Abstract: A wire guidance system for a materials handling vehicle, such as a turret stockpicker, detects an alternating signal carried by a buried wire. Two sets of four sensors each are carried at either end of the vehicle. These sensors define regions, and a procedure is provided to determine in which region the wire is located. The distance and angle of the vehicle is determined by reference to the distance measurements of each sensor set, as calculated by a microcomputer. A self testing circuit is provided to insure proper operation of the sensors and associated circuitry.

Abstract: A materials handling vehicle, such as a turret stockpicker, includes a telescoping mast comprising inner and outer sections. The staging of these sections, and the stopping of the platform assembly is smoothed by monitoring the actual height of the platform and restricting the speed of the platform as it approaches these transition points. The height of these transition points are stored in a digital memory. The platofrm speed is normally determined by a control handle, but as the platform reaches a transition point, the maximum speed of the platform is restricted by a micro-computer which controls a servo controlled hydraulic valve and the hydraulic pump motor supplying hydraulic fluid to the platform lifting cylinders. The maximum rate of platform movement after a transition is returned to the control of the operator.

Abstract: A fork extension and retraction system for use with stockpickers automatically extends and retracts hydraulically extendable forks of a stockpicker when the load handler carrying the forks has moved to its extended position on the load side of the vehicle, and it also automatically retracts the forks if they have drifted from a home position before performing other fork related activities. Switches in the fork carriage assembly sense when the extendable forks are in the home position and near the home position. Other switches sense when the load handler assembly has reached its extreme positions on either side of the operator's platform. Still other switches are used to slow the traverse movement of the load handler assembly as it approaches its extreme positions, thus to cushion the shock of the load handler stopping. A control circuit senses the condition of these switches and controls the operation of both the load handle and the fork extension hydraulic system.

Abstract: An improved system for monitoring lift chains included within mast assemblies in material handling vehicles disables downward movement of the forks upon detection of a first level of slackness in a lift chain. Since upward movement of the forks is not disabled, the forks may be raised to clear any obstruction causing the chain slackness. A lift chain may also be monitored to detect a broken chain in which case all vertical movement of the forks is disabled. In a material handling vehicle wherein the operator is elevated along a first mast and the forks are elevated along a second mast connected to an operator's platform, dual lift chains in the first mast are individually monitored for both slackness and breakage while dual lift chains in the second mast are monitored in common primarily to detect slackness. Lateral and rotational movement of the forks is also disabled for detection of a slack or broken first mast lift chain, but not for detection of a slack or broken second mast lift chain.