Motor vehicles – Power – Electric
Reexamination Certificate
1999-04-29
2001-07-17
Mai, Lanna (Department: 3611)
Motor vehicles
Power
Electric
C280S043120, C280S043230, C280S766100, C180S012000, C180S065510
Reexamination Certificate
active
06260646
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention pertains to the field of pallet trucks and lifts which are manually operable. In particular, this invention relates to pallet trucks which enable the operator to move larger loads in tight or constricted quarters.
BACKGROUND OF THE INVENTION
Pallet trucks are used widely in industry for moving heavy loads on pallets within warehouses and showrooms. Pallet trucks are more compact alternatives to using a forklift, but also require that the load to be moved must stay over a relatively level and smooth surface, as pallet trucks generally do not provide lift from the ground of more than a few inches and do not have suitable stability for moving loads up or down significant inclines.
It is well known within mechanical engineering and physical science that all objects, even those with wheels or casters, have inertia which causes them to remain either at rest or at a stable velocity. In order to start a loaded pallet truck moving from rest, the rest inertia must be overcome by applying an accelerating force to the loaded pallet truck. After the load and truck have been accelerated to a desired speed or velocity, typically walking speed such as 1 or 2 miles per hour, the force needed to sustain that speed is much less than the force which was needed to accelerate the load.
Previous US patents in this field have described methods for moving pallets using manually propelled pallet trucks of various designs, such as 3,982,767 Larsson, et al, 1976, and 4,589,669 Kedem, 1986, for hand-operated pallet trucks having a steerable groundwheels. Typical manual pallet trucks weigh between 180 and 215 pounds. Manual pallet trucks are widely-used for moving pallets however their utility declines as pallet load weights increase and/or transit surfaces become less uniform. This is because it becomes difficult for humans of normal strength to easily overcome the inertia generated by heavy loads at rest, particularly when at rest on rough or uneven surfaces. The force required to manually overcome this inertia can often lead to workplace injuries or fatigue and low productivity. However, many loads which are difficult to accelerate to walking speed are easily sustained at walking speed by a single human operator.
Fully self-propelled pallet trucks such as those described in 4,287,959 Inman, 1981, and 5,245,144 Stammen, 1993, eliminate these concerns by providing a motor means to accelerate the load and sustain its velocity. However, these self-propelled pallet trucks rely on full-time electric propulsion systems which are much heavier, much larger and are significantly more costly to purchase and maintain than the manual variety of pallet trucks. Additionally, self-propelled pallet trucks weigh between 1100 and 1300 pounds, making them useless if the batteries or fuel cell is discharged because a single person is unable to accelerate the loaded truck and sustain its speed. Hence, self-propelled pallet trucks are not as widely used as manual pallet trucks, and are not suitable for applications where maneuvering space is tight.
Therefore, there is a need in the art for a power-assisted pallet truck that minimizes the required operator effort to overcome the inertia of a load at rest, reduces operator fatigue, maintains operator productivity, and reduces injuries to the operator.
There further exists a need in the art for a power-assisted pallet truck which is similar in cost to manufacture and distribute as common manual pallet trucks already on the market, in order to make the product more widely accepted and increase its impact on the reduction of operator injuries.
Additionally, there exists a need in the art for a power-assisted pallet truck of similar weight and maneuverability to manual pallet trucks, such that it can be towed at speed under operator effort, and it can be used in a manual mode when the energy storage cell is discharged.
Finally, there exists a need in the art for a power-assisted pallet truck whose power source is suitable for indoor use, and does not produce toxic fumes or heat. The power source should be quickly rechargeable using common technology found in large warehouse environments.
SUMMARY OF THE INVENTION
The present invention, a power-assisted pallet truck, provides a locomotion means to assist the operator only to overcome the initial rest inertia, while the operator provides the energy and force to sustain the load at speed. The power-assisted pallet truck converts stored energy to mechanical energy using a motor and energy storage means which does not significantly add to the weight or size of a standard, manual pallet truck.
A preferred embodiment using low-weight electric batteries and an electric motor system is disclosed. An alternate embodiment which employs a tank of compressed gas for the energy storage means, and a means for converting released compressed gas to a load accelerating force under operator control, is also disclosed.
An object of the invention is to allow inexpensive construction of the pallet truck, as well as providing a light-weight system which can be manually operated. Because the power-assisted pallet truck only requires a means for locomotion sufficient to overcome the rest inertia, the energy storage means and motor means can be much smaller, lighter, and less expensive than the means employed on a fully self-propelled pallet truck. This addresses the higher weight and cost of self-propelled pallet trucks, and simultaneously meets objectives of the invention to reduce the problems associated with the manual pallet jacks such as injury and lower productivity.
Another object of the invention is to allow maneuvering of pallets in constrained spaces. The size of the power-assisted pallet truck is similar to the size of a manual pallet truck, making it suitable for use in spaces where maneuvering room is restricted, such as elevators, which also meets an objective of the invention.
Yet another object of the invention is for the power-assisted pallet truck to assist the operator in overcoming minor differences in floor height, such as is found between rooms in warehouses, and to assist in the movement across gaps in the floor, such as the gap between an elevator threshold and a warehouse floor. The power-assistance is also useful when moving the loaded pallet truck up a slight incline, such as the ramp between a truck bed and a loading dock.
Finally, since the power-assisted pallet truck is not significantly heavier than a standard manual pallet truck, it can be used by a single operator even when the energy storage device is fully discharged, thereby satisfying another object of the invention.
REFERENCES:
patent: 2469638 (1949-05-01), Framhein
patent: 2592091 (1952-04-01), Weaver
patent: 2601171 (1952-06-01), Schreck
patent: 3249170 (1966-05-01), Qualye
patent: 3261617 (1966-07-01), Becker et al.
patent: 3295881 (1967-01-01), Worthington
patent: 3701211 (1972-10-01), Best
patent: 3982767 (1976-09-01), Larsson et al.
patent: 4047698 (1977-09-01), Ellis
patent: 4065012 (1977-12-01), Rocco
patent: 4103795 (1978-08-01), Miller
patent: 4287959 (1981-09-01), Inman
patent: 4589669 (1986-05-01), Kedem
patent: 4615533 (1986-10-01), Sewell
patent: 4997195 (1991-03-01), Lee
patent: 5113960 (1992-05-01), Prinz
patent: 5245144 (1993-09-01), Stammen
patent: 0601850 (1934-08-01), None
patent: 3322804 (1985-01-01), None
Fernandez Raul U.
Mullock Daniel C.
Frantz Robert H.
Mai Lanna
To Toan
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