US3472125A - Hydraulic servo cylinder override - Google Patents

Description

Oct. 14, 1969 P. H. NOBLE HYDRAULIC SERVO CYLINDER OVERRIDE Filed oct. soI 19e? v ATTORNEYS United States Patent O 3,472,125 HYDRAULIC SERVO CYLINDER OVERRIDE Paul H. Noble, Grafton, Vt., assignor to The Fellows Gear Shaper Company, Springfield, Vt., a corporation of Vermont Filed Oct. 30, 1967, Ser. No. 679,044 Int. Cl. F1511 .I3/44, 9/03, 15/17 U.S. Cl. 91-47 8 Claims ABSTRACT OF THE DISCLOSURE A novel electro-hydraulic servo override mechanism is disclosed to mechanically override position signals for driving a piston to enable piston motion to be terminated in a predetermined position within its cylinder without shutting down the electrical command system by diverting the flow of fluid pressure.

BACKGROUND OF THE INVENTION Field of invention The invention pertains to that art in which motive fluid is applied to opposite working member faces with the motive fluid being applied to or evacuated from one of said faces to cause the working member to move in one direction and being applied simultaneously to or evacuated simultaneously from bot-h of said faces to cause the working member to move in the opposite direction, wherein an hydraulic override system causes the motive fluid to be directed away from the working member causing its motion to cease.

Description of the prior art Industrial electro-hydraulic servo valve applications f have long been plagued by difficulties in over-riding electrical commands during emergency conditions. In the past, where an electronically controlled hydraulic piston where it has been desirable to stop a pistons drive in a given position, or for a period of time without shutting down the system, previous electro-hydraulic control servo systems have not lent themselves to mechanical or hydraulic override devices independent of the electro-hydaulic control system to accomplish positioned control of the piston without sacrificing the inherent flexibility and frequent response of the electro-hydraulic control system, the device herein described provides a means of hydraulically overriding electrical position commands originating from erroneous programming or electrical sequencing failure or merely undesirable piston motion without affecting the normal operating characteristics of the system.

SUMMARY OF THE INVENTION The invention is a unique hydraulic override for an electro-hydraulic servo system. It provides for an outlet port and conduit means therefrom, positioned through the wall of the electro-hydraulically controlled piston cylinder wall. Said port may be opened by fluid pressure from within the cylinder when mechanical means in the conduit are open to allow the hydraulic uid which is driving the piston to pass through said port and conduit thus halting the pressured movement of the piston without affecting the normal operating characteristics of the servo System.

Further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since ICC various changes or modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWING The invention will be understood more readily by references to the following examples. However, these examples are intended to illustrate the invention and are not to be construed to limit the scope of the invention.

FIGURE l is a diagrammatic view, partly in section, of an electro-hydraulic servo mechanism with an override system according to the invention, schematically illustrated; and

FIGURE 2 is a fragmentary diagrammatic view, partly in section, of a variation of the system shown in FIG- URE l.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGURE l, 10 designates a piston assembly, generally comprising a piston 12 and a cylinder barrel 14. A rod 16 connects the piston to any driving, stamping or like members (not shown) which are to be reoiprocated. Such a member might be a platen in an injection molding machine, a milling machine table or any other mechanical element.

The piston reciprocates through the length of the cylinder as the pressure ratio between the head end 18 and the rod end 44 of the cylinder is varied by a conventional servo control system. An illustration of such a control system is shown in FIGURE 1 to be comprised of a pump 20, hydraulic lines 22, 24, 26, 28 and 30, and a reservoir 31 which may connect with a recirculating system, or the like. A restrictor 32 to restrict the flow, and a solenoid operated variable restrictor valve means 34, such as is disclosed in my co-pending application entitled Electro- Hydraulic Servo Control (Ser. No. 679,144, filed Oct. 30, 1967), to alternate direction of the flow completes the electro-hydraulic drive system.

By way of review of prior art, it will be well understood that the variable restrictor means 34 varies the pressure ratio between the end of piston 12 by alternately opening and closing a valve in line 30. When valve means 34 is closed to prevent fluid passage through line 30, fluid ows through pipe 24 and 28 into an 'annular groove 36 in cylinder 14, to build pressure between piston 38 and the front cylinder wall 18. An annular opening is helpful to even distribution of uid pressure across the entire surface of the piston head or rod end. Because the area on the piston head 38 is greater than that on the rod end 40 of the piston due to the space taken by the rod, the piston is d-riven toward the rod end of the cylinder. The uid behind the cylinder flows out through the rear annular groove 42 and pipe 26 and mixes with fluid in pipes 22 and 24.

Once the piston has been driven to the back wall of the cylinder 44, the valve means 34 opens, and because the restriction means 32 in pipe 24 hinders passage of fluid into pipes 28 or 30 and uid may flow freely from pipe 30 into reservoir 31 or the like. Fluid pressure in pipe 26 is therefore greater than that in pipe 28, and the piston is driven toward the front wall 18 of the cyilnder. The fluid between the head of the piston 38 and the front wall of the cylinder 18 escapes from the cylinder through pipe 28, mixing with the restricted fluid flow from pipe 24, and

The override system will now be described in detail. In an electro-hydraulic servo system such as is illustrated, it is desirable to be able to override the electrical signals commanding the drive of the piston without relying upon or interfering with the system itself. To accomplish this, means are provided to divert the ow of hydraulic tluid thereby neutralizing the pressure on the piston faces and causing the piston to come to rest in a predetermined position.

In FIGURE 1 these means are seen to be comprised of a port means 50 located in a predetermined position in the wall of the cylinder, said port means as illustrated is annular. Means 52 connects the port means to a check valve assembly 54; an outlet port conduit 56 connects with a mechanical valve 58; two pipes 60 and 64 are shown leading from valve 58. In the illustration the pipe 60 leads to a reservoir 62, but could lead to a recirculating system, or the like. It will be well understood that alternate circuitry and mechanisms could be fashioned to accomplish the purposes of the invention. Pipe 64 connects valve 58 with pump 20 so that liuid pressure from pump is exerted through pipe 64 equal to the pressure being exerted through pipe 22.

When the mechanical valve 58 is in its normal closed position, the pump 20 causes uid pressure to be directed through pipe 64, valve 58, pipe 56 and exerts said pressure on the downstream side of closed check value 54 with a force equal to or greater than the pressure of the ud being exerted from the inside of the cylinder 38 through the annulus 50 and connecting means 52. Thus, during normal operations, the check valve '54 is shut tight and there is no loss of liuid pressure from within the cylinder to interfere with the uid drive of the piston.

To override the programmed electrical signals commanding reciprocating of the piston, the mechanical valve 58 is opened. This may be done manually or by remote control. The opening of this valve closes oi the pressure ow of the liquid from pipe `64 through valve 58 into pipe S6 described above. At the same time, the opening of the valve 58 opens a conduit to enable uid to iiow from pipe 56 into reservoir 62 or the like. This ow of iluid from pipe 56 reduces the pressure upon the downstream side of closed check valve 54, and the uid pressure from within the cylinder forces the check valve open. With the valve in an open position, fluid from the cylinder ows out of the outlet port 50 thus causing a loss of pressure within the cylinder on one side of the piston and a large pressure differential is created between the rod end and the head end of the piston, depending on the position of the piston relative to the port 50 when the valve 58 is opened. This outow of uid through the outlet port 50 may be referred to as dumping So that the whole process might be better understood, the steps will now be explained beginning with the piston at the rod end 44 of the cylinder barrel when valve 34 fails to open. In this position the rod 16 is fully extended. If the rod were connected to a stamping machine, it would be locked shut. To alleviate this condition, the mechanical valve 58 is opened.

The piston will begin to move toward wall 18 of the cylinder by fluid pressure from pump 20 being exerted through pipes 22 and 26, with pressure to pipe 28 being effectively diminished by the dumping of fluid out of port 50.

This is accomplished by opening valve 58. Pressure from pump 20 through pipe 64 is cut oi, as previously explained, and the fluid ows from pipe 56 through valve 58 and as pressure downstream to the check valve is released, the valve will-open. As the piston moves forward, the fluid in front of the cylinder head 38 passes out of the port 50, pipe 56 and into reservoir 62 or a recirculating system, or the like.

This piston will continue to be driven toward cylinder wall 18 until the piston head 38 comes into contact with annular opening 50. As the piston begins to cover the annular opening the amount of fluid being dumped is proportionately curtailed. As it is curtailed, pressure begins to build in the cylinder between piston head 38 and cylinder wall 18 until the pressure between the head 38 and the wall 18 equals the pressure between the rod end 40 of piston 12 and the cylinder wall 44. Thus the piston automatically comes to rest with the piston head positioned somewhere between the limits of annular groove 50. A mere port opening could be utilized, but an annular groove has been found preferable because it allows drainage to be more equal around the entire piston.

lf the cylinder was located someplace between th groove 50 and the cylinder wall 18 and the valve 32 was closed when the mechanical valve 58 was opened, the fluid pressure passing through pipe 28 would drive the piston back toward wall 44 until the piston head 38 had moved sufficiently into contact with grove S0 that fluid could be dumped. The piston motion would then cease as the uid pressure between piston head 38 and wall 18 automatically becomes equalized with the uid pressure between rod end 40 and cylinder wall 44.

If the valve means 34 were locked open and the valve 58 were not opened the piston would be forcefully driven to wall 18 and would sit there because the fluid pressure coming through pipe 26 would be greater than the Huid pressure passing through pipe 28. Thus, if it is desirable only to have the piston stopped when the valve is open, with the rod completely retracted there is no need for an override system as disclosed. However, one cannot be certain that a default in the electrical system will result in an open valve 34, also there may be a desire to position the piston somewhere else within the cylinder even when the valve 34 is open. This can be done by using the override system and some mechanical positioning means upon rod 16. For example, with the override system positioned as shown in FIGURE 2 and valves 58 and 34 open, fluid pressure from pipe 26 would pass out of port 50(11) thereby eliminating pressure upon rod end 40 once the rod end had passed the port. Since there would be no pressure from pipe 28(a) while the valve 34 is open, the piston 12 could continue to coast to wall 18, unguided by pressure on either end. However, mechanical means can be utilized to grip the rod 16 and easily position the piston forward toward wall 44 anywhere between port 50(a) and cylinder wall 18. An additional feature of the override system with regard to an open valve 34 is that by dumping the driving tluid, the force with which the piston is slammed into wall 18 is greatly reduced. This reduces the chances of cracking a piston or otherwise damaging the system.

These conditions would also exist if it became desirable to stop the motion of the piston while the valve 34 was continuing to open and close according to the programmed sequence. This is true because once the rod end 40 of the piston passes the port 50 fluid pressure would be lost through port 50 so that the piston could not be driven to wall 18, but by the same token the loss of pressure through port 50 would prevent a build-up of pressure between piston head 38 and wall 18 even if valve 34 were momentarily closed, so that the piston could not be driven back to wall 44 but would rather coast between port 50 and wall 18.

The invention as illustrated utilizes both a mechanical valve 58 and a check valve 54. The purpose of the check valve is to allow the mechanical valve 58 to be positioned at a distance from the piston assembly 10 and port 50. Either the mechanical valve or the check valve should be positioned close to the port 50 so that when the mechanical valve is closed and no dumping is taking place, the pipe line connected to the outlet port conduit 50 is isolated near the outlet port. This reduces the total volume of oil under compression from the servo valve to a minimum. By keeping the total volume under compression at a minimum the natural resonant frequency of the servo system is kept as high as possible.

What is claimed is: 1. An electro-hydraulic servo system having a hydraulic override system, comprising:

solenoid valve means for normally controlling the position of a piston within a cylinder by dictating flow of hydraulic uid to opposed sides of said piston in accordance with a programmed sequence,

hydraulic override means for interrupting the programmed sequence of movements for said piston by dumping hydraulic fluid from one side of the piston through a port means which is positioned through a wall of said cylinder at an intermediate point which stops travel of said piston in a lirst direction of movement and which limits travel of said piston in a second direction of movement after it has been stopped from moving in said rst direction, said hydraulic override means including a valve means which can be actuated to release a ow of hydraulic uid through said port means when it is desired to override a programmed sequence of movements for said piston, whereby said piston can be stopped from its programmed sequence of travel at a point which is intermediate its programmed limits of travel, and said port means comprising an annular groove formed within said cylinder wall with an outlet conduit in communication with the annular groove, and including a check valve in said outlet conduit intermediate the cylinder and said valve means, said check valve functioning to permit a one-way flow of hydraulic fluid out of said cylinder when said valve means is actuated to open the outlet conduit, and means included for maintaining said check valve closed during normal operations of the system in accordance with the program dictated by said solenoid valve means.

2. The system of claim 1 wherein said valve means is manually operated.

3. The system of claim 1 wherein said means for maintaining said check valve closed comprises means for applying to the downstream side of the check valve a total pressure which is equal to or greater than iluid pressure in said cylinder on the port means side of said piston.

4. The system of claim 1 wherein said check valve is positioned in close proximity to the communication of said outlet conduit with said cylinder so as to effectively isolate said outlet conduit from the cylinder whereby iluid is maintained at a minimum and the natural resonant frequency of the system is kept as high as possible.

5. A hydraulic system for controlling the position of a reciprocating piston within a cylinder comprising:

a first hydraulic circuit for dictating reciprocating movements of said piston within said cylinder, said rst hydraulic circuit having means for directing a flow of hydraulic iiuid to opposite sides of said piston in accordance with a programmed sequence of operation,

a second hydraulic circuit for overriding the programmed operation of said rst hydraulic circuit by dumping hydraulic fluid from said cylinder, said second hydraulic circuit comprising:

an outlet conduit communicating with the interior of said cylinder at a point intermediate the limits of travel for said piston, said outlet conduit functioning to interrupt travel of the piston by carrying hydraulic iluid out of said cylinder,

a valve means in said outlet conduit for opening and closing the outlet conduit to a reservoir, said valve means in said outlet conduit having two positions, a iirst position for opening said outlet conduit to a reservoir, and a second position for opening said outlet conduit to line pressure from said rst hydraulic circuit, whereby said second circuit can be used to override the operation of said iirst circuit by moving said valve means to its iirst position for dumping hydraulic Huid into said reservoir, and

a check valve means intermediate said valve means and the communication point of said outlet conduit with said cylinder for preventing a ow of hydraulic Huid hack into said cylinder through said outlet conduit.

6. The system of claim S wherein said check valve means is positioned in close proximity to the communication of said outlet conduit with said cylinder so as to effectively isolate said outlet conduit from the cylinder.

7. The system of claim 5 and including means for maintaining said check valve in a normally closed position by a total line pressure in said outlet conduit which equals or surpasses uid pressure in the cylinder in the region of said outlet conduit communication with the cylinder.

8. The system of claim 5 wherein said first hydraulic circuit includes solenoid valve means for dictating a program of reciprocating movements to said piston.

References Cited UNITED STATES PATENTS 1,841,629 l/l932 Pigeolet 91-357 2,675,785 4/1954 Ford 91-357 2,954,755 10/1960 Pecchenino 91-3'57 2,117,595 5/1938 Baule 91--402 2,773,484 l2/l956 Peek 91-402 3,002,497 lO/ 1961 Gulick et al. 91--402 PAUL E. MASLOUSKY, Primary Examiner

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