IN-TECH 2015, International Conference on Innovative Technologies, Dubrovnik, Croatia
This paper describes the implementation of a magnetically suspended shaft for research and educational purposes. The working principle of the special combined axial and radial magnetic bearings and their implementation is explained. Moreover, benefits and drawbacks of the system are taken into consideration. The overall laboratory system consists of two magnetic bearings with their housings, the suspended shaft and the position sensor, control system and power electronics. The two bearings provide suspension forces in both radial and axial direction, stabilizing five degrees of freedom of the shaft actively and enabling it to levitate. Furthermore, ball bearings are used as auxiliary bearings in the power-off state and as a radial displacement limiter. The function of the sensor electronics is to measure the position of the shaft within a bearing and to determine the appropriate bearing current with outer position control loops and nested current control loops. The "Low Voltage Multi-Axis Motor Control and Power Factor Correction Developers Kit" by Texas Instruments (TI) featuring the TMS320F28335 TI DSP Control Card is used for control and power electronics. For measuring the position of the shaft within a bearing, three TI LDC1000 digital inductive proximity sensors are used per bearing. In order to implement the control system the X2C tool is used. This is an open source model based development and code generation tool embedded in the Scilab/Xcos environment. A major role in the algorithm design plays the data processing speed. Thus, the sensor data acquisition time is optimized to increase the speed of the control system.