Elevator – industrial lift truck – or stationary lift for vehicle – Stationary lift for roadway vehicle or required component... – Having specific drive means for support
Patent
1980-10-20
1984-02-14
Rolla, Joseph J.
Elevator, industrial lift truck, or stationary lift for vehicle
Stationary lift for roadway vehicle or required component...
Having specific drive means for support
414631, 414696, B66B 920
Patent
active
044310838
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to lifting mechanisms and, more particularly, to apparatus for positioning materials using parallelogram linkages. Such apparatus include conveying systems and material positioning vehicles.
2. Background Art
Conveying systems and material positioning vehicles often utilize parallelogram linkages to position loads. For example, lift trucks, cranes and front end loaders have such mechanisms. More specifically, a fork lift truck having a mast assembly that is supported by a parallelogram linkage is disclosed in U.S. Pat. No. 4,054,185 entitled "Mast Control Mechanism", by R. Stedman, issued Oct. 18, 1977 and assigned to the assignee of the present invention. The linkage includes one pair of vertically spaced apart arms pivotally connected at their forward ends to the lift truck and pivotally connected at their rearward ends to a second pair of vertically spaced apart arms. The second pair of arms is pivotally connected at their forward ends to the mast of the lift truck. A control linkage pivotally anchored to the lift truck, to the arm of the first pair of arms and to the mast causes the mast to move in a substantially straight path.
Other patents that describe positioning linkages include U.S. Pat. No. 2,980,271 entitled "Lifting Mechanism for Industrial Truck" by Ulinski issued Apr. 18, 1961; U.S. Pat. No. 3,826,392 entitled "Lifting Device" by Farley issued July 30, 1974; U.S. Pat. No. 4,059,172 entitled "Lift Truck Mast Positioning Mechanism" by Stedman issued Nov. 27, 1977 and assigned to the assignee of the present invention; and U.S. Pat. No. 4,084,715 entitled "Lift Truck with Means to Pivot Mast and The Fork Carriage Thereon" by Stedman issued Apr. 18, 1978 and assigned to the assignee of the present invention.
When parallelogram lifting linkages are used on lift trucks to raise and lower the fork carriage, the tips of the forks describe an arc. In the industry this arcuate path is called swing out and the arc is inherent in parallelogram lifting linkages because the lifting arms are mounted on pins and are thus restricted to travel along circular paths.
The arcuate path of the forks raises three problems. The first problem is that during lifting, the center of mass of the load is displaced away from the lift truck and a moment arm is created. Such a moment arm can reduce the capacity of the lift truck because either heavier counterweights or smaller loads may be required. Secondly, when lifting a load, the operator must compensate for the forward motion of the mast assembly lifting the load. This forward motion will cause the operator to reposition the vehicle in order to clear any objects adjacent or behind the load being lifted. In addition, the positioning of the forks for engagement with the load to be lifted or lowered is more difficult because as the forks are being moved vertically, the forks are also moving horizontally with respect to the load. This requires further repositioning of the vehicle. Thirdly, the bottom margin of the outer pair of uprights also travels on an arcuate path when the mast assembly is lowered. If the lift truck is abutting an object such as a tote box, the bottom front corner of the outer upright may swing forward during lowering depending on its elevation and may contact the underlying tote box.
One prior solution to the problem of swing out was to incline the forks at a predetermined angle relative to the mast. This inclination tended to reduce the swing out at two ends of motion but made it very difficult to pick up a tote box at an elevated position with the forks.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of this invention, an apparatus for lifting a member relative to a frame is disclosed. The apparatus comprises an upper pair of links pinned together at a common end and with one remote end pinned to the frame and with the other remote end pinned to the member. In addition, the apparatus comprises a m
REFERENCES:
patent: 2980271 (1961-04-01), Ulinski
patent: 3826392 (1974-07-01), Farley
patent: 4054185 (1977-10-01), Stedman
patent: 4059172 (1977-11-01), Stedman
patent: 4084715 (1978-04-01), Stedman
patent: 4124099 (1978-11-01), Dudynskyj
"Straight-Line Mechanisms", Data Sheet 20, Automotive Design Engineering, Apr. 1, 1964.
Caterpillar Tractor Co.
Hickman Alan J.
Noland Kenneth
Rolla Joseph J.
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