| 摘要 |
A load-lifting mast (10) especially adapted for an automatically-guided, driverless vehicle (20) has automatic features for ensuring accuracy and reliability of operation despite the absence of a driver. For load-lowering purposes, a slack chain sensor (58) senses whether or not the load-supporting carriage (16) is supported by the mast (10), and the carriage (16) is withdravn from the load when no support by the mast (10) is indicated. The slack chain sensor (58) also cooperates with a carriage height control system (54, 56) by overriding it to cause lowering past a target height until the carriage (16) is supported independently of the mast. A carriage height sensor self-calibration system continually recalibrates the height-sensor (54) readings automatically while the mast (10) is in use to compensate for height sensor slip, chain stretching, and other mechanical variables. The slack chain sensor (58) cooperates with the self-calibration system to enable it to reference to the ground or other surface upon which the vehicle (20) travels to compensate for such other variables as tire wear. The mast (10) is preferably powered by an electric motor-driven screw member (32) having a wear-preventing, universal-joint-type connection (40) to the carriage-lifting mechanism (42) to prevent the imposition of unsymmetrical loading on the screw member. The electric motor (34) has field effect transistor controls operable over a wide range of source voltages. |
