Patent Application
20110017562
This disclosure relates to the vibration damping of elongated utility poles such as light poles, flagpoles, traffic signal poles, and the like.
Internal vibrations of vertical utility poles for supporting luminaries and the like which are created by environmental forces acting on such poles, have caused many instances of mechanical failure of the pole and/or the luminaire or other item supported by the pole. For example, such vibrations frequently result in eventual failure of tubular metal poles due to metal fatigue. Moreover, internal vibrations of this type frequently result in mechanical damage to the luminaire and its associated structure supported on the poles. For example, fittings and couplings may be eventually loosened by the vibration, and the electrical components of the luminaire may also be damaged to such an extent as to become inoperative.
Mechanisms for damping such internal vibrations in utility poles have been heretofore proposed, for example, in U.S. Pat. Nos. 3,612,222; 4,130,185: 4,350,233; and 6,234,286. Another prior art damping mechanism is depicted in accompanying
A vibration damping mechanism for elongated poles comprises a generally cylindrical hollow tube including a sidewall having outer and inner side surfaces. The inner side surface forms an elongated inner chamber defining a longitudinal axis and having longitudinally spaced upper and lower ends. An unrestricted inertia mass member comprising a substantially cylindrical rod is disposed in the chamber. The inner side surface provides limited clearance with respect to an outer side face of the rod, wherein the rod is capable of limited movement in the chamber to damp oscillations. A section of the outer side surface of the sidewall is substantially flat along substantially the entire longitudinal extent of the sidewall.
Additionally or optionally, the flat section of the outer surface is formed by a flat portion of the sidewall which also forms a flat section of the inner side surface.
Additionally or optionally, formed portions of the sidewall disposed at respective upper and lower ends of the chamber are bent inwardly to extend across, and close, the upper and lower chamber ends, respectively.
Additionally or optionally, the formed portion disposed at the chamber's lower end is shaped to define a raised pivot engaging a bottom face of the rod at a location laterally inwardly of the rod's outer side face.
A vibration damping mechanism 20 for elongated poles comprises a generally cylindrical hollow metal (e.g., aluminum) tube 22 which includes a sidewall 24 having outer and inner side surfaces 26, 28. The inner side surface forms an elongated inner chamber 30 defining a longitudinal axis A and having longitudinally spaced upper and lower ends 32, 34. An inertia mass member comprising a substantially cylindrical rod 38 is disposed in the chamber. The tube's inner surface 28 provides limited clearance with respect to an outer side face 42 of the rod, and the rod is not attached to the tube, so the rod is unrestricted and thus capable of limited movement in the chamber to damp oscillations of the tube and the vertical pole P to which the tube is attached. The rod has plastic caps 43 fitted on its respective ends to minimize noise.
The sidewall 24 includes a flat first portion 50 which is flat along the entire longitudinal extent of the sidewall to define both an outer flat section 52 of the outer side surface 26 and an inner flat section 54 of the inner side surface 28.
By forming the flat 52 along the tube's outer side surface 26, the tube, when attached to an interior surface S of the pole, as is usually the case (see
The flat 54 formed on the inner side surface 28 of the tube functions to resist spinning or rolling of the rod along that surface. It has been found that such spinning can adversely affect the damping performance.
The tube's sidewall 24 further includes formed second and third portions 60, 62 disposed at respective upper and lower ends of the chamber and radially opposite the flat portion 50. Each of the formed second and third portions is bent (mechanically deformed) inwardly so that an axially innermost section 60a, 62a thereof extends across, and generally closes, the upper and lower chamber ends, respectively. Each bent portion forms a recess 66 in the sidewall 24 that has a width W (
Each of the axially innermost sections 60a, 62a is inclined toward the respective opposite end of the chamber (i.e., the sections 60a, 62a are inclined toward one another) at an angle α with respect to horizontal. The angle α is preferably about 5 degrees with a tolerance of 0 degrees to minus 30 minutes. As a result, the free end or tip of the bottom one 62a of the axially innermost sections makes substantially point contact with the bottom face 64 of the rod, i.e., it defines a raised pivot engaging the bottom face of the rod at a location laterally inwardly of the rod's outer side face 42.
The provision of formed portions 60, 62 at the ends of the tube eliminates the need for separate elements, such as caps and angle members, to close off the tube ends, thereby reducing cost. By shaping at least the lower bent portion 62 to serve as a a raised pivot for the weight to rest upon, the weight is able to move more freely in response to smaller pole vibration displacement. Such facilitated movement enables the damper to intervene earlier in a pole's vibration event.
The damping mechanism 20 is configured symmetrically about a horizontal center line so that it can be installed with either of its ends defining the bottom end. Thus, if the mechanism were inverted from the orientation shown in the figures, the formed section 60a would define the raised pivot for the rod.
The recesses 66 formed in the sidewall 24 serve to expose portions of the flat portion 50. That facilitates mounting of the tube to a pole, because holes 70 are formed through the flat portion 50 in alignment with respective ones of the recesses to accommodate fasteners, such as bolts or screws (not shown) for attaching the tube to the pole P. The tube can be attached to either an exterior surface of the pole as shown in
In summary, it will be appreciated that the improved damping mechanism having formed end sections on the tube eliminates the need for separately attaching additional elements, such as angle members, to the tube's ends. The flat formed on the tube's inner surface eliminates the need to form dimples to prevent spinning of the rod. The flat formed on the tube's outer surface enables the tube to occupy less of the tube's inner volume and thereby minimizes interference with internal wiring. The raised pivot for supporting the rod facilitates early movement and damping action of the rod.
While there has been described a preferred embodiment of the improved damping mechanism, it will be appreciated that modifications and changes can be made by those skilled in the art without departing from the spirit of the improvements, and it is intended that the following claims cover such modifications and changes.
