Fig. 1 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 horizontal. 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 loads vary in weight, it is impossible to set the position of the hook 61 to the center of gravity during cargo operation.
The invention 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, 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 wire paid out from the drum wraps around the lower half of the first roller and then wraps around the upper half of the second roller. 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 laterally balanced.
Sheave arrangement
It is preferable to use a sheave that is fixed to a shaft. If the wire is directly wrapped around the shaft, the wire may slip along the length thereof during the cargo handling operation. The shaft may be rotatably supported (with the sheave integrally rotatable with the shaft).
When the sheave of the second roller is shifted along the roller to the vertically aligned line extending from the center of gravity, the wire is suspended downward right below the center of gravity of the hoist. As a result, the hoist is balanced in a fore-aft direction and is not inclined in the fore-aft direction during an empty load period and a loaded period. This arrangement allows the electric hoist to more smoothly lift a load.
If the fixing positions of the sheaves are shifted between the first roller and the second roller, the wire is stretched between the sheaves at an inclination. As a result, the wire touches and bends at the flange of the sheave other than the groove of the sheave, thereby causing excessive friction there. A cargo handling operation for a long period of time in this condition may lead to a broken wire.
To avoid such a problem, the wire stretched between the sheaves must be clear of the flange of the sheaves. In accordance with the present invention, the sheaves of the first and second rollers are aligned at the same angle as the wire stretched between the sheaves. This arrangement is achieved by inclining the rotary shaft of the sheave. The wire stretched between the sheaves is correctly aligned to the groove of each sheave.
The sheaves can be made to rotate around their shafts. The sheave rotates following the wire which could be moved when the load rolls and pitches. The winding position of the wire along the sheave is appropriately maintained.
In this arrangement, the shaft of the sheave is inclined in a manner such that the shaft is at a right angle with respect to the wire. The wire is thus aligned with the groove of the sheave. In the same way as the cylindrical shaft is inclined, the winding position of the wire is correctly aligned. The wire is prevented from being cut or damaged due to the rubbing of the wire against the flange of the sheave.
