A safety control mechanism for a load line forming part of an extensible boom crane which has a plurality of sections moved relative to each other by power means. The cable supports a load supporting member on one of the crane sections and is reeled or unreeled from a driven drum supported adjacent another of the sections. The safety control means incorporates mechanism which will render the power means inoperative when the tension on the cable reaches a certain level. The safety control means consists of a bracket pivotally supporting the drum and pivoted about an axis. The bracket is normally biased to a first position, with the biasing means accommodating movement from the first position after the tensile load exceeds a lower level to actuate control means, forming part of the power means, to render the power means inoperative when the tensile load on the cable exceeds a desired maximum level.
A crane having a telescoping boom which is extendable and contractable to various lengths, which boom has a cable trained thereover for lifting a load. A tension scale system is provided for the cable of the telescoping boom, which system includes a tension dynamometer located on the stationary or base boom section; the lifting cable is connected to a winch, and then extends along the boom and through a reeving system located on the outermost section of the boom; the cable is then trained over a pulley rotatably mounted on the outermost boom section and the cable is then dead-ended on the base section of the boom by being connected directly to the tension dynamometer on the base section. An electrical connection extends from the tension dynamometer directed to the operator's cab so that the load on the cable may be read directly by the operator in the cab of the crane.
A latching system is disclosed for a telescopic boom, and comprises a ladder structure for positionment longitudinally along a side of a smaller boom section, and a latch plate assembly for a pivotal attachment to a large boom section. Bias means is further provided for applying a biasing force tending to move the latch plate into the ladder detent slot, and counter bias means for applying counter bias force to the latch plate. Linkages are adapted to extend between the latch plate and the tensioned chains which actuate the small boom section outward and inward relative to the large boom section, whereby the tension forces within the chains serve to provide counter biasing forces to the latch plate mechanism.
