1. Field of Invention
This invention relates to improvements in methods and means for the topical cleaning of convoluted surfaces of planar articles, and more particularly to an ultrasonic method and means for cleaning complex articles, especially lenses, diffusers and reflectors for fluorescent light fixtures.
2. State of the Art
In modern office buildings, fluorescent tube lighting is employed for energy economy and tube longevity as well as its generally superior efficiency as compared to incandescent lighting. Various configurations of light diffusers, usually composed of plastic or coated sheet metal, are used to shield the worker from directly seeing the fluorescent tube(s) in the ceiling fixture and also to make the overhead appearance more aesthetic, as well as functional. Such lenses and diffusers are often transparent or translucent sheets formed from durable plastic materials. They may be assembled from fabricated struts and cross-members, sometimes arranged in the manner of the dividers seen in egg crates to isolate the fragile eggs. In addition, reflectors of plastic coated with a thin metallic film, are often fabricated in the shape of multiple parabolas. Unless the context implies something more specific, the term "diffuser lens" is used herein to refer to the entire range of structures that provide for the redirection of light from fluorescent ceiling fixtures, including also the structures commonly known as lenses and as reflectors.
The convoluted surfaces of diffusers predictably catch and retain dust, and soil, as well as particles and tars resulting from tobacco smoking. This result is augmented when ceiling fixtures also have integral louvers or flow channels for drawing air from the working area for filtration and/or temperature and humidity adjustment.
It is part of a good office maintenance routine to remove the diffusers or lenses for periodic cleaning of the unsightly coatings that are being steadily deposited so quickly. To manually scour and scrub these soil-coated lenses is quite laborious, since their surface design has evolved from planar to prismatic, and even to parabolic, rendering time-tested manual scrubbing methods obsolete and economically impractical.
Methods for using ultrasonic transducers to clean solid articles are known, such as are described in U.S. Pat. No. 4,705,054, entitled "Ultrasonic Radiator Cleaning", issued Nov. 10, 1987. Similarly, an apparatus for cleaning a linear object such as an uncoated flexible continuous strip is taught in U.S. Pat. No. 4,605,027 to M. Dallot. Neither of the reference devices is suited, or could be adapted, to treatment of the complex-surfaced light diffusers addressed by the present invention.