US 3713129 A
A protective system for use with a multiple legged crane wherein a sensor is attached to each leg to determine the change in stress in that leg, and the several sensors are grouped to determine tipping along any side of the crane. Tipping is indicated by a reduced stress in the legs on a given side of the crane. The apparatus further furnishes the total hook load by summing the stress on all the legs.
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Description (OCR text may contain errors)
United States Patent 1 91 Buchholz CRANE OVERLOADING PROTECTIVE [4 1 Jan. 23, 1973 3.090126 5/1963 Corti et al. ..340/272 SYSTEM 2.858.070 l0/l958 Scharff .340/267 0  Inventor: Robert T. Buchholz, 15903 Diona Primar y Examzner-Donald .l. Yusko Lane Houston 77058 Assistant ExaminerMichael Slobasky  Filed: March 30, 1970 Attorney-Donald Gunn  Appl. No.: 23,544
 ABSTRACT 52 user. ..340/267 0,212/39 R A protective system for use with a multiple legged [5l] lnt.Cl. ..Go8 b 21/00 Crane wherein a sensor is attached to each leg to  Field of Search ..340/267C,272;2l2/39,145 determine the change in Stress in a g, a d th several sensors are grouped to determine tipping along  References Cited any side of the crane. Tipping is indicated by a reduced stress in the legs on a given side of the crane. UMTED STATES PATENTS The apparatus further furnishes the total hook load by 3,079,080 2/1963 Mason ..2l2/39 MS summing the stress on all the legs.
7 Claims, 2 Drawing Figures 25 3] m LOAD A B WARN/NO V ,.5E/\/5OR v SUMM/NG 27 A COMPARATOR DEV/CE ,27 L LOAD C D 26 22/ SENSOR SUMM/NG B COMPARATOR l 4 lNPUT OR RELAY GA TE DRIVER LOAD sui 4i4 lve J 23' SENSOR C COMPARATOR 3O 9 2 LOAD B D 24 SENSOR SUMM/NG D COMPARATOR L L i": SUMMER DISPLAY PATENTEDJMIZI! I975 79 FIG. I
25 37 LOAO B K K A WARNING 2 JSENSOR SUMM/NG A L COMPARATOR 05 W65 27 LOAO 0 +0 26 22/ SENSOR SUMM/NG B COMPARATOR 4 ,NPUT
28 OR RELAY GA TE OR/vER LOAO A c 23' SENSOR SUMM/NG A c COMPARATOR 30 29 LOAD B 0 24 SENSOR SUMMING D COMPARATOR A f E A B c D HOOK suMMER LOAD DISPLAY Robert I Buchholz INVENTOR BY MAW ATTORNEY CRANE OVERLOADING PROTECTIVE SYSTEM RELATED APPLICATIONS Applicant has no presently pending related applications.
SUMMARY OF PROBLEM AND SOLUTION Four-legged cranes are often used in unloading ships and handling cargo on a large scale. On occasion, very catastrophic injuries or damages have been incurred from the collapse of a boom or the tipping over of a crane. It is difficult for the crane operator to mentally correlate the many factors which relate to stability of the crane to be able to gauge the safe use of the crane. For instance, a load which might be safe when the boom is nearly vertically upright will be unsafe with the boom extended. In a typical four-leg crane, the angle of orientation of the cab and boom likewise determine the stability of the crane. For instance, if the boom is turned at an angle such that it passes over a corner having a leg for support underneath, this posture is considered more stable than the posture in which the boom extends directly over one of the several sides of the crane, but particularly between a pair of adjacent legs. These relationships are trignometric rather than,linear, and hence, it is difficult if not impossible for an operator to visually obtain the quality of feel for the operation of his equipment and to safely use the equipment without tipping or collapsing the crane.
The severity of the danger involved in tipping of a crane cannot be underestimated. Certain systems have been provided in the past, but by and large, they have been found wanting. For instance, an expensive solution to this problem is to provide the legs with a positive lock to the track system on which the crane is moved. Other equipment has been fabricated which utilizes an angle sensor on the boom and which correlates tension in the cables of the boom to the angle to determine a safe hook load. Such equipment is unduly complicated, and requires mathmatical approximations which are substantially inaccurate. Without over extending the present disclosure, it is believed sufficient to note that the equipment of the prior art has been. tested and found wanting.
The present invention is summarized as incorporating a load sensor for each leg of a crane. The most common crane arrangement. is the provision of four legs, somewhat as a table, for supporting the cab of a crane. The legs are appended to the four corners of the structure. A load sensor is attached to each leg to respond to its load. Load sensors provide electrical outputs which are then summed along the various sides of the crane. When the load along a particular side of the crane decreases to a certain level, an alarm is sounded and the operator is required to quickly lighten his load to prevent the crane from tipping. Additionally, the signals from the several load sensors are all summed to form the signal for a hook load display.
Many objects and advantages of the present invention will become more readily apparent from a consideration of the written specification and drawings, wherein:
FIG. I is a representative crane adapted for use with the present invention; and,
FIG. 2 is a schematic block diagram of the crane overload system of the present invention.
In the drawings, attention is first directed to FIG. 1 where a crane is indicated generally by the numeral 10.
a The crane includes preferably four legs such as the legs 11 and 12. The legs are typically symmetrical and extend from a platform 13 on which the cab 14 rotates. The legs 11 and 12 are received on wheel carriages l5 and 16 to permit movement of the crane 10 typically along a track at a port facility or a large industrial plant site. The platform 13 provides a pivot point for the cab 14 as it rotates about a vertical axis. The cab 14 includes the motive means and other controls for the operator with a view of operating the boom 18. The boom 18 extends outwardly at an angle controlled by the operator and a cable 19 supports a load 20 as shown in FIG. 1. The apparatus is used to lift, move, haul, and otherwise relocate substantially heavy weights. For instance, it might be used to unload palletized cargo from a ship, to move a gondola car, and the like.
Attention is next directed to FIG. 2 to correlate the present invention with the crane of FIG. 1 which is typical or appropriate supporting structure on which the present invention is installed. The crane of FIG. 1 is considered very typical or representative. There are other configurations of cranes which may be used with the present invention. The precise nature of the crane is believed beyond the scope and concern of the present disclosure. In FIG. 2, the numerals 21, 22, 23, and 24 all indicate load sensors which are suitably adapted to the several legs of the crane. The crane of FIG. 1 preferably includes four legs which is a common arrangement. Hence, four load sensors are provided in FIG. 2. The load sensors are preferably load cells which are attached to the vertical struts comprising the legs 11 and 12 of the crane. They may also be linear transmitters which are made responsive to the loading on the leg. A strain gauge has been found acceptable for this function also. In any case, the load sensors include a means which is responsive to the stress in the legs of the crane. As will be understood by those skilled in the art, the legs 1 1 and 12 are typically formed of structural steel and they are strained in response to the stresses acting thereon. The strain creates small, even minute deflections in the metal comprising the legs 11 and 12. In any case, the load sensorsare responsive to loading on the legs of the crane. In a typical installation, the load sensor is attached to the leg of the crane. Routinely, the load sensor includes a signal conditioner such as a telemetry transmitter for relaying the signals to the monitoring apparatus which will be described hereinafter. Of course, shielded cables can be used to transmit the signals also. It is a matter of convenience as to how the data is collected. Thus, a telemetry transmitter may be utilized, a signal amplifier and cabling system may be used, or any other arrangement whereby the signals from the several load sensors are conducted to the safety equipment of the present invention.
The numeral 25 indicates a summing comparator for the signals on two of the legs. In FIG. 2, the converter 25 sums the signals from the legs A and B. It should be kept in mind that the legs A and B form a common side of the four-sided, four-legged structure. If the loading in the legs A and B decreases sufficiently, this indicates that a moment tending to overturn the crane toward that side is created. While viewing FIG. I, assume that the leg 12 and the leg immediately behind it but not visible in FIG. 1 are the legs A and B connected with the summing circuit 25 shown in FIG. 2. Assume further that the weight is too heavy for the crane and that there is a tendency to overturn. The tendency to overturn creates a decreased stress in the legs A and B. As the stress decreases, it approaches a critical level. The critical level will be that level just immediately before the crane is overturned. The apparatus of the present invention is preferably installed and calibrated in a manner such that the summing comparator responds to a stress just short of the critical stress occurring just at the moment before overturning. Thus, the circuit means sums the signals from the transducers 21 and 22 and the summed signal is then compared with the calibrated standard. Should the summed signal reach calibrated standard, such as 60 percent of the stress just before tipping, then the crane is overloaded and the summing comparator will form an output for an OR gate 26 for purposes to be described.
The numeral 27 indicates a similar summing circuit but one which is connected to different load sensors. The numerals 28 and 29 further indicate summing circuits also. In the version described, which is cooperative with a four-legged crane, there are four sides. A summing comparator is provided for each side, and it receives input signals from the load sensors associated with the legs at each end of the particular side. Thus, four summing comparators are incorporated in the present invention.
With a summing comparator associated with each side of the crane, the several output signals from the comparators are then input to the OR gate 26. It will be understood that the signals from the summing comparators are binary signals. That is, the summed input signals to each of the several comparators is either less than or greater than the alarm level set for that particular comparator. As mentioned before, the decrease in the stress in the legs on a given side at the instant of overturning will determine an absolute ceiling and an appropriate margin of safety might set the alarm level at an arbitrary amount in excess of the load on tip over. If the sum of the signals on a particular side is greater than the set level, the output of the summing comparator is zero. However, when any one of the summing comparators falls below its limit, it forms a signal which is input to the OR gate 26. The OR gate responds to any input signal to turn on a relay driver 30. The relay driver 30 actuates a warning device which can be a bell, light, blinking signal, or so on, for the protection of the crane operator. This permits the crane operator to take whatever action is necessary, such as raising the boom to lower the tipping moment, or setting the load down on the platform rather quickly.
Attention is next directed to a four-input summing circuit 32. The summing circuit 32 is provided with the signals associated with all four of the legs of the equipment. When the crane is unloaded, a minimum stress is created in each of the several legs. The stress above this minimum results from the loading of the crane. The signals corresponding to the incremental stress are thus summed by the circuit 32. Summing circuits for analog signals are believed well known in the art. The exact details of the summing circuits are thus left to one skilled in the art, and may, in fact, be varied in accordance with the special needs of different installation. in any case, the signals are summed and are used to form a hook load signal on a display 33 for that purpose. The hook load is correctly displayed inasmuch as the weight of the load finds response in each of the four legs. That is to say, the load may be unevenly distributed in each of the four legs, but the total is still displayed accurately.
The apparatus of the present invention is preferably calibrated periodically. As will be understood, cranes vary measurably in size, shape, structure, and other details of construction. Because of this, it is preferable to install the present invention and calibrate each system individually, first with no load, and then with two or three different known loads.
The foregoing has been directed to the preferred embodiment of the present invention. Numerous varia' tions and alterations may be adapted without departing from the present invention. As mentioned above, it matters not whether the signals from the load sensors are sent by transmitter, or through shielded cables to the summing equipment.
The terminology and vocabulary adapted herein is extended to the claims which are appended hereto, which determine the scope of the present invention.
What is claimed is:
1. Protective apparatus for a crane having a plurality of legs and which can potentially be overturned about a side defined by a pair of adjacent legs, comprising load sensor means attached to each of said legs of the crane;
load summing means for summing the load about each side of the crane, said load summing means including connections to the load sensor means in each pair of legs defining a side of the crane; and,
a warning device actuated by said summing means when the load for one of said sides decreases below a predetermined limit.
2. The invention of claim 1 including a summing means for summing the signals from all of said load sensors and for forming an output which is proportional to the hook load on said crane.
3. The invention of claim 1 wherein said crane includes at least three legs, and said three legs define at least two sides thereof, there being a summing comparator connected with the load sensor means defining one of said sides and an additional summing comparator connected with the load sensor means defining the other of said sides, said first and second summing comparators being communicated with an OR gate means for providing a driving signal to said warning device.
4. The invention of claim 1 for use with a crane having four legs arranged in a rectangle and including a load sensor means on each leg, each load sensor means supplying an input signal to two loadsumming means, each of said load summing means forming an indication to said warning device when the signals representative of load fall below a predetermined level.
5. The invention of claim 1 wherein said load summing means forms a binary output, one level indicative of load for the side associated with said summing means above a level considered safe, and the other binary signal indicative of load below a level considered safe and for which said warning device sounds an alarm.
device is rendered operative by a signal from an OR gate means, and said OR gate means receives as inputs thereto the output signals of load summing means for each of the sides of the crane.