US3882759A

US3882759A - Fluid actuated control device

Info

Publication number: US3882759A
Application number: US434090A
Authority: US
Inventors: Charles William Formwalt; John Lewis Frank; Allen Paul Schneider
Original assignee: Deere and Co
Current assignee: Deere and Co
Priority date: 1974-01-17
Filing date: 1974-01-17
Publication date: 1975-05-13
Anticipated expiration: 1992-05-13
Also published as: CA1022039A

Abstract

A device is described for the movement of a rod means into a plurality of positions along a linear path. It consists of an open-ended, longitudinally bored cylinder body containing a piston rod with a fixed piston and with a plurality of stops which limit the movement of two additional pistons slidable relative to the rod and in the bore. One of the additional pistons is limited in its travels by stop means in the bore and the other additional piston has the rod means operatively associated with it. Three fluid passage means have restrictors of a predetermined, fixed ratio of cross-sectional areas, and by selected release and pressurization of the fluid passage means according to a series of combinations in binary code, incremental stepping positions of the rod means are effected.

Description

United States Patent Formwalt et al.

1111 3,882,759 r 1 May 13,1975

[ FLUID ACTUATED CONTROL DEVICE [75] Inventors: Charles William Formwalt, Cedar Pr'mary Exammer paul Maslousky Falls; John Lewis Frank, Waterloo; Allen Paul Schneider, Hudson, all of [571 ABSTRACT Iowa A device is described for the movement of a rod means into a plurality of positions along a linear path. [73] Asslgnee' Deere & Company M It consists of an open-ended, longitudinally bored cyl- [22] Filed: Jan. 17, 1974 inder body containing a piston rod with a fixed piston and with a plurality of stops which limit the movement [21] Appl' 434090 of two additional pistons slidable relative to the rod and in the bore. One of the additional pistons is lim- [52] US. Cl. 91/167; 92/13.1; 92/13.4; ited in its travels by stop means in the bore and the 92/l3.6; 92/75 other additional piston has the rod means operatively [51] Int. Cl. Fl5b 11/18 associated with it. Three fluid passage means have re- [58] Field of Search 91/167; 92/l3.1, 13.4, strictors of a predetermined, fixed ratio of cross- 92/13.6, 75; 235/201 ME, 200 R sectional areas, and by selected release and pressurization of the fluid passage means according to a series of [56] References Cited combinations in binary code, incremental stepping po- UNITED STATES PATENTS sitions of the rod means are effected. 3,713,364 1/1973 Francia 91/167 R, 12 Claims, 2 Drawing Figures L M I J.

"-52 -54 l ss 1e 2o 2s J Z 4 l a i w? I 1 '1' ;.'32---Q'1- W //VA/// A 312 14 I2 24 22 FLUID ACTUATED CONTROL DEVICE BACKGROUND OF THE INVENTION The present invention relates generally to fluid actuated control devices and more specifically to a stepping type fluid actuated control device. Prior to the availability of digital hardware, most control devices used some form of closed loop analog feedback. Direct digital control can eliminate the need for the feedback and various fluid actuated control devices have been developed which consist of a number of actuating elements connected together such that the total amount of extension of a rod means is determined by the combination of elements energized. The required control unit is very simple, consisting only of switches or their equivalents.

In the past, many fluid actuated control devices have been designed in an attempt to achieve direct digital control; however, most have been too complex. Some have required special machining on the piston faces and others required special internal tie rods.

SUMMARY OF THE INVENTION It is a general object of the present invention to provide a simple fluid actuated control device without spe-' BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic cross-sectional view of the fluid actuated control device incorporating the invention; and

FIG. 2 is a fragmentary view showing a modification of the control device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, a fluid actuated control device includes a cylinder body having a longitudinally extending bore with a piston rod 12 positioned within it. On the inner end of rod 12 is a first stop means in the form of a snap ring 14. A second stop means or snap ring 16 is spaced from and between snap ring 14 and the outer end of rod 12. Slidably mounted in the bore and on rod 12 for relative movement between

snap rings

14 and 16 is a first piston 18 which is limited in its bore travel by an inner stop means or snap ring 28 and an outer stop means or snap ring 30. A second piston 20 is slidably mounted in the bore and fixed to rod 12 in a position between and spaced from snap ring 16 and the outer end of rod 12 upon which is a third stop means or snap ring 22. Between and spaced from snap ring 22 and the piston 20 is a fourth stop means or snap ring 24. An additional piston 26 is slidably mounted in the bore and on rod 12 for relative movement between

snap rings

22 and 24, and against piston 26 rests a cylinder rod 32.

In the cylinder body 10, communicating with the bore inwardly of snap ring 28 is a port 34, and between snap ring 30 and piston 20 is a port 36, while an additional port 38 communicates with the bore between

pistons

20 and 26. Pressurizing these ports are feed lines. 46, 48 and 50 with

restrictors

52, 54 and 56 of a predetermined, fixed ratio of cross-sectional areas, the sizing of which will be hereinafter explained, and

threeway valves

40, 42 and 44.

By symbols of the binary code and the symbolism in which 0 denotes the not pressurized condition and l the pressurized condition, the various positions of the cylinder rod 32 may be respectively indicated by the following format wherein the three binary digits represent the pressure condition of

ports

34, 36 and 38.

In the first condition, the only action is due to a biasing means, spring or load represented by the arrow F which acts in the direction of arrow F to bias cylinder rod 32 in the zero step position and bias piston 26 against snap ring 24. This, in turn, acts to bias snap ring 16 against piston 18 which is thus biased against inner snap ring 28.

With only port 34 pressurized, piston 18 is urged against snap ring 30 for one incremental step. The load continues to bias the cylinder rod 32 against piston 26 which in turn is biased against snap ring 24. As before, this acts to bias snap ring 16 against piston 18.

With only port 36 pressurized, piston 20 is urged outwardly by two incremental steps until snap ring 14 is urged against piston 18. The load biases cylinder rod 32 and piston 26 against snap ring 24 which in turn biases piston 20 inwardly and through hydraulic pressure on piston 18, biases it against inner snap ring 28.

With

ports

34 and 36 pressurized, piston 18 is urged against the outer snap ring 30 causing one incremental step and piston 20 is urged outwardly two incremental steps until snap ring 14 is urged against piston 18, resulting in cylinder rod 32 moving a total of three incremental steps. The load acts to bias the cylinder rod 32 and piston 26 against snap ring 24.

With only port 38 pressurized, piston 26 is urged outwardly against snap ring 22 four incremental steps. The load acts by hydraulic pressure to bias piston 20 inwardly until snap ring 16 is biased against piston 18 which in turn is biased against inner stop 28.

With

ports

34 and 38 pressurized, piston 18 is urged against the outer snap ring 30 causing one incremental step and piston 26 is urged outwardly four incremental steps for a total of five incremental steps of cylinder rod 32. The load acting by hydraulic pressure biases piston 20 inwardly which in turn biases snap ring 16 against piston 18.

With

ports

36 and 38 pressurized, piston 20 is urged outwardly by two incremental steps until snap ring 14 is urged against piston 18 and piston 26 is urged outwardly four incremental steps for a total of six incremental steps of cylinder rod 32. The load acting by hydraulic pressure biases piston inwardly which in turn by hydraulic pressure biases piston 18 against inner snap ring 28.

With

ports

34, 36 and 38 pressurized, piston 18 is urged against outer snap ring 30 causing one incremental step, piston 20 is urged outwardly until snap ring 14 is urged against piston 18 causing two incremental steps, and piston 26 is urged outwardly four incremental steps for a total of seven incremental steps of cylinder rod 32.

While it is not a prerequisite that the transition of the fluid actuated control device from one position to an other be completed in the same increment of time without pulsations or that there be no intermediate transient reversals of cylinder rod 32 movement, these desirable features may be obtained by sizing

restrictors

52, 54 and 56 such that their cross-sectional areas are substantially in direct proportion to the number of incremental steps resulting from pressurizing only that respective port. The cross-sectional areas are substantially in direct proportion because one skilled in the art would recognize that compensation must be made for feed line restrictions, internal restriction in the threeway valve, and variations in pressure at each three-way valve from a uniform supply pressure in order to obtain optimum pulsationless, constant movement transitions from one position to another.

Pressurizing port 34 will result in one incremental step, thus the cross-sectional area will be one square unit; pressurizing port 36 will result in two incremental steps, thus the cross-sectional area will be two square units; and pressurizing port 38 will result in four incremental steps, thus the cross-sectional area will be four square units. This assures that each

piston

18, 20 and 26 requires the same amount of time to complete its travel. When port 34 is pressurized, one increment of time will be required to complete one incremental step; when port 36 is pressurized, one increment of time will be required to complete two incremental steps, when

ports

34 and 36 are pressurized, one increment of time will be required to complete three incremental steps;

etc.

With no restrictors, the transient reversal of direction will occur in the transition between three and four incremental steps; e.g. cylinder rod 32 will initially move inwardly because piston 18 will move one step inwardly causing piston 20 to move two steps inwardly while piston 26 will move only one step outwardly relative to piston 20 resulting in a total one step inwardly movement, then piston 26 and cylinder rod 32 will continue to move outwardly to the four incremental step position.

In the same situation, with

restrictors

52, 54 and 56, piston 26 will move further outwardly in the same period of time than piston 20 will move inwardly such that the relative piston motions will cause cylinder rod 32 to move continuously outwardly from the three to the four incremental step position.

In FIG. 2 is shown a fragmentary view showing a modification to the fluid actuated control device which is identical to the device shown in FIG. 1, with the exception that piston 26 is affixed to cylinder rod 32 by means of a weld 27.

While the invention has been described in conjunction with a specific embodiment, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. For example, the use of only two pistons and two ports to obtain three incremental steps. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and scope of the appended claims.

What is claimed is:

l. A fluid actuated control device comprising: a cylinder body having a longitudinally extending bore provided therein and open to one end; a piston rod of a diameter less than the diameter of the bore positioned in the bore; a first stop means on the inner end of the rod; a second stop means on the rod between and spaced from the first stop means and the outer end of the rod; a first piston slidably mounted in the bore and on the rod for relative movement between the first and second stop means; a third stop means on the outer end of the rod; a fourth stop means on the rod between and spaced from the second stop means and the third stop means; an additional piston slidably mounted in the bore and on the rod for relative movement between the third and fourth stop means; inner stop means in the bore limiting inward movement of the first piston; outer stop means in the bore limiting outward movement of the first piston; rod means operatively associated with the additional piston for movement therewith, slidably mounted in the bore and projecting from the one end thereof; first fluid passage means communicating with the bore inwardly of the inner stop means; and additional fluid passage means communicating with the bore between the outer stop means and the additional piston; and means for selectively supplying and exhausting fluid from either or both of the fluid passage means.

2. A fluid actuated control device as claimed in claim 1 further including biasing means for inwardly urging the rod means with a force greater than the thrust of fluid on the base of the piston rod and less than the thrust of fluid on the pistons.

3. A fluid actuated control device as claimed in claim 1 wherein the rod means bears against the additional piston.

4. A fluid actuated control device as claimed in claim 1 wherein the rod means is attached to the additional piston.

5. A fluid actuated control device as claimed in claim 1 wherein the first fluid passage means is of a different cross-sectional area than the second fluid passage means.

6. A fluid actuated control device as claimed in claim 1 wherein the additional fluid passage means has 4 times the cross-sectional area of the first fluid passage means.

7. A fluid actuated control device comprising: a cylinder body having a longitudinally extending bore provided therein and open to one end; a piston rod of a diameter less than the diameter of the bore positioned in the bore; a first stop means on the inner end of the rod; a second stop means on the rod between and spaced from the first stop means and the outer end of the rod; a first piston slidably mounted in the bore and on the rod for relative movement between the first and second stop means; a second piston slidably mounted in the bore and fixed to the rod in a position between and spaced from the second stop means and the outer end of the rod; a third stop means on the outer end of the rod; a fourth stop means on the rod between and spaced from the third stop means and the second piston; an additional piston slidably mounted in the bore and on the rod for relative movement between the third and fourth stop means; inner stop means in the bore limiting inward movement of the first piston; outer stop means in the bore limiting outward movement of the first piston; rod means operatively associated with the additional piston for movement therewith, slidably mounted in the bore and projecting from the one end thereof; first fluid passage means communicating with the bore inwardly of the inner stop means; second fluid passage means communicating with the bore between the outer stop means and the second piston; an additional fluid passage means communicating with the bore between the second and additional pistons; and means for selectively supplying and exhausting fluid to and from any selected one or combination of the fluid passage means.

8. A fluid actuated control device as claimed in claim 6 7 further including biasing means for inwardly urging the rod means with a force greater than the thrust of fluid on the base of the piston rod and less than the thrust of fluid on the pistons. I

9. A fluid actuated control device as claimed in claim 7 wherein the rod means bears against the additional piston.

10. A fluid actuated control device as claimed in claim 7 wherein the rod means is attached to the additional piston.

11. A fluid actuated control device as claimed in claim 7 wherein the first fluid passage means is of a different cross-sectional area than the second fluid passage means and the second fluid passage means is of a different cross-sectional area than the additional fluid passage means.

12. A fluid actuated control device as claimed in claim 7 wherein the additional fluid passage means has 4 times the cross-sectional area of the first fluid passage means and the second fluid passage means has twice the cross-sectional area of the first fluid passage means.

Claims

1. A fluid actuated control device comprising: a cylinder body having a longitudinally extending bore provided therein and open to one end; a piston rod of a diameter less than the diameter of the bore positioned in the bore; a first stop means on the inner end of the rod; a second stop means on the rod between and spaced from the first stop means and the outer end of the rod; a first piston slidably mounted in the bore and on the rod for relative movement between the first and second stop means; a third stop means on the outer end of the rod; a fourth stop means on the rod between and spaced from the second stop means and the third stop means; an additional piston slidably mounted in the bore and on the rod for relative movement between the tHird and fourth stop means; inner stop means in the bore limiting inward movement of the first piston; outer stop means in the bore limiting outward movement of the first piston; rod means operatively associated with the additional piston for movement therewith, slidably mounted in the bore and projecting from the one end thereof; first fluid passage means communicating with the bore inwardly of the inner stop means; and additional fluid passage means communicating with the bore between the outer stop means and the additional piston; and means for selectively supplying and exhausting fluid from either or both of the fluid passage means.

8. A fluid actuated control device as claimed in claim 7 further including biasing means for inwardly urging the rod means with a force greater than the thrust of fluid on the base of the piston rod and less than the thrust of fluid on the pistons.