U.S. patent number 3,641,551 [Application Number 04/785,145] was granted by the patent office on 1972-02-08 for safe load control system for telescopic crane booms.
This patent grant is currently assigned to Grove Manufacturing Company. Invention is credited to William L. Lowe, Russell L. Sterner.
United States Patent |
3,641,551 |
Sterner , et al. |
February 8, 1972 |
SAFE LOAD CONTROL SYSTEM FOR TELESCOPIC CRANE BOOMS
Abstract
An overload prevention and indicator system for telescopic boom
cranes of the stationary and/or mobile types in which the boom is
pivotally raised and lowered in vertical planes by hydraulic lift
motor means, the system including first electrical circuit means
responsive to complete a selected on of a plurality of circuits
corresponding to the length of the boom, the plurality of circuits
being respectively connected in series to a corresponding plurality
of second electrical circuit means, each representative of a
predetermined increment of boom length, responsive to angular
position of the telescopic boom in the vertical plane. The
plurality of angular position outputs of each second electrical
circuit means are connected according to predetermined crane
overload information to a plurality of third circuit means
representative of pressure range increments, and a pressure switch
responsive to fluid pressure in the lift motor means, which is
indicative of boom load, is connected to successively operate said
third circuit means as the fluid pressure in said lift motor means
increases and actuate an indicator and render inoperative selected
operations of the crane when the crane approaches an overload or
tipping condition at the particular length, angle and load
condition at which it is operating at any instant.
Inventors: |
Sterner; Russell L.
(Greencastle, PA), Lowe; William L. (Hagerstown, MD) |
Assignee: |
Grove Manufacturing Company
(Shady Grove, PA)
|
Family
ID: |
25134585 |
Appl.
No.: |
04/785,145 |
Filed: |
December 19, 1968 |
Current U.S.
Class: |
340/522; 340/685;
212/277; 212/278 |
Current CPC
Class: |
B66C
23/905 (20130101) |
Current International
Class: |
B66C
23/90 (20060101); B66C 23/00 (20060101); G08b
021/00 () |
Field of
Search: |
;212/39 ;340/267C |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,177,303 |
|
Sep 1964 |
|
DT |
|
1,162,987 |
|
Feb 1964 |
|
DT |
|
1,000,613 |
|
Aug 1965 |
|
GB |
|
Primary Examiner: Hornsby; Harvey C.
Claims
We claim:
1. A safe load control system for preventing the overloading and/or
tipping of material-handling apparatus of the type comprising an
extensible boom 30-33 pivotally connected 35 on a supporting
structure 36, and extensible fluid motor means 41 connected between
the boom and supporting structure for angularly moving the boom in
the vertical plane; said control system comprising first circuit
means 52, 54, 56 connected 47-51 with said boom and responsive to
the variable extensible length of the boom; a plurality of second
circuit means A1-A12 respectively corresponding to predetermined
boom lengths from the retracted to the fully extended positions,
and each having an input 72 and output means 73; said first circuit
means 52 connected 55 to the inputs 72 of said plurality of second
circuit means A1-A12 and operative to select and connect in circuit
therewith the second circuit means A1-A12 corresponding to the
instantaneous length of said boom 30-33; said output means 73
corresponding to predetermined boom elevation angles; control means
59, 62, 66 connecting said inputs 72 to said boom 30-33 for
response to the varying elevation angles of the boom and operative
to connect the inputs 72 in circuit with the output means 73
corresponding to the instantaneous elevation angle of the boom;
signal circuit means 112; a plurality of switch circuit means
P1-P24 connecting said output means 73 to said signal circuit means
112; pressure-responsive means 79 connected to normally
progressively operate said plurality of switch circuit means P1-P24
in response to the pressure of the fluid in the fluid motor means
41 corresponding to the loading of said boom; whereby the switch
circuit means P1-P24 is only operated to operate the signal circuit
means 112 when the moment of force at a particular boom length and
angle exceeds the safe moment of force for that boom attitude.
2. A safe load control system as set forth in claim 1 in which said
first circuit means comprises a switch means having a movable
contractor and a plurality of output contacts corresponding to said
predetermined boom lengths of said second circuit means.
3. A safe load system as set forth in claim 2 including boom length
responsive means connected on said boom and responsive to extension
and retraction of the boom, and said boom length responsive means
connected to adjust the position of said movable contactor relative
to said plurality of fixed contacts.
4. A safe load system as set forth in claim 1 in which said
plurality of second circuit means each comprises a second switch
means having a plurality of output contacts and a movable input
contactor progressively connectable therewith as the boom elevation
angle increases.
5. A safe load system as set forth in claim 4 in which said control
means includes a cam connected for movement with the boom in the
vertical plane, linkage means connected between said cam and said
movable contactors of said second switch means for movement by said
cam to move said movable contactors in response to varying boom
elevation angles.
6. A safe load system as set forth in claim 5 in which said linkage
means is a flexible element, said cam including a surface profiled
to translate boom elevation angles into the horizontal components
of the angles, and disposed to control said flexible element.
7. A safe load control system for preventing the overloading and/or
tipping of material-handling apparatus of the type comprising an
extensible boom 30-33 pivotally connected 35 on a supporting
structure 36, and vertically swingable to different elevation
angles by extensible lift fluid motor means 41 connected between
the boom and supporting structure, said control system comprising
first electrical circuit means 52 responsive to variations in the
length of the boom, second electrical circuit means A1-A12
responsive to the elevation of the boom in the vertical plane, said
first and second electrical circuit means connected in series and
having a plurality of output circuits 73, said first 52 and second
A1-A12 electrical circuit means operative to complete a circuit to
one of said output circuits 73 corresponding to the moment arm for
the instantaneous operating attitude of the boom, signal circuit
means 112, a plurality of third circuit means P1-P24 corresponding
to predetermined maximum pressure ranges for predetermined moment
arms of the boom connecting said plurality of output circuits 73 to
said signal circuit means 112, pressure-responsive means 79, a body
portion connected for movement by said pressure-responsive means
normally progressively operate said plurality of third circuit
means P1-P24 in response to the fluid pressure in the lift fluid
motor means 41 corresponding to the loading of said boom 30-33, and
said plurality of third circuit means P1-P24 connected to operate
the signal circuit means 112 only when the moment of force at the
particular boom operating attitude exceeds the predetermined
corresponding safe moment of force.
8. A safe load control system as set forth in claim 1, in which
said signal circuit means includes a source of power and a relay
connected in circuit with said plurality of third circuit means,
said relay having contacts, and signal means connected for
operation by said contacts when said relay is operated by said
third circuit means.
9. A safe load control system as set forth in claim 8, including
additional means connected for operation by said contacts to render
at least said extensible fluid motor means inoperative to lower
said boom.
10. A safe load control system as set forth in claim 2, in which
said switch means is a first rotary switch, said plurality of
second circuit means each comprising a second rotary switch having
a plurality of output contacts and a movable input contactor
rotatable into progressive contact with the output contacts thereof
as the boom elevation angle increases, said plurality of output
contacts of said first rotary switch respectively connected to the
movable input contactors of said plurality of second rotary
switches, and the plurality of output contacts of said second
rotary switches connected according to predetermined maximum moment
of force information to said plurality of third circuit means.
11. A safe load control system for preventing the overloading
and/or tipping of material-handling apparatus of the type
comprising an extensible boom pivotally connected on a supporting
structure, and extensible fluid motor means connected between the
boom and supporting structure for angularly moving the boom in the
vertical plane; said control system comprising first circuit means
connected with said boom and responsive to the variable extensible
length of the boom; a plurality of second circuit means
respectively corresponding to predetermined boom lengths from the
retracted to the fully extended positions, and each having an input
and output means; and first circuit means connected to the inputs
of said plurality of second circuit means and operative to select
and connect in circuit therewith the second circuit means
corresponding to the instantaneous length of said boom; said output
means corresponding to predetermined boom elevation angles; control
means connecting said inputs to said boom for response to the
varying elevation angles of the boom and operative to connect the
inputs in circuit with the output means corresponding to the
instantaneous elevation angle of the boom; signal circuit means; a
plurality of third circuit means connecting said output means to
said signal circuit means; a fluid piston-cylinder assembly; a
fluid connection between said piston-cylinder assembly and the
fluid in the bottom portion of said extensible fluid motor means, a
member guided for sliding movement; a lever arm linkage connected
to said guided member and engaged for movement by said
piston-cylinder assembly, said plurality of third circuit means
connected in the path of movement of said guided member for
progressive operation thereby upon increase of fluid pressure in
said piston-cylinder assembly in response to the pressure of the
fluid in the fluid motor means corresponding to the loading of said
boom to correspondingly move said guided member, whereby the third
circuit means is operated to operate the signal circuit means when
the moment of force at a particular boom length and angle exceeds
the safe moment of force for that boom attitude.
12. A safe load control system as set forth in claim 11 in which
said plurality of third circuit means comprise a plurality of
individually operable switch elements having actuator means
protruding into the path of movement of said guided member whereby
said switch elements are operated upon contact of the corresponding
actuator by said guided member.
13. A safe load control system as set forth in claim 11 in which
said third circuit means comprise a plurality of normally closed
switch elements each having an input terminal and an output
terminal, the output terminals of all said switch elements commonly
connected to said signal circuit means, the input terminals of said
switch elements connected according to predetermined maximum moment
of force information to said output means of said plurality of
second circuit means, and said plurality of switch elements
protruding into the path of movement of said guided member to be
moved to an open circuit position when contacted thereby.
14. A safe load control system as set forth in claim 12 in which
said plurality of switch elements are effectively staggered in a
plane substantially parallel with said guided member, and an edge
portion on said guided member movable into contact with said
plurality of actuators, whereby said plurality of switch elements
are progressively operated by said edge portion as the moment of
force of the extensible boom increases.
15. A safe load control system for preventing the overloading
and/or tipping of material-handling apparatus of the type
comprising an extensible boom pivotally connected on a supporting
structure, and extensible fluid motor means connected between the
boom and supporting structure for angularly moving the boom in the
vertical plane; said control system comprising first circuit means
connected with said boom and responsive to the variable extensible
length of the boom; a plurality of second circuit means
respectively corresponding to predetermined boom lengths from the
retracted to the fully extended positions, and each having an input
and output means; said first circuit means connected to the inputs
of said plurality of second circuit means and operative to select
and connect in circuit therewith the second circuit means
corresponding to the instantaneous length of said boom; said output
means corresponding to predetermined boom elevation angles; control
means connecting said inputs to said boom for response to the
varying elevation angles of the boom and operative to connect the
inputs in circuit with the output means corresponding to the
instantaneous elevation angle of the boom; signal circuit means; a
plurality of third circuit means connecting said output means to
said signal circuit means; a fluid piston-cylinder assembly; a
fluid connection between said piston-cylinder assembly and the
fluid in the bottom portion of said extensible fluid motor means, a
member connected for movement by said piston-cylinder assembly,
said plurality of third circuit means connected in the path of
movement of said member for progressive operation thereby upon
increase of fluid pressure in said piston-cylinder assembly in
response to the pressure of the fluid in the fluid motor means
corresponding to the loading of said boom to correspondingly move
said member, whereby the third circuit means is operated to operate
the signal circuit means when the moment of force at a particular
boom length and angle exceeds the safe moment of force for that
boom attitude.
16. A safe load control system as set forth in claim 15 in which
said plurality of third circuit means comprise a plurality of
individually operable switch elements having actuator means
protruding into the path of movement of said member whereby said
switch elements are operated upon contact of the corresponding
actuator by said member.
17. A safe load control system as set forth in claim 15 in which
said third circuit means comprise a plurality of normally closed
switch elements each having an input terminal and an output
terminal, the output terminals of all said switch elements commonly
connected to said signal circuit means, the input terminals of said
switch elements connected according to predetermined maximum moment
of force information to said output means of said plurality of
second circuit means, and said plurality of switch elements
protruding into the path of movement of said member to be moved to
an open circuit position when contacted thereby.
18. A safe load control system as set forth in claim 15 in which
said plurality of switch elements are effectively staggered in a
plane substantially parallel with said member, and an edge portion
on said member movable into contact with said plurality of
actuators, whereby said plurality of switch elements are
progressively operated by said edge portion as the moment of force
of the extensible boom increases.
Description
BACKGROUND OF THE INVENTION
In telescopic boom cranes of either the stationary or mobile types
which are adapted to lift a load by means of a cable depending from
the outer extremity of the boom which is controlled by a winch, and
wherein the booms are rotatable in azimuth and can also be
pivotally angularly raised and lowered in the vertical plane at any
given azimuth, when the moment of force exerted by the boom and the
load being lifted by the boom approaches a value greater than the
moment of resistance exerted by the structure supporting the
telescopic boom, the boom and the supporting structure is subject
to pitching about the tilt axis of the supporting structure, which
may be either a stationary structure or a mobile support frame,
which would cause damage to the crane and injury to the operator.
If the boom-supporting structure is a stationary platform which is
not susceptible to pitching then the boom is susceptible to bending
when the moment of force exerted by the load approaches or exceeds
the bending strength of the boom.
In order to prevent such damage and possible injury to the crane
operator, overload indicator and safe load control systems have
been proposed, one of such systems being shown in U.S. Pat. No.
3,371,800 issued to John L. Grove on Mar. 5, 1968 and owned by the
assignee of the present application. The system shown in the
mentioned patent is one of the few safe load control systems for
use on telescopic crane booms as opposed to fixed length booms. The
problem of determining pitching moments is more difficult for
telescopic boom structures and of devising a safe load control
system for such structures because for any given vertical angular
position of the boom there are a plurality of boom lengths and thus
a plurality of different pitching moments which must be taken into
account in devising an automatic safe load system. The system shown
in U.S. Pat. No. 3,371,800 is sufficiently accurate and reliable
for shorter length and lower lifting capacity telescopic booms but
this system is not sufficiently accurate for use on the much larger
telescopic boom cranes now being produced in the industry which for
instance have telescoping ranges from 27 to 92 feet and from 33 to
105 feet with respective higher lifting capacities in the range of
25 to 55 tons.
With the shorter length telescopic booms it was found that the
center of gravity of the entire boom structure, at any given
elevation angle of the boom, whether extended or retracted, varied
over a relatively short predetermined range so that the problems
involved in devising a safe load control system were relatively
uncomplicated. However, with the present telescopic boom
construction, having much greater extended lengths than heretofore
known in the art, it has been found that the center of gravity of
the boom for the various extended lengths and elevation angles
varies over a much greater and a more complex range which greatly
complicates the problem of devising an efficient safe load control
circuit to warn the operator when the boom is moving toward an area
of unsafe operating conditions. The complex shifting of the center
of gravity as outlined, thus making it more difficult to determine
the tipping moments and safe operating limit of the crane, is
partly attributable to the positioning of the boom lift cylinders
and the positioning of the point of connection of the cylinders of
the boom relative to the boom pivot point, as in the higher
capacity and higher strength telescopic booms it has been found
necessary to change the angular attitude of the lift cylinders
relative to the boom from the attitudes they assumed in the prior
art lower capacity boom. The safe load control system for these
larger capacity cranes, with a much greater operating radius and
thus with a much greater range of operating radii, must, therefore,
be able to supervise the machine stability and capacity limitations
over a much greater range than can be attained with known prior art
systems.
SUMMARY OF THE INVENTION
The deficiencies of the prior art systems are overcome by the
present invention by providing a safe load control system in which
more safe operating range limitations for more operating points in
the operating range of the telescopic boom are programmed into the
system than have heretofore been possible in prior art systems. The
system of the present invention can be constructed to contain
programmed data of safe operating limitations for as many
individual boom operating points at individual boom lengths and
angles, as desired, in the entire operating range of the boom.
A cable connected to the end of the boom on one end and at the
other end to a rotary drum on the boom base section moves the wiper
contact of an electrical switch over successive fixed contacts for
each extension of the boom by a predetermined distance. The movable
contact thus selects a circuit connected to a fixed contact which
is representative of a boom length corresponding to the actual
instantaneous operating length of the boom, and thus completes a
segment of the safe load control circuit. The circuits from the
fixed contacts of the boom length switch are correspondingly
connected to the movable contacts of a plurality of boom angle
switches wherein each switch corresponds to a predetermined length
as represented by one of the fixed contacts on the boom length
switch. The boom angle switches each have a plurality of fixed
contacts successively representative of predetermined increasing
boom elevation angles. A cam mechanism connected to the boom pivot
point, to translate the boom angle into a corresponding linear
horizontal component of the angle, is connected to simultaneously
move the movable contacts of the plurality of boom angle switches
successively into connection with the fixed contacts as the boom
elevation angle increases. Thus for a particular boom elevation
angle the circuit completed by the boom length switch is thus
completed through the movable contactor of the boom angle switch to
the fixed contact thereof representative of the operating angle of
the boom.
A pressure gage having a movable piston therein is connected in
communication with the fluid pressure in the bottom of the boom
lift cylinders, with the movable piston of the gage connected
through a linkage arm to successively open a plurality of normally
closed switches, each representative of a predetermined pressure
range as the pressure in the bottom of the boom lift cylinders
increases. The pressure in the bottom of the lift cylinders varies
according to the boom load. For each operating attitude of the
boom, that is, for each operating point having an individual
elevation angle and boom length, there is a safe operation
limitation beyond which the entire crane may tip or the boom may
bend. The safe operation limitation for any individual working
attitude of the boom can be determined by the pressure in the
bottom of the lift cylinder. When this pressure is determined for a
given boom attitude, that is angle and length, any increase in the
lift cylinder pressure beyond that point would move the crane into
an unsafe area of operation. Therefore, the pressure switches are
connected to render an indication when the boom moves toward an
area of unsafe operation, and at the same time the circuitry
disables or automatically locks out those portions of the boom
hydraulic control system which could be used to manipulate the boom
into the overload condition, and maintains those portions of the
hydraulic control system in engagement by which the boom may be
manipulated away from the unsafe or overload condition.
The fixed contacts of the plurality of boom angle switches are thus
connected to the normally closed pressure switches where the
circuit for any particular fixed angle switch contact is connected
to the pressure switch representative of lift cylinder pressure
beyond which the boom cannot be safely operated at that particular
boom attitude. The circuit previously described is thus completed
through the normally closed pressure switch at the particular
operating angle and the outputs of all the normally closed pressure
switches are connected together to one end of a normally energized
relay. When the boom moves beyond the safe operating limitation for
the particular attitude of the crane at any instant, the pressure
gage linkage arm opens the normally closed pressure switch which
normally completes the circuit for the particular boom attitude
that keeps the relay energized causing the relay to deenergize,
sound an alarm, and, as previously indicated, lock out those
portions of the hydraulically controlled system which could be used
to manipulate the boom further into the unsafe operating range.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a mobile telescopic boom
crane, with parts broken away, showing the general arrangement of
the components of the system of the invention on the crane;
FIG. 2 is a fragmentary cross-sectional view, of the boom length
switch assembly, on an enlarged scale, with parts broken away,
taken substantially on line 2--2 of FIG. 1;
FIG. 3 is an enlarged foreshortened side elevational view of the
boom angle cam and switch assembly shown in FIG. 1;
FIG. 4 is a cross-sectional view taken substantially along line
4--4 of FIG. 3;
FIG. 5 is a top plan view of the boom angle cam assembly of FIG.
3;
FIG. 6 is a side elevational view, partly in section, of the
pressure gage and switch assembly;
FIG. 7 is a fragmentary top plan view thereof taken substantially
on line 7--7 of FIG. 6;
FIG. 8 is an enlarged elevational view of the right-hand end
thereof as seen in FIG. 6, with parts broken away to shown the
arrangement of switch contactors on opposite sides of the switch
assembly;
FIG. 9 is an enlarged fragmentary cross-sectional view taken
substantially on line 9--9 of FIG. 8 and particularly showing the
offset positioning of oppositely disposed switches;
FIG. 10 is a moment arm diagram for a telescopic boom on which are
plotted boom angle, hook distance from the boom pivot point and
hook distance from the center line of boom relation in feet;
FIG. 11 is a circuit connection chart programming the connection of
the boom angle switches to the pressure switches; and
FIG. 12 is a simplified electrical schematic diagram, with only
exemplary circuits completed, of the safe load control circuit of
the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings in greater detail, and particularly to
FIGS. 1 and 2, the system of the invention is shown on a mobile
hydraulic crane having a telescopic boom with a base section 30
connected to telescopically receive therein an inner midsection 31
into which is telescoped an outer midsection 32 which
telescopically receives a fly section 33 having a boom nose
assembly 34 connected to the outer end thereof. The fly section and
the two midsections are connected to be respectively extendible and
retractable by means of double-acting hydraulic rams or the like,
not shown, as disclosed in U.S. Pat. No. 3,371,800. The boom base
section 30 is provided with a pivot 35 by which the boom is
pivotally connected to a pair of spaced upstanding supports 36 on
turntable 37 which is rotatably connected to the base structure 38,
which is disclosed by way of example as comprising a mobile vehicle
chassis, but which may also comprise a stationary structure. The
turntable carrying operator's cab 39 is connected to the base
structure for 360.degree. continuous rotation about the turntable
rotation axis 40. A pair of double-acting elevation or lift fluid
motors, such as hydraulic rams 41, are pivotally connected at 42
and 43 between the turntable 37 and the boom base section 30
respectively, for raising and lowering the boom to selected
elevation angles in the vertical plane about pivot 35. The
hydraulic lift cylinders 41 are controlled for example by a control
system as outlined in the previously mentioned patent.
Hydraulic winches 44 are supported on the end of the boom base
section for controlling hoist cable 45 extending along the top of
the boom and over sheaves in nose assembly 34 to thus control hook
assembly 46 adapted to lift a load. In FIG. 1 the boom sections are
shown in the fully retracted, stored position, and when the boom is
fully elevated in this position, it can be appreciated that the
moment arm of the boom is the smallest at such an attitude and the
moment of force exerted by a particular load connected to cable 45
is a minimum. As the boom is extended by selectively extending the
telescoped sections, the moment arm successively increases and also
successively increases as the boom is lowered so that the moment
arm of the boom is the longest and the moment of force exerted by
the particular load on the lift cable is a maximum when the boom
sections are fully extended when the boom is in its lowermost or
horizontal position. Thus elevating the boom and/or retracting the
telescopic boom sections decreases the moment of force exerted by a
load, while extending the boom sections and/or lowering the boom
increases the moment of force exerted by the load. The moment of
force exerted by a load can also be relieved by lowering the load
on the lift cable by means of the winch to thus unload the
boom.
A spring-loaded cable reel 47, having a cable 48 or the like wound
thereon, is rotatively connected to the side of boom base section
30 by means of a mounting bracket 49. The outer end of cable 48 is
connected at 50 to the outer end of fly section 33. Cable reel 47
is connected through worm gearing 51 or the like to drive the
movable contactor of boom length switch 52 supported by bracket 49
and also shown schematically in FIG. 12. This switch, as well as
the other switches in the safe load control switch circuitry of the
invention, are shown and described as rotary switches, but it is to
be understood that they may also comprise any of the
well-known-type slide switches including linear-type slide
switches. One type of rotary switch which may be used for all of
the rotary switches in the circuit of the invention, for example,
is a switch designated as Model 20M-1201S, manufactured by J-B-T
Instruments, Inc., New Haven, Conn.
As the telescopic boom sections 31, 32 and/or 33 are selectively
extended and retracted relative to the boom base section, cable 48
is respectively pulled off of and reeled up on spring-loaded cable
reel 47. As the reel rotates on its journals, as the boom is
extended, movable connector 54 of boom length switch 52 is rotated
in a clockwise direction (FIG. 12) by worm gearing 51 to
successively move over and make electrical contact with the
plurality of fixed contacts 53. The contacts of this rotatable
switch are of the overlapping type so that as the removable contact
54 moves from one fixed contact 53 to another, the circuit is never
broken. Each fixed contact 53 represents a predetermined length of
the telescopic boom and preferably the plurality of fixed contacts
represent equal increments of boom length, such as, for example,
successive fixed contacts represent successive 4-foot extension
increments of the boom with contact 53-1 representing the fully
contacted length of the boom such as 29 feet, contact 53-2
representing the boom extended to a 33-foot length, etc., and
contact 53-12 representing the boom extended to a length of 73
feet, which, for instance, could be the full extended length of the
boom. It is to be understood that switch 52 may have as many fixed
contacts 53 as desired to accommodate the full length of the boom
in any desired number of length increments, and has been
illustrated in FIG. 12 as having only twelve fixed contacts by way
of example. As the telescopic boom is retracted, movable contactor
54 is rotated counterclockwise as cable 48 is reeled in by spring
loaded reel 47. Switch 52, by means of cable 48, thus continuously
provides the safe load control circuit with boom length information
corresponding to the length of the boom at all instances during
operation of the boom. Switch 52 provides a plurality of output
circuits 55 individually connected to corresponding fixed contacts
53 with the number of output circuits corresponding to the number
of fixed contacts such that the output circuits 55 are
representative of different boom lengths. A circuit 56 connected to
a common source of potential, such as ground, is connected to
movable contact 54 which in turn is connected to one of the output
circuits 55 through the corresponding fixed contact 53, depending
upon the operating length of the boom.
The boom length switch output circuits 55 each terminates in an
individual second circuit means comprised of one of the boom angle
switches A1-A12. The boom angle switches comprise part of the boom
angle cam and switch assembly shown in greater detail in FIGS.
3-5.
The end of boom pivot 35 that extends through support 36 (FIG. 5)
is provided with a body portion 57 connected thereto for movement
with the pivot 35. A bracket assembly 58 is connected to the side
of the corresponding boom support 36 and a boom angle cam 59
through arm 60 is rotatively journaled on bracket 58 such that the
axis of arm 60 is axially disposed in alignment with boom pivot 35.
Arm 60 is connected by linkage 61 to body portion 57, such that
when the telescopic boom is pivoted in the vertical plane about
pivot point 35, the boom is pivoted in the vertical plane about
pivot point 35, the boom angle cam 59 is also correspondingly
pivoted in the vertical plane, since the two members share a common
pivot axis. The perimeter edge of cam 59 is grooved to retain a
cable 62 having one end connected to the lower edge of the cam
through cable tightener 63. The cable passing off of the cam is
threaded over pulley 64 which is journaled on bracket assembly 58
and is disposed in substantially the same horizontal plane as the
cam. From pulley 64 cable 62 extends downwardly into boom angle
switch assembly housing 65 wherein the opposite end of the cable is
connected to pulley 66 journaled to support member 67 within the
housing. Pulley 66 is spring loaded by any appropriate means, such
as by another cable 68 having one end connected to rotate pulley 66
in the opposite direction from cable 62, and the opposite end
terminating in a plate 69 biased by means of a compression spring
70 within tubular housing 71 which tends to pull cable 68 off of
the pulley and thus rotate it in the opposite direction from cable
62. This arrangement enables pulley 66 to automatically retract
cable 62 as the vertical angle of the boom is decreased and cam 59
(FIG. 5) is rotated counterclockwise.
The previously mentioned plurality of boom angle switches A1-A12,
which are disclosed, by way of example only, as comprised of
individual rotary switches, each having a movable or rotatable
contactor 72 and a plurality of fixed contacts 73, are connected in
stacked groups such as A1-A6 and A7-A12 to opposite sides of
support member 67 with the trunnions 74 of pulley 66 connected to
simultaneously rotate the movable contactors 72 of all of the boom
angle switches in unison as the telescopic boom is raised and
lowered in the vertical plane. Each of the boom angle switches
A1-A12 has been shown as having 16 fixed contacts 73-1 to 73-16
wherein successive fixed contacts represent predetermined
increasing boom angles in the vertical plane, as indicated by the
radial lines, in the diagram of FIG. 10, bearing the corresponding
reference numerals of the fixed contacts of boom angle switches
A1-A12. The fixed contacts 73-1 to 73-16 represent equal increments
along the abscissa 75 of the moment arm diagram of FIG. 10, and
this is accomplished by boom angle cam 59, the peripheral edge 76
of which, which controls cable 62 and the movement of the rotatable
contactors 72, is profiled to translate the angular attitude of the
telescopic boom in the vertical plane at any given instance into
the linear horizontal component of the angle, that is, the
component of the angle that lies along the abscissa 75. As
previously indicated the distance between successive fixed contacts
73-1 to 73-16 represent equal horizontal footage increments along
abscissa 75, such as 4 or 5 feet, and it will be noted that when
the boom is moved from the horizontal position designated by
abscissa 75 and fixed contact 73-1 to the maximum elevated
position, designated by fixed contact 73-16, and the similarly
designated radial line in FIG. 10, at lower boom angles it may take
approximately 18.degree. of angular elevation of the boom, for
instance, from the horizontal position, to move movable contactor
72 from fixed contact 73-1 to contact 73-2, whereas at higher boom
angles it may take only approximately 3.degree. of angular
elevational movement of the boom to move the movable contactor 72,
for instance, from fixed contact 73-11 to fixed contact 73-12,
although the horizontal distance along abscissa 75 in each instance
is substantially the same. Cam 59 thus translates the angular
movements of the telescopic boom in the vertical plane into equal
horizontal footage movements for the switch contacts to thus
calculate the moment arm of the boom for any particular elevational
attitude thereof.
Two illustrative examples of connections of portions of the safe
load control circuit of the invention are illustrated in FIGS. 10
and 12 for the operating boom shown at B and C in the moment arm
diagram of FIG. 10. The positions of the movable contactors 54 and
72, shown in full lines in FIG. 12, are representative of the boom
attitude indicated at B, in FIG. 10, whereas the dotted line
positions of the movable contactors indicated in switches 52 and
All are representative of the boom attitude illustrated at C in
FIG. 10. In FIG. 10 it will be noted that the arcs designated
A1-A12 are representative of successive 4 -foot incremental
increases in boom length and correspond to the boom lengths
represented by the correspondingly labeled boom angle switches
A1-A12 in FIG. 12. The telescopic boom, as illustrated at B, is
operating at an extended length in which the hook distance from the
boom pivot 35 is 53 feet. Cable 48 thus positions movable contactor
54 of boom length switch 52 on fixed contact 53-7 which chooses the
circuit 55 that is connected to the movable contactor 72 of boom
angle switch A7 which is representative of the 53 foot operating
length of the boom. Boom length switch 52 thus chooses a particular
boom angle switch, in this case A7, which is representative of the
instantaneous operating length of the boom. Boom angle cam 59
through cable 62 and pulley 66 positions movable contactor 72 on
fixed contact 73-11 of the angle switch, which is representative of
the approximate 63.degree. angle at which the boom is operating and
the cam edge 76, as previously explained, automatically converts
the angular attitude of the boom to the horizontal component of the
angle so that the output circuit 77 from fixed contact 73-11 of
switch A7 represents the length of the moment arm for the extended
length and angular attitude of the boom in the position indicated
at B. From the abscissa 75 it will be observed that the moment arm
is approximately 27 feet.
In a similar manner, the boom indicated at C is shown operating at
a length of 69 feet and at an angle of approximately 31 1/2.degree.
from the horizontal. For this operating length the cable 48 of
length switch 52 positions movable contactor 54 thereof on fixed
contact 53-11 which completes the circuit to the movable contactor
72, dotted line showing, of boom angle switch All which is the
wafer switch that is representative of the 69 foot operating range
of the boom. Movable contactor 72 is positioned by cam 59, etc., in
contact with fixed contact 73-4 of angle switch All, thus
completing the circuit to output circuit 78 connected thereto which
is representative of the boom moment arm of approximately 59 feet,
that is, the horizontal component of the operating attitude of the
boom at the moment it is operating in the position shown at C. The
safe load control circuit of the invention has thus, by a first
circuit means 52, chosen a particular second circuit means All that
is representative of the instantaneous operating length of the
boom, and the second circuit means is correlated with the
instantaneous operating elevation angle of the boom to compute the
instantaneous moment arm of the boom. In a similar manner, the
remaining contacts in the group 53-1 to 53-12 are respectively
connected by output circuits 55 to the movable contactors 72 of the
switches A1 to A12, although these connections are not shown.
A multiplicity of boom operating points in the boom operating range
are connected into the safe load control circuit of the invention
in a comparable way, but for sake of clarity the circuit
connections have been shown in FIG. 12 for only the two positions
of boom operation illustrated in FIG. 10. The circuit shown is
arranged to determine the moment arms for 12 different operating
lengths of the telescopic boom at 16 different elevational angles,
for a total of 192 operating points in the boom operating range. It
can be appreciated that any number of operating points can be
connected into the system merely by increasing the number of switch
circuits or the usable number of fixed contacts in the various
switches, so that the system is applicable to telescopic booms of
any length.
Referring to FIGS. 1, 6-9 and 12 a pressure gage and switch
assembly, indicated generally at 79, is mounted on turntable 37 and
is arranged to sense the pressure of the hydraulic fluid in the
bottom of lift cylinders 41, as this pressure is indicative of the
moment of force exerted by the telescopic boom and the load carried
hereby on the base structure 38. The pressure gage comprises a
cylinder 80 having a piston 81 disposed therein for axial movement
and having a rod end portion 82 extending from the cylinder and
frictionally seated in plate 83 carried by bracket 84 which mounts
the pressure gage at an appropriate place adjacent the lift
cylinders. The opposite end of cylinder 80 is closed and is
provided with an input port 85 connected in fluid communication
with the hydraulic fluid in the bottom of lift cylinders 41 by
means of hydraulic line 86 (FIG. 1). Cylinder 80 is provided with a
head member 87 connected thereto adjacent the rod end of the
cylinder which is provided with through-holes 88 at the four
corners thereof in sliding contact with bolts 89 connected between
bracket 84 and top plate 90. A relatively heavy spring 91 is
disposed about cylinder 80 between the cylinder and bolts 89, and
is confined in a state of initial compression between head member
87 and top plate 90. The initial compression, for example,
equivalent to approximately 1,000 p.s.i. is imparted to spring 91
by tightening nut members 92 on the ends of bolts 89. Top plate 90
is provided with a central aperture 93 larger than the diameter of
cylinder 80 to allow the cylinder to move freely therethrough.
An upstanding bracket 94 is connected to top plate 90 and a lever
arm 95 is pivotally connected at 96 to bracket 94 with the opposite
bifurcated end thereof pivotally connected to arm 97 rigidly
connected to one end of vertically disposed drag linkage 98. The
opposite end of the drag linkage is connected through a horizontal
hinged pivot 99 to a slide member 100 connected for vertical
sliding movement in vertically disposed U-shaped guides 101 which
engage oppositely longitudinal edges of the slide member and which
are connected to bracket 84 through the adjustable mount 102. Slide
member 100 and guides 101 are preferably constructed of electrical
insulation material.
Guides 101 and slide member 100 form the pressure switch assembly
which also includes switch mounting cards 103 and 104 connected to
opposite side vertical surfaces of the guides 101. The switch
mounting cards are preferably constructed of insulation material
and a plurality of normally closed electrical switch members P1,
P3, P5, P7, P9, P11, P13, P15, P17, P19, P21 and P23 are connected
to card 103 in two rows, one above the other, with the adjacent
switches in each row being successively staggered upwardly in the
vertical plane. Normally closed electrical switch members P2, P4,
P6, P8, P10, P12, P14, P16, P18, P20, P22, and P24 are connected to
card 104 in two rows, one above the other, with the adjacent
switches in each row being successively staggered upwardly in the
vertical plane, as best shown in FIG. 8, with the switches on card
104 being vertically offset between the switches on card 103. Each
of these normally closed electrical switches may comprise, for
example, a Cherry Switch No. S25-00T, wherein each switch is
provided with an actuator 105 which protrudes into the path of
movement and is adapted to be contacted by the upper edge of slide
member 100. When the actuator 105, as shown in FIG. 9, is contacted
by the leading edge of slide 100, it is moved inwardly causing the
switch to move from its normally closed position, as indicated by
the position of switch P2, in FIG. 9, to the open position, as
shown by the position of switch P1, in the same figure. The
electrical connections to the various switches are made through the
terminal strips 106, FIGS. 6 and 7, with the normally closed
terminals of all of the switches on both cards commonly connected
to conductor 107 (FIG. 12), the opposite end of which is connected
through coil 108 of normally energized relay 109 on control panel
112 in the crane operator's cab 39, and ON-OFF switch 110 to the
positive terminal of battery 111 which, for instance, may be a
12-volt battery, the opposite terminal of which represents the
common source of potential to which circuit 56 of the boom length
switch 52 is connected.
As the pressure in the bottom of lift cylinders 41 increases which,
for a predetermined load on the boom, is caused by an increase in
the moment of force exerted by the boom on the supporting structure
which is caused by increasing the length of the boom or decreasing
the operating angle of the boom in the vertical plane, or a
combination of both, cylinder 80 moves upwardly on the restrained
piston 81 and the top portion 113 of the cylinder pivots lever arm
95 about connection 96 and moves the opposite end thereof upwardly
in an arc which in turn moves drag linkage 98 upwardly to move the
top edge of slide member 101 successively into contact with the
actuators of switch members P1, P2, P3, P4, etc., to actuate the
switches from the normally closed position in which the electrical
circuit is completed to the open position in which the electrical
circuit is broken. Lever arm 95 is adjustable in length at 114 to
allow for an adjustment for inaccuracies in spring rates between
different springs 91.
The pressure gage and switch assembly 79 is calibrated so that the
leading edge of slide member 100 moves upwardly and progressively
opens one of the successive normally closed switches for each
predetermined equal incremental increase in fluid pressure in the
bottom of the lift cylinders 41. For instance, the electrical
switches P1-P11 on card 103 may be arranged to progressively open
on each increase of 50 or 100 p.s.i. pressure in the lift
cylinders, and the switches P2-P12 on card 104 may be similarly
arranged, but since the switches are offset relative to each other
in the vertical plane, as shown in FIG. 9, a switch will be opened
on each increase in pressure of 25 or 50 p.s.i. The circuit of FIG.
12 utilizes only pressure switches P1-P12 but it is to be
understood that as many pressure switches as desired can be used in
the circuit to give a more refined operation of the system, and any
desired incremental pressure range may be assigned to the switches.
By calculations the maximum safe moment of force, which may be
safely exerted by the boom on the supporting structure without
exceeding the boom strength and which will not cause the supporting
structure to pitch or tip for any operating length and attitude of
the boom, can be calculated and in this manner the hydraulic
pressure in the bottom of the lift cylinders 41 corresponding to
the maximum safe moment of force can be calculated, or this
pressure can be determined by actual tests. In this manner, a
maximum pressure that can be tolerated in the bottom of the lift
cylinders can be determined for every point on the moment arm
diagram of FIG. 10 where the radial lines 73-1 to 73-16 cross the
arcuate lines A1-A12, since these intersections represent the
points in the boom operating range that are programmed into the
safe load circuit. A separate such chart must be made up for each
particular model of extensible boom crane since each model has
individual loading characteristics. With such a pressure chart a
circuit connection chart, such as shown in FIG. 11, can be made up
for each model crane which is utilized for programming the circuit
connections, such as circuits 77 and 78, from the fixed contacts
73-1 to 73-16 of each of the boom angle switches A1-A12 to the
pressure switches P1-P12.
As previously indicated, preselected pressure values are assigned
to the switches P1-P12, such as, for example, switch P2 being
assigned pressure 1,150 p.s.i. and switch P10 the pressure 1,800
p.s.i. This means that whenever the pressure in the bottom of the
lift cylinders exceeds the respective pressures, the respective
switches move from the normally closed position to the open
position to open the safe load circuit.
In the chart of FIG. 11, the boom angle switchs A1-A12 representing
boom extension length appear in the vertical column plotted against
the fixed contacts 73-1 to 73-16 in the horizontal column which are
representative of boom angle. The numbers filling in the the chart
represent the pressure switches P1-P12 to which the fixed contacts
73-1 to 73-16 of the various angle switches A1-A12 are connected.
By way of example, referring to FIG. 10, the maximum pressure that
can be tolerated in the bottom of lift cylinders 41 at the boom
attitude shown at B, for a particular boom, was determined as being
1,800 p.s.i. This is the pressure limitation assigned to switch
P10. This boom operating position is represented in the circuit by
fixed contact 73-11 of angle switch A7. Therefore, in the chart of
FIG. 11, where the columns from switch A7 and contacts 73-11
intersect the number 10 representative of switch P10 appears in
FIG. 12. Output circuit 77 is thus connected to switch P10 as
indicated, and all of the other angle switch contacts in the chart
of FIG. 11 having a similar designation are connected to switch
P10. In the present example it will be seen that contacts 73-11 to
73-13 of switch A7 are all connected to switch P10. From the chart
it will also be noted that contacts in angle switches A1, A2, A4,
A5, and A6 are also connected to switch P10 so output circuits from
six different angle switches, including circuit 77, are connected
to switch P10.
The attitude of the boom illustrated at C, in FIG. 10, is
represented in the safe load circuit by fixed contact 73-4 of boom
angle switch All. The maximum pressure in the bottom of the lift
cylinders which provides safe operation at this boom position was
determined to be 1,150 p.s.i. which pressure is represented by
pressure switch P2. From the coordinates in the chart of FIG. 11,
it will be noted that the number 12 is entered as representing the
pressure switch connection for this point. The chart also shows
that test data indicated that fixed contacts 73-3 and 73-7 of this
same switch are also connected to pressure switch P2 and such
circuit connection is shown by output conductor 78 in FIG. 12. The
chart also indicates that fixed contacts in boom angle switches A9,
A10, and A12 are also connected to pressure switch P2 and thus
output circuits from four different angle switches, including
output circuit 78, are connected to switch P2 as indicated in FIG.
12. The remaining fixed contacts of the angle switches in FIG. 12
connected to the other pressure switches in like manner according
to the connection chart of FIG. 11. Pressure switches P1-P12
represent successively higher pressures.
As previously indicated, the output circuits, such as 77 and 78,
represent the moment arm of the boom at the different operating
positions and when wired to the pressure switches the completed
circuit represents maximum moment of force that can be tolerated
from the boom for the particular position without exceeding safe
operating conditions. For instance, the boom operating at position
C with a certain load may be producing a pressure in the bottom of
the lift cylinders of approximately 1,145 p.s.i. In this position,
the pressure of switch P1 is exceeded and pressure gage 79 moves
slide member 100 upwardly, such that switch P1 is opened as shown
in FIG. 12. The safe load control circuit however is completed by
the circuit including the elements 56, 54, 53-11, 55, All-72, 73-4,
78, P2, 107, 108, 110 and 111. If the boom is extended, for
example, another 3 feet, the boom is moved toward a condition of
unsafe operation as it approaches a tipping condition, and the
pressure in the boom of the lift cylinders exceeds the 1,150 p.s.i.
limitation of switch P2 and slide member 100 is moved upwardly by
pressure gage 79 against the actuator 105 causing switch P2 to move
from the normally closed position to the normally open position,
thus opening the safe load control circuit and deenergizing coil
108 of normally energized relay 109.
In the normally energized position of relay 109 movable contactor
115, connected to battery 111 by circuit 116 energizes green light
117 which indicates that the system is operating and the crane is
operating in a safe condition. When relay 109 is deenergized on the
opening of the pressure switch, such as P2, which completes the
circuit for the particular boom operating attitude, relay
contactors 115 and 118 drop out and through circuit 116 supply
power from battery 111 to relay contacts 119 and 120, respectively,
extinguishing green light 117, illuminating warning light 121,
energizing an audible alarm 122, if desired, and energizing
hydraulic solenoid valves 123, 124, 125 and 126. Light 121 and/or
alarm 122 warn the operator that the overload condition has been
approached for the particular operating attitude of the boom. The
hydraulic solenoid valves comprise hydraulic valves connected into
the hydraulic fluid control system of the crane which are
electrically controlled by solenoids. Valve 123 is the lift
solenoid valve disposed in the hydraulic control circuit of the
hydraulic lift cylinders 41. Valve 124 is disposed in the hydraulic
control circuit of the hydraulic ram that extends and retracts the
boom fly section 33 and reference numeral 125 represents two
solenoid valves connected in the control circuit of the hydraulic
rams which extend and retract the boom inner midsection 31 and
outer midsection 32. The winch solenoid valve 126 is connected in
the hydraulic control circuit of the hydraulic winches 44 which
controls the raising and lowering of hoist cable 45. The hydraulic
control circuit may be substantially the same as that shown and
described in U.S. Pat. No. 3,371,800.
On operation of the safe load control circuit the solenoid valves
123-126 are energized, thus locking out the boom operations of
lifting with the winch 44, extending the boom sections 31, 32, 33,
and lowering the boom by means of lift cylinders 41, since these
operations would move the boom further into the area of unsafe
operation as they would increase the moment of force exerted by the
boom on the supporting structure. However, as in the previously
mentioned patent, the operations of raising the boom with the lift
cylinders, retracting any or all of the boom sections and lowering
the load with the hydraulic winch, are maintained in operating
condition, as these operations manipulate the boom away from or out
of the unsafe operating condition as they decrease the boom moment
arm or unload the boom, thus decreasing the hydraulic pressure in
the bottom of the lift cylinders 41. When the boom is manipulated
back into an attitude of safe operation for the particular load on
the boom the pressure in the bottom of the cylinders no longer
exceeds the pressure programmed into the system for the
instantaneous boom attitude and the pressure switch assembly 79
lowers slide member 100 to the point where the pressure switch in
the group P1-P12 representing the instantaneous boom attitude is
released to again close the safe load control circuit and putting
it back in operating condition by energizing relay 109.
It is to be understood that the system of the invention can be used
merely as an overload indicator system, using the warning light 121
and/or the audible alarm 122 without automatically controlling
operation of the hydraulic solenoid valves in the hydraulic control
system.
The terms and expressions which have been employed herein are used
as terms of description and not of limitation, and there is no
intention, in the use of such terms and expressions, of excluding
any equivalents of the features shown and described or portions
thereof, but it is recognized that various modifications are
possible within the scope of the invention claimed.
* * * * *