Note: Descriptions are shown in the official language in which they were submitted.
q
m
CA 02359770 2001-10-16
1
AIR LIFTING AND BAL,?~NCING UNIT
BACKGROUND OF THE INVENTION
The present invention relates to an improved air
lifting and balancing unit and more particularly to a brake
structure and pneumatic control circuit therefor.
By way of background, ball screw type of air
lifting and balancing units are known. Briefly, in units
of this type pressurized air is s}spplied to a cylinder to
move a piston which acts through a ball screw which, in
to turn, rotates a ball nut having a drum thereon which in
turn lifts a chain or a cable to which a load is attached.
If there should be a loss of load from the end of the chain
or cable, the latter will whip in an unpredictable manner
to possibly cause injury to a workman or equipment. Inso-
far as known, in the past there was no braking structure
associated with an air lifting and balancing unit for
braking the drum to prevent the whipping. Additionally,
insofar. as known, in the past when load lifting was
effected by supplying pressurized air at a substantially
2o constant pressure but at a variable volume, the load could
be lifted at different speeds by the operator. Thus, the
load could be lifted too rapidly or too abruptly, which in
the latter two instances could create abrupt shocks to the
load or undue stresses to the ai.r balancer and to the
chain. Also, the speed of lifting fluctuated greatly when
there were changes in the supply pressure, which, in turn,
often resulted in undesired accelerations of the chain
during lifting. To overcome those problems, adjustable
needle valves were used to limit the lifting speed, but
3o this caused heavier loads to be lifted too slowly. It is
with overcoming the foregoing deficiencies of prior art air
balancing and lifting units that the present invention is
concerned.
CA 02359770 2001-10-16
2
SUMMARY OF THE INVENTION
It is accordingly one important object of the
present invention to provide a brake system for an air
lifting and balancing unit which functions immediately on
excessive acceleration of a drum in response to a loss of
load to tend to avoid the uncontrolled whipping of the
unloaded end of the chain.
Another object of the present invention is to
provide a drum-braking system which is responsive to
to excessive acceleration of the drum due to a loss of
pressurized air which drives the piston.
Yet another object of the present invention is
to provide a pneumatic circuit for a cylinder to cause a
piston thereof to move at a substantially constant speed
regardless of the variations in air pressure supplied
thereto.
A further object of the present invention is to
provide an improved pneumatic control circuit for an air
lifting and balancing unit which ultimately causes a load
2o to be lifted at a substantially constant speed regardless
of variations in air pressure by providing pressurized air
to the piston of the air balancing and lifting unit which
automatically produces a force which is a predetermined
increment aver the effective force applied to the opposite
side of the piston by the load.
Still another object of the present invention is
to provide an improved pneumatic control circuit for an air
lifting and balancing unit which provides extremely smooth
load lifting both at the start of and during the actual
lifting. _
A still further object of the present invention
is to provide an integrated brake and pneumatic control
system for an air lifting and balancing unit wherein the
pneumatic circuit maintains the speed of the unit substan-
tially constant in spite of variations in pressure so that
accelerations which could otherwise occur due to such
variations and which may actuate the brakes are prevented.
m
CA 02359770 2001-10-16
3
Other objects and attendant advantages of the present
invention will readily be perceived hereafter.
The present invention relates to an air lifting
and balancing unit comprising a cylinder, a piston in said
cylinder, a ball screw affixed to aaid piston, a ball nut,
means mounting said ball nut for rotation on said ball
screw, drum means mounted on said ball nut for moving an
elongated member which carries a load, brake means mounted
relative to said drum, and means for causing said brake
1o means to stop rotation of said drum when said drum exceeds
a predetermined acceleration.
The present invention also relates to an air
lifting and balancing unit comprising a cylinder, a piston
in said cylinder, a ball screw affixed to said piston, a
ball nut, means mounting said ball nut for rotation on said
ball screw, a drum mounted on said ball nut for rotation
with said ball nut, an elongated member mounted on said
drum for carrying a load, and pneumatic circuit means in
communication with said cylinder for providing air pressure
2o thereto which applies a force on said piston which is at a
substantially constant incremental value over the force
exerted by said load applied to said piston through said
elongated member and said drum and said ball screw regard-
less of variations in said air pressure to thereby cause
the speed of said elongated member to remain substantially
constant.
The present invention also relates to an air
lifting and balancing unit comprising a cylinder, a piston
in said cylinder, a ball screw affixed to said piston, a
3o bail nut, means mounting said ball nut for rotation on said
ball screw, drum means mounted on said ball nut for
rotation with said ball nut, an elongated member mounted on
said drum means for carrying a load, brake means mounted
relative to said drum means, means for causing said brake
means to stop rotation of said drum means when said drum
means exceeds a predetermined acceleration, and pneumatic
circuit means in communication with said cylinder for
CA 02359770 2001-10-16
4
providing air pressure thereto to produce a force on said
piston which is at a substantially constant incremental
value in opposition to the force transmitted by said load
to said piston to thereby cause the speed of said piston to
S remain substantially constant regardless of variations in
said air pressure and thereby cause the speed of said
elongated member to remain substantially constant.
The present invention also relates to a
pneumatic control circuit for controlling the flow of
to pressurized air to a device having an expandable chamber
requiring an increasing supply of said pressurized air at a
predetermined pressure as said chamber expands comprising a
source of pressurized air, an air relay, first conduit
means for effecting communication between said source and
15 said air relay, a device having a piston and an expandable
chamber, second conduit means for effecting communication
between said air relay and said expandable chamber to drive
said piston against a load, third conduit means for effect-
ing communication between said expandable chamber and said
2o air relay, and means within said air relay for cyclically
comparing the pressure of air from said third conduit means
with the pressure of air from said second conduit means and
causing said pressure in said second conduit means to apply
a substantially constant force to said piston regardless of
25 variations in pressure at said source.
The present invention also relates to a
pneumatic control circuit for controlling the flow of
pressurized air to a chamber of a cylinder for driving a
piston which is subjected to different loads and wherein
3o said chamber expands as said piston moves said load and for
maintaining the speed of said piston at a substantially
constant value regardless of variations in pressure of the
air supplied to said chamber comprising a source of
pressurized air, an air relay, first conduit means for
35 effecting communication between said source and said air
relay, a cylinder having an expandable chamber, a piston in
said cylinder forming a side of said expandable chamber,
CA 02359770 2001-10-16
second conduit means for effecting communication between
said air relay and said expandible chamber, third conduit
means for effecting communication between said expandible
chamber and said air relay, and means within said air relay
5 for cyclically comparing the pressure of air from said
third conduit means with the pressure of air from said
second conduit means and causing said pressure in said
second conduit means to be maintained at a substantially
constant increment over the size of said load to thereby
to cause said piston to always travel at substantially the
same speed regardless of said variations in pressure.
The various aspects of the present invention
will be more fully understood when the following portions
of the specification are read in conjunction with the
accompanying drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary cross sectional view
taken substantially along line 1-1 of FIG. 2 and showing
various components of the air balancer;
2o FIG. 2 is a cross sectional view taken substan-
tially along line 2-2 of FIG. 1;
FIG. 3 is a cross sectional view taken substan-
tially along line 3-3 of FIG. 1;
FIG. 4 is a fragmentary cross sectional view
taken substantially along line 4-4 of FIG. 1 and showing
the brake shoes in a retracted position;
FIG. 4A is a fragmentary cross sectional view
similar to FIG. 4 but showing a modified embodiment having
two sets of brake shoes which provide braking in opposite
directions;
FIG. 5 is a fragmentary cross sectional view
similar to FIG. 4 but showing the brake shoes in a braking
position;
FIG. 6 is a fragmentary enlarged portion of FIG.
4 showing in greater detail the brake shoe in a retracted
position;
CA 02359770 2001-10-16
6
FIG. 7 is a fragmentary plan view of the brake
shoe taken substantially in the direction of arrows 7-7 of
FIG. 6 with the brake drum deleted;
FIG. 8 is a cross sectional view taken substan-
tially along line 8-8 of FIG. 1;
FIG. 9 is a schematic view of the pneumatic
circuit for the air balancer;
FIG. 9A is a schematic view of the air relay
portion of the pneumatic circuit;
to FIG. 10 is a side elevational view of the pocket
wheel which is shown in cross section in FIG. 1;
FIG. 11 is a cross sectional view similar to
FIG. 1 but showing an alternate embodiment of the present
invention;
FIG. 12 is a cross sectional view taken substan-
tially along line 12-12 of FIG. 11 and showing the manner
in which brake shoes are mounted on the drum assembly;
FIG. 13 is a fragmentary plan view of the brake
shoe taken substantially in the direction of arrows 13-I3
of FIG. 12 and showing various details of the brake shoe;
FIG. 14 is a fragmentary cross sectional view
taken substantially along line 14-14 of FIG. 11;
FIG. 15 is a side elevational view of the chain
drum of FIG. 11; and
FIG. 16 is a side elevational view of a cable
drum which can be used in the embodiment of FIG. 11.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Summarizing in advance, the improved air lifting
and balancing unit 10 of the present invention possesses a
plurality of improvements which include (1) a braking
arrangement which becomes activated automatically when the
speed of the drum exceeds a predetermined value, and (2) a
pneumatic circuit which provides air pressure to the piston
of the drum driving cylinder to produce a force thereon
which is at a substantially constant incremental value over
the opposing effective force exerted by the load on said
piston to thereby cause the speed of the drum to produce a
CA 02359770 2001-10-16
7
substantially constant lifting speed regardless of varia-
tions in said air pressure.
The air lifting and balancing unit 10 includes a
housing 11 consisting of three housing portions, namely, a
cylinder tube 12, an anti-rotation tube 13 and a drum
casing 14. The cylinder tube 12 is part of a pneumatic
cylinder 15 having a cylinder bottom or end plate 17
secured to a cylinder head 19 by means of a plurality of
bolts 20. A cylinder piston 21 has an outer periphery with
to a seal 22 therein which is in engagement with the inner
surface 23 of cylinder tube 12. Piston 21 is secured to
the end of ball screw 24 by means of a piston bolt 25 which
is secured against rotation relative to ball screw 24 by a
set screw 27. An O-ring seal 29 is provided between piston
21 and bolt 25. A piston stop 30 is secured to piston 21
by the head of bolt 25. A bolt 31 extends through cylinder
bottom 17 for abutting the head of bolt 25 when the latter
is in its leftmost position. A conduit 32 extends through
cylinder bottom 17 for conducting pressurized air to and
2o from cylinder chamber 33. The pressurized air moves piston
21 from left to right in FIG. 1 to thereby drive ball screw
24 axially without rotation. The opposite end of ball
screw 24 has an anti-rotation bar 34 secured thereto by
retaining screw 35 (FIGS. 1 and 8). A plurality of tie
rods 37 extend between circular anti-rotation end plate 39
and end wall 40 of casing 14. The anti-rotation mounting
tube 13 is secured between anti-rotation end plate 39 and
end wall 40. A pair of rollers 41 are mounted at the
opposite ends of anti-rotation bar 34 to thus move between
3o the rods 37 and prevent the ball screw from rotating while
it moves axially.
Mounted within casing 14 is a ball screw nut 42
having a threaded end 43 which is threaded into end portion
44 of drum 45 and retained against rotation therein by set
screws 47. Drum 45 has one end mounted on the outer race
of radial ball bearing 49, the inner race of which is
suitably mounted on cylinder head 19. The opposite end of
CA 02359770 2001-10-16
8
drum 45 is mounted within the inner race of radial and
axial bearing 50, the outer race of which is mounted in
casing 14 which is provided with wear guides 46 and 48
(FIG. 3). Drum 45 has a pocket wheel 51 formed on the
outer periphery thereof for receiving an elongated flexible
member in the nature of chain 52. The pocket wheel 51 has
pockets 53 (FIGS. 3 and 10) therein which receive chain 52
in the conventional manner. More specifically, links, such
as 52a, lay flat in the pockets and links 52b have edge
to portions which are received in groove 56 in pocket wheel
51. A bracket 54 is secured to casing 14 by bolts 55, and
bracket 54 is to be secured to a suitable support by means
of a nut and bolt arrangement 57.
Broadly, in operation, as pressurized air is
conducted into chamber 33 from conduit 32, piston 20 will
be driven to the right in FIG. 1 to move ball screw 24
axially through ball nut 42 which will thus be caused to
rotate because it is held against axial movement within
casing 14, and this rotation will cause chain 52 to be
2o moved in the direction of arrow 59 (FIG. 3) as drum 45
moves in a clockwise direction as shown by arrow 60 in FIG.
5. The chain 52 will drop into chain container 61 during
clockwise rotation of drum 45.
In accordance with the present invention, brake
shoes 62 are pivotally mounted by pins 63 in diametrically
opposite positions on rim 64 of drum 45. Pins 63 extend
through rim 64 and through ears 66 of brake shoes 62.
Brake shoes 62 are normally biased by springs 65 to a
retracted position wherein their outer surfaces 71 do not
3o contact the inside surface 67 of casing 14 during rotation
of drum 45 at normal speeds. In this respect, a clearance
of about .020 inches has been found satisfactory. In the
retracted position surfaces 68 of the shoes engage the
surfaces 68' of rim 64. However, in the event there is a
loss of load 69 (FIG. 9) which is held by chain 52, there
could be an acceleration of the drum which could result in
a whipping action of the outer end 70 of chain 52 when it
s
CA 02359770 2001-10-16
9
is permitted to fly at an unreasonably high speed. This
could result in injury to a workman or to equipment.
Accordingly, if the drum 45 should tend to accelerate
beyond a predetermined value, brake shoes 62 will be
centrifugally pivoted outwardly about pins 63 from the
retracted position of FIGS. 4 and 6 to the extended
position of FIG. 5 so that their outer surfaces 71 will
engage the inner surface 67 of casing 14 to produce a
wedging action between the drum and casing 14 to stop
1o rotation of the drum. The termination of rotation is
enhanced by the fact that casing 14 is made out of aluminum
whereas brake shoes 62 are made out of steel, which is much
harder than aluminum, and outer surfaces 71 are serrated to
enhance stopping the rotation by biting into the inner
softer surface 67 of casing 1.4, especially if the
coefficient of friction becomes less due to lubrication or
other media between the surfaces. The serrations are
desired for reliability but are not absolutely necessary
for the proper operation.
2o In FIG. 4A an alternate and optional embodiment
of the present invention is disclosed wherein, in addition
to brake shoes 62 which operate during a loss of load, an
additional set of brake shoes 62a is provided which are
identical in all respects to brake shoes 62 but they are
mounted in a reverse direction and are located 90° removed
from brake shoes 62. The purpose of brake shoes 62a is to
effect stopping of drum 45 in the event that it accelerates
beyond a predetermined value when the drum turns in the
counterclockwise direction of FIG. 5, as depicted by arrow
72, which may occur in the event that there is a sudden
loss of air supply to chamber 33 when chain 52 is carrying
a load. Under this set of circumstances, brake shoes 62a
will swing outwardly and wedge and bite into the inner
surface 67 of casing 14. It will be appreciated, however,
that brake shoes 62 swing out only when excessive accelera-
tion is experienced in the direction of arrow 60 of FIG. 5,
and brake shoes 62a will swing outwardly when drum 45
CA 02359770 2001-10-16
experiences excessive acceleration in the direction of
arrow 72 of FIG. 5»
In FIGS. 11-16 alternate embodiments of the
present invention are disclosed. The basic difference
5 between the embodiment of FIGS. 1-8 and FIGS. 11-16 is that
the drum of FIGS. 1-8 is in the nature of a pocket wheel
whereas the drum of the embodiment of FIGS. 11-16 is in the
nature of an elongated drum having a helical groove
arrangement therein for winding a chain or a cable thereon.
1o The air lifting and balancing unit 80 of FIGS.
11-16 includes a casing 8l consisting of a cylinder tube 82
and a drum case 83. A circular cylinder end plate 84 is
located at one end of cylinder tube 82 and a drum end plate
85 is located at the end of casing 83. A circular rubber
cushion pad 86 is mounted against end plate 84. A screw
sleeve 87 receives retainer bolt 89 which threads into the
end 90 of ball screw 91 which is located in the hollow end
92 of screw sleeve 87. The opposite end 93 of ball screw
91 receives retainer bolt 94 which extends through end
2o plate 8~5. When bolts 89 and 94 are tightened, cylinder
tube 82 and drum case 83 will both be drawn up against the
opposite sides of annular center support 95 to maintain the
unit 80 in assembled relationship. A ball nut 97 is
mounted on ball screw 91. The threaded end 99 of ball nut
97 is threaded into nut sleeve mount 100 and is retained
therein by set screw 101. Nut sleeve mount 100 is pinned
to drum 102 by anti-rotation dowel pin 103. The end 104 of
drum 102 is mounted on one race of thrust bearing 105, the
other race of which is mounted on piston 107. Both races
of thrust bearing 105 are mounted on hub portion 109 of
piston 107. Thus, one end 104 of drum 102 is supported on
the hub 109 of piston 107, and the opposite end of drum I04
is mounted on nut sleeve mount 100 which in turn is mounted
on ball nut 97.
In operation, compressed air is conducted to and
from cylinder chamber 110 through conduit 111 in cylinder
end plate 84. When compressed air is permitted to leave
CA 02359770 2001-10-16
11
chamber 110 and drum 102 is caused to rotate, piston 107
will move to the right because the ball nut will rotate and
cause the drum to move axially to the right. The central
portion of piston 107 will ride on the outer surface 112 of
screw sleeve 87 as drum 102 moves to the right. When
piston 107 is located to the right of the position shown in
FIG. 11, and compressed air is admitted to chamber 110,
piston 107 will move to the left and carry drum 102 with
it. In this respect, drum 102 is secured to sleeve mount
l0 100 which is secured to the end 99 of ball nut 97. Thus,
as the ball nut 97 is caused to axially traverse ball screw
91, it will rotate and because of the connections between
ball nut 97 and drum 102, the latter will also rotate. An
elongated flexible member in the nature of chain 114 is
received in helical groove 115 of drum 102 (FIG. 15), and
the end of chain 114 is secured to drum 102 by means of nut
and bolt 113 which passes through nut sleeve mount 100 and
drum 102. A bracket 117' is secured by bolts 119' to
annular center support 95 for suspending the unit 80 from a
2o suitable support.
In accordance with the present invention, brake
shoes 117 are pivotally mounted on diametrically oppositely
located pins 119 which extend through annular rim 120 of
nut sleeve mount 100 and spaced ears I21 of brake shoe 117.
Springs I22 have first ends mounted on pins 123 which
extend through ears 121, and the opposite ends of springs
122 are mounted on bolts 124 having nuts 125 which are used
to move bolts 124 axially to adjust the tension of springs
122. Nuts 125 bear against shoulders 126 of rim 120. The
3o shoes 117 are identical in all respects to shoes 62 of
FIGS. 4-6 and they coact with rim 120 in the same manner as
shoes 62 do with rim 68' and they have the same clearance
with the inside of casing 83.
If the acceleration of nut sleeve mount 100 and
rim 120 thereof should exceed a predetermined value in the
direction of arrow 127 of FIG. 12, brake shoes 117 will
pivot outwardly from their clearance position against the
CA 02359770 2001-10-16
12
bias of springs 122 so that their knurled surfaces 129 will
engage the inner surface 130 of casing 83 to thereby wedge
between the drum and the casing to stop the rotation of
drum I02 to prevent whipping and sudden retraction of the
outer end of chain 114 which carries an attachment device,
such as a hook (not shown), which is conventionally mounted
at the end of the chain. Optionally, shoes, such as 117,
may be mounted in a reverse orientation on rim 120 in
positions 90° removed from existing shoes 117 to provide
to braking in the event that drum 102 exceeds a predetermined
acceleration in the direction of arrow 131, as may occur if
there is a sudden loss of air supply to chamber 110 when
chain 114 is carrying a heavy load. As noted above
relative to FIG. 4A, brake shoes for the last-mentioned
purpose must be oriented in an opposite orientation than
shoes 117 in the manner analogous to shoes 62a of FIG. 4A.
In FIG. 16 a modified embodiment of the drum of
FIGS. 11-15 is shown. Drum 132 has the same internal
structure as drum 102 of FIGS. 11 a,nd 15, and it fits onto
2o a nut sleeve mount, such as 100 of FIG. 11. The only
difference between the drum 102 of FIG. 15 and drum 132 of
FIG. 16 is that the helical groove 133 of drum 132 is for
receiving an elongated flexible member in the nature of a
cable 135 whereas the groove 115 of drum 102 is for
receiving a chain. A suitable attachment, not shown, is
used to secure the end of the cable to drum 132.
In accordance with the second aspect of the
present invention, a pneumatic control circuit 140 (FIG. 9)
is provided to cause the rotational speed of the drum to
3o remain at a substantially constant value regardless of
variations in air pressure applied to the air balancer
unit. In this respect, the load 69 will exert a downward
force on chain 52 which in turn will exert a rotational
force on the drum 45 which in turn will exert an axial
force on ball screw 24 to tend to move piston 21 to the
right (FIG. 9). In order to exert a lifting force on
load 69, air pressure must be supplied to chamber 33 of
CA 02359770 2001-10-16
13
cylinder 12 to force piston 21 to the Left in opposition to
the force exerted on the piston by the ball screw. This is
accomplished in the following manner. A source of
pressurized air 141 is provided which is conducted through
conduit 142, filter 143, pressure regulating valve 144,
conduit 145 and conduit 147 to valve 149 which is normally
biased by spring 150 to a blocking position shown in the
drawings. However, when air pressure is supplied to valve
149, it will be open to permit communication between
to conduit 151 and chamber 33. The purpose of valve 149 is to
prevent downward falling of load 69 in the event there is a
failure of the supplying of air pressure from the source
because, in this instance, the valve 150 will be moved to
its normally closed blocking position. The use of valve
149 is optional.
Conduit 145, which leads from the pressurized
air source 141 is also in communication with conduit 152
which is the inlet conduit to air relay 153 which is a
conventional valve structure, the function of which is to
2o maintain a constant pressure in output line 154 thereof,
during lifting, which is at a predetermined value, for
example, 10 psi over the equivalent force per square inch
on the side of piston 21 which is attached to ball screw
24. Thus, there will be an unbalancing force on piston 21
tending to move it to the left to lif t load 69 and the
force will be 10 psi times the area of the piston to
provide a predetermined total force in excess of the
effective force exerted by load 69 on the opposite side of
piston 21. This loading by air pressure on piston 21 is
3o maintained at an increment of 10 psi over the pressure per
square inch applied on the opposite side of the piston
regardless of any variations in air pressure. The net
result is that the lifting speed of load 69 will remain
substantially constant.
There are a number of conditions to which load
69 is subjected. The first condition is when load 69 is
being lifted. To effect this, the up valve 155 of control
CA 02359770 2001-10-16
14
valve 157 is moved to the open position. This permits flow
of pressurized air through conduit 154, now open valve 155,
conduits 157 and 159, conduit 151 and open valve 149 to
cylinder chamber 33. Thus, pressurized air will be applied
to piston 21 to effect lifting of the Load. Flow from
conduct 159 will also pass through check valve 160 into
conduit 161 to the signal input of air relay 153. As noted
above, the air relay will function to automatically cause
the pressure in chamber 33 to be approximately 10 psi over
to the equivalent pressure applied to the opposite side of
piston 21 by ball screw 24.
The second condition is when the lifted load 69
is maintained in a static balanced condition. This occurs
when valve 155 is moved to the blocked position shown in
the drawing. Thus, flow of pressurized air from conduit 154
to conduit 157 will be terminated, and since valve 155
shuts off this flow, air will be trapped in chamber 33 so
as to maintain the piston 21 in a static position wherein
the air pressure in chamber 33 balances the force exerted
2o by load 69 on piston 21.
The third condition occurs when it is desired to
lower the load 69. In this instance, down valve 162 is
opened so that the force exerted by load 69 moving piston
24 to the right causes a reverse flow of air from chamber
33 through valve 149, conduit 151, conduit 159, conduit
157, now open down valve 162 and needle valve 163 to
atmosphere. Needle valve 163 can be set to meter the air
out of chamber 33 at a controlled rate to thereby cause the
lowering of the load to occur at a rate which is dependent
Soon the size of the load, that is, heavier loads will move
downwardly at a slightly faster rate than ligher loads.
As noted above, the air relay 153 inherently
functions to cause the air pressure in chamber 33 to
produce a force on one side of piston 21 which is equiva-
lent to a given value, for example, 10 psi over the
equivalent pressure produced by load 69 on the opposite
side of piston 2I from chamber 33 when the load 69 is being
CA 02359770 2001-10-16
lifted. Conventional air relay valves of this type are
known as a '°Type 200, Model 200-CC'° air relay manufactured
by ControlAir, Inc. of Amherst, New Hampshire and as a
"Type 20 Precision Air Relay" manufactured by Bellofram
5 Corporation of Newell, West Virginia.
The operation of the pneumatic circuit of FIG. 9
can better be understood by referring also to FIG. 9A which
is a schematic view of the air relay 153 of FIG. 9.
Broadly, the function of the air relay 153 is to provide an
to output pressure in outlet conduit 154 leading to cylinder
chamber 33. This output pressure produces a force on
piston 21 during lifting of load 69 which is a predeter-
mined amount over the opposing force exerted by the ball
screw 24 on piston 21. There are four operational
15 conditions to be considered. The first condition is when
there is no pressure in chamber 33, as when there is no
load 69 on chain 52. The second condition is when the load
69 is being lifted by chain 52 by the application of
pressurized air to chamber 33. The third condition is when
2o the load 69 remains suspended by chain 52. The fourth
condition is when the load 69 is being lowered by chain 52.
In the first condition when there is no load on
chain 52, the supply air enters duct 170 of valve 153 from
inlet conduit 152. Normally, supply valve 171 is biased
slightly off of its seat by startup spring 172 which bears
on the top of diaphragm assembly 186 which bears on closed
relief valve 175, which acts through link 177 to unseat
supply valve 171 against the bias of spring 176. Thus,
source air from conduit 152 will pass through valve
3o chamber 178 and enter duct 179 which leads to outlet
conduit 154. If up valve 155 is closed, the compressed air
will not pass beyond it. The pressure in chamber 178 will
also be sensed in control chamber 180 in view of the fact
that chamber 178 is in communication with control chamber
180 through valve conduit 181. While valve 155 remains
closed and there is no load on chain 52, there will be a
build-up of pressure in chamber 180, but there will be no
CA 02359770 2001-10-16
16
pressure input to hermetically sealed measuring capsule 183
from conduit 161 through valve conduit 182. This pressure
build up, while there is no pressure input to measuring
capsule 183, will cause the measuring capsule, which is
connected to pilot valve 184 by link 185 to cause pilot
valve 184 to close because of the flexing of the wall of
the measuring capsule 183 to which link 185 is connected.
The flexing of this wall back and forth under different
conditions causes the opening and closing of pilot valve
l0 184. Thus, when pilot valve 184 is closed, any air pres-
sure in pilot pressure chamber 187 will dissipate through
bleed orifice I89. This will cause the diaphragm assembly
186, which consists of diaphragm support disc 188 sealed
between pilot diaphragm 173 and control diaphragm 174, to
rise which in turn moves the support disc 188 away from
relief valve 175 to permit control chamber 180 to be vented
through the bore 190 in diaphragm support disc 188 and
exhaust vent 191. This will reduce the pressure in control
chamber 180 which will cause the measuring capsule to move
2o pilot valve 172 to an open position to increase the pres-
sure in pilot pressure chamber 187 to move the diaphragm
assembly 186 downwardly to bear on relief valve 175 to open
supply valve 171. The valve 153 will continually cycle
in the foregoing manner, and the pressure of the regulated
air in duct 179 will be determined in part by the metering
effect produced by supply valve 171 in conjunction with the
bleeding through the pilot pressure chamber 187 and the
flow through bore 190 and exhaust orifice 191, as described
above. The resulting pressure in outlet duct 179 will be
3o determined by the setting of the position of pilot valve
184, with the bias adjusting screw, as discussed more fully
hereafter .
In the second condition, when it is desired to
apply increased air pressure to piston 21 to raise chain
52, up valve 155 is opened to permit the regulated air from
conduit 154 to enter cylinder chamber 33 through the
above-described path. This air is at a relatively low
CA 02359770 2001-10-16
17
pressure because of the fact that it is at a pressure which
is only a given increment above the very low pressure in
the measuring capsule, as determined by the cycling of the
valve 153. The opening of valve 155 will momentarily
create a pressure drop in valve chamber 178 and in control
chamber 180, and there will be a pressure increase in
conduit 161 and in measuring capsule 183, which is in
communication with conduit 161 through a bore (not
numbered) in adjusting screw 194. This will cause the
to measuring capsule 183 to move pilot valve 184 to a more
open position which, in turn, will increase the pressure in
pilot pressure chamber 187 which will move diaphragm
assembly 186 downwardly. This will open the supply valve
171 to a greater extent to permit a pressure increase in
valve chamber 178 arid outlet conduit 154 which will in turn
gradually supply increased pressure to cylinder chamber 33
to move piston 21 to the left to thereby raise load 69.
The increased pressure of chamber 178 will also be communi-
cated to control chamber 180 through valve conduit 181
2o which will provide increased pressure on the outside of
measuring capsule 183 which, in turn, will tend to cause
the measuring capsule to flex and move pilot valve 184 back
toward its seat. Thus, valve 153 will cycle under these
conditions to periodically adjust the pressure in control
25chamber 180 and pilot pressure chamber 187 to thereby cause
an opening and closing movement of pilot valve 184 and a
related opening and closing movement of supply valve 17I
and relief valve 175. More specific ally, if the pressure
in control chamber 180 is nigh relative to the pressure in
3ocapsule 183, pilot valve 184 will close and the pressure in
pilot pressure chamber 187 will bleed out and the relief
valve 175 will open and supply valve 17I will close.
Conversely, if the pressure in capsule 183 is high relative
to the pressure in control chamber 180, the pilot valve
35wi11 be unseated to raise the pressure in pilot chamber 187
which will move diaphragm assembly 186 downwardly to close
relief valve 175 and open supply valve 171, to thereby
CA 02359770 2001-10-16
18
raise the pressure in outlet duct 179 and conduit 154
leading to the cylinder chamber 33. Thus, the valve 153
will cycle to maintain the pressure to chamber 33 by an
amount which is determined by the setting of the bias
adjusting screw 194 which determines the position of pilot
valve 184 relative to its seat on valve portion 172. More
specifically, as noted above, pilot valve 184 is connected
to the wall of control chamber 183 by link 185, and the
axial movement of bias adjusting screw will determine the
to position which pilot valve 184 has relative to its seat.
Thus, the differential between the pressures in control
chamber 180 and in measuring capsule 183 and the position
of pilot valve 184 will determine the opening and closing
positions of pilot valve 184 to in turn determine the
pressure of the air supplied to conduit I54 leading to
chamber 33 as compared to the pressure of the air supplied
to measuring capsule 183.
During lifting of the load, check valve 160 and
needle valve 166 cause the piston 21 to have a soft start
2o and to move smoothly. In this respect, before piston 21
moves, there will be a build-up of pressure in conduit 159,
and this increased pressure is immediately sensed in
measuring capsule 183 because of the flow through check
valve 160, which results in producing an increased pressure
in conduit 154. As piston 21 starts to move, there will be
a drop in pressure in conduits 151 and 159 as the volume of
chamber 33 increases. This drop in pressure cannot be
immediately communicated to measuring capsule 183, which is
now at a higher pressure, because check valve 160 in
3o conduit 161 will close. Needle valve 166 will restrict the
flow of air out of measuring capsule 183 toward conduit I59
at a controlled rate as the volume of chamber 33 increases
and the pressure in chamber 33 and in conduit 159 drops, to
thereby cause the piston 21 to have a soft start and to
move to the left more smoothly than if the needle valve 166
was not present. Also the speed of piston 21 will be faster
because of the above-mentioned increased pressure
CA 02359770 2001-10-16
19
relationship in conduits 154 and 159. This action is
experienced continually as the volume of chamber 33
continues to increase during lifting of load 69 so that
piston 21 will continue to move smoothly to the left as
long as compressed air is supplied to chamber 33. It is
especially noted that the signal received by valve 153 is
obtained from conduit 159 which is at a slightly higher
pressure than chamber 33 as piston 21 moves to the left.
This results in supplying a higher pressure to conduit 159
1o which produces a faster lifting speed than if the pressure
was obtained from chamber 33.
The value of the pressurized air supplied to
chamber 33 will depend on the size of the load 69. In
other words, the parameters of the mechanical and pneumatic
systems are such that when there is a particular load
tending to provide an effective force on piston 21 moving
it to the right, this will cause a pressure to be applied
to the air in chamber 33 which is communicated through
conduits 151 and 161 to the signal input conduit 182. The
larger the load, the greater will be the air pressure force
applied as a signal, and the smaller the load, the smaller
will be the force applied as a signal. Thus, the pilot
valve 184 is set by the bias adjusting screw 194 to provide
pressurized air to outlet conduit 154 at a given increment
over the force applied to the piston by the load which is
translated into the air pressure supplied to measuring
capsule 183.
The third condition of maintaining a load
suspended is effected in the following manner. After the
load 69 has been lifted to the desired extent, the up valve
155 is moved to its blocking position wherein the regulated
air output in conduit 154 can no longer enter conduit 159
leading to cylinder chamber 33 and signal input conduit
161. Furthermore, the air in cylinder chamber 33 will be
blocked because it cannot escape through conduits 151, 159
and 161. Therefore piston 21 will be held in a static
position. However, source air will still communicate with
CA 02359770 2001-10-16
air relay 153 through conduit 152. The relatively high air
pressure in cylinder chamber 33 will still be communicated
to measuring capsule 183 through conduits 151 and 161. A
condition will be reached wherein there is stabilization
5 within the valve 153 at a pressure in excess of the
pressure in measuring capsule 183 because the air pressure
within the measuring capsule 183 will stabilize at a
predetermined value due to cycling, as explained above.
However, this increased pressure leading to conduit 154
to will not go beyond up valve 155 because the latter is
blocked.
The fourth condition which occurs relative to
air relay 153 is when the load 69 is being lowered. This
occurs when down valve 162 of valve 158 is actuated to
15 permit venting of cylinder chamber. 33 to the atmosphere
through the above-described path, namely, conduits 151 and
159 and needle valve 163, which sets the maximum down speed
of a maximum load. The location of valve 163 beyond valve
162 provides more accurate control and lesser capacitative
2o delays for any weight load than if it was positioned in
conduit 159. However, at this time there is a tendency for
pressure in cylinder chamber 33 to~ lessen because it is
vented to the atmosphere, and this lessened pressure is
communicated as a signal through conduits 151 and 161 to
control valve conduit 182 and measuring capsule 183. The
lessening of pressure within measuring capsule 183 while
the supply pressure remains relatively high in valve
chambers 178 and 180, will cause pilot valve 184 to rise to
lessen the pressure in pilot pressure chamber 187 which, in
3o turn, causes the diaphragm assembly 186 to rise, which
opens relief valve 175 and causes supply valve 171 under
the bias of spring 176 to close thereby effecting dissipa-
tion of the pressurized air in chamber 178 through valve
conduit 190 and exhaust vent 191. Thus, there will be a
dropping of air pressure in both the measuring capsule and
control chamber until the situation is stabilized wherein
pilot valve 184 returns to its normally set slightly
CA 02359770 2001-10-16
21
cracked open position. At this point it is to be noted
that supply valve 171 and relief valve 175 occupy the
following relationship relative to each other. When supply
valve 171 is open, relief valve 175 must be closed and vice
versa.
After load 69 has been removed from chain 52, as
by being set on a supporting surface, there will no longer
be a force applied to ball screw 24 tending to move piston
21 to the right, which, in turn, terminates a force from
to piston 21 onto the air in cylinder chamber 33, and thus
this totally reduced pressure is communicated to measuring
capsule 183. This causes pilot valve 184 to be in its
normally open position, and spring 172 will return supply
valve 171 to a slightly cracked position wherein supply air
can move into chamber 178, chamber 180 and duct 154.
However, such pressurized air cannot reach cylinder chamber
33 because up valve 155 is closed. Furthermore, since no
compressed air is now being supplied to the signal input
conduit 161, a stabilized condition will be reached within
2o air relay 153 until the up valve 155 is again opened to
function in the above-described manner.
The bias of the pilot valve 184 is set by
removing pipe plug 193 and adjusting screw 194. Also, the
adjustment of pipe plug 195, which bears on spring 176 will
adjust the relative forces applied to the opposite sides of
diaphragms 173 and 174 by springs 172 and 176.
It will be understood that the above explanation
of the operation of the air relay 153 has been given to
provide an amplified description of how the pneumatic
3ocircuit operates. However, as noted above, the air relay
valve 153 is a conventional well-known commercial valve
which is obtainable from a plurality of sources to provide
a pressurized air output which is at a predetermined
increment higher than the pressure input thereto. However,
insofar as known in conventional practice, the signal
pressure to the measuring capsule is from a source which is
not connected to the area to which the operating pressure
CA 02359770 2001-10-16
22
is supplied. In the present case, it is believed that the
air relay 153 is being used in an entirely different and
unique manner in that the area to which pressure is being
supplied also provides the signal to the air relay for
S controlling the pressure to the area which is being
supplied.
In the above description, the up valve 155 has
been considered in a fully open position, and in this
instance a maximum drum speed will be obtained. However,
1o it will be appreciated that valve 155 can be throttled to
vary the air flow to conduit 159 to cause the piston 21 to
move at less than maximum speeds, at the selection of the
operator. The throttling will produce less than maximum
pressures in chamber 33. It will be appreciated, however,
15 that at any given throttled setting, the piston speed will
remain constant. In this respect, it will be understood
that different size loads travel at different speeds, but
the particular speed at which a load is traveling will
remain substantially constant regardless of variations in
2oair pressure because of the operation of the pneumatic
circuit.
The above-described pneumatic circuit not only
makes the unit operate within a lesser range of speeds
throughout the range of loads applied thereto between no
251oad and full load but also allows the braking device to be
used effectively because by causing the pressures applied
to each load to remain substantially constant,
accelerations of the piston which may occur due to high
variations in pressure are prevented so that the brakes
3owi11 not have to come into play as a result of such
variations.
In actual practice utilizing the above-described
pneumatic circuit, the following data was obtained when a
100 pound load was lifted by an air balancer having a 50
35square inch piston at different applied pressures:
CA 02359770 2001-10-16
23
Lift time for
Pressure in PSI '76 inches of travel
105 6.17 seconds
95 6.23 "
85 6.25 "
75 6. 22 "
65 6.82 "
The following data was obtained for lifting only
a chain with an empty hook:
to Lift time for
Pressure in PSI 82 inches of travel
36 2.37 seconds
117 2.32 "
The foregoing data shows that for a given load,
different pressures will cause the load to be lifted at a
substantially constant speed.
While preferred embodiments of the present
invention have been disclosed, it will be appreciated that
it is not limited thereto but can be otherwise embodied
2o within the scope of the following claims.
