US3537686A

US3537686A - Hoist and balancing apparatus

Info

Publication number: US3537686A
Application number: US733610A
Authority: US
Inventors: Lorne J Mckendrick
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-05-31
Filing date: 1968-05-31
Publication date: 1970-11-03
Anticipated expiration: 1987-11-03

Description

7 N 3, 7 L. J. M KENDRICK HOIST AND BALANCING APPARATUS Filed May 51, 1 968 Nov. 3, 1 0 J. M KENDRICK HOIST AND BALANCING APPARATUS 2 Sheet-Shet 2 Filed May 31, 1968 INVENTOR LORNE J- Mc KENDRICK BY Z M FIG.4

United States Patent 3,537,686 HOIST AND BALANCING APPARATUS Lorne ,I. McKendrick, 9212 Greenfield Road, Detroit, Mich. 48126 Filed May 31, 1968, Ser. No. 733,610 Int. Cl. B66d 1/36 US. Cl. 254-168 16 Claims ABSTRACT OF THE DISCLOSURE A pneumatic hoist in which a supported cylinder and a piston in the cylinder, connected to a load-attachment means, form a chamber for the introduction for compressed air which acts on the piston to develop a lifting force. A system is disclosed for controlling the pressure of compressed air admitted into the chamber. The system is adapted to selectively introduce air having one of three adjustable predetermined pressures chosen to balance either the weight of the load-attachment means, the combined weight of the load-attachment means and the load, or the weight of a load greater than the combination in order to lower, suspend, or raise the load. A safety valve in the system is arranged to trap the air in the cylinder behind the piston in the event of loss of source pressure so that a suspended load cannot accidentally drop.

BACKGROUND OF THE- INVENTION Field of the invention This invention relates to pneumatic hoists adapted to raise, lower and counterbalance a load in a suspended position to permit an operator to manually position a relatively heavy load, and more particularly to a device of this character having a novel control circuit for controlling the pressure of the air admitted into the hoist, a safety valve actuated in the event of loss of air pressure at the source to prevent a suspended load from dropping and novel remote control means for actuating the control circuit.

Description of the prior art A fluid-operated hoist comprising a supported cylinder having a fluid pressure-responsive piston connected to a load which is to be raised or lowered is disclosed in the prior art in British Pat. No. 590,413 and US. Pat. No. 2,176,979. In order to add to the raising and lowering functions of such hoists, means have been disclosed in the prior art which adapt the hoist for counterbalancing loads of different predetermined weights. For example, a system employing a first pressure regulating means'between the source of the pressurized fluid and the chamber for reducing the source pressure to balance the weight of the load-attachment means, and a second pressure regulating means between the source and the cylinder to reduce the source pressure to balance the combined weight of the attachment means and the load was disclosed in Pat. No. 2,613,903 to H. T. Platz.

The broad purpose of the present invention is to disclose a novel form of pneumatic control circuit for such a hoist which adapts the hoist to counterbalance a plurality of loads, of different predetermined weights and in addition to provide a safety valve in such a control circuit to prevent the accidental dropping of a suspended load in the case of a loss of source pressure.

SUMMARY OF THE INVENTION The preferred embodiment of the present invention, comprises a pneumatic hoist having a cylinder adapted for attachment to an overhead support such as a hook, or a trolley; a pressure-responsive piston disposed in the cylinder to form a fluid pressure chamber; and a hoist cable which passes around two sets of pulleys with one end anchored with respect to the cylinder and its other end adapted for attachment to a load. One set of pulleys is fixed against motion in the center of the cylinder and the other set is carried by a guide piston connected by a pair of piston rods which pass on either side of the fixed set of pulleys to the pressure-responsive piston. The admission of compressed air into the chamber forces both pistons toward the center of the cylinder so that the movable pulleys separte from the fixed set of pulleys causing the cable to be drawn into the cylinder a distance equal to the piston storke, multiplied by the number of pulleys. When the pistons are moved away from the center of the hoist, the movable set of pulleys approach the fixed set to allow the cable to lower the load.

The control circuit may take any of several forms but essentially comprises a master pressure-regulating valve disposed in a connection between the source of air pressure and the pressure chamber in the cylinder, a safety valve disposed between the master pressure regulator and the chamber and three control pressure regulator valve means which are connected in such a manner as to control the master pressure regulating valve. Each of the control pressure regulator valve means has an inlet connected with the source of air pressure and an outlet connected with the master pressure regulator to transmit a pneumatic signal of a preset pressure to the master pressure regulator.

The first control pressure regulator valve means signals the master regulator to introduce air pressure into the chamber that will balance the load-attachment means including the hoist cable so that with positive pressure in the chamber the operator can raise and lower the cable to attach the load. The second control pressure regulator means signals the master pressure regulator to reduce the source pressure to a level which when introduced into the chamber will balance a load of a predetermined Weight at tached to the cable in a suspended position. The third control pressure regulator signals the master pressure regulator to admit air into the chamber that is greater than the pressure associated with the second control regulator.

The master pressure regulating valve thus acts as a slave to the three control regulators and responds to the receipt of a signal received from a selected one of the control regulators by introducing a pressure corresponding to the particular signal into the chamber to either move or balance the piston. Thus if the signal is received from the first regulating valve, the master regulator introduces the lowest of the three predetermined pressures into the chamber which allows the operator to raise and loWer the cable for attachment to the load. After the cable has been attached to the load, the operator then actuates the third regulator to raise the load. At a desired height, the operator actuates the second regulator to suspend the load in a balanced condition for manual positioning. The operator can manually position the load with respect to its suspended position a distance which is a function of the compressibility of the air in the cylinder. The hoist is often employed to enable the operator to precisely position a relatively heavy load such as a workpiece in some sort of fixture in a production assembly line. To lower the load, the operator actuates the first control regulator to reduce the pressure in the cylinder behind the piston thereby reducing the lifting forceand allowing the load to lower of its own Weight.

Ordinarily it is desirable for the operator to have the capability of signalling the control regulator means from a remote position with respect to the supported position of the hoist cylinder. In one form of the invention, the control pressure regulator means are pneumatically, pilotactuated from a hand control carried by the operator. In another form of the invention, the control pressure regulators are actuated by a push-pull cable carried by the operator. This latter embodiment has a number of advantages over the pneumatic system. One advantage is that the reduction in the number of pneumatic lines reduces the possibility of one of the lines being accidentally severed and causing a loss of air pressure in at least part of the system. Another advantage of the push-pull cable system lies in its overall simplicity and reliability.

Because the hoist employs positive air pressure in each of its three pressurized conditions, that is, the raise, lower, and load-balancing conditions, as opposed to other systems which apply a positive air pressure and then bleed pressure from the system to move the load, the preferred system readily adapts itself to a safety feature arranged to prevent the load from being accidentally dropped upon the occurrence of an abnormal drop in the source pressure as when a line is ruptured. The safety feature comprises a safety valve connected between the outlet of the master pressure regulator and the inlet of the pressure chamber which is controlled by a connection at the source of the air pressure which senses an abnormal drop in the air pressure. When such a drop occurs, the safety valve closes before the drop in pressure can be reflected from the output of the master pressure regulator. When the safety valve closes, it traps the air pressure in the pressure chamber behind the piston so that if the hoist is in a balancing condition, the load is locked in a suspended position. This safety feature thereby eliminates the possibility of the operator being injured by a dropping load and obviates the possibility of a load being damaged by an accidental impact caused by dropping.

Thus it can be seen that the preferred control system adds to the capability and safety of air hoists of the cylinder and piston type. Other advantages of the present invention will readily become apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description.

DESCRIPTION OF THE DRAWINGS The description refers to the accompanying drawings in which like reference characters refer to like parts throug11- out the several views and in which:

FIG. 1 is a perspective view showing the preferred air hoist and balancing apparatus;

FIG. 2 is a schematic view of one preferred control circuit for the air hoist of FIG. 1;

FIG. 3 is a view of the control regulator valves individually mounted in a support and controlled by a cam; and

FIG. 4 is a view showing the control valves in a different arrangement mounted in a common housing with a spool element arranged to selectively open and close the valves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to the drawings; FIG. 1 illustrates a preferred air hoist and balancing apparatus generally indicated at 10, as comprising an air hoist 12 and a control system 14 mounted on the side of the air hoist. The hoist comprises an elongated cylinder 16 having an end plate 18 closing one end of the cylinder. A support member 20 adjacent the other end of the cylinder is connected to the end plate 18 by rods 22. A support member 24 attached to the cylinder 16 is adapted to support the cylinder to suitable overhead support means (not shown) which may take the form of a hook attached to the ceiling of a building or a suitable trolley system when the hoist is to be moved horizontally. A pressure-responsive piston 26 and a guide piston 28 are slidably disposed in the cylinder 16 and connected to one another by a pair of rods 30, only one of which is shown, so that the two pistons move together within the cylinder.

The edges of the piston 26 are sealingly engaged with the walls of the cylinder 16 to form a fluid pressure chamber 32 between the piston 26 and the end plate 18.

The introduction of compressed air into the chamber 16 produces motion of the piston 26 away from the end plate 18 and enlarges the volume of the chamber 32. Similarly, motion of the piston 26 toward the end plate 18 reduces the volume of the chamber 32.

A plurality of cable pulleys 34 is supported for rotation by a support member 36 at the midsection of the cylinder 16 in such a manner that the pulleys are fixed against motion with respect to the cylinder. A second set of cable pulleys 40 is carried by the piston 28 so that the pulleys 40 move toward and away from the pulleys 34 as the

piston members

26 and 28 reciprocate within the cylinder 16. A load-supporting cable 42 having one end anchored in the cylinder 16 is successively wrapped around the fixed pulleys 34 and the movable pulleys 40 with its outer end extending through an opening 44 in the cylinder below the fixed pulleys. The outer end of the cable 42 is attached to a hook means 46 to form a loadattachment means and is adapted to engage a load 48 having a predetermined weight. The cable 42 is arranged so that as the movable pulleys separate from the fixed pulleys the hook means 46 is raised toward the cylinder and as the movable pulleys move toward the fixed pulleys, the hook means 46 can be moved down and away from the cylinder. The relative motion between the two sets of pulleys causes the hook means 46 on the end of the cable to move a distance which is a function of the stroke of the

pistons

26 and 28 multiplied by the number of pulleys employed.

The load 48, for purposes of illustration, is described as having a predetermined weight which is typical in a production line where the hoist 10 is employed for positioning a succession of workpieces in a fixture, each of the workpieces having a similar weight. The control system 14 is adjusted to accommodate this weight and as illustrated in FIG. 2, provides a connection between a source 50 of fluid under pressure such as compressed air, and the fluid chamber 32. The control system allows the operator to introduce air into the chamber 32 having a selected one of three predetermined pressures each of which corresponds to the balancing pressure of a predetermined Weight. One of the predetermined pressures when introduced into the chamber 32 balances the piston 26 and the Weight of the hook means 46 and cable 42. A second higher pressure can be selected to balance the combined weight of the hook means 46, the cable 42 and the load 48. The third or highest pressure is adapted to counterbalance a weight which is in excess of the combined weight of the hook means 46, the cable 42 and the load 48.

To achieve this balance control, the control circuit 14 has a conduit 52 connecting the source 50 and the inlet of the chamber 32, and a master pressure regulating valve 54 in the conduit of the type which responds to a pneumatic signal by providing a pressure reduction of the source pressure to a pressure corresponding to the signal. The master regulating valve 54 acts as a slave to three

control relay valves

56, 58 and 60, each having an outlet connected by a common fluid connection 62 to the control element of the master regulating valve 54. This system allows a single master pressure regulating valve to respond to a signal from any number of control sources to control the inlet pressure of the chamber 32 as opposed to systems which employ a plurality of control valves, each having an outlet directly to the chamber 32.

The

control valves

56, 58 and 60 each have an input from

pressure regulators

62, 64 and 66 respectively. The

regulators

62, 64 and 66, in turn, each have an inlet connected with the source pressure through a conduit 68 so that the inlet pressure to the master regulator 54 and the

regulators

62, 64 and 66 are the same. The

regulators

62, 64 and 66 are normally adjusted to reduce the air pressure to a predetermined level with the

valves

56, 58 and 60 providing means for selectively opening a connection from one of the control regulators to transmit a pneumatic signal to the master regulator of a pressure corresponding to the output of the selected regulator.

For purposes of illustration, the source pressure is 80 p.s.i. The outlet of the pressure regulator 66 is at 3 p.s.i., the lowest of the three predetermined pressures and corresponds to the pressure that balances the weight of the cable 42 and the hook means 46.

The second regulator 64 is adjusted to reduce the 80 p.s.i. source pressure to 70 p.s.i., which is sufficient when introduced into the chamber 32 to balance the combined weight of the cable 42, the hook means 46 and the load 48 in a suspended position. The third pressure regulator 66 has an output which will balance a suspended weight which is greater than the combined weight of the cable 42, the hook means 46 and the load 48. For purposes of illustration, regulator 66 has an output corresponding to the source pressure, that is to say its inlet and its outlet have the same pressure.

The master regulating valve 54 is adapted to reduce the pressure at its inlet to a pressure corresponding to the signal received from any of the control valves. That is, it will reduced the 80 p.s.i. pressure to 3 p.s.i., 70 psi, or merely pass the source pressure through depending upon which control valve is transmitting a signal.

The

valves

56, 58 and 60 are in turn controlled by hand control means 70 which are arranged to selectively open one of the relay valves, 56, 58 or 60. It is to be understood that normally only one of the control valves will be opened, with the other two being closed at any given time. The master regulating valve 54 has an atmospheric exhaust 72 for relieving the air pressure in the chamber 32 when the selection of the control valves is such that the pressure in the chamber is reduced. The atmospheric outlet also compensates for thermal expansion or displacement of the piston 26 in the cylinder caused by the operator positioning the load so that the pressure within the chamber 32 does not exceed the pressure corresponding to the signal of the master regulator 54.

The hand control means 70 allows the operator of the hoist to remotely actuate the

control valves

56, 58 and 60 which are normally in an overhead position. There are a variety of methods for remotely actuating the control relay valves, two of which will be described and which consist of a pneumatic pilot-actuated means illustrated in FIG. 2, and a push-pull cable means illustrated in FIGS. 3 and 4.

In its pneumatic form, the hand control means 70 comprises elongated

pneumatic lines

74, 76 and 78 each having one end connected to the

valves

60, 58 and 56 respectively, and their opposite ends connected to pilot

valves

80, 82 and 84 which are mounted in a suitable hand grip. The three

pneumatic lines

74, 76 and 78 are enclosed within a protective cover which protects the flexible connections against fracture. The inlets of the

pilot valves

80, 82 and 84 are connected by a flexible pneumatic line 88 to the connection 52 so that they are exposed to the source pressure. The

pilot valves

80, 82 and 84 are arranged for actuation by

cams

92, 94 or 96 in such a manner that when one of the valves is open, the other two are closed. This arrangement is a substantially conventional means for enabling the operator to remotely actuate a pneumatic device, so that a more detailed discussion is not necessary to enable one skilled in the art to assemble such a hand control means.

In practice, assuming the load 48 is disconnected from the hook means 46, the operator actuates the valve 80 to transmit a signal to the relay valve 60 thereby transmitting a pneumatic signal to the master regulator 54 which in turn introduces compressed air into the chamber 32 to balance the weight of the cable 42 and the hook means 46. The operator can then with a nominal effort attach the hook means to the load 48; The natural inherent compressibility of air is such that the operator can pull the cable and move the movable pulleys 40 toward the fixed pulleys 34, in turn moving the piston 26 in such a manner as to reduce the volume of the chamber 32 and compress the air in the chamber 32. The advantage of this compressibility is that the extended portion of the cable 42 is not locked to the hoist but allows the operator to position the hook means 46.

Having attached the hook means 46 to the load 48, the operator then opens the pilot valve 84 which actuates the relay valve 56 so as to transmit a signal to the master regulating valve 54 which responds to the signal by admitting air into the chamber 32 having a pressure producing a force imbalance on the piston 26 so that the piston moves away from the end plate 18 and causes the movable pulleys 40 to separate from the fixed pulleys 34, thereby retracting the cable 42 into the cylinder and raising the load 48.

The load 48 is raised to a desired height at which time the operator actuates the pilot valve 82 which, in turn, opens the relay valve 58 to send a signal to the master regulating valve 54 which admits air into the chamber 32 to balance and suspend the load 48. With the load in its balanced, suspended state, the operator then positions it in a suitable fixture by moving the load with a fairly nominal force; that is to say, even though the balanced load may weigh several hundred pounds, the operator can easily manually position it in a suitable fixture. Having positioned the load, the operator then disconnects the hook means 46 from the load, or lowers the load by opening the valve so that the relay valve 60 signals the master regulating valve 54 to admit low pressure air into the chamber 32 so that the resulting force imbalance created on the piston allows the movable pulleys to move toward the fixed pulleys, which in turn, allows the load to drop.

It is to be noted that there is at all times a positive air pressure in the chamber 32 and that control of the motion of the piston 26 to raise, lower or balance the load is eifected by introducing air under a different predetermined pressure into the chamber 32 as opposed to a system which bleeds the pressure from the chamber to lower the load. To eliminate the possibility of the load accidentally being dropped from a suspended position by a suddent loss in the pressure at the source 50 or by a rupture in one of the pneumatic lines, a safety valve 98 is connected in the conduit 52 between the master regulating valve 54 and the inlet to the chamber 32. The valve 98 is a pilot-actuated valve controlled by a connection 100 which senses the pressure of the air being delivered from the source 50. In the event of a sudden drop in air pressure at the source below some predetermined level, the valve 98 closes, thereby trapping the air in the chamber 32. Assuming the load 48 is in a suspended position, and balanced by air pressure of 70 p.s.i. in the chamber 32, a drop in the pressure from the source pressure of 80 p.s.i. will be sensed by the valve 98 which closes before the drop is reflected in the output of the master pressure regulating valve 54 so that the air confined in the chamber 32 is at substantially the pressure which corresponds to the last signal transmitted to the regulating valve 54.

This safety valve 98 provides an important and significant feature of this system in that it prevents the load from accidentally dropping and injuring the operator, or damaging expensive fixtures or an expensive workpiece that is being raised or lowered by the hoist.

FIG. 3 is a view showing one way in which the

control valves

56, 58 and 60 can be arranged in a compact manner. The

valves

56, 58 and 60 are illustrated as being plunger-actuated valves mounted in a support 102 and having spring-loaded,

depressible plungers

104, 106 and 108 respectively which, when released, open their respective valves to transmit a pneumatic signal to the master regulating valve 54. An elongated spool 110 is slidably mounted on the support 102 and has cam surfaces 112, 114 and 116 adapted to engage the

plungers

104, 106 and 108 respectively. The spool 110 is normally disposed in one of three selected positions. In each of these positions one of its cam surfaces opens its associated relay valve with the other two valves being depressed in a closed condition. As viewed in FIG. 3, the valve 56 is open and the

valves

58 and 60 are closed.

The motion of the spool is controlled by an elongated push-pull cable 118 having its remote end connected to a handle means generally indicated at 120. The handle means comprises a housing member 122 which the operator normally grips in his hand and an actuator member 124 slidably disposed in the housing for motion between three positions corresponding with the three positions of the spool 110. A handle member 126, pivotally mounted on the housing member 122, engages the actuator member 124 so that the operator by tilting the handle 126 in one direction moves the spool member to open one of the relay valves, tilting the handle in its opposite position, moves the spool to open the second of the three relay valves and by positioning the handle 126 so that it is in its neutral position opens the third of the three relay valves.

The advantage of employing a push-pull cable as opposed to a pneumatic remote signalling system is that there are fewer pneumatic connections that can be accidentally severed so as to cause a loss of air pressure in the system. In addition, if the push-pull cable is damaged or kinked, there is no loss of air pressure. Furthermore, the push-pull cable arrangement is a much simpler and reliable mechanism because there is only one cable between the operators handle and the valve as opposed to a plurality of pneumatic hoses which normally connect the handle control with the valves in a pilot actuated system.

It is to be noted that the control valve arrangement illustrated in FIG. 3 employs three separate valves and a spool having cams engageable with each of the valves. FIG. 4 illustrates another similar arrangement but in which the three relay valves are mounted in a single housing 128 having a bore 130 in which is slidably disposed a spool 132. The housing has three

inlets

134, 136 and 140 connected with the regulating

valves

62, 64 and 66 respectively, and a pair of outlets 142 and 144 connected with the master regulating valve 54. In this arrangement, the spool 132 has a pair of annular grooves 146, 148, separated by a land formed so that when the spool 132 is actuated by a push-pull cable 152, it can be disposed in one position, as illustrated in FIG. 4 where it opens a connection between the inlet 140 and the outlet 144 and closes the

inlets

136 and 134. In a second, shifted position, the spool 132 closes the inlet 140, the land 150 closes the inlet 136 and the groove 146 opens the connection between the inlet 134 and the outlet 142. In a third, shifted position, the spool 132 closes the

inlets

140 and 134, and opens the connection between the inlet 136 and the outlet 144. This valve arrangement illustrates another simplified arrangement which may be employed in the preferred control circuit.

Thus it can be seen that I have described in detail, an improved hoist and balancing system using positive fluid pressure at all times to raise, lower and balance a load of a predetermined weight. The preferred system has a number of advantages over other systems utilizing a bleed system where once a positive pressure has been established to support a load and its attachment, the lowering and unloading of the load is accomplished by bleeding some of the pressure to the atmosphere. The disadvantage of the bleed system is that the rate at which the load is lowered depends on the rate that the pressure is bled from the hoist which is subject to area changes in the bleed valve due to the formation of varnishes and other contaminants that are present in air systems. Because of this change in orifice area of the bleed valve periodic readjustments of the control system are required to achieve consistent operation.

By providing the control system with three predetermined balanced pressures that can be admitted into the hoist, the following advantages are available. When the load attachment means alone are in a state of balance,

the operator with a slight effort can move the hook means 46 up or down through the complete range of the hoist cable travel without operating the hand control. After manually lowering the hook means to a position where it can be attached to the load, it remains positioned so that it can be attached to the load. After the load has been attached, the hand control can be repositioned to the position associated with the highest pressure so that the air pressure behind the piston is sufiicient to support as well as raise the load. Normally the difference between the pressure associated with raising the load and the pressure for balancing the load in a suspended position are adjusted or trimmed so that with the higher pressure, due to the inherent friction in the system, the hoist does not raise the load until the operator manually assists in raising the load upward. Once the friction forces in the system have been momentarily overcome, the air pressure is then sufiicient to keep the piston moving and the hoist to continue lifting until the operator applies resistance to the load to stop its motion, whereby the inherent friction in the system then holds the load at rest. The hoist will then support the load in this new position until it is moved upwardly again. The load can be lowered by the operator by applying a manual downward force on the load which requires some effort, however, by positioning the remote control means to admit the air with the lowest pressure into the chamber, the load can then belowered without effort. The system can also be adjusted so that the intermediate pressure and the lowest pressure are relatively close so that the load does not automatically commence dropping when the control is shifted from the intermediate pressure to the lowest pressure until the operator applies a slight manual downward force to overcome the inherent friction of the system so that it commences its downward motion.

The control system has a fail safe feature in that if the air pressure at the source drops, the safety valve traps the pressure existing in the chamber at the occurrence of the pressure drop so that the hoist continues to respond to the last signal received by the master regulating valve. Although under these circumstances the operator is unable to change his selection, he can in fact continue to position the load although he is restricted to the one selection in which the master regulating valve is in at the occurrence of the failure.

The tail safe feature of the present invention provides another significant advantage over those conventional systems in which the pressure in the system is lowered to move the load by bleeding the pressure to atmosphere as opposed to going from one predetermined, positive pressure level to a second, positive pressure level. In the bleed system, if a pressure line is severed, the total system loses pressure and the load drops. In the system illustrating the present invention, the accidental severing of a line results in the load remaining in the condition existing at the occurrence of the failure because of the positive pressure in the pressure chamber and the safety valve.

Although I have described several embodiments of my invention, it is to be understood that various changes and revisions can be made therein without departing from the spirit of the invention as expressed in the scope of the appended claims.

I claim:

1. A hoist and balancing apparatus comprising:

cylinder means adapted for connection to a support;

a piston disposed in said cylinder means to form a movable wall of an expansible fluid pressure chamber having an inlet for receiving fluid under pressure;

load attachment means connected to said piston and adapted for connection with a load to raise the load as the piston is moved in the cylinder;

a source of fluid pressure;

means connecting said source to the pressure chamber of said cylinder, including:

a master pressure regulating valve having an inlet connected to said source, an outlet connected to the inlet of said chamber, said master pressure regulating valve being adapted to receive first and second pneumatic signals and being operable upon receipt of a selected one of said pneumatic signals to deliver fluid to said chamber at a predetermined pressure corresponding to the signal to move said piston; and

control means for transmitting a selected one of said pneumatic signals to said master pressure regulating valve, said control means comprising a first normally closed control regulator valve means having an input connected to said source and an output connected to said master pressure regulating valve, and a second normally closed control regulator valve means having an input connected to said source and an output connected to said master control regulating valve, said first control regulator valve means being adapted to reduce the pressure of fluid received from the source of a first predetermined pressure to produce the first pneumatic signal and said second control regulator valve means being adapted to reduce the pressure of fluid received from the source to a second predetermined pressure to produce the second pneumatic signal, and including means for selectively opening said first and second control regulator valves for the transmission of one of said pneumatic signals to the master pressure regulator valve.

, 2. The combination as defined in claim 1, wherein said last mentioned means comprises an elongated pushpull cable having one end operatively connected to said first and second regulating valves and its opposite end remotely connected with respect to the cylinder to a handle having a control member supported for movement to a first position which opens the first control regulator valve means and movement to a second position which opens the second control regulator valve means for the transmission of a pneumatic signal.

3. The combination as defined in claim 1, wherein said first and second control regulator valve means comprises a valve housing having first and second inlets and an outlet connected to said master pressure regulating valve, said inlets and said outlet being connected to a common bore in the housing, a first pressure regulator having an inlet connected to said source and an outlet connected to the first inlet of said housing, a second pressure regulator having an inlet connected to the source and an outlet connected to the second inlet of said housing, and a spool valve supported in the bore of said housing for motion between the first position in which it opens a connection between the first inlet and the outlet and closes a connection between the second inlet and the outlet, and a second position in which it opens the connection between the second inlet and the outlet and closes the connection between first inlet and the outlet.

4. The combination as defined in claim 1, including a safety valve connected between said master pressure regulating valve and said fluid chamber, said safety valve normally being open for the transmission of fluid under pressure from the master pressure regulating valve to the fluid chamber and being operable upon closing to maintain the fluid pressure in said chamber; and means responsive to a drop in pressure of the fluid delivered from the source to the master pressure regulating valve to close the safety valve.

5. The combination as defined in claim 4, wherein said pressure responsive means senses the fluid pressure delivered from the source to the master pressure regulating valve and is operable to close the safety valve before the pressure drop is reflected in the output in the pressure regulator.

6. The combination as defined in claim 1, wherein said load attachment means is arranged so that a load supported by the attachment means biases the piston in a first direction in the cylinder means and the pressure of the fluid in the chamber biases the piston in the second, opposite direction to develop a lifting force opposing motion of the piston in the first direction so that a reduction in the pressure of the fluid in the chamber reduces the lifting force applied by the piston on the load.

7. The combination as defined in claim 1, wherein the master pressure regulating valve introduces fluid into the chamber of a first pressure to balance a load of a first weight upon receipt of the first pneumatic signal and introduces fluid into the chamber of a second pressure to balance a load of a second weight upon receipt of the second pneumatic signal.

8. The combination as defined in claim 1, wherein said master pressure regulating valve introduces fluid into the chamber of a first pressure to balance a load of a predetermined weight upon receipt of the first pneumatic signal and introduces fluid into the chamber of a second pressure to balance said load attachment means upon receipt of the second pneumatic signal.

9. The combination as defined in claim 8, wherein the master pressure regulating valve introduces fluid of a first pressure into said chamber to balance the load in a suspended position upon receipt of the first pneumatic signal, and introduces fluid of a lesser pressure into the chamber to move the piston and lower the load upon receipt of the second pneumatic signal.

10. The combination as defined in claim 1, wherein the master pressure regulating valve introduces fluid into the chamber of a first predetermined pressure to balance a first load of a predetermined weight in a suspended upon receipt of the first pneumatic signal, and introduces fluid into the chamber of a second predetermined pressure sufficient to balance a second load of a weight greater than the weight of the first load so that introduction of the second pressure into the chamber after the first load has been balanced in a suspended position with the first pressure moves the piston to raise the load as the fluid pressure in the chamber increases from the first pressure to the second pressure.

11. The combination as defined in claim -1, wherein said control means is adapted to selectively transmit one of three predetermined signals to said master pressure regulating valves including a first signal to which the master pressure regulating valve responds by transmitting fluid pressure to the chamber which will balance the weight of said load attachment means, a second signal to which the master pressure regulating valve responds by transmitting fluid pressure to the chamber which will balance the combined weight of said load and said load attachment means, and a third signal to which the master pressure regulating valve responds by transmitting fluid pressure to the chamber which will balance a second load having a weight in excess of said combined weight so that the transmission of the first signal to the master pressure regulating valve causes the piston to lower the load away from the cylinder means, the transmission of the second signal to the master pressure regulating valve causes the piston to balance the load and the load attachment means so that an operator can raise or lower the load by applying a nominal force on the load, and the transmission of the third signal to the master regulating valve causes the piston to raise the load toward the cylinder means.

12. A hoist and balancing apparatus comprising:

cylinder means adapted for connection to a support;

a piston disposed in said cylinder means to form a movable wall of an expansible fluid pressure chamber having an inlet for receiving fluid under pressure; load attachment means connected to said piston and 11 adapted for connection with a load to raise the load as the piston is moved in the cylinder; a source of fluid pressure; means connecting said source to the pressure chamber of said cylinder, including:

a master pressure regulating valve having an inlet connected to said source, an outlet connected to the inlet of said chamber, said master pressure regulating valve being adapted to receive first, second and third pneumatic signals and being operable upon receipt of a selected one of said pneumatic signals to deliver fluid to said chamber at a predetermined pressure corresponding to the signal to move said piston; and

control means for transmitting a selected one of said pneumatic signals to said master pressure regulating valve, said control means comprising first, second and third normally closed regulator valve means each having an input connected to said source and an output connected to said master pressure regulating valve for selective transmission of first, second and third pneumatic signals, respectively, said master pressure regulator being responsive to receipt of the first pneumatic signal to transmit pneumatic pressure to the fluid chamber of said cylinder which will balance the weight of said load attachment means, being responsive to the receipt of the second pneumatic signal to transmit pneumatic pressure to the chamber of said cylinder which will balance the combined Weight of said load and load attachment means, and being responsive to receipt of the third pneumatic signal to transmit pneumatic pressure to the chamber which will balance a load having a predetermined weight in excess of said combined weight so that when the first mentioned load is raised by the load attachment means to the raised position, the transmission of the first signal to the master pressure regulating valve, causes the piston and the load attachment means to lower the load, the transmission of the second signal to the master presure regulator valve causes the load to be balanced in a suspended position and the transmission of a third signal to the master pressure regulating valve causes the piston and the load attachment means to raise the load toward the cylinder.

13. The combination as defined in claim 12, including a cam member engaged with each of said regulating valves and supported for movement to a first position in which it opens the first regulator valve means, a second position in which it opens the second regulator valve means, and a third position in which it opens the third regulator valve means.

14. The combination as defined in claim 13, wherein said master regulating valve and the first, second and third regulator valve means are mounted adjacent said cylinder means, and including a push-pull cable means having one end connected to said cam and its other end adapted to provide means for remotely providing an actuating motion to said cam.

15. A load positioning system comprising:

a pressure energy translating device for positioning a load in response to fluid pressure supplied thereto;

a source of fluid pressure;

valve means responsive to first and second selected fluidic signals for delivery of fluid pressure from said source to said pressure energy translating device at a predetermined pressure corresponding to that selected fluidic signal received by said valve means; and control means for selectively transmitting said fluidic signal comprising first and second normally closed valves, each having an input connected to said source and an output connected to said valve means, said first normally closed valve being adapted to reduce the pressure of fluid received from the source to a first predetermined pressure to produce said first fluidic signal, said second normally closed valve being adapted to reduce pressure received from the source to a second predetermined pressure to produce said second fluidic signal; and means for selectively opening said first and second normally closed valves for the transmission of one of said fluidic signals to said valve means.

16. The combination as defined in claim 15, wherein said first and second selected fluidic signals are pneumatic signals.

References Cited UNITED STATES PATENTS 2,414,451 1/1947 Christensen --54.5 2,939,431 6/1960 Bottje 254-168 3,260,508 7/1966 Powell 254--168 3,418,807 12/1968 Frost 6054.5

HARVEY C. HORNSBY, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 537, 686 Dated November 3 1970 InV8ntO1'(S) L. J. McKendrick It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 12, change "storke" to -stroke- Column 5, line 45, before the numeral 3" insert the numeral --l Column 6, line 41, delete "suddent" and insert -sudden Column 10, line 36, after "suspended" insert -position- Column 11, line 31, after "and" insert -said-- Slfih'iu Aiffi IBM 1:. mm B- m. Goa-1:51am 01' Paint! FORM P0-I USCOMM-DC wan-Poo