US3638530A

US3638530A - Hydraulic counterweight

Info

Publication number: US3638530A
Application number: US855263A
Authority: US
Inventors: John I Hollister
Original assignee: Jackson Products Co
Current assignee: Jackson Products Co
Priority date: 1969-09-04
Filing date: 1969-09-04
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

Hydraulic fluid counterbalance system employing a piston and cylinder one of which, being arranged for connection to the load to be counterbalanced, is connected to the pantograph motion translating mechanism of a position controller or transfer machine. The piston and cylinder are part of a hydraulic system employing check and relief valves to insure constant pressure in the cylinder at any piston position. A pilot-operated check valve response rapidly to system pressure loss to preclude flow from the cylinder and continue the counterweight function despite loss of system pressure.

Description

United States Patent Hollister Feb. 1, 1972 [S4] HYDRAULIC COUNTERWEIGHT 3,l45,734 8/1964 Lee et al 91/420 3,442,l79 5/1969 Comer .91/454 [72] 3,476,019 11/1969 Berg et al ..91/420 {73] Assignee: Jackson Products Company, Tampa, Fla.

. v Primary Examiner-Paul E. Maslousky [22] Flled' Sept Attorney-Nienow 8L Frater [2l] Appl. No.: 855,263

[57] ABSTRACT U.S. 9 86, 9 l Hydraulic counterbalance ys[em employing a piston and 91/454, 91/46| cylinder one of which, being arranged for connection to the f "I081 F15) 13/042- Folb 1/00 load to be counterbalanced, is connected to the pantograph [58] M Search "33/25 A125 25 c; guy/2' motion translating mechanism of a position controller or glllsfi' 420 transfer machine. The piston and cylinder are part of a hydraulic system employing check and relief valves to insure [56] References cued constant pressure in the cylinder at any piston position. A

UNITED STATES PATENTS pilot-operated check valve response rapidly to system pressure loss to preclude flow from the cylinder and continue the 2,069,] 89 1/1937 Taylor ..3 3/25 A countgrweighl f ti n despite loss of system pressure. 3,044,172 7/1962 Sema ....33/25 E 3,030,930 4/1962 Gratzmuller Ji l/454 6 Claims, 2 Drawing Figures LOAD HYDRAULIC COUNTERWElGl-IT This invention relates to improvements in transfer mechanisms and to counterbalance apparatus for transfer mechanisms. An object of the invention is to provide improved position control servomechanisms, sometimes called transfer machines, in which the load is heavily biased in one direction as for example by gravity acting on the mass of the load element. Another object is to provide a counterbalance for a position servomechanism which will enable the control of heavy loads by small-sized control elements having minimum mass whereby the control system introduces minimum momentum into the control function. Another object is to provide a counterweight system arranged so that it will hold the load in the position it occupies at the time of servocontrol system failure notwithstanding that failure.

Other objects are to provide a counterbalance system for position servomechanisms in easily produced, relatively inexpensive, and in reliable form.

The counterweight structure provided by the invention has utility apart from position control servomechanisms. However, it is particularly well suited to application with servomechanisms and the embodiment of the invention selected for illustration in the drawings and detailed description hereinafter is shown in that application. It is shown applied to a position control servomechanism in which motion is translated from the control element to the load through a pantograph which is pivoted about one of its arms. Control movements and counterweight opposition are applied to the pantograph motion translation mechanism by lineal movements. Another object of the invention is to provide a counterweight system which can effectively provide its function by the application of lineal motion in a motion translation system whose elements move arcuately.

These and other objects and advantages of the invention are realized in part by the provision in a transfer mechanism of a pantograph comprising four arms the first and second arms of which each have pivotal connection at one end thereof to a third arm at spaced points and at the other end thereof to the fourth arm at spaced points, the pivotal connections being formed about a substantially parallel axes; the pantograph having pivotal connection about a pantograph axis parallel with the other axes at one of the first and second arms; by the provision of means for pivoting the pantograph about the pantograph axis by lineal displacement of a point in one of said third and fourth arms and by the provision of a counter balance means for applying uniform opposition to pivoting of the pantograph about the pantograph axis, the counterbalance means includes a hydraulic cylinder and a piston. one fixed to the pantograph and movable relative to the other in response to the difference between pressures tending to expand and to compress the cavity within the cylinder.

In the drawings:

HO. 1 is a schematic drawing of a pantograph motion translating system which includes a motion input element and a counterbalance element and which embodies the invention; and

FIG. 2 is a schematic drawing of a fluid-powered counter balance system.

Referring to FIG. 1 x the drawing, the apparatus there shown comprises a position-translating machine. sometimes called a motion transfer machine, in which the position of an output element or load is controlled by a servocontrol unit 13 through the medium of a motion translating system generally designated 12. In the embodiment represented in FIG. 1 the motion or position translation mechanism l2 comprises a pantograph one arm of which is moved or positioned by the piston 14 of a piston and cylinder assembly l6 whose cylinder is designated by the reference number IS. The pantograph comprises four arms, the first two of which are designated and 22. At one end the

arms

20 and 22 have pivotal connection at

pivots

23 and 24 to a third arm 25. The other ends of

arms

20 and 22 have pivotal connection at

points

26 and 27 which are spaced apart on a fourth arm 9H.

The load 10 is secured on an extension of the third arm 25. Input movement to the motion transmission mechanism is applied by motion or displacement of the piston 14 through the piston rod 29 which has connection to arm 28 at a point removed from the

pivot points

26 and 27 through an arm 98 which is pivoted to arm 28 at the pivot point 26.

There is advantage in using a motion translation mechanism which is a pantograph despite the fact that its movements are complex. One of the first and second arms of the pantograph has pivotal connection to a point which is fixed relative to the cylinder 18 of piston and cylinder assembly [6. In this embodiment arm 22 of the pantograph is pinned at pivot point to a support member 3i which is fixed relative to the cylinder 18. This arrangement permits input motion of arm 29 to be accomplished in a straight line. Up and down motion of the piston rod 29 results in up and down motion of the load elementor output element [0.

The piston arm 29 is pivotally connected to the arm 28 at a pivot point 32. The several pivot points 23, 24, 26, 27, 30 and 32 all have parallel or substantially parallel axes. Parallel to these axes is the axes of pivotal interconnection at point 33 of a counterbalancing cylinder and piston assembly 34. The load 10 is assumed in this example to be gravitational so that the effect is to rotate the motion translation mechanism clockwise around the pivot point 30. This rotation is opposed by the pressure within the cylinder 35 of the piston and cylinder assembly 34. The function of the counterbalance is to oppose the gravitational force that pulls the load 10 downwardly and to exactly oppose it in any position in which the arm 28 is placed by up and down motion of the position control piston 14.

The hydraulic counterbalance control system ll, represented by a block in FIG. 1, is shown in greater detail in FIG. 2. The system is represented schematically. Piston 36 is connected through the motion translating mechanism 12, only the direction reversing linkage 37 of which is detailed in the schematic to emphasize the relation of piston motion direction to motion direction of load 10. Motion translation mechanism 12 also includes the piston rod 29. Piston rod 29 is connected to the piston 14 which reciprocates within the cylinder l8. Pressurized hydraulic fluid for the operation of the two

pistons

36 and 14 is supplied from a pressure line or source 40. Flow through the system proceeds to a drain line 41.

The servocontrol unit iii of FIG. I includes a means for applying appropriate pressure differentials across the piston 14. That mechanism is represented in H6. 2 by the scrvocontrol valve 42 the spool of which is formed with two

pistons

43 and 44 which are positioned together by movement of a control shaft 45. Pressurized fluid from line is applied to the space between the two

pistons

43 and 44 through an inlet port 46.

Outlet ports

47 and 48 connect to the lower cavity and the upper cavity of the piston and cylinder assembly [6. respectively. Both of these ports are closed in the intermediate position of the servo valve control shaft so that pressure within these cavities is maintained and the piston 14 remains stationery. If the control shaft 45 is lifted piston 44 clears the port 47 permitting flow from the lower cavity and the piston and cylinder assembly 16 through port 47 and through the lower portion of the servo valve cylinder from whence it flows by an exit port 49 to the drain line 41. This same upward motion of the control shaft 45 lifts piston 43 above port 48 permitting communication from the pressure inlet port 46 through the central portion of the servo valve cylinder to port 48 to the upper cavity of the cylinder 18. Pressurized fluid will flow into the upper cavity and will flow from the lower cavity with the result that piston 14 will be moved downwardly carrying the load downwardly. Downward motion of the load is accompanied by upward motion of piston 36 within the counter balance piston cylinder assembly 34 which is possible only if fluid is dispelled from the cavity 50 of that unit.

Returning to the lower part of FIG. 2. if the valve control shaft 45 is moved downwardly so that

pistons

43 and 44

clear ports

48 and 47. respectively. then pressurized fluid will flow from inlet port 46 through the servo valve between the two pistons and through the port 47 to the lower cavity of the cylinder l8 tending to force the piston 14 upwardly. Fluid flows from the upper cavity of the cylinder through port 48 and the upper portion of the servo valve cylinder through exit port 52 to the drain line 41. The result is that load is lifted. As an incident to upward motion of the load 10 the piston 36 of the counterweight system moves downward so that fluid must flow into the cavity to maintain the counterbalance pressure.

Thus, as the load is moved up and down by the control piston and cylinder assembly [6. piston 36 of the counterweight assembly must move up and down. The direction reversal linkage 37 has been included to make this relationship clear. it is a schematic representation of all of the elements of the motion translation mechanism l2 of FIG. 1 that determine the duration of load motion that is associated with motion of

pistons

14 and 36. Its operation is described above in the description of those elements. To be effective as a counterweight the counterweight system must introduce pressure in cavity 50 which will force the piston 36 downwardly with a force which is equal (taking into account any purchase or force multiplication) to the weight of load 10 or the value of whatever bias urges load ll] to assume a position other than that dictated by the position control system. Thus, the function of the remainder of the counterweight system is to insure that the pressure within cavity 50 remains the same regardless of the volume of that cavity, To this end. the hydraulic system comprises a hydraulic line for connection at its high pressure end to a source of fluid. At its other, low-pressure end. that line is arranged for connection to a lower pressure or drain line such for example as drain line 4]. That line is identified in FIG. 2 as the line which consists of line segment 54 which extends from drain line 4| to the low-pressure side of a pressure relief valve 55. It also includes line segment 56 which extends from the high-pressure side of relief valve to the outlet side of a check valve 59 whose inlet is connected by a line segment 60 to the outlet of a pressure control valve 6] whose inlet line 62 is connected to pressure line 4-0.

The outlet port 63 of the pressure control valve is opened and closed by movement of one of two pistons 64 and 65 which are mounted on a common shaft 66 and between which high-pressure fluid is applied so that the pressure of the hydraulic fluid is applied in opposite directions to the two pistons so that it has no effect in producing motion of the piston. The pressure control valve is moved to open position by an adjustable pressure spring 67. Outlet pressure is sensed by a line 68 and is applied to a small cylinder 69 below the piston rod 66 acting as a pistons to lift the pistons 64 and 65 in a direction tending to close the outlet port 63. This pressure control valve is representative of a variety of valves that might be employed to provide a given or selected pressure at its outlet port. Fluid is free to flow through line 56 to the relief valve 55 and beyond to line 54 the drain only if the pressure in line 56 exceeds the opening pressure of pressure relief valve 55. Ordinarily, the relief valve 55 is set so that no fluid or only a small amount of fluid is permitted to flow through these lines. That is. the opening pressure of valve 55 is set to equal or to be slightly below the outlet pressure of the pressure control valve.

The cavity 50 of the counterweight piston and cylinder assembly is connected to that line 56 at a point intermediate the check valve 59 and pressure relief valve 55. In the embodiment shown it is connected by a line 70 to the outlet port of a pilot-operated check valve 57 whose inlet port is connected by a flow line 58 to the line 56 The valve 57 is biased closed but is held open by a pilot valve 85 when the hydraulic system is pressurized. If piston 36 is moved down in a direction tending to lower the pressure in lines 70 and 58 fluid from the reducing valve 61 is forced to flow through check valve 59 into the cavity 50 to maintain cavity pressure at the prior uniform level. Conversely. if the load moves downwardly so that piston 36 moves upwardly to compress the fluid in cavity 50 its pressure tends to increase. The check valve 59 will be forced closed so that no more fluid can flow into the line 63. Instead, fluid flows out of cavity 50 through lines 70. S8 and $6 and through the pressure relief valve 55 to the outlet 54 and drain 4].

Valve 57 is very sensitive. The area of its pilot valve is enough greater than the area above the check valve 57 so that the force exerted by the pressure source on the pilot valve 85 is greater than the sum of the force of the valve spring and the force exerted on valve Why the pressure source.

Means are included in the system for protecting against loss of pressure at the pressure line. More particularly. the system is arranged so that if there is a sudden loss in pressure at the pressure line due for any reason. such for example as loss of electrical power to the hydraulic pump. fluid will be prevented from flowing out of cavity 50 and the pressure in the cavity will be maintained. in this embodiment that means comprises a pressure sensing flow line which has a high-pressure end for connection to a source of pressurized hydraulic fluid and it has a low-pressure end for connection to a low-pressure or drain line. The pressure-sensing line includes a high-pressure segment connects to the pressure line 40. At its other end line 80 connects to the inlet high-pressure side of a relief valve 8| whose low-pressure side is connected by a line segment 82 to the drain line 41 through a variable flow resistance element 83 and a line segment 84. The variable flow resistance is provided by a throttling valve in this embodiment. The inclusion of the pressure relief valve 81 and the flow-resistance element 83 insures that line segment 82 of the system is pressurized at some value above the drain pressure whenever the pressurc line 40 is pressurized in requisite degree to insure pressure buildup in cavity 50. The pressure at line 82 is applied to the head of the pilot valve 85 which opens in response to that pressure to lift the valve stem 86 of valve 57. The outlet side of that pilot valve is connected by a line 90 to the drain line to form a flow path for fluid flowing through the pilot valve.

It will be apparent that other circuit arrangements may be employed to apply pressurized fluid to the pilot valve to pro' vide loss of pressure protection although the arrangement shown is preferred and is advantageously employed. Upon loss of pressure at line 82 the pilot valve closes forcing the valve stem 86 of valve 57 downwardly so that the valve is closed thus preventing the escape of fluid from the cavity 50 back toward the hydraulic fluid source. Use of a pilot operated valve in series with a regular check valve 59 makes the system very responsive to pressure changes and shuts off reverse flow more rapidly than can be accomplished in the standard check valve whereby a greater degree of protection is afforded and the counterbalance system maintains the load in position even when pressure loss is sudden. The pilot operated valve can be made to maintain cylinder pressure for long periods whereas conventional check valves tend to leak fluid.

I claim:

l. in a transfer mechanism:

a pantograph comprising four arms a first and second arms of which each have pivotal connection at one end thereof to a third arm at spaced points and at the other end thereof to the fourth arm at spaced points. said pivotal connections being formed about substantially parallel axes, said pantograph having a pivotal connection about a pantograph axis parallel with said axes at one of said first and second arms;

means for pivoting said pantograph about said pantograph axis by lineal displacement of a point in one of said third and fourth arms; and

counterbalance means for applying uniform opposition to pivoting of said pantograph about said pantograph axis. said counterbalance means comprising a hydraulic cylinder and piston. one fixed to the pantograph and movable relative to the other in response to the difference between pressures acting to expand and compress the space within the cylinder.

2. The invention defined in claim l. in which said counterbalance further comprises means for maintaining uniform hydraulic pressure within said cylinder over a continuous range of cylinder volumes.

3 The invention defined in claim 1, in which said counterbalance means comprises a hydraulic fluid line for connection between a pressure source and a drain, said line including a check valve and a relief valve in series in that order between its pressure and drain ends; said cylinder having fluid communication with said line at a point intermediate said valves 4. The invention defined in claim 3 in which said fluid line further includes a pilot pressure opened check valve 57 at a point between said cylinder and the pressure end of the line; and which includes means 82 for supplying pilot pressure to said pilot pressure opened valve only when said fluid line is pressurized in given degree.

5. The invention defined in claim 4. in which said means for supplying pilot pressure comprises a pressure-sensing line for connection between the pressure source and drain and including a relief valve and a flow'resistance element downstream therefrom and a fluid connection to said pilot pressure operated valve from a point in said pressure-sensing line intermediate the relief valve and flow-resistance element.

9. A hydraulic counterweight for connection to a movable load comprising in combination:

a hydraulic cylinder and piston, one fixed to the load and the other to a point with respect to which the load is movable, said piston and cylinder being movable relative to one another in response to differences between expansive cylinder pressure and compressive pressure applied thereto;

a hydraulic pressure line for connection between a pressure source and a drain, said line including a check valve and a relief valve in series in that order between its pressure and drain ends; said cylinder having fluid communication with said line at a point intermediate said valves said fluid line including a pilot pressure open valve at a point between said cylinder and the pressure end of said line;

means for supplying pilot pressure to said pressure-opened valve only when said fluid line is pressurized in selected degree; and

a pressure-sensing line for connection between the pressure source and drain and including a flow-resistance element and relief valve upstream from the flow-resistance ele ment, said means for supplying pilot pressure comprising a fluid connection to said pilot pressure operated valve from a point in said pressure-sensing line intermediate the relief valve and flow-resistance elementv

Claims

1. In a transfer mechanism: a pantograph comprising four arms a first and second arms of which each have pivotal connection at one end thereof to a third arm at spaced points and at the other end thereof to the fourth arm at spaced points, said pivotal connections being formed about substantially parallel axes, said pantograph having a pivotal connection about a pantograph axis parallel with said axes at one of said first and second arms; means for pivoting said pantograph about said pantograph axis by lineal displacement of a point in one of said third and fourth arms; and counterbalance means for applying uniform opposition to pivoting of said pantograph about said pantograph axis, said counterbalance means comprising a hydraulic cylinder and piston, one fixed to the pantograph and movable relative to the other in response to the difference between pressures acting to expand and compress the space within the cylinder.

2. The invention defined in claim 1, in which said counterbalance further comprises means for maintaining uniform hydraulic pressure within said cylinder over a continuous range of cylinder volumes.

3. The invention defined in claim 1, in which said counterbalance means comprises a hydraulic fluid line for connection between a pressure source and a drain, said line including a check valve and a relief valve in series in that order between its pressure and drain ends; said cylinder having fluid communication with said line at a point intermediate said valves.

4. The invention defined in claim 3 in which said fluid line further includes a pilot pressure opened check valve 57 at a point between said cylinder and the pressure end of the line; and which includes means 82 for supplying pilot pressure to said pilot pressure opened valve only when said fluid line is pressurized in given degree.

5. The invention defined in claim 4, in which said means for supplying pilot pressure comprises a pressure-sensing line for connection between the pressure source and drain and including a relief valve and a flow-resistance element downstream therefrom and a fluid connection to said pilot pressure operated valve from a point in said pressure-sensing line intermediate the relief valve and flow-resistance element.

9. A hydraulic counterweight for connection to a movable load comprising in combination: a hydraulic cylinder and piston, one fixed to the load and the other to a point with respect to which the load is movable, said piston and cylinder being movable relative to one another in response to differences between expansive cylinder pressure and compressive pressure applied thereto; a hydraulic pressure line for connection between a pressure source and a drain, said line including a check valve and a relief valve in series in that order beTween its pressure and drain ends; said cylinder having fluid communication with said line at a point intermediate said valves, said fluid line including a pilot pressure open valve at a point between said cylinder and the pressure end of said line; means for supplying pilot pressure to said pressure-opened valve only when said fluid line is pressurized in selected degree; and a pressure-sensing line for connection between the pressure source and drain and including a flow-resistance element and relief valve upstream from the flow-resistance element, said means for supplying pilot pressure comprising a fluid connection to said pilot pressure operated valve from a point in said pressure-sensing line intermediate the relief valve and flow-resistance element.