Abstract: A load is gripped between a pair of load-engaging surfaces while the magnitude of any slippage between the load and the surfaces is variably sensed. A slip-correcting system variably predetermines an increase in the grip sufficient at least to decelerate the sensed magnitude of slippage, and the grip is automatically variably increased accordingly. Preferably, the magnitude of slippage sensed is a magnitude of relative movement between the load and the load-engaging surfaces, and preferably the magnitude of relative movement is a time-based magnitude such acceleration. The predetermined increase in the grip resulting from the sensed magnitude of slippage is preferably a predetermined increase in the proximity of the load-engaging surfaces, rather than any particular increase in the gripping force applied by the surfaces. A preferred fluid-powered embodiment of the clamp apparatus is disclosed for use on lift trucks in handling paper rolls and the like.

Abstract: A load-lifting mast especially adapted for an automatically-guided, driverless vehicle has automatic features for ensuring accuracy and reliability of operation despite the absence of a driver. For load-lowering purposes, a slack chain sensor senses whether or not the load-supporting carriage is supported by the mast, and the carriage is withdrawn from the load when no support by the mast is indicated. The slack chain sensor also cooperates with a carriage height control system by overriding it to cause lowering past a target height until the carriage is supported independently of the mast. A carriage height sensor self-calibration system continually recalibrates the height-sensor readings automatically while the mast is in use to compensate for height sensor slip, chain stretching, and other mechanical variables.