CRANE SAFE LOAD INDICATOR

• US 3,870,160 A
• Filed: 06/22/1972
• Issued: 03/11/1975
• Est. Priority Date: 06/25/1971
• Status: Expired due to Term

• Current Assignee: Bernard David Francis Hutchings
• Original Assignee: Bernard David Francis Hutchings
• Inventors: Hutchings, Bernard David Francis
• Primary Examiner(s): Blunk, Evon C.
• Assistant Examiner(s): Nase, Jeffrey V.
• Application Number:
  US05/265,329
• Time in Patent Office: 992 Days
• Field of Search: 212/39 340/267C 338/89 235/151.33
• US Class Current: 212/278
• CPC Class Codes: B66C 23/905 electrical
• CPC Class Codes: B66C 2700/084 Protection measures
• CPC Class Codes: G06G 7/28 for synthesising functions by piecewise approximation

Abstract

A crane safe load indicator for determining the safe load supported by a pivoted boom which can be luffed. The indicator functions by comparing a signal representative of the total turning moment of the boom about its pivot in terms of the angle included between the boom and a hydraulic ram which is supporting it, with a reference signal which is representative of the maximum safe turning moment of the boom about its pivot for the boom luff angle and load radius currently obtaining. A modification of the indicator provides a safe load indication when a fly jib is mounted at the end of the boom. In this modification account is taken of the change in centre of gravity of the boom fly jib and load due to change in boom extension.

Claims

1. A safe load indicator system for use with a crane or other lifting apparatus having a pivotally mounted boom and extensible boom supporting means comprising, means for producing a first signal representative of the actual total turning moment of the boom about its pivot by determining the angle included between the extensible boom supporting means and the boom and the reaction sustained by the extensible boom supporting means in supporting the boom and a load suspended therefrom, means for deriving a second signal determined by the boom luff angle and the length of the boom and which is indicative of the current load radius, means responsive to said second signal for producing a reference signal representative of the maximum safe turning moment of the boom about its pivot and corresponding to the current load radius, and means responsive to the first and the reference signals for providing an indication of the available lifting capacity.

2. A safe load indicator system for use with a crane or lifting apparatus having a pivotally mounted extensible boom and extensible boom supporting means comprising, transducer means for producing a first signal which is a function of the reaction by the extensible boom supporting means in supporting the boom and any load suspended therefrom, angle sensing means for modifying said first signal in accordance with the sine of the angle included between the extensible boom supporting means and the boom to produce a first resultant signal which is representative of the actual total turning moment of the boom about its pivot boom angle sensing means for producing a second signal which is proportional to the cosine of the boom luff angle, boom length sensing means for modifying said second signal in accordance with the boom length to produce a second resultant signal which is representative of load radius, load/radius law generator means adapted for operation in accordance with the load/radius rating of the crane and responsive to said second resultant signal to produce a reference signal which is representative of the turning moment of the boom about its pivot for lifting a maximum safe load at the load radius represented by said second resultant signal, and means responsive to said first resultant signal and said reference signal to produce an output in accordance with any difference therebetween and thus between actual total turning moment and maximum safe turning moment.

3. A safe load indicator system for use with a crane or other lifting apparatus having a pivotally supported boom, a fly jib and extensible boom supporting means comprising, means for producing a signal representative of the actual reaction sustained by the extensible Boom supporting means in supporting the boom, fly jib and any load suspended therefrom at the current boom luff angle, means for producing a reference signal representative of the computed boom supporting means reaction which would be required to sustain the extensible boom supporting means at the boom luff angle currently obtaining with the maximum safe load suspended from the fly jib for said luff angle, and means responsive to said signals for providing an indication of the available lifting capacity.

4. A safe load indicator system as claimed in claim 3, wherein the boom is telescopic to vary its length, and further comprising means for modifying said reference signal in accordance with the boom extension.

5. A safe load indicator system as claimed in claim 4, further comprising means for further modifying said reference signal as a function of the shift of the combined centre of gravity of the boom fly jib and load due to a change in the boom angle.

6. A safe load indicator for use with a crane having a pivotally supported extensible boom, a fly jib and extensible boom supporting means comprising, transducer means for producing a first signal which is a function of the actual reaction force sustained by the extensible boom supporting means in supporting the boom, fly jib and any load suspended therefrom, boom angle sensing means for producing a second signal which is proportional to the boom luff angle, first load/angle law generator means adapted for operation in accordance with the fly load/boom angle rating of the crane and responsive to said second signal to produce a first reference signal which is representative of the extensible boom supporting means reaction which would be required to sustain the boom at maximum extension with the maximum safe fly jib load at the boom luff angle represented by said second signal, boom length sensing means for modifying said first reference signal in accordance with the boom length, second load/angle law generator means also adapted for operation in accordance with the fly load/boom angle rating of the crane and responsive to said second signal to produce a second reference signal which is representative of a change in the centre of gravity of the boom, fly jib and load for a change in boom angle, means for producing a resultant reference signal in response to the modified first reference signal and the second reference signal, and means responsive to said first signal and said resultant reference signal to produce an output in accordance with any difference therebetween and thus between the actual reaction of the extensible boom supporting means due to a fly jib load and the maximum safe computed reaction due to said fly jib load.

7. A safe load control system for a crane having an extensible boom pivotally mounted on a support structure and extensible boom supporting means for adjusting the boom luff angle comprising, means for producing a first signal which is proportional to the reaction of the extensible boom supporting means, means for modifying said first signal as a function of the sine of the angle formed between the boom and the extensible boom supporting means to produce a first resultant signal, means for producing a second signal which is a function of the cosine of the boom luff angle, means for modifying said second signal as a function of the boom length to produce a second resultant signal indicative of the actual load radius, means responsive to said second resultant signal for computing a reference signal representative of the maximum safe turning moment of the boom about its pivot and corresponding to the load radius indicated by said second resultant signal, and means responsive to said first resultant signal and said reference signal for indicating the available lifting capacity of the crane at the current load condition.

8. A control system as claimed in claim 7 wherein said first signal modifying means comprises a potentiometer having a sine law resistance variation and a slider adapted to bE coupled to the extensible boom supporting means to move proportional to the extension of said extensible boom supporting means.

9. A control system as claimed in claim 8 wherein said second signal producing means comprises a second potentiometer having a cosine law resistance variation and a slider adapted to be coupled for movement with the boom and proportional to the boom luff angle and said second signal modifying means comprises a third potentiometer having a linear resistance variation and a slider adapted to be coupled to the boom for movement proportional to the boom extension.