U.S. patent number 3,773,296 [Application Number 05/187,870] was granted by the patent office on 1973-11-20 for pneumatic balancing hoist.
Invention is credited to Lorne J. McKendrick.
United States Patent |
3,773,296 |
McKendrick |
November 20, 1973 |
PNEUMATIC BALANCING HOIST
Abstract
A pneumatic hoist for raising, lowering or balancing a variable
weight load in a suspended position by regulating air pressure in a
power chamber. A hand-held vent valve is employed to select the
pressure necessary to balance the weight of each load as it is
being raised.
Inventors: |
McKendrick; Lorne J. (Milford,
MI) |
Family
ID: |
22690835 |
Appl.
No.: |
05/187,870 |
Filed: |
October 8, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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640 |
Jan 5, 1970 |
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Current U.S.
Class: |
254/386;
137/116.5 |
Current CPC
Class: |
B66D
3/18 (20130101); Y10T 137/261 (20150401) |
Current International
Class: |
B66D
3/00 (20060101); B66D 3/18 (20060101); B66d
003/08 () |
Field of
Search: |
;254/168,186,15FH
;137/116.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Aegerter; Richard E.
Assistant Examiner: Maffei; Merle F.
Parent Case Text
This is a continuation of application Ser. No. 640 filed Jan. 5,
1970 now abandoned.
Claims
Having described my invention, I claim:
1. A hoist suitable for hoisting a series of loads of different
weights, said hoist comprising:
a pneumatically-operated device having a fluid power chamber;
a piston disposed in the power chamber for movement according to
fluid power chamber pressure;
a hoisting member having means at one end for connection to a load,
and the other end connected to hoist the load according to piston
movement;
a source of air under pressure;
an elongated fluid conduit having one end connected to the source
of air pressure;
a pilot operated valve comprising:
means defining an inlet for receiving air from said source of air
under pressure;
means defining an outlet communicating through said pilot operated
valve with said inlet, said outlet operatively communicating with
the fluid power chamber of the pneumatically operated device to
provide pressurized air thereto;
means defining a control chamber;
means defining a passage connecting said control chamber to said
outlet so that outlet pressure is communicated to said control
chamber;
means defining a pilot chamber, said pilot chamber having a passage
to the atmosphere;
a wall disposed between said control chamber and said pilot
chamber, said wall having an opening which connects said control
chamber to said pilot chamber;
a hollow pressure-sensitive device housed in said control chamber,
the interior of said hollow pressure-sensitive device being
operatively connected to said elongated fluid conduit between its
ends so that the interior of said hollow pressure-sensitive device
is subjected to said air pressure from said source, and the outer
surface of said hollow pressure-sensitive device being exposed to
the outlet pressure in said control chamber, so that said
pressure-sensitive device expands and contracts in response to a
differential pressure between the outlet pressure in said control
chamber and the air pressure in the interior of said
pressure-sensitive device;
said inlet of said pilot operated valve being operatively connected
to said elongated fluid conduit between said end of said elongated
fluid conduit connected to the source of air pressure and said
operative connection of said hollow pressure-sensitive device to
said elongated fluid conduit;
a valve operatively connected to the outer surface of said
pressure-sensitive device, said valve being disposed in said
opening in said wall between said control chamber and said pilot
chamber to control the communication between said control chamber
and said pilot chamber to close said opening in said wall when said
pressure-sensitive device expands due to a differential higher
internal pressure, and to open said opening when said
pressure-sensitive device contracts due to a differentially higher
pressure on its outer surface;
a spacer forming a movable wall between said outlet and said wall,
said pilot chamber being defined by said spacer and said wall, said
spacer having a relief passage connected said outlet to the
atmosphere;
a valve disposed in said relief passage to control the opening and
closing of said relief passage;
a valve disposed between said inlet and said outlet to close and
open the communication therebetween,
so that when the outlet pressure is less than either the pilot
pressure or the inlet pressure, the air pressure in said control
chamber is equal to the outlet pressure causing said
pressure-sensitive device to open said valve disposed in said
opening in said wall between said control chamber and said pilot
chamber, and as the outlet pressure increases, the pressure in said
control chamber increases to a value greater than the air pressure
interior to said pressure-sensitive device causing said
pressure-sensitive device to contract closing said valve in said
opening in said wall between said control chamber and said pilot
chamber; and
a control member mounted on the opposite end of the fluid conduit
adjacent said load connecting means of said housing member for
venting air pressure from said elongated fluid conduit to thereby
control the pressure of air admitted to said pressure-sensitive
device thereby controlling the pressure of the air admitted to the
power chamber from the outlet of the pilot-operated valve, the
control member consisting of a single needle valve cooperating with
a port so that said control member is infinitely variable between
fully opened and fully closed positions of said needle valve, a
knob carried by said needle valve and a handle disposed beneath
said knob whereby said handle can be manipulated by the thumb of
the user to rotate said needle valve to permit selective variation
of pilot fluid pressure according to the weight of a load being
hoisted by the hoisting member.
2. A hoist as defined in claim 1, in which the pilot-operated valve
is responsive to a differential between power chamber pressure and
pilot fluid pressure.
3. A hoist as defined in claim 1, including a relief valve means
mounted on said pneumatically-operated device so as to be
responsive to power chamber pressure being greater than pilot fluid
pressure.
4. A hoist as defined in claim 1, including a handle structure
connected to the hoisting member so as to be movable with the
hoisting member, and in which the control member is mounted on the
handle structure.
5. In combination, a pneumatically operated hoist having a hoist
housing, a piston assembly movable in said housing, a first set of
pulleys fixed within said housing, a second set of pulleys within
the housing supported by said assembly for movement therewith
towards and away from said first set of pulleys, a cable wound
around said first and said second set of pulleys having one end
anchored in said housing, the other end of said cable extending out
from said housing for attachment to and support of a load therein,
a fluid pressure chamber defined between the front end of said
piston assembly and one end of said housing, means supplying said
fluid pressure chamber with fluid under pressure to move said
piston assembly and said second set of pulleys towards or away from
said first set of pulleys, said means comprising a
a pilot operated valve including:
means defining an inlet connected with a source of fluid
pressure;
means defining an outlet communicating through said pilot operated
valve with said inlet, said outlet operatively communicating with
the fluid pressure chamber of the said hoist to provide pressurized
air thereto;
means defining a control chamber;
means defining a passage connecting said control chamber to said
outlet so that outlet pressure is communicated to said control
chamber;
means defining a pilot chamber, said pilot chamber having a passage
to the atmosphere;
a wall disposed between said control chamber and and said pilot
chamber, said wall having an opening which connects said control
chamber to said pilot chamber;
a hollow capsule housed in said control chamber, the interior of
said hollow capsule being operatively connected to said elongated
fluid conduit between its ends so that the interior of said hollow
capsule is subjected to said air pressure from said source and the
outer surface of said hollow capsule being exposed to the outlet
pressure in said control chamber, so that said hollow capsule
expands and contracts in response to a differential pressure
between the outlet pressure in said control chamber and the air
pressure in the interior of said hollow capsule;
a valve operatively connected to the outer surface of said hollow
capsule, said valve being disposed in said opening in said wall
between said control chamber and said pilot chamber to control the
communication between said control chamber and said pilot chamber
to close said opening in said wall when said hollow capsule expands
due to a differential higher internal pressure, and to open said
opening when said hollow capsule contracts due to a differentially
higher pressure on its outer surface;
a spacer forming a movable wall between said outlet and said wall,
said pilot chamber being defined by said spacer and said wall, said
spacer having a relief passage connecting said outlet to the
atmosphere;
a valve disposed in said relief passage to control the opening and
closing of said relief passage;
a valve disposed between said inlet and said outlet to close and
open the communication therebetween,
so that when the outlet pressure is less than either the pilot
pressure or the inlet pressure, the air pressure in said control
chamber is equal to the outlet pressure causing said hollow capsule
to open said valve disposed in said opening in said wall between
said control chamber and said pilot chamber and as the outlet
pressure increases, the pressure in said control chamber increases
to a value greater than the air pressure interior to said
pressure-sensitive device causing said hollow capsule to close said
valve in said opening in said wall between said control chamber and
said pilot chamber;
the improvement comprising an elongated fluid conduit having one
end connected to a source of fluid pressure, the interior of said
capsule being connected to the elongated fluid conduit between its
ends, said inlet of said pilot operated valve being connected to
said elongated fluid conduit between said end of said elongated
fluid conduit connected to the source of fluid pressure and said
connection of said capsule to said elongated fluid conduit, and a
control member mounted on the opposite end of the fluid conduit
adjacent th free end of said cable for venting fluid pressure from
said capsule to thereby control the pressure of air admitted to the
fluid pressure chamber, the control member comprising a needle
valve cooperating with a port connected with said fluid conduit so
that said control member is infinitely variable between fully
opened and fully closed positions, said needle valve including a
knob and said control member including a handle portion disposed
below said knob whereby said knob can be rotated by the thumb of
user while its handle portion is grasped to rotate said needle
valve to permit selective variation of pilot fluid pressure
according to the weight of a load being hoisted by the hoisting
member.
Description
BACKGROUND OF THE INVENTION
1. Field Of The Invention
This invention relates to pneumatically-operated hoists, and more
particularly to an air balanced hoist having a hand control for
regulating the air pressure employed to raise each load and to
balance it in a suspended position.
2. Description Of The Prior Art
Hoists employing a pneumatic balancer are useful in industrial
processes in which the load is raised to a suspended position, and
then manually positioned in a fixture or the like by the operator.
The balancer has a piston connected to the load. The piston is in a
power chamber in which air pressure is regulated to move the piston
and thereby either raise or lower the load.
Certain commercially available air-balanced hoists employ a
pilot-operated valve for regulating the power chamber pressure. The
general principles of such regulators are well known to those
skilled in the art. Examples have been disclosed in U.S. Pat. Nos.
2,384,774 issued to C. D. P. Smallpeice, 3,384,350 issued to E. R.
Powell, and others. Typically, a portion of the air at line
pressure is passed through a pilot regulator which reduces the line
pressure to a maximum pilot pressure that depends upon the maximum
weight that is to be hoisted.
A valve which is responsive to pilot pressure changes is disposed
at the inlet of the power chamber to control its pressure and
thereby control the motion of the piston in the following manner.
When the load is connected by a hoisting line to the piston the
operator raises pilot pressure. The pilot-operated valve responds
by raising power chamber pressure until the piston begins to move.
Since pilot pressure is chosen to slightly overbalance the load,
the load is hoisted as the piston moves.
Upon being raised to a suspended position, the load can be manually
positioned by the operator because the load weight is balanced by
air pressure. He can easily stop its upward motion since only a
slight effort is sufficient to compensate for the slight
overbalance of the power chamber pressure. To manually lower the
load, he need only apply a slightly greater downward effort. The
resulting piston motion tends to compress the power chamber air
which causes the pilot-operated valve to open a relief connection
between the power chamber and the atmosphere.
A problem with some air-balanced hoists of the prior art is that
the pilot regulator must be readjusted to accommodate changes in
the load weight. This disadvantage is due to the overhead location
of the pilot regulator which requires the operator to interrupt his
hoisting activity to make the necessary load adjustment.
A limited solution to this problem was disclosed in the
aforementioned Powell patent. A hand-operated control on the lower
end of a flexible conduit has a pair of openings for venting the
pilot air, each opening being related to a different load weight.
The control provides a means for remotely changing the pilot
pressure by bleeding off a predetermined portion of its pressure
depending upon which of the vent openings is connected to the
atmopshere. The problem with this venting arrangement is that the
operator is still limited to a certain number of loads unless he
interrupts the continuity of his hoisting operation. For loads of
other weights, he must readjust either the pilot regulator or the
hand control while the hoist is not being used.
SUMMARY OF THE INVENTION
The broad purpose of the present invention is to provide an
air-balanced hoist having a hand operated control for selecting the
power chamber pressure necessary to balance each load as it is
being hoisted. The operator can control the balancer to accommodate
either large or small variations in load weight while retaining a
sensitivity over the motion of the load that allows a load of
several hundred pounds to be easily positioned.
The preferred embodiment employs a control needle valve for venting
pilot air. The control valve is so mounted on a handle that the
operator can precisely adjust pilot pressure with the thumb of one
hand as he uses his other hand to position the load. Only one
control member need be manipulated to accommodate either a large
change in the load weight as when different work pieces are being
hoisted, or to accommodate small variances in load weight which
occur in certain types of industrial castings. The operator is not
limited to only certain pre-adjusted loads.
Still further objects and advantages of the present invention will
become readily 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 throughout the several
views, and in which:
FIG. 1 is a perspective view of an air-balanced hoist illustrating
the preferred embodiment of the invention;
FIG. 2 is an enlarged view of the hand-operated control valve,
parts being shown in section for purposes of clarity; and
FIG. 3 is a schematic diagram of the preferred hoist and
balancer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, a preferred air-balanced hoist 10, is
illustrated in FIG. 1 for hoisting a load 12. The hoist 10 includes
an elongated housing 14 having a pair of ends 16 and 18 connected
together by tie rods 20.
An eyebolt 22 is connected to the housing 14 for attaching it to an
overhead rail or trolley (not shown). A piston 24 is slidably
mounted in the housing 14 to form a power chamber 26 adjacent end
16. A second piston 28 is also slidably mounted in the housing 14,
and connected by a pair of rods 30 (only one shown) to the piston
24 such that both pistons move as a unit.
Referring to FIG. 3, a pair of sheaves 32 are mounted in a fixed
position adjacent the midsection of housing 14, and a second pair
of sheaves 34 are carried by piston 28. Thus, as piston 24 is moved
away from end 16, piston 28 and sheaves 34 are moved away from
sheaves 32. Similarly sheaves 34 are moved toward sheaves 32 as the
pistons 24 and 28 are moved toward end 16.
A hoist line 36 passes over the two sets of sheaves 32 and 34. One
end of line 36 is connected to the housing 14, and its other end is
connected to a weight 38. As the two sets of sheaves 32 and 34 are
moved toward one another, the hoist line 36 is extended down from
the housing 14 by the weight 38 and as the two sets of sheaves are
moved away from one another the hoist line 36 is retracted up into
the housing. The arrangement is such that the line is extended or
retracted a distance equal to the piston stroke multiplied by the
number of sheaves employed. A fixture 40 is fixed to a load
carrying member 41 which in turn is connected to a hook 42 carried
by weight 38 (FIG. 1). The load 12 is supported by the member 41 so
as to be easily detached from the hoist.
As can best be seen in FIG. 3, a source of air under pressure 44 is
connected by a line 46 to the power chamber 26. A valve 48 is
disposed between the source 44 and the hoist, to open and close
communication between the source and the power chamber. A normally
closed two way valve 50 is disposed in line 46 at the inlet of
power chamber 26. A spring 52 biases valve 50 toward its closed
position, and air pressure sensed through a line 54 connected to
the outlet side of valve 48 biases the valve 50 toward its open
position. The arrangement is such that if valve 48 is closed, or if
there is a loss of pressure from source 44, because of some other
occurrence, the spring 52 closes valve 50. However, valve 50 is
opened in response to the pressure of air pressure from the source
44 in line 54. The valve 50 therefore functions as a fail-safe
device by automatically closing in response to a pressure loss from
the source to trap the air in power chamber 26. The trapped air
prevents the load 12 from being suddenly dropped from a hoisted
position.
A pilot operated valve 56 is disposed in line 46 between valve 48
and valve 50. Such pilot-operated valves are commercially available
as a means for maintaining a certain relationship between a
controlling pilot pressure and the pressure of a controlled device
such as power chamber 26. In the present invention, valve 56
regulates air pressure in power chamber 26 in accordance with
variations in the pilot pressure sensed in pilot line 58. If the
pilot pressure is increased, the power chamber pressure is raised,
and if pilot pressure is reduced, valve 56 operates to reduce the
power chamber pressure.
Valve 56 includes a housing 60 having an inlet 62 for receiving air
from source 44, and an outlet 64 for passing air from the inlet to
power chamber 26. A valve seat 66 is disposed in the housing for
fluidly connecting inlet 62 to outlet 64. A spacer 68 is supported
by a pair of diaphragms 70 and 72 in housing 60 to form a movable
wall between the outlet 64 and an internal wall 74. The spacer 68
has a valve seat for connecting outlet 64 to a relief passage 76
which opens to the atmosphere. A pilot chamber 78 is disposed
between the spacer 68 and one side of wall 74, and a control
chamber 80 is disposed on the opposite side of wall 74.
A passage 82 connects control chamber 80 to outlet 64 so that
outlet pressure is present in the control chamber. An opening 84 in
wall 74 connects the control chamber 80 to pilot chamber 78, and an
opening 86 connects pilot chamber 78 to the atmosphere.
A hollow pressure-sensitive device 88 is disposed in control
chamber 80 with its outer surface being exposed to control chamber
pressure, and its interior being connected to the pilot line 58 so
as to be expanded or collapsed depending upon the differential
between pilot pressure and control chamber pressure. A valve 90 is
carried by device 88 to close opening 84 as the device 88 is
expanded by pilot pressure, and to unblock opening 84 as the device
88 is collapsed by control chamber pressure.
An elongated valve 92 is mounted between the spacer 68 and inlet
62. One end of valve 92 is adapted to open or close communication
between outlet 64 and the relief passage 76, and its other end is
adapted to open or close valve seat 66 to control communication
between inlet 62 and outlet 64.
Pilot-operated valve 56 operates in the following manner. Assuming
a given pilot pressure, if the outlet pressure is less than either
pilot pressure or inlet pressure, the control pressure in control
chamber 80 will be at outlet pressure such that the device 88 is
expanded by the greater pilot pressure to open valve 90. Since
opending 86 is smaller than opening 84, the pressure in pilot
chamber 78 will be substantially the same as both control chamber
pressure and outlet pressure.
Under this condition, both sides of spacer 68 are biased by
substantially the same air pressure, and a spring 94 disposed
between wall 74 and the spacer biases it toward valve seat 66 such
that the upper end of valve 92 closes communication between outlet
64 and relief passage 76. The lower end of valve 92 opens
communication between inlet 62 and outlet 64. With valve seat 66
open, air at the higher inlet pressure passes through outlet 64
toward power chamber 26.
As outlet pressure increases, control chamber pressure also
increases to gradually collapse device 88 and move valve 90 to its
closed position. As soon as valve 90 is closed, the pressure in
pilot chamber 78 rapidly drops as the air exhausts through opening
86. Spacer 68 is then moved toward wall 74 by the outlet pressure
and thereby allows the lower end of valve 92 to move to its closed
position as the outlet pressure reaches pilot pressure.
If outlet pressure thereafter falls below pilot pressure, the
resulting drop in control chamber pressure causes device 88 to
partially collapse and open valve 90 to increase pilot chamber
pressure. Spring 94 then moves spacer 68 to open valve seat 66 and
the foregoing process repeats itself.
Assuming a condition occurs that increases outlet pressure above
pilot pressure when both valve seat 66 and opening 84 are closed,
the spacer 68 is biased away from the upper end of valve 92 by the
outlet pressure until relief passage 76 is opened. Outlet air then
exhausts itself to the atmosphere until outlet pressure is reduced
to pilot pressure. As the outlet pressure is reduced, spacer 68
moves toward valve 92 until relief passage 76 is closed. Thus,
pilot-operated valve 56 continuously operates to maintain outlet
pressure, and thereby power chamber pressure, in accordance with
pilot pressure.
A fluid line 94 connects the inlet of pilot line 58 to the outlet
of the air source 44. A conventional pilot regulator valve 96 in
line 94 provides means for the operator to reduce line pressure as
received from source 44 to a certain level that depends upon the
maximum weight expected to be hoisted. A trim valve 98 is disposed
in line 94 at the outlet of pilot valve 96 to control the rate that
air can be vented through a flexible control conduit or line 100
from line 94. Pilot valve 96 and pilot-operated valve 56 are
preferably mounted on one end of hoist housing 14 which is normally
mounted in an overhead position. Control line 100 extends down from
the housing 14, and a control valve 102 is disposed at the lower
outlet end of the control line.
As can best be seen in FIGS. 1-2, the control valve 102 is mounted
on fixture 40 to allow the operator to manually position the load
12 as it is being hoisted or balanced in a suspended position.
Control valve 102 includes a body 104 having an orifice 106 for
venting pilot air to the atmopshere. A needle valve 108 is mounted
on body 104 for regulating air flow through orifice 106.
A knob 110 is carried on needle valve 108 adjacent a handle 112.
The handle provides means for the operator to manually position
fixture 40. Knob 110 is so mounted adjacent handle 112 such that
the operator's thumb can easily rotate needle valve 108 to
precisely control the rate of air flow through orifice 106.
It is apparent that by operating control valve 102, the operator
can raise and lower pilot pressure. When orifice 106 is closed,
pilot pressure in pilot lines 58 is normally the same as the outlet
pressure of the pilot valve 96. As the control valve 102 is
manipulated to open orifice 106, pilot air is vented to the
atmosphere thereby reducing the pressure in pilot line 58 below the
outlet pressure of the pilot valve. The reduction in pilot pressure
in pilot line 58 is proportional to the opening of orifice 106.
A spring 114 is mounted between needle valve knob 110 and body 102
to provide a slight frictional resistance to the turning effort and
thereby provide the operator with a sensitivity in regulating the
air flow rate. In addition, trim valve 98 provides an additional
sensitivity by governing the manner in which pilot pressure is
reduced. It provides an inherent time delay in the rate that pilot
pressure responds to the opening of control valve 102. Thus
although the operator may quickly fully open control valve 102 from
a fully closed position, the change in pilot pressure sensed by the
pilot-operated valve 56 will be at a lesser rate to prevent the
load 12 from being suddenly dropped by an inexperienced
operator.
In summary, the operator controls the motion of load 12 by
controlling pilot pressure. Because he can precisely vary pilot
pressure, he can easily raise, lower, or balance the load 12 in a
suspended position. Assuming the load 12 is attached to fixture 40
and is to be raised to a balanced position, the operator closes
control valve 102 to increase pilot pressure. Power chamber
pressure is accordingly increased to move piston 24 and retract the
line 36 into housing 14. As the load 12 is raised, the operator
manipulates control valve to lower pilot pressure until piston 26
is balanced between the bias of the power chamber pressure in one
direction, and the bias of the load in the opposite direction. When
the piston 24 is so balanced, the load 12 is balanced in a
motionless suspended position.
The operator can easily compensate the power chamber pressure for
either large or small variations in the weight of individual loads.
He can perform the necessary adjustment in pilot pressure as each
load is being hoisted. He need not interrupt his hoisting activity
to adjust the pilot valve for large changes in load weight. He
easily controls the pilot pressure with his thumb and without
special tools.
To lower the load 12 from its suspended position, the operator
opens control valve 102 to lower pilot pressure. Since the control
valve is open and venting pilot air when the fixture 40 is in its
lower position between loads, the pilot valve 96 is preferably
adjusted for the maximum weight that is expected to be hoisted
during a given hoisting activity in order to conserve compressed
air. If the maximum weight that is normally hoisted is changed, the
pilot valve 96 is appropriately adjusted.
* * * * *