A Flexible Optical Fiber Goniometer For Dynamic Angular Measurements

The electronic measurement of the angle between two planes is generally performed by using of the so called electrogoniometers. The major drawback in using such devices is the presence of a fixed hinge that imposes a fixed centre of rotation. This can cause problems to measure the bending angle in some joints, like Cardan or human joints, which have a variable rotation centre. Based on an optical fiber, a sensor measuring the relative angle in a rotating joint has been developed. It makes use of the intensity modulation of a laser beam propagating in a single-mode optical-fiber, due to the changes of its polarization status originated by the rotation of contiguous portions of fiber, where controlled birefringence has been induced by a fixed radius fiber loop. A prototype of this sensor has been developed with a range of the relative angle of 90deg with a resolution of less than 0.01deg and a standard deviation of 0.1deg. Main advantages of this innovative sensor are lightness, flexibility, high speed of reaction and high accuracy. This paper describes the implemented sensor, the equipment implemented for the test and the results of laboratory activities are reported and discussed.