Moment monitoring system for hydraulic-piston type cranes

Claim 1

In a crane burden manipulation apparatus comprising a weighty base member normally stably supported upon a suitable underlying substrate whereby at apparatus stable conditions the base member extends vertically along an upright-axis, said crane further comprising an elongate boom type burden manipulation member having a tip end located remotely laterally outwardly offset from the apparatus base member and also having a butt end pivotably attached at a butt-pivot to the base member whereby the elongate boom is supported by the underlying substrate through said weighty base member, the crane apparatus also comprising a dualdirectional hydraulic-piston including a plunger portion surrounded by and extendable from a casing with the plunger at a plunger-pivot being pivotably attached to the boom laterally outwardly from the butt-pivot and with the casing at a casingpivot being pivotably attached to the base member remote from the boom, said crane apparatus including a pumpable reservoir of hydraulic motive fluid controllably deliverable through a first line and through a second line communicating with the casing interior on opposite sides of the extendable plunger thereby permitting selectable changes in the boom angularity and in the resultant burden moment, the improvement of burden moment monitoring system and including compensation means for the progressive decrease in burden moment critical-level as the boom angle becomes steeper with respect to the underlying substrate and said system comprising: A. Hydraulic pressure differential sensing means comprising a cylinder internally provided with a reciprocatable barrier for motive hydraulic fluid, said first line and second line sources of motive fluid communicating with the cylinder interior on the forward and the rearward sides respectively of said reciprocatable barrier; B. A hydraulic pump comprising a housing internally provided with a ram that is co-reciprocatable with said barrier and located externally of the pressure differential sensing means cylinder, the hydraulic pump housing chamber being substantially filled with hydraulic metering fluid which is isolated from the hydraulic motive fluid; C. A pressure-responsive device communicating with and sensitive to the metering fluid of said hydraulic pump; D. At least one transducer of the hydraulic-electrical type and including said pressure-responsive device; E. A warning indicator electrically connected to the transducer to caution the crane operator that some prescribed subcriticallevel pressure of metering fluid has been attained whereby the crane operator might take corrective action to decrease the burden moment by increasing the boom angle through the dualdirectional hydraulic-piston; and F. Yieldable resistance means bearing against the pressureresponsive device to make said deVice less sensitive to the hydraulic metering fluid and progressively less so at steeper boom angles thereby providing compensation means.