The present invention relates to an electric hoist for raising and lowering a heavy load in a cargo handling operation, and has, as a major component, an electric winch that is constantly suspended in a horizontally aligned posture thereof.
Electric winches typically have a relatively simple structure in which a drum is coupled to a drive shaft of an electric motor such as a geared motor through a reduction device. A variety of types of electric winches are commercially available in wide ranges of price and performance.
In October 2002 discloses a heavy load lifting hoist using an electric winch. FIG. 8 illustrates the disclosed structure. A horizontal extending arm 51 is connected to a vertically aligned pole 50 and an electric winch 52 is supported on the arm 51. A clamp 54 having a socket 53 is fixed to the pole 50. A wedge 55 is welded to one end of the arm 51. With the wedge 55 received in the socket 53, the arm 51 is secured to the pole 50. The other end of the arm 51 is supported by a brace 56. A cover frame 57 covers the electric winch 52. Arranged on the cover frame 57 are two brackets 58 through which the arm 51 extends. The electric winch 52 is supported by the arm 51 with the arm 51 extending through the brackets 58.
The electric winch 52 is used as a hoist in this structure that a wire 60 (alternatively, a rope or a chain) wound around a drum 59 is suspended. The electric winch 52 supported by two brackets 58 is free from being inclined during lifting of a heavy cargo. In view of safety cargo handling operation, an uninclined electric winch 52 is important to maintain an appropriate positional relationship between the wire 60 and the drum 59 and to prevent the wire 60 from being wound on the drum 59 on a one-sided manner and from being unwound unintentionally from the drum 59.
The pole 50 in the conventional art must be erected if the electric winch 52 is used in a cargo handling operation within a plant building or warehouse. Since the pole 50 is not permanently installed, the area that permits the pole 50 to be erected is limited. It is not practical to newly erect the pole 50 within a plant building or a warehouse. If the arm 51 is secured to the ceiling of a building, the pole 50 is dispensed with. Even in this case, the area that permits the arm 51 to be installed is also limited.
A simplest fixing method of the electric winch 52 is to suspend it. More specifically, the electric winch 52 is easily suspended as an electric hoist if a suspension tool such as a wire is available in a cargo handling place.
FIG. 9 illustrates such an example. A hook 61 is arranged on the electric winch 52. The hook 61 is secured to the electric winch 52 at the center of gravity thereof in an empty load condition. By hanging the hook 61 on a wire 62 that is suspended from an appropriate posture on the ceiling, the electric winch 52 remains in a horizontal posture thereof. The electric winch 52 includes the motor and drum side by side. During cargo lifting, a load acts on the drum causing the center of gravity of the entire electric winch 52 to be shifted toward the drum. The electric winch 52 is thus inclined downward at the drum 59 in response to the weight of the load. If the cargo handling operation is performed with the electric winch 52 inclined, the wire 60 may be wound in a one-sided fashion on the drum 59. Such an operation is dangerous. Since the load is varied in weight, it is impossible to set the position of the hook 61 to the center of gravity during cargo operation.
Accordingly, it is an object of the present invention to provide an electric hoist as a suspended electric winch that maintains a horizontal posture in any cargo handling operation.
An electric hoist of the present invention in one aspect includes an electric winch including a drum axially connected to a drive shaft of a motor, a suspension hook attached to the electric winch right above the center of gravity of the electric winch, the electric winch being in a horizontal posture thereof in and empty load state thereof, a first roller arranged on the opposite side of the electric winch from the suspension hook and turning the direction of a wire paid out from the drum toward the center of gravity, and a second roller for turning the direction of the wire to be aligned with a vertical line downward extended from the center of gravity of the electric winch. The hook for suspending the electric winch may be a ring. The hook may be directly secured to the electric winch or to the cover frame already discussed in the Description of the Related Art. The wire paid out from the drum is wrapped around the first roller along about the lower half circumference thereof and wrapped around the second roller along about the upper half of the circumference thereof. The wire thus runs to be aligned with a line vertically downward extending from the center of gravity of the electric winch (right below the position of the hook). As a result, the center of gravity of the electric winch in the suspended electric winch and the center of gravity of the load are in alignment. Regardless of whether the electric winch is in an empty load condition or a loaded condition, the hoist remains to be laterally balanced.
In accordance with the present invention, the electric winch is suspended in the simplest suspension method when the electric winch is used as the electric hoist. The suspension method is implemented in many plants and warehouses without any particular facility. The electric winch in the suspended posture thereof is balanced in a fore-after direction and a lateral direction, and continuously maintains a horizontal aligned posture during a load empty period and a load raising and lowering period. A cargo handling operation using the electric winch is safely performed. Since the position of the first and second roller for causing the wire paid out from the drum to run vertically downward right below the center of gravity is adjusted, no excessive friction takes place between the wire and the rollers. No increase in the burden on the motor occurs.