High Speed Optical 3D Shape Measurement Based On Temporal Frequency Encoding And Applications

High-speed high-precision three-dimensional surface measurement has a large number of potential applications in a variery of areas such as advanced manufacturing, medical imaging, scientific research and so on. For example, the data of real-time three-dimensional dragonfly wings will help us understand the principles of flight and design aircraft better. At present, there have been many three-dimensional detection methods, but to achieve accurate three-dimensional measure for rapid change is still very difficult.Digital fringe projection are widely used in 3D measurement due to its high-speed, high-precision potential.3D scanner based on comercial projectors can achieve real-time (30 Hz) three-dimensional measuring. Such a device is capable of acquireing slowly changing scene. However it is not adequate for fast changing scene. For high-speed three-dimensional measurements (120 Hz or more), we usually apply single shot digital fringe projection to illuminate object and high-speed camera to acquire data. With the development of hardware, high-speed binary fringe projector are able to project fringes at 4000fps and the prices are acceptable. However, the price of such rate cameras are extremely high, and there are a lot of restrictions, such as the recording time is limited, data is not real-time transmissed.In order to overcome the current shortcomings of the high-speed three-dimensional measurement, this thesis presents a high-speed three-dimensional measurement scheme based on time-frequency coding which use high frame rate projectors to project different fringes at different times, and a lower frame rate camera to record. Several number of deformation fringes are exposure in a frame. Since the three-dimensional information is encoded in the spectrum nearby fringe frequency, and these fringes are designed different in frequencies, the spatial frequency domain modification is seperated. Through the analysis of image processing, we can get various stripes corresponding three-dimensional data that corresponds to different time. The scheme does not change the frame rate of camera but utilize the high-speed projector’s frame rate to improve the frame rate of three-dimensional measurement meanwhile to reduce the cost of the measurement system.This work is consist of three parts:we firstly analyze the feasibility of time-frequency encoding scheme based on the key steps of the system, such as filter design, striped design, etc. Secondly, according to the principles, a system was designed and the dynamic face data is measured. Finally, we give an application example, the measurement results are used in crystal engraving.