This paper presents a portable optical sensor capable of measuring complex multi-axis strain fields without the need for special surface preparation or stringent sensor-to-surface alignment. The sensor consists of three to four electronic
speckle photography (ESP) modules. The design of each modular element is based on a previously developed 5-axis
(five degree of freedom) surface displacement measurement technique, and is able to measure two dimensional in-plane surface movement, unaffected by other degrees of freedom (displacement and rotation) movement. Identical modular strain elements are arranged in a Rosette grid layout so that accurate and robust multi-axis surface strain measurement can be achieved.
Experiments were conducted to demonstrate the multi-axis strain field measurement capability of this optical sensor by
using a test bed that provided a known directional planar strain field, and excellent results were obtained. In particular, experiments have shown that the principle strain can be accurately extracted independent of the orientation of the device. This portable optical sensor will allow precise non-contact measurement of practical complex strain fields such as those encountered in bridge abutments, and portions of beams near critical infrastructure support locations; in other words, wherever plane strains depart from uni-axial behavior. Its unique hand-held portable capability offers distinct advantages over laboratory strain measurement setups, allowing accurate robust non-contact measurements to be achieved even in a harsh field application environment.
This paper describes a novel optical system capable of measuring 5-axis (five degrees of freedom) object surface movement without the need for special surface preparation or stringent alignment. The compact optical system is based on electronic speckle photography (ESP) and is designed to be insensitive to out-of-plane movement. Experiments were conducted to measure the 5-axis motion simulated by a 6-axis motion system. The results show that the optical system accurately resolves the motion on every axis successfully, with the expected insensitivity to out-of-plane displacements. A possible application of the technique in strain measurement is also addressed in the paper.