston l4 and this'will stop the further advance of the piston.

A restricted opening 10 having an internal diameter of substantially one-eighth of an inch is placed in the advancing inlet 36 to limit the rate of flow of gas under pressure into the advancing end of the cylinder. This restricts the rate at which the piston 14 advances and causes it to advance slowly and in short steps. The effect of this is to prevent the piston from obtaining so much momentum that it advances beyond the desired position thereby causing the work-gripping member to slam against the work and damaging it. However, there is no restriction in the retracting inlet 38 and hence the rate of flow of the gas to retract the piston is not retarded and it will quickly retract. The combination of the slow advance and the quick retraction makes the motor more adaptable for the use of various applications.

In the embodiment described herein, the control valve 46 is more particularly adapted for the use with compressed air rather than with i steam vapor. In the event it becomes necessary to use the servo-motor with steam, a poppet type of valve may be substituted for the sleeve type valve 46, thereby eliminating the packing glands which would not be eflicient for use with steam.

The essential features of any control valve is that the valve be placed in the line between the source of gas under pressure and the retracting inlet 38 and that it beoperated by the exhaust valve stem from a normally open position to a closed position.

Although onlyone embodiment of the invention is shown and. described herein, it will be understood that this application is intended to cover such changes or modifications as come within the spirit of the invention or scope of the following claims.

I claim:

1. A servo-motor comprising a cylinder having a piston retracting inlet at one end and a piston advancing inlet at the other end, a piston movable between said inlets and having a retracting end and an advancing end, an exhaust outlet for said cylinder communicating with both said retracting and advancing ends, a piston rod fixed to said piston, an exhaust valve movable in one direction to connect said advancing end with said exhaust outlet and to disconnect said retracting end from said exhaust outlet and movable in an opposite direction to disconnect said advancing nd from said exhaust outlet and connect said retracting end to said exhaust outlet, an exhaust valve stem connected with said exhaust valve and movable relative to said piston rod to control the movements of said exhaust valve, a source of gas under pressure continually connected to said advancinginlet, a control valve connected between said source and said retracting inlet and normally biased to open position during advance and retraction of said piston whereby said piston is advanced when said exhaust valve connects said retract"- ing end of said piston to said exhaust outlet and is retracted when said exhaust valve connects" the advancing end of said piston to said exhaust outlet, and means for closing said control valve to disconnect said source from said retracting inlet whenever said piston rod While said exhaust valve connects said retracting end to said exhaust outlet is restrained from advanicng and thereby prevent Lmdue losses through said exhaust outlet while advancing force is being maintained on said piston.

2. A servo-motor comprising a-fixed cylinder having a piston retracting inlet at one end and a piston advancing inlet at the other end, an exhaust outlet for said cylinder located between said inlets, a piston and exhaust valve therefor movable between said inlets, a piston rod fixed to said piston and adapted to be engaged with a work-gripping member, an exhaust valve stem connected with said exhaust valve and movable relative to said piston rod to control the movement of said exhaust valve, a source of gas under pressure continuously connected to said advancing inlet, a normally open control valve connected between said source and said retracting inlet whereby said piston is advanced when said exhaust valve connects the retracting end 01' said piston to said exhaust outlet and is retracted when said exhaust valve connects the advancing end of said piston to said exhaust outlet, and means for closing said control valve to disconnect said source from said retracting inlet whenever said piston rod by reason of contact between the work and the work-gripping member is restrained from advancing while said exhaust valve connects the retracting end of said piston to said exhaust outlet and thereby prevent undue losses through said exhaust outlet while advancing force is being maintained on said piston.

3. A servo-motor and control as claimed in claim 2 in'which said advancing inlet has a restricted opening to allow only enough gas to flow therethrough during the time the exhaust valve is connecting the retracting end of said piston to said exhaust outlet to advance said piston slowly enough so that a work-gripping member motivated thereby is prevented from slamming against the work.

4. A servo-motor comprising a cylinder having a piston retracting inlet at one end and a piston advancing inlet at the other end, a piston movable between said inlets and having a retracting end and an advancing end, an exhaust outlet for said cylinder communicating with both said retracting and advancing ends, a piston rod fixed to said piston, an exhaust valve movable in one direction to connect said advancing end with said exhaust outlet and to disconnect said retracting end from said exhaust outlet and movable in an opposite direction to disconnect said advancing end from said exhaust outlet and connect said retracting end to said exhaust out-

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