US 3915070 A
Apparatus for providing an indication of the position of the piston within a fluidic actuator. The apparatus comprises means positioned within the actuator cylinder and coupled to the piston for converting longitudinal motion of the piston to rotary motion which is transmitted out of the cylinder to a suitable indicator.
Description (OCR text may contain errors)
United States Patent Mailliet Oct. 28, 1975 APPARATUS FOR INDICATING THE  References Cited POSITION OF THE PISTON OF A FLUIDIC UNITED STATES PA S ACTUATOR 243,450 6/1881 Lafargue 92/33 x  Inventor: Pierre H. Mailliet, Luxembourg, 2,704,047 5 o... 116/124 R Luxemburg 2,936,737 5/1960 Miller 92/31 x 3,077,179 2/1963 Evanson 116/127 X  Ass1gnee: S.A. des Anciens Etablissements 3,186,311 6/1955 Carlson... 92/33 X Paul Wurth, Luxembourg, 3,386,340 6/1968 Engle 91/61 Luxemburg 3,633,534 l/1972 Hersey.... 116/124 R 3,766,831 10/1973 Yeakley 91/61  F1led: Oct. 19, 1973  Appl. No.: 408,198 Primary Examiner-Richard 1C. Queisser Assistant ExaminerDaniel M. Yasich  Foreign Application Priority Data 57 ABSTRACT Oct. 23, 1972 Luxemburg 66347 1 Apparatus for providing an indication of the position 52 us. c1 92/5 R; 92/33; 92/113; of the piston Within a fiuidic actuator The apparatus 116/127 comprises means positioned within the actuator cylin-  Int. Cl. F01B 31/12 der and coupled to the Piston for Converting longitudi'  Field 01 Search 116/124 R, 124 A, 124 F, 1191 motion of the piston I9 rotary motion which is 1 16/127; 91/1, 61; 60/699; 92/5 R, 31, 33, transmitted out of the cylinder to a suitable indicator.
8 Claims, 3 Drawing Figures US. Patent Oct.28, 1975 Sheet20f2 3,915,070
APPARATUS FOR INDICATING THE POSITION OF THE PISTON OF A FLUIDIC ACTUATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the determination of the position of movable members and particularly of longitudinally movable members which are moved in response to a pressurized fluid. More specifically, this invention is directed to means for accurately and continuously determining the position of the piston of a hydraulically or pneumatically operated actuator in a manner which does not require contact with the actuator output shaft or to a load coupled thereto. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art There are numerous situations where the position of the piston of a hydraulic or pneumatically operated actuator is important control data. In the prior art, in an effort to provide such data, piston position has conventionally been determined as a function of the position of the load on the actuator. Thus, it is conventional prior art practice to interconnect a piston actuator and load by means of rod connections or intermediate gears and to employ the connections or gears to generate a signal commensurate with piston position. The determination of piston position via a comparatively complicated intermediate device, which is of necessity susceptible to failure and which must be redesigned and reconstructed for each operating environment, has obvious inherent deficiencies. Additionally, because of the peculiar arrangement of the load, many situations are encountered wherein the use of an intermediate device is either impossible or not economically feasible. When an intermediate position sensing device could not be employed, and access to the movable load was possible, the prior art has typically resorted to the use of a plurality of load operated limit switches which provide stepwise information with respect to the position of the load. There are numerous instances where access to the load is impossible or stepwise positional information is insufficient for control purposes and/or the use of an intermediate position signal generating device between the piston and load is impossible.
In view of the problems briefly discussed above, the prior at has long sought a mechanism directly located on the cylinder of a hydraulically or pneumatically op- 1 erated jack or actuator for providing information regarding the position of the piston in the jack continuously and completely independently of the load on the piston. It is to be noted that attempts have been made to provide positional information with respect to hydraulically operated jacks by measuring the quantity of hydraulic fluid flow to or from the jack. These prior art flow measuring devices have been comparatively fragile, complicated and inaccurate.
The sensor portion of a positional measuring device for a hydraulic or pneumatically operated actuator must obviously be at least partly arranged within the piston cylinder. The problems associated with sensing the position of a piston located within a cylinder and having no direct engagement point outside of the cylinder are substantial and numerous. Thus, by way of example, the means for transmitting a signal commensurate with piston longitudinal motion through the cylinder casing must be sealed against leakage at the comparatively high pressures which occur. Additionally, frictional contact must be minimized within the cylinder since any metal fragments resulting from abrasion will damage the piston rings and/or the cylinder walls thereby destroying the jack itself. Furthermore, although the piston in a hydraulic or pneumatically operated jack is provided with excellent guidance and support in its working or longitudinal direction, the piston is typically not restrained from rotation within the cylinder casing. The possibility of rotational motion obviously greatly complicates the problem of accurately sensing piston position within the cylinder and thereafter transmitting such motion outside of the cylinder.
It has been suggested that the above briefly described problems could be solved by means of affixing a tubular indicator extension to the piston within an actuator cylinder; the extension passing through an end wall of the cylinder and being provided with a scale relating to piston position. In the case of an actuator having a large stroke this proposed solution would present space problems in addition to the sealing problems alluded to above. Thus, not only would space have to be provided for the lengthy extension, and the extension would be susceptible to damage, but additionally the high working pressures within the cylinder would make it virtually impossible to obtain an adequate sliding seal for the extension.
SUMMARY OF THE INVENTION The present invention overcomes the above briefly discussed and other deficiencies and disadvantages of the prior art by providing a technique and apparatus for continuously and accurately determining the position of a piston of a hydraulically or pneumatically operated actuator. Apparatus in accordance with the present invention includes means disposed within the cylinder of a fluid operated actuator for converting longitudinal movements of the piston into rotational motion which is transmitted through a cylinder wall to a suitable indicator. Apparatus in accordance with the present invention is further characterized by means which prevents unintentional rotary motion of the longitudinal-torotational converting means, such as might be caused by rotation of the actuator piston, thereby insuring accurate positional measurements.
In a preferred embodiment of the invention the piston of a hydraulically or pneumatically operated actuator, and possibly also the piston rod, are provided with a recess or blind hole which extends inwardly from a first end of the piston. A shaft rotatably supported at the cylinder wall, and specifically to a cylinder cover plate, extends into the recess in the piston. At least a portion of the shaft is constructed so as to perform the function of a worm gear. An extension of the rotatable shaft penetrates the cylinder wall and is connected to an indicator located to the exterior of the cylinder.
Also in accordance with the preferred embodiment of the invention, a setting ring or nut is carried by the inner wall of the recess in the piston. The setting ring moves with the piston and engages the portion of the shaft which functions as a worm gear whereby longitudinal movement of the setting ring results in rotation of the shaft. In order to avoid unintentional rotation of the setting ring, which would falsify the measured value, apparatus in accordance with the present invention may also include means which guides the setting ring in the longitudinal direction while preventing rotational movement thereof. The means for guiding the setting ring may takethe form of a slotted tube affixed to the cylinder cover plate and projecting into the piston recess. The slotted tube, when employed, will be rigid and will be coaxial with the setting ring; the setting ring being provided with wedges which travel in slots in the tube. In one embodiment the setting ring is positioned to the interior of the slotted tube and is provided with means for simultaneously guiding and imparting rotation to the worm gear portion of the shaft. In a preferred embodiment, the portion of the shaft which performs the function of worm gear was constructed such that a complete working stroke of the piston was converted into a complete or partial rotation of the shaft.
BRIEF DESCRIPTION OF THE DRAWING The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the several figures and in which:
FIG. 1 is a longitudinal view, partly in section, of a portion of an actuator having incorporated therein the piston position measuring apparatus of a preferred embodiment of the present invention;
FIG. 2 is a cross-sectional side view of the embodiment of FIG. 1 taken through the portion of the device located within the actuator cylinder; and
FIG. 3 is a side elevation view, partly in section, of an indicating instrument which may be associated with the apparatus of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, the cylinder of a fluid operated actuator is indicated at 6. A cover plate 2 for a first end of cylinder 6 is affixed to the cylinder by means of bolts such as bolt 4. A longitudinal movable piston 8 is located within cylinder 6; piston 8 being provided with sealing rings 10 and 12 in the conventional manner. The piston 8 is attached to a piston rod 14; rod 14 ultimately being coupled to the load mechanism operated by the actuator. In FIG. 1 the piston 8 is shown in its most inward position; i.e., at the beginning of a stroke. In the interest of facilitating understanding of the invention, the means whereby the operating fluid is supplied to the interior of the actuator cylinder has not been shown. It will be understood that the operating fluid will be delivered to the rear side of piston 8 via suitable passages provided therefore in cover plate 2 and, if necessary, operating fluid may be delivered to the other side of piston 8 via a port provided in the wall of cylinder 6.
In accordance with the present invention longitudinal movements of piston 8 and piston rod 14 are converted into rotary movement of a shaft 16 and the rotational movement of shaft 16 is transmitted to an indicator located to the exterior of the actuator. The foregoing objective is achieved by providing the piston 8 and rod 14 with a central recess or blind hole 18. The shaft 16 is introduced into recess 18 and the recess and shaft are dimensioned such that the shaft does not leave the recess during the operating stroke of the piston. The portion 7 of the shaft 16 which is located within the actuator cylinder and extends into recess 18 is constructed as elongated gear means as for example, an extended worm gear or as a square bar twisted about its longitudinal axis Drive means comprising a setting ring or nut 5 17, which may most clearly be seen from joint consideration of FIGS. 1 and 2, is mounted so as to move with piston 8. The setting ring 17 is also mounted, in the manner to be described in detail below, so as to be restrained against rotation. The setting ring 17 engages and thus imparts rotational movement to the twisted square bar or gear comprising shaft 16.
The setting ring 17 is held in a piston rod insert 20 by means of contact with abutting face 22 of insert 20,
which prevents longitudinal movement of the nut 17 relative to the positon from the right to the left as the apparatus is shown in FIG. 1, and by a spacer 24 and a split ring 26. Insert 20 is screwed into an internal thread provided in the recess 18 of the piston-piston rod assembly. As will be obvious to those skilled in the art, the piston 8 and insert 20 can, if desired, be integral.
Any unintentional rotational movement of setting ring 17 will lead to an incorrect indication of piston position. Accordingly, to prevent the rotation of setting ring 17, a slotted supporting tube is rigidly attached, for example by welding, to a base plate 28. The base plate 28 is attached to cylinder cover plate 2 by means of bolts and 42. The supporting pipe 30 also extends into recess 18 in the piston-piston rod assembly. As may best be seen from FIG. 2, the supporting tube 30 is provided, in the disclosed embodiment, with two longitudinally extending grooves 32 and 34. The setting ring or nut 17 is shaped so as to define a pair of generally coaxial passages. The innermost of these passages is of suitable shape so as to engage the twisted square bar comprising shaft 16. The second or outwardly disposed passage in nut 17 receives the slotted support tube 30. The setting ring 17 is provided with inwardly extending longitudinal projections 36 and 38 which respectively engage grooves 32 and 34 of the supporting pipe 30. Accordingly, the setting ring 17 is guided in the longitudinal direction along the supporting tube 30 and can not rotate with respect thereto. The setting ring or nut 17, although an integral member, may be considered as two elements; a first element being located outside of the supporting tube 30 and the second element being located within the tube 30, the two elements being interconnected by the slot in tube 30 as shown in FIG. 2.
The portion of the setting ring 17 located to the exterior of the support tube 30 is carried longitudinally by piston 8 via insert 20 and, as noted, rotational movement of setting ring 17 is prevented by means of the engagement of projections 36 and 38 on ring 17 with grooves 32 and 34 of tube 30. The portion of setting ring 17 located to the interior of tube 30, however, engages and causes rotation of the stationary shaft 16 during longitudinal movement of the piston. As may be seen from FIG. 2, sufficient clearance is provided between tube 30, setting ring 17 and shaft portion 7 of 16 so that excessive abrasion or friction is avoided and maximum measuring precision is insured. In operation the piston 8 and piston rod 14 can rotate without influencing the longitudinal position measurement.
The shaft 16, or more precisely a cylindrical extension thereof, is passed out of the actuator cylinder through an aperture provided in the cylinder cover plate 2. The aforementioned base plate 28, in the manner to be described below, provides for the support of shaft 16 as it extends out of the actuator cylinder. A sealing ring 44 insures against leakage between the interior and exterior of the cylinder betweenplates 2 and The base plate 28 is also provided with a central aperture. Bearing means for the mounting of shaft 16 are positioned in the aperture in plate 28 in the manner shown; the bearings being indicated at 46, 48 and 50. The bearings 46, 48 and 50 are located against a internal shoulder in the aperture in plate 28 and are restrained against longitudinal movement in the opposite direction by means of a bearing bracket 52; bracket 52 in turn being attached to base plate 28 via bolts 54 and 56. A sealing ring 58 is provided to prevent leakage of pressurized fluid from the interior of the actuator cylinder to the outer atmosphere past the supporting bearings for shaft 16. Additionally, the bearing bracket 52 carries a gland 60 to provide additional sealing.
The end of shaft 16 which extends out of the actuator; i.e., the portion of the shaft which extends outwardly past the base plate 28, is provided with a keyway 62. As will be described below in the discussion of FIG. 3, the keyway 62 permits the coupling of shaft 16 to a position indicator.
As will be obvious to those skilled in the art, should the portion of shaft 16 which extends into piston-piston rod recess 18 become unduly long with respect to its cross-section, a sagging of the shaft could result. Should the possibility of a bending or sagging of shaft 16 be presented due to the dimensions of the actuator, shaft 16 may be rotatably supported at its inwardly disposed end in the manner shown in FIG. 1. The supporting and mounting of shaft 16 at the inwardly disposed end is achieved by means of apparatus 164 which is affixed to the slotted supporting pipe 30 and is provided with a ball bearing 166; bearing 166 receiving a cylindrical tip portion .of shaft 16.
Referring now to FIG. 3, the keyway 62 of shaft 16 may be engaged by a connecting member 64. Connecting member 64 is rigidly and eccentrically coupled to a transfer arm 66 which, in turn, drives a shaft 68. The
shaft 68 is supported and mounted in a bearing block 70 which is attached, by means of a plate 72, to the outer casing of the actuator. The shaft 68 extends through plate 72 and is connected to a box nut 76 via a coupling slip ring 74. An indicator finger or dial 78 is attached, in any suitable manner, to the box nut 76.
The coupling slip ring 74 is retained by means of a further ring 80 afiixed to shaft 68 in the manner shown. The box nut 70 is elastically and uniformly urged against the slip ring 74 by means of the internal spiral spring 82. The elastic coupling of the box nut to the slip ring prevents bending of the indicator dial or finger 78 in the event of an accidental blockage of the natural movement thereof. The attachment plate 72 also serves to support an indicator panel 84 which is positioned bethe quantity of packing material expelled is of interest to the operator, who must due to safety considerations remain a considerable distance from the tap hole, and may be determined as a function of the longitudinal furnace tap hole plugging machine. In such clay guns movement of a hydraulically operated piston. The pres ent invention has proven to be extremely reliable in the severe working=environment of proximity to a blast furnace. z I
'As will now be obvious to those skilled in the art, the present invention comprises an accurate and substantially maintenance-free means for determining the position of the piston of a hydraulically or pneumatically operated actuator. In accordance with the present invention the conversion of the longitudinal movement of the piston into the rotation of an output shaft greatly facilitates solution of the problem of providing adequate sealing'between the interior of the actuator and the outside atmosphere and,-in fact, permits such sealing to be achieved with conventional apparatus. Additionally, the incorporation of the slotted supporting pipe 30 of the present invention permits the above described measuring device to be utilized in apparatus wherein the piston and piston rod are not axially aligned. The apparatus of the present invention can be universally employed as a result of the independence of the measuring device from the particular load on the actuator.
While a preferred embodiment of the present invention has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.
What is claimed is:
1. Apparatus for determining the position of a piston of a fluid operated actuator, the piston being movable longitudinally within a cylinder and being provided with a recess in a first end thereof, the position determining. apparatus comprising:
elongated gear means extending into the recess in the actuator piston;
means mounting said gear means for rotation, said mounting means being at least in part supported from a wall of the actuator cylinder which faces the piston first end;
drive means mounted on the actuator piston for movement therewith, said drive means engaging said gear means, longitudinal motion of the actuator piston with respect to said gear means being coupled to said gear means by said drive means and producing rotation of said gear means;
means for transmitting the rotational motion of said gear means through said actuator cylinder wall, said motion transmitting means being coupled to said gear means; and
means positioned exteriorly of the actuator cylinder and connected to said transmitting means for providing an indication of piston longitudinal position.
2. The apparatus of claim 1 wherein said means mounting said gear means for rotation comprises:
bearing means supported by said actuator cylinder wall; and
means for preventing leakage: of fluid between the interior and exterior of said cylinder about said bearing means.
3. The apparatus of claim 1 further comprising:
means for preventing rotation of said gear means in response to rotational movements within the actuator, said rotation preventing means interconnecting said drive and mounting means.
with at least a first passage which engages said elongated gear means, said ring means further being provided with at least a first projection which engages said supporting member. 6. The apparatus of claim wherein said ring means comprises:
a nut, said nut defining a pair of generally coaxial passages therethrough, the inner of said passages engaging said elongated gear means and the outer of said passages receiving said supporting member.
7. The apparatus of claim 6 wherein said supporting member comprises:
a slotted tube. 8. The apparatus of claim 7 wherein said means mounting said gear means for rotation comprises:
bearing means supported by said actuator cylinder wall; and
means for preventing leakage of fluid between the interior and exterior of said cylinder about said bear- I ing means.