US2954755A

US2954755A - Hydraulic positioning device

Info

Publication number: US2954755A
Application number: US691937A
Authority: US
Inventors: Paul L Pecchenino
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1957-10-23
Filing date: 1957-10-23
Publication date: 1960-10-04
Anticipated expiration: 1977-10-04

Description

Oct. 4, 1960 P. L. PECCHENINO HYDRAULIC POSITIONING DEVICE Filed Oct. 23, 195'? Ill ilii INVENTOR. PAUL L. PECCHE/W/VO AGENT 2,954,755 Patented Oct. 4, 1960 HYDRAULIC POSITIDNIN G DEVICE Paul L. Pecchenino, Santa Clara County, Calif., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Oct. 23, 1957, Ser. o. 691,937

9 Claims. Cl. 12138) This invention relates to a hydraulic positioning device. Mo-re particularly, it relates to such a device of the exhaust port sensing type wherein the opening of an exhaust port in a cylinder intermediate of two equalized pressure supply ports causes a piston to move to the opened port position, i.e., to seek or sense the opened port. Accordingly, this invention provides a port sensing piston wherein the exhaust port need not be intermediate of two pressure supply ports.

In the prior art, these so-called port sensing pistons, wherein a piston has equal forces applied to its two end faces until a low pressure discharge port is opened on one side of the piston causing it to move in that direction, normally employ fluid supply ports in each end of a cylinder which houses the piston. For the reasons explained below, these supply ports are necessarily confined solely to the function of supplying fluid under pressure to the cylinder. However, this invention provides a valve, piston, and cylinder arrangement whereby the end ports, normally restricted only to supplying substantially equal pressures to opposite end faces of a port sensing piston, may also be selectively opened to exhaust as well as to pressure. This enables the piston to see an end (supply) port position not previously possible. By employing the simplified and novel structure of this invention less ports (and their associated struc- 'ture) are required in this invention than was previously considered feasible to eifect an equivalent number of discrete positions in such devices.

It is an object of this invention, therefore, to provide an improved port sensing piston device wherein conventional pressure supply ports are not required.

It is another object of this invention to provide a simplified port sensing piston device wherein the extreme port positions function selectively as either pressure transmitting ports or as discrete port positions to be sensed.

In the prior art as described above, the problem with using the extreme port positions for anything more than pressure supply ports was that if they were opened to sump, the piston would travel up to and beyond the opened port. With the piston beyond the end port, fluid pressure could not be directed in behind the piston, i.e., between the piston and the end of the cylinder in order to, reverse its direction. With the piston positioned over one of the two extreme ports, the only practical way to supply this pressure was considered to be fluid supply ports. employed in the cylinder ends. In short, it was thought that the piston must always be between two supply ports. Since the piston of this invention need not always be so located, it is another object of this invention to provide a port sensing piston wherein the piston is not always required to be between two pressure supply ports.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings which disclose, by way of example, the principle of the invention and the best mode which has been contemplated of applying that principle.

In the drawings: 1

Fig. 1 is a sectional schematic view of the invention.

Fig. 2 is an enlarged isometric view of the piston in Fig. 1.

Fig. 3 is an enlarged isometric view of another embodiment of the piston of this invention.

According to this invention, the piston is fitted loosely within its cylinder and provided with a sealing ring of negative overlap. Negative overlap may be defined as the gap created by a piston which is narrower than a port thereunder. The ports in the extreme positions in the cylinder are arranged to receive fluid under pressure or to exhaust fluid to sump as desired.

Briefly stated, with the piston located over an intermediate port position and with one of the extreme ports open to sump and the other open to supply, the piston will move toward the end port open to sump, say for example to the right. According to the invention, after the piston has arrived over the end port, the area of the flow path around the piston produced by its loose fit within the cylinder, i.e., the annular area defined by the outer circumference of the piston and the inner circumference of the cylinder, must be greater than the area of the flow path caused by negative overlap to the right of the piston, in order to eifect a centering of the piston over an end port in its exhausting condition. This is explained by the fact that the differential in area will preserve a small opening between the sealing ring and the lip of the extreme right-hand port (in the example). Further, the sealing ring of the piston employed is sufficiently narrow with respect to the port that negative overlap is provided to its left side (as well as to its right) in order to keep the piston centered over the port, as explained more fully below. The differential in flow path areas also becomes important, as explained below, in initiating movement of the piston toward the other end of the cylinder when the end port under the piston is conditioned to supply fluid under pressure.

If the piston approaches either of the end ports at too high a speed, it can overshoot the port to an extent which entirely eliminates negative overlap between the side of the piston in the direction of its travel and the nearest end of the cylinder. Should this occur, the balancing forces required to center the piston would no longer be present and the piston would become locked at one end of the cylinder. Although this is no problem at lower piston speeds, it is prevented at higher speeds by providing damping skirts on each side of the piston, as explained below. These skirts provide damping for all intermediate ports as well. Of course, such overshooting could be prevented by installing fixed stops at each end of the cylinder. However, this is not preferred since such stops would not provide desirable damping for the intermediate ports.

With the piston in an extreme position, reversing the condition of the port thereunder to connect it to supply (while opening one of the ports to the left to sump) will cause the piston to travel leftward. This is due to the negative overlap to the right (in the example) and the loose fit which allow some of the fluid to build up behind the piston and start it on its way leftward.

Referring to the drawings and particularly to Figs. 1 and 2, there is shown schematically in longitudinal section a cylinder 111, the ends of which are designated 112 and 113. In a row along the bottom side of cylinder 1 11 is a series of five indexing ports 114-, 115, 116, 117 and 118. Intermediate ports 115 through 117 are connected by

conduits

145, 146, and 147, respectively, and

valves

155, 156 and 157, respectively, to a manifold 148 leading to a sump 132.

A piston rod 121 is coaxial with the longitudinal axis of cylinder 111 and passes through each end thereof. Secured to rod 121 is a piston assembly 122, shown in one piece. This assembly consists of a right cylinder which is divided into three right cylindrical parts; as viewed from the side, the center portion, which functions substantially to close off ports 114 through 118, as explained more fully below, may be called the sealing ring 123, and at each side of ring 123 is a portion which may be called a

damping skirt

124, 125. Ring 123 is separated from each

skirt

124, 125 by

circumferential grooves

126, 127. Thus, the two

circumferential grooves

126, 127 define ring 123 therebetween. Ring 123 is narrower than any one of ports 114 through 118. Each of

grooves

126, 127 is connected with the piston end faces 119 by tapered slots 128. The depth of slots 128 is greatest at the end faces 119 and least at

grooves

126, 127. The clearance 129, or spacing between piston 122 and the wall of cylinder 1 11, has been exaggerated in the drawings so that it will be more apparent.

The end ports 114. and 118 are connected to conduits 134 and 135 respectively. These conduits can be connected to the pressure side of a pump 139 or directly to sump 132 via a pair of three-

way valves

136 and 137, respectively, provided at the intersection of connection 138 with each of conduits 134 and 135. In order to drive piston 122 to an intermediate port position, both ports 1-14 and 118 are connected to pump pressure and an intermediate port 115 through 117 is opened to sump 132.

This creates a pressure differential across piston 122 causing itto move toward the opened port. When piston 122 has arrived over the selected intermediate port, the fluid flow out of the port will become substantially equal from both sides of piston 122 due to negative overlap of ring 123. This has the effect of centering piston 122 over the opened port.

The slots 128 and

grooves

126, 127, required only for high velocity operation, as explained above, serve to damp the piston travel as the piston approaches a port open to exhaust by gradually cutting oif the flow of fluid as the skirt covers the port. The size of the slots and grooves governs the damping effect. The same eifect may be obtained without slots by tapering the skirts 324, 325

(as shown in the piston 322 in 'Fig. 3) so as to reduce flow gradually to an opened port 114 through 118 as its sealing ring 323 approaches. As was the case with ring 123, ring 323 is constructed with negative overlap as regards port 114 through 118. Using the alternative embodiment shown in Fig. 3, the annular area of the flow path, defined as the area between .the outer circumference of piston 322 and the inner circumference of cylinder 111, is gradually decreased as the piston approaches an open port. However, this annular area is always greater than the area of the flow path via negative overlap in order to preserve centering over the end ports as noted above.

In order to drive piston 122 to one of the end ports 114 and 118 (for example, to 118),, valve 137 is turned to connect port 118 to sump 132 while port 114 remains connected to pump pressure via valve 136 and crossconnection 138. This condition is shown in Fig. 1. Ring 123 will center itself (and piston 122) over port 118, just as it did as explained above with respect to intermediate ports 115 through 117, due to the equalized flow past piston 122.

In the operation of the device, if it is desired to move the piston to the right end port 118, for example, the three-way valve 137 is opened to sump.132 and closed to pump 139. All intermediate ports 115, 116, 117 are closed and fluid under pressure is delivered to cylinder 111 through the other end port 114 by turning the left three-way valve 136 so that it passes fluid from pump 139 to port 114. This action also closes off the. discharge path of port 114 to sump 132. This arrangement creates a pressure drop across piston. 122 in the direction of end port 118, thereby moving piston 122 toward port 118.

As the piston approaches port 118 (and skirt portion moves over the port), the flow through port 118 will be reduced to a minimum gradually, as explained above, by forcing fluid through slots 128 and groove 127. 'This prevents the piston from .overshooting the port at high speeds of operation. With piston 122 now centered over port 118, if it is desired to reverse its direction and drive it leftward to one of the left-hand ports, valve 137 is turned to connect port 118 to pump supply and one of the ports 114 through 117 is opened. to sump (the others remaining closed). Since piston 122 is centered over port 118 and since it fits loosely within cylinder 111, some of the fluid supplied to cylinder 111 passes into the end portion of cylinder 111 between the right end face 119 of piston 122 and end 113, thereby driving piston 122 to the left. In this way, end ports 114 and 1'18 are utilized as sensing or indexing ports, Whereas in port sensing pistons of the prior art they had to be used exclusively for supplying pressure.

As stated above, in the prior art if the end ports had been connected to exhaust, the piston would have traveled beyond the port and all pressure would be supplied to a single face 'of the piston, thereby locking the piston at one end of its cylinder. However, the loose fit or clearance 129 of this invention, together with the negative overlap of sealing ring 123 (as well as the action of damping

skirts

124 and 125 at high operational speeds), insures against this condition. by providing a path for the fluid to get in behind piston 122. Thus, by solving this problem, the port sensing piston and cylinder arrangement of this invention possesses two additional ports which can be sensed by the piston, i.e., the end ports, whereas the end ports of the prior art were confined to supplying fluid only.

While there have been shown and described and pointed out the fundamental novel features'of the invention as applied to the preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. A fluid operated device comprising a closed ended cylinder, a piston within said cylinder movable therealong, a series of ports in said cylinder spaced at intervals along its length, the active length of said piston having less peripheral thickness along said cylinder than the coacting opening in the same direction of any one of said ports, and means for applying greater fluid pressure to a first of said ports with the periphery of said piston substantially centered thereover than to another of said ports to move said piston toward said other port assisted by pressure from said first port.

2. A fluid operated device comprising a closed ended cylinder, a piston within said cylinder movable therealong, a series of ports in said cylinder spaced at intervals along its length, the active length of said piston being less than the coact-ing opening of any said port, and means for applying greater fluid pressure to an end one of said ports with the periphery of said piston substantially centered thereover than to an interior port to move said piston toward said interior port assisted by pressure from said end port.

3. A fluid operated device comprising a closed ended cylinder, a piston loosely fitted within said cylinder movable lengthwise with respect thereto, said piston having asealing ring therearound, a series of ports in said cylinder spaced at intervals along its length, the terminal ones of said ports exceeding the thickness in the direction of piston movement of said sealing ring, the area between the piston and cylinder in a plane perpendicular to the cylinder axis being greater than the exposed port opening area of said terminal ports which is exposed to that side of said piston away irom said other ports when said piston is substantially centered over said terminal ports, and means for selectively applying different fluid pressures at said terminal ports, whereby when said piston is arrested at one of said ports its subsequent movement toward another of said ports is assisted by pressure supplied by the port at which said piston is arrested.

4. A fluid operated device comprising a closed ended cylinder, a piston loosely fitted within said cylinder movable therealong, said piston including a sealing ring, a series of ports in said cylinder spaced at intervals along its length, the opening of said ports along the length of said cylinder exceeding the thickness of said sealing ring, the area between the piston and cylinder in a plane perpendicular to the cylinder axis being greater than the area of the exposed port opening when said piston is centered thereover, and means for applying greater fluid pressure to an end port over which said piston is centered than to another of said ports to initiate movement of said piston toward said port of lower pressure.

5. A fluid operated device comprising a cylinder closed at each end, a plurality of ports in the wall of said cylin der spaced along its length, a piston loosely fitted within said cylinder movable lengthwise therein, said piston having less effective peripheral thickness in the direction of its travel than the width of any said ports in the same direction, the area between the piston and cylinder in a plane perpendicular to the cylinder axis being greater than the exposed port opening area of said ports with said piston substantially centrally positioned'thereover, means for exhausting fluid from said cylinder via one of said ports to position said piston over said exhausting port, and means for supplying fluid under pressure to said cylinder via said port at which said piston is positioned to assist in moving said piston therefrom to a port open to lower pressure.

6. A flud operated device comprising a cylinder closed at each end, a plurality of ports in the wall of said cylinder spaced along its length, a piston loosely fitted within said cylinder movable longitudinally therein, said piston including a sealing ring, said sealing ring having less peripheral thickness in the direction of piston travel than the width in the same direction of any of said ports, the area between the piston and cylinder in a plane perpendicular to the cylinder axis being greater than the exposed port opening area of said ports with said piston substantially centrally positioned thereover, means for exhausting fluid from said cylinder via one of said ports to position said piston over said exhausting port, means for preventing said piston from traveling beyond said port, and means for supplying fluid under pressure to said cylinder via said port at which said piston is positioned to assist in moving said piston therefrom to a port open to lower pressure.

7. A fluid operated device comprising a cylinder closed at each end, a plurality of ports in the lateral wall of said cylinder spaced along its length, a piston loosely fitted within said cylinder movable longitudinally therein, said piston including a sealing ring, said sealing ring having less peripheral thickness in the direction of piston travel than the Width of the terminal ones of said ports in the same direction, the area between the piston and cylinder in a plane perpendicular to the cylinder axis being greater than the exposed port opening area of said terminal ports which is exposed to that side of said piston which is away from said other ports when said piston is substantially centered over one of said terminal ports, means for exhausting fluid from said cylinder via one of said terminal ports to position said piston thereover, means for gradually reducing the flow of said exhausting fluid via said terminal ports to prevent said piston from traveling beyond said terminal ports in their exhausting condition, and means for supplying fluid under pressure to said cylinder via said terminal port with said piston positioned thereover to assist in moving said piston to a port open to lower pressure.

8. A fluid operated device comprising a cylinder closed at each end, a piston within said cylinder movable longitudinally with respect thereto, said piston having a sealing ring portion therearound, a series of ports in said cylinder spaced at intervals along its length, means -for substantially centrally positioning said sealing ring portion over one of said ports, means for supplying fluid to said cylinder at a first pressure via said one port, means for exhausting said fluid from said cylinder at a lower pressure via another of said ports to provide a pressure differential between said one port and said other port, and means for applying said pressure difierential across said piston when said sealing ring portion is substantially centrally positioned over said one port to assist in initiating movement of said piston along said cylinder toward said other port.

9. A fluid operated device comprising a cylinder closed at each end, a piston within said cylinder movable longitudinally with respect thereto, said piston having a sealing ring portion therearound, a series of ports in said cylinder spaced at intervals along its length, said series including a port at each end thereof, means for substantially centrally positioning said sealing ring portion over one of said end ports, means for supplying fluid to said cylinder at a first pressure via said one end port, means for exhausting said fluid from said cylinder at a lower pressure via another of said ports to provide a pressure differential between said one end port and said other port, and means for applying said pressure diflerential across said piston when said healing portion is substantially centrally positioned over said one end port to assist in initiating movement of said piston along said cylinder toward said other port.

References Cited in the file of this patent UNITED STATES PATENTS 2,219,965 Smitt Oct. 29, 1940 2,380,705 Procter July 31, 1945 2,596,242 Hill May 13, 1952 2,833,602 Bayer May 6, 1958 2,907,304 Macks Oct. 6, 1959 FOREIGN PATENTS 551,207 Germany Oct. 21, 1930