A mast structure of a forklift truck is composed of two vertically and parallelly extending channel members each of which has front and rear flanges. The thickness of the rear flange is so larger than that of the front flange that a ratio (e.sub.1 /e.sub.2) of a front-side figure center distance (e.sub.1) between a front-most end of the channel member and a center of figure in cross-section to a rear-side figure center distance (e.sub.2) between a rear-most face of the channel member and the center of figure is within a range of 1.1.ltoreq.e.sub.1 /e.sub.2 .ltoreq.1.5, thereby effectively improving flexural and torsional rigidities of the mast channel member of the forklift truck.
A mast structure for a storage and retrieval machine is disclosed which includes first and second vertical members having lengths affixed to each other. The second vertical member includes a plate extending along the length of the second vertical member and spaced from the first vertical member in the direction of the path of travel of a base of the storage and retrieval machine. The first and second vertical members respectively have cross-section areas perpendicular to their lengths which are substantially equal to each other. The first and second vertical members together have a physical center and a centroidal axis both extending along the length of the members which may be adjacent to each other and preferably coincide with each other so that the two members together have a maximum section modulus in the direction of the path of movement of the base. The first vertical member has a tubular cross-section shape for guiding a carriage of the storage and retrieval machine along the length of the mast structure which is of a rectangular shape. The second vertical member is tapered so that the cross-section area of the second vertical member decreases in an upward direction to decrease the section modulus of the mast structure at its upper end where impact loading is less.
A two- or multi-stage mast-hydraulic cylinder construction (4, 5) for a truck mast, and method for manufacturing the intergrated structer (4, 5), are discloused. The fixed mast assembly has its substantially vertical beams (4, 5) and its cylinder liners (29) provide an integrated structure (4, 5), wherein the cylinder liners (29) are constituted by channels integrated inside the beams (4, 5), said integrated structures having their centre of mass at the centre of the cylinder liner (29) or in the immediate vicinity thereof, that the integrated structure (4, 5) is capable of being manufactured by hot extrusion or cold drawing, and that the integrated structure (4, 5) is provided with one flange (13), one side of which comprises a bearing surface (16) and the opposite side comprises a support surface (17), said surfaces (16, 17) lying in a plane transverse to the operating direction of a truck, and with at least one second flange (19) for locating the centre of mass at the centre of the cylinder liner (29) or in the immediate vicinity thereof.
A stacking mast for being attached to a lift truck and for moving a load between a negative position and a positive position. The stacking mast includes an elongated first mast, the first mast including a lower end for being attached to the lift truck and including an upper end; an elongated second mast, the second mast including a lower end and an upper end; a floating carriage having a first securing structure for being slidably secured to the first mast and a second securing structure for being slidably secured to the second mast; a support carriage slidably attached to the second mast for supporting the load; and lift structure for moving the support carriage between a lower position and an upper position on the second mast and for moving the second mast between a lower position and an upper position on the first mast. A second embodiment is also described in which one or both of the first or second masts may telescope, allowing a reduced un-telescoped height for passing through doorways or under obstacles, while substantially preserving the full positive and negative lift.
An improved fork lift truck having a scissor-actuated horizontal carriage motion system mounted on a horizontal frame. The carriage motion system providing for selectable positioning in a compact space of a lift assembly between a position forward of and behind the front wheels. The lift assembly provides downward pressure and is vertically moveable from and to a position which is below ground level and a further position above the level of the fork lift truck. The fork lift truck also provides a pair of outriggers which discontinue movement and remain stationary if they contact an obstruction, while the other outriggers continue to extend, the outriggers being moveable both horizontally and vertically relative to the remainder of the lift truck.
