U.S. patent number 3,854,128 [Application Number 05/312,225] was granted by the patent office on 1974-12-10 for safety device for crane.
This patent grant is currently assigned to Unic Corporation. Invention is credited to Susumu Yamagishi.
United States Patent |
3,854,128 |
Yamagishi |
December 10, 1974 |
SAFETY DEVICE FOR CRANE
Abstract
A safety device for a crane comprises apparatus for detecting a
work length of the crane, a device for determining a safety or
rated load corresponding to the detected work length, an instrument
for detecting a load actually lifted, and apparatus for comparing
the lifted load with the rated load to produce an output signal for
operating an alarm device or stopping the crane when the lifted
load is equal to or more than the rated load. The safety device
employs elements which produce electric signals, corresponding to
rated and lifted loads, which are compared.
Inventors: |
Yamagishi; Susumu (Tokyo,
JA) |
Assignee: |
Unic Corporation (Tokyo,
JA)
|
Family
ID: |
11466603 |
Appl.
No.: |
05/312,225 |
Filed: |
December 4, 1972 |
Foreign Application Priority Data
Current U.S.
Class: |
340/522; 340/685;
212/281; 212/278 |
Current CPC
Class: |
B66C
23/905 (20130101) |
Current International
Class: |
B66C
23/00 (20060101); B66C 23/90 (20060101); B66c
013/48 (); G08b 021/00 () |
Field of
Search: |
;340/267C
;212/39A,39R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Swann, III; Glen R.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Claims
What is claimed is:
1. A sefety device for a crane comprising boom length detecting
means for detecting a boom length including means for generating a
first electric signal corresponding to boom length, work radius
detecting means for receiving said first signal and for generating
directly a second electric signal corresponding to work radius,
said second signal being a product of said first signal and a third
cosine signal corresponding to a boom inclination angle, said
cosine signal being generated in said work radius detecting means,
lifted load detecting means for detecting a lifted load including
means for generating a fourth electric signal corresponding to the
lifted load, a rated load determining means including means for
converting said second signal received therein to a fifth electric
signal indicating a rated load corresponding to said work radius,
said rated load determining means including a polygonal line
function generator having an operational amplifier circuit and
diode switches for changing amplification factors according to said
second signal, and comparator means for comparing said fifth signal
with said fourth signal to produce a sixth output signal providing
information concerning safe crane operation when said lifted load
is equal to or more than said rated load.
2. A safety device as set forth in claim 1, wherein said boom
length detecting means (1) comprises a cord reel (12) adapted to
extend and retract a cord according to a boom length, a helical
potentiometer (13) responsive to the movement of said cord to
convert the boom length to an electric resistance, and a negative
feedback amplifier circuit connected to the electric resistance for
providing an electric voltage signal comprising said first
signal.
3. A safety device as set forth in claim 1, wherein said work
radius detecting means (2) comprises a potentiometer, the
resistance winding of which is wound in a cosine manner and a
slider interlocked with a main boom (14) wherein a turned angle of
the slider is proportional to a boom inclination angle (.theta.),
an output voltage signal (L) from said boom length detecting means
(1) being applied to the ends of said resistance winding of said
potentiometer for producing a signal (L cos.theta.), corresponding
to a work radius, which is generated from the turning angle of the
slider, said signal (L) comprising said first signal and said
signal (L cos.theta.) comprising said second signal.
4. A safety device as set forth in claim 1, wherein said lifted
load detecting means (4) comprises a load cell (11) in which a real
stress acting on a wire rope for lifting is converted into an
electric signal which is applied to an amplifier to obtain a signal
of electric voltage (W.sub.L) corresponding to the lifted load,
said voltage (W.sub.L) comprising said fourth signal.
5. A safety device as set forth in claim 1, wherein said rated load
determining means (3) comprises an operational amplifier circuit
and diode switches for changing amplification factors according to
an input voltage (L cos.theta. = R) comprising said second signal,
said amplification factors being (W.sub.2 -W.sub.1)/(R.sub.2
-R.sub.1), (W.sub.3 -W.sub.2)/(R.sub.3 -R.sub.2), and (W.sub.4
-W.sub.3)/(R.sub.4 -R.sub.3) corresponding to respective ranges of
work radii, wherein R.sub.1 - R.sub.4 are work radii and W.sub.1 -
W.sub.4 are corresponding rate loads.
6. A safety device as set forth in claim 1, wherein said comparator
means (5) comprises a differential amplifier, to the respective
input terminals of which the fourth signal (W.sub.L) and a rated
load signal (W.sub.O) comprising said fifth signal are supplied to
discriminate the positive or negative value of the difference
between the signals (W.sub.O) and (W.sub.L) and wherein when the
lifted load is equal to or more than the rated load, said
differential amplifier produces an output signal comprising said
sixth signal to operate an alarm device (6).
7. A safety device as set forth in claim 6, wherein said alarm
device (6) comprises a relay adapted to be operated by said output
signal from said differential amplifier to close its contacts so
that an alarm buzzer sounds.
8. A safety device as set forth in claim 6, wherein said alarm
device (6) comprises a relay adapted to be operated by said output
signal from said differential amplifier to close its contacts so
that the operation of the crane is stopped.
9. A safety device as set forth in claim 6, wherein said alarm
device (6) comprises a relay adapted to be operated by said output
signal from said differential amplifier to close its contacts so
that an alarm lamp is lighted.
10. A safety device for a crane comprising boom length detecting
means (1) including a cord reel (12) adapted to extend and retract
a cord according to a boom length, a first helical potentiometer
(13) responsive to the movement of said cord to convert the boom
length to an electric resistance, and a first negative feedback
amplifier circuit, connected to the electric resistance, for
providing a first electric output voltage signal (L), a work radius
detecting means (2) including a second potentiometer, the
resistance winding of which is wound in a cosine manner, and a
slider interlocked with a main boom (14) wherein a turned angle of
the slider is proportional to a boom inclination angle (.theta.),
the output voltage signal (L) from said boom length detecting means
(1) being applied to the ends of said resistance winding of said
second potentiometer for producing a second signal (L cos.theta.),
corresponding to work radius, which is generated from the turning
angle of the slider, lifted load detecting means (4) including a
load cell (11) in which a real stress acting on a wire rope for
lifting is converted into a third electric signal which is applied
to a first amplifier to obtain a fourth signal of electric voltage
(W.sub.L) corresponding to the lifted load, rated load determining
means (3) including a second operational amplifier circuit and
diode switches for changing amplification factors according to an
input voltage (L cos.theta. = R) comprising said second signal to
provide a fifth electric signal corresponding to a rated load
signal (W.sub.O), said amplification factors being (W.sub.2
-W.sub.1)/(R.sub.2 -R.sub.1), (W.sub.3 -W.sub.2)/(R.sub.3 -R.sub.2)
and (W.sub.4 -W.sub.3)/(R.sub.4 -R.sub.3) corresponding to
respective ranges of work radii wherein R.sub.1 -R.sub.4 are work
radii and W.sub.1 -W.sub.4 are corresponding rated loads, and
comparator means (5) including a second differential amplifier, to
the respective input terminals of which the fourth signal (W.sub.L)
and the fifth signal (W.sub.O) are supplied to discriminate the
positive or negative value of the difference between the signals
(W.sub.L) and (W.sub.O) and wherein when the lifted load is equal
to or more than the rated load, said differential amplifier
produces a sixth output signal to operate an alarm device (6), said
alarm device including a relay adapted to be operated by said sixth
output signal from said differential amplifier to close its
contacts.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a safety device for a crane adapted to
always monitor an excessive load lifted by the operating crane over
a safety load associated with a length of a boom and hence a work
radius of the crane.
2. Description of the Prior Art
Recently, there has been a tendency for cranes to become larger and
therefore the operator's delayed judgement and false operation are
important problems to solve. These factors may cause serious
accidents particularly in large type cranes.
To avoid such accidents, it is necessary to monitor an unexpected
excessive load over a safety load of a crane to obtain correct data
for safety.
In the prior art, there have been cranes equipped with alarm
devices which warn of abnormal conditions on a single matter such
as overloading or instability in a horizontal plane. In other more
primitive cases, operators have determined the safety condition
with reference to rated curves of the cranes in comparison with
individual values of measured boom inclination angles, boom lengths
and lifted loads. In these procedures, the recognition of dangerous
conditions or the confirmation of safety cannot be made
continuously so that operational efficiency may remain at a
relatively low level.
There also are prior art cranes, equipped with means for
continuously measuring a boom inclination angle and a load at a
constant boom length. That is, a pressure value at a derrick crane
and a pressure value under its rated load are converted into
approximate voltage values in a stepwise manner to provide an
automatic determination of the safety of the crane. In the
arrangement, however, it is necessary to adjust the means whenever
the boom length varies during the crane operation, so that the
arrangement does not contribute to a good improvement in
efficiency.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above
disadvantages in the prior art. One of its purposes is the
provision of a safety device for a crane comprising boom length
detecting means for detecting boom length as an electric signal,
work radius detecting means for receiving said boom length signal
and generating directly as an electric signal corresponding to work
radius, a product of said boom length signal and a cosine signal
which is obtained by converting a boom inclination angle into an
electric signal, lifted load detecting means for detecting a lifted
load as an electric signal, rated load determining means for
converting said work radius electrical signal received therein to a
signal indicating a rated load corresponding to said work radius,
and comparator means for comparing said signal indicating said
rated load with said signal indicating said lifted load to produce
an output signal for stopping the crane operation or operating an
alarm device when said lifted load is equal to or more than said
rated load.
The term "rated load" used herein is intended to mean a safety load
corresponding to the length of a boom of a crane actually used and
hence a work radius of the crane.
An object of the invention is to provide an improved safety device
for a crane which is provided with a simplified circuit
arrangement, and capable of automatically continuously checking for
safe crane operation even if the length of the crane varies and
preventing any false operation thereby improving the efficiency in
the crane operation.
Another object of the invention is to provide a safety device for a
crane capable of automatically continuously checking for safe crane
operation by comparison of a load actually lifted with a rated load
to meet the work radius obtained from a boom length and a boom
inclination angle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the principle of the safety
device according to the invention;
FIG. 2 is a diagram showing one example of a rated load curve;
FIG. 3 is a diagrammatical elevation of a truck crane employing the
safety device according to the invention;
and
FIG. 4 is a circuit arrangement showing one embodiment of a rated
load determining means employed in the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the invention will be explained in detail
hereinafter with reference to the drawings.
The block diagram of FIG. 1 illustrates the principle of the device
according to the invention. In the diagram, boom length detecting
means 1 converts a boom length (L) into an electric signal L for
detecting the boom length and work radius detecting means 2
converts a boom inclination angle (.theta.) into an electric signal
cos.theta. and extracts an electric signal L cos.theta. as a
product of the signal cos.theta. and the signal L of the boom
length produced in the boom length detecting means 1. The signal L
cos.theta. indicates a work radius R of a crane.
Rated load determining means 3 in FIG. 1 extracts a rated load
W.sub.0 =f(R) in the form of an electric voltage corresponding to
the length of the crane work radius L cos.theta.=R received as an
input in the rated load determining means. Lifted load detecting
means 4 converts the load actually lifted into an electric signal
W.sub.L which is transmitted together with the rated load signal
W.sub.0 to comparator means 5 which discriminates the positive or
negative value of the difference W.sub.0 -W.sub.L. In case the load
signal W.sub.L is equal to or more than the rated load signal
W.sub.0, that is W.sub.0 -W.sub. L .ltoreq.0, the comparator means
5 produces an output signal which operates alarm device or crane
operation stopping means 6.
In the event the load signal W.sub.L is less than the rated load
signal W.sub.0, that is W.sub.0 -W.sub.L >0, the comparator
means 5 does not produce any output signal because the alarm device
or crane operation stopping means 6 need not be operated.
While the safety device according to the invention can be applied
to any crane of fixed or adjustable length boom, the invention will
be specifically explained hereinafter with reference to a truck
crane incorporating the safety device.
Referring to FIG. 3, a truck 7 is equipped with a swivel slide 8,
pivotal points 9 for a boom, luffing cylinders 10, a load cell 11
for detecting a load, a cord reel 12, a potentiometer 13 for
measuring the boom length, the main boom 14 and a hook 15.
In the embodiment, the boom length detecting means 1 shown in FIG.
1 consists of the cord reel 12 adapted to extend and retract a cord
according to the boom length, the helical potentiometer 13 which
converts the boom length to an electric resistance with the aid of
the cord reel 12, and a negative feedback amplifier circuit (FIG.
1) which converts the electric resistance to an electric voltage
signal. With the arrangement, the boom length detected by the cord
reel 12 is converted into the electric signal as electric voltage
L. The work radius detecting means 2 consists of a potentiometer
(FIG. 3) mounted on the pivotal point 9, the resistance winding of
which is wound in a cosine manner and a slider of which is
interlocked with the main boom 14 such that a turned angle of the
slider is proportional to a boom inclination angle (.theta.). When
the output voltage L from the boom length detecting means 1 is
applied to the ends of the resistance winding of the potentiometer,
it produces a signal L cos.theta. illustrating the work radius
which has been converted from the turning angle of the slider.
The lifted load detecting means 4 comprises the conventional load
cell 11 in which a real stress acting on a wire rope for lifting is
converted into an electric signal which is applied to an amplifier
(not shown) to obtain a signal of electric voltage W.sub.L
corresponding to the load.
The rated load determining means 3 comprises a circuit as shown in
FIG. 4 to obtain a load curve W.sub.0 =f(R) such for example as the
curve shown in FIG. 2 having an abscissa R (work radius) and an
ordinate W.sub.0 (rated load). The voltage amplifier circuit shown
in FIG. 4 is provided with an operational amplifier circuit and
diode switches for changing over amplification factors according to
the input voltage L cos.theta.=R. As can be seen from FIG. 2, the
amplification factor within the range of the work radius from zero
to R.sub.1 is zero because the load signal W.sub.1 is constant and
equal to the rated load signal W.sub.0 and the amplification
factors within the ranges from R.sub.1 to R.sub.2, R.sub.2 to
R.sub.3 and R.sub.3 to R.sub.4 are (W.sub.2 -W.sub.1)/(R.sub.2
-R.sub.1), (W.sub.3 -W.sub.2)/(R.sub.3 -R.sub.2) and (W.sub.4
-W.sub.3)/(R.sub.4 -R.sub.3), respectively.
The rated load W.sub.0 is determined as a function of the work
radius R = Lcos .theta. by the use of the circuit as shown in FIG.
4. The polygonal line function generator in FIG. 4, which consists
of diodes, resistances and an arithmetic unit, operates in a manner
known by those skilled in the art and disclosed in various electric
engineering reference books. The theory and technique of
constructing such polygonal line function generators are set forth
in Electronic Analog Computers by Korn et al., McGraw-Hill, 1956,
pages 290-297 and Operational Amplifiers, Design and Applications
by Graeme et al., McGraw-Hill, 1971, pages 250-253. The function
generator is so constructed that when it receives as an input a
voltage corresponding to R = Lcos .theta., it will generate an
output voltage corresponding to the rated load W.sub.0.
Voltages corresponding to the maximum rates load W.sub.1 and work
radii R.sub.1, R.sub.2 and R.sub.3 are (r.sub.8 /r.sub.1)E and
(r.sub.2 /r.sub.3)E, (r.sub.4 /r.sub.5)E and (r.sub.6 /r.sub.7),E
respectively. Rated loads corresponding to R.sub.1, R.sub.2 and
R.sub.3 are W.sub.1, W.sub.2 and W.sub.3. Moreover, there are
following relationships, (W.sub.1 -W.sub.2)/(R.sub.1 -R.sub.2) =
-r.sub.8 /r.sub.2, (W.sub.2 -W.sub.3)/(R.sub.2 -R.sub.3) =
-([r.sub.8 /r.sub.2 ] - [r.sub.9 /r.sub.4 ]) and (W.sub.3 -
W.sub.4)/(R.sub.3 - R.sub.4) =-([r.sub.8 /r.sub.2 ] - [r.sub.9
/r.sub.4 ] - [r.sub.9 /r.sub.6 ]). Owing to the smoothing effect of
the diodes, the polygonal line is changes into a smooth curve to
improve the accuracy of approximate values.
The comparator means 5 consists of, for example, a differential
amplifier, to the both input terminals of which the signals W.sub.0
and W.sub.L are supplied to discriminate the positive or negative
value of the difference between the signals. When the load signal
W.sub.L is equal to or more than the rated load signal W.sub.0,
that is, W.sub.0 -W.sub.L .ltoreq.0, an output from the
differential amplifier causes a relay of the crane operation
stopping means 6 to be operated to close its contacts, so that an
alarm lamp is lighted, an alarm buzzer is energized or the
operation of the crane is stopped. In the event of W.sub.0 -W.sub.L
<0, the comparator means does not produce any output to make the
alarm device operate or stop the operation of the crane.
As above described, the safety device according to the invention
can always continuously monitor any excessive load more than a
rated load meeting a work radius of the crane over the wide ranges
of the boom length, the boom inclination angle and the lifted load
without using a complicated electronic circuit, so that a crane
operator can be absorbed in the crane operation without consuming
time to consider the safety of the crane. Therefore, the efficiency
in crane operation can be considerably improved.
Furthermore, the problem of delayed judgement of the operator,
which is encountered in the prior art in any dangerous condition,
can be solved and when an operator falsely operates a crane, it is
automatically brought into an inoperative state so that any
dangerous condition caused by the malfunction can be avoided.
Moreover, the safety device according to the invention can be
advantageously applied to any kind of cranes having fixed or
adjustable length booms.
While the present invention has been shown and described in a
certain form only, it will be obvious to those skilled in the art
that it is not so limited but is susceptible of various changes and
modifications without departing from the spirit and scope
thereof.
* * * * *