The present invention relates to maintenance of elevated structures, and more particularly to the controlled manipulation of a load in connection with such maintenance, for cleaning components of the structures.
The manipulation of loads in connection with tower structure construction and maintenance is a key to the viability of such structures. For example, some important structures have been erected at remote and foreboding sites only because it has been possible to fly the components to each site by helicopter, the parts being attached to each structure while the helicopter hovers with the load properly positioned and oriented. See, for example, U.S. Pat. No. 4,378,919 to H. Smith that discloses apparatus by which a load suspended from a helicopter is free to swing beneath the helicopter, yet the rotational position of the load about a vertical axis is controlled by yaw manipulation of the helicopter. The Smith disclosure includes a yoke by which the load is suspended on a pair of cables, the yoke being restrained from rotation under the helicopter by a ring-shaped tubular structure that forms a pair of slots for receiving opposite ends of the yoke. A linkage allows the tubular structure to move back and forth in response to swinging of the cargo hook.
The Smith device is subject to several disadvantages. For example, the linkage is somewhat complex, having several swinging joints. Also, the slot in the tubular structure must provide extra clearance for the yoke to allow for lateral tipping of the tubular structure, reducing the effectiveness of the structure in yaw control. Further, anchor points for the linkage must be provided on the aircraft structure. Moreover, there are times when further control of a suspended load beyond mere rotational control is needed. For example, in one aspect of tower structure maintenance, it is desired to clean critical portions of the structure, such as insulators of high voltage power transmission towers.
Presently, the insulators are cleaned at relatively long range using deionized water at high pressure. This can be done from the ground using what amounts to a fire truck, and a man carrying a hose can also climb the tower. Attempts to do this from the air have had limited success because water is too heavy for economical transport by helicopter, and a second crew member is required for operating a nozzle turret that is needed for directing the stream sufficiently accurately. This greatly increases the of weight to the load, and the hardware is expensive. The expense of the hardware is aggravated by the need for of FAA certification. See, for example, U.S. Pat. No. 4,090,567 to Tomlinson that discloses a fire fighting helicopter, and U.S. Pat. No. 4,477,239 to Kurtgis that discloses a tower insulator cleaning apparatus that is carried by helicopter. Also, when the helicopter is large enough for carrying a meaningful load, two pilots are required under FAA regulations.
Water creates its own problems in that when it is contaminated by dirt from the insulator, it becomes conductive, creating a danger of arcing. Moreover, there are large reactive forces to contend with. "Dry cleaning" has also been done using a blast of air and particles of walnut shells, sand, corn husks or the like. But the air blast has a short range of only two or three feet, tending to preclude effective cleaning from a nozzle mounted on the helicopter, which must fly close to the wires. Also, when hoses are used, such as by a man climbing the tower, the losses are prohibitive.
As mentioned above, a disadvantage of the Kurtgis apparatus is that at least two crew members are required, and only a relatively small quantity of the liquid spray can be carried. Also, the helicopter must fly at a low altitude approximately corresponding to the height of each insulator to be cleaned. This presents the danger that a gust of wind or other emergency might cause the helicopter to crash into the tower and/or the transmission lines, with disastrous consequences. Moreover, the center insulator on a conventional "single circuit" tower is nearly inaccessible from the side, and must be cleaned at long range.
A further disadvantage of the Kurtgis apparatus is that the nozzle is located at the end of a long boom for clearing the ends of the rotor blades. This makes the nozzle particularly difficult to aim accurately. This difficulty is aggravated by the independent control of the position and orientation of the helicopter by its pilot, and the separate aiming of the nozzle in both yaw and elevation by the boom operator. Moreover, the nozzle and/or the boom can get caught in the tower, with the consequent likelihood of crashing the helicopter because neither the boom with its nozzle, nor the remainder of the heavy cleaning apparatus and its operator can be released in an emergency.
Thus there is a need for a highly mobile apparatus with which to manipulate a load, such as in dispensing a cleaning medium, accurately in both yaw and elevation. Also, there is a need for such apparatus that is safe to operate in close proximity to high voltage power transmission lines and towers. There is a further need that such apparatus be adapted for effectively and rapidly cleaning large numbers of tower components, and be inexpensive to build and easy to operate.