Crane load indicating arrangement

• US 3,913,690 A
• Filed: 05/09/1974
• Issued: 10/21/1975
• Est. Priority Date: 05/16/1973
• Status: Expired due to Term

• Current Assignee: Bernard David Francis Hutchings, Robert William Hubbard
• Original Assignee: Bernard David Francis Hutchings, Robert William Hubbard
• Inventors: Hutchings, Bernard David Francis, Hubbard, Robert William
• Primary Examiner(s): Miller, Jr., George H.
• Application Number:
  US05/468,249
• Time in Patent Office: 530 Days
• Field of Search: 177/45,145,147,151,1,25,136 214/2
• US Class Current: 177/25.12
• CPC Class Codes: B66C 13/50 Applications of limit circuits or of limit-switch arrangements for winding mechanisms B66D1/56
• CPC Class Codes: B66C 23/905 electrical

Abstract

A crane load indicating arrangement for a crane having a luffing boom and which provides a load indication in terms of total effective load, the load indication being with respect to both radius related duties and angle related duties. The arrangement provides a load indication with and without a fly jib attached to the end of the boom and also includes means for compensating for boom deflection.

Claims

1. A load indicating arrangement for a crane having a pivoted boom comprising, means for producing a first output signal representative of the total turning moment of the boom about its pivot in supporting a load, means for producing a second output signal representative of the horizontal distance between the boom pivot point and the load, means for producing a third output signal which is the quotient obtained by dividing said first output signal by said second output signal, said third output signal being thus representative of total effective load, a law generator unit for each mode of operation of the crane, each unit being adapted to produce a fourth output signal representative of the maximum safe load for the crane in the instant mode of operation, and means for comparing said fourth output signal with said third output signal to provide an indication of the actual crane load relative to the maximum safe load.

2. An arrangement as claimed in claim 1, wherein said indication of the actual crane load relative to the maximum safe load is given by a meter calibrated in percentage of safe working load, said meter being coupled to the output of an operational amplifier having said third output signal and said fourth output signal applied jointly to an input terminal thereof and which has its gain divided by said fourth output.

3. An arrangement as claimed in claim 1, wherein said indication of the actual crane load relative to the maximum safe load is given by a meter having a zero which is offset mechanically to a calibration point from which it is driven on the one hand into an overload region of its scale when said third output signal is greater than said fourth output signal and on the other hand into a safe region indicating available lifting capacity when said third output signal is less than said fourth output signal.

4. An arrangement as claimed in claim 1 further comprising, means for producing a fifth output signal which is determined by the boom deflection, and means for modifying the value of said second output signal by summing therewith said fifth output signal.

5. An arrangement as claimed in claim 1 wherein said first output signal producing means comprises, transducer means for producing an output signal which is a function of the reaction sustained by the boom supporting means in supporting the boom and any load suspended therefrom, and angle sensing means for modifying said output signal in accordance with the sine of the angle included between the boom supporting means and the boom thereby to produce said first output signal.

6. An arrangement as claimed in claim 1 wherein said means for producing a second output signal includes means for producing a sixth output signal which is representative of the length of the boom, means for producing a seventh output signal which is representative of the cosine of the boom luff angle, and means for multiplying said sixth and seventh output signals to derive the second output signal as the product thereof.

7. An arrangement as claimed in claim 6, including means for producing an eighth output signal for modifying the value of said sixth output signal by an amount which is representative of the change in load radius error that occurs between maximum and minimum boom extensions when an offset fly jib is fitted, together with means for changing said amount as a function of boom luff angle, and means for selecting the value of said sixth output signal having regard to the effective boom length due to the offset fly jib.

8. An arrangement as claimed in claim 1 wherein the crane is adapted to provide at least two modes of operation and for modes of operation involving radius-related duties each law genErator unit concerned is responsive to said second output signal, whereas for modes of operation involving anglerelated duties each law generator unit concerned is responsive to an output signal which is representative of the boom luff angle.

9. An arrangement as claimed in claim 8, including switch means for selectively connecting said second output signal or said boom luff angle output signal to a law generator unit.

10. An arrangement as claimed in claim 1 further comprising, means for producing a fifth output signal which is representative of the position of the centre of gravity of the boom structure and varies with a change in boom length, and means for combining said fifth output signal with said third output signal to produce a corrected third output signal.

11. An arrangement as claimed in claim 10 further comprising, means for producing a sixth output signal which is representative of the weight of the boom structure, means jointly responsive to said fourth and sixth output signals to produce a seventh output signal, and means for comparing a given percentage of said seventh output signal with the output obtained from the comparison of said third and fourth output signals to provide an indication on the actual hook load relative to a percentage of the maximum safe hook load.

12. An arrangement as claimed in claim 11, including means for combining said third, fifth and sixth output signals to provide a eighth output signal which is representative of actual hook load.

13. A load indicator apparatus for a crane having a pivotally mounted extensible boom comprising, means for producing a first signal representing the total turning moment of the boom and its load about its pivot, means for producing a second signal representing the horizontal distance of the load from the boom pivot point, means for combining said first and second signals for producing a third signal representing the total effective boom load, means for deriving a fourth signal representing the maximum safe load for the crane for the prevailing crane operating conditions, and means for comparing said third and fourth signals to derive an output signal indicative of the available lifting capacity of the crane.

14. A load indicator apparatus as claimed in claim 13 wherein said crane is adapted to provide at least two modes of operation, one of which is determined primarily by the load radius and the other by the boom luff angle, means for producing a signal representing the boom luff angle, said fourth signal deriving means including law generator means having input means selectively connected to receive said second signal or said luff angle signal in said one or the other modes of operation, respectively.

15. A load indicator apparatus as claimed in claim 13 further comprising means for producing a fifth signal representing the position of the boom center of gravity, and means for combining said third and fifth signals to correct the third signal as a function of the change in the boom center of gravity with a variation in the length of the extensible boom.

16. A load indicator apparatus as claimed in claim 13 further comprising means for modifying the second signal for fly jib operation of the crane comprising, means for producing a fifth signal representing the boom length, means for producing a sixth signal representing the boom luff angle, means responsive to said sixth signal to provide a correction thereto, means for producing a seventh signal representing the cosine of the boom luff angle, and means for combining said fifth signal, the corrected sixth signal and the seventh signal to derive the modified second signal.

17. A load indicator apparatus as claimed in claim 13 further comprising, means for producing a fifth signal representing the deflection of the boom under load, and means for modifying the second signal by combining therewith said fifth signal, said third signal being derived by combining the first signal with the modified second signal.

18. A load indicAtor apparatus as claimed in claim 13 further comprising boom support means, and wherein said first signal producing means comprises, means for producing a fifth signal which is a function of the reaction force sustained by the boom support means, means for producing a sixth signal representing the sine of the angle formed by the boom and the boom support means and means for combining said fifth and sixth signals to derive said first signal, and wherein the means for producing the second output signal comprises, means for producing a seventh signal representing boom length, means for producing an eighth signal representing the cosine of the boom luff angle, and means for combining said seventh and eighth signals to derive said second signal.