Structure Design And Analysis Of High Precision Three-dimensional Fine-tuning Frame For Return Measurement

With the development of photoelectric detecting technology, faint and fast optical signals are mostly detected in the practical projects. So the photoelectric detector must have high sensitivity, fast response, high quantum efficiency (QE), wide spectrum sensitivity and high signal noise ratio (SNR). The avalanche photodiode (APD) is relied on light-induced carriers generated by the avalanche effect in the region of high electric field for the current gain. It has advantages of high sensitivity and quantum efficiency, possessing internal gain, high speed response and chip size. The APD is widely used in laser radar, laser orientation, laser ranging, optical fiber communication and optical fiber sensor. In order to get fast response, the size of PN junction of APD must be very narrow, which makes the active area of the APD very tiny usually from 0.1 to 1.0 millimeter. So it should be fine-tuned precisely to make it work well.A new structure of three-dimensional fine-tuning frame was designed in this dissertation for return measurement avalanche photodiode of horizontal two-axis turntable laser tracking device. Firstly, the return measurement system of the turntable was introduced in detail. Then according to the design requirement of the fine-tuning frame, the structure form of the frame was established. Then the main parts of the frame were designed by theoretical calculation. The 3D entity model of the frame was built by using UG software. Then the finite element model was established by MSC.Patran to put up linear static and modal analysis, in order to get the frame's deformation, stress distribution, natural frequency and modal shape. Then the vibration and precision tests were done to the frame entity to verify the finite element modal analysis's reliability and measure the frame's tuning distinguish ability. Finally the return detecting probability estimation and ground return measurement test was done to the two-axis turntable.Software analysis and experiment results show that the fine-tuning frame is satisfied with the project requirement and can achieve the precise fine-tuning of the avalanche photodiode to make it work well. The ground return measurement test is accomplished by using the frame. The frame has excellences such as small size, easy to operate and high tuning accuracy.