US3054385A - Fluid actuator having cushioned stop - Google Patents

Description

i Spt. 18,Y 1962 J. c. HANNA 3,054,385

FLUID ACTUATOR HAVING CUSHIONED STOP Filed March 20, 196].

United dtates atent Patented Sept. 18, 1952 ddee 3,054,335 FLUED ACTUATGR AACVING CUSHINED STP .lohn Clark Hanna, Evanston, ill., assigner to Hanna Engineering Works, Chicago, lli., a corporation of Illinois Filed Mar. 20, 1961, Ser. No. 96,745 11 Claims. (Cl. 121-38) The present invention relates to a liuid actuator capable of employing air or hydraulic fluid and having means for bringing the piston to a controlled cushioned stop at the end of the stroke.

Edorts have lbeen made in the past to design actuators in which the piston is brought to a gradual stop at the end of the stroke. Many cushioning systems, especially those for hydraulic actuators, provide for a sharp closing of the port or aperture so that there is a checking action with abrupt deceleration of the piston rather than a progressive cushioning action. In some instances cushioning has been accomplished with a sacrifice in speed of response over the major portion of the stroke. Also previous designs of cushioned actuators have tended to be rather complex and hence expensive as compa-red to actuators without the cushioning feature.

Accordingly it is an object of the present invention to provide an actuator having improved cushioning means permitting rapid -response over the major portion of the stroke but providing improved and gradual cushioning at the end of the stroke. It is another object to provide a cushioned actuator in which the cushioning takes place in a controlled fashion over an appreciable distance at the terminal portion of the stroke, a feature which may be referred to for convenience as long cushioning but in which such distance maybe tailored to the need with only minor changes in construction.

It is another object of the present invention to provide an improved uid actuator having a number of different paths of uid flow of progressively smaller cross section and covering a wider range of cross section than is available in cushioned actuators of conventional design.

It is a further object of the present invention to provide an improved fluid actuator having cushioning at the end of the stroke but which is of relatively simple and inexpensive construction, permitting such actuators to be used in many applications previously served by actuators of the conventional non-cushioned type. In this connection it is an object to provide an actuator which does not require the meeting of any close tolerances, particularly as regards -concentricity of the interiitting elements.

It is an object, also, to provide an actuator which provides long cushioning but which is nevertheless compact, having about the same length and diameter as actuators of the same capacity but which do not have the cushioning feature. It is a more specific object to provide an improved actuator in which the cushioning means is largely embodied in the construction of the piston thereby enabling use of a simple and standard form of cylinder to keep costs to the minimum and to permit addition of the cushion feature simply by substitution of the modified piston and piston rod. In this connection it is an object to provide a iiuid actuator embodying cushioning and in which the cushioning characteristics may Lbe varied over wide limits simply by substituting parts having a slightly different surface configuration.

it is another object to provide a cushioned actuator which is applicable to both pneumatic and hydraulic systems and which is capable of operating reliably over long periods of time without care or maintenance.

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawing in which:

CII

FIGURE l is a longitudinal section of an actuator constructed in accordance with the present invention.

FIG. 2 is a transverse section taken along the line 2--2 in FIG. l.

FiG. 3 is a fragmentary stop motion view showing the relative positions of the parts during the initial portion of the cushioning action.

FIG. 4 is a fragmentary longitudinal section similar to FIG. 3 but showing the positions of the parts during the terminal portion of the cushioning action.

FIG. 5 is a fragmentary section showing movement of the plug member upon reversal of the stroke.

While the invention has been described in connection with a preferred embodiment, it will be understood that l do not intend to be limited to the particular embodiment shown but intend to cover the various alternative and equivalent constructions included within the spirit and scope of the appended claims.

Turning now to the drawings and particularly to FIG- URE l, there is shown a iiuid actuator having ya cylinder or tube 11. Enclosing the left hand end of the cylinder is a head having a iiuid connection 16 while enclosing the right hand end is a head 17 having a liuid connection 13. Mounted `for reciprocation within the cylinder is a piston 2li having a piston rod 21 which is sea-led with respect to the head 17 by means of suitable packing 22. It will be apparent that movement of the piston to the right is brought about `by applying pressure fluid at the connection 16 and by exhausting fluid from the connection 18. Such pressure connections are reversed in 'order to cause movement of the piston in the opposite or left hand direction.

In carrying out the present invention an annular barrier is provided surrounding the piston rod 21 and adjacent the fluid connection 18 to define, with the piston rod, an annular clearance space for flow of the displaced fluid, and an annular plug member is provided having a yieldable lost motion connection with respect to the pist-on so that as the piston approaches its limit of movement the plug member defines an escape passage which is closed down for inhibiting flow of fluid. 'Ihus in the present instance there is provided an annular plug member which surrounds the piston rod 21 and which is supported, with respect to the piston, on three axially extending pins 31 (see FIG. 2). Such pins are preferably integral with the annular plug member 30 and are freely slidable in bores 32 formed in the piston. Small coil springs 33 seated in the bores 32 serve to maintain the plug member 30 in -an extended position in which the plug member is spaced in advance ofthe piston during the course of its forward or right hand movement. Stop means are provided for normally positioning the annular plug member at a predetermined spacing in advance of the piston. In the present instance this stop function is provided by a shoulder 35 on the piston rod which seats on a surface 36 formed on the inner surface of the annular plug member. 'Ihe shoulder 3S and surface 36 preferably have mating chamfers so that the plug member is centered in addition to being aX- ially positioned.

Arranged in the path of movement of the plug member 39 is an annular barrier 4t) having an inner edge 41 which surrounds the piston rod 21 and which, with the piston rod, defines an annular escape passage 42' for the displaced iiuid. The annular escape passage 42 serves an entryway to a chamber 43 within the head 17 and which in turn communicates with the fluid connection 18. While the barrier member 4t) may be separate, it is preferred to make such barrier member integral with the head 17 as shown.

it is one of the features of the present construction that the annular plug member has a tapered outer surface 44 which, with the inner edge of the barrier, defines a first Ythe escape passage is not snapped closed abruptly but is closed gradually as the leading edge enters, and gradually lls, the passage. For the purpose of providing a seal between the plug member 30 and the barrier 40, the barrier is preferably provided with a chamfered seat 4S which cooperates with an O-ring 46 recessed in a suitable groove in the face of the plug member.

It will be apparent from what has been thus far stated that upon application ofV fluid pressure to the left handV side of the piston 20 by means of fluid connection 16, the other connection 18 being connected to the sump, movement of the piston 20 will take place to the right. Such movement may take place rapidly since the annular escape passage 42 may be dimensioned to have a large escape area so that through the barrier 40. However, as the piston approaches the end of its stroke the annular plug member 30 progressively enters the passage-42 in the barrier 40 which there is little or no initial throttling of fluid at the time that the piston comes to rest. While it is true that the escape path 62 remains open during the time that uid passes through the escape paths 42 and 52, the frictional 4resistance is so high that such escape path 62 is not effective until the very end of the piston stroke.

As a result of the above it will be apparent that iiuid is conducted through escape paths which have an effective cross sectional area which Varies through wide limits. Thus the path 42 normally provided in the barrier 40 offers little resistance and permits rapid response. Gradual closing of the path 42 by the annular plug 30 provides an initial build-up of resistance as the plug moves into the opening. The auxiliary escape path 52 between the plug and the rod provides greater resistance with progressive increase in throttling effect. Finally the path 62 provides maximum resistancefor terminating the complete deceleration cycle. In practice, the ratio of the maxi- V mum to minimum cross sectional area may be on the progressively inhibits the escape of displaced uid and with resulting deceleration of the piston 20, the plug coming to rest with its vO-ring 46 seated on the chamfered seat 45 on the barrier.

In accordance with the present invention an auxiliary fluid escapepath is provided along the piston rod which becomes eective after the plug member is seated on the barrier and incident to taking up the lost motion between Y the plug member `and the piston to provide a progressively increased throttling action and a progressive cutting off of iiuid flow. More specifically in'accordance with the invention, the piston rod is necked down adjacent the piston to define a tapered section which cooperates with the inner edge of the annular plug member to provide an escape path which is gradually reduced in cross section as the piston continues to the end of its range of movement. Thus in the Ypresent instance the piston rod 21 is necked down to provide a tapered, frusto conical section 50 which cooperates with the inner edge 51 of the plug member 30 to provide an auxiliary escape passage 52. Preferably the necked down section 50 tapers progressively from a reduced diameter d1 to a diameter d2 immediately adjacent the piston. The piston rod has a terminal section'53 which is Vcylindrical and which provides Ya telescoping clearance fit with respect to the inner edge 51 of the plug member.

That the auxiliary escape path 52 is of progressively re-Y duced area during the nal movement of the piston will be apparent upon inspection'of the stop motion views, FIGS. 3 and 4. FIG; 3 shows the condition as it exists immediately after the plug member 30 seats'on the barrier 40. VContinued movement of the piston, which is permitted by the lost motion connection with the plug member, causes separation to occur at the stop which provides communication at '56 between the plug member and the piston rod. With the plug member 30 stationary, continue'd movement of the piston causes the Vgradual pinching down of the area available at'52 for fluid ow so that there is a progressively increased throttling eiect within Y the auxiliary passage 52 which tends to absorb the energy of impact and which causes the piston to approach its limit of movement with smooth deceleration. The auxiliary Yescape path 52 is finally reduced to zero, as indicated in fFIG. 4, by the telescoping of the inner edge 51 of the plug member over the terminal surface 53 on the piston rod.

In accordance with one of the aspects of the present invention, the velocity of the piston at the terminal portion of the piston movement is controlled by providing a third escape path through the barrier and which is effective even after theauxiliary uid passage is fully closed. Thus there is provided a small, linal lluid passage which is bored through the barrier 40 and which has an adjusting screw 61 for precise control of the elective area of an escape path 62.V The uid thus undergoes a final throttling action which determines the degree of deceleration order of 1000 to l with progressive variation in between. It is one of thefeatures of the present construction that the cushioning efIect can be caused to take place over an appreciable portion of the total stroke. Thus a piston rod 21 may be used in which the necked down portion 5t) has an appreciable length "l so thatV the deceleration occurs over a large portion-of the stroke. Moreover a piston rodmay be chosen having a minimum diameter d1 which may vary over relatively wide limits to produce a Wide variation in the range of throttling effect. In short, selection of l and d1 determine the length and slope of the response curve and in both of these factors a wide range of choice may be made. Y

Where the diameter d1 is made small to provide substantial initial iiow of fluid after the Vlug member 30- is seated, it is desirable to chamfer out or relieve the inner surface of the plug member as indicated at 65, so that there is adequate downstream area and so that the throttling action, is, for the most part, concentrated at the passage 52. It will be understood, of course, that the amount of taper illustrated in the drawing has been exaggerated for ease in understanding and in a practical Y case will be less than that shown. Preferably the piston rod 21 is threaded into the piston as indicated at 68 so that piston rods having a somewhat diierent configuration of d and l may be readily substituted.

It is one of the more detailed features of the present construction that means are provided for causing bottoming of the piston at the right hand end of the cylinder prior to any bottoming of the piston on the annular plug member 30. In the present embodiment the piston is free to bottom on the barrier with the piston being recessed so that the annular plug member is free to retreat from the barrier thus opening the passageway 42 upon lreversal of pressure and in spite of the fact that the piston is at its limit of movement for immediate fluid iow` in the opposite direction and for prompt reversal of the direction of movement of the piston. This condition is illustrated in FIG. 5. Here it is assumed that pressure has been applied atY the fluid connection 1S, thereby pressurizing the chamber 43. Such pressure causes the plug member 30 to unseat7 moving it to the left into the recess 70 and compressing the springs 33. This frees the fluid aperture 42 so that the pressure fluid is applied over the entire face of the piston, whereupon the piston moves to the left to complete the return stroke. lThe present device is particularly well suited to applications Where rapid and repeated reversals of pressure and stroke must be made.

While the cushioning in the present device Vtakes place in several successive stages, the device is nevertheless simple and minimum annular roomY is required for the cushioning elements. Consequently. the construction does not require any incre-ase inroutside dimensions as compared to actuators ofVV about the same capacity but lacking the cushioning feature. It is one of the practical features of the present construction that the cushioning components are for the most part embodied right in the piston and piston rod and that the cylinder and cylinder heads are of simple straight forward construction usable with pistons of the non-cushioning type. This makes it possible to employ standard cylinders and cylinder heads for both types of actuators. Moreover it is possible in the present construction to convert from non-cushioned to cushioned action simply by substitution of a different piston assembly and without modification of the cylinder itself. A desired change in characteristics may be brought about simply by unscrewing the piston rod and by substituting one of slightly different taper. The device is inherently simple and inexpensive to construct and is capable of operating over long periods of time either pneumatically or with hydraulic fluid and without necessity for care or maintenance.

While the invention has been applied to only one end of the actuator 10, nevertheless it Will be apparent to one skilled in the art that the same mechanism may be employed at the left hand end of the actuator for cushioning in both directions. Moreover, it will be understood that while the piston rod is extended through the head ll, this is not necessary in order to practice the invention, and, if desired, the piston rod 21 could be terminated just to the right of the shoulder 35, with a conventional piston rod and gland being substituted at the left hand side of the piston. Consequently the word surrounding in the following claims relates to radial position and not necessarily to radial alinement.

The present application is a continuation-in-part of my prior application, Serial No. 30,992, filed May 23, 1960, now abandoned.

I claim as my invention:

l. In a fluid actuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod telescoped through at least one of said heads, said heads each having provision for making connection With a source of pressure lfluid, an annular lbarrier in said sylinder adjacent at least one of said uid connections surrounding said piston rod and cooperating with said rod to deiine an annular escape passage for escape of displaced fluid as the piston is driven in the direction of the barrier, an annular plug member surrounding said piston rod and having a yieldable lost motion connection with the piston for normally holding the same spaced in advance of said piston so that as the piston approaches its limit of movement the plug member seats against said barrier closing down said escape passage for inhibiting escape of displaced fluid thereby slowing down the piston, said piston rod having a section adjacent the piston in the form of a tapered plug so as to dene, with the inside edge of the annular plug member, an auxiliary escape path for the displaced iluid which is gradually reduced in cross section as the piston reaches the end of its movement.

2. In a iluid actuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod telescoped through at least one-of said heads, said heads each having provision for making connection with a source of pressure fluid, an annular barrier in said cylinder adjacent at least one of said fluid connections and radially spaced from said piston rod so that its inner edge denes an annular clearance space for flow of displaced iiuid as the piston is driven in the direction of 'the barrier, an annular plug member .surrounding the piston rod and having a yieldable lost motion connection with respect to the piston so that when the piston is driven toward the barrier the annular plug member moves t0- ward the clearance space, the outer surface of said plug member and the inner edge of said barrier being so formed as to define between them a first tapered escape passage which is gradually reduced in cross section for progressive initial throttling of the iluid followed by seating of the plug member on said barrier, the inner sur- 5 face of the plug member and the outer `surface of the piston rod being so formed as to dene between them a second escape passage which is gradually reduced in cross section upon the continued movement of the piston for progressive final throttling of the fluid to -bring said piston to a cushioned stop.

3. ln a fluid actuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod telescoped through at least one of said heads, said heads each having provision for making connection with a source of pressure tluid, an annular barrier in said cylinder adjacent at least one of said fluid connections surrounding said piston rod and cooperating with said rod to define an annular escape passage for escape of displaced iluid as the piston is driven in the direction of the barrier, an annular plug member surrounding said piston rod and having -a yieldable lost motion connection with respect to the piston for normally holding the same spaced in advance of said piston so that as the piston approaches its limit of movement the plug member seats against said barrier closing down said escape passage for inhibiting escape of displaced fluid thereby slowing down the piston, and means between the plug member and piston rod defining an auxiliary escape path along the piston rod for the displaced fluid and which is gradually reduced in cross section as the lost motion is taken up for progressively cutting oil fluid flow as the piston continues to the end of its movement.

4. In a iluid actuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod telescoped through at least one of said heads, said heads each having provision for making connection with a source of pressure iluid, an annular barrier in said cylinder adjacent at least one of .said lluid connections surrounding said piston rod and defining 4an escape passage through said barrier for escape of displaced uid as the piston is driven in the direction of the barrier, a plug member having a yieldable lost motion connection with respect to the piston for normally holding the same in advance of said piston and `free of said escape passage vbut movable with respect to the piston so that as the piston approaches its limit of movement the plug member seats against said barrier closing down said escape passage for inhibiting escape of displaced iluid thereby slowing down the piston, and means including a tapered surface interposed 'between the barrier and the piston rOd defining an auxiliary escape path for the displaced fluid along the piston rod and which is gradually reduced in cross section as the lost motion is taken up vfor progressively cutting off fluid flow as the piston continues to the end of its movement.

5. In a fluid actuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod telescoped through at least one of said heads, said heads each having provision for making connection with a source of pressure iluid, an annular barrier in said cylinder adjacent at least one of said fluid connections surrounding said piston rod and defining an escape passage through Isaid barrier for escape of displaced fluid as the piston is driven in the direction of the barrier, a plug member having a yieldable lost motion connection with respect to the piston for normally holding the same in advance of said piston and free of said escape passage but movable with respect to the piston so that as the piston approaches its limit of movement the plug member seats against said Ibarrier closing down said escape passage for inhibiting escape of displaced iluid, said piston rod being necked down in the Vicinity of the piston to provide an auxiliary escape path for the displaced uid along the piston rod, and means providing a relatively stationary surface cooperating with the necked down portion of the piston rod and so arranged that the escape path is ton rod telescoped through at least one of said heads,

said Iheads each having provision for making connection with a source of pressure iiuid, an annular barrier in said cylinder adjacent at least one of said Vfluid connections surrounding said piston rod and defining an escape passage through said barrier for escape of displaced iiuid as theV piston Vis driven inthe direction of the barrier, a plug member having a yieldable lost motion connection with respect to the piston for normally holding the sarne in advance of said piston and free of said escape passage but movable with respect to the piston, said plug member having a tapered leading edge'so that as the piston approaches its limit of movement the plug member proggressively enters said passage and seats against said barrier for inhibiting escape of displaced iiuid and thereby slowing down the piston, and means dening an auxiliary escape path along said piston rod forthe displaced fluid, said escape path being of tapered configuration so that the path is gradually reduced in cross section as the lost motion is taken up for progressively cutting ofi fluid iiow as the piston continues to the end of its movement.

7. In -a fluid actuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod telescoped through at least one of said heads, said heads each having provision for making connection with a source of pressure iiuid, van annular barrier in said cylinder adjacent yat least one of said fluid connections surround- Ving said piston rod and cooperating with said rod to define an annular escape passage for escape of displaced fluid as the piston Vis driven in the direction of the barrier, an

- annular plug member surrounding said piston rod'and having a yieldable lost motion connection with the piston Vfor normally lholding the same in advance of said piston and free of the escape passage for escape of fluid through the latter, said annular plug member and said barrier including a surfacerof tapered coniiguration'between them so that as the pistonsapproaches its limit of movement the plugmember progressively reduces the" cross section of the escape passage and seats against said barrier for inhibiting escape ofdisplaced iiuid thereby slowing down lthe piston, said plug member and piston rod defining an auxiliary escape passage for escape of uid along the piston rod and including a surface of tapered configuration between them so that subsequent movement of the piston reduces the cross section of the auxiliary escape passage for progressively cutting ot fluid ow.

8.1m a fluid actuatorY the combination comprising a cylinder having heads lat each end for enclosing the same, al piston slidable in said cylinder and having a piston rod telescoped through at least one of saidheads, Vsaid heads each having provision for making connection with a source of pressure iiuid, an annular barrier in said cylinder adjacent lat least one of said iiuid connections surroundingV said piston rod and cooperating with said rod to deiine an annular escape passage for escape of displaced Yuid as the piston is driven in barrier, an annular plug member surrounding said piston rod having a yieldable lost motion connection with respect to the piston for normally positioning the plug member spaced in advance of said piston so that as the piston approaches its limit of movement'the plug member seats against saidbarrier closing down said escape passage for inhibiting escape of displaced iiuid thereby slowing down the piston, means including a tapered surface between the plug member and piston rod dening an auxiliary escape path for the displaced iluid which is gradually reduced in the direction of the cross section as the lost motion is taken up for progressively cutting ott fluid iiow as the piston continues to the end of its movement, and means providing an adjustable aperture in said barrier for limiting the terminal velocity of the piston. j

9. In a iiuid lactuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod Vtelescoped through at least one of said heads, said heads each having provision for making connection with a source of pressure fluid, an annular barrier in said cylinder adjacent at least one of said fluid connections surrounding said piston rod and cooperating with said rod to define an annular escape passage for escape of displaced uid `as the piston is driven in the direction of the barrier, an annular plug member surrounding said piston rod carried by the piston and having a yieldable lost motion connection with respect to the piston for normally holding the plug member spacedyin advance of said vpiston so ythat as the piston approaches its limit of movevment the plug member seats against said barrier closing down said escape passage forvinhibitingY escape of displaced iiuid, means between the plug member and piston rod defining an auxiliaryjescape path for the displaced uid which is gradually reduced in cross section as the lost motion is talien up for progressively cutting ot`r` uid ilow `as the piston continues to lthe end of its movement, and means lfor bottoming'the pistonV prior to bottoming of the piston on the plug member so that reversal of fluid pressure yat the fluid connections is accompanied by unseating of the plug memberfor flow of iiuid and movement of the piston in the opposite direction.

10. In a fluid actuator the combination comprising a cylinder having heads at each end for enclosing the same, a piston slidable in said cylinder and having a piston rod telescoped through at least onev of said heads, said heads each having provision for marking connection with a source of pressure iiuid, an annular barrier in said cylinder adjacent at least one of said fluid connections and surrounding said piston rod, means deiining'a first escape passage for permitting escape ofdisplaced fluid as the piston is driven in the direction of the barrier, means for closing down said first escape passage as theV piston appreaches the barrier for inhibiting escape of the displaced fluid, `and means surrounding the piston rod for defining a second escape passage ofl tapered configuration for the escape of the displaced fluid along the, piston rod and which is so formed as to be gradually reduced in cross section as the piston continues to the end of its movement to provide `a cushioned stop. l

1l. In a fluid actuator the combination comprising a cylinder `having heads at each end for enclosing the same, a piston slidable in said cylinder and having `a piston rod telescoped through at least one of said heads, said heads each having provision for malcing connection with a source of pressure fluid, an Iannular barrier insaid cylinder adjacent lat least one of said iiuid connections and radially spaced from'said piston rod to define a clearance space for flow of displaced uid as the piston is dniven in the direction of the barrier, an annular plug member carried by the piston for plugging the clearance space, said plug member having a plurality of supporting pins telescoped into said piston, spring means for urging the plug member into a normal position in which itis spaced ahead of said piston and providing a yieldable lost motion connection therewith, said pins being integral with said plug member, and means interposed between the plug member and the piston rod defining an auxiliary path for the escape of the displaced iiuid along the piston rod which is so formed as to be gradually reduced in cross section as the lost motion is taken up to provide a cushioned stop.

No references cited.

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