Inner Surface Roughness Measurement Of Holes Based On Reflective Intensity Modulation Fiber Optic Sensor

Surface roughness reflects surface quality directly, which is one of the most commonly used parameters that describe the surface topography. It determines the working performance of parts in many fields, such as mechanical, electronic, biomedical and optical industries. Surface roughness measurement has long been a hot issue for researchers in the last several decades. With the development of industries and adoption of new technologies, increasing numbers of measurement methods have been proposed in every field. Some classical surface roughness measurement methods have been reviewed in this dissertation. The development of the inner surface roughness measurement techniques is analyzed. And the problems about the applying of RIM-FOSs in the surface roughness measurement are discussed. A new measurement method based on a novel RIM fiber optical inner surface roughness sensor is proposed. The method can nondestructively measure the inner surface roughness of holes with small diameters such as 5mm, 8mm and 10mm.The working principle of RIM-FOS is fully studied in theory. A new intensity modulation function of a single fiber pair is derived under certain assumptions. The main influence factors of the RIM-FOS intensity modulation characteristics are analyzed theoretically. And the characteristic parameters closely related to surface roughness measurement are explained and introduced. According to simulation conclusions, basic design principles of the RIM fiber optical surface roughness sensor have been determined finally. Consequently, a sensor that is coaxial, two-double, and"1input 12 outputs"is primarily designed (named Sensor I).On the basis of Sensor I, a micro prism is utilized, and the novel inner surface roughness sensor is developed (namely Sensor II).The intensity modulation model will be affected directly by the distribution assumption of emission intensity. Then the intensity modulation function of a single fiber pair is derived as the emission intensity is Gaussian distribution. And the intensity modulation function of Sensor I is established assuming that reflective surface is an ideal mirror. Besides, scattering of a rough surface is studied deeply. The intensity modulation function of a rough surface is derived on certain conditions based on the Beckmann's scattering geometry model. Then a theoretical model of RIM-FOS for surface roughness measurement is proposed, which can guide the surface roughness measurement effectively. Finally, as to the inner surface roughness measurement of holes, the controlling of working distance and bias of the sensor head are discussed and analyzed qualitatively.Based on the conclusions of theoretical analysis, the intensity modulation characteristics of SensorI and SensorII have been studied experimentally. Characteristics that are relevant to surface roughness measurement are analyzed. Comparative analysis on characteristic curves of two sensors shows the influence of the micro prism. And the results show that SensorII has good capability in surface roughness measurement. The influence of the reflective surface to the characteristics of SensorII has been analyzed by abundant experiments. The factors include roughness value, machining method and shape of the surface. The experiment results show the defined measurement parameter by two outputs of the sensor can distinguish surfaces effectively. Simultaneously, the proper range of the working distance is found. However, the machining method and shape of the reflective surfaces affect the sensor characteristics to varing degree. Hence, when surface roughness is measured by a RIM-FOS, surfaces with different machining methods and curvature radius must be measured respectively.A surface roughness measurement system based on the designed Sensor II is set up. The inner surfaces of holes with different diameters are measured non-destructively. The measurement results are compared with those obtained by a TimeSurf TR220 roughness instrument. The measurement validity, accuracy and range of the proposed measurement method are verified and discussed, some main influencing factors are analyzed, and some future tasks are figured out.In conclusion, the study shows that the designed RIM fiber optical inner surface roughness sensor is not only small, simple and economical, but also with a high accuracy and a large measurement range. Therefore, its wide applications for non-destructive inner surface roughness measurement of relative small parts can be expected.