Material or article handling – Vertically swinging load support – Shovel or fork type
Reexamination Certificate
2000-12-07
2003-11-04
Lillis, Eileen D. (Department: 3652)
Material or article handling
Vertically swinging load support
Shovel or fork type
C414S680000, C414S728000, C180S211000, C212S231000
Reexamination Certificate
active
06641355
ABSTRACT:
The present invention relates generally to the field of self propelled lift trucks. More particularly, it relates to the transportable variety which require an extremely low unladen weight relative to its load carrying capacity.
There are many types of lift trucks designed for material handling applications.
A number of such lift trucks use piston-cylinder arrangements or chain-link drive mechanisms combined with sprocket wheels to raise and/or lower the lifting tines on a vertical mast. Others use an articulating linkage and gantry structure to raise and/or lower the lifting tines. While, yet others, use a telescopic lifting arm articulated about a horizontal axis perpendicular to the longitudinal axis of the lift truck to raise and/or lower the lifting tines. For example, such vehicles are disclosed in U.S. Pat. Nos. 3,858,730; 4,345,873; 4,365,921; 4,531,615; 4,621,711; 4,826,474; 4,921,075; 4,986,721; 5,061,149; 5,199,861; 5,478,192; D384,477; European Patent Specification 0 701 963 B1, and Irish Patent Specification S75661.
The materials handling lift truck of the present invention is adapted to be securely mounted and transported on the back of a carrier vehicle, such as a trailer or truck. In this manner, the lift truck can be conveniently transported directly to the work site, along with the load to be moved.
For a lift truck to be effectively used in this manner, it should be lightweight, and yet at the same time, should be capable of lifting heavy loads. Form following function dictates that to provide heavy lifting capability while minimizing the weight of the lift truck, it is advantageous for the lifting tines to have the capacity to be shifted from a position forward of the front wheels to a position behind them thereby relocating the centre of gravity of the load towards the centre of gravity of the vehicle and thus increasing the lifting capacity of the lift truck. For this reason, the aforementioned type lift truck generally has a U-shaped frame with the open end toward the front, at least two front wheels and at least one steerable rear wheel, such that the lifting device thereby extends from a most retracted position between the lateral members of the U-shaped frame.
The prior art also discloses lift trucks which utilize heavy counterweights thereby increasing the load handling capability of the lift truck. Such mechanisms are inconsistent with the need to minimize the weight of a lift truck designed to be transported on the back of a carrier vehicle, since such counterweights reduce the useful payload capability of the carrier vehicle as well as increase the moment load applied at the rear of the carrier vehicle.
Prior art lift trucks may avoid the need to use heavy counterweights by positioning the lifting tines and the load they carry between the front and the rear wheels. However, this type of design has been generally limited to applications where the load to be lifted is at ground level. For example, such vehicles are disclosed in U.S. Pat. Nos. 3,610,453 and 3,861,535.
In general, all lift trucks of the prior art, capable of being transported on carrier vehicles have the disadvantage of obstructing the field of view from the operator's station.
The transportable lift trucks of the prior art generally have minimal ground clearance and are not as capable of travelling over rough or bumpy terrain, but are more suited to paved ground.
A feature that some lift trucks of the prior art provide is a “sideshift” mechanism. That is, the ability to move the tine carriage and lifting tines a fixed distance left or right of the longitudinal axis of the lift truck thus providing the vehicle operator the ability to manipulate the pickup or drop off of a load without having to readjust the position of the whole vehicle which would typically involve reversing/driving forward the vehicle in order to renegotiate a more optimum load approach. The method in which, and distance that the lifted load can be shifted from the longitudinal axis of the lift truck is critical on transportable type lift trucks since their function dictates a compact and light design.
In the case of prior art trucks that utilize an integrated pivot and “sideshift” assembly, namely those that utilize a telescopic lifting arm articulated about a horizontal axis as the lifting device, the lifting device thus having the capability of being displaced transversely in the horizontal plane as well as being articulated in the vertical plane, has the disadvantage, in that, with the lifting device and “sideshift” structure assembly being shifted transversely in the horizontal plane, there results a significant shift laterally of the lift truck's centre of gravity; such a shift thus leading to a notable reduction in the permissible amount of “sideshift” in order to maintain vehicle stability. Furthermore, this arrangement has the disadvantage in that it involves high fabrication costs and significant maintenance costs in exchange for a relatively minimal guarantee of functional reliability.
In the case of prior art trucks that have a “sideshift” mechanism or system that connects the vertical mast to the tine carriage supporting the lifting tines, or the telescoping lifting arm to the tine carriage supporting the lifting tines; this system has the disadvantage of increasing the total space occupied by the lift truck behind the carrier vehicle, this distance corresponding to the depth of the structure required for the “sideshift” mechanism. This increases the length of the overall assembly being transported, including both the carrier vehicle and the lift truck being transported. This system also has the disadvantage of reducing the useful load of the carrier vehicle since the moment load applied by the lift truck is increased by an amount corresponding to this distance. The useful load of the carrier vehicle is also further reduced by an amount corresponding to the additional weight of the “sideshift” structure. Furthermore, the front lifting tines being separated from the lifting device by a distance corresponding to the depth of the “sideshift” structure has the disadvantage in that it reduces the lift truck's useful lift capacity when in a static loading position since there is a resultant shift in the load's centre of gravity due to this added distance being applied forward of the front wheels. The lift truck's useful lift capacity is again further reduced by an amount corresponding to the additional weight of the “sideshift” structure being also applied forward of the front wheels when in a static loading position.
Another inherent disadvantage of prior art lift trucks of the type that utilize a telescopic lifting arm articulated about a horizontal axis as the primary lifting device is that the load follows a convex arc as it is being raised from the ground level to its maximum lifting height, or vice versa. This in turn tends to move the load's centre of gravity forward thereby reducing the maximum rated lifting capacity of the lift truck. The consequence of this is apparent. Without the lift truck operator intervening and retracting the telescoping arm, the likelihood of the lift truck toppling is high.
In general, all lift trucks of the prior art, capable of being transported on carrier vehicles, in order to maintain a minimal overhang when mounted and transported on the back of a trailer or truck have the disadvantage in that the lift truck operator safety cage is intentionally kept short which results in the rear portion of the operator's seat being outboard of or projecting past the rear of the lift truck and operator safety cage. This obviously limits the amount of protection that the back of lift truck operator safety cage can provide to the operator which consequently leaves the operator especially prone from the rear.
All lift trucks of the prior art, capable of being transported on carrier vehicles, in general, have the disadvantage in that they do not provide an automatic method for positively captivating the lift truck when mounted and transported on the bac
McInerney James J.
McInerney James P.
Ipsolon llp
Liftcon Technologies Limited
Lillis Eileen D.
Lowe Michael
LandOfFree
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