Moment monitoring system for boom-cable type cranes

Claim 1

In a boom-cable type 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 uprightaxis, said crane further comprising an elongate boom burden member having a tip end located remotely laterally offset from the apparatus base member upright axis and also having a butt end pivotably attached to said base member whereby the elongate boom is supported by the underlying substrate through the weighty base member, said crane apparatus boom-cable being controllably windable about a powerably revolvable drum located at the base member and proceeding from said drum to the boom tip end and thence ultimately connected at the boom-cable dead end to said base-member, said crane apparatus base member also including drum powering means and ancillary operator controls for said revolvable drum thereby permitting selectable burden moment changes with respect to the stable base member upright-axis and upon reaching a critical-level the burden moment will render the base member unstable with respect to the underlying substrate and to the detriment of said crane''s stability, the improvement of burden moment monitoring system and comprising: A. Sensing means of the variable liquid pressure type and comprising a reciprocatable pump interposed as a connector link between the boom-cable dead-end and the apparatus base member and located in the vicinity of the boom butt end and said sensing means also comprising an elongate hose through which is urged increasing magnitudes of liquid pressure from said pump as the boom-cable at increasing burden moment conditions exerts increasing tension upon said pump connector link; and B. At least one transducer of the hydraulic-electrical type actuatably connected to a stationary hose portion of said variable liquid pressure sensing means, and a warning indicator electrically connected to the transducer to caution the crane apparatus operator and personnel that some prescribed subcritical-level of liquid pressure from the hydraulic pump has been attained whereby the crane operator through said powering means may take corrective action through said revolvable drum to decrease the burden moment and thereby prevent the base member and the entire crane apparatus from being rendered unstably supported on the underlying substrate.