US3913081A

US3913081A - Crane load warning system

Info

Publication number: US3913081A
Application number: US408832A
Authority: US
Inventors: Martin W Hamilton
Original assignee: Eaton Corp
Current assignee: Eaton Corp
Priority date: 1973-10-23
Filing date: 1973-10-23
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14
Also published as: JPS5078049A; FR2248226B1; CA1015702A; FR2248226A1; IT1022663B; GB1476525A; DE2450135A1; AU7425574A

Abstract

A warning system for a crane which has means for measuring the load being hoisted by the crane and comparing it with a maximum preset load so as to give a warning if the maximum is exceeded as well as having a high-low alarm switch circuit which generates a percentage of the load being hoisted such that when the load is being lowered a warning is indicated if the load on the hoist falls to the preset percentage of the actual load. This condition indicates that the load is supported by an obstacle which is a dangerous condition.

Description

United States Patent [191 Hamilton Oct. 14, 1975 CRANE LOAD WARNING SYSTEM [75] Inventor: Martin W. Hamilton, Arlington Prmwry Exammer Dlavld 1 Trafton Attorney, Agent, or Fzrml-ltll, Gross, Simpson, Van Heights, 1]].

Santen, Steadman, Chiara & Stmpson [73] Assignee: Eaton Corporation, Carol Stream,

57 ABSTRACT [22] Filed: 1973 A warning system for a crane which has means for [21] Appl. No.: 408,832 measuring the load being hoisted by the crane and comparing it with a maximum preset load so as to give a warning if the maximum is exceeded as well as hav- [52] [1.5. Cl.2 340/267 C; 340/272 ing a g alarm switch Circuit which generates a [51] III. Cl. G08B 21/00 percentage f the load b g hoisted Such that when [58] Fleld 0f Search 340/267 C, 272 the load is being lowered a warning is indicated if the load on the hoist falls to the preset percentage of the [56] References C'ted actual load. This condition indicates that the load is UNITED TAT ATE supported by an obstacle which is a dangerous condi- 3,63l,537 12/1971 Zibolski et al. 340/267 C tion- 3,7l0,368 l/1973 Hamilton 340/267 C 3,740,741 6/1973 Jones 340/267 0 8 Clam, 3 Drawmg figures w: CELL /5 ea k4 MAM/ M g AUX /9 2 2;, ozmmmr M /6 ZERO 4 R5 2/ 2.??? can/W04 22 a Q if! ,t 525 9 V4 .sw/m/ 37 7 /2 3 Lt/ 1 /tta a2 33 0 F; 521? i as A US. Patent Oct. 14,1975 Sheet 10f2 3,913,081

US. Patent Oct. 14, 1975 Sheet 2 Of2 3,913,081

CRANE LOAD WARNING SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates in general to improved crane load warning systems which monitor a plurality of hoisting lines so as to produce a warning if the maximum allowable load is exceeded and also which provides for a warning if the load is supported by an obstacle.

2. Description of the Prior Art Warning systems have been provided which produced an alarm as the load on the hook of the crane exceeded allowable limits. However, such systems generally utilized a single hoisting system and were designed to measure substantially static tension in the hoisting cables and were not capable of detecting a dangerous condition, as for example, when the load on the crane is being temporarily supported by an obstacle which when removed will allow the load to drop and thus exert extreme dynamic loads on the cables.

SUMMARY OF THE INVENTION The present invention relates to a crane load warning system which monitors the load in a plurality of hoisting systems on the crane and produces a warning when the loads are exceeded. In addition, means are provided for indicating when the load is being temporarily supported by an obstacle which is a second dangerous condition in that if the load drops from the obstacle tremendous stress and strain will be applied to the crane and to the ropes. The present invention allows the invention to be set for high load and as the load is lifted an alarm system is energized if the load is greater than the safe load. As the load is lowered, the invention provides for setting to a low alarm position which will actuate an alarm in the event the load catches on an obstacle and when the load is brought to rest on its desired position.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from thespirit and scope of the novel concepts of the disclosure, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a crane having two separate hoisting systems.

FIG. 2 is a simplified block diagram of the invention, and

FIG. 3 is a detail schematic view of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The tipping moment of a crane is based on the load on the hook and the operating radius of the load or its distance from the center of the rotation of the machine. The load rating of the wire rope being used is also another basic limiting factor. Depending on the load to be hoisted, the wire rope must be reeved with enough parts of line to divide the load evenly among individual parts so that no one rope part carries more than its rated load. The mechanical and safety factors gained by using multiple parts of line is offset by the slower speed in hoisting and to provide the desired speed in hoisting on light loads as well as multiple lines for heavier loads, many machines utilize two separate hoisting systems which are identified as a main block having multiple pulleys and rope parts to obtain a mechanical advantage and a whip line with one or two parts of line. Line breakage or tipping of the machine can occur when either of these hoisting systems are under load which exceeds the allowable limit. Another dangerous condition that exists, which can tip the machine or break the lines, is the sudden application of a load that normally would be within the rating of the machine. This condition could occur, for example, if a load is being lowered and engages an obstacle while the crane continues to unwind cable. When the load falls off of the obstacle, it will drop some distance thereby producing very large and generally dangerous dynamic conditions on the machine and the cable. The present invention relates to a crane load warning system which monitors, displays and gives a warning when an overload on the crane occurs, as well as, provides and gives a warning when the load is hung up by an obstacle as the load is being lowered.

In a specific example, a machine utilizing the present invention might be lifting a 100,000 pound load from a dock after which it is swung around and lowered into the hold of a ship. Before being lifted, the control switch of the present invention is set for the high position and a hundred thousand pounds is dialed into the alarm switch. When the load clears the ground, the alarm will activate indicating that the load is on the crane and the control switch will then be turned to its low position turning off the alarm. The machine then swings and lowers the load into the hold of the ship. Assume that the load catches on the side of the hold or touches bottom and the weight on the hook decreases to 80,000 pounds or less. This will actuate the lower alarm thus warning the crane operator so that he does not allow the cable to continue to unwind before the load has swung free of the obstacle'thus preventing the load from dropping with slack line and so as to overload the line. Also, when the load touches the bottom position where it is to be unloaded, the alarm will activate thus indicating that it has arrived at the bottom position and the crane can be unloaded and the control switch returned to the high position to turn off the alarm, and the system is, thus, ready for the next lift.

FIG. 1 illustrates a crane 41 which has a cab 42 and a boom 40. A first hoisting system is illustrated lifting a beam 46 and includes a hook 43 and a multiple cable system with a load cell 10 mounted in one of the cables to measure its tension. A second auxiliary rapid lifting system is provided by hook 48 supported on a single line extending from the extension 50 of the boom and a load cell 11 measures the tension in the cable connected to the hook 48.

FIG. 2 is a block diagram of the invention and illustrates the two load cells 10 and 11 which receive inputs from an oscillator 17 which might provide a 2,500 hertz signal which excites the load cells so that they provide outputs and supply them to a switching junction box 13. Selector switch 12 in the switching junction box is movable to engage the output of load cell 10 through a variable resistor R1 or alternatively is movable to engage the output of load cell 11 through a variable resistor R2. The particular output from either load cell 10 or 11 would be selected based upon which of the hoisting systems of FIG. 1 is being utilized. The output from the switching junction box 13 is applied to the input of an operational amplifier 14 which also receives an input from a zero control 16 and which in turn receives an input from the oscillator 17. Resistors R4 and R3 are connected between the output of the operational am plifier l4 and its input and at least one of the resistors is variable. A demodulator 18 receives an input from the oscillator 17 and an input from the operational amplifier 14 and supplies an output through a variable resistor R to an indicator 19 which has indicator needle 21. Thus, the needle 21 of the indicator 19 continuously displays the single line load directly and continuously.

The output of the demodulator is also supplied to a first differential amplifier 22 which also receives a second input from a wiper contact 51 that engages a resistor R6 connected between ground and a positive DC voltage. A gate 32 is connected to the output of differential amplifier 22 and supplies an input to switch 33 which controls an indicator light 34 and an audio alarm 36. The wiper contact 51 is used to set a maximum load limit; and if the output of the demodulator l8 supplied to the differential amplifier 22 equals or exceeds said preset load as established by the position of the wiper contact 51, the input to the gate 32 will go to zero, thus producing an output from the gate which will energize the switch 33 and the

alarms

34 and 36.

The output of the demodulator 18 also is supplied to a high/low alarm switch 23 through input 29. In a first position of the switch, the output of the demodulator 18 is supplied to the negative input through lead 27 of the differential amplifier 31. In this position of the high/low alarm switch, a second input is supplied through lead 28 to the plus input of the differential amplifier 31 which is derived from a digital alarm switch 37 which receives a DC voltage through a calibrating resistor R7 and has digital load setting wheels 38 and provides an output to input 24 of the high/low alarm switch 23. A voltage divider is connected between lead 24 and ground and comprises resistors R8 and R9 so that a fixed or variable percentage of the maximum allowable load limit can be applied on lead 26 to the high/low alarm switch. For example, the input supplied to lead 26 might be 80% of that applied at input 24. In operation let it be assumed that a load is being lifted and the high/low alarm switch is set so that the output of the demodulator 18 is applied to the input 27 of the differential amplifier 31 and the output of the digital alarm switch 37 is applied through lead 24 to the positive input of differential amplifier 31. Under this condition, if the load on the load cell equals or exceeds the preset load as determined by the setting of the wheels 38, differential amplifier 31 will have an output that goes to zero and thus the gate 32 will be energized closing switch 33 to energize the

alarms

34 and 36. This position of the high/low alarm switch 23 would be utilized as a load is being lifted. When the load is being lowered the high/low alarm switch would be moved to the low position thus connecting the output of the demodulator 18 to the input 28 of the differential amplifier 31 and the input 27 of the differential amplifier would be connected to lead 26 which is the junction point between resistors R8 and R9. In this position of the switch, if the load signal from the demodulator 18 falls to 80% or less of the down reference signal, the gate 32 will be energizedand the alarms will be actuated.

FIG. 3 is a detailed schematic diagram of the invention and common parts illustrated in FIG. 2 are illustrated by the same numerals and references in FIG. ,3.

FIG. 3 illustrates the load cells 10 and 11 and the selector switch 13 with movable contact 12 which supplies an input to the operational amplifier 14. The oscillator 17 supplies inputs on leads 71 and 72 to the load' cells and also supplies an input to a calibration circuit having resistors R31, R32 and R34 connected across leads 71 and 72. A wiper contact 73 makes slide contact with a,

resistor R31 and has its other side connected to acapacitor C1 which is connected to the operational am,-

plifier 14 through a resistor R21. A wiper contact 74.

engages resistor R32 and is connected through a resistor R33, a capacitor C4, and a normally opened switch S1 to the operational amplifier l4. A wiper contact 76 engages resistor R34 and is connected through capaci: tor C5 to the input of the operational amplifier 14. A resistor R22 is connected between ground and an input to the operational amplifier 14. The output of the oscillator is fed through wiper contact 76 and condenserCS and a resistor R16, a wiper contact 77, a resistor R17, resistor R18, and parallel resistors R19 andR20 to the demodulator 19. A lead 78 is connected to lead 72 and to ground through a capacitor C15 and resistor R27. A transistor T2 has its emitter connected to ground and its collector connected to the input of the demodulator 18. A resistor R26 is connected between R27 and the base of transistor T2. The output of the demodulator. I

18 is supplied through resistors R23 and R24 to indicator 19. A capacitor C3 is connected between ground and the meter 19. A first differential amplifier 22 provides an alarm signal when a single line load signal is being monitored and has its negative input connected to one side of resistor R29 which has its other side connected to the output of the demodulator 18 to monitor the single line load cell output. A capacitor C2 is connected between the negative input tothe differential amplifier 22 and ground. The positive input to, the dif-' ferential amplifier 22 is connected to a wipercontact 51 which engages resistor R6 whichhas its other side connected to ground and its other is connected to a its base connected to the output of the gate 32and its emitter connected to a positive voltage source and its emitter connected through a diode D5 to a negative voltage source.

A second differential amplifier 31 measures the hook load and its negative input 27 is connected toa movable switch contact 66 in the high/low alarm switch 23. A capacitor C6 is connected between lead 27 and the positive input lead 28. The positive input lead ISCOII'. nected to switch contact 67 of the high/low alarm switch 23. Lead 29 is connected through the resistor R29 to the output of demodulator 18 andis connected to two switch contacts, one of which is engageable with" movable contact 66, and the other. which is engageable by movable contact 67. In the first position, the wiper contact 66 supplies the output of the demodulator l8 1 to the negative input of differential amplifier 31; and in the second position of movable contacts 66 and 67, the output of the demodulator 18 is supplied to the positive input 28 of the differential amplifier 31. Resistors R8 and R9 are connected between one contact of the high/low switch 23 and ground and a second contact of the switch is connected from resistor R9 to engage movable contact 66. The alarm digit switch 37 has an input connected to a resistor R28 which has its other side grounded and is connected through a variable resistor R7 to a positive voltage source. A condenser C7 is connected between a portion of R7 and ground. An operational amplifier 82 is connected to the output of the alarm digit switch 37 and supplies an input through lead 81 to the contact of switch 23 which is connected to the resistor R8. A second input to operational amplifier 82 is supplied by lead 83 which is connected to a movable contact 84 which is engageable with stepped contacts across which resistors 87a-k are connected. One end of resistor 87a is connected to a resistor R50 which has its other side connected to ground One end of resistor 87k is connected to lead 81.

The oscillator 17 comprises a transistor T1 which receives a positive bias voltage on its emitter and supplies an output to operational amplifier 61. The operational amplifier 61 is connected to a wiper contact 88 which engages a resistor R13 which is connected to a resistor R12 that feeds between a pair of oppositely poled diodes DI and D2 connected across an inductor Ll. A capacitor C11 is connected across the inductor L1 and a matrix 63 is connected between the inductor L1 and resistor R11 which has its other side connected to the emitter of transistor T1. Resistors R14 and R15 are connected in series to the resistor R13 and a capacitor C10 is connected between wiper contact 88 and resistor R15. Diode D3 is connected in parallel with resistor R15.

In a practical embodiment constructed and utilized, the following component values were used: R11, ohms; R12, 2,550 ohms; R13, 2K ohms; R14, 2,610 ohms; R15, 470 ohms; R16, 51.1K ohms; R17, 100K ohms; R18, 51 ohms; R19, 4.75K ohms; R20, 4.75K ohms; R21, 1.5M ohms; R22, 10K ohms; R23, 562 ohms; R24, 500 ohms; R29, 1.5K ohms; R26, 10K ohms; R27, 1.5K ohms; R31, 5K ohms; R32, 10K ohms; R33, 51.1K ohms; R34, 10K ohms; and 87a-k, 200 ohms each.

Capacitors had the following values: C1, 2.2 mfd; C3, 2.2 mfd; C4, 2.2 mfd; C5, 100 pf; C7, 2.2 mfd; C9, 2.2 mfd; C10, 15 mfd; C12, 2.2 mfd; and C15, 2.2 mfd.

In operation, the movable contacts 66 and 67, respectively engage lead 29 and lead 81. The alarm digit switch 37 and the contact 84 will be adjusted to the maximum load on the hook of the crane and the inputs to the differential amplifier from lead 81 to the positive input 28 and from lead 29 to the negative input 27 would be compared and if the output of the demodulator 18 which is proportional to the output of the load cell approaches or becomes equal or greater to the signal supplied to input 28 the output of the differential amplifier will go to zero thus keying the gate 32 to actuate the

alarms

34 and 36 through the switch 33. This position of the switch 23 is used as a load is being hoisted for setting. When the load clears the ground, switch 23 is moved to the low position, wherein contact 66 engages the contact connected to the junction point between the resistors R8 and R9 and the movable contact 67 engages the contact connected to lead 29. This reverses the input to the differential amplifier such that the output of the demodulator 18 is now supplied to the positive input of the differential amplifier. The resistors R8 and R9 are voltage dividers which might, for example, be a 20% voltage divider such that if the load signal equals or falls below 20% down reference signal the output of the differential amplifier will go to zero and key the gate32thus actuating the alarms 34 and-36 through the transistor T3.

It is seen that the present invention provides means for monitoring a plurality of load cells and also prevents overload of a crane due to the load being accidentally supported on an obstacle and allowing slack in the supporting cable and dropping which would overload the crane. Such conditions are indicated to the operator who can immediately take corrective action, thus, preventing overload of the crane.

When the switch 23 is in the position illustarted in FIG. 3, the signal on lead 81 will be adjusted by the.

manual switches so that it equals the actual load signal on lead 29. Then switch 23 is moved to connect lead 26 with the negative input 27 of amplifier 31 which gives a signal of that on lead 81. Simultaneously, the signal on lead 29 is supplied to the positive input 28 of amplifier 31 and if the load on the crane drops to 80% of its initial value the alarm will be energized.

Although this invention has been described with respect to preferred embodiments, it is not to be so limited as changes and modifications may be made which are within the full intended scope as defined by the appended claims.

I claim as my invention:

1. A load monitoring and warning device comprising, a load cellconnected in circuit to produce an output signal proportional to the actual load on a crane, a differential amplifier with first and second input terminals and having an output terminal, a reference signal generator settable to obtainan output signal equal to the static output signal from said load cell, a voltage divider connected to said reference signal to produce a signal which is a percentage of said static output signal from said load cell, switch means having a first position for connecting said output signal from said load cell to the first input terminal of said differential amplifier and said output signal from said reference signal generator to said second input terminal of said differential amplifier so that said output can be set to be equal to said output signal from said load cell, and said switch means movable to a second position to connect said output signal from said load cell to said second input terminal of said differential amplifier and to connect said voltage divider to said first input terminal of said differential amplifier.

2. A load monitoring and warning device for a crane according to claim 1 including an alarm means connected to the output of said differential amplifier to indicate in the first position of said switch means when the output signal of said reference signal generator equals the static output signal from said load cell and to indicate in the second position of said switch means when the actual load on said load cell has dropped to or below said percentage of said static output signal.

3. A load monitoring and warning device for a crane according to claim 2 including a manual control for said reference signal generator for setting its output signal.

according to claim 5, wherein saidalarm means is connected to said output of saidsecond differential amplifier to indicate when the actual load signal equals or exceedsithe maximum load signalu 7. A load monitoring and warning device for a crane according to claim 6, wherein said alarm means includes an audible alarm.

8. A load monitoring and warning device for a crane according to claim 6, wherein said alarm means ill-,

cludes a visible alarm.

Claims

1. A load monitoring and warning device comprising, a load cell connected in circuit to produce an output signal proportional to the actual load on a crane, a differential amplifier with first and second input terminals and having an output terminal, a reference signal generator settable to obtain an output signal equal to the static output signal from said load cell, a voltage divider connected to said reference signal to produce a signal which is a percentage of said static output signal from said load cell, switch means having a first position for connecting said output signal from said load cell to the first input terminal of said differential amplifier and said output signal from said reference signal generator to said second input terminal of said differential amplifier so that said output can be set to be equal to said output signal from said load cell, and said switch means movable to a second position to connect said output signal from said load cell to said second input terminal of said differential amplifier and to connect said voltage divider to said first input terminal of said differential amplifier.

4. A load monitoring and warning device according to claim 3 including a load indicator connected to the load cell.

5. A load monitoring and warning device according to claim 4 including a second differential amplifier with first and second input terminals and an output terminal, said output signal from said load cell connected to said first terminal of said second differential amplifier, and a maximum load signal generator connected to the second input terminal of said second differential amplifier.

6. A load monitoring and warning device for a crane according to claim 5, wherein said alarm means is connected to said output of said second differential amplifier to indicate when the actual load signal equals or exceeds the maximum load signal.

7. A load monitoring and warning device for a crane according to claim 6, wherein said alarm means includes an audible alarm.

8. A load monitoring and warning device for a crane according to claim 6, wherein said alarm means includes a visible alarm.