Analysis and Development of a Passive Mechanical Vibration Abatement Device for Traffic Monitoring Cameras

Abstract

Departments of Transportation throughout the United States and elsewhere employ close-circuit television (CCTV) cameras for roadway monitoring as part of increasingly sophisticated traffic management systems. Cameras used for this purpose are attached to various highway structures and poles as high as 65 ft, all susceptible to wind- and ground-induced vibrations which adversely affect image quality. This paper describes the engineering analysis, development, and testing of a low-cost, biaxial mechanical vibration isolator specifically aimed at horizontal high-frequency motion abatement in pole-mounted camera applications and similarly conditioned supports. The device works on the principle of force and displacement transmissibility reduction via the use of a lightly damped sprung interface with a tuned natural frequency. The isolator is inserted between the top of the structure (pole) and the seat of the camera, and operates by rejecting undesirable high-frequency modal vibrations experienced by the main support; this has the effect of diminishing high-acceleration ground inputs which are principally responsible for image distortion. While favorable to high-frequency performance, the physics of this configuration prescribe the presence of a low-frequency displacement or pan of the sprung mass (albeit found to be free of blur in experiment). This characteristic is complementary to that of electronic image stabilization technology, whose performance suffers when significant motion is present in the incoming video feed. For this reason, the proposed mechanical solution is presented as an ancillary technique to image processing in installations where high frequency or displacement conditions prevail at the camera support.