U.S. patent number 3,740,534 [Application Number 05/146,682] was granted by the patent office on 1973-06-19 for warning system for load handling equipment.
This patent grant is currently assigned to Litton Systems, Inc.. Invention is credited to Soo Chul Chung, Charles F. Kezer.
United States Patent |
3,740,534 |
Kezer , et al. |
June 19, 1973 |
WARNING SYSTEM FOR LOAD HANDLING EQUIPMENT
Abstract
A warning system for load handling equipment is shown capable of
warning an operator of the load handling equipment, such as a crane
hoist, that his lifted load is about to cause a failure due to the
crushing of the boom or tipping of the crane. A memory stores
information peculiar to the crane hoist, while control logic
selects data corresponding to a set of boom angles and applies the
data to a differential amplifier. The amplifier compares the
selected angles against the actual boom angle and applies an
indicating signal to the control logic as the selected angle
matches the boom angle. The control logic then selects the stored
maximum stress for the matched angle and applies this stress
through a digital to analog converter to a second differential
amplifier where a comparison is made with a stress generated by the
lifted load. As the load approaches its maximum, an alarm circuit
provides a warning to the equipment operator.
Inventors: |
Kezer; Charles F. (Mineola,
NY), Chung; Soo Chul (Mineola, NY) |
Assignee: |
Litton Systems, Inc. (Beverly
Hills, CA)
|
Family
ID: |
22518508 |
Appl.
No.: |
05/146,682 |
Filed: |
May 25, 1971 |
Current U.S.
Class: |
701/50; 212/277;
212/278; 702/173; 702/113; 701/124; 340/685 |
Current CPC
Class: |
B66C
23/905 (20130101) |
Current International
Class: |
B66C
23/00 (20060101); B66C 23/90 (20060101); G06g
007/22 (); G08b 021/00 () |
Field of
Search: |
;235/151,151.3,151.33,184,189 ;340/267C,272,282 ;73/100
;212/39A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Morrison; Malcolm A.
Assistant Examiner: Smith; Jerry
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A warning system for producing a warning signal indicating a
condition of failure or approach to failure of load handling
equipment, comprising:
memory means for storing digital data pertaining to discrete
operating parameters of said load handling equipment;
selection means for selecting portions of the stored digital data
from within said memory means in dependence upon at least one
operating condition of said equipment;
digital to analog conversion means for converting said selected
digital data from within said memory means into analog signals;
means for generating analog signals representing at least two
further operating conditions of said load handling equipment;
at least two comparator means for receiving and comparing said
analog signals converted from selected digital data from said
memory means with said generated analog signals representing at
least two further operating conditions and producing, without
interpolation between discrete values of said stored digital data,
a warning signal when the compared signals reach a predetermined
relation.
2. A warning system for load handling equipment as claimed in claim
1, additionally comprising:
said load handling equipment including a crane having a cab mounted
boom lifted by cables;
said means for generating analog signals including load cell means
for measuring the load to be lifted by the boom, one of said
further operating conditions thus including said load;
a back hitch pin assembly connecting said crane cable to said crane
cab; and
a pin within said back hitch pin assembly housing said load cell,
whereby said warning system may be installed within said crane by
changing pins within said back hitch pin assembly and connecting
said warning system thereto without connecting externally from said
cab.
3. A warning system for load handling equipment as claimed in claim
1, additionally comprising:
means for generating fixed signals for said analog signals
representing said at least one operating condition and for said
analog signals representing said at least two further operating
conditions of said load handling equipment; and
switching means for connecting said fixed signals to said warning
system including said memory means for establishing a predetermined
test sequence to test said warning system including said memory
means thereof.
4. A warning system for load handling equipment, comprising:
memory means for storing data peculiar to said equipment;
selection means for selecting portions of the stored data from
within said memory means and presenting said stored data as
sequential sets of output data;
first holding and converting means for receiving one set of
sequentially presented output data;
first sensing means for sensing one equipment parameter;
comparing means to which said first holding and converting means
and said first sensing means are connected being connected to said
selection means for presenting an output signal thereto when said
one set of sequentially presented output data reaches a
predetermined proportion of said one equipment parameter;
second holding and converting means for receiving a second set of
sequentially presented output data from said memory means after
said output signal is presented to said selection means;
second sensing means for sensing a second equipment parameter;
compraing means to which said second holding and converting means
and said second sensing means are connected for generating an
output warning signal when said second set of sequentially
presented output data reaches a predetermined proportion of said
second equipment parameter.
5. A warning system for load handling equipment such as a crane,
comprising:
memory means for storing data peculiar to said crane including
stored data for first and second crane parameters;
sensing means for selecting portions of the stored data within said
memory means to reflect present operating conditions of said
crane;
logic means for selecting the remaining portions of the stored data
within said memory means to selectively provide said data as output
data;
first converting means connected to said logic and memory means for
converting said output data into a signal representing possible
values of said first crane parameter;
first parameter measuring means for generating a first parameter
signal;
comparing means connected to said logic means for comparing the
signals from said first converting means and said first parameter
measuring means and for applying an output signal to said logic
means as said compared signals approach each other;
second converting means connected to said logic and memory means
for converting said output data into a signal representing maximum
values of said second crane parameter as said output signal from
said last mentioned comparing means is received by said logic
means;
second parameter measuring means for generating a signal
representing said second crane parameter; and
comparing and warning means for comparing said signal representing
maximum values of said second crane parameter with said signal
representing said second crane parameter and for generating a
warning as said second crane parameter signal approaches said
maximum value of said second crane parameter signal.
6. A warning system for load handling equipment as claimed in claim
5, wherein:
said sensing means includes a first sensor having switching means
for providing logic signals to said logic means for enabling
portions thereof and disabling other portions thereof and thereby
controlling the selection of said stored data from within said
memory means; and
said sensing means further includes a second sensor having
switching means for providing logic signals directly to said memory
means for controlling the selection of said stored data from within
said memory means.
7. A warning system for load handling equipment as claimed in claim
6, wherein:
said stored data for said first crane parameter is boom angle
data;
said stored data for said second crand paprameter is maximum boom
load data;
said first sensor is an extended, retracted sensor for generating a
digital signal; and
said second sensor is a boom length sensor for generating a
plurality of digital signals.
8. A warning system for load handling equipment as claimed in claim
5, wherein:
said memory means includes a read only digital memory;
said stored data for first and second crane parameters includes
stored digital boom angle data and digital maximum load data;
said first crane parameter measuring means includes boom angle
measuring means and said second crane parameter measuring means
includes load measuring means;
said sensing means include means for disabling portions of said
read only digital memory depending upon the sensed crane
conditions;
said first and second converting means connected to said logic and
memory means include registers for receiving said stored digital
data, and digital to analog converters for generating and applying
analog signals to said comparing means and said comparing and
warning means; and
said comparing means and said comparing and warning means include
comparator amplifiers connected for comparing said analog signals
and for generating said output signal as the compared analog
signals reach a predetermined proportion.
9. A warning system for load handling equipment as claimed in claim
8, additionally comprising:
said comparing and warning means including two comparator
amplifiers;
a resistive network connecting said two comparator amplifiers to
said second converting means and said load measuring means;
said warning means further including first and second switching
means connected to receive said output signals from said two
comparator amplifiers, and first and second indicating means
connected to said first and second switching means for providing a
first and then a second warning signal as said crane approaches and
then reaches a dangerous operating condition.
10. A warning system for load handling equipment as claimed in
claim 9, additionally comprising:
a test circuit including a reference potential, resistive network
and delay switching means for generating a first reference signal
and a delayed second reference signal; and
switch means for disconnecting said load measuring means from said
two comparator amplifiers and instead connecting said test circuit
thereto for providing said first reference signal and said delayed
second reference signal to said two comparator amplifiers, whereby
said first and second indicating means are respectively
energized.
11. A warning system for load handling equipment as claimed in
claim 8 for further indicating the percentage of safe load being
handled by said crane, additionally comprising:
third converting means including a digital to analog converter
connected to receive said signal representing maximum load from
said register within said second converting means;
a comparator amplifier connected to receive signals from said third
converting means and said load measuring means for comparing said
signals;
an indicating device connected to receive the output signal from
said last mentioned comparator amplifier; and
said output from said last mentioned comparator amplifier connected
to said third converting means for providing a reference voltage
thereto, whereby said indicating device indicates percentage of
safe load being handled.
12. A warning system for load handling equipment as claimed in
claim 8 for further indicating the weight of the load being handled
by said crane, additionally comprising:
said memory means for storing digital data peculiar to said crane
further including stored slope data and crane cable tension at zero
load data;
third and fourth converting means connected to said memory means
including registers for repsectively receiving said slope data and
said crane cable tension at zero load data and digital to analog
converters for generating analog signals representing said slope
data and crane cable tension at zero load data;
a comparator amplifier connected to receive said crane cable
tension at zero load signal from said third digital to analog
converter and connected to receive said signal representing the
crane load from said load measuring means, the output of said
comparator amplifier thereby equalling the difference between said
measured crane load and said zero load;
said fourth digital to analog converter connected to receive said
slope data and connected to receive said output from said last
mentioned comparator amplifier as a reference potential, the output
signal therefrom thereby represents a value proportional to the
load being handled; and
indicating means connected to receive said last mentioned output
signal for indicating the weight of the load being handled.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a warning system for load handling
equipment and, more particularly, to a warning system for load
handling equipment such as a crane warning system for use within a
crane hoist that senses various crane parameters during the lifting
of a load for providing a warning signal to the operator of the
crane as the crane approaches a dangerous condition.
It is well known in the prior art to provide load handling
equipment including cranes with safety or warning systems in
various forms. For example, one crane safety device, shown in U.S.
Pat. 2,858,070, by Schaff, provides a crane with load and angle
measuring sensors which are used to compute the moment of the crane
and generate a warning signal when the crane is in danger of
overturning. The Schaff device utilizes analog signals to provide a
computation of the lifting moment. This device has several
limitations; for example, the moment generated by the load is a
function of the variable length of the crane boom and is not
accounted for within the analog system measuring only load and boom
angle. Secondly, when the boom is in a near vertical position, the
maximum lifting ability of a crane may be limited by the strength
of the boom itself. In this near vertical position, the boom is in
danger of crushing under the stress of a lifted load. Further, the
crane is in danger of tipping backwards, a circumstance which has
cost more than one life of a crane operator. Warning the operator
of a possible tipping condition in the forward condition alone,
therefore, will not provide the operator with suitable information
necessary for his safety, the safety of those working around him,
or the safety of his equipment. Finally, the conditions which cause
the boom of a crane to tip or crush do not follow straight line
functions and do not readily lend themselves to computations by
typical analog devices of the prior art.
Some of these problems were presented along with a solution in a
pending patent application, Ser. No. 864,728, filed Oct. 8, 1969,
by Albert A. Sanchez, entitled Crane Safety System, now U.S. Pat.
No. 3,638,211. This crane safety system uses a memory which stores
stress and angle information peculiar to the crane in which it is
being utilized. The boom angle is converted from an analog signal
to a digital signal and applied to control and process units where
it is matched against a stored angle. Once the measured boom angle
has been matched as closely as possible to the stored boom angle,
the maximum stresses for the stored boom angles on the high and low
side of the measured angle are presented to the process unit by the
control unit which interpolates these values and provides a digital
output representing the maximum interpolated stress for the
measured boom angle. This digital information is then converted to
an analog signal where it is compared against an analog input
signal representing the boom load. An alarm is actuated as the
signal representing the boom load approaches the signal
representing the maximum stress. This arrangement, while
functioning adequately, requires a control and process unit capable
of conducting the needed interpolation. It is also necessary to
convert the boom angle from an analog to a digital signal for use
during interpolation. The requirements for conversion and
interpolation complicate the logic required within the control and
process units of the system and add to the construction cost of the
crane warning system.
SUMMARY OF THE INVENTION
The present invention eliminates these disadvantages by providing a
simplified arrangement utilizing a read only memory which requires
no data manipulation or interpolation. The crane warning system of
the present invention eliminates the need for analog to digital
converters, reduces the number of control components required,
simplifies the control logic, and simplifies the memory required.
Further, the simplified warning system is more easily adaptable to
modification and variations. For example, th present system is
provided with a test circuit which automatically tests the
operability of the system by the simple push of a buttom.
Accordingly, it is an object of the present invention to provide an
improved crane warning system that is capable of warning a crane
operator of an impending failure.
Another object of the invention presented herein is to provide a
crane warning system which utilizes fewer components than prior
warning systems, which requires a simplified memory and logic
arrangement wherein the stored data is not converted or otherwise
manipulated, and which eliminates the necessity for conversion of
the input data.
A further object of the invention presented herein is to provide a
crane warning system with simplified self testing circuitry, with
an indicating means for indicating the percent of safe load being
lifted, and with means indicating the weight of the lifted
load.
In accomplishing these and other objects, there has been provided a
read only memory which is addressed by control logic for selecting
and reading out a series of stored angles. Each stored angle is
compared with the measured boom anlge until a matched angle is
found. The control logic then selects and reads out the maximum
stress for the matched boom angle which is compared with the
measured boom load. If the measured boom load is within a
predetermined range of the stored maximum stress, an indicating
signal is applied to the control panel of the crane warning system
for warning the operator.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the present invention and of the objects
and appendant advantages thereof will be obtained by reference to
the following description when considered in connection with the
accompanying drawings, wherein:
FIG. 1 is a side elevational view, showing a crae hoist in which
the crane warning system of the present invention may be
utilized;
FIG. 2 is a schematic block diagram, showing the circuitry of the
crane warning system;
FIG. 3 and 4 are schematic diagrams, showing the circuitry of the
present invention in greater detail;
FIG. 5 is a schematic diagram, showing the switching circuitry of
FIGS. 3 and 4 in more detail;
FIG. 6 is a timing diagram, illustrating the switching sequences of
the control logic;
FIG. 7 is a schematic diagram, illustrating the test circuitry of
the present invention; and
FIG. 8 and 9 are schematic block diagrams, similar to FIG. 2,
incorporating circuitry for indicating the load as a percentage of
maximum safe load and for measuring and indicating the load in
pounds.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, FIG. 1 shows a crane 10 having a
crane transportation system including, in this illustration, a
truck frame 12 and truck cab 14. A crane cab 16 which houses the
operator and his controls is rotatably mounted upon the truck frame
12 by means of a turn table bearing plate 18. The truck frame 12 is
normally transported upon crawler treads or drivable tires 20. If
the crane 10 is mounted on drivable tires, it may be operated
either on the tires 20 or on outriggers 22 which, when extended,
increase the lifting capacity thereof. If the crane 10 is mounted
upon crawler treads, the treads may be extended to increase the
lifting capacity in a manner similar to the extension of the
outriggers 22. A boom structure 24 is hinged at the base of the
crane cab 16 from which a weight hoist cable 26 may be rigged. The
end of the hoist cable 26 may be equipped with a suitable hook
block, sling, clamsheel, dragline, or magnet shown at 28 as a hook
block driven from a cable drum, not shown, to provide lifting
capacity.
The boom structure 24 is lifted by a gantry hard line 30 attached
to a gantry strut 32 that, in turn, is connected to the crane cab
16 by a gantry hoist cable 34. The angle between the center line of
the boom structure 24 and the horizontal plane is referred to
herein as the vertical boom angle .theta..
The vertical boom angle .theta. is measured by a boom angle sensor
44 including a pendulum potentiometer mounted within a housing on
the boom structure 24. The pendulum potentiometer consists of a
weighted wiper arm mounted within an oil filled housing for
contacting a slide wire mounted therein. The oil provides motion
damping as the weighted wiper arm moves to orient itself in a
downward pointing direction. The wiper arm thus generates an analog
signal which represents the boom angle .theta.. A boom length
sensor 50 consisting of a multiposition switch adjusted by the
operator to correspondence to the length of the boom 24 is mounted
within the crane cab 16 to provide a digital input to a memory
within the crane warning system circuitry. An extended or retracted
sensor 52 may be also located within the crane cab 16 in the form
of a two position switch. In the alternative, this switch could be
located in the area of the outriggers 22 and arrange to function
automatically depending upon the extended or retracted position
thereof. A boom load sensor 54 including a load cell constructed
from a plurality of strain gages arranged in a wheatstone bridge
circuit may be mounted within the back hitch pin 56 which connects
the gantry hoist cable 34 to a counter weight 57 mounted on the cab
16. The boom load sensor 54 could alternatively be located within
the clevis 58 which connects the gantry hard line 30 to the gantry
strut 32.
The circuitry that forms the crane warning system is shown
generally in FIG. 2 wherein the boom angel sensor 44 is connected
to the input stage of a comparator amplifier 60 whose output stage
is connected through an angle matching circuit 62 to a control
logic circuit 64. The control logic circuit 64 is synchronized by
clock pulses generated by a clock 66 connected thereto. The output
of the control logic circuit 64 includes a plurality of memory
address lines 68 over which digital bit information is addressed to
a read only memory 70. The read only memory 70 stores angle and
stress information relating to various crane operating conditions.
The boom length sensor 50 and the extended or retracted sensor 52
apply digital information to the read only memory 70 for limiting
the selection of the boom angle and stress information stored
therein to the conditions applied thereto. Other crane condition
sensors 72 may also be utilized to limit the selection of
information from the read only memory 70, such as a sensor for
sensing the quadrant in which the boom 24 is operating or a sensor
for sensing the type of counterweight that is being used. The
output of the memory 70 is applied by digital output lines 74 to a
first shift register 76 for storing angle information whose output,
in turn, is applied through a first digital to analog converter 78
to the input stage of the comparator amplifier 60.
The digital output lines 74 are also connected to a second shift
register 80 from which signals representing the maximum stress are
applied to a second digital to analog converter 82. The analog
output of a digital to analog converter 82 is applied to the input
stage of a comparator amplifier or differential amplifier 84. The
boom load sensor 54 applies an analog signal generated by the load
cell therein via a load cell amplifier 86 to the second input
terminal in the input stage of the differential amplifier 84. The
output stage of the differential amplifier 84 connects to an
indicator or control panel 88 and then to ground. The indicator 88
provides an indication to the operator of the crane when the load
sensed by the boom load sensor 54 approaches the maximum load
stored within the memory 70.
In operation, the boom length sensor 50 and the extended or
retracted sensor 52 select the appropriate portion of the read only
memory 70 which is to be sequentially applied to the shfit
registers 76 and 80. The control logic 64 sequentially applies a
series of stored, increasing angles to the angle register 76 under
the control of signals generated over a load angle line 90
connected to the angle shift register 76. The angles sequentially
stored within the register 76 are applied by the digital to analog
converter 78 to the input stage of the comparator amplifier 60.
When the stored angle becomes greater than the boom angle, the
output of the comparator amplifier 60 applies a signal to the angle
matching circuit 62. This signal initiates a laod stress signal
within the control logic 64 via a laod stress line 92 to the stress
shift register 80. The digital signals loaded within the register
80 are then converted by converter 82 to analog signals and
compared by the differential amplifier 84 with the measured load
from the boom sensor 54. As the measured load from boom sensor 54
becomes substantially equal to the load represented by the stress
stored within the memory 70, the differential amplifier 84 applies
a signal to the indicator 88 which, in turn, warns the operator of
the dangerous condition.
The details of the circuitry shown generally in FIG. 2 are shown
more completely in FIGS. 3 and 4. In FIG. 3, clock 66 is connected
to the clock terminal of a first JK flip-flop FF1 whose 1 output
terminal connects to the clock terminal of a second JK flip-flop
FF2 in turn connected to flip-flops FF3 and FF4. These flip-flops
are mounted within a first counter 94 and are mutually connected to
ground by a NAND gate 96. The 1 output terminal of flip-flop FF4 is
connected to the clock input terminal of flip-flop FF5 arranged
within a second counter circuit 98 including flip-flops FF5-FF8
connected internally in an identical manner to the first counter 94
and to ground via a NAND gate 100. Through this counter
arrangement, the circuit logic is driven by clock pulses which are
generated by the first two flip-flops FF1 and FF2 including C.sub.0
from the 1 output of FF1 and C.sub.1 from the 1 output of FF2. The
remaining six flip-flops FF3-FF8 generate command pulses over the
memory address lines 68 to address the memory 70 wherein the
various angles stored therein are sequentially selected and read
therefrom. In the preferred embodiment, the angles include 16
angles which are sequentially read from the memory 70.
The 1 output terminal of FF1 is connected through an inverter 102
to the input terminals of AND gates 104 and 106, while the 1 output
terminal of FF2 is connected through an inverter 108 to the second
input terminal of the AND gate 104 and first input terminal of AND
gate 110. The noninverted signal C.sub.0 from flip-flop FF1 is
connected to the second input terminal of AND gate 110 and the
first input terminal of an AND gate 112. Similarily, output C.sub.1
of flip-flop FF2 is connected directly to the second output
terminals of AND gate 106 and AND gate 112.
The output of AND gate 110, C.sub.0 C.sub.1, is applied to the
input terminal of a pulse shaping circuit 114 which consists of a
one shot multivibrator for shortening the pulse applied thereto and
applies the pulse from the output terminal thereof via a conductor
116 to the input terminal of the read only memory 70. This signal
is utilized to initiate the sequential cycling of the memory. The
output of the AND gate 106 conducts the signals C.sub.0 C.sub.1 to
the clock terminal of a JK flip-flop FF9, to the first input
terminal of a NAND gate 118, and to the first input terminal of an
AND gate 120. The output of AND gate 112, C.sub.0 C.sub.1, is
applied to the clock terminal of a JK flip-flop FF10.
The 1 output terminal of flip-flop FF3 connects the signal B.sub.0
through an inverter 122 to the input terminal of a NAND gate 124
and a NAND gate 126, while the output of flip-flop FF4 connects the
signal B.sub.1 1through an inverter 128 to the input terminal of
the NAND gate 124 and a third NAND gate 130. The noninverted output
of flip-flop FF3 is connected to a second input terminal of NAND
gate 130, a first input terminal of a NAND gate 132, the first
input terminal of an AND gate 134, and an input terminal 5 of the
read only memory 70. Similarily, the noninverted output signal of
flip-flop FF4 connects to the input terminals of NAND gates 126 and
132, to the second input terminal of AND gate 134, and to the input
terminal 4 of read only memory 70. The outputs of NAND gates 124
and 126 are connected to the first and second input terminals of a
NAND gate 136 whose output signal controls the load angle timing
and connects to the second input terminal of AND gate 120. In the
same manner, the outputs of NAND gates 130 and 132 connect to the
input terminals of a NAND gate 138 whose output signal controls the
load stress timing and connects to the second input terminal of the
NAND gate 118.
The outputs of flip-flops FF5-FF8; B.sub.2,B.sub.3, B.sub.4,
B.sub.5, are connected through inverters 140, 142, 144 and 146,
respectively, to the four input terminals of an AND gate 148.
Similarily, the noninverted outputs of these flip-flops are
connected directly to the four input terminals of a second AND gate
150. Through these connections, the AND gate 148 provides a timing
signal which is high or positive only during the first of the 16
sequential angles; while the AND gate 150 provides a timing signal
which is high only during the last or 16th angle of the sequential
set of angles. The output of AND gate 148 connects to the J input
terminal of the flip-flop FF10 while the output of AND gate 150
connects to the third input terminal of AND gate 134.
The J input terminal of flip-flop FF9 receives a feedback signal
from the angle matching circuitry 62 over matched angle line 152
through an inveer 154. inverter 1 output terminal of the flip-flop
FF9 is connected to the input termimal of an AND gate 156 whose
second input terminal connects to the matched angle line 152. The
output of AND gate 156 connects to the K input terminal of
flip-flop FF10, the third input terminal of AND gate 118, and over
an enable load signal line 158 to the input stage of the stress
register 80. The 1 output terminal of flip-flop FF10 connects to
the first input of an NAND gate 160 whose second input is connected
to the output of AND gate 134. The output of NAND gate 160 connects
to the input of a NAND gate 162 whose second input terminal is
connected to the output of the NAND gate 118. The output of the
NAND gate 162 connects to the load stress line 92 which also
connects to the stress register 80. The signal from NAND gate 160
is utilized to reset the flip-flop FF9 through NAND gate 162 having
the output thereof connected to the input terminal of an inverter
164. A second inverter 166 receives the timing signal from the AND
gate 134 and applies this inverted signal to the input terminal of
an NAND gate 168 whose second input terminal is connected to the
inverter 164. The output of NAND gate 168 is connected to the K
input terminal of flip-flop FF9. The signal applied over this
circuit is utilized to reset the flip-flop FF9 after the boom angle
has matched the stored memory angle or, if there is no match,
during the 16 th angle.
The extended or retracted sensor 52 will be described in greater
detail hereinbelow with regard to FIG. 7. However, it should be
noted here that the extended or retracted sensor 52 includes a
retracted signal line and an extended signal line, 170 and 172
respectively. The retracted signal line 170 connects to the third
input terminals of NAND gates 126 and 132, while the extended
signal line 172 connects to the third input terminals of NAND gates
124 and 130. The signals over the extended or retracted lines, 170
and 172, are utilized to enable NAND gates 124, 130 or 126, 132
depending on whether the crane is being operated with its tires or
crawler treads extended or retracted. It will be seen that the
signals B.sub.0 and B.sub.1 from flip-flops FF3 and FF4,
respectively, are used to establish the timing utilized to address
the extended or retracted condition to the memory which, in the
preferred embodiment, includes stored angle and stress information
for each extended or retracted condition. The noninverted signals
B.sub.2, B.sub.3, B.sub.4 and B.sub.5 are connected over lines 68
to the input terminals 3, 2, 1 and 0, respectively, of the read
only memory 70. These signals are utilized to select the proper
angle during the sequential selection of the angle and stress
information from the memory.
As mentioned hereinabove, the read only memory 70 receives a memory
initiate signal over the conductor 116. The selection of the total
information stored within the memory is limited by the digital
input received from the boom length sensor 54 which is connected to
the input terminals 6-9 thereof. This digital information disables
a large portion of the memory and enables only that portion thereof
relating to the length of the boom being immediately utilized by
the crane. In the preferred embodiment, the angle and or stress
information is stored within the memory for both extended or
retracted conditions and one condition or the other is selected
from the memory under the control of the extended or retracted
sensor 52. As each angle is selected from the memoroy under control
of the digital input received at input terminals 0-5, the
information representing that angle is read out from output
terminals 0-7 over digital output lines 74 to the input terminals
of the first shift register 76 utilizing FF11-FF18 for storage. The
shift register 76 is ideally suited for use as a digital storage of
binary information between the read only memory 70 and the digital
to analog converter 78. Information presented at each data input D
of the register 76 is transferred to the Q outputs when the clock,
applied over line 90, is high. The Q outputs will follow the data
inputs D as long as the clock remains high. When the clock goes
low, the information present at the data inputs D at the time the
transfer occured, is retained at the Q outputs until the clock is
permitted to go high. In the arrangement shown here, the data
terminals D are connected to the output terminals of a memory unit
70 while the Q terminals are connected to the input terminals of
FET switching circuits 174 and 176. The internal circuitry of the
FET switching circuits is shown in greater detail in FIG. 5. The
output from these FET switching circuits 174 and 176 is applied to
the input of a resistive ladder network 178.
The digital output lines 74 from the read only memory 70 are also
connected directly to the input terminals of AND gates 180-187. The
second input terminal of each of the AND gates 180-187 is connected
to the enable load signal line 158, wherein information stored
within the read only memory 70 is passed through the AND gates
180-187 when a positive signal is applied over the enable load
signal line 158. The output of each of these AND gates 180-187 is
applied to the data input terminals D of the second shift register
80 which is comprised of flip-flops FF19-26. The clock terminal of
each of the flip-flops FF19-26 is connected to the load stress line
92. A positive signal over this line transfers the data received
from the AND gates 180-187 to the digital to analog converter 82
which consists of third and fourth FET switching circuits 196 and
198 connected to the input of a ladder resistive network 200.
The output of the first ladder resistive network 178 is connected
to the first input terminal of an amplifier 202 whose second input
terminal is connected by a resistor 294 to ground. The output
terminal of the amplifier 202 connects through a variable feedback
resistor 206 to the second input terminal thereof. This amplifier
functions as a booster amplifier to increase the voltage and
current outputs of the resistance ladder network 200 and completes
the circuit of the first digital to analog converter 78. The output
of amplifier 202 connects to the inverting input terminal of the
comparator amplifier 60. The boom angle sensor 44 is connected to
the input terminal of a current amplifier 208 whose output terminal
connects in feedback relationship to the second input terminal
thereof. The output terminal of the current amplifier 208 is
further connected to the noninverting input terminal of the
comparator amplifier 60 and to the input terminal of a current
meter 210. The current meter 210 mounts on the indicator panel 88
and is provided with a scale for indicating the boom angle .theta.
of the boom structure 24. Comparator amplifier 60 connects via
resistor 212 to the base of an NPN transistor 214. The collector of
transistor 214 is connected to a +5 volt power source via a
resistor 216 while the emitter thereof is connected to ground. The
matched angle line 152 is connected to the junction between the
collector of transistor 214 and the resistor 216 for providing a
signal to the input of flip-flop FF9 and AND gate 156. Thus, it
will be seen that the angle matching circuit 62 includes the
transistor 214 and resistors 212 and 216.
The output of the resistive ladder network 200 is connected to the
input terminal of a unity gain amplifier 218 having the output
thereof connected to a second input terminal in a feedback
arrangement. The output terminal of the amplifier 218 also connects
to the inverting input terminal of a comparator amplifier 220 and
through a resistor 222 to the inverting input terminal of a second
comparator amplifier 224. The inverting terminal of amplifier 224
is connected to ground through a resistor 226. The output from the
boom load sensor 54 includes a positive and negative terminal
connected to the positive and negative input terminals of the load
amplifier 86 having an output terminal connected through a variable
resistor 228 to the negative input terminal thereof and the
positive terminal connected to ground through resistor 229 for
providing a high gain amplifier. The output terminal of the load
amplifier 86 is also connected directly to the second noninverting
input terminal of the comparator amplifier 220 and through a
resistor 230 to the second noninverting input terminal of the
second comparator amplifier 224. The output of the first comparator
amplifier 220 connects to a relay K-1 which, when actuated, closes
a single-pole, single-throw switch 232 for applying a positive
voltage to a warning buzzer 234 and an overload lamp 236.
Similarily, the output of the second comparator amplifier 224
connects to a relay K-2 which closes a second single-pole,
single-throw switch 238 for applying a positive voltage to a
caution lamp 240. In the preferred embodiment, the combination of
resistors 222, 226 and 230 provides a resistive network wherein the
relay K-2 is energized when the actual load reaches 85 percent of
the stress signal stored within the read only memory 70. Relay K-1
is energized when these signals are equal.
The FET switching circuits 174, 176, 196 and 198 include four
individual FET swtiching circuits, shown more clearly in FIG. 5. An
input signal E.sub.IN is received through a resistor 242 at the
base of a PNP transistor 244. The emitter of transistor 244 is
connected to a positive potential through a resistor 246 and to
ground through a second resistor 248. The collector of the
transistor 244 connects to a negative potential through a resistor
250 and to the base of an NPN transistor 252 through a resistor
254. The collector of transistor 244 connects to the gate of a
field effect transistor 256 having its drain terminal connected to
ground and the source terminal connected to an output terminal
E.sub.OUT. The collector of the NPN transistor 252 is connected to
the positive potential via resistor 257 and to the gate of a second
field effect transistor 258 whose source connects to a positive
voltage supply and whose drain connects to the output terminal
E.sub.OUT. In operation, an increasing input signal at E.sub.IN
turns off the transistor 244 and applies a decreasing potential to
the gate of the FET 256 for removing the output terminal E.sub.OUT
from its connection to ground therethrough. As the potential
decreases at the base of transistor 252, it is turned off for
increasing the potential to the gate of the FET 258 for connecting
the output terminal E.sub.OUT to the positive potential. Through
this arrangement, digital outputs from the shift registers 76 and
80 are converted to precise voltage levels for application to the
resistance ladder networks 178 and 200.
The operation of the crane warning system illustrated in FIGS. 3
and 4 will be understood more easily by reference to the timing
digram of FIG. 6. As mentioned, the clock signal is reduced to
signals C.sub.0 C.sub.1, C.sub.0 C.sub.1, and C.sub.0 C.sub.1 by
the counter 94 and AND gates 106, 110 and 112. The signals B.sub.0,
B.sub.1, B.sub.2, B.sub.3, B.sub.4 and B.sub.5 which control the
angle addressed from the memory are generated by the second portion
of the counter 94 and the second counter 98. Each of the 16
sequential angles are read out of the read only memory 70 to the
angle register 76 under the control of the signals from the
counters 94 and 98. Assuming the crane crawler treads or outriggers
are extended, NAND gates 124 and 130 are enabled while NAND gates
126 and 132 are disabled. Thus, the B.sub.0 B.sub.1 signal is
applied to the AND gate 120 through NAND gate 136; while the
C.sub.0 C.sub.1 timing signal is also applied thereto. It will be
seen that this causes the angle from the memory .THETA..sub.M to be
read therefrom during the first portion of each of the sequential
angles. This signal is applied through the first register 76 to the
digital to analog converter 78 under the control of a singnal is
also the AND gate 120 applied over the load angle line 90. The
digital signal is converted to an analog signal by the resistive
ladder network 178 as indicated by the signal .THETA..sub.M extend,
shown in FIG. 6. It will be remembered that the angle signal
applied to the comparator amplifier 60 will be either .THETA..sub.M
extend or retract depending on the position of the extended or
retracted sensor 52 which enables or disables the gates 124, 126,
130 and 132.
As the memory angle is sequentially read from the read only memory
70, the analog output signal applied from the amplifier 202 to the
comparator amplifier 60 increases to represent increasing stored
boom angles .theta..sub.M. When the stored boom angle becomes equal
to or greater than the actual boom angle, the output signal of th
amplifier 60 will decrease to a zero level thereby turning off the
transistor 214 and applying a high potential over the matched angle
line 152 to the inverter 154 and AND gate 156. In the example
illustrated in FIG. 6, this occurs during the fourth sequential
angle.
During the initiation of each cycle of 16 sequential angles, the
first angle read into the shift register 76 normally produces a low
output from the angle matching circuit 62 which is applied over
line 152 to the AND gate 156 and inverted by the inverter 154 to be
applied as a high signal to the J input terminal flip-flop FF9. As
the clock signal C.sub.0 C.sub.1 is applied to the clock terminal
of flip-flop FF9, the output at the 1 terminal thereof goes high on
the trailing edge of the timing signal, see FIG. 6. This high in
combination with the low from line 152 causes the output of the AND
gate 156 to remain low. When the angles are matched, the low signal
on line 152 goes high for applying a second high to the input of
AND gate 156 and causing the output thereof to go high, as shown in
the fourth angle of FIG. 6.
During the first angle of the 16 angle sequence, flip-flop FF10
receives at the J input terminal a positive signal from the AND
gate 148. Thus, the 1 output terminal goes high when the trailing
edge of the timing signal C.sub.0 C.sub.1 is applied from the AND
gate 112 to the clock terminal of flip-flop FF10, as shown in FIG.
6. As the angles are matched, the resulting positive signal applied
to the K input terminal of flip-flop FF10 causes that flip-flop to
toggle on the negative going edge of the timing signal C.sub.0
C.sub.1 for producing a zero output at the 1 terminal. The low
applied to the input of the NAND gate 160 combines with the low
applied to the other input terminal from the NAND gate 134. As the
gate 160 is a NAND gate, it will be seen that the change from high
to low at the 1 output terminal of flip-flop FF10 causes no change
in the output of the NAND gate 160, due to the continuous presence
of a low on the second input terminal thereof. The low on the
second input terminal of the NAND gate 160 is generated from the
AND gate 134, and it will be seen that the AND gate 134 goes high
only during the last quarter of the sixteenth angle when the signal
B.sub.0 B.sub.1 B.sub.2 B.sub.3 B.sub.4 B.sub.5 is applied to the
input terminal of the NAND gate 160. This signal is utilized for
the prupose of resetting the flip-flop FF9 and alarming should
there be no match between the stored angles and the anles within
the memory 70. When a matched angle is present, flip-flop FF10
prevents the signal from AND gate 134 from affecting the NAND gate
162 during the 16 th angle.
As the boom angle is matched with the memory angle, the positive
output of the AND gate 156 is applied to the input terminal of the
NAND gate 118 along with the timing signals C.sub.0 C.sub.1 and the
signals B.sub.0 B.sub.1 . The B.sub.0 B.sub.1 signal is applied
through the NAND gate 130 which is enabled by the high signal
applied over the extended signal line 172, as hereinabove
described. Thus, the output of the NAND gate 118, which is normally
high, goes low as the timing signals C.sub.0 C.sub.1 , B.sub.0
B.sub.1 and the high from the AND gate 156 are applied thereto. As
shown in FIG. 6, the output of the NAND gate 162 goes high as the
input from the NAND gate 118 goes low. It will be recalled that the
input from NAND gate 160 remains high.
The output from the AND gate 156 is also applied as a positive
signal over the enabled load stress line 158 to the AND gate
180-187. It will be seen that the AND gates 180-187 are thereby
enabled depending upon the digital stress information applied
thereto from the memory 70. When the load stress signal, as shown
on line 162 FIG. 6, is applied over the load stress line 92 to the
clock terminals of flip-flops FF19-FF26 within the stress register
80, the stress information then applied to the data terminal D of
these flip-flops is read into the FET switching circuits 196 and
198 within the second digital to analog converter 82. The signal is
then applied through the resistive ladder network 200 to the unity
gain amplifier 218 and the comparator amplifiers 220 and 224. If
the analog signal applied thereto is equal to or less than the
analog signal applied from the boom load sensor 54, the output of
the comparator amplifier 220 will energize the relay K-1 for
closing the switch 232 and energizing the buzzer 234 and light 236
in the indicator panel 88. If the stress signal from the converter
82 is within a fixed proportion of the stress signal applied by the
boom load sensor 54, the output of the amplifier 224 will energize
relay K-2 for closing the switch 238 and energizing the caution
light 240. The ratio between the boom load at which the caution
light 240 is energized and that required to energize light 236 is
determined by the resistance network established by resistors 222,
226 and 230. It will be seen that the meter 210 within the
indicator panel 88 provides a visual indication of the boom angle
to the operator of the crane via the connection to the output of
amplifier 208.
A crane operator while manipulating a load can place the crane boom
at an angle so low that the crane can not safely lift any load or
at an angle so high as to create a backward tipping condition. The
present invention provides an alarm for either of these conditions
by alarming when the boom angle is either less than the lowest
stored memory angles, i.e., boom too low, or greater than all
stored memory angles, i.e., boom too high.
Should the boom angle be greater than any of the stored memory
angles, it will be seen that the signal applied over the matched
angle line 152 never goes high. Thus, the output of an AND gate 156
remains low with the result that the output of NAND gate 118 always
remains high. Under these circumstances the output of the NAND gate
162 remains high until a timing signal from gate 134 applies a high
to the NAND gate 160. As discussed hereinabove, the output of the
flip-flop FF10 is high. Thus, the ouput of gate 160 goes low
causing the output of gate 162 to go high during the last portion
of the sixteenth angle, as shown in FIG. 6. As the ouput of gate
162 goes high, a load stress signal is applied over the line 92 to
the stress shift register 80. However, as no enable load stress
signal has been applied to the gates 180-187 over the line 158, the
signal loaded into the register 80 is an all zero signal and the
output applied to the comparator amplifiers 220 and 224 is
therefore an analog signal representing a zero load. Obviously,
this zero load is less than the boom load for causing an alarm
condition which is immediately sensed by the devices within the
indicator panel 88. As the output of the AND gate 156 never went
high, there was never a high signal applied to the K input terminal
of flip-flop FF10 and the output thereof remains high through the
next cycle. However, the high from the NAND gate 162 is also
applied to the inverter 164 and the NAND gate 168 which receives an
input from the AND gate 134 via inverter 166. The normal output of
the NAND gate 168 is low and changes to high with either the last
portion of the 16 th angle or the high output from NAND gate 162.
When this occurs, the high input to the K input terminal of the
flip-flop FF9 causes the 1 output terminal to go low as the clock
signal C.sub.0 C.sub.1 goes low. It will be seen that the flip-flop
FF9 is reset at the very last portion of the 16 th angle in the
event that the boom angle and stored angle are never match. When
there is a match as described above, the flip-flop FF9 is reset on
the negative going edge of the timing pulse C.sub.0 C.sub.1 during
the presence of the positive output from the NAND gate 162.
Conversely, if the boom angle is less than the first memory angle
applied to the comparator amplifier 60, the output over the angle
matching line 152 would be high. This would apply a low to the J
input terminal of flip-flop FF9 causing the output at the 1 output
terminal thereof to remain low. The high applied to the AND gate
156 directly from the line 152 causes that gate output to remain
low throughout the 16 th sequential angles. Under this
circumstance, an alarm condition would occur at the end of the 16
th angle in the same way that an alarm is generated when the boom
angle is too large.
The preferred embodiment of the present invention includes a
push-to-test button 260, shown in FIG. 7, which is located on the
indicator 88. In FIG. 7, the push-to-test circuitry is illustrated
along with other details of the crane warning system. For example,
the extended or retracted sensor 52 includes a single-pole,
single-throw switch 262 whose contact arm is connected to a
positive potential through a resistor 264. In the extend position,
a positive potential is applied to the extended signal line 172;
while an negative signal is applied through an inverter 266 to the
retracted signal line 170. When the switch 262 is closed, the
normally closed terminal is connected to ground for removing the
positive potential from the line 172 and thereby placing a positive
or high signal on the retracted line 170.
The boom length sensor 50 is illustrated as a plurality of
single-pole, multithrow switches 268, 270, 272 and 274 ganged
together such that one pole of each switch is connected to ground
for each of the four illustrated switch positions. The wiper arms
of switches 268, 270, 272 and 274 are each connected to an input
terminal of NAND gates 276, 278, 280 and 282 is connected to a
positive potential through a single resistor 286 and to the wiper
arm of a switch 288 within a first relay K-4. The normally opened
terminal of the switch 288 is connected to ground. When the
push-to-test switch 260 is depressed for energizing the relay K-4,
the switch 288 connects the input of each of the AND gates 276,
278, 280 and 282 to ground for disabling the boom length sensor 54.
This same relay includes a second switch 290 which connects the
extended or retracted sensor 52 to ground for ensuring that the
output on the extended line 172 is low while the output on the
retracted line 170 is high.
The boom angle sensor 44 is connected into the circuit shown in
FIG. 7 at the terminals labeled pendulum pot. These terminals
include two inputs labeled IN and 60.degree. and an output labeled
OUT. In the normal operating condition, the relay K-4 provides a
path through which the signal from the boom angle sensor 44, in the
form of a signal from a pendulum potentiometer, is applied from the
IN terminal, through the switch 292, to the OUT terminal. When the
relay K-4 is energized by pushing the push-to-test button, the boom
angle OUT terminal is connected to the fixed potential applied at
the 60.degree. terminal. Thus, the relay K-4 disables the boom
length sensor, places the extended or retracted sensor in the known
condition, and places a known condition at the output of the boom
angle sensor 44.
The load cell within the boom load sensor 54 is connected to the
normally closed terminals of switches 294 and 296 which make up the
first and second switches of a relay K-3. The wiper arms of
switches 294 and 296 are connected directly to the output terminals
of the boom load sensor 54. Thus, under normal operating
conditions, the load cell signal passes directly through the
push-to-test circuit. Once the push-to-test switch 260 has been
energized, the relay K-3 closes switches 294 and 296 for connecting
the negative terminal of the boom load sensor to ground through the
normally opened terminal of the switch 294 and connecting the
positive terminal of the boom load sensor to a test circuit through
the normally opened terminal of the switch 296. This test circuit
includes a third switch 298 within the relay K-3. The wiper arm of
the switch 298 is connected to one electrode of the capacitor 300
having a second electrode connected to a source of positive
potential. The second electrode and positive potential are
connected through a resistor 302 to the normally closed terminal of
the switch 298. Thus, it will be seen that the capacitor 300 is
charged to a fixed potential across the electrodes thereof during
the normal operation of the crane. The first electrode of capacitor
300 is also connected to the cathode of a diode 304 whose anode
connects to the base of a PNP transistor 306. The emitter of the
transistor 306 connects to a source of positive potential while the
cathode thereof connects through a resistor 308 to a junction 310
which, in turn, connects to ground through a variable resistor 312.
The emitter of transistor 306 is also connected to the junction 310
through a resistor 314. The junction 310 is then connected to the
normally opened terminal of the switch 296 to complete the test
circuit.
When the push-to-test switch 260 is depressed, the negative
terminal of the boom load sensor output is connected to ground and
the positive terminal thereof is connected to the junction 310. At
the same time, the output of the test circuit is connected to
ground through the normally opened terminal of the switch 298 and a
resistor 316. The positive potential applied to the emitter of
transistor 306 from capacitor 300 causes a first level of potential
to be applied to the normally opened contact of the switch 296 over
the positive line of the boom sensor to the amplifier 86. As the
capacitor 300 discharges through the resistor 316, the transistor
306 is turned off for increasing the potential at the junction 310
and increasing the signal applied over the positive terminal of the
boom load sensor. Thus, the push-to-test button establishes a first
lower level signal which energizes the caution lamp 240 and
provides a second larger output signal which energizes the buzzer
234 and the caution lamp 236. Through this arrangement, an operator
may depress the switch 260 and establish that his warning devices
within the indicator panel 88 of the crane warning system are
properly functioning.
The indicators illustrated in FIG. 2 and FIGS. 3-4 are capable of
providing a warning as the lifted load approaches and becomes
greater than the maximum load stored within the read only memory
70. FIG. 8 illustrates a circuit which may be embodied within the
present invention for providing a percent of safe load indicator.
That is, a crane operator can often be assisted by a continuous
indication of the remaining lift capacity of his crane. This
infomation is helpful, for example, as an operator lowers or raises
his boom while manipulating or reaching with a load. Under these
dynamic conditions, an arbitrary warning that the crane is
approaching a dangerous condition may occur too late for the
operator to take corrective action. The presentation of the
percentage of safe load information is accomplished in the present
invention by unique circuitry which allows for relatively simple
manipulation of the existing crane warning system. For example, the
output of the stress register 80 in FIG. 8 is applied to a third
digital to analog converter 320 and also to the second digital to
analog converter 82. This information is converted and applied
through a comparator amplifier 322 and a voltage follower amplifier
324 to the input terminal of a percent of safe load indicating
meter 326. The signal from the amplifier 324 is also feedback to
the digital to analog converter 320 wherein it is used as the
reference voltage. A power supply 328 is utilized to provide a
fixed voltage reference to the boom load sensor 54 and to the
second digital to analog converter 82 each of which are connected
to the comparator amplifier 84. The output V.sub.L of the load cell
amplifier 86 is applied to the indicator panel 88, as described
hereinabove, and is also applied to the second input terminal of
the comparator amplifier 322.
In operation both digital to analog converters 82 and 320 take
their inputs from the digital values of the maximum safe load
stored in the stress register 80. Digital to analog converter 82
operates from the fixed voltage from the power supply 328. The
digital to analog converter 320, however, uses as its reference
voltage the output voltage V.sub.R of the differential amplifier
322. The amplifier 324 is a unity gain voltage follower amplifier,
while differential 322 is a high gain amplifier having a gain of u.
The output of the differential amplifier 322 is thus proportioned
to the difference between the input voltage V.sub.L from the load
cell amplifier 86 and the input voltage E.sub.0 is proportional to
the load value L.sub.M contained in the stress register 80 and the
reference voltage V.sub.R fedback from the amplifier 324. The
reference voltage may be expressed as follows:
V.sub.R = (V.sub.L - E.sub.0) u
V.sub.L is defined as aL where a is the scaling factor and L is the
load, and E.sub.0 is defined as bL.sub.M V.sub.R where b is a
scaling factor and L.sub.M the maximum stored load for a given
crane condition. Thus, substituting these values in the equation
above for V.sub.L and E.sub.0 V.sub.R may be expressed as
follows:
V.sub.R = (aL-BL.sub.M V.sub.R ) u
V.sub.R (1 + ubL.sub.M) = aLu
As the quantity ubL.sub.M is much larger than 1 the equation can be
approximated as follows:
V.sub.R ubL.sub.M = aLu
V.sub.R = (a/b) (L/L.sub.M)
a and b can be choosen to make V.sub.R = 10 .sup.. (L/L.sub.M) thus
the 10 volt full scale meter 326 will read full scale when L =
L.sub.M and with the scale marked 0 to 100 percent it will indicate
percent of load with respect to the maximum safe load value stored
in the memory 70.
A final embodiment of the present invention is shown in FIG. 9
wherein the crane warning system is used to provide a load weight
indication. In this arrangement the equation for the back hitch
tension is expressed in terms of:
BHT = mL + b
Where L = load, m = slope and b = back hitch tension at zero load.
The quantities m and b are constant for each combination of boom
length and boom angle. Therefore, by solving the above equation, it
is possible to express the load L in terms of:
L = (BHT - b)/m The quantities b and 1/m can be stored in an
expanded read only memory 70 of the crane warning system along with
the values of boom angle and maximum stress.
FIG. 9 illustrates how the load equation can be solved. Two
additional registers 330 and 332 are provided for receiving the
back hitch tension at zero load b and the inverted slope value 1/m
, respectively. The registers 330 and 332 each connect to a digital
to analog converter 334 and 336. The power supply 328 which
supplies power to the boom load sensor 54 also provides the fixed
reference voltage to the digital to analog converter 334. The
output of the digital to analog converter 334 is applied to a
comparator amplifier 338 which also receives the amplified input
from the boom sensor 54. The output of the comparator amplifier 338
is the quantity BHT-b, i.e., the back hitch tension at zero load
subtracted from the actual back hitch tension. This output voltage
signal is used as a reference voltage for the digital to analog
converter 336 which receives its input from the register 332. The
output of the digital to analog converter 336 drives a meter 340
through an amplifier 342. As the output of the digital to analog
converter 336 is proportional to both the digital input 1/m and the
reference voltage from the amplifier 338, its output is
proportional to load. The scale on the meter 340 is therefore
chosen to allow a 10 volt input to indicate full scale or 100
percent of the rated load of the crane. Thus, it will be seen, that
the scale will be adjusted for each condition of the crane and will
reflect the load sensed by the boom load sensor 54 in terms of
pounds.
A crane warning system has been described herein which is capable
of storing a large amount of tabulated information peculiar to the
particular crane within which the system is used. This information
is then selected from storage by narrowing the portion of the
memory in which the information is stored that may be utilized
during any given set of crane operating conditions. By storing all
the necessary information and selecting only that portion necessary
for a given crane condition, the crane warning system of the
present invention is capable of instantaneously sensing all
conditions of pending crane failure. The memory arrangement of the
present invention provides a crane warning system that alarms as
the load lifted by the crane exceeds a maximum predetermined value
including loads which create a potential tipping of the crane or a
potential crushing of the boom. An alarm is further provided if the
operator of the crane places the boom in a position too low or too
high for the crane he is operating. Further, the crane operator is
provided with a crane warning system that warns of pending crane
failure through the utilization of circuitry which is capable of
alarming before a maximum load is reached, circuitry which
indicates a percent of safe load remaining, or circuitry which
indicates the load in pound. These circuits are all easily
incorporated into the main circuitry of the present invention.
There has also been described a simple push-to-test circuit which
allows the crane operator to quickly establish that his warning
devices are functioning properly.
* * * * *