US3593980A

US3593980A - Pneumatic balancer

Info

Publication number: US3593980A
Application number: US817764A
Authority: US
Inventors: Kenneth A Mchenry
Original assignee: Chicago Pneumatic Tool Co LLC
Current assignee: Chicago Pneumatic Tool Co LLC
Priority date: 1969-04-21
Filing date: 1969-04-21
Publication date: 1971-07-20
Anticipated expiration: 1988-07-20

Abstract

A pneumatic load-balancing unit capable of automatically balancing pneumatically at a specific level any weight within the capacity of the unit following manual actuation of a control valve connected with a pressure air supply; and to allow this weight to be manually moved or floated with predetermined ease above and below the balance level within the stroke range of a piston carrying the weight. The unit includes a cylinder containing the piston upon the rod of which the weight is attachable. Air pressure in a reservoir connected in a closed circuit with the cylinder functions to counterbalance the weightloaded piston. Since the level of the piston will change with a change in the weight load, then in order to return the workloaded piston to its normal level, the control valve is manually opened. A system of valves automatically responds to pressure airflowing through the control valve to either admit increased pressure air or to relieve pressure air from the closed circuit as needed to return the piston to its normal balance level. The pressure in the closed circuit remains constant following restoration of the piston to its normal balance level and release of the control valve. The closed circuit normally permits free airflow between the cylinder and the reservoir except when the system of valves is caused to function, then it provides a restricted flow. The restricted flow develops back pressure which functions to snub movement of the piston so as to aid in bringing the piston to a stabilized condition. In a modified form, an arrangement between the control valve and the system of valves requires only a momentary opening of the control valve so as to initiate operation of the system of valves, after which the control valve may be released. The system of valves then functions automatically until the work-loaded piston is restored to its normal level.

Description

United States Patent Primary Examiner.lames B. Marbert Att0rneyStephen J. Rudy ABSTRACT: A pneumatic load-balancing unit capable of automatically balancing pneumatically at a specific level any weight within the capacity of the unit following manual actuation of a control valve connected with a pressure air supply;

and to allow this weight to be manually moved or floated with predetermined ease above and below the balance level within the stroke range of a piston carrying the weight. The unit includes a cylinder containing the piston upon the rod-of which the weight is attachable. Air pressure in a reservoir connected in a closed circuit with the cylinder functions to counterbalance the weight-loaded piston. Since the level of the piston will change with a change in the weight load, then in order to return the work-loaded piston to its normal level, the control valve is manually opened. A system of valves automatically responds to pressure airflowing through the control valve to I either admit increased pressure air or to relieve pressure air from the closed circuit as needed to return the piston to its normal balance level. The pressure in the closed circuit remains constant following restoration of the piston to its normal balance level and release of the control valve.

The closed circuit normally permits free airflow between i the cylinder and the reservoir except when the system of valves is caused to function, then it provides a restricted flow. The restricted flow develops back pressure which functions to snub movement of the piston so as to aid in bringing the piston to a stabilized condition.

In a modified form, an arrangement between the control valve and the system of valves requires only a momentary opening of the control valve so as to initiate operation of the system of valves, after which the control valve may be released. The system of valves then functions automatically until the work-loaded piston is restored to its normal level.

34 i t if 32 U 40\ 36'] a 2/ j I! 7; ,2; 27

PATENTED JUL20 um al llilll ATTORNEY lav PNEUMATIC BALANCER BACKGROUND OF THE INVENTION This invention is concerned with a load-balancing unit which is used to counterbalance the weight of a load suspended therefrom, and is designed so that manual application of a relatively light force to theload will raise or lower the load within the stroke range of the unit.

A device of this general nature is known from US. Pat. No. 2,939,431 but in this known device, once the load has been initially balanced, it is required that the pressure be increased or decreased in the system each time the load is raised or lowered from its initially balanced condition.

The objective of the present invention is to provide a pneumatic-balancing unit which functions automatically following actuation of a control valve to bring a work loaded piston to a pneumatically balanced condition at a specific level intermediately of the ends of a piston cylinder, after which the loaded piston may be manually raised or lowered with ease above or below this level within the stroke range of the piston without the necessity of increasing or decreasing the pressure in the system, and in which unit the loaded piston automatically returns to its initially balanced level when manually released.

ln the present invention, a work-loaded piston is connected 1 in a closed pneumatic circuit with a reservoir, the pressure of the circuit serving to counterbalance the loaded piston at a predetermined level until a change in the piston load causes a change in the balance level of the piston. A system of valves subject to pneumatic operation following manual operation of a control valve functions automatically to increase or decrease the pressure in the closed circuit as needed to rebalance the piston at its normal level following replacement of the weight load on the piston.

BRIEF DESCRlPTlON OF THE DRAWINGS FIG. 1 is a schematic diagram of a work load balancing unit embodying the invention; and

FIG. 2 is a schematic diagram ofa modified arrangement of the unit shown in FIG. ll.

DESCRIPTION OF PREFERRED EMBODIMENT The pneumatic load-balancing unit includes a pneumatic piston cylinder in which a piston 11 is pneumatically slida ble. A vent hole 12 in the cylinder causes the upper cylinder portion 13 to be all times at atmospheric pressure. The piston rod 14 passes through the bottom head of the cylinder and carries an external hook 15 upon which a work load W is attachable. The unit is adapted by means of a bracket 16 to be suspended from a hoist 17. The work-loaded piston is pneumatically counterbalanced by means of pressure airflowing in a closed circuit between the lower cylinder portion 18 and a pneumatic reservoir 19. ln use, the unit is supported by the hoist at a preselected level, manual pressure is then applied to the work load to position it within the range of the piston stroke at a precise level for a work operation. When the manual pressure is released, the pressure in the closed circuit will return the work-loaded piston to its normal counterbalanced position.

The closed circuit is defined by a pair of

parallel passages

21 and 22 connecting the reservoir with the lower cylinder portion 18. A normally open pilot operable valve 23 in passage 22 allows free airflow between the reservoir and the cylinder. At certain times, as will be later described, valve 23 will be caused to close. Even when valve 23 is closed, airflow between the reservoir and the cylinder will continue over the bypass passage 21 but at a slower rate because of a restriction 24 in the passage.

It is desired that the work-loaded piston be counterbalanced at a predetermined balance point in the cylinder, so that the loaded piston may be manually moved or floated above and below the balance point throughout the stroke range of the piston with a minimum of energy. The load capacity of the piston is determined by its diameter. [t is apparent in a pneumatic closed circuit, as here, that when the work load on the piston is replaced with a heavier or lighter load, the counterbalanced position of the piston will change accordingly. To return the piston to its predetermined balance point following a load change, it is necessary to either increase or decrease the pressure in the closed circuit as needed. Here, the center of the cylinder has been selected as the predetermined balance point.

To effect admission or release of pressure air from 'the closed circuit, the unit includes a normally closed pilot operable main valve 25. The latter connects by means of a line 26 with the lower cylinder portion; and connects by means of a line 27 through a pilot operable supply valve 28 with a pressure air supply line 29. A spring 31 normally biases the supply valve 28 to open condition. The pilot end 32 of valve 28 connects by means ofa line 33 with a port 34 of the cylinder. Port 34 is locatedat a point which will be just below the piston when the piston is centered, as indicated by the broken line C, in the cylinder. The main valve 25 also connects through line 27 with an exhaust line 36 which leads through a pilot operable exhaust valve 35 to exhaust 38. A spring 39 normally biases the exhaust valve to closed condition. The pilot end 40 of the exhaust valve connects by means of a line 41 with a port 42 of the cylinder. Port 42 is located at a point which will be just above the piston when the piston is centered in the cylinder, as indicated by the broken line C. It is apparent that when the piston is below port 34, as in FIG. 1, the supply valve 28 will be open under the bias of its spring since its pilot end is vented through the cylinder; and when the piston is above port 34 the supply valve 28 will be closed by cylinder air pressure acting over line 33 on its pilot end 32. It is also apparent than when the piston is below port 42, the exhaust valve 35 will be closed under the bias of its spring 39; and when the piston is above port 42, the exhaust valve 35 will be opened by cylinder air pressure acting over line 41 on its pilot end 40. But, as long as the main valve 25 remains closed, supply line air cannot be admitted to the lower cylinder portion 18; nor can pressure air be released therefrom. It is also apparent that when the piston obtains a centered position (broken line C) between

ports

34 and 42, the exhaust valve 35 and the supply valve 28 will both be closed. When both of these valves are closed, it is clear that even if valve 25 should be open, pressure air cannot be admitted to or released from the lower cylinder portion 18.

Opening and closing of the main valve 25 is controlled by means of a manually operable control valve 43. The latter is normally closed so as to block supply line airflow over a branch line 44 to a line 45 connected with the pilot end46 of the main valve 25. Line 45 also connects with a line 47 connected to the pilot end 48 of valve 23. An exhaust bleed port 49 connects through the chamber of the control valve with line 45 so that when control valve 43 is returned to closed condition by its spring 5]., pressure air acting on the pilot ends of valves .23 and 25 can exhaust through port 49 permitting

valves

23 and 25 to restore to normal.

ln summary of the operation to effect centering and balancing of the work-loaded piston following replacement of the work load W with a load of heavier or lighter weight, assume the replaced load is relatively heavier. The piston will accordingly be drawn by its load, because of the then existing pressure in the closed circuit, toward the lower end of the cylinder as in FIG. 1, and the supply valve 28 will open. Valve 43 is next manually depressed and held in open condition. Supply air then caused to flow over branch line 44 acts on the

pilot ends

48 and 46 to open the main valve 25 and to close valve 23. The action that takes place thereafter in bringing the piston 111 to a balanced centered condition (broken line C) automatically follows. Supply airflows through

valves

28 and 25 to the lower cylinder chamber 18 and through the restricted passage 21 to the reservoir 19. The piston progressively rises with the increased pressure As the piston rises aboveport 34, the supply valve 28 closes to stop further supply airflow through the main valve 25. lf, in moving upwardly, the piston should overtravel port 42, the exhaust valve 35 will open and pressure air from chamber 18 below the piston will escape through the exhaust valve 35. The piston will accordingly move downward as the cylinder pressure decreases. The piston accordingly finally centers and stabilizes between ports 42 and-34 in broken line position C. When this condition is reached, the control valve 43 is manually released by the operator and

valves

25 and 23 are restored by their springs to normal.

If, next, the work load is replaced with a relatively lighter load, the piston will be forced by the then existing pressure in the closed circuit toward the upper end of the cylinder above port 42 and the exhaust valve 35 will open. The control valve 43 is next operated,-as before, to effect closing of valve 23 and opening of valve 25. Cylinder pressure air accordingly exhausts through

valves

25 and 35 causing the piston to move downwardly. As the piston moves below port 42, the exhaust valve 35 closes. The downward movement of the piston is dampened by the back pressure resulting from the restricted flow through the reservoir passage 21 and the piston finally centers and stabilizes between

ports

42 and 34.

Valves

25 and 23 restore to normal as the control valve is manually released.

It is noted from the above, that before the control valve 43 may be released it must be held in open condition until the work-loaded piston is centered. FIG. 2 shows a modified control valve arrangement which requires only a momentary opening action of the control valve 43 for a time sufficient to cause actuation of

valves

25 and 23, after which it may be released. In this modified arrangement, an extension 4111 of line 41 is connected with the under area of the diaphragm chamber 50 of a pilot operable relief valve 51 and an extension 33a of line 33 is connected with the opposite area. Valve 51 connects an exhaust port 52 with a restricted passage 53 connected with line 45. A check valve 54 is connected in line 45 between the restricted passage 53 and the manually operable control valve 43. in the operation of this modified arrangement connecting the control valve with the unit, the control valve 43 is manually depressed and momentarily thereafter released. The momentary depression of the control valve is sufficicnt to cause actuation of

valves

23 and 25 by supply pressure air from branch line 44. The check valve 54 prevents relief of pressure air in line 45 through the exhaust 49 of the control valve. When the piston is above or below both

ports

42 and 34, there isno differential pressure acting on the pilot of the relief valve 51, and the latter remains closed. But when the piston finally stabilizes at its center point between

ports

42 and 34, the differential pressure that develops in the upper side of the diaphragm chamber 50 of the relief valve opens the latter, allowing

valves

25 and 23 to restore to normal as the pressure air in

lines

47 and 45 exhausts through the relief valve to port 52. The restriction 55 in passage 53 operates to delay exhausting of

lines

45 and 47 until the motion of the piston in coming to a stabilized centered condition ceases.

In the unit disclosed, the piston cylinder is designed to be held stationary permitting relative movement of the piston. It is apparent that in some applications the piston may be designed to be held stationary so as to permit relative movement of the cylinder.

lclaim:

l. A pneumatic load-balancing unit comprising: a cylinder containing a slidable piston; a reservoir containing pressure air for flowing in a normally closed circuit between the reservoir and the area of the cylinder below the piston; the piston having an externally projecting piston rod adapted to carry a work load; the pressure of air in the closed circuit serving to counterbalance the piston in the cylinder at a level determinable by the load placed upon the piston rod; and an arrangement ofinterconnected valves connecting the circuit with a pressure air supply line and with an exhaust line; the arrangement including a main valve having a normally closed condition; the arrangemcnt being adapted when the main valve is open to cause exhaust to the exhaust line of pressure air from the circuit during the time the piston is above a specific upper level, to cause admission of supply line air to the circuit during the time the piston is below a specific lower level, and to block both exhaust of pressure air from the circuit and admission of supply line air to the circuit when the piston obtains a balanced position between said levels, and the circuit remaining closed to both the supply and exhaust lines in the normally closed condition of the main valve regardless of change occurring in the level of the piston relative to said upper and lower levels.

2. A pneumatic load balancing unit as in claim 1, wherein said balanced position between said levels is substantially at the midpoint of the piston cylinder.

3. A pneumatic load balancing unit as in claim 1, wherein the arrangement of valves includes an exhaust valve having under the bias of a spring a closed condition blocking a connection of the main valve with the exhaust line when the piston is below said upper level and having under pressure of air in the circuit an open condition communicating the main valve with the exhaust line when the piston is above the said upper level; and includes a supply line valve having under the bias of a spring an open condition allowing supply line airflow to the main valve when the piston is below said lower level and having a closed condition under pressure of air in the circuit blocking supply line airflow to the main valve when the piston is above said lower level. I

4. A pneumatic load-balancing unit as in claim 1, wherein means is provided for causing restricted pressure airflow'in the circuit between the reservoir and the area of the cylinder below the piston during the time that the main valve is open.

5. A pneumatic load-balancing unit as in claim 1, wherein selectively operable valve means is provided in a branch of the supply line for applying supply line air to a pilot end of the main valve to cause opening of the latter.

. 6. A pneumatic load-balancing unit as in claim 5, wherein the selectively operable valve means is a manually operable normally closed control valve, and means is provided for automatically effecting after restoration of the control valve to normal relief of the air applied to the pilot end of the main valve. I

7. A pneumatic load-balancing unit comprising: a cylinder containing a slidable piston; a reservoir containing pressure airflowing in a normally closed circuit between the reservoir and the area of the cylinder below the piston, the cylinder area above the piston being at all times vented; the piston having an externally projecting piston rod adapted to carry a work load; the pressure of air in the closed circuit serving to counterbalance the piston in the cylinder at a level determinable by the load carried by the piston rod; a main pilot operable valve connected with the circuit having a normally closed condition under the bias of a spring blocking communication of the circuit with an exhaust line and with a pressure air supply line; and exhaust pilot operable valve having its pilot end con nected by a port at a specific upper level with the cylinder so as to be subject to pressure of air in the cylinder; the exhaust valve having a closed condition under the bias of a spring blocking the exhaust line when the piston is below said specific upper level in the cylinder, and having an open condition when the piston is above said specific upper level so as to allow exhaust of pressure air from the circuit to the exhaust line when the main valve is open; a supply line pilot operable 1 Valve having its pilot end connected with the cylinder by a port at a specific lower level so as t be subject to pressure of air in the cylinder; the supply line valve having an open condition under the bias of a spring when the piston is below said specific lower level in the cylinder so as to allow supply line airflow to the circuit when the main valve is open, and having a closed condition blocking the supply line when the piston is above said specific lower level, and the circuit remaining closed to the exhaust and supply lines during the period that the main valve is closed regardless of variations being made in the load value earried by the piston rod and regardless of the consequent change oecurmg in the level of the piston relative to said specific upper and lower levels.

8. A pneumatic load-balancing unit as inclaim 7 wherein

Claims

1. A pneumatic load-balancing unit comprising: a cylinder containing a slidable piston; a reservoir containing pressure air for flowing in a normally closed circuit between the reservoir and the area of the cylinder below the piston; the piston having an externally projecting piston rod adapted to carry a work load; the pressure of air in the closed circuit serving to counterbalance the piston in the cylinder at a level determinable by the load placed upon the piston rod; and an arrangement of interconnected valves connecting the circuit with a pressure air supply line and with an exhaust line; the arrangement including a main valve having a normally closed condition; the arrangement being adapted when the main valve is open to cause exhaust to the exhaust line of pressure air from the circuit during the time the piston is above a specific upper level, to cause admission of supply line air to the circuit during the time the piston is below a specific lower level, and to block both exhaust of pressure air from the circuit and admission of supply line air to the circuit when the piston obtains a balanced position between said levels, and the circuit remaining closed to both the supply and exhaust lines in the normally closed condition of the main valve regardless of change occurring in the level of the piston relative to said upper and lower levels.

3. A pneumatic load balancing unit as in claim 1, wherein the arrangement of valves includes an exhaust valve having under the bias of a spring a closed condition blocking a connection of the main valve with the exhaust line when the piston is below said upper level and having under pressure of air in the circuit an open condition communicating the maiN valve with the exhaust line when the piston is above the said upper level; and includes a supply line valve having under the bias of a spring an open condition allowing supply line airflow to the main valve when the piston is below said lower level and having a closed condition under pressure of air in the circuit blocking supply line airflow to the main valve when the piston is above said lower level.

4. A pneumatic load-balancing unit as in claim 1, wherein means is provided for causing restricted pressure airflow in the circuit between the reservoir and the area of the cylinder below the piston during the time that the main valve is open.

6. A pneumatic load-balancing unit as in claim 5, wherein the selectively operable valve means is a manually operable normally closed control valve, and means is provided for automatically effecting after restoration of the control valve to normal relief of the air applied to the pilot end of the main valve.

7. A pneumatic load-balancing unit comprising: a cylinder containing a slidable piston; a reservoir containing pressure airflowing in a normally closed circuit between the reservoir and the area of the cylinder below the piston, the cylinder area above the piston being at all times vented; the piston having an externally projecting piston rod adapted to carry a work load; the pressure of air in the closed circuit serving to counterbalance the piston in the cylinder at a level determinable by the load carried by the piston rod; a main pilot operable valve connected with the circuit having a normally closed condition under the bias of a spring blocking communication of the circuit with an exhaust line and with a pressure air supply line; and exhaust pilot operable valve having its pilot end connected by a port at a specific upper level with the cylinder so as to be subject to pressure of air in the cylinder; the exhaust valve having a closed condition under the bias of a spring blocking the exhaust line when the piston is below said specific upper level in the cylinder, and having an open condition when the piston is above said specific upper level so as to allow exhaust of pressure air from the circuit to the exhaust line when the main valve is open; a supply line pilot operable valve having its pilot end connected with the cylinder by a port at a specific lower level so as t be subject to pressure of air in the cylinder; the supply line valve having an open condition under the bias of a spring when the piston is below said specific lower level in the cylinder so as to allow supply line airflow to the circuit when the main valve is open, and having a closed condition blocking the supply line when the piston is above said specific lower level, and the circuit remaining closed to the exhaust and supply lines during the period that the main valve is closed regardless of variations being made in the load value carried by the piston rod and regardless of the consequent change occuring in the level of the piston relative to said specific upper and lower levels.

8. A pneumatic load-balancing unit as in claim 7, wherein selectively operable valve means is provided in a branch of the supply line for applying supply line air to the pilot of the main valve to cause opening of the latter.