1. Field of the Invention
The present invention relates to a hoisting apparatus for a load such as luminaires used at high elevations, and particularly a hoisting apparatus with a horizontal stabilizing means for a load holder, to which the load is detachably attached.
2. Disclosure of the Prior Art
In high-ceilinged structures such as concert hall, gymnasium, and convention hall, a hoisting apparatus has been utilized to readily carry out maintenance work of luminaires operated at high elevations. For example, as shown in FIG. 10, European Patent Publication No. 1193442 A2 discloses this kind of hoisting apparatus. That is, this hoisting apparatus 1S is mainly composed of a base 2S secured to a ceiling, a load holder 3S, to which a luminaire is detachably attached, a pair of cables 4S extending between the base and the load holder, a drive unit (not shown) mounted to the base, to which one ends of the cables are connected, so that the drive unit is operative to take in or let out the cables from the base.
From the viewpoint of facilitating the maintenance work of the luminaire under safe working condition, this hoisting apparatus also has a cable-length adjusting means in the load holder 3S, by which the cable length can be readily adjusted such that a descending position of the load holder matches a position adequate for the maintenance work of the luminaire to avoid dangerous operations at high elevations,
As shown in FIGS. 11A to 11C, the cable-length adjusting means comprises a winding shaft 60S of a round-bar shape, which is rotatably supported in a holder case 30S of the load holder 3S. Each of the cables 4S is fixed connected at its one end to a winding drum (not shown) of the drive unit and at the opposite end to the winding shaft 60S. The winding shaft 60S also has an elongate hole 64S, to which a dedicated tool 48S can be inserted through a slit 34S formed in the upper surface of the holder case 30S to inhibit the rotation of the winding shaft. In addition, the winding shaft 60S has engagement grooves 65S at its opposite ends, to which a tip of the dedicated tool 48S can be engaged. The grooves 65S of the winding shaft 60S are exposed to be accessible from outside of the holder case 30S, as shown in FIG. 10.
By use of the cable-length adjusting means described above, the cable length can be adjusted as follows. That is, the tip of the dedicated tool 48S is engaged to one of the grooves 65S of the winding shaft 60S, and then the winding shaft is rotated by the dedicated tool to wind desired amounts of the cables thereon. In this hoisting apparatus, since both of the cables 4S are wound around the winding shaft 60S in the same winding direction, as shown in FIG. 11A, the winding operation of the cables can be achieved by rotating the winding shaft 60S. In addition, since a proper tension is applied to the cables 4S under the suspended condition of the load holder 3S, it is possible to readily wind the cables around the winding shaft 60S without looseness. After the desired amounts of the cables 4S are wound on the winding shaft 60S, the dedicated tool 48S is removed from the groove 65S, and inserted into the elongate hole 64S of the winding shaft through the slit 34S of the holder case 30S, so that the rotation of the winding shaft is inhibited to prevent unwinding of the cables 4S from the winding shaft.
By the way, from another viewpoint of preventing an inclination of the load holder with the luminaire, an improvement of the conventional hoisting apparatus is being awaited. For example, due to variations in cable length, and variations in position of the cable ends respectively connected to the winding shaft and the winding drum of the drive unit, it is difficult to provide the same effective length between the pair of cables. This means that the inclination of the load holder may easily occurs.
According to the hoisting apparatus described above, it is possible to adjust the cable length by rotating the winding shaft to obtain the desired effective length of the cables between the base and the load holder. However, since both of the cables are wound around the winding shaft in the same winding direction, this cable-length adjusting means do not have a function of correcting the inclination of the load holder in a horizontal position. In other words, when one of the cables is wound around the winding shaft by rotating the winding shaft, the other one is also wound around the winding shaft. Therefore, the inclination of the load holder can not be solved by the rotation of the winding shaft.
Thus, from the above viewpoint of stably maintaining the load holder in a horizontal position, there is still room for improvement of the conventional hoisting apparatus.