GB1295341A - - Google Patents

Abstract

1295341 Measuring boom bending moments electrically WARNER & SWASEY CO 4 Feb 1970 [14 Feb 1969] 5266/70 Heading G1N [Also in Division B8] Apparatus for determining the total bending moment acting on a self-supporting telescopic boom 15 of a crane includes a strain gauge Tγ attached to the boom at a point immediately adjacent the pivot 22, which connects the boomlift piston and cylinder unit 23 to the boom so that the strain it senses is substantially linearly proportional, for all boom lengths and elevation angles, to the total bending moment due to the weights of the load W z and the boom sections W 1 -W 5 . Signals representing the bending moments for each of the boom sections separately, due only to boom weight, are produced in a com- puting circuit Fig. 5 (not shown) in which potentiometers (R 11 -R 51 ) are varied according to the lengths (l 1 -l 5 ) of the respective sections (16-20) of the boom, whilst the wiper (28) of a potentiometer (26) is connected with the boom to vary the input voltage to the circuit as the cosine of the boom elevation angle, #. The signals are fed to a further circuit Fig. 6 (not shown) and combined with signals representing the bending moments for each section, due to the load weight only, to produce total bending moment signals for each section. These are fed to comparators (S 1 -S 5 ) respectively and compared with reference values (E 26 -E 56 ) respectively to actuate an alarm lamp (Q 1 -Q 5 ) when the bending moment exceeds 85% of the allowable limit and a further alarm lamp (P 1 -P 5 ) when it exceeds 100% at which point an audible alarm (X) is actuated. The circuit is coupled with a potentiometer (36) of which the setting represents the sine of the boom slewing angle so that where the tipping moment is more critical than the total bending moment, the comparator (S 1 ) is responsive to slewing angle as a reference value in place of the maximum allowance bending moment from the potentiometer (35). In a further embodiment, Fig. 7 (not shown) for use where not all the boom sections are extensible, the length-proportional potentiometers are replaced by fixed resistors. Fig. 9 (not shown) illustrates a simplified circuit for use with a strain transducer which yields a constant output signal for all boom lengths and boom angles when the rated load for the given length and angle is applied to the boom. Actual load weight W z is indicated on a device (49) whilst a galvo (54) indicates what percentage of rated boom capacity is being utilized. Fig. 10 shows the strain transducer in a housing bolt 67 clamped under a compressional preload between blocks 63, 64 spaced apart along the base section 16 of the boom.