Note: Descriptions are shown in the official language in which they were submitted.
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PNEUMATIC MULTI-WEIGHT BALANCING DEVICE
Field of the Invention
[0001] The present invention relates to pneumatic load balancing devices
capable of
weightlessly balancing a load. More particularly, the present invention
relates to
pneumatic manipulators capable of semi-automatically balancing any desired
load.
Background
[0002] Lifting devices for lifting heavy loads are known in the art. One type
of lifting
device is the hoist or crane, which is capable of lifting loads vertically
using cables, chains,
ropes or the like. The use of flexible members means that a load cannot be
rigidly
positioned in three dimensional space, which is a disadvantage in certain
applications.
The manipulator is another type of lifting device capable of both lifting
heavy objects and
rigidly positioning objects in three-dimensional space. For example,
pneumatically
assisted manually operated manipulators have found widespread use. These
manipulators typically consist of an arm that extends outwardly in a generally
horizontal
direction from a mast about which it is permitted to rotate and from which it
is also
permitted to pivot arcuately in a generally vertical direction in a
pneumatically assisted
manner via a lift cylinder. The arm may include one or more extension members
serially
disposed from an end of the arm distal from the mast that are similarly
permitted to rotate
and/or pivot. This arrangement permits the positioning of the distal end of
the arm or
extension member at a desired location in three dimensional space. An end
effector is an
attachment coupled to the distal end of the arm or extension member and
adapted for the
manipulation of a desired object or for the conduct of a particular task. For
example, an
end effector may include clamping means, pincer means, magnetic means or the
like that
are shaped and/or sized for the securement of a desired object to be
positioned.
[0003] There are generally at least two types of manipulators. A conventional
manipulator
uses push-button controls connected directly with the lift cylinder to
manually raise or lower
the load by increasing or decreasing cylinder pressure. This type of
manipulator includes
no regulators or other pressure control system and functions merely by
controlling the lift
cylinder directly. Another type of manipulator is the load balancing
manipulator. In a load
balancing manipulator, a regulator in fluid communication with the lift
cylinder is adjusted to
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a pre-determined pressure selected so that the weight of the object being
manipulated is
just balanced by the cylinder. In this manner, the object becomes weightless
with respect
to the operator, who is then able to manually position the object in three
dimensional
space. This allows the operator to quickly move and accurately position a work
piece at a
desired location in order to perform a certain task.
[0004] One problem with prior art load balancing manipulators is that the
pressure of the
cylinder must be pre-selected according to the weight of the load being
balanced. This
means that only loads of a single pre-determined weight may be moved using the
manipulator. Normally, two regulators are provided; a first regulator for
balancing the "no
load" weight of the manipulator itself at a first pressure and a second
regulator for
balancing the "with load" weight of the manipulator and the load being carried
at a second
pressure greater than the first pressure. In certain instances, additional
third or fourth
regulators may be provided to allow the operator the flexibility to select
additional discrete
weights. This arrangement of pneumatic components means that the manipulator
is
fundamentally limited in only being able to lift a limited number of pre-
selected weights.
[0005] Attempts have been made to make the second regulator dial-adjustable so
as to
allow an operator to adjust the pneumatic pressure until a particular load is
balanced.
Although this removes the limitation on pre-selection of the weights, the
manipulator must
be re-adjusted each time a load of different weight is lifted. This approach
still limits the
manipulator in terms of the flexibility to quickly lift any desired weight.
[0006] Attempts have been made in the prior art to provide automatically self-
adjusting
load balancing hoists for lifting any attached weight; however, these attempts
have not
been put into widespread commercial use with manipulators. In addition, fully
automatic
systems requiring no operator decision making to determine the pressure
required to
balance any particular load are complicated and expensive. A semi-automatic
system that
relies upon an operator decision to determine an appropriate load balancing
pressure for
the load being lifted is less complicated and often provides greater operator
confidence
than a fully automatic load balancing system.
[0007] US 4,500,074 describes a fluid operated hoist having a pilot fluid
controlled
regulator for setting the load balancing fluid pressure of the hoist. A pilot
fluid regulator is
carried by a load carrying unit of the hoist. A linkage automatically adjusts
the pressure
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provided by the pilot fluid regulator in response to lifting of the load to
thereby adjust the
pilot fluid controlled regulator. A manual bypass may also be engaged to
actively lift the
load. The linkage system adds complexity to the load carrying unit of the
hoist and is
potentially susceptible to breakdown. This system also uses at least two
regulators to
achieve load balancing; it would be desirable to reduce the number of
regulators in order to
reduce system complexity and increase reliability.
[0008] US 3,526,388 describes a load balancing hoist having a novel valve
mechanism
for automatically sensing the pilot pressure necessary to balance a particular
load. The
novel valve is located on a load carrying member of the hoist. The novel valve
introduces
cost and complexity to the system and it would be desirable to eliminate the
need for the
novel valve.
[0009] US 3,758,079 describes a load balancing hoist having a pressure sensor
in the
hoist chamber that is used to automatically determine the pressure required to
lift the load.
This system uses electronic controls, making it more complicated and expensive
to
implement and repair, and is susceptible to electronic malfunction.
[0010] US 5,613,419 discloses an electronically controlled manipulator capable
of lifting a
plurality of loads. The manipulator employs electronic load cells to sense a
load condition
and has a microprocessor that automatically controls a valve in order to apply
appropriate
cylinder pressure to balance the load. Electronic controls introduce cost,
complexity and
likelihood of malfunction. It would be desirable to eliminate electronic
controls, sensors,
etc. in a load balancing manipulator.
[0011 ] US 5,816,132 describes a load sensing pneumatic manipulator that
automatically
senses the outlet pneumatic pressure needed to maintain the load in a static
condition and
automatically adjusts this outlet pressure. Control over outlet pressure is
less responsive
and reliable than control over pressure applied directly to the lifting
cylinder. To the
knowledge of the inventor, this system has not been implemented commercially.
[0012] The devices disclosed in these prior art references are fully
automatic, complex
and not in widespread commercial use. None of these prior art references
discloses a
semi-automatic load balancing device capable of lifting any desired weight
that is simple to
operate and maintain. There is therefore still a need in the art for improved
multi-weight
balancing devices. Although many of the principles used in load balancing
hoists may be
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applicable to pneumatic manipulators, significant differences can still exist.
For example,
in many applications it is important to be able to rigidly position a load in
three dimensional
space, which many load balancing hoists are unable to do. There is therefore a
particular
need in the art for improved multi-weight balancing pneumatic manipulators.
[0013] At present, most manipulators float the load in a balanced state,
switching between
a no-load balance point and a loaded balance point. The switching between
states is
normally done abruptly by causing a valve to switch from the no-load air
pressure to the
load pressure, and vise-versa. This abrupt switching poses the problem that it
can
sometimes lead to un-natural motion, which is disconcerting to operators. It
would be
desirable to improve upon this by providing more natural switching between
conditions.
[0014] In addition, manipulators must be designed to be intrinsically safe in
the event of a
failure or unforeseen work condition. As a safety feature, there is usually a
velocity fuse
which restricts air flow if the flow in and out of the lift cylinder if it
goes over a certain
speed, or equipment similar to the velocity fuse to similarly limit air
exhaust speed.
Another speed limiting device that is sometimes used is a brake that engages
when the
manipulator arm is moved too quickly. As an additional safety measure, there
may also
sometimes be provided a device that bleeds the air in the lift cylinder if the
supply pressure
fails.
[0015] There are normally 3 emergency situations to deal with:
1. the loss of the load, where the load falls out of the jaws of the end
effector, and the
manipulator arm accelerates upwardly, out of control;
2. the loss of air supply pressure, for example due to an airline break on the
manipulator
or outside the manipulator, where the manipulator suddenly collapses, out of
control;
or,
3. an accidental activation of the end effector release mechanism.
[0016] In the first situation, the velocity fuse acts to trap the air in the
lift cylinder, in a
situation where the air should actually be exhausted as quickly as possible.
The velocity
fuse therefore acts to worsen the danger in a lost load situation.
[0017] In the second situation, most existing safety systems sensing the loss
of air
pressure employ a valve that either locks the air in the lift cylinder or
drains it away slowly.
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They will not generally sense that the pressure is below a safe level; they
sense only that
the supply has been completely lost. In many situations, the supply drops to
an
intermediate level that is somewhat less than the minimum necessary to lift
the load, but is
still a substantial pressure insufficient to cause activation of the lift
cylinder locking valve.
[0018] In the third situation, the objective generally is to quickly lower the
lift cylinder
pressure until it is at a level low enough that it is safe to open the jaws.
This safe level can
be the no-load pressure set to balance the weight of the manipulator when no
load is
present. When pressed prematurely, while the load is unsupported, the effect
is a rapid
descent of the manipulator, until the velocity fuse or brake limits the rate
of descent. If the
release mechanism has been pressed, it is desirable to lower the object as
quickly as
possible; however, rapid lowering of the object is impeded by the velocity
fuse.
[0019] One additional problem caused by the use of a velocity fuse or a brake
is that both
of these devices undesirably limit the speed of movement of the manipulator
during normal
use. These devices must be set so that they engage quickly in a safety event.
One
drawback therefore is that these devices can sometimes be triggered when
working quickly
with the manipulator, as rapid movements of the operator cause air to exhaust
at a rate
comparable to the trip setting of the velocity fuse. This is disconcerting to
operators, since
the manipulator locks up and prevents further movement until the fuse is re-
set. This can
lead to widespread loss of production efficiency, particularly in an assembly
line setting.
Unlike hoists, which are provided to lift very heavy loads, manipulators are
often provided
to speed up work by allowing an operator to more naturally and quickly lift
loads of a
moderate weight; the problem of velocity fuse tripping is therefore more
prevalent in
manipulators than in hoists.
[0020] US 3,791,627 discloses a load balancing hoist having three different
bleed valves
on the outlet of the main lift cylinder. The first two valves are for lowering
the load by
relieving air pressure from the lift cylinder. The third valve allows a slower
release of air
and is engaged as an alternative to the first two valves in the event of loss
of air supply
pressure. This allows the load to slowly be lowered to the ground. This system
works only
in the event of air supply failure, rather than lost load condition and is
applicable to a hoist,
rather than a manipulator.
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[0021] There is therefore still a need in the art for improved safety devices
for use with
load balancing pneumatic manipulators, particular in the event of a lost load
condition.
[0022] Various types of actuators are used to operate pneumatic valves. One
type of
actuator is the manual push button. Another is a solenoid operated via an
electric switch.
It is also known in the art to employ a neutrally biased sliding actuator or
shuttle that
reciprocates between upper and lower positions in order to operate two valves
in a
mutually exclusive fashion. However, these actuators are not known in
combination with a
semi-automatic system for balancing any load and can provide more intuitive
operation
than other actuator systems.
[0023] US 3,880,393 discloses a manually operated shuttle valve containing two
spring
returned three way valves. The springs maintain the shuttle in a neutral
position. When an
operator lifts on the shuttle, an upper valve is engaged and when the operator
pushes
downwardly on the shuttle, a lower valve is engaged. These valves are
connected to
different portions of the pneumatic load balancing circuit.
[0024] US 5,269,644 discloses a load balancer having a manual control switch
comprising
a reciprocating sleeve centrally spring balanced between two inductive
proximity switches.
Movement of the sleeve upwardly causes the upper switch to engage, and the
lower switch
to disengage; the opposite also applies. The shuttle is located near an
operator controller
of the load balancer.
[0025] The advantages of this type of actuator in combination with a semi-
automatic load
balancing pneumatic lifting device have not been previously realized.
Summary of the Invention
[0026] According to the present invention, there is provided a load-balancing
device
comprising: a vertical mast; an arm extending outwardly from the mast, the arm
pivotally
attached at a proximal end to the mast to permit arcuate vertical movement of
the arm
relative to the mast; a pneumatic lift cylinder connected with the arm; an
inflatable reservoir
for storing a volume of air at a selected reservoir pressure, an inflation
valve for controlling
inflation of the reservoir; and, an amplifier in fluid communication with the
reservoir, the
amplifier for providing a separate flow of air to the lift cylinder at the
reservoir pressure, the
reservoir pressure selected to maintain the device in a balanced condition
when a load is
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being lifted. The device may comprise a load-balancing pneumatic manipulator.
The
device may further comprise a deflation valve permitting deflation of the
reservoir. The
inflation and/or deflation valves may be operable from an operator control
center using an
actuator, for example a pneumatic push button or an electric switch. The
inflation and
deflation valves may be operable from the operator control center in a
mutually exclusively
fashion via a neutrally biased reciprocating actuator to selectively inflate
or deflate the
reservoir. The reservoir may comprise a closed vessel of a pre-specified
volume. The
reservoir may comprise a closed-ended length of tubing of pre-specified
volume. The
volume of the reservoir may be selected based in part upon the weight of the
loads being
lifted.
[0027] According to the present invention, there is further provided a method
of semi-
automatically lifting first and second objects of different weights using a
load balancing
device as previously described, the method comprising: securing the first
object to be lifted
using an end-effector; operating the inflation valve to increase the reservoir
pressure to a
value sufficient to place the device in a balanced condition when the first
object is lifted;
releasing the first object from the end-effector and reducing the reservoir
pressure;
securing the second object to be lifted using the end-effector; and, operating
the inflation
valve to increase the reservoir pressure to a value sufficient to place the
device in a
balanced condition when the second object is lifted. The reservoir pressure
may be
decreased automatically when the first object is released. Alternatively, the
reservoir
pressure may be decreased by operation of the deflation valve. The reservoir
pressure
may be decreased simultaneously with the release of the first object. The
reservoir
pressure may be decreased to a value sufficient to place the device in a
balanced
condition either when no load is lifted or when a load of minimum weight is
lifted.
[0028] According to the present invention, there is yet further provided a
load balancing
pneumatic manipulator having a controlled air release system comprising: a
pneumatic lift
cylinder having a piston chamber with a vent for releasing air from the
cylinder upon
changes in volume of the chamber in order to maintain a substantially constant
chamber
pressure; a blocking valve in fluid communication with the vent that closes
upon load
release in order to preserve the chamber pressure; and, a release metering
valve in fluid
communication with the vent when the blocking valve is closed upon load
release in order
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to reduce the chamber pressure at a first rate. The blocking valve may also
close upon
decrease of air supply pressure below a threshold value in order to preserve
the chamber
pressure. The threshold value may be greater than or equal to the pressure
required to
maintain the manipulator in a balanced condition when a load of maximum weight
is being
lifted; alternatively, the threshold value may be set at a value indicative of
a loss of air
supply pressure, for example slightly below the lowest supply pressure
observed during
routine operation. The threshold value may be greater than or equal to 70, 75,
80, 85, or
90 psi. The manipulator may further comprise a lost air supply metering valve
in fluid
communication with the vent when the blocking valve is closed upon decrease of
air supply
pressure below the threshold value in order to reduce the chamber pressure at
a second
rate. The second rate may be less than the first rate. The manipulator may yet
further
comprise a part present valve operable to cause air to be rapidly exhausted
from the
chamber in the event that a load being carried by the manipulator is
inadvertently lost.
[0029] According to the present invention, there is still yet further provided
a load
balancing pneumatic manipulator having a controlled air release system
comprising: a
pneumatic lift cylinder having a piston chamber with a vent for releasing air
from the
cylinder upon changes in volume of the chamber in order to maintain a
substantially
constant chamber pressure; a blocking valve in fluid communication with the
vent that
closes upon decrease of air supply pressure below a threshold value or upon
load release
in order to preserve the chamber pressure; a release metering valve in fluid
communication with the vent when the blocking valve is closed upon load
release in order
to reduce the chamber pressure at a first rate; and, a lost air supply
metering valve in fluid
communication with the vent when the blocking valve is closed upon decrease of
air supply
pressure below a threshold value in order to reduce the chamber pressure at a
second
rate. The manipulator may further comprise an operator activated release valve
in fluid
communication with the blocking valve, the release valve operable to close the
blocking
valve upon load release. The manipulator may yet further comprise a supply
sense valve
in fluid communication with the blocking valve, the supply sense valve
operable to close
the blocking valve upon decrease of air supply pressure below a threshold
value. The
supply sense valve may be adjustable to automatically close the blocking valve
upon
decrease of air supply pressure below the threshold value.
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[0030] The foregoing invention provides many useful advantages. The use of a
semi-
automatic system for lifting any weight is less complex and less costly to
manufacture than
a fully automatic system. The use of a reservoir in place of a regulator
allows any desired
lift cylinder pressure to be selected at the touch of a push button, rather
than by manual
(e.g. dial type) adjustment. This in turn allows objects of different weights
to be lifted with
minimal operator intervention. The controls for adjusting reservoir pressure
are robust and
can be located on an operator control center (for example, near the end-
effector) without
fear of damage. The reservoir is also particularly amenable to use with a
neutrally biased
reciprocating actuator. This type of actuator allows the operator to gently
lift upon
handlebars of the operator control center until the reservoir pressure is
sufficient to
balance the weight of the object, at which point the actuator naturally
returns to a neutrally
biased position. This type of intuitive and seamless operation is of great
advantage in an
industrial setting, particularly when it is desirable to rapidly lift objects
of different weights.
[00311 The air release system of the present invention provides improved
safety as
compared with prior art systems. By venting at a first rate during inadvertent
or deliberate
release of the object being lifted before it is appropriately positioned to do
so, the system
allows the object to be rapidly lowered in a controlled fashion without
dropping the object.
The use of a second rate upon loss of air supply pressure allows the
manipulator to safely
lower the object being lifted at a much slower rate, so that an operator has
time to
appropriately position it without damaging the object, while at the same time
allowing the
operator and bystanders to evacuate the immediate area. These advantages are
obtained
while at the same time eliminating the need for a velocity fuse, which is
prone to being
activated during normal work operations if an operator is working more quickly
than the
fuse is designed to allow. When a lost load condition exists, the lift
cylinder is allowed to
rapidly vent to prevent upward acceleration of the manipulator; this is an
improvement as
compared with use of a velocity fuse, which traps air within the lift cylinder
and
exacerbates the rapid acceleration problem. The combination of the foregoing
provides a
particularly safe and easy to use manipulator capable of allowing an operator
to intuitively
lift objects of different weights.
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Brief Description of the Drawings
[0032] Having summarized the invention, preferred embodiments thereof will now
be
described with reference to the accompanying drawings, in which:
[0033] Fig. 1 shows a lifting device according to the present invention in
side view;
[0034] Fig. 2 shows a pneumatic circuit incorporating an inflatable reservoir
for setting the
lift cylinder load balancing pressure;
[0035] Figs. 3a-c shows a neutrally biased reciprocating actuator for use in
combination
with the circuits of the present invention;
[0036] Fig. 4 shows a pneumatic circuit for an air release system
incorporating two bleed
valves having two different venting rates; and,
[0037] Fig. 5 shows a combined pneumatic circuit incorporating the features of
both Fig. 2
and Fig. 4.
Detailed Description
[0038] Referring to Fig. 1 a, a load balancing lifting device is shown. The
lifting device
comprises a pneumatically assisted manually operated load balancing
manipulator,
generally denoted as 1, that comprises a vertical mast 2 with an arm 3
extending outwardly
therefrom. The arm 3 is rotatably attached to the mast 2 by a first rotation
means 4 that
permits rotation of the arm about a first vertical axis 5 passing through the
mast 2. The
proximal end of the arm 3 is mounted to the first rotation means 4 by way of a
pivot
assembly 6 that permits the arm 3 to arcuately move as well as rotate. A
second rotation
means 7 is provided at the distal end of the arm 3 and is mounted in a manner
that permits
a second rotation axis 8 to remain vertical at all times, irrespective of the
angular
orientation of the arm 3. In the embodiment shown, the vertical orientation of
the rotation
means 7 is maintained using a parallelogram linkage 9, although other means,
for example
trunnion mounts or gimbals, could also be used.
[0039] One end of a horizontal extension member 10 is attached to the second
rotation
means 7 at the distal end of the arm 3. The opposite end of the horizontal
extension
member 10 includes a third rotation means 11 to which is mounted a vertical
extension
member 12. The length of both the horizontal and vertical extension members
10, 12 is
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chosen based on the intended application of the manipulator 1. Additional
extension
members, either horizontal or vertical, may be added depending on the range
and degree
of motion required for a particular application. An attachment 14, also known
as an end-
effector, is provided on the vertical extension member 12. The attachment 14
may be
designed for special purpose or general purpose lifting operations and may
comprise, for
example, a clamp, a pincer, a magnet, a scoop, vacuum cups, etc. An operator
control
center 13 is provided proximal the attachment 14 that comprises a set of
handlebars 16. In
certain embodiments, the operator control center comprises a neutrally biased
actuator 17,
as will be described in greater detail hereinafter.
[0040] A pneumatic lift cylinder 15 supports the arm 3 via a linkage located
near the
proximal end of the arm and is operable to resiliently bias the arm against
the weight of an
object being carried by the manipulator. In operation, the pneumatic lift
cylinder 15
normally has at least two operating pressures: a first (lower) pressure chosen
to offset the
weight of the arm and extension members so that the position of the
manipulator may be
manually adjusted; and, a second (higher) pressure chosen to offset the weight
of the
object as well as the arm and extension members. Switching from the first to
the second
pressures occurs when an operator 18 attempts to manually lift the object with
the
manipulator and switching from the second to the first pressure occurs when
the object is
released. In this manner, the manipulator appears to the operator to remain
neutrally
buoyant, irrespective of whether or not an object is being carried by the
manipulator.
[0041] The pneumatically assisted manually operated load balancing manipulator
shown
here is but one embodiment of a suitable load balancing device. Persons
skilled in the art
will realize that various load balancing devices may be used in the same way
to achieve
the same function. In fact, any lifting device that permits an object to be
rigidly positioned
at a selected location in three-dimensional space in a pneumatically load
balanced
condition may be used.
[0042] Referring to Fig. 2, a schematic diagram is shown whereby a reservoir
20 is
inflatable by operation of an inflation valve 21, which opens to connect the
air supply 22
with the reservoir. The inflation valve 21 is actuated by an inflation
actuator 23 that
comprises a push button or toggle located on the operator control center 13.
When the
inflation actuator 23 is released, the inflation valve 21 reverts to a
normally closed
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condition. This causes inflation of the reservoir 20 to cease and stabilizes
the pressure
within the reservoir. A deflation valve 24 is also provided, which opens to
connect the
reservoir 20 to atmospheric conditions in order to allow air within the
reservoir to be
exhausted. In a similar manner to the inflation valve 21, the deflation valve
24 is actuated
by a deflation actuator 26 comprising a push button or toggle that is located
on the
operator control center 13. Use of the deflation actuator 26 therefore causes
the pressure
within the reservoir 20 to decrease. In this manner, any desired pressure may
readily be
established within the reservoir 20.
[0043] The reservoir 20 is in fluid communication with a pressure controlled
amplifier 27,
also known as a volume booster, via a selector valve 28. The amplifier 27
provides a flow
of air at the same pressure as established in the reservoir 20 to the lift
cylinder 15. The
pressure within the reservoir 20 can be set by the operator 18 at a value
sufficient to offset
the weight of the object being lifted through use of the actuators 23, 26,
thereby
establishing an identical pressure in the lift cylinder 15 and placing the
load in a balanced
condition. The selector valve 28 operates to complete the fluid connection
between the
amplifier 27 and the reservoir 20 only when the attachment 14 is activated and
an object is
confirmed to be secure for lifting. In this manner, the reservoir 20 is
prevented from
communicating a pressure to the lift cylinder 15 that could cause the
manipulator to shoot
upwardly in a potentially dangerous fashion if an object were not secured by
the
attachment 14. Under all other conditions, the selector valve 28 causes
communication
between a no-load regulator 29 and the amplifier 27. The no-load regulator 29
is in
communication with the air supply and is set at a pressure sufficient to
balance the weight
of the manipulator itself; this allows the manipulator to be moved in a
balanced condition
when no object is being lifted. This fail-safe arrangement of the selector
valve 28 ensures
that the manipulator is balanced at all times, regardless of whether or not a
load is lifted.
[0044] The reservoir 20 is inflated each time an object is lifted and deflated
when the
object is released. This deflation of the reservoir 20 upon object release
provides an
important safety feature, preventing inadvertent upward movement if a lighter
object is
subsequently lifted. The reservoir 20 is preferably connected in a manner such
that its
minimum pressure is the pressure of the no-load regulator 29. This prevents
the
manipulator from collapsing under its own weight when a load is first engaged,
prior to
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inflation of the reservoir 20 to the desired balancing pressure. In one
circuit arrangement,
an optional load regulator 30 can be used in combination with the reservoir
20, so that a
higher minimum reservoir pressure is constantly maintained. This minimum
reservoir
pressure is provided via load valve 31 and preferably selected to correspond
to the
minimum load desired to be balanced by the manipulator, so that only a
relatively small
degree of inflation is required to lift heavier loads and little or no
inflation is required to lift
the minimum load. Although this arrangement allows a desired reservoir
pressure
(sufficient to balance a particular load) to be established more quickly than
if the reservoir
were inflated from no-load pressure each time, it also requires foreknowledge
of the
minimum load in order to set the load regulator 30 and introduces additional
cost and
complexity into the pneumatic circuit. For this reason, setting the minimum
reservoir
pressure at the no-load pressure is preferred in most circumstances; this
obviates the need
for the optional load regulator 30, thereby simplifying the pneumatic circuit
and reducing
the overall number of regulators.
[0045] Although the inflation valve 21 and deflation valve 24 are described as
being
separate, these valves may optionally be co-located or provided within a
common body or
housing. In one embodiment, the inflation valve 24 may comprise a three way
valve which
is operable to provide two mutually exclusive flow paths, one connected with
the air supply
and the other allowing the reservoir 20 to be exhausted. Persons skilled in
the art will be
able to contemplate other arrangements of components whereby the
aforementioned
function can be obtained and these variations are included within the scope of
the present
invention.
[0046] Referring to Figs. 3a, 3b, 3c, in one embodiment the operator control
center 13
may include a reciprocating actuator 17. The reciprocating actuator 17
includes a central
block 40 to which handles 16 may be mounted. The central block 40 is
vertically
translatable upwardly and downwardly along a linear bearing or rod 42 and is
resiliently
biased toward a neutral position via upper and lower springs 43, 44. This
permits
temporary upward and downward movement of the block 40 from the neutral
position in
response to the operator 18 lifting up or pushing down on the handles 16. At
the upper
and lower limits of travel of the block 40, the inflation actuator 23 and
deflation actuator 26,
respectively, are engaged. The inflation and deflation actuators 23, 26 cause
the inflation
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and deflation valves 21, 24 to operate in order to increase or decrease,
respectively, the
reservoir pressure. As used herein, the terms "operate" or "operable"
generally mean that
the valves are opened; however, arrangements can be contemplated by those
skilled in
the art whereby valves could be closed in order to achieve the same effect on
reservoir
pressure. When initially lifting the object, the operator 18 pulls upwardly on
the handles
16, until the reservoir 20 is inflated sufficiently to balance the weight of
the manipulator and
the object being lifted. At this point, the object rises slightly and the
handles 16 naturally
return to their neutrally biased position, causing the reservoir pressure to
stabilize. The
reservoir 20 can thereby be inflated in a very natural manner by the operator
18 without
requiring knowledge of the pressure need to balance the object. The actuator
17 may
include a detente (not shown) or similar means to hold the block 40 in the
neutral position
until sufficient force is exerted to break the block free from the detente and
move it toward
its upper or lower extremity of travel. The actuator may include a manual lock
feature (not
shown) to prevent movement of the actuator once the reservoir pressure has
been
established.
[0047] One additional use of the reciprocating actuator 17 comes into effect
particularly
when very heavy loads are being lifted. In this case, the components of the
manipulator
system increase in size to the point that inertia, friction and air flow
restrictions become
more significant relative to the strength of the operator 18, even when the
load is neutrally
balanced. It can sometimes be useful to have a slight over-pressure (when
raising) or
under-pressure (when lowering) to aid in overcoming inertia. The pressure
increase or
decrease has the effect of gently boosting the manual raising or lowering of
the object to
assist the operator 18 in overcoming the inertia, friction and air flow
restrictions of the
manipulator system. By continuing to lift on the handles 16, even after the
reservoir
pressure has been increased to the point that the weight of the load is
balanced, a slight
over-pressure can naturally be established in the reservoir 20. Once the
object has begun
moving upwardly, pushing down on the handles 16 causes the pressure in the
reservoir to
decrease to the point that the load is again balanced. In this manner, a
slight boost can be
achieved naturally by the operator without introducing additional complexity
to the operator
controls and without the use of extra regulators or other equipment.
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[0048] Referring to Fig. 4, a selector valve 28 is provided in combination
with an amplifier
27 in order to selectively provide a no-load or load balancing lift cylinder
pressure to the lift
cylinder 15, depending upon the position of the selector valve 28. The no-load
pressure is
provided by a no-load regulator 29 and the load balancing pressure can be
provided by an
inflatable reservoir 20 or a load regulator 30 in combination therewith, all
as previously
described with reference to Fig. 2. The selector valve 28 only directs the
load balancing
pressure to the amplifier 27 when the part present valve 50 operates to
provide a pressure
signal indicating that an object is secured by the attachment 14. In a lost-
load condition,
the pressure signal from the part present valve 50 is lost and the selector
valve 28 reverts
to its normal position in which the no-load pressure is supplied to the
amplifier 27. The lift
cylinder then rapidly vents so that the manipulator does not shoot upwardly,
potentially
endangering the operator 18 or bystanders. With appropriate component
selection, the lift
cylinder 15 can be vented in less than one second during this condition.
[0049] In the event of an air supply failure, the loss of pressure signal is
transmitted by the
supply sense valve 51 to the blocking valve 53 via the override valve 52. The
supply
sense valve 51 is adjustable and may be set at any desired threshold value to
indicate a
loss of supply. This value can be greater than or equal to the pressure
required to
maintain the manipulator in a balanced condition when a load of maximum weight
is being
lifted. In this case, when any loss of air supply occurs that is insufficient
to maintain the
manipulator in a balanced condition when the heaviest load is present, the
manipulator
goes into a shut-down condition, thereby providing safety under all possible
load
conditions. In cases where the maximum load is not known in advance, the
threshold may
be set at a value which indicates a loss of air supply, for example a value
that is slightly
lower than the minimum pressure experienced during normal fluctuation through
use. The
loss of pressure signal is then relayed to the blocking valve 53, which moves
into its
normally closed position to block exhausting of air from the lift cylinder 15
backward
through the amplifier 27. Air is thereby permitted only to exhaust from the
cylinder
chamber vent through the release selector valve 54. The normal position of the
release
selector valve 54 is to a flow path passing through an air loss metering valve
55. This
valve is set with a relatively slow flow rate to allow the pressure trapped
within the chamber
of the lift cylinder 15 to slowly leak out until the object being lifted comes
to rest gently on
the ground.
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[0050] When an object is released from the attachment 14, either during normal
operating conditions or by accident, the pressure signal to the release
selector valve 54 is
exhausted. This causes the release selector valve 54 to direct its flow path
through a
release metering valve 56. The release metering valve 56 permits a higher flow
rate than
the air loss metering valve 55 so that air is more rapidly vented during
normal release
conditions. An added safety benefit is provided through improved operation of
the load
sense valve 57. The load sense valve 57 is provided to monitor the pressure in
the lift
cylinder 15 and allow the attachment 14 to release the object being lifted
only when the
pressure has reached a lower and safer level. The controlled rate of descent
provided by
the release metering valve 56 makes the operation of the load sense valve 57
much more
reliable, since it can more easily track and respond to a slower-moving change
in pressure
within the lift cylinder 15.
[0051] Referring to Fig. 5, a combined pneumatic circuit is shown that
incorporates the
features of Fig. 2 and Fig. 4. Like features are denoted by like reference
numerals. The
features described with reference to Figs. 2 and 4 can be provided separately
or in
combination in a manipulator according to the present invention. When provided
in
combination, the result is a semi-automatic load balancing manipulator that
allows any
weight to be lifted quickly and safely.
[0052] The foregoing embodiments are illustrative of the invention and are
meant to be
construed in a non-limiting sense. Those skilled in the art will recognize
that further
features, variation and sub-combinations of the present invention may be
provided without
departing from the spirit of the invention as described herein, and are
intended by the
inventor to be encompassed by the following claims.
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