The invention relates in general to a moving crank mechanism (10) that is particularly adapted for use in a conveyor system. A moving crank remains in a substantially parallel position with respect to a fixed reference plane as the crank member is driven by its offset opposed ends (12, 14) along an endless loop. In particular, the invention relates to a closed loop vertical lift unit adapted for use in an automated high-speed storage system. The vertical lift unit is adapted to be used as a primary storage location or as a lift for carrying objects in transit between levels in a storage system. The vertical lift unit includes a plurality of crank members (16) with generally rigidly mounted shelves (26) that are adapted to carry objects continuously and indefinitely as the shelves travel through a vertically oriented closed path.