Stacker crane having narrow mast structure

Claim 1

A crane comprising a horizontally movable overhead trolley, an upright rigid mast having at an upper end thereof a connection with the trolley that confines it to rotation about its own axis relative to the trolley, the lower end of said rigid mast being spaced a substantial distance above a floor, an intermediate mast movable relative to said rigid mast down to and up from a lowered position in which a bottom end of the intermediate mast is at a substantially smaller distance above the floor, a carriage movable up and down relative to both of said masts and having means thereon for supporting a load, and a winch carried by the trolley and connected with the carriage for raising and lowering it, said crane being characterized by: A. one of said masts having a lengthwise projecting pilot element fixed thereon (1) which is of smaller cross-section than the other of said masts and (2) which is telescopingly received in said other of the masts to guide the intermediate mast for motion between its said lowered position and a raised position in which the top end of the intermediate mast is contiguous to the lower end of the rigid mast; B. each of said masts having a pair of guide rails extending vertically therealong, one at each of a pair of opposite sides thereof, the guide rails on the intermediate mast being vertically aligned with respective guide rails on the rigid mast; C. biasing means reacting between the rigid mast and the intermediate mast to urge the latter toward its raised position; D. guide means on said carriage cooperating with said guide rails on the masts to confine the carriage to vertical motion relative to the masts; and E. cooperating abutment means on the carriage and on the intermediate mast, engaged when the carriage is near the bottom of the intermediate mast, to constrain the intermediate mast to move up and down with the carriage between its raised and its lowered positions.