# Patent

## Title
Equipment handling system

## Abstract

Apparatus and method for second stage calibration of this equipment are as described herein with reference to FIG. 2.

## Background
## Claims

1. A method of calibrating a safe load indicating apparatus for use in a crane of the type having a pivoted telescopically extensible boom and a rating table for each mode of operation of the crane, said apparatus including; means for producing a first signal representative of the turning moment of the boom about its pivot point, means responsive to said first signal for producing a working output signal representative of the actual loading on the crane, law generator means having for each mode of crane operation an input/output characteristic which defines a rating curve corresponding to the crane rating table for the appertaining mode of crane operation, said law generator means providing for each mode of operation a reference output signal representative of the maximum safe loading for the crane, and means responsive to said reference and working output signals for providing an indication of available crane lifting capacity, said method comprising the steps of: that mode, but with no load suspended therefrom, calibration signal representative of the calculated turning moment which would be produced by a load equal to the maximum safe load for the specified boom configuration thereby to produce a calibration working output signal, and the appertaining mode until said reference output signal equates to said calibration working output signal and is thus representative of the maximum safe loading of the existing boom configuration.

2. A method according to claim 1 comprising the further steps of setting the boom successively to each of a plurality of the configurations specified in the rating table for the given mode, and adjusting the value of the calibration signal for each setting of the boom so that it is in each case representative of the calculated turning moment which would be produced by a load equal to the maximum safe load for that boom setting.

3. A safe load indicating apparatus for a crane having a pivotally mounted extensible boom comprising, means responsive to the crane boom for producing a first signal corresponding to the turning moment of the boom about its pivot point, law generator means having for each mode of operation of the crane an input/output characteristic defining a rating curve corresponding to the rating table for the appertaining mode of crane operation and an input terminal therefor, means for selectively applying to said input terminal a further signal that represents either the horizontal distance of the load from the boom pivot point or the boom luff angle, said further signal being independent of the crane load, and calibration means for compensating said apparatus for error caused by a discrepancy between the actual and the theoretical position of the boom center of gravity, said calibration means including a source of calibration signal whose output is adjustable to a plurality of voltage levels each corresponding to a turning moment due to the weight of the maximum safe load alone and corresponding to given position settings of the boom, and means for injecting said calibration signal into the apparatus so as to be additive to said first signal, said first signal, during a calibration operation, being produced with the boom in an unloaded condition, and said law generator means includes means for adjusting the input/output characteristic thereof during a calibration operation so as to derive a second signal indicating the maximum safe load for the crane at each given position setting of the boom.

4. Apparatus according to claim 3 further comprising, a unity-gain non-inventing amplifier having an input terminal, means for applying both the calibration signal and the first signal to said input terminal of the unity-gain non-inverting amplifier, and means for combining a signal produced at the output of the unity-gain amplifier with said second signal to provide an indication of available lifting capacity.

5. Apparatus according to claim 3 in which the source of calibration signals comprises a potentiometer connected across a stabilised reference voltage supply.

6. Apparatus according to claim 3, further comprising means for measuring the magnitude of the calibration signal.

7. Apparatus as claimed in claim 3 further comprising means for comparing a signal determined by said first signal and said calibration signal with said second signal to derive an output signal indicative of the available lifting capacity of the crane.

8. A method of calibrating a safe load indicating apparatus for a crane having a pivotally mounted telescoping boom and a rating table for each mode of crane operation, said apparatus including means for producing a first electric signal corresponding to the turning moment of the boom about its pivot point, means responsive to said first signal for producing a working output signal representative of the actual loading on the crane, law generator means having for each mode of operation of the crane an input/output characteristic which defines a rating curve corresponding to the crane rating table for the appertaining mode of crane operation, said law generator means providing for each mode of operation a reference output signal representative of the maximum safe loading for the crane, means responsive to said reference and working output signals for providing an indication of available crane lifting capacity, and means for producing a further signal independent of the crane load and representative of the load radius or boom luff angle, said method comprising the steps of: setting the crane for operation in a given mode, setting the unloaded crane boom to a predetermined position so that said first electric signal producing means derives a first electric signal corresponding to the turning moment of the unloaded boom at said predetermined boom position, producing a calibration signal corresponding to the maximum safe load turning moment for the load alone at said predetermined boom position and combining said calibration signal with said first electric signal, and applying said further signal to said law generator means and adjusting the input/output characteristic of said law generator means to derive a reference signal at said predetermined boom position.

9. The method of claim 8 comprising the further steps of setting the unloaded crane boom successively to a plurality of further predetermined positions permitted by the rating table for a given operation mode, adjusting the calibration signal for each boom setting so as to correspond to the maximum safe load turning moment for each of said boom settings, and for each of said further positions repeating said steps of combining the calibration and first electric signals, applying said further signal to said law generator means and adjusting the law generator input/output characteristic to derive said reference signal.