US3695145A

US3695145A - Piston position monitor

Info

Publication number: US3695145A
Application number: US84298A
Authority: US
Inventors: John M Horn
Original assignee: Allis Chalmers Corp
Current assignee: Voith Hydro Inc
Priority date: 1970-10-27
Filing date: 1970-10-27
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03

Abstract

A device is disclosed which maintains the preset position of a reciprocating fluid servomotor. The device includes a spool valve with the spool connected to the servomotor piston rod. Any drifting of the servomotor piston causes the spool to open a port directing pressure fluid to the servomotor to return the piston to its preselected position.

Description

United States Patent Horn 1 [451 Oct. 3, 1972 [54] PISTON POSITION MONITOR [72] Inventor: John M. Horn, York, Pa.

[73] Assignee: Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

[22] Filed: Oct. 27, 1970 [21] Appl. No.2 84,298

[52] US. Cl ..91/390, 91/466 [51] Int. Cl ..FlSb 13/16 [58] Field of Search ..91/390, 368, 387, 466

[56] References Cited UNITED STATES PATENTS 2,966,891 l/l96l Williams ..91/387 2,877,743 3/1959 Liaaen ..91/390 3,331,289 7/1967 Horst ..91/390 3,568,570 3/1969 Winders ..9 1 I390 Primary ExaminerPaul E. Maslousky Attorney-John P. Hines, Robert B. Charles L. Schwab Benson and 7] ABSTRACT A device is disclosed which maintains the preset p0sition of a reciprocating fluid servomotor. The device includes a spool valve with the spool connected to the servomotor piston rod. Any drifting of the servomotor piston causes the spool-to open a port directing pressure fluid to the servomotor to return the piston to its preselected position.

2 Claims, 1 Drawing Figure PISTON POSITION MONITOR This invention pertains in general to pressure fluid operated servomotors and more particularly to a device for maintaining the preselected position of the servomotor piston.

In all hydraulic or pneumatic servomotors where precise position is required, a complete feedback system is used. The feedback system sends a signal from the servomotors to the main control valve which signal is translated into movement of the servomotor piston back to its preselected position. Where the distance between the servomotor and the control is great, the feedback system becomes somewhat complicated. In many instances, it would be sufficient or satisfactory to position the device if it would remain in the selected position without drifting. However, due to loads that are overcome by the servomotor and inherent leakage in commercial quality systems, there is tendency to drift.

It is therefore the invention and general object of this invention to provide a monitoring device which will maintain a preselected position of the servomotor piston without requiring a feedback system to the main control valve.

An additional object of the subject invention is to provide a monitoring device of the hereinbefore described type which is located closely adjacent to the piston which is to be monitored.

A more specific object of the subject invention is to provide a monitoring device of the hereinbefore described type wherein the piston rod of the servomotor to be monitored is connected directly to and activates the monitoring device.

An additional object of the subject invention is to provide a piston monitoring device of the hereinbefore described type wherein the piston rod of the servomotor overrides the monitor when it is desired to reposition the servomotor piston, and the monitor is auto- I matically reset at the newly selected position of the plston.

These and other objects of the subject invention will become more fully apparent as the following description is read in light of the attached drawing which shows a cross sectional view of a piston position monitor constructed in accordance with the invention.

Referring to the drawing, the invention is shown for purposes of illustration in connection with a hydraulic servomotor generally designated 6. This servomotor is of the double-acting type having a cylinder 7 and a piston 8 reciprocally contained within the cylinder. Although the invention is described in connection with a linear reciprocating piston it has equal application to a rotary reciprocating piston. A piston rod 9 attached to the piston extends without the cylinder 7. In the conventional manner in connection with a double-acting hydraulic servomotor, inlet and discharge ports are 11 and 12 are provided on opposite sides of the piston 8. These ports are connected to a conventional control valve (not shown) which is activated to selectively position the piston rod 9. The opposite end of the piston rod is connected to the work which is desired to be moved.

The monitoring device of this invention is positioned closely adjacent to the servomotor 6 so that it can be acted upon by the piston rod 9. To this end the monitoring device generally designated 13 may be attached directly to the servomotor cylinder 7. The monitoring device is composed of a valve housing member 14 and a reciprocating valve control member or spool 16 contained in a bore provided within the valve housing. The spool 16 has a bore therethrough through which the piston rod 9 extends. Means are provided to connect the spool 16 to the rod 9 so that the spool will move with the piston rod but will permit the rod to move relative to the spool when the spool is held from further movement. Such connecting means are herein shown for purposes of illustration as a fabric washer or packing 17 provided in a groove in the spool 16. A conventional packing gland nut 18 is threaded onto the end of the spool 16 and can be adjusted to increase or decrease the frictional engagement between the spool and the piston rod.

Stop means are provided to limit the extent of movement of the spool 16. To this end and as shown herein for purposes of illustration, a flange 19 is provided on the spool 16. A hole is provided through the flange 19 through which extends a threaded stud 21. This stud is contained within a threaded bore provided in the valve housing 14. Lock nuts 22 are provided on the stud so as to selectively adjust the extent of movement of the spool.

The valve housing 14 is provided with a pair of pressure outlet ports 23 and 24 which are connected in fluid communication to the servomotor cylinder 7 through passageways 26 and 27 on opposite sides of the piston 8. It should be noted that the passageways 26 and 27 connecting the valve outlets to the servomotor cylinder are much smaller than the main control valve port 11 and 12. This is to insure that the main control valve can easily overcome any force exerted by the monitoring valve 13.

The valve housing 14 is also provided with a pair of drain ports 28 and 29 which are connected by conduit to a system sump (not shown). A pressure fluid inlet port 31 is also provided in the valve housing 14 which is connected by means of a conduit to a source of pressurized fluid which may be the main system source of pressurized fluid or an auxiliary source.

The spool 16 is provided with an annular pressure chamber 32 and a pair of spaced

annular drain chambers

33 and 34 which are isolated from the pressure chamber by means of the annular lands 36 and 37.

OPERATION Assuming that the piston 8 has been moved to the desired position as shown in the drawing by the main control valve, the operation of the monitoring valve is as follows:

If the load on the piston 8 is to the left as shown in the drawing, any leakage in the system will cause the piston to drift to the left. Because of the frictional connection between the spool 16 and the piston rod 9, the spool will drift to the left with the piston. This will cause the pressure chamber 32 to uncover the discharge port 23 directing pressure fluid to the lefthand side of the cylinder 7 through the passageway 26. Pressurized fluid will continue to enter the cylinder until the piston 8 moves back to its original position. Since the spool 16 moves with the piston rod, the discharge port 23 will be covered by the land 36 when the piston has been returned to its original piston.

If it is desired to reposition the piston rod 9 to the left, the main control valve will be activated delivering pressurized fluid to the right-hand side of the piston 8. This will cause the piston rod and the spool 16 to move to the left until the flange 19 contacts the lock nuts 22. At this point the force on the piston will overcome the holding force of the frictional engaging means permitting the piston to be moved further to the left to its new desired location. Since the spool is now engaging the lock nuts 22, fluid from the monitoring device will enter the left side of the cylinder 7 only very slightly causing the piston to move to the right until the spool recenters itself in the position shown in the drawing. From that point, the monitoring device will operate in the manner above described maintaining the piston in the newly located position.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A position monitoring device for a pressure fluid operated servomotor having a cylinder, a piston slidable therein and a piston rod connected to the piston and extending to the exterior of the cylinder, said device comprising: a housing connected to said cylinder defining a chamber through which said piston rod extends; a pressurized fluid inlet port in said housing connected in communication to a source ofpressurized fluid, a pressure fluid delivery port in said housing connected in fluid communication to a said cylinder; a control spool located within said housing in a manner to permit movement thereof relative to said housing; stop means associated with said housing and said control spool limiting movement therebetween to a predetermined amount; attaching means connecting said control spool to said piston rod for limited movement therewith within said chamber, said attaching means adjusted to permit movement of said piston rod relative to said control spool only after said stop means is engaged; and a passageway in said control spool selectively allignable with said housing ports upon movement of said piston rod from its set position to connect said pressure fluid to said cylinder to return said piston to its set position.

2. The position monitoring device set forth in claim 1 wherein said spool has a bore therethrough through which said piston rod extends and further comprising: an annular frictional packing surrounding said piston rod and engaging said spool; and a pressure nut threaded on said spool surrounding said piston rod and engaging said packing to selectively adjust the holding force between said piston rod and said spool.

Claims

1. A position monitoring device for a pressure fluid operated servomotor having a cylinder, a piston slidable therein and a piston rod connected to the piston and extending to the exterior of the cylinder, said device comprising: a housing connected to said cylinder defining a chamber through which said piston rod extends; a pressurized fluid inlet port in said housing connected in communication to a source of pressurized fluid, a pressure fluid delivery port in said housing connected in fluid communication to a said cylinder; a control spool located within said housing in a manner to permit movement thereof relative to said housing; stop means associated with said housing and said control spool limiting movement therebetween to a predetermined amount; attaching means connecting said control spool to said piston rod for limited movement therewith within said chamber, said attaching means adjusted to permit movement of said piston rod relative to said control spool only after said stop means is engaged; and a passageway in said control spool selectively allignable with said housing ports upon movement of said piston rod from its set position to connect said pressure fluid to said cylinder to return said piston to its set position.