GB2077856A

GB2077856A - Digital Positioner and Method of Operation

Info

Publication number: GB2077856A
Application number: GB8116423A
Authority: GB
Original assignee: Halliburton Co
Current assignee: Halliburton Co
Priority date: 1980-06-02
Filing date: 1981-05-29
Publication date: 1981-12-23
Also published as: IT8122042A0; IT1137172B; NL8102627A; AU7113081A; BR8103390A; NO811849L; DE3121128A1

Abstract

A digital positioner (10) having a plurality of concentric pistons (150, 170, 200, 260) upon which fluid pressure acts through various driving ports (A, B, C, D) and an air spring port (E) in the housing of the positioner, movement of one or more pistons effecting movement of an axial positioner rod (80) a discrete distance depending upon which of the plurality of driving ports is pressured. Substantially uniform fluid pressure is employed at all of the driving ports and the air spring port. The positioner rod is returned to a predetermined position when pressure is removed from all driving ports. <IMAGE>

Description

SPECIFICATION Digital Positioner and Method of Operation Baclcground of the Invention Digital positioners have been employed in commercial and industrial applications for some time, particularly for transmission and machine control. Such positioners may employ air, oil, water or other fluids acting against one or more pistons to longitudinally move a rod between a plurality of discrete positions.

The prior art fluid pressure operated positioners suffer from various disadvantages that impair the efficiency of their operation. For example, most prior art devices employ a mechanical spring to return the positionerto an initial, or neutral position. Such springs tend to wear and fatigue after a time, rendering them less effective and, in many field applications, are inhibited in operation by debris and contaminants in the operating fluid. Many prior art positioners require pressure regulators on the fluid feed lines, and/or require different pressures on different lines. In addition to rendering these devices unduly complex, this also results in a relatively narrow fluid pressure range which may be utilized to drive the device.Some positioners require ratchet mechanism to effect precise positioning, a mechanical feature which renders these devices less reliable. Finally, the prior art devices suffer from "races," or false shifts between positions, when operating under less than ideal conditions, with resulting damage to the positioner as well as to the mechanism which the positioner is controlling.

Summary of the Invention The digital positioner of the present invention comprises an outer housing within which are disposed a plurality of concentric pistons which are acted upon by fluid (for example, air) pressure to move a coaxial rod. The distance of rod movement is controlled by which of several driving ports in the housing are pressured. Six different positions are possible, and air pressure is also employed through an air spring port to return the positioner rod to an initial position when air pressure is removed from all driving ports. The present invention does not employ mechanical springs or ratchets, and requires no pressure regulators, in contrast to the prior art. Thus, the design of the invention is uncomplicated and relatively compact.In addition, due to the area ratios employed in the piston design of the invention a much wider range of fluid pressure may be employed than is possible with the prior art. Furthermore, only four logic, or supply lines, in addition to a constantly-pressured return line, are required to effect the six different positions.

Finally, the positioner of the present invention is not subject to races, even under field conditions in relatively hostile environments.

Brief Description of the Drawings The foregoing advantages and the preferred embodiment of the invention will be better understood from the specification taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a horizontal cross-sectional elevation of the digital positioner of the present invention with its positioner rod in a first, or neutral, position.

Fig. 2 is a horizontal cross-sectional elevation of the present invention with the positioner rod in a second position.

Fig. 3 is a horizontal corss-sectional elevation of the present invention with the positioner rod in a third position.

Fig. 4 is a horizontal cross-sectional elevation of the present invention with the positioner rod in a fourth position.

Fig. 5 is a horizontal cross-sectional elevation of the present invention with the positioner rod in a fifth position.

Fig. 6 is a horizontal cross-sectional elevation of the present invention with the positioner rod in a sixth position, showing a coupling attached to the positioner rod.

Fig. 7 is an end view of the present invention with coupling attached.

Fig. 8 is a logic diagram illustrating which driving ports are pressured for the various rod positions.

Detailed Description of the Preferred Embodiment Referring to Fig. 1, the invention is shown in its preferred embodiment. Digital positioner 10 comprises a hollow cylindrical housing 1 2 having circular end cap 14 affixed thereto by a plurality of screws and lock washers 22, a seal being effected between housing 12 and end cap 14 by gasket 1 5. Fig. 7 shows end cap 14 in elevation with screws and lock washers 22 thereon. End cap 14 has an axial aperture therethrough with substantially uniform bore 1 6 having annular channel 1 8 opening thereon, annular channel 18 having circular seal 20 disposed therein.

Housing 12 possesses driving ports A, B, C and D, the radially outer ends of which, 24, 26 and 28 and 30, are internally threaded to permit the connection of fluid supply lines, not shown. The radially inner ends of driving ports A, B, C and D comprise passages 32, 34, 36 and 38, respectively, all of which lead to the interior of the housing 12. Passages 34, 36 and 38 are intercepted by annular channels 40, 42 and 44 in the interior surface of housing 12. Describing the interior of housing 12, chamfered surface 46 leads to first bore 48 of substantially uniform diameter, which is terminated at its junction with annular channel 40. Chamfered surface 49 leads to substantially uniform second bore 50, of lesser diameter than first bore 48.Second bore 50 is terminated at its junction with annular channel 42, which leads to substantially uniform third bore 52 via chamfered surface 51. Third bore 52 is of lesser diameter than second bore 50, and is terminated at its junction with annular channel 44, which leads via chamfered surface 53 to substantially uniform fourth bore 54, of lesser diameter than third bore 52. Fourth bore 54 is terminated by chamfered surface 55, leading to annular channel 56, from which extends substantially uniform fifth bore 58. Fifth bore 58 and third bore 52 are of the same diameter, the reason for which being explained hereafter in conjunction with the operation of the invention.

Chamfered surface 60 extends from fifth bore 58 to the righthand end of housing 12.

Longitudinal, radially-offset passage 62 intercepts annular channel 42 at its inner extent in housing 12 and is closed by pressure plug 64 which is threaded into cylindrical passage 62 at its outer extent. Oblique passage 66 extends from longitudinal passage 62 through the wall of fifth bore 58.

Breather filter vent 70 is threaded into radial passage 68, which extends from the exterior of housing 12 through the wall of fourth bore 54.

Air spring cap 72 is fixed to the righthand end of housing 12 by a plurality of screws with lock washers 22, a seal being effected between housing 12 and air spring cap 72 by spring end gasket 73. Air spring cap 72 has axial aperture 74 of substantially uniform diameter therethrough.

Positioner rod 80 extends through axial aperture 16 in end cap 14, diameter 82 of rod 80 being sealingly contacted by seal ring 20 in annular channel 18. At the outer-most extent of positioner rod 80 is threaded bore 84, to which a coupling may be connected to transmit the various positions of rod 80 to the mechanism which is to be controlled by the digital positioner 10. Diameter 82 of rod 80 extends into housing 1 2 for a substantial axial distance, after which the bore increases at radially flat leading face 85 to diameter 86 for a short axial distance, and again increases at radially flat driving face 87 to diameter 88, which is only slightly less than that of fourth bore 54 which surrounds it, a seal being effected between positioner rod 80 at diameter 88 and the wall of fourth bore 54 by seal ring 92 carried within annular channel 90.Diameter 94 at the righthand extent of rod 80 is of slightly less diameter than diameter 88, and terminates in end face 96 which possesses diametrically oriented groove 98 therein. Chamfered surface 100 leads to substantially uniform bore 102 within the righthand extent of positioner rod 80, bore 102 ending at flat circular surface 106, of the same diameter as annular channel 104 to which bore 102 leads.

Air spring piston 110, which is coaxial with positioner rod 80, extends within bore 102 and is slidably engaged with the wall of bore 102 at area 112, of substantially uniform diameter. A seal is effected between the wall of bore 102 and air spring piston 110 at area 112 by seal ring 116 carried within annular channel 114 opening on area 112. From area 112, air spring piston 110 extends to the inner wall of air spring cap 72 at a lesser, substantially uniform diameter 11 8.

Annular channel 120, which opens on the surface of diameter 11 8, carries O-ring 122. Air spring piston 110 protrudes through axial aperture 74 in air spring cap 72 at area 124, the diameter of which is slightly less than that of axial aperture 74 a seal being achieved between area 124 and the wall of aperture 74 by O-ring 128, which is contained in annular channel 126 in air spring piston 110. The outermost extent of air spring piston 110 is threaded at 130, while the innermost extent is terminated at radially flat surface 132, which is pierced by axial passage 134 extending to threaded area 1 36 at air spring port E, leading to the exterior of the digital positioner 10 for connection to a fluid supply line, not shown.Threaded end 1 30 of air spring piston 110 is concentrically surrounded by flat washer 138, which is adjacent to lock washer 140, both of which are held against air spring cap 72 by hex jam nut 142 which is threaded onto threaded end 130.

A plurality of pistons concentrically surround positioner rod 80. Piston 150, with radially flat front wall 149, has bore 1 52 therethrough, a seal being achieved between positioner rod 80 and piston 1 50 by seal ring 1 56 in annular channel 1 54, which opens onto the wall of bore 1 52. The radial exterior of piston 1 50 comprises an area 151 of relatively small diameter, and a second area 1 58 of a diameter slightly smaller than that of first bore 48 of housing 12, with radially flat driving face 1 53 therebetween.A seal is achieved between area 158 and the wall of first bore 48 by seal ring 1 62 carried in annular channel 1 60 in piston 1 50. Piston 1 50 is slidable with respect to both positioner rod 80 and the wall of first bore 48. Radially flat end face 1 64 of first piston 130 possesses diametrically oriented groove 1 66 therein.

Adjacent first piston 1 50 is second piston 1 70.

Second piston 1 70 has radially flat front wall 1 71, and axial bore 174 through which positioner rod 80 slidably passes, a seal being achieved between piston 170 and positioner rod 80 by seal ring 1 78 carried in annular channel 176. The radial exterior of second piston 1 70 has a first area 1 72 of reduced diameter, and radially flat driving face 1 73 leading to second area 1 80 of a diameter only slightly less than that of second bore 50 and in slidable engagement therewith.

Seal ring 184 in annular channel 1 82 creates a seal between the wall of second bore 50 and second piston 170. Radially flat end wall 106 of second piston 1 70 has diametrically oriented groove 1 88 therein.

Third piston 200 is adjacent second piston 170 and has flat leading wall 201. Third piston 200 concentrically and slidably surrounds positioner rod 80, which slidably passes through axial bore 204 of third piston 200, a seal being chieved by seal ring 208 in annular channel 206, which opens on the wall of bore 204. Area 202 on the radial exterior of third piston 200 is of relatively small diameter, and terminates at radially flat driving face 203 while area 210 is of only slightly less diameter than that of third bore 52, a slidable seal being achieved between area 210 and the bore wall by seal ring 214 carried in annular channel 212, which opens on area 210. Radially flat end wall 21 6 of third piston 200 has diametrically oriented groove 218 therein.

Fourth piston 260 concentrically surrounds air spring piston 110 and slides thereon via bore 261 in sealing engagement therewith, a seal being achieved between air spring piston 110 and fourth piston 260 by O-ring 122, previously described. Area 262 on the exterior of fourth piston 200 is of slightly less diameter than that of fifth bore 58, seal ring 266 carried in annular channel 264 slidably sealing between area 262 and the wall of fifth bore 58. End wall 270 of piston 200 is radially flat. Area 268 on the radial exterior of piston 260 is of comparatively small diameter relative to area 262. Driving face 263 extends radially from area 262 to area 268, and front face 265 extends to bore 261.

A plurality of annular chambers of variable axial length, 1 68, 1 90, 220, 224, 228 and 230, are created by the assembly of pistons and positioner rod 80. Driving port A opens upon chamber 1 68, driving port B on chamber 190, driving port C on chamber 220, and driving port D on chamber 224, while chamber 228 communicates with the exterior of housing 12 through vent 70. Chamber 230 communicates with chamber 220 through longitudinal passage 62.

Cylindrical chamber 226 opens to air spring port E through axial passage 134 in air spring piston 110.

Referring to Fig. 6, a coupling 240 is shown attached to positioner rod 80. Such a coupling may be used to transmit movement of positioner rod 80 to control, for example, a transmission for an internal combustion engine. Coupling housing 242 is fixed to rod 80 by bolt 250 and washer 248, which are not shown in section. Clevis pin 244, which passes through aligned apertures 243 on coupling housing 242 is held thereon by pin head 245 and shear pin 246. Fig. 7, which is a view of the left-hand end of positioner 10, shows coupling 240 in elevation.

Operation of the Preferred Embodiment Referring to Figs. 1 through 6 and 8, the operation of digital positioner 10 will be described. Fig. 1 shows digital positioner 10 with positioner rod 80 in its most extended position. In this position, as shown in Fig. 8, driving ports A, B, C and D are not pressured, while air spring port E is connected to a fluid (air) pressure line. Air pressure acts on circular surface 106 of positioner rod 80 in chamber 226 to force positioner rod 80 to the limit of its outward travel, which is restricted by the interposition of first, second and third pistons 1 50, 1 70 and 200, respectively, between end cap 14 and leading face 85 of positioner rod 80.

Fig. 2 depicts digital positioner 10 with positioner rod 80 in a second position, driving port A and air spring port E being under fluid pressure in this position, as shown in Fig. 8. Fluid pressure acts upon front face 149 and driving face 1 53 of first piston 1 50. End face 1 64 of first piston 1 50 contacts front face 1 71 of second piston 170, and end face 186 of second piston 170 contacts front face 201 of third piston 200.

End face 21 6 of third piston 200 presses against leading face 85 of positioner rod 80. As the surface area of front face 149 and driving face 1 53 is greater than that of circular surface 106 on positioner rod 80, driving port A and air spring port E being at substantially the same pressure, positioner rod 80 will move to the right to the axial extent of first bore 48. As chamber 228 is open to the exterior of housing 12 through vent 70, there is virtually no resistance to the movement of positioner rod 80. Fourth piston 260 does not move, as no fluid pressure or other force is applied to it.

Fig. 3 depicts digital positioner 10 with positioner rod 80 in a third position, driving ports A and B and air spring port E being under pressure as shown in Fig. 8. Fluid pressure acts upon front face 149 and driving face 1 53 of first piston 1 50, and upon front face 1 71 and driving face 173 of second piston 170, fluid pressure reaching chamber 1 68 directly through driving port A, and chamber 1 90 through diametrical groove 166 in end face 1 64 of first piston 1 50. While groove 1 66 is shown vertically in communication with driving port A, it should be understood that this orientation is necessary, for annular channel 40 will communicate fluid pressure from driving port A to groove 1 66 at any orientation.End face 1 86 of second piston 170 contacts front face 201 of third piston 200, the end face 21 6 of which contacts leading face 85 of positioner rod 80.

Second piston 170 will move to the right to the axial extent of second bore 50, moving positioner rod 80 further to the right then in Fig. 2 as the force exerted on second piston 1 70 is greater than that exerted on circular surface 106 of positioner rod 80 due to the difference in surface areas. The maintenance of pressure on piston 150 eliminates the tendency to false shift, or race, when pressure is applied to driving port B, as chamber 1 90 may only expand in one direction.

Again, chamber 228 is open to the exterior of housing 12 through vent 70, thereby avoiding any resistance to movement of positioner rod 80. As in Fig. 2, fourth piston 260 does not move.

Fig. 4 depicts digital positioner 10 with positioner rod 80 in a fourth position. Driving ports A, B and C, as well as air spring port E, are under fluid pressure as shown in Fig. 8. End face 21 6 of third piston 200 contacts leading face 85 of positioner rod 80, fluid pressure being exerted on front face 201 and driving face 203 of third piston 200 through driving port C into chamber 220 via annular channel 42, and diametrical groove 1 88 in end face 1 86 of second piston 1 70. As the surface area of front face 201 and driving face 203 of third piston 200 is greater than that of circular surface 106, all ports being at substantially the same pressure, third piston 200 moves to the right-hand axial extent of third bore 52, moving positioner rod 80 to its fourth position, as shown.Maintenance of fluid pressure through driving ports A and B when pressuring chamber 220 through driving port C permits chamber expansion in only one direction, eliminating the tendency to race. Fourth piston 260, while pressured through annular channel 42, longitudinal passage 62 and oblique passage 66, does not move as it is at its left-hand axial extent in fifth bore 58. Fig. 5 depicts digital positioner 10 with positioner rod 80 in a fifth position Driving ports A, B, C and D, as well as air spring port E are under fluid pressure, the pressure supplied to all ports being substantially the same. First piston 150, second piston 170, and third piston 200 are disposed at the right-hand axial extent of first bore 48, second bore 50 and third bore 52, respectively.Pressurized fluid is supplied to chamber 1 68, 1 90 and 220 as previously noted, and to chamber 224 through port D via annular channel 44 and diametrical groove 218 in end face 216 of third piston 200. As the surface area of leading face 85 and driving face 87 on positioner rod 80 is greater than that of circular surface 106 of positioner rod 80, positioner rod 80 will move to the right in fourth bore 54, its travel being arrested by contact with front face 270 of fourth piston 260, which is maintained in position due to the fluid pressure exerted on its front face 265 and driving face 263 through longitudinal passage 62 from driving port C.

Pressure on the combined surface areas of front face 265 and driving face 263 and circular surface 106 acts against positioner rod movement past the point shown in Fig. 5. As noted previously, maintenance of pressure on driving ports A, B and C while pressing driving port D provides positive shifting. As in the other positions, chamber 228, open to the exterior of housing 12, provides no resistance to movement.

Fig. 6 depicts digital positioner 10 with positioner rod 80 in a sixth position. Driving ports A, B and D, as well as air spring port E, are under fluid pressure as shown in Fig. 6. As the surface area on leading face 85 and driving face 87 on positioner rod 80 is greater than that of circular surface 106, positioner rod 80 will move to the right in fourth bore 54. Unlike Fig. 5, however, driving port C is not under pressure, and, as a result, fourth piston 260 is not maintained in its left-hand position in fifth bore 58. Positioner rod 80 may therefore move to the right an additional distance until fourth piston 260 contacts air spring cap 72. Third piston 200, also being unpressured, has moved to the left in third bore 52, contacting end face 1 88 of second piston 170.

As noted above, the maintenance of pressure on driving port A when moving from the position of Fig. 2 to that of Fig. 3 prevents racing, or false shifts, as in prior art devices, since there is no expansion of chamber 1 90 to the left, but only to the right, the direction of intended movement for positioner rod 80. The same principle applies to moving from the position of Fig. 3 to that of Fig. 4, and from Fig. 4 to Fig. 5. When shifting to the position shown in Fig. 6 from that of Fig. 5, pressure is reduced on both third piston 200 and fourth piston 260 at the same time, so that there is no inherent tendency for the positioner to move left or right, movement being effected solely by fluid pressure on faces 85 and 87 of positioner rod 80.

If it is desired to shift back to the fifth position shown in Fig. 5 from that of Fig. 6, pressure need only be applied through driving port C, which will move fourth piston 260 to the left. It should be noted that fluid moves into and out of all portions of chamber 228 due to the presence of diametrical groove 98 in the end face 96 of positioner rod 80, even when end face 96 abuts front face 270 of fourth piston 260.

In like manner, movement from the position of Fig. 5 to that of Fig. 4 is accomplished merely by depressing driving port D, shifting to the position of Fig. 3 by depressuring driving port C, to the position of Fig. 2 by depressuring driving port B, and to the initial position of Fig. 1 by depressuring driving port A. In all positions, air spring port E remains under pressure. All movement of the positioner rod in either direction is effected through the difference in surface areas acted upon by fluid pressure, the pressure supplied to all ports being substantially uniform. During movement of the positioner rod, chamber 228 expands and contracts freely, being open to the exterior of housing 1 2.

Selection of area ratios of pistons results in relatively wide range of fluid operating pressures.

For example, the preferred embodiment shown may be operated with pressures of 50 to 500 PSIG, with a preferred operating pressure of approximately 100 PSIG.

It is apparent that the present invention possesses numerous advantages over the prior art, among them ease of construction and assembly, compactness, simplicity of operation and positive and precise positioning with no mechanical elements such as springs or ratchets.

It should be apparent to one of ordinary skill in the art that various additions, deletions, substitutions and modifications may be made to the preferred embodiment disclosed, without departing from the spirit and scope of the invention as claimed hereafter.

Claims

1. A digital positioner, comprising: housing means having first, second, third, fourth and fifth longitudinally spaced bore means therethrough, and having longitudinal passagemeans communicating between said third and fifth bore means; positioner means in said housing means, said positioner means having a longitudinally extending rod means with chamber means at one extremity thereof, said rod means extending through said housing means in slidable sealing engagement therewith and an exterior portion of said positioner means being in slidable sealing engagement with the wall of said fourth bore;; first, second and third driving piston means disposed within said first, second and third bore means and about said rod portion of said positioner means, said first, second and third driving piston means being in slidable sealing engagement with the wall of the bore within which they are disposed, and in slidable sealing engagement with said rod portion of said positioner means; air spring piston means having passage means therethrough extending from the exterior of said housing to said chamber, within which one extremity of said air spring piston means is disposed in slidable sealing engagement with the wall thereof; fourth driving piston means disposed in said fifth bore means about said air spring piston means and in slidable sealing engagement with both said air spring piston and the wall of said fifth bore means; and port means communicating with said first, second, third and fourth bore means from the exterior of said housing means.

2. The digital positioner of claim 1 wherein all of said bore means are coaxial.

3. The digital positioner of claim 1 wherein said piston means and said positioner means are coaxial.

4. The digital positioner of claim 1 wherein said bore means, piston means and positioner means are coaxial.

5. The digital positioner of claim 1 wherein said first, second, third and fourth driving piston means each comprise a portion of one diameter, and a longitudinally adjacent portion of substantially smaller diameter, a radially flat front face adjacent said smaller diameter portion, and radially flat end face adjacent said larger diameter portion, and a radially flat driving face extending from said smaller to said larger diameter portion.

6. The digital positioner of claim 5 wherein said first, second and third driving pistons each possess a diametrically oriented groove in their respective end faces.

7. The digital positioner of claim 6, wherein said second, third and fourth ports communicate with an annular channel adjacent first, second and third bore means, respectively.

8. The digital positioner of claim 1 wherein the cross-sectional area of said first bore means is greater than that of said second bore means, which is greater than that of said third bore means, which is greater than that of said fourth bore means and the cross-sectional area of said fifth bore means is of substantially equal area to that of said third bore means.

9. The digital positioner of claim 1 wherein the cross-sectional area of said chamber is less than that of any of said bore means.

1 0. The digital positioner of claim 1 wherein said fourth bore means is substantially open to the exterior of said housing.

11. The digital positioner of claim 1 wherein said rod portion of said positioner means possesses coupling means at one end thereof.

12. A digital positioner, comprising: housing means; positioner means longitudinally movably disposed within said housing means; first, second, third and fourth fluid pressure responsive driving means for said positioner rod means; and first and second fluid pressure responsive return means to oppose said first, second, third and fourth driving means.

1 3. The digital positioner of claim 12 wherein said fluid pressure is supplied to said driving means and said return means through ports in said housing means.

14. The digital positioner of claim 12 wherein the force exerted by each of said driving means and said return means is a function of crosssectional area acted upon by said fluid pressure.

1 5. The digital positioner of claim 12 wherein said ports comprise five ports.

1 6. The digital positioner of claim 1 5 wherein: said first driving means is responsive to fluid pressure through said first port; said second driving means is responsive to fluid pressure through said second port; said third driving means and said first return means being responsive to fluid pressure through said third port; said fourth driving means being responsive to fluid pressure through said fourth port; and said second return means being responsive to fluid pressure through said fifth port.

1 7. The digital positioner of claim 12 wherein said first driving means exerts more force on said positioner means than said second driving means, which exerts more force than said third driving means, which exerts more force than said fourth driving means, which exerts more force than said first return means, which exerts more force than said second return means.

1 8. A method of operating a fluid pressure operated digital positioner having five fluid pressure supply ports, comprising: applying pressure to a first port to maintain said positioner in a first operating position; applying pressure to a second port while maintaining pressure on said first port, to move said positioner to a second operating position; applying pressure to second and third ports while maintaining pressure on said first port, to move said positioner to a third operating position; applying pressure to second, third and fourth ports while maintaining pressure on said first port, to move said positioner to a fourth operating position; applying pressure to second, third, fourth and fifth ports while maintaining pressure on said first port, to move said positioner to a fifth operating position; and applying pressure to second, third and fifth ports while maintaining pressure on said first port, to move said posftionerto a sixth operating position.

1 9. A digital positioner substantially as herein described with reference to Figures 1 to 7 of the accompanying drawings.