Design Of Independent-axis Motion Controller For Industrial Computed Tomography

Industrial CT (Industrial Computed Tomography) is considered to be the bestmeans of nondestructive testing. In recent years, along with the progress of thedevelopment of computer science and the detector technology, the performance ofindustrial CT has been improving continuously. It has developed from the low-energyindustrial CT which can meet general industrial application to the high energy industrialCT which can meet large complex structure of object inspection. At present, there aremany kinds of industrial CT of high-energy x-rays, such as2MeV,4MeV,6MeV,9MeV etc, and they get a better development in the corresponding areas. The technologyof China’s industrial CT starts late, but it has obtained some achievements anddeveloped rapidly. Because of the blockade of foreign technology and the limitation ofvarious factors, the industrial CT product has lower degree in modularization,industrialization and standardization than others. Now, the existing control system ofthe industrial CT machine mostly adopts the PC plus control board of integrated controlstructure or general numerical control system. The two control schemes have betterversatility, but they are difficult to find failure and to maintenance because of highintegration. Not only do they limit the freedom of moving axis, but also their layout andwiring of whole system is complex. For simplifying the control system, it needs todesign the independent-axis motion controller which could satisfy the industrial CTcontrol’s requirements, and has a better versatility and flexibility.Firstly, the background and significance of the industrial CT motion control systemis introduced, then this paper analyses the characteristics of the motion control systemwhich are in industrial CT and the requirements of the single axis motion control. At thesame time, it analyses the status and comprises the performance of controller at homeand abroad. Lastly, the overall structure scheme of independent axis is determined bycombining with the motion characteristics and requirements of industrial CT. Thehardware design of controller adopts the structure of ARM plus FPGA instead of thestructure of original PLC. It can reduce the design difficulty of the system, and improvethe flexibility and versatility.Secondly, the hardware and software are designed basing on the hardware structureof ARM plus FPGA. This page introduces every hardware module and analyses thehardware’s anti-interference of controller. In chorus, we adopt μ C/OS-II as the real-time operation system of controller in the aspect of hardware and make thecontroller to operate independently. The controller’s task is divided and realizedrespectively by using the multitask mechanism of μ C/OS-II. The communicationbetween controller and control computer is realized according to the communicationprotocol of independent axis in the ARM, and the signals with pulse, direction, drivecontrol and feedback are realized in the FPGA.Finally, the mechanism method is adopted to build model for controlled objectbased on the positional servo system of PMSM, and the principle of PMSM is analyzed.The pros and cons of the moving control algorithms such as PID control, interpolationalgorithm and acceleration and deceleration control are analyzed as well as itsapplications. Then the PID parameters tuning method which is based on geneticalgorithm is introduced. The control method about the acceleration and deceleration ofthe S curve is used to realize the acceleration and deceleration of the independent axiscombining the motion characteristics of independent axis of industrial CT.