Research On Key Problems In High Resolution Out-of-plane Displacement Measurement

With the rapid enhancement of our country's comprehensive national strength and the increasing application of different kinds of structures in aerospace,shipbuilding,automobile and other manufacturing fields,it generally indicates that structures are in the development of being large and elaborate,which promotes measurement techniques to develop toward the direction of high resolution,large area and large range.Optical measurement methods have become the crucial means in the measurement of different kinds of structures for their being non-contact and with high sensitivity,however,there still exists none test method that could solve the contradiction between the high measurement resolution and large area or that between the high measurement resolution and large range.In this thesis,based on the optical measurement methods and out-of-plane displacement measurement,we proposed schemes to solve those two contradictions respectively,then built up the out-of-plane displacement measurement systems respectively,and finally experiments were carried out to test the properties of our systems.Since there were kinds of out-of-plane displacement measurement methods,we divided those methods in two categories,contact ones and non-contact ones,then principle,measurement resolution and measurement range of each measurement method was elaborately introduced,and finally the current drawbacks and main problems of each method when employed to solve those two contradictions was discussed.Fringe projection is the most common used one among the structured light measurement methods,but it faces severe cycle ripple noises from digital devices.First the elaborate analysis was made,then two algorithms,based on fringe characteristic analysis and multiple fixed-step phase shifting,were developed to decrease the noises,and experiments were conducted to verify the effectiveness of the two algorithms,finally the properties and application conditions of two algorithms were compared.Based on the properties of fringe projection and geometric Moire,the Moire projection method was proposed to solve the contradiction between the high measurement resolution and large area,which projected full-field high-density fringes onto the measured object with large surface by employing an optical system,then imaged the projected fringes and reference grating simultaneously to form the geometric Moire.Additionally,a measurement system based on Moire projection was built up,and in-site measurement experiment was conducted with the employment of temporal phase shifting and moving least square fitting techniques.Based on the ultra resolution of optical interfeometry and PZT technique,the optical tracking method was proposed to solve the contradiction between the high measurement resolution and large range by employing the PZT actuator as the measurement device.Additionally,the image based tracing algorithm was developed to control the measurement system.To obtain the measurement results from diffuse surface and mirror surface,the measurement systems were built up respectively,and finally different experiments were carried out to test the effectiveness of the systems respectively.