小型高频X射线机的控制策略及样机研制

Control Strategy and Prototype Development of small High Frequency X-Ray Machine

摘要: 阴极空间电荷效应、灯丝电流漂移是X射线发射管的固有特性，是X射线机管电压、管电流精确控制的瓶颈问题。传统控制方案有缺陷，难以满足X射线机小型轻量、高效率、快速响应、高性能等要求。该文提出了新的控制策略，解决了这个难题：基于X射线机管电流的闭环控制策略，用占空比作为非线性实时动态补偿X射线管阴极空间电荷效应的影响，构建前馈控制环节，对管电压大范围变动实现快速预调；构建X射线管灯丝电流作副控变量的串级控制，应对管电流的滞后，减少整个X射线发射过程的时间常数。自主研制了4套小型高频X射线机样机，构建MC34067管电压控制电路、TL494管电流控制电路，单片机根据管电压范围段进行阴极空间电荷效应的非线性补偿，并对新研制样机的控制效果进行测试。试验结果表明，该X射线机的控制新策略有效，电路装置可靠，拍摄效果良好。

Abstract: Cathode Space Charge Effect (CSCE) and Filament Current Drift (FCD) are inherent characteristics of X-ray emitting tube, which is the key problem for the precise control of tube voltage and tube current in X-ray machines. The traditional control scheme is defective and difficult to meet the requirements of small and lightweight, high efficiency, fast response and high performance of X-ray machines. A new control strategy is proposed in this paper to solve this challenge. Based on the closed-loop control strategy of X-ray tube current, the duty cycle is used as a nonlinear real-time dynamic compensation for X-ray tube Cathode Space Charge Effect (CSCE), and the feed-forward control is constructed to achieve rapid pre-adjustment for a wide range of variations of the tube voltage; The serial control of X-ray tube filament current as a subcontrol variable is constructed to cope with the hysteresis of the tube current and to reduce the time constant of the whole X-ray emission process. Four sets of small high-frequency X-ray machine prototypes are developed independently, MC34067 tube voltage control circuit and TL494 tube current control circuit are constructed, and the microcontroller compensates the Cathode Space Charge Effect nonlinearly according to the tube voltage range section, and the control effect of the newly developed prototype is tested. The test results show that the new strategy for controlling the X-ray machine is effective, the circuit device is reliable, and the X-ray photos are clearly.