Polymer optical fiber curvature measuring technique based on speckle pattern image processing

• Autor(a) principal: Hägele, Johann Clemens
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/9678
• topic: Sensor de curvatura; Engenharia Elétrica; Speckle; Processamento de imagens; Fibras ópticas; Polímeros; Reconhecimento de padrões; 621.3

A self-developed light intensity-modulated curvature measuring principle for the measurement of bending angles within a range from −120 ◦ to +130 ◦ under application of a Polymer Optical Fiber is described in the present work. The determination of the bending angle is based on the graphical analysis of the speckle-pattern that is affected by the curved fiber. The contours of speckles in a defined region of interest in the speckle-pattern are made visible by an edge-detection algorithm and their amount is set in relation to the bending angle. The digital image of a speckle-pattern represents a source of image information that facilitates the further analysis by a variety of image processing techniques. The purpose of this work is the evaluation of a graphical analysis of a speckle-pattern for the curvature measurement. The research incorporates the basic study of general effects on the fiber under curvature until the development of a final measurement setup that facilitates a reliable and precise measurement of the bending angle. Coherent light with a wavelength of 632.8 nm is propagated through a looped Polymer Optical Fiber and received by a 5-Megapixel Charge-Coupled-Device-camera, positioned on the fiber output face. An especially designed acrylic goniometer facilitates the defined bending of the fiber for different fiber loop configurations. Different fiber arrangements and spatial image filters are evaluated under consideration of precision of bending angle gauging and computational efficiency. A developed digital signal processing routine performs a signal noise reduction and precision improvement for the bending angle measurement. Practical results revealed the existence of a non-linear dependence in static and dynamic operation in the range from −120 ◦ to +130 ◦ between the geometrical arrangements of the fiber, the average pixel intensity, the amount of detected speckle contours and the bending angle. A potential application of the sensor for the measurement of human joint movement and posture in the medical field of rehabilitation is possible. The curvature measurement for an application in the robotic field or industrial application is also convenient.